Cd1−xMgxTe film characteristics and optical emission spectroscopy during sputtering

Cd1−xMgxTe is an attractive II–VI semiconductor alloy candidate for obtaining energy gaps wider than the 1.5 eV of CdTe needed for polycrystalline thin-film tandem cells. Reaching an ideal 1.7 eV bandgap for a doublejunction tandem requires only x≈0.13, and results in only a slight perturbation of the lattice constant from CdTe. Cd1−xMgxTe can be doped either p or n type and is completely miscible across the alloy range. We have shown that these alloy films can easily be prepared by sputtering, however, the sputtering rate is substantially lower than for CdTe and the attainable cell performance has been poor, both before and after activation treatments with chlorine-containing vapors. In this work we have applied optical emission spectroscopy (OES) using selected peaks of Ar⁺, Cd⁺, Mg, Te⁺ and correlated the results with characteristics of the deposited films. Results were obtained as a function of rf sputter power and sputter gas pressure.