Damage characteristics of n-GaN thin film surfaces etched by ultraviolet light-assisted helium plasmas

Damage characteristics of n-GaN thin film surfaces etched by ultraviolet (UV) light-assisted He plasmas at various gas pressures have been investigated from the viewpoint of the UV light irradiation effect. During the plasma etching, the surface is additionally irradiated with UV light emitted from a black light lamp. The peak wavelength of the emitted UV light corresponds to that of the GaN band-gap energy. The result is compared with that obtained only by use of He plasma. A morphological change in the surface etched by the UV light-assisted He plasma depends on gas pressure, whereas the He plasma only does not cause the morphological change in the surface regardless of gas pressure. The additional UV light irradiation causes a morphological change in the surface etched for a long time of more than 60 min at high gas pressures between 6.7 and 13 Pa. The morphology of the surface etched at a low gas pressure of 1.3 Pa does not change from that of the as-grown surface even with increasing etching time. The additional UV light irradiation also enhances the etch depth and suppresses a decrease in N/Ga ratio at the surface compared with that obtained only by use of the He plasma.