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  • 1.
    Ciechonski, Rafal
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Device characteristics of sublimation grown 4H-SiC layers2005Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    At present, focus of the SiC crystal growth development is on improving the crystalline quality without polytype inclusions, micropipes and the occurrence of extended defects. The purity of the grown material, as well as intentional doping must be well controlled and the processes understood. High-quality substrates will significantly improve device performance and yield. One of the aims of the licentiate thesis is further understanding of polytype inclusion formation as well as impurity control in SiC bulk crystals grown using PVT method also termed seeded sublimation method. We have identified a carbonization of the source as a major reason behind the polytype inclusion occurrence during the growth. The aim of this work was further understanding of sublimation growth process of 4H-SiC bulk crystals in vacuum, in absence of an inert gas. For comparison growth in argon atmosphere (at 5 mbar) was performed. The effect of the ambient on the impurity incorporation was studied for different growth temperatures. For better control of the process in vacuum, tantalum as a carbon getter was utilized.

    The major focus of the thesis was put on further understanding of the PVT epitaxy with an emphasis on the high growth rate and the purity of grown layers.

    High resistivity 4H-SiC samples grown by sublimation with high growth rate were studied. The measurements show resistivity values up to high 104 Ωcm. By correlation between the growth conditions and SIMS results, we apply a model in which it is proposed that an isolated carbon vacancy donor-like level is a possible candidate responsible for compensation of the shallow acceptors in p-type 4H-SiC. A relation between cathodoluminescence (CL) and DL TS data is taken into account to support the model.

    To meet the requirements for high voltage blocking devices such as high voltage Schottky diodes and MOSFETs, 4H-SiC epitaxial layers have to exhibit low doping concentration in order to block reverse voltages up to few keV and at the same time have a low on-state resistance (Ron). High Ron leads to enhanced power consumption in the operation mode of the devices. In growth of thick layers for high voltage blocking devices, the conditions to achieve good on-state characteristics become more challenging due to the low doping and pronounced thicknesses needed, preferably in short growth periods. In case of high-speed epitaxy such as the sublimation, the need to apply higher growth temperature to yield the high growth rate, results in an increased concentration of background impurities in the layers as well as an influence on the intrinsic defects.

    On-state resistance Ron estimated from current density-voltage characteristics of Schottky diodes on thick sublimation layers exhibits variations from tens of mΩ.cm2 to tens of Ω.cm2 for different doping levels. In order to understand the occurrence of high on-state resistance, Schottky barrier heights were first estimated for both forward and reverse bias with the application of thermionic emission theory and were in agreement with a literature reported values. Decrease in mobility with increasing temperature was observed and its dependencies of T-1.3 and T-2.0 for moderately doped and low doped samples, respectively, were estimated. From deep level measurements by Minority Carrier Transient Spectroscopy, an influence of shallow boron related levels and D-center on the on-state resistance was observed, being more pronounced in low doped samples. Similar tendency was observed in depth profiling of Ron. This suggests a major role of boron in a compensation mechanism.

    Metal-Oxide-Semiconductor (MOS) capacitors were fabricated and characterized on 4H-SiC epilayers grown by PVT (sublimation) epitaxy and compared to the properties of similar structures on CVD grown layers. Detailed investigations of the PVT structures indicate a stable behaviour of the interface traps from roomtemperature up to 475 K. The amount of positive oxide charges Qo is 6.83x109 cm-2 at room temperature and decreases with temperature increase which suggests temperature stability of processed devices. The density of interface states Dit obtained by AC conductance method is lower in the case of PVT sample.

    AI203 as an alternative gate dielectric was studied. The implementation of this high-k dielectric is required in the case of high electric fields at which the usage of SiO2 may result in the reliability problems. The electrical properties of AI2O3 as a gate dielectric in MOS structures based on n- and p-type 4H-SiC grown by sublimation method were investigated and compared to the properties of similar structures utilizing SiO2.

    Delarbeten
    1. Effect of Ambient on 4H-SiC Bulk Crystals grown by Sublimation
    Öppna denna publikation i ny flik eller fönster >>Effect of Ambient on 4H-SiC Bulk Crystals grown by Sublimation
    2003 (Engelska)Ingår i: Materials Science Forum, Vols. 433-436 / [ed] Peder Bergman and Erik Janzén, 2003, Vol. 433-436, s. 75-78Konferensbidrag, Publicerat paper (Refereegranskat)
    Abstract [en]

    Sublimation bulk growth in vacuum using graphite crucibles and such with tantalum shielding of the crucible walls has been studied. Residual nitrogen, aluminum and boron doping in the material grown in vacuum is presented. Activation energies of growth rate in respect to growth temperature in vacuum are deduced. The estimated values are 21 kcallmole for growth temperatures below 2075°C and 128 kcal/mole in the range of growth temperatures between 2075°C and 2275°C. Cathodoluminescence spectra taken from samples grown in the graphite crucible in absence of tantalum under different pressures show nitrogen-alurninum DAP transition and strong luminescence from deep boron. This is not the case for samples grown in the tantalum environment.

    Nyckelord
    Bulk Growth, Doping, Boron, Tantalum, Cathodoluminescence
    Nationell ämneskategori
    Naturvetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-12782 (URN)10.4028/www.scientific.net/MSF.433-436.75 (DOI)
    Konferens
    ECSCRM 2002. Linköping, Sweden, September 1-5, 2002
    Tillgänglig från: 2007-12-04 Skapad: 2007-12-04 Senast uppdaterad: 2013-11-07
    2. Structural instabilities in growth of SiC crystals
    Öppna denna publikation i ny flik eller fönster >>Structural instabilities in growth of SiC crystals
    2005 (Engelska)Ingår i: Journal of Crystal Growth, ISSN 0022-0248, Vol. 275, nr 1-2, s. e461-e466Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Misoriented grains, which may occur on the growth front of 6H–SiC boules have been studied in relation to their appearance during sublimation growth. The effect was obtained by applying growth conditions at which the source powder was gradually approaching graphitisation and the vapour becoming C-rich. The high off-orientation of the grains is demonstrated through etching in molten KOH and transmission light optical microscopy. Micropipes propagating in the single crystal area and facing the misoriented grain have been studied, and it is shown that they may either be terminated at the grain or their propagation is altered to be parallel with the grain boundary. It has been found that the polytype of the grains may switch from 6H to 4H, which is explained by the change of the Si/C ratio in the vapour.

    Nyckelord
    Crystal morphology; Volume defects; Growth from vapor; Single crystal growth; Semiconductor silicon compounds
    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:liu:diva-12783 (URN)10.1016/j.jcrysgro.2004.11.020 (DOI)
    Tillgänglig från: 2007-12-04 Skapad: 2007-12-04 Senast uppdaterad: 2013-11-07
    3. Growth of device quality 4H-SiC by high velocity epitaxy
    Öppna denna publikation i ny flik eller fönster >>Growth of device quality 4H-SiC by high velocity epitaxy
    2004 (Engelska)Ingår i: Materials Science Forum, Vols. 457-460, 2004, Vol. 457-460, s. 201-204Konferensbidrag, Publicerat paper (Refereegranskat)
    Abstract [en]

    Thick (>20 μm) 4H-SiC layers in doping range of low 1015-1016 cm-3 were grown by sublimation epitaxy at a growth rate of similar to50 mum/hour. Two inch 25 μm thick layers were fabricated with standard thickness deviation of 3.77%. Effect of important process parameters on the material grade has been discussed. The Schottky diodes processed on this material sustained 900V reverse voltage at a current of 1.7 x 10-8 A, while measured on MOS capacitors the interface state density was as low as similar to6-9 x 1010 cm-2.

    Nyckelord
    fast growth, sublimation epitaxy, 4H-SiC, device quality, schottky diode, MOS capacitor, interface state density
    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:liu:diva-48297 (URN)10.4028/www.scientific.net/MSF.457-460.201 (DOI)
    Konferens
    ICSCRM 2003, Lyon, Fance, October 5-10, 2003
    Tillgänglig från: 2009-10-11 Skapad: 2009-10-11 Senast uppdaterad: 2013-11-07
    4. Effect of boron on the resistivity of compensated 4H-SiC
    Öppna denna publikation i ny flik eller fönster >>Effect of boron on the resistivity of compensated 4H-SiC
    2003 (Engelska)Ingår i: Journal of electronic materials, ISSN 0361-5235, Vol. 32, nr 5, s. 452-457Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    High-resistivity 4H-SiC samples grown by sublimation with a high growth rate are studied. The measurements show resistivity values up to a high of 104 Ωcm. The secondary ion mass spectroscopy (SIMS) results revealed a presence of only common trace impurities such as nitrogen, aluminum, and boron. To understand the compensation mechanism in these samples, capacitance deep-level transient spectroscopy (DLTS) on the p-type epilayers has been performed. By correlation between the growth conditions and SIMS results, we apply a model in which it is proposed that an isolated carbon vacancy donorlike level is a possible candidate responsible for compensation of the shallow acceptors in p-type 4H-SiC. A relation between cathodoluminescence (CL) and DLTS data is taken into account to support the model.

    Nyckelord
    SiC sublimation epitaxy, DLTS, compensation, deep levels, carbon vacancy, high resistivity, semi-insulating
    Nationell ämneskategori
    Naturvetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-12784 (URN)10.1007/s11664-003-0177-0 (DOI)
    Tillgänglig från: 2007-12-04 Skapad: 2007-12-04 Senast uppdaterad: 2013-11-07
    5. Evaluation of On-state Resistance and Boron-related Levels in n-type 4H-SiC
    Öppna denna publikation i ny flik eller fönster >>Evaluation of On-state Resistance and Boron-related Levels in n-type 4H-SiC
    2005 (Engelska)Ingår i: Materials Science Forum, Vols. 483-485, 2005, Vol. 483-485, s. 425-428Konferensbidrag, Publicerat paper (Refereegranskat)
    Abstract [en]

    Specific on-resistance Ron estimated from current density-voltage characteristics of Schottky diodes on thick layers exhibits variations from tens of mΩ.cm2 to tens of Ω.cm2 for different doping levels. In order to understand the occurrence of high on-state resistance, Schottky barrier heights were first estimated for both forward and reverse bias with the application of thermionic emission theory and were in agreement with a literature reported values. Decrease in mobility with the temperature was observed and its dependencies of T–1.3 and T–2.0 for moderately doped and low doped samples respectively were estimated. From deep level measurements by Minority Carrier Transient Spectroscopy, an influence of shallow boron related levels and D-center on dependence of on-state resistance was observed, being more pronounced in low doped samples. Similar tendency was observed in depth profiling of Ron. This suggests a major role of boron in a compensation mechanism thus resulting in high Ron.

    Nyckelord
    On-state resistance, I-V, C-V, MCTS, Sublimation, High-speed epitaxy, Deep
    Nationell ämneskategori
    Naturvetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-12785 (URN)
    Konferens
    ECSCRM2004
    Tillgänglig från: 2007-12-04 Skapad: 2007-12-04 Senast uppdaterad: 2013-11-07
    6. Electrical Analysis and Interface States Evaluation of of Ni Schottky diodes on 4H-SiC thick epilayers
    Öppna denna publikation i ny flik eller fönster >>Electrical Analysis and Interface States Evaluation of of Ni Schottky diodes on 4H-SiC thick epilayers
    2005 (Engelska)Ingår i: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 202, nr 13, s. 2508-2514Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    This work has been focused on characterization of thick 4H-SiC layers produced by sublimation epitaxy. Nickel Schottky contacts have been fabricated in order to characterize the grown material and evaluate the interfacial layer between metal and semiconductor. The characterization study includes current-voltage and capacitance-voltage high temperature measurements, from which Schottky barrier, net donor concentration and on-state resistance values have been extracted. The diodes show a typical behavior of J-V and C-V curves with temperature, with Schottky barrier heights of 1.3 eV ÷ 1.4 eV and net donor concentration of 4 × 1015 cm-3 ÷ 1 × 1016 cm-3. From the Bardeen's model on reverse J-V, the density of states of the interfacial layer has been estimated to 7 × 1011 eV-1 cm-2 ÷ 8 × 1011 eV-1 cm-2, a value that is similar to the density of states of oxide layers in deliberated MOS structures realized on the same epilayers.

    Ort, förlag, år, upplaga, sidor
    John Wiley & Sons, 2005
    Nyckelord
    73.20.Hb, 73.30.+y, 73.40.Ns, 73.61.Le
    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:liu:diva-12786 (URN)10.1002/pssa.200521147 (DOI)
    Tillgänglig från: 2007-12-04 Skapad: 2007-12-04 Senast uppdaterad: 2017-05-11Bibliografiskt granskad
    7. Evaluation of MOS structures processed on 4H–SiC layers grown by PVT epitaxy
    Öppna denna publikation i ny flik eller fönster >>Evaluation of MOS structures processed on 4H–SiC layers grown by PVT epitaxy
    2005 (Engelska)Ingår i: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 49, nr 12, s. 1917-1920Artikel i tidskrift (Refereegranskat) Published
    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.

    Nationell ämneskategori
    Naturvetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-30706 (URN)10.1016/j.sse.2005.08.008 (DOI)16318 (Lokalt ID)16318 (Arkivnummer)16318 (OAI)
    Tillgänglig från: 2009-10-09 Skapad: 2009-10-09 Senast uppdaterad: 2017-12-13
    8. Electrical behavior of 4H-SiC metal-oxide-semiconductor structures with Al2O3 as gate dielectric
    Öppna denna publikation i ny flik eller fönster >>Electrical behavior of 4H-SiC metal-oxide-semiconductor structures with Al2O3 as gate dielectric
    Visa övriga...
    2005 (Engelska)Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 97, nr 12, s. 124507-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    The electrical properties of Al2O3 as a gate dielectric in metal-oxide-semiconductorstructures based on n- and p-type 4H-SiC grown by sublimation method have been investigated and compared to the properties of similar structures utilizing SiO2. The electrically active defects in the structures are studied by capacitance–voltage (C–V) and current–voltage (I–V) methods. The results show that the type as well as spatial and energy distributions of defects in Al2O3/SiC and SiO2/SiC samples are different. The structures with Al2O3 on p-type 4H-SiC demonstrate much better electrical characteristics than the p-type 4H-SiC/SiO2 structures. It is demonstrated that the conduction process in the former is governed by Fowler–Nordheim electron tunneling from the Al gate whereas in the latter the hole tunneling from SiC is the more probable process. This difference combined with the higher defect density in p-type SiC/SiO2 structures defines the higher leakage currents compared to the structures utilizing Al2O3.

    Nationell ämneskategori
    Naturvetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-30684 (URN)10.1063/1.1938267 (DOI)16289 (Lokalt ID)16289 (Arkivnummer)16289 (OAI)
    Tillgänglig från: 2009-10-09 Skapad: 2009-10-09 Senast uppdaterad: 2017-12-13
  • 2.
    Ciechonski, Rafal
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik. Linköpings universitet, Tekniska högskolan.
    Growth and characterization of SiC and GaN2007Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    At present, focus of the SiC crystal growth development is on improving the crystalline quality without polytype inclusions, micropipes and the occurrence of extended defects. The purity of the grown material, as well as intentional doping must be well controlled and the processes understood. High-quality substrates will significantly improve device performance and yield. One of the aims of the thesis is further understanding of polytype inclusion formation as well as impurity control in SiC bulk crystals grown using PVT method also termed seeded sublimation method. Carbonization of the source was identified as a major reason behind the polytype inclusion occurrence during the growth. The aim of this work was further understanding of sublimation growth process of 4H-SiC bulk crystals in vacuum, in absence of an inert gas. For comparison growth in argon atmosphere (at 5 mbar) was performed. The effect of the ambient on the impurity incorporation was studied for different growth temperatures. For better control of the process in vacuum, tantalum as a carbon getter was utilized.

    The focus of the SiC part of the thesis was put on further understanding of the PVT epitaxy with an emphasis on the high growth rate and purity of grown layers.

    High resistivity 4H-SiC samples grown by sublimation with high growth rate were studied. The measurements show resistivity values up to high 104 cm. By correlation between the growth conditions and SIMS results, a model was applied in which it is proposed that an isolated carbon vacancy donor-like level is a possible candidate responsible for compensation of the shallow acceptors in p-type 4H-SiC. A relation between cathodoluminescence (CL) and DLTS data is taken into account to support the model.

    To meet the requirements for high voltage blocking devices such as high voltage Schottky diodes and MOSFETs, 4H-SiC epitaxial layers have to exhibit low doping concentration in order to block reverse voltages up to few keV and at the same time have a low on-state resistance (Ron). High Ron leads to enhanced power consumption in the operation mode of the devices. In growth of thick layers for high voltage blocking devices, the conditions to achieve good on-state characteristics become more challenging due to the low doping and pronounced thicknesses needed, preferably in short growth periods. In case of high-speed epitaxy such as the sublimation, the need to apply higher growth temperature to yield the high growth rate, results in an increased concentration of background impurities in the layers as well as an influence on the intrinsic defects.

    On-state resistance Ron estimated from current density-voltage characteristics of Schottky diodes on thick sublimation layers exhibits variations from tens of mΩ.cm2 to tens of Ω.cm2 for different doping levels. In order to understand the occurrence of high on-state resistance, Schottky barrier heights were first estimated for both forward and reverse bias with the application of thermionic emission theory and were in agreement with literature reported values. Decrease in mobility with increasing temperature was observed and its dependencies of T–1.3 and T–2.0 for moderately doped and low doped samples, respectively, were estimated. From deep level measurements by Minority Carrier Transient Spectroscopy (MCTS), an influence of shallow boron related levels and D-center on the on-state resistance was observed, being more pronounced in low doped samples. Similar tendency was observed in depth profiling of Ron. This suggests a major role of boron in a compensation mechanism.

    In the second part of the thesis growth and characterization of GaN is presented. Excellent electron transport properties with high electron saturate drift velocity make GaN an excellent candidate for electronic devices. Especially, AlGaN/GaN based high electron mobility transistors (HEMT) have received an increased attention in last years due to their attractive properties. The presence of strong spontaneous and piezoelectric polarization due to the lattice mismatch between AlGaN and GaN is responsible for high free electrons concentrations present in the vicinity of the interface. Due to the spatial separation of electrons and ionized donors or surface states, 2DEG electron gas formed near the interface of the heterostructure exhibits high sheet carrier density and high mobility of electrons. Al0.23Ga0.77N/GaN based HEMT structures with an AlN exclusion layer on 100 mm semiinsulating 4H-SiC substrates have been grown by hot-wall MOCVD. The electrical properties of the two-dimensional electron gas (2DEG) such as electron mobility, sheet carrier density and sheet resistance were obtained from Hall measurements, capacitance-voltage and contact-less eddy-current techniques. The effect of different scattering mechanisms on the mobility have been taken into account and compared to the experimental data. Hall measurements were performed in the range of 80 to 600 K. Hall electron mobility is equal to 17140 cm2(Vs)-1 at 80 K, 2310 cm2(Vs)-1 at room temperature, and as high as 800 cm2(Vs)-1 at 450 K, while the sheet carrier density is 1.04x1013 cm-2 at room temperature and does not vary very much with temperature. Estimation of different electron scattering mechanisms reveals that at temperatures higher than room temperature, experimental mobility data is mainly limited by optical phonon scattering. At relevant high power device temperature (450 K) there is still an increase of mobility due to the AlN exclusion layer.

    We have studied the behaviour of Ga-face GaN epilayers after in-situ thermal treatment in different gas mixtures in a hot-wall MOCVD reactor. Influence of N2, N2+NH3 and N2+NH3+H2 ambient on the morphology was investigated in this work. The most stable thermal treatment conditions were obtained in the case of N2+NH3 gas ambients. We have also studied the effect of the increased molar ratio of hydrogen in order to establish proper etching conditions for hot-wall MOCVD growth.

    Delarbeten
    1. Effect of Ambient on 4H-SiC Bulk Crystals grown by Sublimation
    Öppna denna publikation i ny flik eller fönster >>Effect of Ambient on 4H-SiC Bulk Crystals grown by Sublimation
    2003 (Engelska)Ingår i: Materials Science Forum, Vols. 433-436 / [ed] Peder Bergman and Erik Janzén, 2003, Vol. 433-436, s. 75-78Konferensbidrag, Publicerat paper (Refereegranskat)
    Abstract [en]

    Sublimation bulk growth in vacuum using graphite crucibles and such with tantalum shielding of the crucible walls has been studied. Residual nitrogen, aluminum and boron doping in the material grown in vacuum is presented. Activation energies of growth rate in respect to growth temperature in vacuum are deduced. The estimated values are 21 kcallmole for growth temperatures below 2075°C and 128 kcal/mole in the range of growth temperatures between 2075°C and 2275°C. Cathodoluminescence spectra taken from samples grown in the graphite crucible in absence of tantalum under different pressures show nitrogen-alurninum DAP transition and strong luminescence from deep boron. This is not the case for samples grown in the tantalum environment.

    Nyckelord
    Bulk Growth, Doping, Boron, Tantalum, Cathodoluminescence
    Nationell ämneskategori
    Naturvetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-12782 (URN)10.4028/www.scientific.net/MSF.433-436.75 (DOI)
    Konferens
    ECSCRM 2002. Linköping, Sweden, September 1-5, 2002
    Tillgänglig från: 2007-12-04 Skapad: 2007-12-04 Senast uppdaterad: 2013-11-07
    2. Structural instabilities in growth of SiC crystals
    Öppna denna publikation i ny flik eller fönster >>Structural instabilities in growth of SiC crystals
    2005 (Engelska)Ingår i: Journal of Crystal Growth, ISSN 0022-0248, Vol. 275, nr 1-2, s. e461-e466Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Misoriented grains, which may occur on the growth front of 6H–SiC boules have been studied in relation to their appearance during sublimation growth. The effect was obtained by applying growth conditions at which the source powder was gradually approaching graphitisation and the vapour becoming C-rich. The high off-orientation of the grains is demonstrated through etching in molten KOH and transmission light optical microscopy. Micropipes propagating in the single crystal area and facing the misoriented grain have been studied, and it is shown that they may either be terminated at the grain or their propagation is altered to be parallel with the grain boundary. It has been found that the polytype of the grains may switch from 6H to 4H, which is explained by the change of the Si/C ratio in the vapour.

    Nyckelord
    Crystal morphology; Volume defects; Growth from vapor; Single crystal growth; Semiconductor silicon compounds
    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:liu:diva-12783 (URN)10.1016/j.jcrysgro.2004.11.020 (DOI)
    Tillgänglig från: 2007-12-04 Skapad: 2007-12-04 Senast uppdaterad: 2013-11-07
    3. Effect of boron on the resistivity of compensated 4H-SiC
    Öppna denna publikation i ny flik eller fönster >>Effect of boron on the resistivity of compensated 4H-SiC
    2003 (Engelska)Ingår i: Journal of electronic materials, ISSN 0361-5235, Vol. 32, nr 5, s. 452-457Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    High-resistivity 4H-SiC samples grown by sublimation with a high growth rate are studied. The measurements show resistivity values up to a high of 104 Ωcm. The secondary ion mass spectroscopy (SIMS) results revealed a presence of only common trace impurities such as nitrogen, aluminum, and boron. To understand the compensation mechanism in these samples, capacitance deep-level transient spectroscopy (DLTS) on the p-type epilayers has been performed. By correlation between the growth conditions and SIMS results, we apply a model in which it is proposed that an isolated carbon vacancy donorlike level is a possible candidate responsible for compensation of the shallow acceptors in p-type 4H-SiC. A relation between cathodoluminescence (CL) and DLTS data is taken into account to support the model.

    Nyckelord
    SiC sublimation epitaxy, DLTS, compensation, deep levels, carbon vacancy, high resistivity, semi-insulating
    Nationell ämneskategori
    Naturvetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-12784 (URN)10.1007/s11664-003-0177-0 (DOI)
    Tillgänglig från: 2007-12-04 Skapad: 2007-12-04 Senast uppdaterad: 2013-11-07
    4. Evaluation of On-state Resistance and Boron-related Levels in n-type 4H-SiC
    Öppna denna publikation i ny flik eller fönster >>Evaluation of On-state Resistance and Boron-related Levels in n-type 4H-SiC
    2005 (Engelska)Ingår i: Materials Science Forum, Vols. 483-485, 2005, Vol. 483-485, s. 425-428Konferensbidrag, Publicerat paper (Refereegranskat)
    Abstract [en]

    Specific on-resistance Ron estimated from current density-voltage characteristics of Schottky diodes on thick layers exhibits variations from tens of mΩ.cm2 to tens of Ω.cm2 for different doping levels. In order to understand the occurrence of high on-state resistance, Schottky barrier heights were first estimated for both forward and reverse bias with the application of thermionic emission theory and were in agreement with a literature reported values. Decrease in mobility with the temperature was observed and its dependencies of T–1.3 and T–2.0 for moderately doped and low doped samples respectively were estimated. From deep level measurements by Minority Carrier Transient Spectroscopy, an influence of shallow boron related levels and D-center on dependence of on-state resistance was observed, being more pronounced in low doped samples. Similar tendency was observed in depth profiling of Ron. This suggests a major role of boron in a compensation mechanism thus resulting in high Ron.

    Nyckelord
    On-state resistance, I-V, C-V, MCTS, Sublimation, High-speed epitaxy, Deep
    Nationell ämneskategori
    Naturvetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-12785 (URN)
    Konferens
    ECSCRM2004
    Tillgänglig från: 2007-12-04 Skapad: 2007-12-04 Senast uppdaterad: 2013-11-07
    5. Electrical Analysis and Interface States Evaluation of of Ni Schottky diodes on 4H-SiC thick epilayers
    Öppna denna publikation i ny flik eller fönster >>Electrical Analysis and Interface States Evaluation of of Ni Schottky diodes on 4H-SiC thick epilayers
    2005 (Engelska)Ingår i: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 202, nr 13, s. 2508-2514Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    This work has been focused on characterization of thick 4H-SiC layers produced by sublimation epitaxy. Nickel Schottky contacts have been fabricated in order to characterize the grown material and evaluate the interfacial layer between metal and semiconductor. The characterization study includes current-voltage and capacitance-voltage high temperature measurements, from which Schottky barrier, net donor concentration and on-state resistance values have been extracted. The diodes show a typical behavior of J-V and C-V curves with temperature, with Schottky barrier heights of 1.3 eV ÷ 1.4 eV and net donor concentration of 4 × 1015 cm-3 ÷ 1 × 1016 cm-3. From the Bardeen's model on reverse J-V, the density of states of the interfacial layer has been estimated to 7 × 1011 eV-1 cm-2 ÷ 8 × 1011 eV-1 cm-2, a value that is similar to the density of states of oxide layers in deliberated MOS structures realized on the same epilayers.

    Ort, förlag, år, upplaga, sidor
    John Wiley & Sons, 2005
    Nyckelord
    73.20.Hb, 73.30.+y, 73.40.Ns, 73.61.Le
    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:liu:diva-12786 (URN)10.1002/pssa.200521147 (DOI)
    Tillgänglig från: 2007-12-04 Skapad: 2007-12-04 Senast uppdaterad: 2017-05-11Bibliografiskt granskad
    6. High 2DEG mobility of HEMT structures grown on 100 mm SI 4H-SiC substrates by hot-wall MOCVD
    Öppna denna publikation i ny flik eller fönster >>High 2DEG mobility of HEMT structures grown on 100 mm SI 4H-SiC substrates by hot-wall MOCVD
    Visa övriga...
    2007 (Engelska)Ingår i: Journal of Applied PhysicsArtikel i tidskrift (Refereegranskat) Submitted
    Nationell ämneskategori
    Naturvetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-12787 (URN)
    Tillgänglig från: 2007-12-04 Skapad: 2007-12-04 Senast uppdaterad: 2015-03-11
    7. In-situ treatment of GaN epilayers in hot-wall MOCVD
    Öppna denna publikation i ny flik eller fönster >>In-situ treatment of GaN epilayers in hot-wall MOCVD
    Visa övriga...
    (Engelska)Manuskript (Övrigt vetenskapligt)
    Identifikatorer
    urn:nbn:se:liu:diva-12788 (URN)
    Tillgänglig från: 2007-12-04 Skapad: 2007-12-04 Senast uppdaterad: 2015-03-11
  • 3.
    Ciechonski, Rafal
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Lundskog, Anders
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Forsberg, Urban
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Kakanakova-Georgieva, Anelia
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Pedersen, Henrik
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Janzén, Erik
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    High 2DEG mobility of HEMT structures grown on 100 mm SI 4H-SiC substrates by hot-wall MOCVD2007Ingår i: Journal of Applied PhysicsArtikel i tidskrift (Refereegranskat)
  • 4.
    Ciechonski, Rafal
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Syväjärvi, Mikael
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Kakanakova-Georgieva, Anelia
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Yakimova, Rositsa
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Effect of boron on the resistivity of compensated 4H-SiC2003Ingår i: Journal of electronic materials, ISSN 0361-5235, Vol. 32, nr 5, s. 452-457Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    High-resistivity 4H-SiC samples grown by sublimation with a high growth rate are studied. The measurements show resistivity values up to a high of 104 Ωcm. The secondary ion mass spectroscopy (SIMS) results revealed a presence of only common trace impurities such as nitrogen, aluminum, and boron. To understand the compensation mechanism in these samples, capacitance deep-level transient spectroscopy (DLTS) on the p-type epilayers has been performed. By correlation between the growth conditions and SIMS results, we apply a model in which it is proposed that an isolated carbon vacancy donorlike level is a possible candidate responsible for compensation of the shallow acceptors in p-type 4H-SiC. A relation between cathodoluminescence (CL) and DLTS data is taken into account to support the model.

  • 5.
    Ciechonski, Rafal
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Syväjärvi, Mikael
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Porro, Samuele
    Polytechnic of Turin, Physics Department, Torino, Italy.
    Yakimova, Rositsa
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Evaluation of On-state Resistance and Boron-related Levels in n-type 4H-SiC2005Ingår i: Materials Science Forum, Vols. 483-485, 2005, Vol. 483-485, s. 425-428Konferensbidrag (Refereegranskat)
    Abstract [en]

    Specific on-resistance Ron estimated from current density-voltage characteristics of Schottky diodes on thick layers exhibits variations from tens of mΩ.cm2 to tens of Ω.cm2 for different doping levels. In order to understand the occurrence of high on-state resistance, Schottky barrier heights were first estimated for both forward and reverse bias with the application of thermionic emission theory and were in agreement with a literature reported values. Decrease in mobility with the temperature was observed and its dependencies of T–1.3 and T–2.0 for moderately doped and low doped samples respectively were estimated. From deep level measurements by Minority Carrier Transient Spectroscopy, an influence of shallow boron related levels and D-center on dependence of on-state resistance was observed, being more pronounced in low doped samples. Similar tendency was observed in depth profiling of Ron. This suggests a major role of boron in a compensation mechanism thus resulting in high Ron.

  • 6.
    Ciechonski, Rafal
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Syväjärvi, Mikael
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    ul-Hassan, Jawad
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Yakimova, Rositsa
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Structural instabilities in growth of SiC crystals2005Ingår i: Journal of Crystal Growth, ISSN 0022-0248, Vol. 275, nr 1-2, s. e461-e466Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Misoriented grains, which may occur on the growth front of 6H–SiC boules have been studied in relation to their appearance during sublimation growth. The effect was obtained by applying growth conditions at which the source powder was gradually approaching graphitisation and the vapour becoming C-rich. The high off-orientation of the grains is demonstrated through etching in molten KOH and transmission light optical microscopy. Micropipes propagating in the single crystal area and facing the misoriented grain have been studied, and it is shown that they may either be terminated at the grain or their propagation is altered to be parallel with the grain boundary. It has been found that the polytype of the grains may switch from 6H to 4H, which is explained by the change of the Si/C ratio in the vapour.

  • 7.
    Ciechonski, Rafal
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Syväjärvi, Mikael
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Wahab, Qamar Ul
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Yakimova, Rositsa
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Evaluation of MOS structures processed on 4H–SiC layers grown by PVT epitaxy2005Ingår i: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 49, nr 12, s. 1917-1920Artikel i tidskrift (Refereegranskat)
    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.

  • 8.
    Ciechonski, Rafal
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Yakimova, Rositsa
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Syväjärvi, Mikael
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Janzén, Erik
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Effect of Ambient on 4H-SiC Bulk Crystals grown by Sublimation2003Ingår i: Materials Science Forum, Vols. 433-436 / [ed] Peder Bergman and Erik Janzén, 2003, Vol. 433-436, s. 75-78Konferensbidrag (Refereegranskat)
    Abstract [en]

    Sublimation bulk growth in vacuum using graphite crucibles and such with tantalum shielding of the crucible walls has been studied. Residual nitrogen, aluminum and boron doping in the material grown in vacuum is presented. Activation energies of growth rate in respect to growth temperature in vacuum are deduced. The estimated values are 21 kcallmole for growth temperatures below 2075°C and 128 kcal/mole in the range of growth temperatures between 2075°C and 2275°C. Cathodoluminescence spectra taken from samples grown in the graphite crucible in absence of tantalum under different pressures show nitrogen-alurninum DAP transition and strong luminescence from deep boron. This is not the case for samples grown in the tantalum environment.

  • 9. Ewing, D.J.
    et al.
    Porter, L.M.
    Wahab, Qamar Ul
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Ciechonski, Rafal
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Syväjärvi, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Yakimova, Rositsa
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Inhomogeneous electrical characteristics in 4H-SiC Schottky diodes2007Ingår i: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 22, nr 12, s. 1287-1291Artikel i tidskrift (Refereegranskat)
    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.

  • 10.
    Forsberg, Urban
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Lundskog, Anders
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Kakanakova-Georgieva, Anelia
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Ciechonski, Rafal
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Janzén, Erik
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Improved hot-wall MOCVD growth of highly uniform AlGaN/GaN/HEMT structures2009Ingår i: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 311, nr 10, s. 3007-3010Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The inherent advantages of the hot-wall metal organic chemical vapor deposition (MOCVD) reactor (low temperature gradients, less bowing of the wafer during growth, efficient precursor cracking) compared to a cold-wall reactor make it easier to obtain uniform growth. However, arcing may occur in the growth chamber during growth, which deteriorates the properties of the grown material. By inserting insulating pyrolytic BN (PBN) stripes in the growth chamber we have completely eliminated this problem. Using this novel approach we have grown highly uniform, advanced high electron mobility transistor (HEMT) structures on 4 semi-insulating (SI) SiC substrates with gas-foil rotation of the substrate. The nonuniformities of sheet resistance and epilayer thickness are typically less than 3% over the wafer. The room temperature hall mobility of the 2DEG is well above 2000 cm(2)/V s and the sheet resistance about 270 Omega/sqr.

  • 11.
    Kakanakova-Georgieva, Anelia
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Ciechonski, Rafal
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Forsberg, Urban
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Lundskog, Anders
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Janzén, Erik
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Hot-Wall MOCVD for Highly Efficient and Uniform Growth of AIN2009Ingår i: Crystal Growth & Design, ISSN 1528-7483, Vol. 9, nr 2, s. 880-884Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We demonstrated successful growth of AIN at a temperature of 1200 degrees C in a set of hot-wall MOCVD systems with the possibility of straightforward scaling up the process on larger wafer areas to meet the demand of device technologies. We outlined several aspects of the carefully optimized design and process parameters with relevance to achievement of a high overall growth rate (1 and up to 2 mu m/h), efficiency, and uniformity, which to a great extent depends on how consumption of growth-limiting species by gas-phase adduct formation can actively be prevented. Mixing of the precursors upstream from the deposition area facilitates uniform epitaxial growth, while the greater uniformity of substrate temperature inherent to the hot-wall reactor and rotation of the wafer are of fundamental importance for layer-growth uniformity. The AIN layer thickness can be controlled with an accuracy of +/- 1.3% on 2 in. wafers. The low-temperature cathodoluminescence spectrum of the AIN epitaxial material is strongly dominated by the intense near band-gap deep UV emission at about 208 nm.

  • 12.
    Lundskog, Anders
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Forsberg, Urban
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Kakanakova-Georgieva, Anelia
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Ciechonski, Rafal
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Ivanov, Ivan Gueorguiev
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Darakchieva, Vanya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Janzén, Erik
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Fagerlind, M.
    Shiu, J-Y.
    Rorsman, N.
    Highly Uniform Hot-Wall MOCVD Growth of High-Quality AlGaN/GaN HEMT-Structures on 100 mm Semi-Insulating 4H-SiC Substrates2007Ingår i: ICNS-7,2007, 2007Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

       

  • 13. Paskaleva, A
    et al.
    Ciechonski, Rafal
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Syväjärvi, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Atanassova, E
    Yakimova, Rositsa
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Characterization of 4H-SiC MOS structures with Al2O3 as gate dielectric2005Ingår i: Materials Science Forum, Vols. 483-485, 2005, Vol. 483, s. 709-712Konferensbidrag (Refereegranskat)
    Abstract [en]

    The electrical properties of Al2O3 as a gate dielectric in MOS structures based on n- and p-type 4H-SiC grown by sublimation method have been investigated and compared to the properties of similar structures utilizing SiO2. The electrically active defects in the structures are studied by CV method. The results show that the type as well as spatial and energy distribution of defects in Al2O3/SiC and SiO2/SiC samples are different. The structures with Al2O3 on p-type 4H-SiC demonstrate much better C-V characteristics than the p-type 4H-SiC/SiO2 structures.

  • 14. Paskaleva, A
    et al.
    Ciechonski, Rafal
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Syväjärvi, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Atanassova, E
    Yakimova, Rositsa
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Electrical behavior of 4H-SiC metal-oxide-semiconductor structures with Al2O3 as gate dielectric2005Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 97, nr 12, s. 124507-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The electrical properties of Al2O3 as a gate dielectric in metal-oxide-semiconductorstructures based on n- and p-type 4H-SiC grown by sublimation method have been investigated and compared to the properties of similar structures utilizing SiO2. The electrically active defects in the structures are studied by capacitance–voltage (C–V) and current–voltage (I–V) methods. The results show that the type as well as spatial and energy distributions of defects in Al2O3/SiC and SiO2/SiC samples are different. The structures with Al2O3 on p-type 4H-SiC demonstrate much better electrical characteristics than the p-type 4H-SiC/SiO2 structures. It is demonstrated that the conduction process in the former is governed by Fowler–Nordheim electron tunneling from the Al gate whereas in the latter the hole tunneling from SiC is the more probable process. This difference combined with the higher defect density in p-type SiC/SiO2 structures defines the higher leakage currents compared to the structures utilizing Al2O3.

  • 15. Pirri, CF
    et al.
    Porro, S
    Ferrero, S
    Celasco, E
    Guastella, S
    Scaltrito, L
    Yakimova, Rositsa
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Syväjärvi, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Ciechonski, Rafal
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    De Angelis, S
    Crippa, D
    Growth, morphological and structural characterization of silicon carbide epilayers for power electronic devices applications2005Ingår i: Crystal research and technology (1981), ISSN 0232-1300, E-ISSN 1521-4079, Vol. 40, nr 10-Nov, s. 964-966Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Silicon carbide (SiC) is a wide band gap semiconductor, interesting for its physical properties such as high breakdown field, high saturated drift velocity and high thermal conductivity, which has been intensively studied in the last years. Although the high potentiality of this material, the SiC technology shows at the moment some limitations, indeed, the reliability of SiC-based devices is strictly correlated to the defects present in the crystalline structure. 4H-SiC epilayers were grown by Hot Wall Chemical Vapor Deposition (at 1600 degrees C) and by Sublimation techniques (at 2000 degrees C). A surface investigation of the epilayers has been performed finding particular physical finger-prints correlated with several kind of defects aimed at giving an important feedback to the epitaxial growth processes. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  • 16.
    Porro, Samuele
    et al.
    Department of Physics, Polytechnic of Torino, Torino, Italy.
    Ciechonski, Rafal
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Syväjärvi, Mikael
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Yakimova, Rositsa
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Electrical Analysis and Interface States Evaluation of of Ni Schottky diodes on 4H-SiC thick epilayers2005Ingår i: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 202, nr 13, s. 2508-2514Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This work has been focused on characterization of thick 4H-SiC layers produced by sublimation epitaxy. Nickel Schottky contacts have been fabricated in order to characterize the grown material and evaluate the interfacial layer between metal and semiconductor. The characterization study includes current-voltage and capacitance-voltage high temperature measurements, from which Schottky barrier, net donor concentration and on-state resistance values have been extracted. The diodes show a typical behavior of J-V and C-V curves with temperature, with Schottky barrier heights of 1.3 eV ÷ 1.4 eV and net donor concentration of 4 × 1015 cm-3 ÷ 1 × 1016 cm-3. From the Bardeen's model on reverse J-V, the density of states of the interfacial layer has been estimated to 7 × 1011 eV-1 cm-2 ÷ 8 × 1011 eV-1 cm-2, a value that is similar to the density of states of oxide layers in deliberated MOS structures realized on the same epilayers.

  • 17.
    Syväjärvi, Mikael
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik. Linköpings universitet, Tekniska högskolan.
    Ciechonski, Rafal R.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik. Linköpings universitet, Tekniska högskolan.
    Yazdi, Gholamreza R.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik. Linköpings universitet, Tekniska högskolan.
    Yakimova, Rositsa
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik. Linköpings universitet, Tekniska högskolan.
    Fast epitaxy by PVT of SiC in hydrogen atmosphere2005Ingår i: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 275, nr 1-2, s. e1103-e1107 Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Epitaxial growth in hydrogen atmosphere has been studied in relation to sublimation epitaxial growth. A new type of features with a hexagonal shape are observed in the layers grown in hydrogen atmosphere. The morphological details of the features have been studied with optical microscopy and atomic force microscopy. An interactive relation of the defect appearance with the step flow growth mode seems to be present. The results are compared with growth in vacuum, argon, and helium conditions. The possible influence of thermal component to a reactive one in hydrogen etching is discussed.

  • 18.
    Syväjärvi, Mikael
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Yakimova, Rositsa
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Ciechonski, Rafal
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Davydov, D
    Lebedev, Alexander
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi.
    Janzén, Erik
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Origin and behaviour of deep levels in sublimation growth of 4H-SiC layers2003Ingår i: Materials Science Forum, Vols. 433-436, 2003, Vol. 433-4, s. 169-172Konferensbidrag (Refereegranskat)
    Abstract [en]

    The characteristics of boron incorporation and the resultant electrical behaviour have been studied for sublimation grown epilayers. Some factors which influence are the purity of the source material, growth temperature and growth time. The electrical activity of the shallow and deep level of boron has been investigated in relation to growth parameters and from the results the nature of the deep boron complex is discussed. The use of TaC coated graphite crucibles resulted in a decrease of the Z(1,2) concentration to less than low E13 cm(-3) which is the concentration obtained using graphite crucibles.

  • 19.
    Syväjärvi, Mikael
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Yakimova, Rositsa
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Ciechonski, Rafal
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Janzén, Erik
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Comparison of SiC sublimation epitaxial growth in graphite and TaC coated crucibles2003Ingår i: Diam. relat. Mater. Vol.12, 2003, Vol. 12, nr 10-11, s. 1936-1939Konferensbidrag (Refereegranskat)
    Abstract [en]

    The growth behaviour in graphite crucibles of different constructions and crucibles coated with TaC are studied with respect to growth performances such as growth rate, epilayer thickness variation and doping as well as deep levels. The variation of growth rate and the epilayer surface morphology with crucible position relative to the coil used for induction heating to applied growth temperature is studied. At low growth rate defects extended along the steps are observed. © 2003 Elsevier B.V. All rights reserved.

  • 20.
    Syväjärvi, Mikael
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Yakimova, Rositsa
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Ciechonski, Rafal
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Kakanakova-Georgieva, Anelia
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Storasta, Liutauras
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Janzén, Erik
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Deep levels in 4H-SiC layers grown by sublimation epitaxy2003Ingår i: Optical Materials, Vol. 23, 2003, Vol. 23, nr 1-2, s. 61-64Konferensbidrag (Refereegranskat)
    Abstract [en]

    Deep levels arising from incorporation of boron in epitaxial layers are presented together with studies of the Z1,2 deep level. The resultant concentrations are related to growth conditions such as growth time and growth temperature. From this the nature and incorporation of the unresolved deeper boron level is commented. The electrical activity of deep boron centers are compared with the actual amount of boron in the material and concerning their relative concentration differences. © 2003 Elsevier Science B.V. All rights reserved.

  • 21.
    Yakimova, Rositsa
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Syväjärvi, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Ciechonski, Rafal
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Wahab, Qamar Ul
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Growth of device quality 4H-SiC by high velocity epitaxy2004Ingår i: Materials Science Forum, Vols. 457-460, 2004, Vol. 457-460, s. 201-204Konferensbidrag (Refereegranskat)
    Abstract [en]

    Thick (>20 μm) 4H-SiC layers in doping range of low 1015-1016 cm-3 were grown by sublimation epitaxy at a growth rate of similar to50 mum/hour. Two inch 25 μm thick layers were fabricated with standard thickness deviation of 3.77%. Effect of important process parameters on the material grade has been discussed. The Schottky diodes processed on this material sustained 900V reverse voltage at a current of 1.7 x 10-8 A, while measured on MOS capacitors the interface state density was as low as similar to6-9 x 1010 cm-2.

  • 22. Ziane, D
    et al.
    Bluet, JM
    Guillot, G
    Godignon, P
    Monserrat, J
    Ciechonski, Rafal
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Syväjärvi, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Yakimova, Rositsa
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Chen, L
    Mawby, P
    Characterizations of SiC/SiO2 interface quality toward high power MOSFETs realization2004Ingår i: Materials Science Forum, Vols. 457-460, 2004, Vol. 457-460, s. 1281-1286Konferensbidrag (Refereegranskat)
    Abstract [en]

    The low channel mobility in N-MOS 4H-SiC transistor is a major key issue for the development of power devices with satisfactory on state characteristics. Previous works have demonstrated that this low channel mobility is due to high interface state density (Dit) near the conduction band edge. Furthermore, the realization of SiC MOSFETs sustaining high reverse field necessitates thick epitaxial layer growth. An important thickness (> 30 gm) unfortunately involves important surface roughness which may result in a high interface trap density (Dit) and surface potential fluctuation (sigma(s)) at the SiC/SiO2 interface. In this study, we focus on SiO2/SiC MOS interface quality characterization as a function of process conditions and material properties (dopant type, thick layer growth technique). Investigations of the oxide quality on thick layers grown by CVD and PVT has been realized using CV under UV lightening and GV techniques. We evidenced that the Dit value (between 10(10) cm(-2).eV(-1) and 9x10(10) cm(-2).eV(-1) from 0.9 Ev to 0.2 eV below Ec) and sigma(s) value (60 mV) were slightly lower for thick PVT layers. A discrepancy in the Dit values obtained from C-V and G-V measurements is attributed to the large surface potential standard deviation. Results from an original oxide growth process using a deposited sacrificial silicon layer under UHV conditions are also presented.

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