Hybrid density functional theory study on zinc blende GaN and diamond surfaces and interfaces: Effects of size, hydrogen passivation, and dipole corrections

Abstract

GaN-diamond heterojunctions show promise in high electron mobility transistor applications. This prompts the need for accurate models of structural and electronic properties. We detail here a hybrid density functional theory study of zinc blende (ZB) GaN and diamond heterostructures using slab supercell models. The dependence of electronic properties on supercell size, pseudo-hydrogen passivation, and dipole corrections is detailed. The larger bulk modulus of diamond is shown to provide a templating structure for GaN to grow upon, where the large lattice mismatch is accounted for through the inclusion of a cationic Ga adlayer. Looking at both type I and II surfaces and interfaces of GaN shows the instability of zb GaN without an adlayer (type II), where increased size, pseudo-hydrogen passivation and dipole corrections do not remove the spurious interaction between the top and bottom layers in type II GaN. Layer dependent density of states, local potential differences, and charge density differences show that the type I interface (with a Ga adlayer) is stable with an adhesion energy of 0.704 eV/Å2 (4.346 J/m2); interestingly, the diamond charge density intercalates into the first layer of GaN, which was seen experimentally for wurtzite GaN grown over diamond. The type II interface is shown to be unstable which implies that, to form a stable, thin-film zb interface between GaN and diamond, the partial pressure of trimethylgallium must be controlled to ensure a Ga layer exists both on the top and bottom layer of the GaN thin film atop the diamond. We believe our results lead to a better understanding of the GaN/diamond multifaceted interface present in the GaN overgrowth on diamond heterojunction used in electronic device applications.