Influence of microstructure on the carrier concentration of Mg-doped GaN films

Room-temperature Hall effect measurements of (0001) Mg-doped GaN films grow n on sapphire substrates by metalorganic chemical vapor deposition show a r eduction in hole concentration for Mg concentrations greater than 10(20) cm (-3). A combination of secondary ion mass spectrometry and transmission ele ctron microscopy indicates a steadily increasing Mg incorporation during gr owth and the formation of inversion domains at these high concentrations. W e discuss mechanisms that could give rise to a reduction of the hole concen tration at high Mg doping levels. (C) 2001 American Institute of Physics.