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Deep levels in as-grown and electron-irradiated n-type GaN studied by deep level transient spectroscopy and minority carrier transient spectroscopy
Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.ORCID iD: 0000-0002-9840-7364
Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
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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.

Place, publisher, year, edition, pages
2016. Vol. 119, no 9
Keyword [en]
Deep level, GaN, DLTS, irradiation
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:liu:diva-121709DOI: 10.1063/1.4943029ISI: 000372351900075OAI: oai:DiVA.org:liu-121709DiVA: diva2:858378
Note

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

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Available from: 2015-10-02 Created: 2015-10-02 Last updated: 2016-04-20Bibliographically approved
In thesis
1. Electronic properties of intrinsic defects and impurities in GaN
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. 55 p.
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 (print) (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

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