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Electrical properties, electronic defects, and photoluminescence (PL) of Nb-doped β-Ga2O3 crystals grown by the floating zone method have been studied in the temperature range from 10 to 350 K. The activation energies of shallow and deep traps were obtained and compared with their counterparts. The 0.25-Nb-doped Ga2O3 crystal has a metallic behavior at room temperature and a semiconducting behavior at low temperatures. This behavior was interpreted by the quantum corrections to the electrical resistivity resulting from the weak localization and Coulomb interaction. In addition, the 0.25-Nb-doped Ga2O3 crystal has a shallow donor ionization energy of 0.03 eV, indicating that it requires less energy to enable n-type conductivity. Hence, Nb is a good choice for improving the electrical conductivity of the β-Ga2O3 crystal. Three defect trap states were found at EC-0.81 eV, EC-0.49 eV, and EC-0.12 eV below the conduction band edge. The PL spectra of the undoped sample show two characteristic bands in the UV and blue regions under the excitation wavelength of 256 nm. On the other hand, in the Nb-doped β-Ga2O3 sample, a novel UV emission band with a shorter wavelength was observed. [ABSTRACT FROM AUTHOR]

Gallium oxide crystal materials has enormous potential in the fields of power devices and optoelectronics due to its excellent performance and the advantage of being able to grow by melt method. In recent years, numerous experts at home and abroad have also started researching gallium oxide single crystal materials. High quality and low defect gallium oxide single crystal materials are extremely important for subsequent epitaxy and device preparation. At present, the mainstream growth method internationally is edge-defined film-fed growth method (EFG), which has advantages such as short growth cycle, large size, and stable growth. However, there is still great room for progress in crystal defect control. This article focuses on the morphology of corrosion pits in gallium oxide single crystals, and processes samples of gallium oxide single crystals grown by EFG. Corrosion experiments were conducted under different acid and alkali conditions. A detailed introduction was given to the different observed corrosion pit morphologies, and the impact of crystal defects on the corrosion pit morphologies was analyzed. This is of great significance for the future research on the growth mechanism of gallium oxide single crystals and crystal defects. [ABSTRACT FROM AUTHOR]

To increase the n-type conductivity of single-crystal substrates, the Sn element was purposefully inserted into β-Ga2O3 crystals as n-type dopants. However, it was found that the color of the β-Ga2O3 crystal changed significantly after high-temperature remelting in the edge-defined film-fed growth (EFG) method. According to Hall and optical transmission spectroscopy, the carrier concentration in the colorless region is significantly lower than that in the blue region, resulting in a decrease in electrical conductivity after high-temperature remelting of Sn-doped β-Ga2O3. This is a challenge for the application of β-Ga2O3 as an electronic power device. Therefore, we focused on the impact of the two color boundary areas on the structure, electronic, optical properties, and (100) surface defects after high-temperature remelting, and discussed the reason for this color change. Inductive coupled plasma emission spectroscopy (ICP) was used to detect the content of Sn. According to the results of high-resolution X-ray diffraction and atomic force microscopy, compared with the low crystal in the colorless area, the single crystal in the blue area showed higher crystal quality. The PL results indicate that the colorless area has more defects caused by oxygen vacancies than the blue area. [ABSTRACT FROM AUTHOR]

Twins are common defects in β-Ga2O3 crystals that affect the development of large single crystal substrates. To investigate the generation and development of twins, we grew a (100) oriented β-Ga2O3 crystal using edge-defined film-fed growth (EFG). We characterized the (010) sample containing twins by polarized light stress meter, chemical etching, laser scanning confocal microscopy (LSCM) and transmission electron microscopy (TEM). The polarized light stress meter clearly distinguishes areas containing twins from those without. After H3PO4 etching at 150 °C for 1 h, LSCM observations revealed etch pits with mirror symmetry across the (100) twin boundary, with an angle of approximately 77° between the array of etch pits and the boundary. The twins originate at the boundary (102¯) along the [2¯01¯] direction, which is nearly perpendicular to the (100) plane, and then grow in steps on the side near the interior of the crystal. The twin boundary on the side near the edge of the crystal first undergoes stepwise extension and then gradually bends and grows, eventually forming a (100) twin boundary on both sides. TEM observations reveal a different arrangement of atomic density on either side of the twin boundary possessing the [2¯01¯] orientation component. Furthermore, both (102¯) and (100) are slip planes for the β-Ga2O3 crystal, indicating that the generation of twins is closely related to the slip plane. [ABSTRACT FROM AUTHOR]

The long-range crystallographic order and anisotropy in β-(AlxGa1−x)2O3 (x = 0.0, 0.06, 0.11, 0.17, 0.26) crystals, prepared by optical floating zone method with different Al composition, is systematically studied by spatial correlation model and using an angle-resolved polarized Raman spectroscopy. Alloying with aluminum is seen as causing Raman peaks to blue shift while their full widths at half maxima broadened. As x increased, the correlation length (CL) of the Raman modes decreased. By changing x, the CL is more strongly affected for low-frequency phonons than the modes in the high-frequency region. For each Raman mode, the CL is decreased by increasing temperature. The results of angle-resolved polarized Raman spectroscopy have revealed that the intensities of β-(AlxGa1−x)2O3 peaks are highly polarization dependent, with significant effects on the anisotropy with alloying. As the Al composition increased, the anisotropy of Raman tensor elements was enhanced for the two strongest phonon modes in the low-frequency range, while the anisotropy of the sharpest Raman phonon modes in the high-frequency region decreased. Our comprehensive study has provided meaningful results for comprehending the long-range orderliness and anisotropy in technologically important β-(AlxGa1−x)2O3 crystals. [ABSTRACT FROM AUTHOR]

The introduction of different elements into semiconductors to achieve conductivity control of n-type doping has considerable scientific significance and practical application prospects, which can further promote their extensive application in the field of electronic devices. Herein, a series of V-doped beta-gallium oxide (β-Ga2O3) single crystals with different concentrations were cultivated using the optical floating zone method. The influence of V doping on the structural, electrical, and optical properties of β-Ga2O3 single crystals was systematically investigated. The characterization results revealed that V-doped β-Ga2O3 single crystals exhibited superior crystalline quality; moreover, the free carrier concentration increased from 6.9 × 1016 cm−3 to 6.4 × 1018 cm−3 and then decreased to 3.1 × 1016 cm−3 with an increase in the V concentration. The optical transmission of the crystals initially decreased in the infrared region and then increased, which is related to the change in the conductive electrons. The intensities of the two absorption peaks located at approximately 400 nm and 610 nm increased with increasing V doping concentration. From the Raman scattering spectra, the inhibition of V on the [GaIIO6] octahedral peak intensity became evident with increasing V content. These valuable findings may contribute to the research on β-Ga2O3-based electronic and optical devices. [ABSTRACT FROM AUTHOR]

In this paper, the effects of oxygen vacancy and gallium vacancy on the optical and scintillation properties of undoped β-Ga2O3 crystal and 2.5 mol % Al doped gallium oxide were investigated. For the undoped β-Ga2O3, the transmittance is improved after annealing in oxygen or nitrogen atmosphere. After the introduction of Al element, the absorption cutoff appears slightly blue shift, and the band gap increases. For the undoped as-grown β-Ga2O3 single crystals, the decay time consists of a fast component (τ1) of the order of nanoseconds, and two slow components (τ2, τ3) of tens to hundreds of nanoseconds. The contribution of the fast decay time component in the decay times is 2.78%. While for Al-doped β-Ga2O3, the faster (τ1) time is 2.33 ns for the as-grown one, and the contribution is 68.02%. However, the pulse height spectrum shows that the introduction of 2.5 mol % Al will reduce the light yield of the β-Ga2O3 crystal. [ABSTRACT FROM AUTHOR]

A crack extending downward along the seed of a beta-gallium oxide (β-Ga2O3) crystal grown using the edge-defined film-fed growth (EFG) method severely affects the efficiency of crystal slicing. In this study, the influence of the crack on the structural, electronic, and optical properties, as well as the defects in the β-Ga2O3 crystal, was investigated. The causes of the crack were also discussed in this study. Compared with the low crystalline crystal on the right side of the crack, the single crystal on the left side exhibits superior crystalline quality, according to the high-resolution X-ray diffraction and Raman scattering spectra. The Hall data and optical transmission spectra reveal that the crack has a negligible effect on the carrier concentration and optical bandgap. The PL results indicate that the right crystal has more defects caused by oxygen vacancies than the left crystal. Rugby-ball-shaped dislocation etch pits were discovered using a chemical etching approach. The average dislocation densities on the left and right sides of the crack were 9 × 103 cm−2 and 3 × 104 cm−2, respectively. [ABSTRACT FROM AUTHOR]

X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy and Raman spectroscopy were applied to study β-Ga2O3 single crystals before and after annealing. By systematic analysis, the mechanism of the carrier concentration decrease after annealing was explained using electronic trap of GaI3+. XPS measurements showed that the O content increases while the Ga3+ content decreases after annealing, which is related to the carrier concentration decrease. The shift of blue emission band center which related to donors was attributed to the electron capture by Ga3+ nearby conduction band. The Raman spectra confirmed this capture, as based on the Raman peak intensity changes, and the electrons were judged to be mainly captured by GaI of β-Ga2O3. [ABSTRACT FROM AUTHOR]