Evolution of stress relaxation and yellow luminescence in GaN/sapphire by Si incorporation

We report a systematic study accomplished with a series of undoped and Si-doped GaN epilayers grown on sapphire (0001) with the carrier concentration of 4.0×10¹⁹- 1.6×10¹⁹ cm^-3 in order to investigate the evolution of stress relaxation and yellow luminescence by Si incorporation. As the Si doping becomes higher, the bound exciton peaks are gradually shitted to lower energy due to relaxation of the thermal residual stress with the linear coefficient of ΔE/ Δσ∥ =42 meV/GPa. The present results show that both the full width at half maximum of double-crystal x-ray diffractometry and the photoluminescence intensity ratio of the yellow luminescence to edge emission gradually increase as the Si incorporation becomes heavier. We suggest that the Si doping in GaN epilayers induces overall defects and gives rise to stress relaxation during the cool-down process, and the yellow luminescence may be originated from a complex of V^Ga and the Si-induced defect.