Fig. 1. (Color online) (a) Schematic diagram of (010) principal-face β-Ga₂O₃ bulk crystals grown by EFG method. (b) (010) principal-face macro-morphology image of TLDs, showing obvious branching tendency of evolution process with (001) pulling direction from right to left. (c) Enlarged-morphology image of red rectangular block from (b). (d) Micro-morphology image of TLDs of yellow rectangular block in (b). (e) 2-inch diameter (010) principal-face non-TLDs β-Ga₂O₃ single crystal.

Fig. 2. (Color online) (a) SEM image of (010) principal-face β-Ga₂O₃ bulk crystals growth cross section at early pulling stage, the bright region with branches is cross-sectional TLDs, enlarged images of (b)−(f) are different location in (a) marked by yellow rectangular block, and the location of (b) is termination point of TLDs, exhibiting destructive effect for crystalline structure of β-Ga₂O₃ bulk crystals. (g) SEM image of growth cross section at later growth stage of the same bulk crystal, the bright region is cross-sectional TLDs, showing the worse surface morphology than early stage in (a), enlarged images of (h) and (i) are also marked in (g), indicating severe deteriorating scene of TLDs.

Fig. 3. (Color online) (a) XRD pattern and (b) X-ray rocking curve of (010)-oriented substrate from (010) principal-face β-Ga₂O₃ single crystal. (c) Laue diffraction image, (d) indexation of Laue spots, and (e) identification of (010)-oriented crystallographic plane, manifesting great symmetry and consistency.

Fig. 4. (Color online) (a) UV−VIS−NIR transmittance spectra of (010)-oriented β-Ga₂O₃, the inset is optical bandgap with 4.4 eV of (010) plane. (b) MWIR transmittance spectra of (010)-oriented β-Ga₂O₃, showing wide transmission range from UV to MWIR band. (c) Temperature-dependent resistivity of (010)-oriented β-Ga₂O₃. (d) Fe acceptor activation energy with 0.78 eV was fitted with Arrhenius equation.