First-principles calculations of the near-edge optical properties of β-Ga2O3

Abstract

We use first-principles calculations based on many-body perturbation theory to investigate the near-edge electronic and optical properties of β-Ga 2 O 3 . The fundamental band gap is indirect, but the minimum direct gap is only 29 meV higher in energy, which explains the strong near-edge absorption. Our calculations verify the anisotropy of the absorption onset and explain the range (4.4-5.0 eV) of experimentally reported band-gap values. Our results for the radiative recombination rate indicate that intrinsic light emission in the deep-UV range is possible in this indirect-gap semiconductor at high excitation.Our work demonstrates the applicability of β-Ga 2 O 3 for deep-UV detection and emission.The β phase of gallium oxide (β-Ga 2 O 3 ) is a promising wide-band-gap semiconductor for power electronics, deep-UV optoelectronics, and transparent conductors. Its large band gap results in a high breakdown voltage (8 MV/cm) desirable for power electronics, 1 such as field effect transistors (FETs) and Schottky barrier diodes. [2][3][4] The large gap also results in visible and ultra-violet (UV) transparency.Solar-blind photodetectors have been successfully fabricated with β-Ga 2 O 3 nanostructures, such as nanowires 5 and nanobelts 6 . These devices demonstrate the potential of β-Ga 2 O 3 in electronic and optoelectronic applications.Despite numerous experimental and theoretical studies on β-Ga 2 O 3 , the nature and value of its fundamental band gap remain controversial. The room-temperature (RT) gap from optical absorption measurements ranges from 4.4 to 5.0 eV. 7 This controversy is partially due to the anisotropy of the crystal structure, which causes the absorption onset to depend on the polarization of the incident light.In addition, the small energy difference between the direct and indirect gaps has led to claims that the fundamental gap is direct. 8,9 Other open questions regard luminescence from this material. Most photoluminescence studies do not show the intrinsic emission across the gap in the deep UV (~265-278 nm) but only emission in the UVA to visible range (~350-600 nm). 10 An exception is the report by Li et al (2010) of luminescence at ~265 nm and ~278 nm, which correspond to the experimentally reported

Quasiparticle band structure and optical properties of rutile GeO2, an ultra-wide-band-gap semiconductor

“…In the case of -Ga2O3, the fundamental band gap is indirect, so absorption is weak until ~30 meV above the band gap when the energy of the direct gap is reached. 38 As we have already shown for r-GeO2, the electronic transition from the VBM to the CBM is forbidden, so absorption is suppressed for a 600 meV energy range until the second VB to CBM energy is reached. This behavior is notably different for dipole-allowed direct-gap materials such as GaN, for which the absorption coefficient increases strongly for energies above the band gap.…”

Computational study of electron paramagnetic resonance parameters for Mg and Zn impurities in β -Ga2O3

“…Monoclinic β-Ga 2 O 3 with a band gap of about 4.7±0.1 eV, [1][2][3][4][5] has recently attracted attention as an ultra-wideband-gap semiconductor for transistor and transparent conducting applications. 6,7 As for any new semiconductor, a thorough understanding of the defects and dopants and ultimately their control is crucial to the development of this material.…”

Room-temperature stability of excitons and transverse-electric polarized deep-ultraviolet luminescence in atomically thin GaN quantum wells

“…5). We determined the bimolecular radiative recombination coefficients of free carriers using the method of Kioupakis et al, 18,19 and the radiative lifetimes of excitons from BSE calculations using the method of Palummo et al 20 We investigated atomically thin GaN QWs between 1 monolayer (ML) and 4 MLs thick separated by AlN barriers between 1 ML and 9 MLs thick. To simulate pseudomorphic growth on AlN, the basal plane lattice constant was fixed to that of bulk AlN (0.3112 nm) 21 while relaxing the atom positions and c-axis length.…”