Transport\nProperties of Doped Wide Band Gap Layered\nOxychalcogenide Semiconductors Sr<sub>2</sub>GaO<sub>3</sub>Cu<i>Ch</i>, Sr<sub>2</sub>ScO<sub>3</sub>Cu<i>Ch</i>,\nand Sr&l

The structural, electrical,\nand optical properties of a series\nof six layered oxychalcogenides with the general formula Sr<sub>2</sub><i>M</i>O<sub>3</sub>Cu<i>Ch</i>, where M = Ga,\nSc, or In and <i>Ch</i> = S or Se, have been investigated.\nFrom this set, we report the structure and properties of Sr<sub>2</sub>GaO<sub>3</sub>CuSe for the first time, as well as the full structural\ndetails of Sr<sub>2</sub>ScO<sub>3</sub>CuSe, which have not previously\nbeen available. A systematic study of the suitability of all of the\nSr<sub>2</sub><i>M</i>O<sub>3</sub>Cu<i>Ch</i> phases as <i>p</i>-type conductors has been carried out,\nafter doping with both sodium and potassium to a nominal composition\nof <i>A</i><sub>0.05</sub>Sr<sub>1.95</sub><i>M</i>O<sub>3</sub>Cu<i>Ch</i>, (<i>A</i> = Na or K),\nto increase the hole carrier concentration. Density functional theory\ncalculations were used to determine the electronic band structure\nand predict the transport properties, while optical properties were\ndetermined using UV–vis spectroscopy, and structures were confirmed\nusing Rietveld refinement against powder X-ray diffraction data. Room-temperature\nconductivity measurements were carried out on both pristine samples\nand doped samples, 18 compositions in total, using four-point probe\nmeasurements. We found that the most conductive sample was K<sub>0.05</sub>Sr<sub>1.95</sub>GaO<sub>3</sub>CuSe, with a measured conductivity\nof 0.46 S cm<sup>–1</sup>, collected from a sintered pellet.\nWe have also been able to identify a relationship between the conductivity\nand the geometry of the copper chalcogenide layer within the Sr<sub>2</sub><i>M</i>O<sub>3</sub>Cu<i>Ch</i> series\nof compounds. As this geometry can be controlled through the material\ncomposition, the identification of this structure–property\nrelationship highlights a route to the selection and identification\nof materials with even higher conductivities.