Properties of a potential transparent p-type semiconductor Cu$_{3}$TaQ$_{4}$ (Q = S or Se)

Physical, optical and electrical properties of powder samples of the Cu$_{3}$TaQ$_{4}$ (Q = S or Se) series are investigated to determine the potential as a transparent semiconductor. The series crystallizes in a P-43m sulvanite structure. The sulfide has a lattice parameter of a = 5.5036(4) {\AA} and the selenide has a lattice parameter of a = 5.6535(7) {\AA}. The optical band gaps are 2.75eV for Cu$_{3}$TaS$_{4}$ and 2.36eV for Cu$_{3}$TaSe$_{4}$. Seebeck coefficients of +27$\mu $V/K for Cu$_{3}$TaS$_{4}$ and +24$\mu $V/K for Cu$_{3}$TaSe$_{4}$ confirm that both materials are p-type. FLAPW band structure calculations indicate that the band gap is indirect.