We describe the growth of hexagonal GaN on Si(111) by gas source molecular beam epitaxy with ammonia. The initial deposition of Al, at 1130–1190 K, resulted in a very rapid transition to a two-dimensional growth mode of AlN. The rapid transition is essential for the subsequent growth of high quality GaN and AlGaN. This procedure also resulted in complete elimination of cracking in thick (>2 μm) GaN layers. For layers thicker than 1.5 μm, the full width at half maximum of the (0002) GaN diffraction peak was less than 14 arc sec. We show that a short period superlattice of AlGaN/GaN grown on the AlN buffer can be used to block defects propagating through GaN, resulting in good crystal and luminescence quality. At room temperature, the linewidth of the GaN exciton recombination peak was less than 40 meV, typical of the best samples grown on sapphire.

Catalytic growth of GaN nanowires by hydride vapour phase epitaxy is demonstrated. Nickel-gold was used as a catalyst. Nanowire growth was limited to areas patterned with catalyst. Characterization of the nanowires with transmission electron microscopy, x-ray diffraction, and low temperature photoluminescence shows that the nanowires are stoichiometric 2H-GaN single crystals growing in the [0001] orientation when grown on sapphire, with occasional stacking faults along the c-axis as the only defect type observed in most of the wires. A red shift observed in the photoluminescence was too large to be explained by the minor strain observed alone, and was only marginally affected by temperature, suggesting a superposition of several factors.

Hexagonal AlN layers were grown on Si(111) by gas-source molecular-beam epitaxy with ammonia. The transition between the (7×7) and (1×1) silicon surface reconstructions, at 1100 K, was used for in situ calibration of the substrate temperature. The initial deposition of Al, at 1130–1190 K, produced an effective nucleation layer for the growth of AlN. The Al layer also reduced islands of SiNx that might be formed due to background NH3 on the silicon surface prior to the onset of epitaxial growth. The transition to two-dimensional growth mode, under optimum conditions, was obtained after the initial AlN thickness of ∼7 nm.

We report on the growth of β-Ga2O3 thin films using trimethylgallium (TMGa) as a source for gallium and pure O2 for oxidation. The growth rate of the films was found to linearly increase with the increase in the molar flow rate of TMGa and reach as high as ∼6 μm/h at a flow rate of 580 μmol/min. High purity, lightly Si-doped homoepitaxial β-Ga2O3 films with a good surface morphology, a record low temperature electron mobility exceeding 23 000 cm2/V s at 32 K, and an acceptor concentration of 2 × 1013 cm−3 were realized, showing an excellent purity film. Films with room temperature (RT) electron mobilities ranging from 71 cm2/V s to 138 cm2/V s with the corresponding free carrier densities between ∼1.1 × 1019 cm−3 and ∼1.5 × 1016 were demonstrated. For layers with the doping concentration in the range of high-1017 and low-1018 cm−3, the RT electron mobility values were consistently more than 100 cm2/V s, suggesting that TMGa is suitable to grow channel layers for lateral devices, such as field effect transistors. The results demonstrate excellent purity of the films produced and confirm the suitability of the TMGa precursor for the growth of device quality β-Ga2O3 films at a fast growth rate, meeting the demands for commercializing Ga2O3-based high voltage power devices by metalorganic chemical vapor deposition.

We report on the low pressure metal organic chemical vapor deposition of single crystal, wurtzitic layers of GaN and GaN/InGaN heterostructures on (111) GaAs/Si composite substrates. The structural, optical, and electrical properties of the epitaxial layers are evaluated using x-ray diffraction, transmission electron microscopy, photoluminescence, and measurements of minority carrier diffusion length. These measurements demonstrate high quality of GaN grown on the composite substrate.

We report on the growth of ZnSnP2 on GaAs(100) substrates by gas source molecular beam epitaxy. Samples were grown in the temperature range of 300–360 °C. A small change in the Sn/Zn flux ratio at constant substrate temperature was found to result in a transition from a lattice mismatched, Δa/a∼0.4%–0.7%, disordered crystal structure to a lattice matched, ordered chalcopyrite structure. Infrared reflectance and Raman measurements were used to monitor this phase transition. Formation of the two different crystal modifications is discussed in terms of vapor–solid and vapor–liquid–solid growth modes.

β-Ga2O3 metal-semiconductor field-effect transistors are realized with superior reverse breakdown voltages (VBR) and ON currents (IDMAX). A sandwiched SiNx dielectric field-plate design is utilized that prevents etching-related damage in the active region and a deep mesa-etching was used to reduce reverse leakage. The device with LGD=34.5μm exhibits an IDMAX of 56 mA/mm, a high ION/IOFF ratio >108 and a very low reverse leakage until catastrophic breakdown at ∼4.4kV. A power figure of merit (PFOM) of 132 MW/cm2 was calculated for a VBR of ∼4.4kV. The reported results are the first >4kV-class Ga2O3 transistors to surpass the theoretical FOM of Silicon.

Using contactless electroreflectance, we determined the band gap of the two known phases of epitaxial ZnSnP2. Induced by small changes in Sn/Zn flux ratio during epitaxy, the order-disordered transition between the chalcopyrite and sphalerite phases reduces the band gap by 300 meV. The chalcopyrite ordered phase, unambiguously identified from x-ray diffraction, exhibits a band gap of 1.683 eV at 293 K. The band gap of the disordered sphalerite phase is 1.383 eV. Using the volume-averaged order parameter measured on the chalcopyrite sample, we find that its morphology is best described by the presence of perfectly ordered domains inside a disordered matrix.