UCL Discovery

Abstract

The electronic structure and phase stability of MgTe, ZnTe, and CdTe were examined in the zinc-blende (B3), wurtzite (B4), and NiAs-type (B8) crystal structures using a first-principles method. Both the band-gap and valence-band maximum (VBM) deformation potentials of MgTe, ZnTe, and CdTe in the B3 structure were analyzed, revealing a less negative band-gap deformation potential from ZnTe to MgTe to CdTe, with a VBM deformation potential increase from CdTe to ZnTe to MgTe. The natural band offsets were calculated taking into account the core-level deformation. Ternary alloy formation was explored through application of the special quasirandom structure method. The B3 structure is found to be stable over all (Zn,Cd)Te compositions, as expected from the preferences of ZnTe and CdTe. However, the (Mg,Zn)Te alloy undergoes a B3 to B4 transition above 88% Mg concentration and a B4 to B8 transition above 95% Mg concentration. For (Mg,Cd)Te, a B3 to B4 transition is predicted above 80% Mg content and a B4 to B8 transition above 90% Mg concentration. Using the calculated band-gap bowing parameters, the B3 (Mg,Zn)Te [(Mg,Cd)Te] alloys are predicted to have accessible direct band gaps in the range 2.39(1.48)-3.25(3.02) eV, suitable for photovoltaic absorbers.