Cs-based gamma-radiation detector material Cs$_2$Hg$_6$S$_7$: First-principles study of extrinsic doping*

Semiconductor X-ray/$\gamma$-ray radiation detectors have broad applications, yet finding superior detector materials that work at room temperature is a challenge because of its contradictory requirements. In a previous study, the ternary compound Cs$_2$Hg$_6$S$_7$ was proposed as a possible candidate because of its high density, optimal band gap and high $\mu\tau$ values. However, the low resistivity originating from p-type carriers is a detrimental factor that limits its performance. As a strategy to increase the resistivity, we investigated compensation by extrinsic doping. Using first-principles density functional theory calculations we focused on finding a proper dopant which gives a shallow donor level that leads to a compensation of hole carriers. We tested a number of extrinsic dopants and, as a result, we found that indium is a promising dopant for the strategy to increase the resistivity of Cs$_2$Hg$_6$S$_7$.