Growths of monoclinic (Al
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x Ga1−x )2O3thin films up to 99% Al contents are demonstrated via metalorganic chemical vapor deposition (MOCVD) using trimethylgallium (TMGa) as the Ga precursor. The utilization of TMGa, rather than triethylgallium, enables a significant improvement of the growth rates (>2.5 μm h−1) of β‐(Alx Ga1−x )2O3thin films on (010), (100), and (01) β‐Ga2O3substrates. By systematically tuning the precursor molar flow rates, growth of coherently strained phase pure β‐(Alx Ga1−x )2O3films is demonstrated by comprehensive material characterizations via high‐resolution X‐ray diffraction (XRD) and atomic‐resolution scanning transmission electron microscopy (STEM) imaging. Monoclinic (Alx Ga1−x )2O3films with Al contents up to 99, 29, and 16% are achieved on (100), (010), and (01) β‐Ga2O3substrates, respectively. Beyond 29% of Al incorporation, the (010) (Alx Ga1−x )2O3films exhibit β‐ to γ‐phase segregation. β‐(Alx Ga1−x )2O3films grown on (01) β‐Ga2O3show local segregation of Al along (100) plane. Record‐high Al incorporations up to 99% in monoclinic (Alx Ga1−x )2O3grown on (100) Ga2O3are confirmed from XRD, STEM, electron nanodiffraction, and X‐ray photoelectron spectroscopy measurements. These results indicate great promises of MOCVD development of β‐(Alx Ga1−x )2O3films and heterostructures with high Al content and growth rates using TMGa for next‐generation high‐power and high‐frequency electronic devices. -
A new record‐high room‐temperature electron Hall mobility (
μ RT = 194 cm2 V−1 s−1atn ≈ 8 × 1015 cm−3) for β‐Ga2O3is demonstrated in the unintentionally doped thin film grown on (010) semi‐insulating substrate via metal‐organic chemical vapor deposition (MOCVD). A peak electron mobility of ≈9500 cm2 V−1 s−1is achieved at 45 K. Further investigation on the transport properties indicates the existence of sheet charges near the epilayer/substrate interface. Si is identified as the primary contributor to the background carrier in both the epilayer and the interface, originating from both surface contamination and growth environment. The pregrowth hydrofluoric acid cleaning of the substrate leads to an obvious decrease in Si impurity both at the interface and in the epilayer. In addition, the effect of the MOCVD growth condition, particularly the chamber pressure, on the Si impurity incorporation is studied. A positive correlation between the background charge concentration and the MOCVD growth pressure is confirmed. It is noteworthy that in a β‐Ga2O3film with very low bulk charge concentration, even a reduced sheet charge density plays an important role in the charge transport properties.