The influence of the annealing ambient on strain and doping in GaN during high-temperature processing

We have investigated the influence of the annealing ambient on the high-tem perature processing of GaN using visible and ultraviolet micro-Raman scatte ring. The E-2 phonon was monitored to detect strain in GaN, the A(1)(LO) ph onon-plasmon mode to detect changes in the free carrier concentration. Firs t, second and third-order Raman spectra were analyzed. Compressive strain i nduced by: annealing was only found in GaN layers annealed in oxygen and wa s significantly enhanced by the addition of water vapor to the annealing am bient. This suggests the inclusion of oxygen into GaN to play an important role for strain introduced during high-temperature processing. For annealin g temperatures above 900 degrees C, changes in the free carrier concentrati on were observed.