First-principles study of band alignments in the p-type hosts BaM2X2 (M = Cu, Ag; X = S, Se)

摘要

The electronic structures of four semiconductor compounds BaCu2S2, BaCu2Se2,BaAg2S2, and BaAg2Se2 are studied by density functional theory using bothsemi-local and hybrid functionals. The ionization energies and electronaffinities were determined by aligning the electronic states with the vacuumlevel by calculating the electrostatic profile within a supercell slab model.The ionization energy and electron affinity of the compounds were calculatedusing the Heyd-Scuseria-Ernzerhof (HSE) functionals and range from 4.5 to 5.4eV and 3.1 to 3.4 eV, respectively. The replacement of Cu by Ag slightlyincreases the ionization energy and electron affinity, while the replacement ofS by Se decreases the ionization energy but slightly increases the electronaffinity. Overall, the low ionization energies and small electron affinitiessuggest that these compounds possess good p-type doping propensities. The bandgaps are somewhat small to be ideal candidates for transparent semiconductingbehavior. The replacement of Cu with Ag in the barium sulfide compounds canincrease the band gap from 1.62 eV to 2.01 eV.