GaN nucleation mechanism on a surface template of oxidized AlAs

The surfaces of oxidized AlAs (AlOx) layers on Si(111) substrates are studied to understand the mechanism by which single crystal alpha-GaN can be grown by metalorganic chemical vapor deposition (MOCVD) on AlOx that appears to be an amorphous/fine-grain phase. Contact mode atomic force microscopy (C-AFM) and reflection high energy electron diffraction (RHEED) are used to study the AlOx surface on which a GaN nucleation layer (GaN-NL) is grown. The results indicate that an oriented alpha-Ga2O3 layer is formed on AlOx which is covered by a GaAs cap layer during oxidation. We infer that the alpha-Ga2O3 acts as a surface template that provides the order necessary for the subsequent growth of single crystal alpha-GaN. Characterization using RHEED and selective area electron diffraction (SAD) in cross sectional transmission microscopy (XTEM) reveals that the in-plane crystallographic orientation has a unique alignment between the various layers - GaN, alpha-Ga2O3 and the Si substrate. This in-plane alignment is understood by considering the atomic arrangement of each material on the plane perpendicular to [111](Si) at each interface. Moreover a comparison is made between alpha-GaN grown on alpha-Ga2O3 and on alpha-Al2O3(0001) to characterize structural defects in a-GaN. The formation of specific structural defects, a large number of planar defects ran perpendicular to [111](Si) in alpha-GaN/alpha-Ga2O3 is discussed in conjunction with GaN-NL on alpha-Ga2O3.