Electron beam-induced increase of electron diffusion length in p-type GaN and AlGaN/GaN superlattices

The diffusion length, L, of electrons in Mg-doped p-GaN grown by metal-organic chemical vapor deposition was found to increase linearly from 0.55 to 2.0 μm during 1500 s of electron beam irradiation. Similar trends were observed for p-type Mg-doped GaN and AlGaN/GaN superlattices grown by molecular-beam epitaxy. While the electron diffusion length in p-(Al)GaN depends on irradiation time, the diffusion length of holes in n-GaN remains unchanged, with L∼0.35 μm. We attribute the observed diffusion length change in p-(Al)GaN to an increase in the minority carrier lifetime. This increase is likely due to electron beam-induced charging of the deep metastable centers associated with Mg doping. The concentration of these centers was estimated to be ∼1018 cm−3. The minority carrier diffusion length increase in p-(Al)GaN, which occurs during electron injection, may lead to self-improvement of the bipolar transistor characteristics.