Raman investigation on the surface carrier concentration of single GaN microrod grown by MOCVD

Raman measurement was applied to investigate the carrier concentration distribution along the [0001] direction of single GaN microrod. By measuring the Raman shifts of longitudinal phonon-plasmon (LPP) modes at different locations, the carrier concentration distributions along the sidewall of the microrod were obtained in the [0001] direction. It was found that the carrier concentration at the bottom of the microrod was 9.07×1016 cm−3, which was higher than that at the top. Carrier concentration gradient existed along the growth direction of the microrod. This was mainly due to the uneven distribution of some donor impurities (eg: oxygen impurities) during the growth process. Furthermore, based on the E2high mode, the distributions of residual stress and crystal qualities were characterized along the [0001] direction.