We have studied the oxidation of layered compound GaSe with no dangling bonds on the cleaved surface using XPS and AES techniques. At room temperature, the cleaved surface is not oxidized in an oxygen atmosphere. When subjected to Ar ion sputtering, the surface starts to exhibit the behavior of metallic Ga owing to dissipation of the first sublayer of Se in the primitive layer, Se–Ga–Ga–Se. The thin layer of metallic Ga thus exposed is easily oxidized. In the thermal oxidation of cleaved GaSe in air, the oxygen diffuses into the primitive layer and combines with Ga, severing the intralayer bonding between the Se and Ga atoms. At temperature higher than 450°C, the oxygen is also intercalated between the primitive layers from the sides perpendicular to the layers. No Se oxides are observed under any of the oxidation conditions.

The capacitance-voltage (C-V) and forward biased current-voltage (I-V) characteristics, electroluminescence (E.L) and photovoltaic effect of GaSe–SnO2 heterojunction diodes are measured. SnO2 layer is deposited on the c-plane of GaSe by using the spray method. The C-V and I-V characteristics of these diodes reveal the existence of a high resistivity layer, probably due to the diffusion of Sn into GaSe. The width of this layer is about 2.6 µm. And the current transport mechanism at low voltage is space-charge-limited. The trap density and the energy level of the trap from the valence band estimated by Lampert theory are about 5×1013∼1×1014 cm-3 and 0.4∼0.6 eV, respectively. The electroluminescence spectra at 275 K show one emission band due to free exciton recombination.

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The depth profile of the elemental composition of the GaSe–SnO2 heterostructure has been studied by XPS and AES. The SnO2 layer was prepared by spraying a solution of SnCl4 and SbCl3 in ethyl alcohol on to the the cleaved surface of GaSe heated to ∼400°C in air. After the solution had been sprayed on for about 5 secs., an SnO2 layer of thickness ∼460 Å formed, and a Ga2O3 layer of thickness ∼120 Å formed under the SnO2 layer. The Ga2O3 layer is a likely origin of the high-resistivity layer observed in the GaSe–SnO2 heterostructure.