LAUSR

Carbon‐doping of GaN layers with thickness in the mm‐range is performed by hydride vapor phase epitaxy. Characterization by optical and electrical measurements reveals semi‐insulating behavior with a maximum of specific resistivity of 2 × 1010 Ω cm at room temperature found for a carbon concentration of 8.8 × 1018 cm−3. For higher carbon levels up to 3.5 × 1019 cm−3, a slight increase of the conductivity is observed and related to self‐compensation and passivation of the acceptor. The acceptor can be identified as CN with an electrical activation energy of 0.94 eV and partial passivation by interstitial hydrogen. In addition, two differently oriented tri‐carbon defects, CN‐a‐CGa‐a‐CN and CN‐a‐CGa‐c‐CN, are identified which probably compensate about two‐thirds of the carbon which is incorporated in excess of 2 × 1018 cm−3.