Surface properties of the gallium monochalcogenides

The electronic properties of atomically clean and contaminated cleaved basal surfaces of GaS, GaSe, and GaTe have been investigated by analysis of emitted photoelectron yield, photoelectron energy and contact potential differences. The photoelectric thresholds Ø, work functions φ and electron affinity χ have been established. Large values of φ for GaS and GaSe account for the difficulty encountered in establishing ohmic contacts to p-type crystals. Auger electron spectroscopy demonstrates the extreme inertness of basal surfaces of all three materials but shows that GaTe is more reactive than GaSe or GaS. These results are discussed in the context of intrinsic and extrinsic surface states in these materials.