Photoluminescence and Photocurrents of GaS_1–xSe_x Nanobelts

Two-dimensional layered structures have recently drawn worldwide attention because of their intriguing optical and electrical properties. GaS and GaSe are attractive layered materials owing to their wide band gap. Herein, we synthesized GaS 1– x Se x belt-type multilayers (nanobelts) with uniform morphology ([21̅1̅0] hexagonal-phase long axis) by a chemical vapor transport method, and investigate their composition-dependent optical and optoelectronic properties. The GaS 1– x Se x exhibited strong visible-range photoluminescence at 490–620 nm (2.0–2.5 eV), with a unique composition dependence: longer decay time for the S-rich compositions ( x ≤ 0.5). Photocurrent measurements were performed on individual nanobelts by fabricating photodetector devices; higher photocurrents were found for x ≤ 0.5. First-principles calculations predicted that oxygen chemisorption can cause the direct and indirect band gaps of GaS to converge, similar to the band structures of GaSe, and thus enhance the optical properties. On the basis of the band alignment (predicted by calculation) for the Schottky barriers in the metal–semiconductor–metal photodetector, we proposed the origin of the higher photocurrent for GaS than for GaSe.