First-principles study of SrTe and BaTe: Promising wide-band-gap semiconductors with ambipolar doping

Transparent wide-band-gap (WBG) semiconductors are crucial components in diverse (opto)electronic and energy devices. Using first-principles calculations, we demonstrate that alkaline earth tellurides MTe (M = Sr or Ba) are promising WBG semiconductors that can be ambipolarly doped and transparent to visible light. Because of their large direct band gaps (3.74 eV for SrTe and 3.09 eV for BaTe), 100 nm thick MTe films exhibit significant transmittance (over 80%) for visible light. The effective mass of electrons and holes in MTe is predicted to be small (<1 m0) enough to show high carrier mobilities. From the analysis of the defect properties, we show that the major carrier type (electrons vs. holes) and its concentration can be controlled by adjusting the synthetic conditions. We also find that the valence band maximum of MTe is relatively shallow. Thus, MTe can be utilized as an electron-blocking (hole-transport) layer in emerging perovskite solar cells.