Doping modulation in GaN imaged by cross-sectional scanning tunneling microscopy

We investigated the imaging mechanisms of a Si doping modulation in GaN by cross-sectional scanning tunneling microscopy (STM). The Si doping modulation gives rise to a voltage and tip dependent height modulation of at least 0.4 A. The origin of the height modulation in constant-current STM images is traced to two mechanisms. A doping-induced modu-lation of the band edge energies yields a voltage dependent electronic contrast and an additional mechanical relaxation of the doping-induced strain at the cleavage surface is respon-sible for a voltage independent modulation of 0.35 A.