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Recent advancements in β-Ga2O3 materials’ growth and device developments are briefly reviewed with the focus on low-pressure chemical vapor deposition (LPCVD) of β-Ga2O3. β-Ga2O3 films are grown on off-axis c-sapphire and (010) β-Ga2O3 substrates via high-temperature LPCVD (HT-LPCVD) with growth temperatures ranging between 950 and 1050 °C. The effects of HT-LPCVD growth conditions on material properties are comprehensively studied. With relatively higher growth temperatures, an increased O2 flow rate is required to maintain β-Ga2O3 crystalline quality with high electron mobility. The growth rate of the HT-LPCVD β-Ga2O3 film scales with the increase of growth temperature and O2 flow rate. The film growth rate is strongly related to the sapphire substrate off-axis angle, which determines the preferred nucleation sites from the step edges. The transport properties of samples grown on substrates with different off-axis angles are compared. The optimized growth temperature for obtaining films with high electron mobility varies with the off-axis angle. From this comprehensive study, high-quality β-Ga2O3 films grown on c-sapphire are achieved with room temperature mobilities of 126 cm2/V s (6° off-axis c-sapphire), 116 cm2/V s (8° off-axis c-sapphire), and 119 cm2/V s (10° off-axis c-sapphire) at carrier concentrations of mid-1016 cm−3. β-Ga2O3 LPCVD homoepitaxy optimized at elevated growth temperatures is performed on Fe-doped semi-insulating (010) Ga2O3 substrates. With controllable Si doping, record-high room temperature mobilities of 156 cm2/V s (150 cm2/V s) are achieved with doping concentrations of 3 × 1016 cm−3 (1.5 × 1017 cm−3) at a growth temperature of 1050 °C. Secondary ion mass spectroscopy analysis shows more than an order of magnitude reduction of C and H impurity incorporation with increased growth temperature. Results from this work demonstrate that HT-LPCVD growth is a promising method to produce high-quality β-Ga2O3 films on both off-axis c-sapphire and native Ga2O3 substrates with a fast growth rate and superior transport properties critical for high power device applications.

Unintentional impurity incorporation in GaN drift layers represents a challenging issue that can limit their potential performance in vertical power devices. In this paper, we focus on studying the origins of Fe impurity incorporation in metal-organic chemical vapor deposition (MOCVD) grown GaN materials. Acting as a compensator in n-type GaN drift layers, Fe impurities can reduce the electron mobility in GaN and limit the lowest controllable doping level. Two sources, the sample cleaning process and growth susceptor, were identified as the main mechanisms of Fe incorporation in the MOCVD GaN growth process. It was found that solvent cleaning of the wafer can introduce significant Fe contamination at the growth interface, which would slowly be incorporated into the GaN epilayer, thus causing background Fe impurity as high as 1017 cm−3 level. Moreover, the Fe impurity in the coating material on the susceptor can introduce additional Fe impurity during the growth process. Our studies revealed that the Fe impurity level could be significantly suppressed by more than two orders when an alternative cleaning process was used and the susceptor surface was fully covered by substrates. Characterization of the Fe impurity concentrations was performed via secondary ion mass spectrometry. The trap level (EC − 0.57) eV from deep-level transient spectroscopy that had previously been attributed to Fe confirmed the carrier compensation effect from Fe. Room temperature Hall mobility as high as 1007 cm2/V s was achieved on the MOCVD grown low-Fe GaN. Results from this work will provide guidance for achieving high purity GaN toward high performance GaN vertical power devices.

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