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Investigation of deep levels in bulk GaN
Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
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. , 52 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1696
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:liu:diva-112262DOI: 10.3384/lic.diva-112262ISBN: 978-91-7519-169-0 (print)OAI: oai:DiVA.org:liu-112262DiVA: diva2:764674
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
List of papers
1. Investigation of deep levels in bulk GaN material grown by halide vapor phase epitaxy
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
2. Radiation-induced defects in GaN bulk grown by halide vapor phase epitaxy
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, 102103- p.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
3. 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

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Duc, Tran Thien

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