Investigation of the growth mechanism of layered semiconductor GaSe

Heteroepitaxial films of lamellar semiconductor GaSe were grown on MoS2 cleaved surfaces by molecular beam epitaxy, and its growth mechanism was investigated by atomic force microscope. At the initial stage of the growth, triangular islands of GaSe with a unit layer thickness are formed. There exist two types of domains, which have opposite orientations of the triangles. It is suggested that the difference in the orientation corresponds to the difference in stacking positions of SeGaGaSe four hexagonal atomic sheets in the unit layer. It is also revealed that stacking polytypes of GaSe can be determined by observing the orientation of triangular islands in each unit layer in a multilayer film. Most of GaSe films have the ε- and/or γ-type stacking. But some domains really have the β-type one which rarely appear in a bulk single-crystal of GaSe.