Mechanism leading to semi-insulating property of carbon-doped GaN: Analysis of donor acceptor ratio and method for its determination
- Koller, C.
- Lymperakis, L.
- Pogany, D.
- Pobegen, G.
- Ostermaier, C.
DOIAbstract
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, DAR<1) and the auto-compensation model (ACM, DAR=1). 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 b...
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