Growth of β-Ga2O3 Single-Crystal Microbelts by the Optical Vapor Supersaturated Precipitation Method

Abstract

Monoclinic β-Ga2O3 microbelts were successfully fabricated using a one-step optical vapor supersaturated precipitation method, which exhibited advantages including a free-standing substrate, prefect surface, and low cost. The as-grown microbelts possessed a well-defined geometry and perfect crystallinity. The dimensions of individual β-Ga2O3 microbelts were a width of ~50 μm, length of ~5 mm, and thickness of ~3 μm. The SEM, XRD, HRTEM, XPS, and Raman spectra demonstrated the high single-crystalline structure of β-Ga2O3 microbelts. Twelve frequency modes were activated in Raman spectra. The optical band gap of the β-Ga2O3 microbelt was calculated to be ~4.45 eV. Upon 266 nm excitation, 2 strong UV emissions occurred in photoluminescence spectra through the radiative recombination of self-trapped excitons, and the blue emission band was attributed to the presence of donor-acceptor-pair transition. The individual β-Ga2O3 microbelt was employed as metal-semiconductor-metal deep-ultraviolet photodetector, which exhibits the photoresponse under 254 nm. This work provides a simple and economical route to fabricate high-quality β-Ga2O3 single-crystal microbelts, which should be a potential synthetic strategy for ultra-wide bandgap semiconductor materials.

Unravelling the Surface Oxidation-Induced Evolution of the Electronic Structure of Gallium

“…Note that the Ga 2p 3/2 line (in contrast to the Ga 3d spectrum) of the sample oxidized in air for 1 month can basically be described by one speciesagain due to the higher surface sensitivity of the former. We find these Ga oxide contributions at higher BE (Ga 2p 3/2 : 1119.3 eV and Ga 3d: 21.2 eV, Figure b,c) compared to the Ga 2 O 3−δ contributions of the samples oxidized in 1 × 10 –6 mbar of O 2 , and thus we attribute them to stoichiometric Ga 2 O 3 , in agreement with the literature (Ga 2p 3/2 = 1119 ± 0.3 eV, Ga 3d = 20.8 ± 0.4 eV). ,, …”

Temperature-dependent Raman-active phonon modes and electron−phonon coupling in β-Ga2O3 microwire

“…atoms in crystal will be enhanced, which will weaken the interaction between atoms and that between unit cells, leading to a decrease in the vibration frequency and redshifts of Raman peak position. 28) However, the experimental results show that the five peaks of the B g (1) , A g (2) , A g (3) , A g (4) and A g (6) modes first exhibit blueshifts and then redshifts, a phenomenon different to that of the corresponding Raman shifts of bulk single crystal, and their first-order temperature coefficients are negative. This is possibly due to the fact that the effect of temperature on interatomic spacing along the growth direction is different to that perpendicular to the growth direction.…”

“…[1][2][3] β-Ga 2 O 3 bulk single crystal, thin film and other materials made of β-Ga 2 O 3 have been extensively studied. Recently, high-quality β-Ga 2 O 3 microwire has been grown by CVD, 4,5) optical vapor supersaturated precipitation 6) and exfoliation. 7,8) The distinct high aspect ratio of the microwire gives it an unexpectedly high absorption cross-section, enhancing its capacity for sufficient photon harvest.…”

“…Thus, the libration in the microwire is more similar to that in bulk single crystal. In the middle-frequency range (250 ∼ 500 cm −1 ), the FWHM of the Raman peaks of the microwire are also much narrower, where the FWHM of B g (3) and A g (6) of the microwire are even narrower than 75% of those of bulk single crystal. The B g (3) mode represents the symmetry of the rotations of the two O I in Ga I (O I ) 2 groups around the b axis in opposite directions.…”

“…The B g (3) mode represents the symmetry of the rotations of the two O I in Ga I (O I ) 2 groups around the b axis in opposite directions. The A g (6) peak represents the symmetry of the rock of the two O I in Ga I (O I ) 2 groups around the b-axis and the translations of Ga II 3+ along the axis perpendicular to the b and c axes. This also indicates that the symmetry of Ga I (O I ) 2 groups and Ga II 3+ in microwire is higher.…”