Growth and band gap determination of theZrSxSe2−xsingle crystal series

Abstract

Single crystals of layered transition-metal dichalcogenide compounds of ${\text{ZrS}}_{x}{\text{Se}}_{2\ensuremath{-}x}$ with composition $0\ensuremath{\le}x\ensuremath{\le}2$ were grown by the chemical-vapor-transport technique and characterized with the help of different methods. Indirect gap transitions with remarkably high values of the absorption coefficient $\ensuremath{\alpha}$ $(h\ensuremath{\nu})$ and the energy-gap values have been extracted from the optical-absorption measurements. An approximate linear dependence of the band gaps on the composition parameter $x$ has been observed, qualifying them to become promising candidates for band gap engineering. The range of the obtained band gaps, which varies from 1.18 eV for ${\text{ZrSe}}_{2}$ to 1.7 eV for ${\text{ZrS}}_{2}$, is suitable for photovoltaic applications in both single- and multiple-junction cells. Additionally, a significant absorption-coefficient tail near the fundamental absorption edge is discussed, which is found to obey the Urbach rule.