Ultra-wide bandgap β-Ga2O3 films: Optical, phonon, and temperature response properties

Abstract

Optical and phonon interactions of Ga2O3 thin films with nanocrystalline morphology were studied at extreme temperatures. The films were grown using a sputtering technique and analyzed via temperature response transmission, Raman scattering, and high-resolution deep-UV photoluminescence (PL). Raman modes indicated that the structure corresponds to the β-phase. The optical-gap at the range of 77–620 K exhibited a redshift of ∼200 meV, with a temperature coefficient of ∼0.4 meV/K. The optical-gap at room-temperature is 4.85 eV. The electron–phonon interaction model at that temperature range pointed to a low energy phonon, ∼31 meV, that is involved in the thermal properties of the optical-gap. Detailed Urbach energy analysis indicated that defects are the dominant mechanism controlling the band-edge characteristics even at an elevated temperature regime where phonon dominance is usually expected. Defects are attributed to the disordered forms of graphite that were detected via Raman scattering and to the granular morphology of the film. A deep-UV laser with an above-bandgap exaction line of 5.1 eV was employed to map the PL of the films. The highly resolved spectra, even at room-temperature, show a strong emission of ∼3.56 eV attributed to self-trapped holes (STHs). The STH is discussed and modeled in terms of the self-trapped exciton. Moreover, a very distinct but low-intensity emission was found at 4.85 eV that agrees with the value of the optical-gap and is attributed to bandgap recombination. The intensity ratio between the STH and that of the bandgap was found to be 6:1.

Self-trapped holes, oxygen vacancies and electrocatalytic performance of Zn-doped β-Ga2O3 microspindles

“…The compound of bound electron and STH corresponds to a self-trapped exciton (STE). 26 Both STHs and STEs can generate light emission at 3.1–3.6 eV and inhibit deep UV emission from the transition of the band edge. As a result, the broad UV bands of both the undoped and Zn-doped β-Ga 2 O 3 centered at about 3.2 eV may come from the transition of STEs induced by the STHs in the β-Ga 2 O 3 lattice.…”

The Nonradiative Properties of Self‐Trapped Holes in Ultra‐Wide Bandgap Gallium Oxide Film

“…In this study, β-Ga 2 O 3 thin films, ≈300 nm, were grown on quartz and silicon substrates via magnetron radio frequency magnetron sputtering at 400 C. After growth, the films were annealed at 1100 C in an ambient atmosphere for 3 h. Further details on growth can be found in ref. [9]. The PL and Raman experiments were acquired employing a high-resolution Jobin-Yvon T64000 micro-Raman and PL system optimized for the UV range.…”

“…[1] As a result, the holes become highly immobile, which may be a deterrent to achieving p-type β-Ga 2 O 3 and moreover impede the deep UV photoluminescence (PL) due to free e-h pair recombination at the bandgap energy range. In contrast, when a free electron from the conduction band, or an exciton, recombines with STH, a characteristic light emission at the near UV ≈3 V is expected, [1,9,10] which can be very efficient even at room temperature. [9] As the luminescence of the STH is an inherent property of β-Ga 2 O 3 , and most often is the only dominant light emission, addressing its properties is of merit contributing to fundamental knowledge as well as to the technological applications of this material.…”

“…In contrast, when a free electron from the conduction band, or an exciton, recombines with STH, a characteristic light emission at the near UV ≈3 V is expected, [1,9,10] which can be very efficient even at room temperature. [9] As the luminescence of the STH is an inherent property of β-Ga 2 O 3 , and most often is the only dominant light emission, addressing its properties is of merit contributing to fundamental knowledge as well as to the technological applications of this material. This research focuses on the temperature response of the STH PL and phonon dynamics at 77-622 K that addresses their fundamental properties and may provide vital knowledge for the thermal management of devices operating at extreme temperatures.…”

Dehydroxylation and structural transition in α-GaOOH investigated by in situ X-ray diffraction

“…Gallium oxide (Ga 2 O 3 ) is an ultra-wide-bandgap semiconductor with a bandgap energy of 4.5-5.3 eV (depending on its crystal structure), which is much broader than those of GaN and SiC (Kawamura & Akiyama, 2022;Meng et al, 2021;Thapa et al, 2021). Therefore, Ga 2 O 3 is considered a promising candidate for future power device applications, and further high performance is expected compared with GaN and SiC power devices (Zhang et al, 2022).…”