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There is increasing interest in the alpha polytype of Ga 2 O 3 because of its even larger bandgap than the more studied beta polytype, but in common with the latter, there is no viable p-type doping technology. One option is to use p-type oxides to realize heterojunctions and NiO is one of the candidate oxides. The band alignment of sputtered NiO on α-Ga 2 O 3 remains type II, staggered gap for annealing temperatures up to 600 °C, showing that this is a viable approach for hole injection in power electronic devices based on the alpha polytype of Ga 2 O 3 . The magnitude of both the conduction and valence band offsets increases with temperature up to 500 °C, but then is stable to 600 °C. For the as-deposited NiO/α-Ga 2 O 3 heterojunction, ΔE V = −2.8 and ΔE C = 1.6 eV, while after 600 °C annealing the corresponding values are ΔE V = −4.4 and ΔE C = 3.02 eV. These values are 1−2 eV larger than for the NiO/β-Ga 2 O 3 heterojunction.
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Thermal Stability of Transparent ITO/n-Ga 2 O 3 /n+-Ga 2 O 3 /ITO Rectifiers
The thermal stability of n/n + β -Ga 2 O 3 epitaxial layer/substrate structures with sputtered ITO on both sides to act as rectifying contacts on the lightly doped layer and Ohmic on the heavily doped substrate is reported. The resistivity of the ITO deposited separately on Si decreased from 1.83 × 10 −3 Ω.cm as-deposited to 3.6 × 10 −4 Ω.cm after 300 °C anneal, with only minor reductions at higher temperatures (2.8 × 10 −4 Ω.cm after 600 °C anneals). The Schottky barrier height also decreased with annealing, from 0.98 eV in the as-deposited samples to 0.85 eV after 500 °C annealing. The reverse breakdown voltage exhibited a negative temperature coefficient of −0.46 V.C −1 up to an annealing temperature of 400 °C and degraded faster at higher temperatures. Transmission Electron Microscopy showed significant reaction at the ITO and Ga 2 O 3 interface above 300 °C, with a very degraded contact stack after annealing at 500 °C.
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- Award ID(s):
- 2015795
- PAR ID:
- 10318497
- Date Published:
- Journal Name:
- ECS Journal of Solid State Science and Technology
- Volume:
- 10
- Issue:
- 11
- ISSN:
- 2162-8769
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract The band alignment of sputtered NiO on β -Ga 2 O 3 was measured by x-ray photoelectron spectroscopy for post-deposition annealing temperatures up to 600 °C. The band alignment is type II, staggered gap in all cases, with the magnitude of the conduction and valence band offsets increasing monotonically with annealing temperature. For the as-deposited heterojunction, Δ E V = −0.9 eV and Δ E C = 0.2 eV, while after 600 °C annealing the corresponding values are Δ E V = −3.0 eV and Δ E C = 2.12 eV. The bandgap of the NiO was reduced from 3.90 eV as-deposited to 3.72 eV after 600 °C annealing, which accounts for most of the absolute change in Δ E V −Δ E C . Differences in thermal budget may be at least partially responsible for the large spread in band offsets reported in the literature for this heterojunction. Other reasons could include interfacial disorder and contamination. Differential charging, which could shift peaks by different amounts and could potentially be a large source of error, was not observed in our samples.more » « less
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The (Sm x Ga 1−x ) 2 O 3 alloy system is a potential new dielectric for compound semiconductors such as GaAs. Using molecular beam epitaxy under metal-modulated growth conditions, we grew the binary oxide, Sm 2 O 3 , at two substrate temperatures (100 and 500 °C) and optimized the structural, morphological, and electrical properties of the films. Decreasing the Sm cell temperature suppressed the formation of the monoclinic phase and promoted the growth of the cubic phase. Next, the ternary oxide, (Sm x Ga 1−x ) 2 O 3 , was deposited to investigate the effects of Ga incorporation. Optimization experiments were used to determine the effects of substrate temperature and samarium cell temperature (i.e., growth rate) on film stoichiometry, phase distribution, and microstructure in these films. Films grown at 500 °C showed significant surface roughness and the presence of multiple crystalline phases. Since all of the Sm-based oxides (i.e., samarium oxide with and without gallium) were found to have unbonded Sm metal, annealing experiments were carried out in oxygen and forming gas to determine the effects of annealing on film stoichiometry. The motivation behind annealing in forming gas was to see whether this commonly used technique for reducing interface densities could improve the film quality. GaAs metal-oxide-semiconductor diodes with (Sm x Ga 1−x ) 2 O 3 showed breakdown fields at 1 mA/cm 2 of 4.35 MV/cm, which decreased with increasing Sm unbonded metal content in the films.more » « less
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The band alignment of Atomic Layer Deposited SiO 2 on (In x Ga 1−x ) 2 O 3 at varying indium concentrations is reported before and after annealing at 450 °C and 600 °C to simulate potential processing steps during device fabrication and to determine the thermal stability of MOS structures in high-temperature applications. At all indium concentrations studied, the valence band offsets (VBO) showed a nearly constant decrease as a result of 450 °C annealing. The decrease in VBO was −0.35 eV for (In 0.25 Ga 0.75 ) 2 O 3 , −0.45 eV for (In 0.42 Ga 0.58 ) 2 O 3 , −0.40 eV for (In 0.60 Ga 0.40 ) 2 O 3 , and −0.35 eV (In 0.74 Ga 0.26 ) 2 O 3 for 450 °C annealing. After annealing at 600 °C, the band alignment remained stable, with <0.1 eV changes for all structures examined, compared to the offsets after the 450 °C anneal. The band offset shifts after annealing are likely due to changes in bonding at the heterointerface. Even after annealing up to 600 °C, the band alignment remains type I (nested gap) for all indium compositions of (In x Ga 1−x ) 2 O 3 studied.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1149/2162-8777/ac3ace
