Lateral $\beta $ -Ga ₂ O ₃ MOSFET for power switching applications with a 1.8 kV breakdown voltage and a record power figure of merit of 155 MW/cm ² are demonstrated. Sub- $\mu \text{m}$ gate length combined with gate recess was used to achieve low ON-state resistances with reasonable threshold voltages above −24 V. The combination of compensation-doped high-quality crystals, implantation-based inter-device isolation, and SiN _x -passivation yielded in consistently high average breakdown field strengths of 1.8–2.2 MV/cm for gate–drain spacings between 2 and 10 $\mu \text{m}$ . These values outperform the results of more established wide-bandgap device technologies, such as SiC or GaN, and the major Ga ₂ O ₃ material promise—a higher breakdown strength—is well demonstrated.

We present a systematic study on the influence of the miscut orientation on structural and electronic properties in the homoepitaxial growth on off-oriented β-Ga₂O₃ (100) substrates by metalorganic chemical vapour phase epitaxy. Layers grown on (100) substrates with 6° miscut toward the [00$\overline{1}$ ] direction show high electron mobilities of about 90 cm² V⁻¹ s⁻¹ at electron concentrations in the range of 1–2 × 10¹⁸ cm⁻³, while layers grown under identical conditions but with 6° miscut toward the [001] direction exhibit low electron mobilities of around 10 cm² V⁻¹ s⁻¹. By using high-resolution scanning transmission electron microscopy and atomic force microscopy, we find significant differences in the surface morphologies of the substrates after annealing and of the layers in dependence on their miscut direction. While substrates with miscuts toward [00$\overline{1}$ ] exhibit monolayer steps terminated by ($\overline{2}$ 01) facets, mainly bilayer steps are found for miscuts toward [001]. Epitaxial growth on both substrates occurs in step-flow mode. However, while layers on substrates with a miscut toward [00$\overline{1}$ ] are free of structural defects, those on substrates with a miscut toward [001] are completely twinned with respect to the substrate and show stacking mismatch boundaries. This twinning is promoted at step edges by transformation of the (001)-B facets into ($\overline{2}$ 01) facets. Density functional theory calculations of stoichiometric low index surfaces show that the ($\overline{2}$ 01) facet has the lowest surface energy following the (100) surface. We conclude that facet transformation at the step edges is driven by surface energy minimization for the two kinds of crystallographically inequivalent miscut orientations in the monoclinic lattice of β-Ga₂O₃.

Homoepitaxial (100) β-Ga₂O₃ films were grown on substrates with miscut angles of 2°, 4°, and 6° toward [00$\overline{1}$ ] by metal organic vapor phase epitaxy. Step-flow growth mode, resulting in smooth film surfaces and high crystalline quality, could only be achieved if the diffusion length on the film surface corresponds approximately to the width of the terraces. Otherwise, 2D islands or step-bunching is obtained, which results in a deteriorated crystalline quality and reduced Hall mobility of the electrons. By varying the growth parameters such as the O₂/Ga ratio, Ar push gas flow, and chamber pressure, the diffusion length could be adjusted so that step-flow growth mode could be achieved at all miscut angles. Furthermore, the growth rate could remarkably be increased from 1.6 nm/min to 4.3 nm/min. For homoepitaxial β-Ga₂O₃ films grown in step-flow growth mode, TEM measurements revealed a high crystalline quality, which is correlated with a high Hall mobility of 131 cm²/V s at a carrier concentration of 1.6 × 10¹⁷cm⁻³, which is comparable with β-Ga₂O₃ single crystal bulk values. This study clearly points out the high potential of β-Ga₂O₃ films for high performance MOSFETs if the influence of the deposition parameters on the structural and electrical properties is well understood.

Two inch diameter, highly conducting (Si-doped) bulk β-Ga₂O₃ single crystals with the cylinder length up to one inch were grown by the Czochralski method. The obtained crystals revealed high structural quality characterized by narrow x-ray rocking curves (FWHM ≤ 25 arc sec) and high surface smoothness (RMS < 200 pm) of the epi-ready wafers. The free electron concentration and Hall mobility at room temperature were in the range of 1.6–9 × 10¹⁸ cm⁻³ and 118 – 52 cm² V⁻¹ s⁻¹, respectively, which are not affected by a heat treatment at temperatures up to 1000 °C in an oxidizing atmosphere. Temperature-dependent electrical properties of the crystals revealed a degenerated semiconducting state. Both high structural quality and electrical properties make the crystals well suited as substrates for homoepitaxy and electronic device fabrication in the vertical configuration.

A high growth rate process above 1 µm/h was achieved for Si-doped (100) β-Ga₂O₃ homoepitaxial films grown via metalorganic vapor phase epitaxy (MOVPE) while maintaining high crystalline perfection up to a film thickness of 3 µm. The main growth parameters were investigated to increase the growth rate and maintain the step-flow growth mode, wherein the enhanced diffusion channel due to the formation of a Ga adlayer was proposed to be the possible growth mechanism. Si doping allowed precise control of the n-type conductivity of the films with electron concentrations ranging from 1.5 × 10¹⁷ to 1.5 × 10¹⁹ cm⁻³ and corresponding mobilities from 144 to 21 cm² V⁻¹ s⁻¹, as revealed by Hall effect measurements at room temperature. Secondary ion mass spectrometry confirmed homogeneous Si doping through the film and a one-to-one correlation between the Si concentration and the electron concentration. Low defect density in the films was determined by x-ray diffraction measurements. The demonstration of a high growth rate process of β-Ga₂O₃ films with μm level thickness and smooth surface morphology via MOVPE is critical for high power electronics with vertical device architecture.