Excimer laser ablation of CdTe

Abstract

KrF excimer laser irradiation (248 nm) of CdTe (100) at fluences below the melting threshold removes surface atoms and produces reversible changes in composition and structure that depend on the laser fluence and number of laser pulses. At fluences below 65 mJ/cm², the products desorbed from the surface consist of neutral Cd atoms and Te₂ molecules, and the velocity distributions of the desorbed products are well-described by a Maxwell-Boltzmann distribution. At higher fluences, Cd⁺, Te⁺, and Te₂ ⁺ are also ejected, and the velocity distributions of the neutral and ion species become non-Maxwellian. Over the temperature range from 380–400°C the instantaneous laser-induced desorption rates are more than six orders of magnitude higher than the vacuum sublimation rates measured over the same temperature range. The composition of the CdTe surface can be reversibly controlled from stoichiometric to a Te-rich condition by varying the laser fluence over the range from 15 to 65 mJ/cm². The dynamics of the photo-stimulated desorption and the fluence dependent changes in surface composition are described in terms of the kinetic competition between the formation and desorption of Te₂ and the desorption of Cd atoms from the laseri-rradiated surface.