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In this work, we investigated the epitaxial growth of (010) β-Ga2O3and β-(AlxGa1–x)2O3films using metalorganic chemical vapor deposition (MOCVD) with trimethylgallium (TMGa) as the precursor, aiming for high growth rates for thick films. We observed pyramid-shaped defects in the β-Ga2O3epitaxial films, characterized by polygon-shaped bumps and inverted pyramids embedded in the epi-films. To improve the surface morphology and suppress the defects formation, we developed a novel approach that incorporates a small amount of aluminum (Al) during the growth process. This addition led to significant improvements in surface morphology and reductions in both the density and size of defects for the low-Al β-(AlxGa1–x)2O3films, with a growth rate of 5.5 μm/h. Our findings demonstrate the effectiveness of this approach in optimizing the surface morphology of thick β-(AlxGa1–x)2O3films with rapid growth rates. We achieved the best surface for β-(AlxGa1–x)2O3in an 11 μm-thick film with approximately 2% Al composition, grown at a rate of 5.5 μm/h. However, we also observed that defect density and size increase with film thickness. Room temperature Hall measurements were used to characterize the electrical properties of the low-Al β-(AlxGa1–x)2O3films, which revealed a decrease in Si incorporation efficiency and room temperature mobility with increasing Al composition. Results indicated that increasing the chamber pressure led to a decrease in both growth rate and Al composition at a constant [TMAl]/[TMGa + TMAl] molar flow rate ratio. The β-(AlxGa1–x)2O3films (∼11 μm) with optimal surface quality were grown at chamber pressures between 60 and 100 torr. This work demonstrates the feasibility of growing (010) low-Al β-(AlxGa1–x)2O3thick films with high growth rates and minimal surface defects using MOCVD. Our findings provide valuable insights into β-(Al)GaO growth and suggest that introducing Al is an effective strategy for improving the surface morphology of β-(Al)GaO films. These results have important implications for the development of high-performance (Al)GaO-based vertical power devices.

Abstract: In this work, we systematically investigate the effects of growth parameters on the structural and surface morphological properties of β-(AlxGa1−x)2O3thin films grown on (010) β-Ga2O3substrates via metalorganic chemical vapor deposition (MOCVD). By varying [TMAl]/[TEGa + TMAl] molar flow rate ratio, growth temperature and chamber pressure, (i) the structural and physical properties of β-(AlxGa1−x)2O3films including Al incorporations, growth rates, strain properties, rocking curve full width at half maximum, and (ii) the surface morphological properties are investigated. Higher [TMAl]/[TEGa + TMAl] molar flow ratio leads to higher Al incorporation in β-(AlxGa1−x)2O3films. Higher growth temperature promotes lower growth rates with substantial surface roughening, although the Al incorporation remains similar for a given [TMAl]/[TEGa + TMAl] molar flow ratio. In addition, increasing chamber pressure leads to lower growth rates and lower Al incorporation in the AlGaO films. This study reveals that the MOCVD growth window for (010) β-(AlxGa1−x)2O3films becomes narrower as the Al composition increases. Graphic abstract:

Pulsed-mode metal–organic chemical vapor deposition (MOCVD) growth of ZnSn(Ga)N2on GaN-on-sapphire templates was investigated with the goal of developing stoichiometric, high-quality, epitaxial ZnSnN2-GaN films for integration with GaN-based device structures. It was determined that pulsed-mode growth, during which the Sn precursor was pulsed, enabled the achievement of higher growth temperatures and the avoidance of the formation of Sn droplets, compared to continuous growth. The crystal quality improved with the insertion of a GaN regrown layer prior to the pulsed-mode growth. The stoichiometric ZnSnGa2N4alloy was achieved with a TMSn pulsing time of 15 s in the 1 min growth loop. The valence band offset (VBO) between ZnSnGa2N4and GaN was determined experimentally via X-ray photoelectron spectroscopy to be 0.96 ± 0.10 eV. This value is in good agreement with the predicted value of 0.9 eV, assuming a linear dependence of the VBO on the alloy composition. The results from this work will provide additional design freedom based on III-N/II-IV-N2heterostructures for electronic and optoelectronic devices.

In this work, metalorganic chemical vapor deposition (MOCVD) of (010) β-Ga2O3with fast growth rates was investigated using trimethylgallium (TMGa) as the gallium (Ga) precursor. Key growth parameters including precursor/carrier gas flow, growth temperature, chamber pressure, and group VI/III molar flow ratio were systematically mapped. Surface morphology and charge transport properties of the homo-epi (010) β-Ga2O3thin films were probed to correlate with the crystalline quality. The growth rate of (010) β-Ga2O3thin film increases as the TMGa flow rate increases, and high-quality epi-film is achievable with a fast growth rate up to ∼3 μm/h. By tuning the n-type dopant silane flow rate, the net charge carrier concentration was tuned from ∼1016to 1019cm–3. Room-temperature mobility as high as 190 cm2/V·s was measured for a sample grown with a growth rate of 2.95 μm/h and an electron concentration of 1.8 × 1016cm–3. Temperature-dependent Hall measurement revealed a peak mobility value of ∼3400 cm2/V·s at 53 K. The extracted low compensation level of NA∼ 1.5 × 1015cm–3indicates the high purity of the MOCVD growth of the (010) β-Ga2O3film using TMGa as the Ga precursor. Quantitative secondary-ion mass spectroscopy characterization revealed a relatively high C concentration of 7 × 1016cm–3, indicating that C does not serve as a compensator or a donor in MOCVD grown β-Ga2O3. The results from this study demonstrate the feasibility to grow high-quality Ga2O3thin films with fast growth rates, critical for developing high power electronic device technology.