SEM observation and analysis of InGaN/GaN multiple quantum well structure using obliquely polished sample

The InGaN/GaN multiple quantum well structures on sapphire substrates were observed by scanning electron microscope (SEM) using obliquely polished samples. From the contrast change across the p-n junction, piezoelectric fields were deduced. The direction of the piezoelectric field was consistent with the theoretical prediction, but the strength was smaller. Strain-stress calculation showed that strain relief along the surface is not significant; therefore, it is not responsible for the smaller value of the obtained field strength. As one cause, carrier distribution in the wells under the steady-state condition was pointed out. Potential profile along the surface was different for the samples polished from the surface and from the substrate. This was confirmed by the SEM contrast profile.