Luisa Scolfaro | Searcharxiv

arXiv2025

Self-trapped holes and acceptor impurities in orthorhombic Ga2O3

The electronic and optical properties of self-trapped holes in kappa-phase orthorhombic Ga2O3 in conjunction with isoelectronic and acceptor dopants were studied using hybrid density functional theory. Hole trapping was found to be energetically favorable in all systems investigated and was further stabilized by acceptor dopants with large ionization energies. The electronic structures revealed emergent states in the band gap ranging from 0.2 to 1.2 eV above the valence band maximum, primarily composed of O 2p orbitals in all cases, with a notable contribution from Zn 3d orbitals in the Zn-doped system. Hole trapping resulted in a pronounced red shift and the emergence of additional absorption peaks, producing optical characteristics that were in closer agreement with experimental observations. In each system, the trapped hole localized near the dopant atom, predominantly on adjacent O atoms, accompanied by local lattice distortions. The valence band remained largely non-dispersive even in the presence of a hole; hole states lied near the Fermi level for isoelectronic dopants and deeper in the band gap for acceptor dopants. These findings indicate that isoelectronic doping may find an avenue for p-type doping in this polymorph of Ga2O3 if a means to mitigate self-compensation is found.

cond-mat.mtrl-sci↗

arXiv2021

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

GaN based high electron mobility transistors show promise in numerous device applications which elicits the need for accurate models of bulk, surface, and interface electronic properties. We detail here a hybrid density functional theory study of zinc blende (zb) GaN and diamond bulk and surface properties, and zb GaN on diamond interfaces using slab supercell models. Details are provided on the dependence of electronic properties with respect to supercell size, the use of pseudo-hydrogen to passivate the bottom GaN layer, and dipole corrections. The large bulk modulus of diamond provides a templating structure for GaN to grow upon, where a 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 can shed light towards a better understanding of the GaN/diamond multifaceted interface present in the GaN overgrowth on diamond samples.

cond-mat.mtrl-sci↗