The goal of this Exploratory Express project was to explore the possibility of tunable ferromagnetism in Mn or Cr incorporated epitaxial Ga2O3 films. Tunability of magnetic properties can enable novel applications in spintronics, quantum computing, and magnetism-based logics by allowing control of magnetism down to the nanoscale. Carriers (electrons or holes) mediated ferromagnetic ordering in semiconductor can lead to tunable ferromagnetism by leveraging the tunability of carrier density with doping level, gate electric field, or optical pumping of the carriers. The magnetic ions (Cr or Mn) in Ga2O3 act as localized spin centers which can potentially be magnetically coupled through conduction electrons to enable ferromagnetic ordering. Here we investigated tunable ferromagnetism in beta Ga2O3 semiconductor host with various n-doping levels by incorporating 2.4 atomic percent Mn or Cr. The R&D approach involved growth of epitaxial Ga2O3 film on sapphire or Ga2O3 substrate, implantation of Mn or Cr ions, annealing of the samples post implantation, and magnetic measurements. We studied magnetic behavior of Mn:Ga2O3 as a function of different n-doping levels and various annealing temperatures. The vibrating sample magnetometry (VSM) measurement exhibited strong ferromagnetic signals from the annealed Mn:Ga2O3 sample with n-doping level of 5E19 cm-3. This ferromagnetic behavior disappears from Mn:Ga2O3 when the n-doping level is reduced to 5E16 cm-3. Although these results are to be further verified by other measurement schemes due to the observation of background ferromagnetism from the growth substrate, these results indicate the possibility of tunable ferromagnetism in Mn:Ga2O3 mediated by conduction electrons.
We present progress on the synthesis of semimetal Cd3As2 by metal–organic chemical-vapor deposition (MOCVD). Specifically, we have optimized the growth conditions needed to obtain technologically useful growth rates and acceptable thin-film microstructures, with our studies evaluating the effects of varying the temperature, pressure, and carrier-gas type for MOCVD of Cd3As2 when performed using dimethylcadmium and tertiary-butylarsine precursors. In the course of the optimization studies, exploratory Cd3As2 growths are attempted on GaSb substrates, strain-relaxed InAs buffer layers grown on GaSb substrates, and InAs substrates. Notably, only the InAs-terminated substrate surfaces yield desirable results. Extensive microstructural studies of Cd3As2 thin films on InAs are performed by using multiple advanced imaging microscopies and x-ray diffraction modalities. The studied films are 5–75 nm in thickness and consist of oriented, coalesced polycrystals with lateral domain widths of 30–80 nm. The most optimized films are smooth and specular, exhibiting a surface roughness as low as 1.0 nm rms. Under cross-sectional imaging, the Cd3As2-InAs heterointerface appears smooth and abrupt at a lower film thickness, ~30 nm, but becomes quite irregular as the average thickness increases to ~55 nm. The films are strain-relaxed with a residual biaxial tensile strain (ϵxx = +0.0010) that opposes the initially compressive lattice-mismatch strain of Cd3As2 coherent on InAs (ϵxx = - 0.042). Importantly, phase-identification studies find a thin-film crystal structure consistent with the P42/nbc space group, placing MOCVD-grown Cd3As2 among the Dirac semimetals of substantial interest for topological quantum materials studies.
This work provides the first demonstration of vertical GaN Junction Barrier Schottky (JBS) rectifiers fabricated by etch and regrowth of p-GaN. A reverse blocking voltage near 1500 V was achieved at 1 mA reverse leakage, with a sub 1 V turn-on and a specific on-resistance of 10 mΩ-cm2. This result is compared to other reported JBS devices in the literature and our device demonstrates the lowest leakage slope at high reverse bias. A large initial leakage current is present near zero-bias which is attributed to a combination of inadequate etch-damage removal and passivation induced leakage current.