Structural property and optical band edge of Ag(In0.5Al0.5)S2

Abstract

Single crystals of Ag(In0.5Al0.5)S2 were grown by chemical vapor transport using ICl3 as a transport agent. The as-grown Ag(In0.5Al0.5)S2 essentially shows dark red and its absorption edge close to red-to-green energy portion. The stoichiometric content of the Ag(In0.5Al0.5)S2 was evaluated by energy dispersion X-ray spectroscopy. The X-ray diffraction measurement confirmed that the crystal is single phase and crystallized in the chalcopyrite structure. The lattice constants of the crystals were determined to be a = 5.763 ± 0.08 A and c = 10.623 ± 0.016 A, respectively. Raman spectroscopy revealed a prominent A1 (282 cm−1) peak (i.e. main characteristic mode), which verified the chalcopyrite structure of the Ag(In0.5Al0.5)S2. The absorption-edge anisotropy of the Ag(In0.5Al0.5)S2 has been studied by polarization-dependent transmission measurements with the linearly polarized lights along \({\text{E}}\parallel \,{ }\) (denoted as E‖) and along \({\text{E}} \bot \,{ }\) (denoted as E⊥) onto the {112} plane of the crystal. The unpolarized band gap determined by transmission measurement was about 2.31 ± 0.01 eV, which is lying in between the lower E‖ (~2.24 ± 0.01 eV) and higher E⊥ (~2.40 ± 0.01 eV) polarized gaps. The absorption-edge anisotropy by the E‖ and E⊥ polarizations has been clearly demonstrated herein. On the basis of the experimental results, the structure and optical band edge of the Ag(In0.5Al0.5)S2 is thus realized.