Effects of dry etching processes on optical properties of ZnTe surface layers in ultraviolet region

We report on the ultraviolet reflection measurements of zinc telluride (ZnTe) crystals exposed to CH4/H2 gases under different rf plasma powers in combination with the critical points model. The effects of dry etching on optical properties such as dielectric function, refractive index and distinction coefficient in perturbed ZnTe surface layers have been investigated in the photon energy range of 3-6 eV. All of the optical coefficients decrease with the increase of plasma power, which has been explained as the effects of the etch-induced defects. The temperature-dependent ultraviolet reflection measurements on the reactive ion etching (RIE) ZnTe crystals reveal resembled effects while either increasing the rf power or increasing the experimental temperature due to the similar role of the electron-phonon and electron-defect scattering.