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

Al0.24Ga0.76N thin film surfaces were irradiated simultaneously with CF4 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 CFx fluorocarbons incorporated into the surface, in comparison with CF4 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 CFx fluorocarbons from those caused by CF4 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 CF4 plasma onto the surface.