We report on growth and electrical properties of α-Ga2O3films prepared by halide vapor phase epitaxy (HVPE) at 500 °C on α-Cr2O3buffers predeposited on sapphire by magnetron sputtering. The α-Cr2O3buffers showed a wide microcathodoluminescence (MCL) peak near 350 nm corresponding to the α-Cr2O3bandgap and a sharp MCL line near 700 nm due to the Cr+intracenter transition. Ohmic contacts to Cr2O3were made with both Ti/Au or Ni, producing linear current–voltage ( I– V) characteristics over a wide temperature range with an activation energy of conductivity of ∼75 meV. The sign of thermoelectric power indicated p-type conductivity of the buffers. Sn-doped, 2- μm-thick α-Ga2O3films prepared on this buffer by HVPE showed donor ionization energies of 0.2–0.25 eV, while undoped films were resistive with the Fermi level pinned at ECof 0.3 eV. The I– V and capacitance–voltage ( C– V) characteristics of Ni Schottky diodes on Sn-doped samples using a Cr2O3buffer indicated the presence of two face-to-face junctions, one between n-Ga2O3and p-Cr2O3, the other due to the Ni Schottky diode with n-Ga2O3. The spectral dependence of the photocurrent measured on the structure showed the presence of three major deep traps with optical ionization thresholds near 1.3, 2, and 2.8 eV. Photoinduced current transient spectroscopy spectra of the structures were dominated bymore »
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Structural and electrical properties of thick κ -Ga 2 O 3 grown on GaN/sapphire templates
Thick (23 µm) films of κ-Ga 2 O 3 were grown by Halide Vapor Phase Epitaxy (HVPE) on GaN/sapphire templates at 630 °C. X-ray analysis confirmed the formation of single-phase κ-Ga 2 O 3 with half-widths of the high-resolution x-ray diffraction (004), (006), and (008) symmetric reflections of 4.5 arc min and asymmetric (027) reflection of 14 arc min. Orthorhombic κ-Ga 2 O 3 polymorph formation was confirmed from analysis of the Kikuchi diffraction pattern in electron backscattering diffraction. Secondary electron imaging indicated a reasonably flat surface morphology with a few (area density ∼10 3 cm −2 ) approximately circular (diameter ∼50–100 µm) uncoalesced regions, containing κ-Ga 2 O 3 columns with in-plane dimensions and a height of about 10 µm. Micro-cathodoluminescence (MCL) spectra showed a wide 2–3.5 eV band that could be deconvoluted into narrower bands peaked at 2.59, 2.66, 2.86, and 3.12 eV. Ni Schottky diodes prepared on the films showed good rectification but a high series resistance. The films had a thin near-surface region dominated by E c − 0.7 eV deep centers and a deeper region (∼2 µm from the surface) dominated by shallow donors with concentrations of ≤10 16 cm −3 . Photocurrent and photocapacitance spectra showed the presence of more »
- Award ID(s):
- 1856662
- Publication Date:
- NSF-PAR ID:
- 10330130
- Journal Name:
- APL Materials
- Volume:
- 10
- Issue:
- 6
- Page Range or eLocation-ID:
- 061102
- ISSN:
- 2166-532X
- Sponsoring Org:
- National Science Foundation
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Two-inch diameter α -Ga 2 O 3 films with thickness ∼4 μ m were grown on basal plane sapphire by Halide Vapor Phase Epitaxy (HVPE) and doped with Sn in the top ∼1 μ m from the surface. These films were characterized with High-Resolution X-ray Diffraction (HRXRD), Scanning Electron Microscope (SEM) imaging in the Secondary Electron (SE) and Micro-cathodoluminescence (MCL) modes, contactless sheet resistivity mapping, capacitance-voltage, current-voltage, admittance spectra, and Deep Level Transient Spectroscopy (DLTS) measurements. The edge and screw dislocations densities estimated from HRXRD data were respectively 7.4 × 10 9 cm −2 and 1.5 × 10 7 cm −2 , while the films had a smooth surface with a low density (∼10 3 cm −2 ) of circular openings with diameters between 10 and 100 μ m. The sheet resistivity of the films varied over the entire 2-inch diameter from 200 to 500 Ω square −1 . The net donor concentration was ∼10 18 cm −3 near the surface and increased to ∼4 × 10 18 cm −3 deeper inside the sample. The deep traps observed in admittance and DLTS spectra had levels at E c −0.25 eV and E c −0.35 eV, with concentration ∼10 15 cmmore »
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Halide vapor phase epitaxial (HVPE) Ga 2 O 3 films were grown on c-plane sapphire and diamond substrates at temperatures up to 550 °C without the use of a barrier dielectric layer to protect the diamond surface. Corundum phase α-Ga 2 O 3 was grown on the sapphire substrates, whereas the growth on diamond resulted in regions of nanocrystalline β-Ga 2 O 3 (nc-β-Ga 2 O 3 ) when oxygen was present in the HVPE reactor only during film growth. X-ray diffraction confirmed the growth of α-Ga 2 O 3 on sapphire but failed to detect any β-Ga 2 O 3 reflections from the films grown on diamond. These films were further characterized via Raman spectroscopy, which revealed the β-Ga 2 O 3 phase of these films. Transmission electron microscopy demonstrated the nanocrystalline character of these films. From cathodoluminescence spectra, three emission bands, UVL′, UVL, and BL, were observed for both the α-Ga 2 O 3 /sapphire and nc-Ga 2 O 3 /diamond, and these bands were centered at approximately 3.7, 3.2, and 2.7 eV.
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