Atomistic modeling of energy band alignment in CdTe(1 0 0) and CdTe(1 1 1) surfaces

Abstract

An atomic-scale perspective of energy band alignment in CdTe surfaces has not been spatially studied despite the major role surfaces play in forming interfaces within CdTe-based thin film photovoltaic devices. Atomistic modeling based on density functional theory coupled with surface Green’s function is used for calculating energy band alignment of CdTe surfaces. The CdTe(100) ((1 × 1) and c(2 × 2) reconstruction) and CdTe(111) ((1 × 1) and (2 × 2) reconstruction) facets without and with surface relaxation provide insightful band bending characteristics that influence charge carrier transport. Results show that unrelaxed (1 × 1) CdTe(100) and CdTe(111) surfaces bend the valence band downward with surface polarity dictating the surface potential magnitude. The reconstructed CdTe(100) c(2 × 2) and CdTe(111) (2 × 2) surfaces result in favorable surface electronic features in relation to their unreconstructed variants. In addition, the structurally relaxed CdTe(111) surfaces develop an internal energy cusp potential that may enhance hole charge transport toward the back of CdTe solar cell devices. Energy band alignments calculated within the study lead to a detailed understanding of how CdTe surfaces may affect CdTe-based thin film photovoltaic applications.