| Silicon has been the backbone of modern electronics for decades; however, it is not readily compatible with some new types of electronics, such as optoelectronics or spintronics. We aim at overcoming this limitation by combining gallium-selenide (GaxSey) materials with silicon (Si) through heteroepitaxial growth. GaxSey materials are compatible with Si, and are optically and potentially magnetically active semiconductors. Their unusual crystal structures, layered GaSe and defected zinc-blende Ga2Se 3, may be exploited for unprecedented nanostructure formations.; This dissertation demonstrates that GaxSey thin films can be grown epitaxially on Si(100) and (111) substrates into various nanostructure forms, namely 0-dimensional (0-D) "dots", 1-D "wires", 2-D "layers", and 3-D "bulk". We have found that hexagonal layered GaSe is formed on Si(111) with or without arsenic termination (Si(111):As), and defected zinc-blende Ga2Se3 is formed on arsenic terminated Si(100) (Si(100):As). The surfaces of GaSe/Si(111) and Ga 2Se3/Si(100):As are covered by triangle nanodots and oriented nanowire structures, respectively. We propose that different symmetry and bonding of the substrate surfaces induces different configurations of vacancies, resulting in the distinct surface nanostructures. We have achieved a thorough understanding for nanostructure formations of GaxSey by considering vacancies and surfaces as additional "elements" for stabilizing the structures. In contrast to layered GaSe/Si(111), we have found that Ga2Se3-GaAs alloy is formed in a zinc-blende phase at the interface of GaSe/Si(111):As. This signifies the bonding configuration of each element is responsible for determining the local composition; however, the atomic arrangement defined by the substrate symmetry plays a more decisive role in selecting GaxSey crystal structure for Ga xSey/Si heteroepitaxy. Through this study, we propose a generalized concept describing the stable structures of the selenide materials, applicable in both nano- and macro-scopic scales. |
