Defects responsible for lifetime degradation in electron irradiated n-GaN grown by hydride vapor phase epitaxy

The effects of room temperature 6 MeV electron irradiation on the donor concentration, deep trap spectra, and diffusion lengths of nonequilibrium charge carriers were studied for undoped n-GaN grown by hydride vapor phase epitaxy. Changes in these parameters begin at a threshold electron fluence of 5 × 10¹⁵ cm⁻². The diffusion lengths after this fluence decrease by a factor of 3, accompanied by a drastic increase in the density of deep electron traps with the level near E_c - 1 eV. There is a strong correlation between the changes in the density of these traps and the diffusion length of irradiated n-GaN, indicating that these centers control the lifetime in radiation damaged n-GaN. This is in sharp contrast to the starting material, where the lifetimes are controlled by other deep electron traps at E_c - 0.56 eV. The concentration of the latter is not strongly affected by high energy electron irradiation.