Quantification of unintentional doping in non‐polar GaN using scanning capacitance microscopy

Zhu, T and Kappers, M J and Moram, M A and Oliver, R A


Unintentional doping in non-polar a -plane (11-20) gallium nitride (GaN) grown on r -plane (1-120) sapphire has been characterized using scanning capacitance microscopy. A conductive interface layer has been observed adjacent to the GaN/sapphire interface, and its average thickness has been quantified and found to increase as the duration of an initial period of three-dimensional growth is increased. By using a Si doped calibration staircase structure, the conductive interface region is found to contain an average carrier concentration of (2.5 ± 0.3) x 10\^18 cm-3. We also observe unintentionally-doped features extending at 60° from the GaN/sapphire interface. We suggest that these inclined features may be due to impurity incorporation around prismatic stacking faults. The carrier concentration decreases along the inclined feature with distance from the GaN/sapphire interface. In addition, the inclined features are found more frequently in a sample subjected to an additional annealing process, which may provide evidence that the unintentional doping arises from oxygen diffusion from the sapphire substrate.

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Department of Materials
Imperial College London
Royal School of Mines
Exhibition Road
London, SW7 2AZ - UK