High thermopower and birefringence in layered mercury-based halides

Abstract

This work presents a theoretical investigation of mercury-based halides in both bulk and monolayer form. These compounds are direct bandgap semiconductors in bulk and monolayer form as it is evident from the analysis of structural and electronic properties. Birefringence values have been used to ascribe anisotropic optical properties, which may host future opto-electronic device applications. The values of mobilities for both the carriers in HgI2 are consistent with the experimental values. The low value of lattice thermal conductivity and favorable carrier mobilities provide a better scope for thermoelectric properties. The least bandgap of HgI2 further enables thermoelectric applications, and the thermopower is found to be high with a value of 580 μV/K for holes and nearly 320 μV/K for electrons. The thermoelectric efficiency for holes is quite appreciable with a figure of merit zT around 0.5 at 300 K for a carrier concentration of 1019 cm−3. In case of monolayers, the thermopower of HgI2 monolayer is found to be higher than its bulk counterpart. Our findings show that these compounds have robust transport and optical properties, which await future experimental verifications.