Effects of ultraviolet wavelength and intensity on AlGaN thin film surfaces irradiated simultaneously with CF4 plasma and ultraviolet

Abstract Al 0.24 Ga 0.76 N thin film surfaces were irradiated simultaneously with CF 4 plasma and ultraviolet (UV) at wavelengths of 280 and 310 nm. The UV wavelength and intensity were varied without changing the plasma-generating conditions. These UV photon energies were larger than the band-gap energy of AlGaN film. A compositional change in the simultaneously-irradiated surface depended on the UV wavelength. The 280-nm UV irradiation caused a greater degree of nitrogen deficiency than that introduced by 310-nm UV irradiation, causing the Ga- and Al-rich surface. Moreover, the 280-nm UV irradiation increased the amounts of F atoms and CF x fluorocarbons incorporated into the surface, in comparison with CF 4 plasma-only irradiation. In contrast, the 310-nm UV irradiation reduced the amount of the incorporated F atoms and hardly increased the amount of the incorporated CF x fluorocarbons from those caused by CF 4 plasma-only irradiation. These became more prominent with increasing UV intensity. These UV wavelength-dependent results can be discussed in terms of four factors: the UV photogenerated-hole-assisted oxidation, the localized surface plasmon resonance, the UV-induced migration of gallium and aluminum vacancies forming stable complexes with F, and the sticking of F-related radicals from CF 4 plasma onto the surface.