Effect of annealing on defects in As-grown and gamma-ray irradiated n-GaN layers

gamma-irradiation induced defects (Co-60, dose of 3 x 10(19) cm(-2)) in n-G aN epilayers with a carrier concentration of 10(17) cm(-3) (slightly doped) and 10(18) cm(-3) (heavily doped) grown by low-pressure MOCVD on (0001) sa pphire substrates have been investigated. The gamma-irradiation decreases t he electron concentration (n) for the slightly doped epilayers, while it in creases that for the heavily doped epilayers. At the same time, the gamma-i rradiation causes a decrease in the electron mobility (mu) for all epilayer s. For heavily doped epilayers, the concentration increase continues during annealing at temperatures up to 250 degrees C and it has been associated w ith the activation of neutral complexes. Two electron traps with E = 0.155 eV and 0.95 eV appeared in the gamma-irradiated slightly doped epilayers. T he values of n and mu have restored their original Values, which have been measured in the as-grown epilayers, after annealing at 550 degrees C.