Valence band ordering in β-Ga₂O₃studied by polarized transmittance and reflectance spectroscopy

Abstract

The polarized transmittance and reflectance spectra of β-Ga2O3 crystals are investigated, and the data are interpreted in terms of the monoclinic crystal band structure. The energies of the absorption edge can be divided into six ranges, and these ranges can be assigned to the transitions from the valence bands to the conduction band minimum according to the selection rules. The indirect bandgap-energy of 4.43 eV is smaller than the direct bandgap-energy of 4.48 eV at RT; and the energy difference of 0.05 eV nearly matches the theoretically calculated values of 0.03–0.04 eV.

Time‐resolved spectroscopy of luminescence in a wide gap Si‐doped β‐Ga2O3

“…By assuming the direct band‐to‐band transitions, the band gaps E g are estimated to be 4.7 and 4.5 eV for the b‐ and c‐polarizations, respectively. The anisotropic E g agrees nicely with the reported values in the literature . It is noted that the weak transmission is observed between 260 and 270 nm for the c ‐axis.…”

Ultrawide‐Bandgap Semiconductors: Research Opportunities and Challenges

“…First, it has a bandgap wider than 4.5 eV, leading to a high breakdown electric field of ≈9 MV cm −1 . [62,[116][117][118][119] Second, it displays good controllability of n-type conduction over a wide range of n ≈ 10 15 -10 19 cm −3 through Si or Sn doping, [86,120,121] and an even more widely tunable resistivity spanning the range ≈ 10 −3 -10 12 Ω·cm. Third, as seen in Figure 1, its estimated Baliga figure of merit (BFOM) is higher than those of WBG SiC and GaN (despite its relatively lower mobility), though not as high as those of UWBG AlN, diamond, and c-BN.…”

Band-to-band transitions, selection rules, effective mass, and excitonic contributions in monoclinic β−Ga2O3

“…Fundamental band-to-band transitions in β-Ga 2 O 3 have been investigated using density functional theory (DFT) calculations [9,10,[26][27][28], optical absorption [26], reflection [29,30], and ellipsometry [8,9]. Due to monoclinic symmetry, the polarization of a given band-to-band transition may not necessarily align with any of the high-symmetry crystal axes.…”

“…For polarization along the crystal axis b, the absorption onset was unambiguously shifted by 0.2 eV towards shorter wavelength. Onuma et al investigated polarized transmittance and reflectance spectra [30]. As a result of their investigations, an indirect gap band-to-band transition around 4.43 eV and a direct gap transition around 4.48 eV parallel to the c axis were proposed, without considering excitonic effects.…”