Laser Molecular Beam Epitaxial Growth and Properties of III-Nitride Thin Film Heterostructures on Silicon

Abstract

The principal goal of this research was the investigation and process development of epitaxial growth mechanisms for the direct depositions of heteroepitaxial GaN thin films directly on Si(111) and Si(100) substrates without the incorporation or the formation of an interlayer at the GaN/Si interface. The research involved the design, development and implementation of a physical vapor deposition system based on a laser ablation process in an ultra high vacuum environment. Consideration is given to the role and control of substrate temperature as a function of elapsed deposition process time and its influence on lowering interfacial energies and limiting silicon nitride interlayer formation.

The research results show that crack-free growth of 2 μm thick heteroepitaxial AlN and GaN thin films on Si(111) substrates can be achieved without the use of interlayer films. These thin film depositions resulted in atomically clean and chemically abrupt interfaces, while restricting the formation of silicon nitride at the interface.

The resulting AlN and GaN epitaxial relationship on Si(111) is confirmed as [0002]║Si[111], [2110]║Si[110], and [0110]║Si[211]. The III-Nitride thin film on Si(111) is established by domain matching epitaxy (DME) exhibiting a ratio of (2110):(110) interplanar distances of 6:5 for GaN:Si and 5:4 ratio for AlN:Si with clean interfaces along silicon nitride free terraces of the Si(111) surface. Moreover, variations in the domain matching epitaxy were observed to result in the further reduction of residual interfacial strain with the incorporation of domain matching ratios of 5:4 for GaN/Si(111) and 6:5 for AlN/Si(111) occurring with a calculated frequency of nine 5:4 ratios for each 6:5 plane matching ratio for GaN/Si(111) and two 6:5 ratios for each 5:4 plane matching ratio for AlN/Si(111).

For the case where silicon nitride (SiNx) is allowed to form at the interface, elemental analysis using electron energy loss spectroscopy provided evidence that the formation of SiNx occurs as a result of subsequent nitrogen diffusion to the GaN/Si interface after the GaN epitaxy is established.