In this work, we report record electron mobility values in unintentionally doped β-Ga2O3 films grown by metal-organic chemical vapor deposition. Using degenerately Sn-doped regrown n+ β-Ga2O3 contact layers, we were able to maintain Ohmic contact to the β-Ga2O3 films down to 40 K, allowing for reliable temperature-dependent Hall measurement. An electron mobility of 176 cm2/V s and 3481 cm2/V s were measured at room temperature and 54 K, respectively. The room and low temperature mobilities are both among the highest reported values in a bulk β-Ga2O3 film. A low net background charge concentration of 7.4 × 1015 cm−3 was confirmed by both temperature dependent Hall measurement and capacitance-voltage measurement. The feasibility of achieving low background impurity concentration and high electron mobility paves the road for the demonstration of high performance power electronics with high breakdown voltages and low on-resistances.

We demonstrate a marked increase in the possible growth domain and growth rate of the O plasma-assisted molecular beam epitaxy of β-(AlxGa1−x)2O3, by adding the element In during growth. We explain these enhancement results from a metal-exchange catalytic effect. This mechanism allows us to synthesize β-(AlxGa1−x)2O3/β-Ga2O3 heterostructures at growth conditions that are not accessible in the absence of In, stabilizing the monoclinic β-phase. We demonstrate the growth of β-(AlxGa1−x)2O3 at growth temperatures up to 900 °C. Moreover, we illustrate how additional In on the β-(AlxGa1−x)2O3 surface acts as a surface active agent, improving the crystal quality of the synthesized β-(AlxGa1−x)2O3/β-Ga2O3 heterostructures. These structures are shown to be of the highest crystal quality up to an Al concentration of x = 0.2. We predict the novel growth mode introduced for ternary III–O thin film synthesis — shown by the example of β-(AlxGa1−x)2O3 — to be applicable for a wide range of thin film materials, whose individual constituents possess material properties similar to those discussed for the constituents contributing to β-(AlxGa1−x)2O3.

We report on a high performance Pt/n−Ga2O3/n+Ga2O3 solar blind Schottky photodiode that has been grown by metalorganic chemical vapor deposition. The active area of the photodiode was fabricated using ∼30 Å thick semi-transparent Pt that has up to 90% transparency to UV radiation with wavelengths < 260 nm. The fabricated photodiode exhibited Schottky characteristics with a turn-on voltage of ∼1 V and a rectification ratio of ∼108 at ±2 V and showed deep UV solar blind detection at 0 V. The Schottky photodiode exhibited good device characteristics such as an ideality factor of 1.23 and a breakdown voltage of ∼110 V. The spectral response showed a maximum absolute responsivity of 0.16 A/W at 222 nm at zero bias corresponding to an external quantum efficiency of ∼87.5%. The cutoff wavelength and the out of band rejection ratio of the devices were ∼260 nm and ∼104, respectively, showing a true solar blind operation with an excellent selectivity. The time response is in the millisecond range and has no long-time decay component which is common in photoconductive wide bandgap devices.

We report on record electron mobility values measured in lightly Si doped homoepitaxial β-Ga2O3 grown by metal-organic chemical vapor deposition. The transport properties of the films were studied using temperature-dependent Hall measurements. Numerous (010) β-Ga2O3 layers grown at different conditions showed peak electron mobility exceeding 104 cm2/V s at low temperature (LT), with the highest value of 11 704 cm2/V s at 46 K. The room temperature electron mobilities of the films were between 125 cm2/V s and 160 cm2/V s with the net background charge concentration between ∼5 × 1015 cm−3 and ∼2 × 1016 cm−3. The obtained LT mobility values for β-Ga2O3 were found to be comparable to or higher than the highest LT electron mobilities in bulk SiC and GaN films in the literature. The results demonstrate the capability of metalorganic chemical vapor deposition (MOCVD) for growing high quality ultrapure β-Ga2O3 epitaxial films that are suitable for high power electronic device applications.

In this work, the growth of (010), (001), and 2¯01 β-Ga2O3 by plasma assisted molecular beam epitaxy was investigated. The presence of an indium flux during growth markedly expands the growth regime for β-Ga2O3 across all orientations to higher growth temperatures and growth rates. This metal oxide catalyzed growth allows for similar growth rates of around 5 nm/min across all three orientations, more than twice that of conventional (010) growth and seven times that of (001) growth without indium. Smooth surface morphologies for (010) and (001) β-Ga2O3 were demonstrated, while 2¯01 was significantly rougher. Additionally, doping with Sn was achieved across all orientations and Hall measurements demonstrated higher electron mobility (55 cm2/Vs for a carrier concentration of 3.3 × 1018 cm−3) for (001) β-Ga2O3 grown via metal oxide catalyzed epitaxy than conventional growth.