Insights toward chlorine passivation effects on electronic structures of CdTe([formula omitted]) and CdTe([formula omitted]) surfaces via atomistic modeling

Abstract

A systematic study of varied chlorine passivation concentrations (0, 25, 50, and 100%) along Te-terminated CdTe(1¯00) (2×1) and CdTe(1¯1¯1¯)(1×1) surfaces is presented using high-fidelity atomistic computational simulations to describe the CdTe surface electronic structure. The atomistic modeling approach incorporates quantum mechanical-based calculations via density functional theory coupled with a surface Green’s function formalism. Results show that fractional amounts of Cl manipulate the band alignment features of the CdTe(1¯00) (2×1) facet by introducing surface electronic states that bend the bands upward. The fully chlorine passivated (100%) CdTe(1¯00) (2×1) case reestablishes flat band conditions. As for the CdTe(1¯1¯1¯) (1×1) surface, a Cl concentration of 50% mitigates upward band bending effects as well as reduces the surface electronic states present along the highly polar facet. The study also indicates that Cl concentrations of at least 50% for the CdTe(1¯00) and CdTe(1¯1¯1¯) low-index plane orientations are necessary to decrease the CdTe electron affinity and could be used to improve band alignment found within CdTe solar cells. The investigation of Cl passivation effects on Te-terminated CdTe surfaces provides a unique atomic-scale perspective on the critical role Cl passivation has for electronic characteristics found in CdTe thin-film photovoltaic devices.