Electrical and optical properties in sputtered GaSe thin films

Sputtered films of polycrystalline GaSe (poly-GaSe) with good crystallinity were first prepared on silica substrate at Ts=723 and 873 K, while amorphous GaSe (a-GaSe) films were obtained below Ts≈720 K. The dark conductivity of a-GaSe was measured and showed intrinsic conduction, and that of poly-GaSe showed p-type conduction, thermally activated through deep acceptor centers located at 0.45 and 0.75 eV above the valence band. Experimental optical absorption in a-GaSe obeyed the indirect transition process with an optical gap of 1.8 eV, while that in poly-GaSe obeyed the forbidden direct transition with an optical gap of 1.83–1.96 eV. Measured photocurrent spectra have enabled us to determine a band model associated with deep acceptor centers in poly-GaSe.