Optical characterization of Mo1−xWxS2 single crystals

Abstract

A systematic optical study of Mo1-xWxS2 single crystals grown by the chemical vapor transport method in a wide range composition (0 ≤ x ≤ 1) is presented. The optical characterization was carried out using piezoreflectance (PzR) and photoluminescence (PL) measurements at room temperature. The origin and composition x dependence of A and B excitons are evaluated from PzR, indicating that the nature of the direct band edges is similar to the Mo1-xWxS2 compounds. Radiative recombination processes near indirect band gap in Mo1-xWxS2 single crystals are investigated by PL. The strong sharp lines attributed to recombination of excitons bound on electron-attractive neutral centers are observed in PL of 2H-MoS2 and 2H-WS2 but they are not visible in PL spectra of Mo1-xWxS2 single crystals. The broad-bands emission observed in PL spectra of Mo1-xWxS2 compounds are ascribed to recombination via deep centers due to the intrinsic defects of the layered crystals.