Effect of Annealing on Defects in As-Grown and γ-Ray Irradiated n-GaN Layers

Abstract

γ-irradiation induced defects (60Co, dose of 3 × 1019 cm—2) in n-GaN epilayers with a carrier concentration of 1017 cm—3 (slightly doped) and 1018 cm—3 (heavily doped) grown by low-pressure MOCVD on (0001) sapphire substrates have been investigated. The γ-irradiation decreases the electron concentration (n) for the slightly doped epilayers, while it increases that for the heavily doped epilayers. At the same time, the γ-irradiation causes a decrease in the electron mobility (μ) for all epilayers. For heavily doped epilayers, the concentration increase continues during annealing at temperatures up to 250 °C and it has been associated with the activation of neutral complexes. Two electron traps with E = 0.155 eV and 0.95 eV appeared in the γ-irradiated slightly doped epilayers. The values of n and μ have restored their original values, which have been measured in the as-grown epilayers, after annealing at 550 °C.