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DOE OSTI2020

Materials Data on VGa by Materials Project

VGa crystallizes in the hexagonal P-6m2 space group. The structure is three-dimensional. V is bonded to six equivalent V and six equivalent Ga atoms to form VV6Ga6 cuboctahedra that share corners with eighteen equivalent VV6Ga6 cuboctahedra, edges with six equivalent VV6Ga6 cuboctahedra, edges with twelve equivalent GaV6Ga6 cuboctahedra, faces with eight equivalent VV6Ga6 cuboctahedra, and faces with twelve equivalent GaV6Ga6 cuboctahedra. All V–V bond lengths are 2.78 Å. All V–Ga bond lengths are 2.70 Å. Ga is bonded to six equivalent V and six equivalent Ga atoms to form GaV6Ga6 cuboctahedra that share corners with eighteen equivalent GaV6Ga6 cuboctahedra, edges with six equivalent GaV6Ga6 cuboctahedra, edges with twelve equivalent VV6Ga6 cuboctahedra, faces with eight equivalent GaV6Ga6 cuboctahedra, and faces with twelve equivalent VV6Ga6 cuboctahedra. All Ga–Ga bond lengths are 2.78 Å.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on VGa(CuO2)2 by Materials Project

VGa(CuO2)2 crystallizes in the monoclinic P2/m space group. The structure is three-dimensional. V3+ is bonded to six O2- atoms to form VO6 octahedra that share edges with two equivalent VO6 octahedra and edges with four equivalent GaO6 octahedra. There are four shorter (2.04 Å) and two longer (2.09 Å) V–O bond lengths. There are two inequivalent Cu1+ sites. In the first Cu1+ site, Cu1+ is bonded in a linear geometry to two equivalent O2- atoms. Both Cu–O bond lengths are 1.86 Å. In the second Cu1+ site, Cu1+ is bonded in a linear geometry to two equivalent O2- atoms. Both Cu–O bond lengths are 1.86 Å. Ga3+ is bonded to six O2- atoms to form GaO6 octahedra that share edges with two equivalent GaO6 octahedra and edges with four equivalent VO6 octahedra. There are four shorter (2.01 Å) and two longer (2.04 Å) Ga–O bond lengths. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded to one V3+, one Cu1+, and two equivalent Ga3+ atoms to form a mixture of distorted corner and edge-sharing OVGa2Cu tetrahedra. In the second O2- site, O2- is bonded to two equivalent V3+, one Cu1+, and one Ga3+ atom to form a mixture of distorted corner and edge-sharing OV2GaCu tetrahedra.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Effect of lithium diffusion into Ga 2 O 3 thin films

The integration of lithium based compounds (e.g., Li:NiO/Ga 2 O 3 , LiGa 5 O 8 /Ga 2 O 3 ) in Ga 2 O 3 based pn-heterojunctions raises concerns about interface stability, i.e., Li diffusion effects on Ga 2 O 3 properties. In this work the ex-situ diffusion of Li is investigated in three different Ga 2 O 3 epilayers systems [(001) κ-Ga 2 O 3 and (−201) β-Ga2O3 heteroepitaxy on (001) α-Al 2 O 3 , and (010) β-Ga 2 O 3 homoepitaxy] at relevant temperatures for the synthesis / processing of Li-based epilayers. It is here experimentally demonstrated and quantified the Li diffusion in all the investigated Ga 2 O 3 epilayers systems and Li bulk (D Li,bulk ) and 2D defects (D Li,2D ) diffusion coefficients are provided. In the case of the (010) β-Ga 2 O 3 homoepitaxial layer (nominally free of structural defects), hybrid functional theory calculations foresee a diffusion mechanism mediated by Ga vacancies (VGa). Moreover, in the (010) β-Ga 2 O 3 homo-layer a significant effect on its functional properties (e.g., additional Raman vibrational modes, induced conductivity in an otherwise insulating sample) upon the Li-diffusion process is experimentally highlighted and tentatively related to the passivation of acceptor defects (i.e., formation of V Ga -nLi complexes).

Defects↗

DOE OSTI2020

Radiative capture rates at deep defects from electronic structure calculations

We present a methodology to calculate radiative carrier capture coefficients at deep defects in semiconductors and insulators from first principles. Electronic structure and lattice relaxations are accurately described with hybrid density functional theory. Calculations of capture coefficients provide an additional validation of the accuracy of these functionals in dealing with localized defect states. We also discuss the validity of the Condon approximation, showing that even in the event of large lattice relaxations the approximation is accurate. We test the method on GaAs:VGa-TeAs and GaN:CN, for which reliable experiments are available, and demonstrate very good agreement with measured capture coefficients.

36 MATERIALS SCIENCE↗