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Duc Tran, Thien
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Publications (9 of 9) Show all publications
Duc Tran, T., Pozina, G., Amano, H., Monemar, B., Janzén, E. & Hemmingsson, C. (2016). Deep level study of Mg-doped GaN using deep level transient spectroscopy and minority carrier transient spectroscopy. Physical Review B, 94(4), Article ID 045206.
Open this publication in new window or tab >>Deep level study of Mg-doped GaN using deep level transient spectroscopy and minority carrier transient spectroscopy
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2016 (English)In: Physical Review B, ISSN 2469-9950, Vol. 94, no 4, article id 045206Article in journal (Refereed) Published
Abstract [en]

Deep levels in Mg doped GaN have been studied using deep level transient spectroscopyand minority charge carrier transient spectroscopy. Two traps are revealed in the investigatedtemperature range. In the substrate, one electron trap labelled ET1 (EC – 0.158 eV) is observedand in the Mg-doped layer, one hole trap labelled HT1 has been revealed. By varying theelectric field, it is found that the hole trap HT1 exhibits an electric field enhanced hole emissionrate. Using four theoretical models based on 3-dimensional Coulombic Poole-Frenkel effect, 3-dimensional square well Poole-Frenkel effect, phonon assisted tunneling, and 1-dimensionalCoulombic Poole-Frenkel effect including phonon assisted tunneling, the experimental data arefitted in order to justify the field enhanced emission process. It is found that the 1-dimensionalCoulombic Poole-Frenkel model including phonon assisted tunneling is consistent with theexperimental data. Since the trap exhibits Poole-Frenkel effect, we suggest it is acceptor like.From the theoretical model, the zero field activation energy of HT1 and an estimate of the holecapture cross section have been determined as Ev+0.57 eV and 1.9x10-15 cm2, respectively.Since the level is only observed in Mg-doped material, it is suggested that the trap can beassociated with a Mg related defect.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2016
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-121705 (URN)10.1103/PhysRevB.94.045206 (DOI)000381484500007 ()
Note

Funding agenices: Swedish Research Council [621-2010-3850]; Swedish Energy Agency [38338-1]

Vid tiden för disputation förelåg publikationen endast som manuskript

Available from: 2015-10-02 Created: 2015-10-02 Last updated: 2016-09-26Bibliographically approved
Duc Tran, T., Pozina, G., Nguyen, T. S., Kordina, O., Janzén, E., Ohshima, T. & Hemmingsson, C. (2016). Deep levels in as-grown and electron-irradiated n-type GaN studied by deep level transient spectroscopy and minority carrier transient spectroscopy. Journal of Applied Physics, 119(9)
Open this publication in new window or tab >>Deep levels in as-grown and electron-irradiated n-type GaN studied by deep level transient spectroscopy and minority carrier transient spectroscopy
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2016 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 119, no 9Article in journal (Refereed) Published
Abstract [en]

By minority carrier transient spectroscopy on as-grown n-type bulk GaN produced by halide vapor phase epitaxy (HVPE) one hole trap labelled H1 (EV + 0.34 eV) has been detected. After 2 MeV-energy electron irradiation, the concentration of H1 increases and at fluences higher than 5×1014 cm-2, a second hole trap labelled H2 is observed. Simultaneously, the concentration of two electron traps, labelled T1 (EC - 0.12 eV) and T2 (EC - 0.23 eV) increases. By studying the increase of the concentration versus electron irradiation fluences, the introduction rate of T1 and T2 using 2 MeV-energy electrons was determined to 7X10-3 cm-1 and 0.9 cm-1, respectively. Due to the low introduction rate of T1 and the low threading dislocation density in the HVPE bulk GaN material, it is suggested that the defect is associated with a primary defect decorating extended structural defects. The high introduction rate of the trap H1 suggests that the H1 defect is associated with a primary intrinsic defect or a complex.

Keywords
Deep level, GaN, DLTS, irradiation
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-121709 (URN)10.1063/1.4943029 (DOI)000372351900075 ()
Note

Funding agencies:  Swedish Research Council (VR); Swedish Energy Agency

Vid tiden för disputation förelåg publikationen som manuskript

Available from: 2015-10-02 Created: 2015-10-02 Last updated: 2017-12-01Bibliographically approved
Duc Tran, T., Pozina, G., Nguyen, T. S., Ohshima, T., Janzén, E. & Hemmingsson, C. (2016). Electronic properties of defects in high-fluence electron irradiated bulk GaN. Physica status solidi. B, Basic research, 253(3), 521-526
Open this publication in new window or tab >>Electronic properties of defects in high-fluence electron irradiated bulk GaN
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2016 (English)In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 253, no 3, p. 521-526Article in journal (Refereed) Published
Abstract [en]

Using deep level transient spectroscopy, deep levels and capture cross sections of defects introduced by high-fluence electron irradiation of thick halide vapour phase epitaxy grown GaN has been studied. After irradiation with 2 MeV electrons to a high-fluence of 5×1016 cm-2, four deep trap levels, labelled T1 (EC – 0.13 eV), T2 (EC – 0.18 eV), T3 (EC – 0.26 eV) T4 and a broad band of peaks consisting of at least two levels could be observed. These defects, except T1 and T3, were annealed out after annealing at 650 K for 2 hours. The capture cross section is found to be temperature independent for T2 and T3, while T1 shows an decresing capture cross section with increasing temperature, suggesting that electron capturing to this deep level is governed by a cascade capturing process.

Place, publisher, year, edition, pages
John Wiley & Sons, 2016
Keywords
Deep level, GaN, DLTS, irradiation
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-121707 (URN)10.1002/pssb.201552521 (DOI)000371634800018 ()
Note

Funding agencies: Swedish Research Council (VR); Swedish Energy Agency

Available from: 2015-10-02 Created: 2015-10-02 Last updated: 2017-12-01Bibliographically approved
Duc, T. T. (2015). Electronic properties of intrinsic defects and impurities in GaN. (Doctoral dissertation). Linköping: Linköping University Electronic Press
Open this publication in new window or tab >>Electronic properties of intrinsic defects and impurities in GaN
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

With its outstanding properties such as a wide direct bandgap (3.4 eV), high electron mobility and high breakdown voltage, GaN and its alloys with In and Al are considered as one of the most important semiconductors for optoelectronic devices and high-power and high-frequency transistors. The most important application of GaN today is high-brightness blue LEDs, which is used for white LEDs. With the discovery of GaN-based blue LED, Isamu Akasaki, Hiroshi Amano and Shuji Nakamura were awarded the Nobel Prize in 2014. Intrinsic defects and impurities are important in semiconductors since they influence the electronic properties. An impurity is one or several foreign atoms in the host crystal while an intrinsic defect is an imperfection in the host’s crystal lattice. Normally, impurities and intrinsic defects can be introduced either intentionally or unintentionally into semiconductors during the growth process, during processing of the device or from the working environment. Especially for GaN, due to the lack of native substrates, most of the GaN-based device structures are fabricated on foreign substrates such as silicon carbide (SiC) or sapphire (Al2O3). Growth on foreign substrates gives rise to high threading dislocation densities, and they can give rise to electronically active intrinsic defects that influence the performance of the device.

This thesis is focused on electrical characterization of intrinsic defects and impurities in GaN grown by halide vapor phase epitaxy (HVPE) and metalorganic vapor phase epitaxy (MOCVD). In the first part of the thesis, impurities and intrinsic defects in freestanding thick HVPE grown GaN and Mg-doped MOCVD grown GaN is studied. In thick HVPE grown GaN, six electron traps were detected, where two of them were introduced by the polishing process. For three of the traps, the temperature dependence of the electron capture cross section was studied. From their electron capture properties, it was suggested that the traps are  associated with point defects. In Mg-doped MOCVD grown GaN, one hole trap of high concentration was observed. The hole emission rate is enhanced by increasing electric field and by study the emission process in detail by simulation, it is suggested that the emission process is governed by both the Poole-Frenkel effect and phonon-assisted tunneling.

In the second part, intrinsic defects in GaN introduced intentionally by electron irradiation with different fluences have been studied. In electron irradiated HVPE grown GaN, three electron-irradiation-induced electron traps appeared after 2 MeV electron irradiation at a fluence of 1 × 1014 cm2. Due to the annealing behavior, two of the levels were suggested to be related to primary intrinsic defects. In addition, the temperature dependence of the electron capture cross sections for three levels in electron-irradiated GaN was studied. The temperature dependence of one of them showed that the electron capturing is governed by a cascade capturing process, whereas no temperature dependence was observed for the other levels. The thermal stability of electron traps introduced by 2 MeV electron irradiation was studied. Isochronal annealing shows that most of the defects, which has been associated to nitrogen vacancies, annealed out already at 550 K and by using isothermal annealing the activation energy of one of the process was determined. By minority carrier spectroscopy and deep level transient spectroscopy, hole and electron traps in as-grown and 2 MeV ntype electron irradiated GaN were studied. One hole trap was observed in the as-grown material. By electron irradiation, it was observed that the concentration increases. Simultaneously, the concentration of two electron traps increases. Due to the low introduction rate of one of the electron traps, it is suggested that the defect is associated with a primary defect decorating extended structural defects. The high introduction rate of the hole trap suggests that the defect is associated with a primary intrinsic defect or a complex.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. p. 55
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1701
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-121710 (URN)10.3384/diss.diva-121710 (DOI)978-91-7685-950-6 (ISBN)
Public defence
2015-10-26, Planck, Fysikhuset, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2015-10-02 Created: 2015-10-02 Last updated: 2015-10-07Bibliographically approved
Duc Tran, T., Pozina, G., Nguyen, T. S., Janzén, E., Kordina, O., Ohshima, T. & Hemmingsson, C. (2015). Thermal behavior of irradiation-induced-deep levels in bulk GaN.
Open this publication in new window or tab >>Thermal behavior of irradiation-induced-deep levels in bulk GaN
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2015 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Bulk GaN grown by halide vapor phase epitaxy and irradiated by 2 MeV electrons at a fluence of 5×1016 cm-2 were studied by deep level transient spectroscopy. After irradiation, two new peaks labelled D0 (EC – 0.18 eV) and D1 (EC – 0.13 eV) are observed. From isochronal annealing studies in the temperature range of 350 - 600 K, it is observed that peak D0 is completely annealed out already at 550 K while the broad peak D1 has a more complex annealing behavior. The concentration of D1 is decreasing during annealing and its peak position is shifted to higher temperatures, until a relatively stable peak labelled D2 (EC – 0.24 eV) is formed. From an isothermal annealing study of D2, it is concluded that the annealing process can be described by a first order annealing process with an activation energy and prefactor of 1.2 eV and 6.6 × 105 s-1, respectively. From the large pre-factor it is concluded that the annihilation of D2 is governed by a long-range migration process. From its annealing behavior, it is suggested that trap D2 may be related to the VGa.

Keywords
Deep level, GaN, DLTS, irradiation
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-121708 (URN)
Available from: 2015-10-02 Created: 2015-10-02 Last updated: 2015-10-02Bibliographically approved
Duc, T. T., Pozina, G., Son, N. T., Janzén, E., Ohshima, T. & Hemmingsson, C. (2014). Capture cross section of electron-irradiation-induced defects in bulk GaN grown by halide vapor phase epitaxy.
Open this publication in new window or tab >>Capture cross section of electron-irradiation-induced defects in bulk GaN grown by halide vapor phase epitaxy
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2014 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Electron-irradiation-induced defects in GaN grown by halide vapor phase epitaxy is studied by deep level transient spectroscopy in which the capture cross section and its temperature dependence of the deep levels was determined by the filling pulse method. Before irradiation, one trap level, labelled ET4 (EC – 0.244 eV), was observed. After performing electron irradiation with an energy of 2 MeV at a fluence of 5 × 1016 cm-2, four deep trap levels, labelled ET1 (EC – 0.178 eV), ET2 (EC – 0.181 eV), ET3 (EC – 0.256 eV) and ET5 appeared. After annealing at 650K for 2 hours, only two irradiation induced deep levels, ET1 and ET3, were observed. By varying the rate windows, the temperature dependence of the capture cross section of the two deep levels ET1 and ET2 and ET3 was studied. The temperature behavior of ET2 and ET3 capture cross section is independent on temperature whereas the capture cross section of the deep level ET1 depends strongly on the temperature. It is suggested that electron capturing is govern by a multiphonon process to the level ET1.

National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-112261 (URN)
Available from: 2014-11-20 Created: 2014-11-20 Last updated: 2015-09-22Bibliographically approved
Duc, T. T. (2014). Investigation of deep levels in bulk GaN. (Licentiate dissertation). Linköping: Linköping University Electronic Press
Open this publication in new window or tab >>Investigation of deep levels in bulk GaN
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The first gallium nitride (GaN) crystal was grown by hydride vapor phase epitaxy in 1969 by Maruska and Tietjen and since then, there has been an intensive development of the field, especially after the ground breaking discoveries concerning growth and p-type doping of GaN done by the 2014 year Nobel Laureates in Physics, Isamu Akasaki, Hiroshi Amano and Shuji Nakamura. GaN and its alloys with In and Al belong to a semiconductor group which is referred as the III-nitrides. It has outstanding properties such as a direct wide bandgap (3.4 eV for GaN), high breakdown voltage and high electron mobility. With these properties, GaN is a promising material for a variety of applications in electronics and optoelectronics. The perhaps most important application is GaN-based light-emitting-diodes (LED) which can produce a highbrightness blue light. Since the bandgap of GaN can be controlled by alloying it with aluminium (Al) or indium (In) for a larger or smaller bandgap, respectively, GaN is very important for optoelectronic applications from infrared to the deep ultraviolet region. There are other semiconductors with bandgap similar to GaN such as SiC, and the first commercially blue light emitting LEDs where manufactured in SiC, however, SiC has an indirect bandgap with a low efficiency of emitting photons, and today, the SiC based LEDs have been completely replaced by the considerable more efficient GaN based LEDs.

One problem, which has hampered the development of GaN based devices, is the lack of native substrate of GaN. Due to that, most of the GaN based devices are fabricated on foreign substrates such as SiC or Al2O3. Growing on a foreign substrate results in high threading dislocation (TD) densities (~109 cm-2) and stress in the GaN layer due to lattice mismatch and difference of thermal expansion coefficient between GaN and the substrate. The high TD density and the stress influence the performance of the devices.

Another important aspect related to GaN which has attracted manystudies is how defects affect the efficiency of GaN-based devices.Therefore, it is necessary to understand the properties and to identifythem. When we know there properties, one can estimate how they willinfluence the behavior of devices, and thereby, optimize the performance of the device for its application. Basically, a fundamental knowledge of defect properties, and how to introduce them in a controlled manner, or to avoid them, is important in order to optimize the performance of devices. Defects can be introduced both intentionally and unintentionally into semiconductors during the growth process, during processing of the device or from the working environment, for example, devices working in a radioactive ambient are more likely to have defects induced by irradiation.

This thesis is focused on electrical characterization of defects in bulk GaN grown by halide vapor phase epitaxy (HVPE) by using deep level transient spectroscopy. Other measurement techniques like currentvoltage measurement (IV), capacitance-voltage measurement (CV) and Hall measurement were also been used. Defects related to the growth process and the polishing process are discussed in Paper 1. In Paper 2 and Paper 3, we focus on intrinsic defects in GaN introduced intentionally by electron irradiation. This type of defects are important since they can be unintentionally introduced during growth of the material, in the fabrication process of devices or if it is exposed to a radioactive environment. By electron irradiation, we can in a controlled manner introduce intrinsic defects for studies and by varying the electron beam energy and doses we can judge the nature of them. After electron irradiation, we observed several electrically active defects. These defects were characterized by DLTS to get important parameters such as activation energy, trap concentration, trap profile and capture cross-section. Especially, from temperature-dependent capacitance transient studies, we have determined the mechanism of the electron capturing process for some of them.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. p. 52
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1696
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-112262 (URN)10.3384/lic.diva-112262 (DOI)978-91-7519-169-0 (ISBN)
Presentation
2014-12-18, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Funder
Swedish Research Council
Available from: 2014-11-20 Created: 2014-11-20 Last updated: 2015-09-22Bibliographically approved
Duc, T. T., Pozina, G., Son, N. T., Janzén, E., Ohshima, T. & Hemmingsson, C. (2014). Radiation-induced defects in GaN bulk grown by halide vapor phase epitaxy. Applied Physics Letters, 105(10), 102103
Open this publication in new window or tab >>Radiation-induced defects in GaN bulk grown by halide vapor phase epitaxy
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2014 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, no 10, p. 102103-Article in journal (Refereed) Published
Abstract [en]

Defects induced by electron irradiation in thick free-standing GaN layers grown by halide vapor phase epitaxy were studied by deep level transient spectroscopy. In as-grown materials, six electron traps, labeled D2 (E-C-0.24 eV), D3 (E-C-0.60 eV), D4 (E-C-0.69 eV), D5 (E-C-0.96 eV), D7 (E-C-1.19 eV), and D8, were observed. After 2MeV electron irradiation at a fluence of 1 x 10(14) cm(-2), three deep electron traps, labeled D1 (E-C-0.12 eV), D5I (E-C-0.89 eV), and D6 (E-C-1.14 eV), were detected. The trap D1 has previously been reported and considered as being related to the nitrogen vacancy. From the annealing behavior and a high introduction rate, the D5I and D6 centers are suggested to be related to primary intrinsic defects.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2014
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-111755 (URN)10.1063/1.4895390 (DOI)000342758700028 ()
Note

Funding Agencies|Swedish Research Council (VR); Swedish Energy Agency

Available from: 2014-10-31 Created: 2014-10-31 Last updated: 2017-12-05Bibliographically approved
Duc Tran, T., Pozina, G., Janzén, E. & Hemmingsson, C. (2013). Investigation of deep levels in bulk GaN material grown by halide vapor phase epitaxy. Journal of Applied Physics, 114(15)
Open this publication in new window or tab >>Investigation of deep levels in bulk GaN material grown by halide vapor phase epitaxy
2013 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 114, no 15Article in journal (Refereed) Published
Abstract [en]

Electron traps in thick free standing GaN grown by halide vapor phase epitaxy were characterized by deep level transient spectroscopy. The measurements revealed six electron traps with activation energy of 0.252 (E1), 0.53 (E2), 0.65 (E4), 0.69 (E3), 1.40 (E5), and 1.55 eV (E6), respectively. Among the observed levels, trap E6 has not been previously reported. The filling pulse method was employed to determine the temperature dependence of the capture cross section and to distinguish between point defects and extended defects. From these measurements, we have determined the capture cross section for level E1, E2, and E4 to 3.2 × 10−16 cm2, 2.2 × 10−17 cm2, and 1.9 × 10−17 cm2, respectively. All of the measured capture cross sections were temperature independent in the measured temperature range. From the electron capturing kinetic, we conclude that trap E1, E2, and E3 are associated with point defects. From the defect concentration profile obtained by double correlated deep level transient spectroscopy, we suggest that trap E4 and E6 are introduced by the polishing process.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-102085 (URN)10.1063/1.4825052 (DOI)000326117900032 ()
Note

Funding Agencies|Swedish Research Science Council (VR)||Swedish Energy Agency||

Available from: 2013-12-02 Created: 2013-11-29 Last updated: 2017-12-06
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