Atomistic modeling of energy band alignment in CdTe(100) and CdTe(111) surfaces

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(1 0 0) ((1 x 1) and c(2 x 2) reconstruction) and CdTe(1 1 1) ((1 x 1) and (2 x 2) reconstruction) facets without and with surface relaxation provide insightful band bending characteristics that influence charge carrier transport. Results show that unrelaxed (1 x 1) CdTe(1 0 0) and CdTe (11 1) surfaces bend the valence band downward with surface polarity dictating the surface potential magnitude. The reconstructed CdTe(1 0 0) c(2 x 2) and CdTe(1 1 1) (2 x 2) surfaces result in favorable surface electronic features in relation to their unreconstructed variants. In addition, the structurally relaxed CdTe(1 1 1) 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.