Electrical properties from photoinduced charging on Cd-doped (100) surfaces of CuInSe2 epitaxial thin films

The photoresponse of Cd-doped CuInSe2 (CIS) epitaxial thin films on GaAs(100) was studied using x-ray photoelectron spectroscopy under illumination from a 532 nm laser between sample temperatures of 28-260 degrees C. The initial, air-exposed surface shows little to no photoresponse in the photoelectron binding energies, the Auger electron kinetic energies or peak shapes. Heating between 50 and 130 degrees C in the analysis chamber results in enhanced n-type doping at the surface and an increased light-induced binding energy shift, the magnitude of which persists when the samples are cooled to room temperature from 130 degrees C but which disappears when cooling from 260 degrees C. Extra negative charge trapped on the Cu and Se atoms indicates deep trap states that dissociate after cooling from 260 degrees C. Analysis of the Cd modified Auger parameter under illumination gives experimental verification of electron charging on Cd atoms thought to be shallow donors in CIS. The electron charging under illumination disappears at 130 degrees C but occurs again when the sample is cooled to room temperature. (C) 2016 American Vacuum Society.