We determine the fundamental electronic and optical properties of the high-thermal-conductivity III-V semiconductor boron arsenide (BAs) using density functional and many body perturbation theory including quasiparticle and spin-orbit coupling corrections. We find that the fundamental band gap is indirect with a value of 2.049 eV, while the minimum direct gap has a value of 4.135 eV. We calculate the carrier effective masses and report smaller values for the holes than the electrons, indicating higher hole mobility and easier p-type doping. The small difference between the static and high frequency dielectric constants indicates that BAs is only weakly ionic. We also observe that the imaginary part of the dielectric function exhibits a strong absorption peak, which corresponds to parallel bands in the band structure. Our estimated exciton binding energy of 43 meV indicates that excitons are relatively stable against thermal dissociation at room temperature. Our work provides theoretical insights on the fundamental electronic properties of BAs to guide experimental characterization and device applications.

The ultrahigh thermal conductivity of boron arsenide makes it a promising material for nextgeneration electronics and optoelectronics. In this work, we report measured optical properties of cubic boron arsenide crystals including the complex dielectric function, refractive index, and absorption coefficient in the ultraviolet, visible, and near-infrared wavelength range. The data were collected at room temperature using spectroscopic ellipsometry as well as transmission and reflection spectroscopy. We further calculate the optical response using density functional and many-body perturbation theory, considering quasiparticle and excitonic corrections. The computed values for the direct and indirect band gaps (4.25 eV and 2.07 eV) agree well with the measured results (4.12 eV and 2.02 eV). Our findings contribute to the effort of using boron arsenide in novel electronic and optoelectronic applications that take advantage of its demonstrated ultrahigh thermal conductivity and predicted high ambipolar carrier mobility.

Heteroanionic compounds that contain more than one type of anion have many unique and attractive properties, which make them desirable for numerous applications. However, because of challenges in synthesis and the complexity of their phase spaces, heteroanionic compounds are much less explored than more traditional homoanionic (single-anion) compounds. In this work, we perform a systematic screening for synthesizable, stable, heteroanionic oxysulfide, oxyselenide, and oxytelluride compounds ABXO (A and B are metals; X = S, Se, and Te) using high-throughput density functional theory calculations. 129 hitherto unknown ABXO compounds are predicted to be thermodynamically stable, therefore potentially synthesizable, and most of them are semiconductors. The calculated band gaps and other electronic and ionic properties are used to further screen potential compounds with promising applications such as thermoelectrics, transparent conductors, and solid-state electrolytes for Li/Na ion batteries. Our initial study on ABXO oxychalcogenides shows that heteroanionic compounds possess an extremely rich phase space with a variety of interesting properties and with a large number of these compounds still awaiting experimental synthesis.

Ultrawide-band-gap (UWBG) semiconductors are promising for fast, compact, and energyefficient power-electronics devices. Their wider band gaps result in higher breakdown electric fields that enable high-power switching with a lower energy loss. Yet, the leading UWBG semiconductors suffer from intrinsic materials limitations with regards to their doping asymmetry that impedes their adoption in CMOS technology. Improvements in the ambipolar doping of UWBG materials will enable a wider range of applications in power electronics as well as deep-UV optoelectronics. These advances can be accomplished through theoretical insights on the limitations of current UWBG materials coupled with the computational prediction and 2 experimental demonstration of alternative UWBG semiconductor materials with improved doping and transport properties. As an example, we discuss the case of rutile GeO2 (r-GeO2), a waterinsoluble GeO2 polytype which is theoretically predicted to combine an ultra-wide gap with ambipolar dopability, high carrier mobilities, and a higher thermal conductivity than β-Ga2O3. The subsequent realization of single-crystalline r-GeO2 thin films by molecular beam epitaxy provides the opportunity to realize r-GeO2 for electronic applications. Future efforts towards the predictive discovery and design of new UWBG semiconductors include advances in first-principles theory and high-performance computing software, as well as the demonstration of controlled doping in high-quality thin films with lower dislocation densities and optimized film properties.

BAs is III-V semiconductor with ultra-high thermal conductivity, but many of its electronic properties are unknown. This work applies predictive atomistic calculations to investigate the properties of BAs heterostructures, such as strain effects on band alignments and carrier mobility, considering BAs as both a thin film and a substrate for lattice-matched materials. The results show that strain decreases the band gap independent of sign or direction. In addition, biaxial tensile strain increases the in-plane electron and hole mobilities by more than 60% compared to the unstrained values due to a reduction of the electron effective mass and of hole interband scattering. Moreover, BAs is shown to be nearly lattice-matched with InGaN and ZnSnN2, two important optoelectronic semiconductors with tunable band gaps by alloying and cation disorder, respectively. The results predict type-II band alignments and determine the absolute band offsets of these two materials with BAs. The combination of the ultra-high thermal conductivity and intrinsic p-type character of BAs, with its high electron and hole mobilities that can be further increased by tensile strain, as well as the lattice-match and the type-II band alignment with intrinsically n-type InGaN and ZnSnN2 demonstrate the potential of BAs heterostructures for electronic and optoelectronic devices.