Photoelectric properties of defect chalcogenide HgGa₂X₄ (x=S, Se, Te)

We present results of ab initio study of ordered vacancy compounds of mercury. The electronic structure, charge density, optical and transport properties of the semiconductor family HgGa₂X₄ (X=S, Se, Te) are calculated using the full potential linearized augmented plane wave method which is based on the density functional theory. A direct bandgap is observed in these compounds, which reduces in the order S>Se>Te. From the density of states it is observed that there is strong hybridization of Hg-d, Ga-d and X-p states. The optical properties show a red shift with increasing size and atomic no. of the chalcogenide atoms. We have also reported the transport properties of mercury thiogallates for the first time. The selenide compound exhibits n-type nature whereas HgGa₂S₄ and HgGa₂Te₄ show p-type behavior. The power factor and ZT for the HGS increases at low temperatures, the figure of merit is highest for HgGa₂Se₄ (1.17) at 19 K.