Van der Waals epitaxy versus homoepitaxy of low temperature GaAs (111) layers

In the design of GaAs devices, material selection for heteroepitaxy is limited due to the large amount of strain produced by lattice mismatch. To overcome this problem, a new growth method has been proposed called van der Waals Epitaxy (VDWE). This process attempts to decouple the interface through the growth of a van der Waals bonded crystal layer in-between the two materials with dissimilar lattice constants, thereby accommodating the lattice mismatch. Typical van der Waals materials such as GaSe, have hexagonal crystal structures and are grown with the c-axis perpendicular to the surface due to the nature of the bonding. These materials have a low surface energy and are not very reactive. In addition, they are only stable at relatively low temperatures. This poses two constraints to the growth of GaAs on GaSe. Initial experiments were done to investigate the possibility of growing GaAs (111) layers homoepitaxially at temperatures compatible with van der Waals crystals, with high crystallinity and a smooth surface. Twinned growth layers 1.7μm thick, were obtained at 350°C on a GaAs (111)B substrate using MBE. Further experiments looked at homoepitaxial growth on (111)A substrates and at slightly higher temperatures. These results were then compared to GaAs layers grown on GaSe layers in which nucleation occurs on a van der Waals surface as opposed to the covalently bonded GaAs substrate. The relative quality of the layers was analyzed using RHEED and TEM.