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  • 1.
    Ahuja, R.
    et al.
    Condensed Matter Theory Group, Department of Physics, Uppsala University, P.O. Box 530, SE-751 21 Uppsala, Sweden.
    Ferreira, Da Silva A.
    Ferreira Da Silva, A., Instituto de Física, Universidade Federal da Bahia, Campus Universitario de Ondina, 40 210 340 Salvador, Ba, Brazil.
    Persson, C.
    Condensed Matter Theory Group, Department of Physics, Uppsala University, P.O. Box 530, SE-751 21 Uppsala, Sweden.
    Osorio-Guillen, J.M.
    Osorio-Guillén, J.M., Condensed Matter Theory Group, Department of Physics, Uppsala University, P.O. Box 530, SE-751 21 Uppsala, Sweden.
    Pepe, I.
    Instituto de Física, Universidade Federal da Bahia, Campus Universitario de Ondina, 40 210 340 Salvador, Ba, Brazil.
    Järrendahl, Kenneth
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Lindquist, O.P.A.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Edwards, N.V.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Wahab, Qamar Ul
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Johansson, B.
    Condensed Matter Theory Group, Department of Physics, Uppsala University, P.O. Box 530, SE-751 21 Uppsala, Sweden.
    Optical properties of 4H-SiC2002In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 91, no 3, p. 2099-2103Article in journal (Refereed)
    Abstract [en]

    The optical band gap energy and the dielectric functions of n-type 4H-SiC have been investigated experimentally by transmission spectroscopy and spectroscopic ellipsometry and theoretically by an ab initio full-potential linear muffin-tin-orbital method. We present the real and imaginary parts of the dielectric functions, resolved into the transverse and longitudinal photon moment a, and we show that the anisotropy is small in 4H-SiC. The measurements and the calculations fall closely together in a wide range of energies. © 2002 American Institute of Physics.

  • 2.
    Arshad, Sana
    et al.
    NED University of Engn and Technology, Pakistan.
    Ramzan, Rashad
    United Arab Emirates University, U Arab Emirates.
    Wahab, Qamar-ul
    Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    50-830 MHz noise and distortion canceling CMOS low noise amplifier2018In: Integration, ISSN 0167-9260, E-ISSN 1872-7522, Vol. 60, p. 63-73Article in journal (Refereed)
    Abstract [en]

    In this paper, a modified resistive shunt feedback topology is proposed that performs noise cancelation and serves as an opposite polarity non-linearity generator to cancel the distortion produced by the main stage. The proposed topology has a bandwidth similar to a resistive shunt feedback LNA, but with a superior noise figure (NF) and linearity. The proposed wideband LNA is fabricated in 130 nm CMOS technology and occupies an area of 0.5 mm(2). Measured results depict 3-dB bandwidth from 50 to 830 MHz. The measured gain and NF at 420 MHz are 17 dB and 2.2 dB, respectively. The high value of the 1/f noise is one of the key problems in low frequency CMOS designs. The proposed topology also addresses this challenge and a low NF is attained at low frequencies. Measured 811 and S22 are better than -8.9 dB and -8.5 dB, respectively within the 0.05-1 GHz band. The 1-dB compression point is -11.5 dBm at 700 MHz, while the IIP3 is -6.3 dBm. The forward core consumes 14 mW from a 1.8 V supply. This LNA is suitable for VHF and UHF SDR communication receivers.

  • 3.
    Arshad, Sana
    et al.
    NED University of Engn and Technology, Pakistan.
    Ramzan, Rashad.
    United Arab Emirates University, U Arab Emirates.
    Zafar, Faiza
    NED University of Engn and Technology, Pakistan.
    Wahab, Qamar-Ul
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering. NED Univ Engn and Technol, Dept Elect Engn, Pakistan.
    Highly Linear Inductively Degenerated 0.13 mu m CMOS LNA using FDC Technique2014In: 2014 IEEE ASIA PACIFIC CONFERENCE ON CIRCUITS AND SYSTEMS (APCCAS), IEEE , 2014, p. 225-228Conference paper (Refereed)
    Abstract [en]

    In this paper, a highly linear, inductively degenerated, common source narrowband LNA is presented. An extremely simple feed-forward distortion circuit (FDC) which consists of an appropriately sized ac-coupled diode connected NMOS is proposed. This circuit generates distortion components at output, when added at the input node as a feed forward element (M-6). These distortion components partially cancel the 3rd order nonlinearity of the cascode pair (M-2 and M-3), thus improving the overall linearity of LNA. The prototype is manufactured in standard 0.13 mu m CMOS process from IBM. Simulation and partial measurement results show the S11 and S22 to be -19.27dB and -7.14dB respectively at 2.45GHz. The simulation results of the LNA demonstrate a power gain of 18.5dB, NF of 4.38dB, input referred 1dBCP of -11.76dBm and IIP3 of +0.7dBm consuming 27.7mA from 1.0V power supply. The proposed LNA achieves the best input referred IIP3 reported in recent literature using 0.13 mu m CMOS in 2.4GHz frequency band.

  • 4. Asghar, M.
    et al.
    Hussain, I.
    Noor, N.
    Iqbal, F.
    Wahab, Qamar Ul
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Bhatti, A.
    Properties of dominant electron trap center in n-type SiC epilayers by means of deep level transient spectroscopy2007In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, no 7Article in journal (Refereed)
    Abstract [en]

    Characterization of dominant electron trap in as-grown SiC epilayers has been carried out using deep level transient spectroscopy. Two electron traps E1 and Z1 at Ec-0.21 and Ec-0.61 are observed, respectively, Z1 being the dominant level. Line shape fitting, capture cross section, and insensitivity with doping concentration have revealed interesting features of Z1 center. Spatial distribution discloses that the level is generated in the vicinity of epilayers/substrate interface and the rest of the overgrown layers is defect-free. Owing to the Si-rich growth conditions, the depth profile of Z1 relates it to carbon vacancy. The alpha particle irradiation transforms Z1 level into Z 1/Z2 center involving silicon and carbon vacancies. Isochronal annealing study further strengthens the proposed origin of the debated level. © 2007 American Institute of Physics.

  • 5.
    Asghar, M.
    et al.
    Islamia University of Bahawalpur, Pakistan .
    Iqbal, F.
    Islamia University of Bahawalpur, Pakistan .
    Faraz, Sadia
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Jokubavicius, Valdas
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Characterization of deep level defects in sublimation grown p-type 6H-SiC epilayers by deep level transient spectroscopy2012Conference paper (Refereed)
    Abstract [en]

    In this study deep level transient spectroscopy has been performed on boron-nitrogen co-doped 6H-SiC epilayers exhibiting p-type conductivity with free carrier concentration (N-A-N-D)similar to 3 x 10(17) cm(-3). We observed a hole H-1 majority carrier and an electron E-1 minority carrier traps in the device having activation energies E-nu + 0.24 eV, E-c -0.41 eV, respectively. The capture cross-section and trap concentration of H-1 and E-1 levels were found to be (5 x 10(-19) cm(2), 2 x 10(15) cm(-3)) and (1.6 x 10(-16) cm(2), 3 x 10(15) cm(-3)), respectively. Owing to the background involvement of aluminum in growth reactor and comparison of the obtained data with the literature, the H-1 defect was identified as aluminum acceptor. A reasonable justification has been given to correlate the E-1 defect to a nitrogen donor.

  • 6.
    Asghar, M.
    et al.
    Islamia University of Bahawalpur, Pakistan .
    Iqbal, F.
    Islamia University of Bahawalpur, Pakistan .
    Faraz, Sadia Municha
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Jokubavicius, Valdas
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Study of deep level defects in doped and semi-insulating n-6H-SiC epilayers grown by sublimation method2012Conference paper (Refereed)
    Abstract [en]

    Deep level transient spectroscopy (DLTS) is employed to study deep level defects in n-6H-SiC (silicon carbide) epilayers grown by the sublimation method. To study the deep level defects in n-6H-SiC, we used as-grown, nitrogen doped and nitrogen-boron co-doped samples represented as ELS-1, ELS-11 and ELS-131 having net (N-D-N-A) similar to 2.0 x 10(12) cm(-3), 2 x 10(16) cm(-3) and 9 x 10(15) cm(3), respectively. The DLTS measurements performed on ELS-1 and ELS-11 samples revealed three electron trap defects (A, B and C) having activation energies E-c - 0.39 eV, E-c - 0.67 eV and E-c - 0.91 eV, respectively. While DLTS spectra due to sample ELS-131 displayed only A level. This observation indicates that levels B and C in ELS-131 are compensated by boron and/or nitrogen-boron complex. A comparison with the published data revealed A, B and C to be E-1/E-2, Z(1)/Z(2) and R levels, respectively.

  • 7.
    Ashraf, H.
    et al.
    Radboud University Nijmegen.
    Imran Arshad, M.
    Islamia University Bahawalpur.
    Muniza Faraz, Sadia
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Ul Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hageman, P. R.
    Radboud University Nijmegen.
    Asghar, M.
    Islamia University Bahawalpur.
    Study of electric field enhanced emission rates of an electron trap in n-type GaN grown by hydride vapor phase epitaxy2010In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 108, no 10Article in journal (Refereed)
    Abstract [en]

    Electric field-enhanced emission of electrons from a deep level defect in GaN grown by hydride vapor phase epitaxy has been studied. Using the field dependent mode of conventional deep level transient spectroscopy (DLTS), several frequency scans were performed keeping applied electric field (12.8-31.4 MV/m) and sample temperature (300-360 K) constant. Arrhenius plots of the resultant data yielded an activation energy of the electron trap E ranging from E-c -0.48 +/- 0.02 eV to E-c-0.35 +/- 0.02 eV, respectively. The extrapolation of the as-measured field dependent data (activation energy) revealed the zero-field emission energy (pure thermal activation energy) of the trap to be 0.55 +/- 0.02 eV. Various theoretical models were applied to justify the field-enhanced emission of the carriers from the trap. Eventually it was found that the Poole-Frenkel model associated with a square well potential of radius r=4.8 nm was consistent with the experimental data, and, as a result, the trap is attributed to a charged impurity. Earlier, qualitative measurements like current-voltage (I-V) and capacitance-voltage (C-V) measurements were performed, and screening parameters of the device were extracted to ascertain the reliability of DLTS data.

  • 8.
    Azam, Sher
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Jonsson, R.
    Janzén, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Wahab, Qamar Ul
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Performance of SiC Microwave Transistors in Power Amplifiers2008In: Proc. of MRS Symposium on wide bandgap semiconductor electronics 8, 2008, p. 203-208Conference paper (Refereed)
    Abstract [en]

    The performance of SiC microwave power transistors is studied in fabricated class-AB power amplifiers and class-C switching power amplifier using physical structure of an enhanced version of previously fabricated and tested SiC MESFET. The results for pulse input in class-C at 1 GHz are; efficiency of 71.4 %, power density of 1.0 W/mm. The switching loss was 0.424 W/mm. The results for two class-AB power amplifiers are; the 30-100 MHz amplifier showed 45.6 dBm (∼ 36 W) output powers at P1dB, at 50 MHz. The power added efficiency (PAE) is 48 % together with 21 dB of power gain. The maximum output power at P1dB at 60 V drain bias and Vg= -8.5 V was 46.7 dBm (∼47 W). The typical results obtained in 200-500 MHz amplifier are; at 60 V drain bias the P1dB is 43.85 dBm (24 W) except at 300 MHz where only 41.8 dBm was obtained. The maximum out put power was 44.15 dBm (26 W) at 500 MHz corresponding to a power density of 5.2 W/mm. The PAE @ P1dB [%] at 500 MHz is 66 %.

  • 9.
    Azam, Sher
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Jonsson, R.
    Swedish Defense Research Agency (FOI), SE-581 11, Linköping, Sweden.
    Svensson, Christer
    Linköping University, Department of Electrical Engineering, Electronic Devices. Linköping University, The Institute of Technology.
    Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Broadband Power Amplifier performance of SiC MESFET and CostEffective SiGaN HEMTManuscript (preprint) (Other academic)
    Abstract [en]

    This paper describes the broadband power amplifier performance of two differentwide band gap technology transistors at 0.7 to 1.8 GHz using cost effective NitronexGaN HEMT on Silicon (Si) and Cree Silicon Carbide MESFET. The measured resultsfor GaN amplifier are; maximum output power at Vd = 28 V is 42.5 dBm (~18 W), amaximum PAE of 39 % and a maximum gain of 19.5 dB is obtained. The measuredmaximum output power for the SiC amplifier at Vd = 48 V was 41.3 dBm (~13.7 W),with a PAE of 32 % and a power gain above 10 dB. At a drain bias of Vd = 66 V at700 MHz for SiC MESFET amplifier the Pmax was 42.2 dBm (~16.6 W) with a PAE of34.4 %.

  • 10.
    Azam, Sher
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Jonsson, R,
    Swedish Defense Research Agency (FOI), SE-581 11, Linköping, Sweden.
    Svensson, Christer
    Linköping University, Department of Electrical Engineering, Electronic Devices. Linköping University, The Institute of Technology.
    Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    High Power, High Efficiency SiC Power Amplifier for Phased ArrayRadar and VHF ApplicationsManuscript (preprint) (Other academic)
    Abstract [en]

    Wide band gap semiconductor (SiC & GaN) based power amplifiers offer severalsystem critical advantages such as less current leakage, better stability at high temperatureand easier impedance matching. This paper describes the design and fabrication of a singlestageclass-AB power amplifier for 30 to 100 MHz using SiC Schottky gate MetalSemiconductor Field Effect Transistor (MESFET). The maximum output power achieved is46.2 dBm (~42 W) at 50 V DC supply voltage at the drain. The maximum power gain is 21dB and a maximum PAE of 62 %. The amplifier performance was also checked at a higherdrain bias of 60 V at 50 MHz. At this bias voltage the maximum output power was 46.7dBm (~47 W) with a power gain of 21 dB and a maximum PAE of 42.7 %. An averageOIP3 of 54 dBm have been achieved for this amplifier.

  • 11.
    Azam, Sher
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Jonsson, R.
    Wahab, Qamar Ul
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    The limiting frontiers of maximum DC voltage at drain of SiC microwave power transistors in case of Class A power amplifiers2007In: International Semiconductor Device Research Symposium 2007 ISDRS-07,2007, IEEE , 2007Conference paper (Refereed)
    Abstract [en]

       

  • 12.
    Azam, Sher
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Jonsson, Rolf
    Fritzin, Jonas
    Linköping University, Department of Electrical Engineering, Electronic Devices. Linköping University, The Institute of Technology.
    Alvandpour, Atila
    Linköping University, Department of Electrical Engineering, Electronic Devices. Linköping University, The Institute of Technology.
    Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    High Power, Single Stage SiGaN HEMT Class E Power Amplifier at GHz Frequencies2010In: IEEE International Bhurban Conference on Applied Sciences and Technology, IEEE , 2010Conference paper (Refereed)
  • 13.
    Azam, Sher
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Jonsson, Rolf
    Swedish Defense Research Agency (FOI), Box 1165, SE-581 11 Linkoping, Sweden.
    Fritzin, Jonas
    Linköping University, Department of Electrical Engineering, Electronic Devices. Linköping University, The Institute of Technology.
    Alvandpour, Atila
    Linköping University, Department of Electrical Engineering, Electronic Devices. Linköping University, The Institute of Technology.
    Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    High Power, Single Stage SiGaN HEMT Class EPower Amplifier at GHz FrequenciesManuscript (preprint) (Other academic)
    Abstract [en]

    A high power single stage class E power amplifier is implemented with lumped elements at 0.89-1.02GHz using Silicon GaN High Electron Mobility Transistor as an active device. The maximum drain efficiency (DE) and power added efficiency (PAE) of 67 and 65 % respectively is obtained with a maximum output power of 42.2 dBm (~ 17 W) and amaximum power gain of 15 dB. We obtained good results at all measured frequencies.

  • 14.
    Azam, Sher
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Jonsson, Rolf
    Swedish Defense Research Agency (FOI), Box 1165, SE-581 11 Linköping, Sweden.
    Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Designing, Fabrication and Characterization of Power Amplifiers Based on 10-Watt SiC MESFET & GaN HEMT at Microwave Frequencies2008In: IEEE European Microwave Week, October 10-15, Amsterdam, The Netherlands, 2008, p. 444-447Conference paper (Refereed)
    Abstract [en]

    This paper describes the design, fabrication and measurement of two single-stage class-AB power amplifiers covering the frequency band from 0.7-1.8 GHz using a SiC MESFET and a GaN HEMT. The measured maximum output power for the SiC amplifier at Vd = 48 V was 41.3 dBm (~13.7 W), with a PAE of 32% and a power gain above 10 dB. At a drain bias of Vd= 66 V at 700 MHz the Pmax was 42.2 dBm (~16.6 W) with a PAE of 34.4%. The measured results for GaN amplifier are; maximum output power at Vd = 48 V is 40 dBm (~10 W), with a PAE of 34% and a power gain above 10 dB. The results for SiC amplifier are better than for GaN amplifier for the same 10-W transistor.

  • 15.
    Azam, Sher
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Jonsson, Rolf
    Swedish Defense Research Agency (FOI), Box 1165, SE-581 11 Linköping, Sweden.
    Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Single-stage, High Efficiency, 26-Watt power Amplifier using SiC LE-MESFET2006In: Microwave Conference, 2006. APMC 2006. Asia-Pacific December 12-15, 2006, p. 441-444Conference paper (Refereed)
    Abstract [en]

    This paper describes a single-stage 26 W negative feedback power amplifier, covering the frequency range 200-500 MHz using a 6 mm gate width SiC lateral epitaxy MESFET. Typical results at 50 V drain bias for the whole band are, around 22 dB power gain, around 43 dBm output power, minimum power added efficiency at P1 dB is 47% at 200 MHz and maximum 60% at 500 MHz and the IMD3 level at 10 dB back-off from P1 dB is below -45 dBc. The results at 60 V drain bias at 500 MHz are, 24.9 dB power gain, 44.15 dBm output power (26 W) and 66% PAE.

  • 16.
    Azam, Sher
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Jonsson, Rolr
    Swedish Defense Research Agency (FOI), SE-581 11, Linköping, Sweden.
    Svensson, Christer
    Linköping University, Department of Electrical Engineering, Electronic Devices. Linköping University, The Institute of Technology.
    Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Comparison of Two GaN TransistorsTechnology in Broadband Power AmplifiersManuscript (preprint) (Other academic)
    Abstract [en]

    This paper compares the performance of two different GaN technology transistors(GaN HEMT on Silicon substrate (PA1) and GaN on SiC PA2) utilized in two broadbandpower amplifiers at 0.7-1.8 GHz. The study explores the broadband power amplifierpotential of both GaN HEMT technologies for Phased Array Radar (PAR) and electronicswarfare (EW) systems. The measured maximum output power for PA1 is 42.5 dBm(~18 W) with a maximum PAE of 39 % and a gain of 19.5 dB. While the measuredmaximum output power for PA2 is 40 dBm with PAE of 35 % and a power gain slightlyabove 10 dB. We obtained high power, gain, wider band width and unconditionalstability without feedback for amplifier based on GaN HEMT technology fabricated on Sisubstrate.

  • 17.
    Azam, Sher
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Svensson, Christer
    Linköping University, Department of Electrical Engineering, Electronic Devices. Linköping University, The Institute of Technology.
    Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    A New Load Pull TCAD Simulation Technique for Class D, E & FSwitching Characteristics of TransistorsManuscript (preprint) (Other academic)
    Abstract [en]

    We have further developed a computational load pull simulation technique inTCAD. It can be used to study the Class-D, E & F switching response of the transistors. Westudied our enhanced version of previously fabricated and tested SiC transistor. Thesimulated Gain (dB), Power density (W/mm), switching loss (W/mm) and power addedefficiency (PAE %) at 500 MHz were studied using this technique. A PAE of 84 % at500MHz with 26 dB Power gain and power density of 2.75 W/mm is achieved. Thistechnique allows the prediction of switching response of the device before undertaking anexpensive and time-consuming device fabrication. The beauty of this technique is that, weneed no matching and other lumped element networks to study the large signal switchingbehavior of RF and microwave transistors.

  • 18.
    Azam, Sher
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Svensson, Christer
    Linköping University, Department of Electrical Engineering, Electronic Devices. Linköping University, The Institute of Technology.
    Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Pulse Input Class-C Power Amplifier Response of SiC MESFET using Physical Transistor Structure in TCAD2008In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 52, no 5, p. 740-744Article in journal (Refereed)
    Abstract [en]

    The switching behavior of a previously fabricated and tested SiC transistor is studied in Class-C amplifier in TCAD simulation. The transistor is simulated for pulse input signals in Class-C power amplifier. The simulated gain (dB), power density (W/mm) and power added efficiency (PAE%) at 500 MHz, 1, 2 and 3 GHz was studied using computational TCAD load pull simulation technique. A Maximum PAE of 77.8% at 500 MHz with 45.4 dB power gain and power density of 2.43 W/mm is achieved. This technique allows the prediction of switching response of the device for switching amplifier Classes (Class-C–F) before undertaking an expensive and time consuming device fabrication. The beauty of this technique is that, we need no matching and other lumped element networks for studying the large signal behavior of RF and microwave transistors.

  • 19.
    Azam, Sher
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Svensson, Christer
    Linköping University, The Institute of Technology. Linköping University, Department of Electrical Engineering, Electronic Devices.
    Wahab, Qamar Ul
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Designing of high efficiency power amplifier based on physical model of SiC MESFET in TCAD.2007In: International Bhurban conference on applied sciences technology.,2001, 2007Conference paper (Refereed)
    Abstract [en]

       

  • 20.
    Azam, Sher
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Svensson, Christer
    Linköping University, Department of Electrical Engineering, Electronic Devices. Linköping University, The Institute of Technology.
    Wahab, Qamar Ul
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Jonsson, R.
    Swedish Defence Research Agency.
    Comparison of Two GaN Transistor Technologies in Broadband Power Amplifiers2010In: MICROWAVE JOURNAL, ISSN 0192-6225, Vol. 53, no 4, p. 184-192Article in journal (Refereed)
    Abstract [en]

    This article compares the performance of two different GaN transistor technologies, GaN HEMT on silicon substrate (PA1) and GaN on SiC (PA2), utilized in two broadband power amplifiers operating at 0.7 to 1.8 GHz. The study explores the broadband power amplifier potential of both GaN HEMT technologies for phased-array radar (PAR) and electronic warfare (EW) systems. The measured maximum output power for PA1 is 42.5 dBm (18 W) with a maximum PAE of 66 percent and a gain of 19.5 dB. The measured maximum output power for PA2 is 40 dBm with a PAE of 37 percent and a power gain slightly above 10 dB. The high power gain, ME, wider bandwidth and unconditional stability was obtained without feedback for the amplifier based on GaN HEMT technology, fabricated on Si substrate.

  • 21.
    Bano, Nargis
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Hussain, I
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Nour, Omer
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Ul Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Kwack, H S
    CEA, CNRS.
    Le Si Dang, D
    CEA, CNRS.
    Depth-resolved cathodoluminescence study of zinc oxide nanorods catalytically grown on p-type 4H-SiC2010In: Journal of Luminescence, ISSN 0022-2313, E-ISSN 1872-7883, Vol. 130, no 6, p. 963-968Article in journal (Refereed)
    Abstract [en]

    Optical properties of ZnO nanorods (NRs) grown by vapour-liquid-solid (VLS) technique on 4H-p-SiC substrates were probed by cathodoluminescence (CL) measurements at room temperature and at 5 K complemented with electroluminescence. At room temperature the CL spectra for defect related emission intensity was enhanced with the electron beam penetration depth. We observed a variation in defect related green emission along the nanorod axis. This indicates a relatively poor structural quality near the interface between ZnO NRs and p-SiC substrate. We associate the green emission with oxygen vacancies. Analysis of the low-temperature (5 K) emission spectra in the UV region suggests that the synthesized nanorods contain shallow donors and acceptors.

  • 22. Brillson, L.J.
    et al.
    Tumakha, S.P.
    Gao, M.
    Ewing, D.J.
    Porter, L.M.
    Okojie, R.S.
    Zhang, M.
    Pirouz, P.
    Wahab, Qamar Ul
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Ma, X.
    Sudharshan, T.S.
    Onishi, T.
    Tsukimoto, S.
    Murakami, M.
    The impact of surface defects on SiC Schottky and ohmic contact formation2005In: International Semiconductor Device Research Symposium,2005, 2005Conference paper (Refereed)
  • 23. Carlsson, F.H.C.
    et al.
    Wahab, Qamar Ul
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Bergman, Peder
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Electroluminescence from 4H-SiC Schottky Diodes2001In: Mat. Res. Soc. Symp. Proc., Vol. 640, 2001, p. H4.8-Conference paper (Refereed)
  • 24.
    Chang, KC
    et al.
    Carnegie Mellon Univ, Dept Mat Sci & Engn, Pittsburgh, PA 15213 USA Linkoping Univ, Dept Phys, S-58183 Linkoping, Sweden.
    Nuhfer, NT
    Carnegie Mellon Univ, Dept Mat Sci & Engn, Pittsburgh, PA 15213 USA Linkoping Univ, Dept Phys, S-58183 Linkoping, Sweden.
    Porter, Lisa
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Wahab, Qamar Ul
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    High-carbon concentrations at the silicon dioxide-silicon carbide interface identified by electron energy loss spectroscopy2000In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 77, no 14, p. 2186-2188Article in journal (Refereed)
    Abstract [en]

    High carbon concentrations at distinct regions at thermally-grown SiO2/6H-SiC(0001) interfaces have been detected by electron energy loss spectroscopy (EELS). The thickness of these C-rich regions is estimated to be 10-15 Angstrom. The oxides were grown on n-type 6H-SiC at 1100 degrees C in a wet O-2 ambient for 4 h immediately after cleaning the substrates with the complete RCA process. In contrast, C-rich regions were not detected from EELS analyses of thermally grown SiO2/Si interfaces nor of chemical vapor deposition deposited SiO2/SiC interfaces. Silicon-rich layers within the SiC substrate adjacent to the thermally grown SiO2/SiC interface were also evident. The interface state density D-it in metal-oxide-SiC diodes (with thermally grown SiO2) was approximately 9x10(11) cm(-2) eV(-1) at E- E-v=2.0 eV, which compares well with reported values for SiC metal-oxide-semiconductor (MOS) diodes that have not received a postoxidation anneal. The C-rich regions and the change in SiC stoichiometry may be associated with the higher than desirable D-it's and the low channel mobilities in SiC-based MOS field effect transistors. (C) 2000 American Institute of Physics. [S0003-6951(00)01940-9].

  • 25.
    Ciechonski, Rafal
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Wahab, Qamar Ul
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Yakimova, Rositsa
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Evaluation of MOS structures processed on 4H–SiC layers grown by PVT epitaxy2005In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 49, no 12, p. 1917-1920Article in journal (Refereed)
    Abstract [en]

    MOS capacitors have been fabricated on 4H–SiC epilayers grown by physical vapor transport (PVT) epitaxy. The properties were compared with those on similar structures based on chemical vapor deposition (CVD) layers. Capacitance–voltage (CV) and conductance measurements (GV) were performed in the frequency range of 1 kHz to 1 MHz and also at temperatures up to 475 K. Detailed investigations of the PVT structures indicate a stable behaviour of the interface traps from room temperature up to 475 K. The amount of positive oxide charge QO is 6.83 × 109 cm−2 at room temperature and decreases with temperature increase. This suggests that the processed devices are temperature stable. The density of interface states Dit obtained by Nicollian–Brews conductance method is lower in the structure based on the PVT grown sample.

  • 26.
    Ellison, A
    et al.
    Linkoping Univ, IFM, SE-58183 Linkoping, Sweden Linkoping Univ, Okmetic AB, SE-58183 Linkoping, Sweden ABB Corp Res, SE-72178 Vasteras, Sweden.
    Zhang, J
    Magnusson, W
    Linkoping Univ, IFM, SE-58183 Linkoping, Sweden Linkoping Univ, Okmetic AB, SE-58183 Linkoping, Sweden ABB Corp Res, SE-72178 Vasteras, Sweden.
    Henry, Anne
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Wahab, Qamar Ul
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Bergman, Peder
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Nguyen, Tien Son
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Fast SiC epitaxial growth in a chimney CVD reactor and HTCVD crystal growth developments2000In: Materials science Forum, Vols. 338-342, Trans Tech Publications Inc., 2000, Vol. 338-3, p. 131-136Conference paper (Refereed)
    Abstract [en]

    The epitaxial growth of SiC is investigated in a CVD process based on a vertical hot-wall, or "chimney", reactor geometry. Carried out at increased temperatures (1650 to 1850 degreesC) and concentrations of reactants, the growth process enables epitaxial rates ranging from 10 to 50 mum/h. The growth rate is shown to be influenced by two competing processes: the supply of growth species in the presence of homogeneous gas-phase nucleation, and, the etching effect of the hydrogen carrier gas. The quality of thick (20 to 100 mum) low-doped 4H-SiC epitaxial layers grown at rates ranging between 10 and 25 mum/h are discussed in terms of thickness uniformity, surface morphology and purity. The feasibility of high voltage Schottky rectifiers (V-BR from 2 to similar to3.8 kV) on as-grown chimney CVD epilayers is reported. In a second part, recent developments of the High Temperature Chemical Vapor Deposition (HTCVD) technique for SiC crystal growth are described. Using pure gases (SiH4 and C2H4) as source material and growth temperatures of 2100-2300 degreesC, this technique enables at present growth rates ranging from 0.4 to 0.8 mm/h. 6H and 4H-SiC crystals of thickness up to 7 mm and diameters up to 40 mm have been grown. We report micropipe densities of similar to 80 cm(-2) over areas of 0.5 cm(2) in 35 mm diameter 4H-SiC wafers sliced from HTCVD grown crystals. Undoped wafer demonstrators exhibit semi-insulating behavior with a bulk resistivity higher than 7.10(9) Omega cm at room temperature.

  • 27.
    Eriksson, J.
    et al.
    Department of Microelectronics, Chalmers University of Technology.
    Rorsman, N.
    Department of Microelectronics, Chalmers University of Technology.
    Zirath, H.
    Department of Microelectronics, Chalmers University of Technology.
    Jonsson, Rolf
    FOA Defence Research Establishment, Linköping, Sweden.
    Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Rudner, Staffan
    FOA Defence Research Establishment, Linköping, Sweden.
    A comparison between physical simulations and experimental results in 4H-SiC MESFETs with non-constant doping in the channel and buffer layers2001In: Maretials Science Forum Vols. 353-356, Stafa-Zurich, Switzerland: Trans Tech Publications Inc., 2001, Vol. 353-356, p. 699-702Conference paper (Refereed)
    Abstract [en]

    The performance of SiC MESFETs, fabricated on a structure with non-constant doping-profiles in the channel and buffer layers have been studied. A good correspondence between experimental DC-characteristics and physical simulations was obtained, when using the doping profiles from SIMS measurements.

  • 28. Ewing, D.J.
    et al.
    Porter, L.M.
    Wahab, Qamar Ul
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Ciechonski, Rafal
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Syväjärvi, Mikael
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Yakimova, Rositsa
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Inhomogeneous electrical characteristics in 4H-SiC Schottky diodes2007In: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 22, no 12, p. 1287-1291Article in journal (Refereed)
    Abstract [en]

    Hundreds of current-voltage (I-V) measurements of Ni, Pt and Ti Schottky diodes on 4H-SiC were conducted at low applied voltages. The SiC substrates contained homoepitaxial layers grown by either chemical vapor deposition or sublimation. While near-ideal contacts were fabricated on all samples, a significant percentage of diodes (∼7%-50% depending on the epitaxial growth method and the diode size) displayed a non-ideal, or inhomogeneous, barrier height. These 'non-ideal' diodes occurred regardless of growth technique, pre-deposition cleaning method, or contact metal. In concurrence with our earlier reports in which the non-ideal diodes were modeled as two Schottky barriers in parallel, the lower of the two Schottky barriers, when present, was predominantly centered at one of the three values: ∼0.60, 0.85 or 1.05 eV. The sources of these non-idealities were investigated using electron-beam- induced current (EBIC) and deep-level transient spectroscopy (DLTS) to determine the nature and energy levels of the defects. DLTS revealed a defect level that corresponds with the low- (non-ideal) barrier height, at ∼0.60 eV. It was also observed that the I-V characteristics tended to degrade with increasing deep-level concentration and that inhomogeneous diodes tended to contain defect clusters. Based on the results, it is proposed that inhomogeneities, in the form of one or more low-barrier height regions within a high-barrier height diode, are caused by defect clusters that locally pin the Fermi level. © 2007 IOP Publishing Ltd.

  • 29. Ewing, D.J.
    et al.
    Porter, L.M.
    Wahab, Qamar Ul
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Ma, X.
    Sudharsan, T.S.
    Tumakha, S.
    Goa, M.
    Brillson, L.J.
    Inhomogeneities in Ni4H-SiC Schottky barriers: Localized Fermi-level pinning by defect states2007In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, no 11Article in journal (Refereed)
    Abstract [en]

    We investigated arrays of Ni, Pt, or Ti Schottky diodes on n -type 4H-SiC epitaxial layers using current-voltage (I-V) measurements, electron beam induced current (EBIC), polarized light microscopy, x-ray topography, and depth-resolved cathodoluminescence spectroscopy. A significant percentage of diodes (∼7%-30% depending on epitaxial growth method and diode size) displayed "nonideal" or inhomogeneous barrier height characteristics. We used a thermionic emission model based on two parallel diodes to determine the barrier heights and ideality factors of high- and low-barrier regions within individual nonideal diodes. Whereas high-barrier barrier heights increased with metal work function, low-barrier barrier heights remained constant at ∼0.60, 0.85, and 1.05 eV. The sources of these nonidealities were investigated with a variety of spectroscopic and imaging techniques to determine the nature and energy levels of the defects. EBIC indicated that clusters of defects occurred in all inhomogeneous diodes. Cathodoluminescence spectra revealed additional peaks in the nonideal diodes at 2.65, 2.40, and 2.20 eV, which complement the low-barrier barrier heights. It is proposed that defect clusters act to locally pin the Fermi level, creating localized low-barrier patches, which account for the inhomogeneous electrical characteristics. © 2007 American Institute of Physics.

  • 30. Ewing, D.J.
    et al.
    Porter, L.M.
    Wahab, Qamar Ul
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Tumakha, S.
    Brillson, L.J.
    A Study of Inhomogeneous Schottky diodes on n-type 4H-SiC2006In: International Conference on Silicon Carbide and Related Materials 2005 ICSCRM 2005,2005, Materials Science Forum, V. 527-529: Trans Tech Publications , 2006, p. 911-Conference paper (Refereed)
    Abstract [en]

      

  • 31.
    Faraz, Sadia Muniza
    et al.
    Department of Electronic Engineering, NED University of Engineering and Technology, 75270, Karachi, Pakistan.
    Alvi, Muhammed Naveed
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Nur, Omer
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Ul Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Annealing Effects on Electrical and Optical Properties of N-ZnO/P-Si Heterojunction Diodes2011In: Advanced Materials Research Vol. 324 (2011) pp 233-236, Trans Tech Publications Inc., 2011, p. 233-236Conference paper (Refereed)
    Abstract [en]

    The effects of post fabrication annealing on the electrical characteristics of n-ZnO/p-Si heterostructure are studied. The nanorods of ZnO are grown by aqueous chemical growth (ACG) technique on p-Si substrate and ohmic contacts of Al/Pt and Al are made on ZnO and Si. The devices are annealed at 400 and 600 oC in air, oxygen and nitrogen ambient. The characteristics are studied by photoluminescence (PL), current–voltage (I-V) and capacitance - voltage (C-V) measurements. PL spectra indicated higher ultraviolet (UV) to visible emission ratio with a strong peak of near band edge emission (NBE) centered from 375-380 nm and very weak broad deep-level emissions (DLE) centered from 510-580 nm. All diodes show typical non linear rectifying behavior as characterized by I-V measurements. The results indicated that annealing in air and oxygen resulted in better electrical characteristics with a decrease in the reverse current.

  • 32.
    Hallin, Christer
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Wahab, Qamar Ul
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Ivanov, Ivan Gueorguiev
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Bergman, Peder
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Janzén, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Homoepitaxial On-Axis Growth of 4H- and 6H-SiC by CVD2004In: Materials Science Forum, Vols. 457-460, Trans Tech Publications Inc. , 2004, p. 193-Conference paper (Refereed)
  • 33.
    Janzén, Erik
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Bergman, Peder
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Danielsson, Örjan
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Forsberg, Urban
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Hallin, Christer
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    ul-Hassan, Jawad
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Henry, Anne
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Ivanov, Ivan Gueorguiev
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Kakanakova-Gueorguie, Anelia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Persson, Per
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Wahab, Qamar Ul
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    SiC and III-nitride Growth in a Hot-wall CVD Reactor2005In: Materials Science Forum, ISSN 0255-5476, volume 483-485, Trans Tech Publications , 2005, Vol. 483-485, p. 61-66Conference paper (Refereed)
  • 34.
    Johansson, Rolf
    et al.
    FOA Defence Research Establishment, Linköping, Sweden.
    Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Rudner, Staffan
    FOA Defence Research Establishment, Linköping, Sweden.
    Physical simulations on the Operation of 4H-SiC Microwave Power Transistors2000In: Materials Science Forum Vols. 338-342, Scientific.Net , 2000, p. 1263-1266Conference paper (Refereed)
  • 35. Jonsson, Rolf
    et al.
    Eriksson, J
    Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Rudner, Staffan
    Rorsman, N
    Swedish Def Res Agcy, FOI, SE-58111 Linkoping, Sweden Linkoping Univ, Dept Phys, SE-58183 Linkoping, Sweden Chalmers, Dept Microelect, SE-41296 Gothenburg, Sweden Linkoping Univ, Dept Elect Engn, SE-58183 Linkoping, Sweden.
    Zirath, H
    Swedish Def Res Agcy, FOI, SE-58111 Linkoping, Sweden Linkoping Univ, Dept Phys, SE-58183 Linkoping, Sweden Chalmers, Dept Microelect, SE-41296 Gothenburg, Sweden Linkoping Univ, Dept Elect Engn, SE-58183 Linkoping, Sweden.
    Svensson, C
    Evaluation of SiC MESFET structures using large-signal time-domain simulations2002In: Materials Science Forum Vols. 389-393, 2002, Vol. 389-3, p. 1395-1398Conference paper (Refereed)
    Abstract [en]

    When designing transistors for microwave power applications a good understanding of their large signal behaviour in a real circuit context is essential. We have used the device simulator Medici in a novel way to simulate the large signal high frequency time domain properties of different SiC MESFET structures. The simulations show that even for transistors with good DC properties the exact design of the channel-buffer and the buffer-substrate regions is important when a good high power RF performance is required. Our simulations indicate that output power densities above 6W/mm are possible if heating problems are solved.

  • 36.
    Jonsson, Rolf
    et al.
    Swedish Def Res Agcy, FOI, S-58183 Linkoping, Sweden.
    Ul Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Rudner, Staffan
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    DC and RF performance of insulating gate 4H-SiC depletion mode Field Effect Transistors2004In: Materials Science Forum, Vols. 457-460, 2004, Vol. 457-460, p. 1225-1228Conference paper (Refereed)
    Abstract [en]

    A depletion mode 4H-SiC MOSFET for RT applications is studied using drift-diffusion physical device simulations. The structure is basically the same as for a MESFET. A MOS gate with a 30 nm thick SiO2 layer replaces the Schottky gate. A 40% increase in the drain current was observed for a positive gate bias of 7 V compared to 0 V. The small signal AC analysis showed f(T) and f(max) to be 15.7 and 52.9 GHz respectively.

  • 37.
    Jonsson, Rolf
    et al.
    FOA Defence Research Establishment, Linköping, Sweden.
    Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Rudner, Staffan
    FOA Defence Research Establishment, Linköping, Sweden.
    DC and RF performance of insulating gate 4H-SiC depletion mode field effect transistors2004In: Materials Science Forum Vols. 457-460, 2004, p. 1225-1228Conference paper (Refereed)
  • 38.
    Jonsson, Rolf
    et al.
    FOI, Linköping.
    Wahab, Qamar Ul
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Rudner, Staffan
    FOI, Linköping.
    Svensson, Christer
    Linköping University, The Institute of Technology. Linköping University, Department of Electrical Engineering, Electronic Devices.
    Computational load pull simulations of SiC microwave power transistors2003In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 47, no 11, p. 1921-1926Article in journal (Refereed)
    Abstract [en]

    The design of power transistors for microwave applications requires a good understanding of their large signal behaviour in a real circuit context. The computational load-pull simulation technique is a powerful new way to evaluate the full time-domain voltages and currents of microwave power transistors during realistic operation. With this method it is possible to relate details in the time domain voltages and currents to corresponding variations in carrier densities, electrical field, etc. in the device. We have utilised the standard device simulator Medici, directly driven by sine voltage sources on both input and output. The resulting data from the simulations was then analysed using Matlab. Several 4H-SiC MESFET structures were evaluated by this technique and we found the p-type buffer layer doping and thickness to be crucial to obtain an optimum RF power. A 4H-SiC MESFET structure was found to have an output power of 6.2 W/mm at 1 GHz. ⌐ 2003 Elsevier Ltd. All rights reserved.

  • 39.
    Kashif, Ahsan-Ullah
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Arnborg, T.
    Johansson, Thomas
    Linköping University, The Institute of Technology. Linköping University, Department of Electrical Engineering, Electronics System.
    Svensson, Christer
    Linköping University, The Institute of Technology. Linköping University, Department of Electrical Engineering, Electronic Devices.
    Wahab, Qamar Ul
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    A new large signal simulation technique to study non-linear effects of microwave power transistor2007In: International Semiconductor Device Research Symposium 2007 ISDRS-07,2007, IEEE , 2007Conference paper (Refereed)
  • 40.
    Kashif, Ahsan-Ullah
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Azam, Sher
    National Engineering and Scientific Commission (NESCOM), P.O. Box 2801, Islamabad, Pakistan.
    Hayat, Khizar
    National Engineering and Scientific Commission (NESCOM), P.O. Box 2801, Islamabad, Pakistan.
    Imran, Muhammad
    National Engineering and Scientific Commission (NESCOM), P.O. Box 2801, Islamabad, Pakistan.
    Svensson, Christer
    Linköping University, Department of Electrical Engineering, Electronic Devices. Linköping University, The Institute of Technology.
    Wahab, Qamar-ul
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Switching Behavior of Microwave Power Transistor Studied in TCAD for Switching Class Power Amplifiers and Experimental Verification by LDMOS based Class-F Power Amplifier2010Manuscript (preprint) (Other academic)
    Abstract [en]

    This paper presents a TCAD study of high speed switching behavior of RF power-transistor in class-F Power Amplifier. We utilized finite harmonics loads for achieving maximum efficiency, without external circuitry. The in house developed computational load–pull (CLP) simulation technique is further extended to investigate the odd harmonic effects of RF transistor in class-F operation. An LD-MOSFET is studied which provided 81.2 % power added efficiency (PAE) at 1 GHz. The concept is experimentally verified by fabricating a class-F PA using same transistor. In the measurement, 76 % PAE is achieved, which is close to the TCAD simulated results. TCAD is an excellent tool to study the behavior of active devices. It has an ability to enhance and optimize the performance of transistor according to system specifications before fabrication.

  • 41.
    Kashif, Ahsan-Ullah
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Azam, Sher
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Svensson, Christer
    Linköping University, The Institute of Technology. Linköping University, Department of Electrical Engineering, Electronic Devices.
    Wahab, Qamar Ul
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Flexible power amplifier designing form device to circuit level by computational load-pull simulation technique2008In: Microelectonics Technology and Devices - SBMicro 2008, Vol. 14, issue 1: J. Swart, S. Selberherr, A. Susin, J. Diniz, N. Morimoto, Pennington, New Jersey: Electrochemical Society , 2008, Vol. 14, p. 233-239Conference paper (Refereed)
    Abstract [en]

    Matchingnetwork is major issue in broadband power amplifiers due tothe fact that the transistor impedances are varying both withfrequency and signal level. Thus it is difficult to matchthese impedances both at the input and output stages. Thetunable matching networks are very demanding and desired for buildingflexible systems, but their accuracy depends on the transistor performanceunder the large signal operation. Computational load pull (CLP) simulationtechnique is a unique way to extract the impedances ofpower transistor at desired frequencies which make the design ofmatching network much easier for multiple bands power amplifiers. AnLDMOS transistor is studied and its optimum impedances are extractedat 1, 2 and 2.5 GHz. Through optimum impedance, thetunable matching networks can be easily design for broadband amplifiers.

  • 42.
    Kashif, Ahsan-Ullah
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Johansson, T.
    Svensson, Christer
    Linköping University, The Institute of Technology. Linköping University, Department of Electrical Engineering, Electronic Devices.
    Arnborg, T.
    Wahab, Qamar Ul
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Enhancement in RF performance of LDMOS transistor utilizing large signal TCAD physical simulation2007In: Conference on RF measurement technology RFMTC07,2007, 2007Conference paper (Other academic)
  • 43.
    Kashif, Ahsan-Ullah
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Johansson, T.
    Infineon Technologies Nordic AB, SE-164 81 Kista, Sweden.
    Svensson, Christer
    Linköping University, Department of Electrical Engineering, Electronic Devices. Linköping University, The Institute of Technology.
    Azam, Sher
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Arnborg, T.
    Ericsson AB, SE-221 83 Lund, Sweden.
    Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Influence of interface state charges on RF performance of LDMOS transistor2008In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 52, no 7, p. 1099-1105Article in journal (Refereed)
    Abstract [en]

    Si-LDMOS transistor is studied by TCAD simulation for improved RF performance. In LDMOS structure, a low-doped reduced surface field (RESURF) region is used to obtain high breakdown voltage, but it reduces the transistor RF performance due to high on-resistance. The interface charges between oxide and the RESURF region are studied and found to have a strong impact on the transistor performance both in DC and RF. The presence of excess interface state charges at the RESURF region results not only higher DC drain current but also improved RF performance in terms of power, gain and efficiency. The most important achievement is the enhancement of operating frequency and RF output power is obtained well above 1 W/mm up to 4 GHz.

  • 44.
    Kashif, Ahsan-Ullah
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Jonsson, R.
    Wahab, Qamar Ul
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Further enhancement of Load pull simulation technique to study non linear effects of LDMOS in TCAD2008In: Giga Hertz Symposium,2008, 2008Conference paper (Other academic)
  • 45.
    Kashif, Ahsan-Ullah
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Svensson, Christer
    Linköping University, Department of Electrical Engineering, Electronic Devices. Linköping University, The Institute of Technology.
    Azam, Sher
    National Engineering and Scientific Commission (NESCOM), P.O. Box 2801, Islamabad, Pakistan.
    Hayat, Khizar
    National Engineering and Scientific Commission (NESCOM), P.O. Box 2801, Islamabad, Pakistan.
    Imran, Muhammad
    National Engineering and Scientific Commission (NESCOM), P.O. Box 2801, Islamabad, Pakistan.
    Wahab, Qamar-ul
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    A TCAD Approach to Design a Broadband Power Amplifier2010Manuscript (preprint) (Other academic)
    Abstract [en]

    Technology Computer Aided Design (TCAD) provides an alternate method to study the power amplifier (PA) design prior to fabrication. It is very useful for the extraction of an accurate large signal model. This paper presents a design approach from device to circuit level to study broadband PA performance of RF-LDMOS using computational load-pull (CLP) analysis. To validate the TCAD approach, we have designed a broadband (1.9 - 2.5 GHz) class AB power amplifier. The concept is verified by designing an output broadband matching network at optimum impedance value (Zf) of RF-LDMOS using ADS software. The large signal results verify this concept and RF output power of 30.8 dBm is achieved with comparable gain and efficiency.

  • 46.
    Kashif, Ahsan-Ullah
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Svensson, Christer
    Linköping University, Department of Electrical Engineering, Electronic Devices. Linköping University, The Institute of Technology.
    Hayat, Khizar
    National Engineering and Scientific Commission (NESCOM), P.O. Box 2801, Islamabad, Pakistan.
    Azam, Sher
    National Engineering and Scientific Commission (NESCOM), P.O. Box 2801, Islamabad, Pakistan.
    Akhter, Nauman
    National Engineering and Scientific Commission (NESCOM), P.O. Box 2801, Islamabad, Pakistan.
    Imran, Muhammad
    National Engineering and Scientific Commission (NESCOM), P.O. Box 2801, Islamabad, Pakistan.
    Wahab, Qamar-ul
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    A TCAD approach for non-linear evaluation of microwave power transistor and its experimental verification by LDMOS2010In: Journal of Computational Electronics, ISSN 1569-8025, E-ISSN 1572-8137, Vol. 9, no 2, p. 79-86Article in journal (Refereed)
    Abstract [en]

    A simulation technique is developed in TCAD to study the non-linear behavior of RF power transistor. The technique is based on semiconductor transport equations to swot up the overall non-linearity’s occurring in RF power transistor. Computational load-pull simulation technique (CLP) developed in our group, is further extended to study the non-linear effects inside the transistor structure by conventional two-tone RF signals, and initial simulations were done in time domain. The technique is helpful to detect, understand the phenomena and its mechanism which can be resolved and improve the transistor performance. By this technique, the third order intermodulation distortion (IMD3) was observed at different power levels. The technique was successfully implemented on a laterally-diffused field effect transistor (LDMOS). The value of IMD3 obtained is −22 dBc at 1-dB compression point (P 1 dB) while at 10 dB back off the value increases to −36 dBc. Simulation results were experimentally verified by fabricating a power amplifier with the similar LDMOS transistor.

  • 47.
    Kashif, Ahsan-Ullah
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Svensson, Christer
    Linköping University, Department of Electrical Engineering, Electronic Devices. Linköping University, The Institute of Technology.
    Ul Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Reduction in on-resistance of LDMOS transistor for improved RF performance2009In: Microelectronics Technology and Devices - SBMicro 2009, Vol. 23, issue 1 / [ed] D. De Lima Monteiro, O. Bonnaud, N. Morimoto, Pennington, New Jersey: The Electrochemical Society , 2009, p. 413-420Conference paper (Refereed)
    Abstract [en]

    Inan LDMOS transistor, a low doped drift (LDD) region atthe drain side is created to enhance the breakdown voltage(BVDS), but this increases on-resistance (Ron) which degrades the transistorRF performance. In this paper, the LDD region of LDMOStransistor is optimized using two different techniques, (i) a dualimplanted-layer p- and n-region in LDD and (ii) an excessinterface charge at the RESURF of LDD. Both techniques areused to enhance the carrier density for lower Ron. Thecomparison revealed that excess interface charge provides 43 % reductionin Ron with BVDS of 70 V, while the dual-implantedregion provides 26 % reduction in Ron together with BVDSof 64 - 68 V.

  • 48.
    Kashif, Ahsan-Ullah
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Svensson, Christer
    Linköping University, The Institute of Technology. Linköping University, Department of Electrical Engineering, Electronic Devices.
    Wahab, Qamar Ul
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    High power LDMOS transistor for RF-amplifiers.2007In: International Bhurban conference on applied sciences technology.,2007, 2007Conference paper (Refereed)
    Abstract [en]

       

  • 49.
    Khan, H. R.
    et al.
    NED University of Engn and Technology, Pakistan.
    Qureshi, A. R.
    NED University of Engn and Technology, Pakistan.
    Zafar, F.
    NED University of Engn and Technology, Pakistan.
    ul Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    PWM with Differential Class-E Amplifier for Efficiency Enhancement at Back-Off Power Levels2014In: 2014 IEEE 57TH INTERNATIONAL MIDWEST SYMPOSIUM ON CIRCUITS AND SYSTEMS (MWSCAS), IEEE , 2014, p. 607-610Conference paper (Refereed)
    Abstract [en]

    A simplified output matching network for pulse width modulated Class-E Power Amplifier for efficiency enhancement at back-off power level is proposed. The shunt capacitance and the series inductance in the Class-E PA are realized through capacitor banks that are tuned according to the duty cycle to meet ZVS conditions. The differential PA design is implemented in 130 nm CMOS technology achieving maximum Pout of 24.8 dBm at 1.8 GHz with PAE better than 38% at 50% duty cycle. The output power is modulated with the input duty cycle and provides 6.2 dB back-off power level keeping PAE almost constant around 38%.

  • 50.
    Khan, H. R.
    et al.
    NED University of Engn and Technoloy, Pakistan.
    Qureshi, A. R.
    NED University of Engn and Technoloy, Pakistan.
    Zafar, F.
    NED University of Engn and Technoloy, Pakistan.
    Wahab, Qamar Ul
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Design of a Broadband Current Mode Class-D Power Amplifier with Harmonic Suppression2014In: 2014 IEEE 12TH INTERNATIONAL NEW CIRCUITS AND SYSTEMS CONFERENCE (NEWCAS), IEEE , 2014, p. 169-172Conference paper (Refereed)
    Abstract [en]

    Current Mode Class-D Power Amplifiers (CMC-DPA) are attractive for fully integrated PA implementation as the output capacitance of the active device can be absorbed in the output matching network that can be realized with minimum number of components. This paper presents a simplified design approach for CMCD PA design using an integrated balun transformers. Also, expressions are derived for the optimum device sizing for second harmonic suppression resulting in improved efficiency. The amplifier is implemented in 130 nm CMOS process and encapsulated in QFN package. Measurement results show that the amplifier exhibits broadband response between 1.4 GHz and 2.1 GHz with peak output power of 26.8 dBm at 1.8 GHz using a 2.4 V supply. PAE remains above 40% for the entire range while peak PAE and drain efficiency are 45% and 48%, respectively.

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