Transport Properties of Doped Wide Band Gap Layered Oxychalcogenide Semiconductors Sr₂GaO₃CuCh, Sr₂ScO₃CuCh, and Sr₂InO₃CuCh (Ch = S or Se)

The structural, electrical, and optical properties of a series of six layered oxychalcogenides with the general formula Sr₂MO₃CuCh, where M = Ga, Sc, or In and Ch = S or Se, have been investigated. From this set, we report the structure and properties of Sr₂GaO₃CuSe for the first time, as well as the full structural details of Sr₂ScO₃CuSe, which have not previously been available. A systematic study of the suitability of all of the Sr₂MO₃CuCh phases as p-type conductors has been carried out, after doping with both sodium and potassium to a nominal composition of A_0.05Sr_1.95MO₃CuCh, (A = Na or K), to increase the hole carrier concentration. Density functional theory calculations were used to determine the electronic band structure and predict the transport properties, while optical properties were determined using UV–vis spectroscopy, and structures were confirmed using Rietveld refinement against powder X-ray diffraction data. Room-temperature conductivity measurements were carried out on both pristine samples and doped samples, 18 compositions in total, using four-point probe measurements. We found that the most conductive sample was K_0.05Sr_1.95GaO₃CuSe, with a measured conductivity of 0.46 S cm^–1, collected from a sintered pellet. We have also been able to identify a relationship between the conductivity and the geometry of the copper chalcogenide layer within the Sr₂MO3CuCh series of compounds. As this geometry can be controlled through the material composition, the identification of this structure–property relationship highlights a route to the selection and identification of materials with even higher conductivities.