Carbon impurities in GaN form both acceptors and donors. Donor-to-acceptor ratios (DARs) determine the semi-insulating behavior of carbon-doped GaN (GaN:C) layers and are still debated. Two models are discussed; both can theoretically achieve semi-insulating behavior: the dominant acceptor model (DAM, ) and the auto-compensation model (ACM, ). We perform a capacitance–voltage analysis on metal/GaN:C/nGaN (n-doped GaN) structures, exhibiting Fermi-level pinning in GaN:C, 0.7 eV above the valence band maximum. This observation coupled with further interpretation clearly supports the DAM and contradicts the ACM. Furthermore, we reveal a finite depletion width of a transition region in GaN:C next to nGaN, where carbon acceptors drop below the Fermi level becoming fully ionized. Calculation of the potential drop in this region exhibits DAR values of 0.5–0.67 for GaN:C with total carbon concentrations of cm and cm. Based on those results, we re-evaluate formerly published density functional theory (DFT)-calculated formation energies of point defects in GaN. Unexpectedly, growth in thermodynamic equilibrium with the bulk carbon phase contradicts our experimental analysis. Therefore, we propose the consideration of extreme carbon-rich growth conditions. As bulk carbon and carbon cluster formation are not reported to date, we consider a metastable GaN:C solid solution with the competing carbon bulk phase being kinetically hindered. DFT and experimental results agree, confirming the role of carbon at nitrogen sites as dominant acceptors. Under N-rich conditions, carbon at gallium sites is the dominant donor, whereas additional nitrogen vacancies are generated under Ga-rich conditions.
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14 November 2021
Research Article|
November 09 2021
Mechanism leading to semi-insulating property of carbon-doped GaN: Analysis of donor acceptor ratio and method for its determination
C. Koller
;
C. Koller
a)
1
KAI GmbH
, Europastraße 8, 9524 Villach, Austria
a)Author to whom correspondence should be addressed: christian.koller2@k-ai.at
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L. Lymperakis;
L. Lymperakis
2
Max-Planck-Institut für Eisenforschung GmbH
, Max-Planck-Straße 1, 40237 Düsseldorf, Germany
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D. Pogany;
D. Pogany
3
Institute of Solid State Electronics, TU Wien
, Gußhausstraße 25a, 1040 Vienna, Austria
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G. Pobegen
;
G. Pobegen
1
KAI GmbH
, Europastraße 8, 9524 Villach, Austria
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C. Ostermaier
C. Ostermaier
4
Infineon Technologies Austria AG
, Siemensstraße 2, 9500 Villach, Austria
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a)Author to whom correspondence should be addressed: christian.koller2@k-ai.at
J. Appl. Phys. 130, 185702 (2021)
Article history
Received:
June 23 2021
Accepted:
October 18 2021
Citation
C. Koller, L. Lymperakis, D. Pogany, G. Pobegen, C. Ostermaier; Mechanism leading to semi-insulating property of carbon-doped GaN: Analysis of donor acceptor ratio and method for its determination. J. Appl. Phys. 14 November 2021; 130 (18): 185702. https://doi.org/10.1063/5.0060912
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