Electrical and Optical Properties of Layered Oxysulfides with CuS Layers: Sr−Cu−M−O−S System (M = Zn, Ga, In)

The electrical and optical properties of layered oxysulfides (Sr−Cu−M−O−S system (M = Zn, Ga, In)), which have common CuS layers, were studied to examine their potential as wide-gap p-type semiconductors. The attempts of electrical conductivity control by Na doping demonstrated that the conductivities of the Sr 2 - x Na x Cu 2 ZnO 2 S 2 (σ = 2.2 × 10 - 8 S cm - 1 for x = 0.0) and Sr 2 - x Na x CuGaO 3 S (σ = 2.2 × 10 - 4 S cm - 1 for x = 0.0) at room temperature increased up to 1.2 × 10 - 1 and 2.4 × 10 - 2 S cm - 1 for x = 0.1, respectively, with an increase in Na concentration. In addition, both Hall and Seebeck measurements proved that these conductive oxysulfides were p-type semiconductors. The diffuse reflectance spectra of the materials revealed that the optical absorption edges were approximately 450 nm for Sr 2 Cu 2 ZnO 2 S 2, 480 nm for Sr 2 CuGaO 3 S, and 540 nm for Sr 2 CuInO 3 S. It became evident from these results that the layered oxysulfides (Sr−Cu−M−O−S system (M = Zn, Ga, In)) were wide-gap p-type semiconductors utilizing the CuS layers as electrical conduction paths.