A photoemission determination of the band diagram of the Te/CdTe interface

Abstract

Two experiments designed to assist in understanding the physics of certain back contacts on p-type CdTe solar-cell devices are described. In the first experiment, x-ray photoelectron and Auger electron spectroscopies are used to show that etching CdTe in HNO3:H3PO4 results in a Te layer on the CdTe surface. In the second experiment, photoemission spectroscopy is used to explore the electronic properties of evaporated Te deposited on thin-film, polycrystalline p-CdTe in an effort to develop a band diagram for the Te/p-CdTe interface. The motivation for developing the band diagram derives from previous observations that chemically etching polycrystalline p-CdTe solar-cell device material before application of the back contact reduces the series resistance of the device. The key results are that the evaporated Te overlayer is p type and that the valence-band offset between Te and p-CdTe is favorable for low-series-resistance contact, ΔEv=0.26±0.1 eV.