Optical and electrical properties of GaSe thin films prepared by PECVD

Gallium selenide (GaSe) thin films on sapphire (001) were first prepared by plasma enhanced chemical vapor deposition (PECVD), where high-purity elemental Ga and Se were used as starting materials. The nonequilibrium low-temperature RF discharge plasma (40.68 MHz) at reduced pressure (0.1 Torr) served to initiate chemical transformations. Gradual increase of the plasma discharge power while keeping other process parameters unchanged leads to an insignificant increase of gallium concentration in GaSe films. This results in a decrease in surface roughness and an increase in the value of the optical band gap of the films from 1.65 to 2.10 eV. All films consist of the δ-GaSe phase with average lattice parameters a = 3.77 Å and c = 32.10 Å. There is a tendency to form a texture oriented along the c axis with increasing plasma power. Conductivity of gallium selenide films showed an activation mechanism of charge transport. For the films deposited at 30, 50 and 70 W, the activation energies were about 0.5, 0.1 and 0.04 eV, respectively. The luminescent properties of GaSe thin films were also investigated.