Heteroepitaxial films of Ga 2 O 3 were grown on c-plane sapphire (0001). The stable phase β-Ga 2 O 3 was grown using the metalorganic chemical vapor deposition technique, regardless of precursor flow rates, at temperatures between 500 • C and 850 • C. Metastable α-and ε-phases were grown when using the halide vapor phase epitaxy (HVPE) technique, at growth temperatures between 650 • C and 850 • C, both separately and in combination. XTEM revealed the better lattice-matched α-phase growing semi-coherently on the substrate, followed by ε-Ga 2 O 3 . The epitaxial relationship was determined to be [1100]
IMPACT STATEMENTThis study demonstrates one of the first epitaxial growths of multiple polymorphs of Ga 2 O 3 on sapphire (0001) substrates, including its β-, α-, and ε-phases. Epitaxial relationship is confirmed through HRTEM.
ARTICLE HISTORY
InGaN films have been grown on GaN and AlGaN epitaxial layers by metalorganic vapor phase epitaxy. The "composition pulling effect" during the initial InGaN growth stages has been studied as a function of the lattice mismatch between the InGaN and the underlying epitaxial layer. The crystalline quality of the InGaN is good near the InGaN/GaN interface and the composition is close to that of GaN. However, with increasing InGaN film thickness, the crystal quality deteriorates and the indium mole fraction increases. The composition pulling effect becomes stronger with increasing lattice mismatch. It is suggested that indium atoms are excluded from the InGaN lattice during the early growth stages to reduce the deformation energy from the lattice mismatch. TEM observations of the InGaN/GaN structure reveal that the degradation of the crystalline quality of InGaN films grown on GaN is caused by pit formation which arises from edge dislocations propagating through the InGaN film from the underlying GaN.
Schottky diodes based on (2¯01) β-Ga2O3 substrates and (010) β-Ga2O3 homoepitaxial layers were formed using five different Schottky metals: W, Cu, Ni, Ir, and Pt. Based on a comparison of the effects of different wet chemical surface treatments on the Ga2O3 Schottky diodes, it was established that a treatment with an organic solvent, cleaning with HCl and H2O2, and rinsing with deionized water following each step yielded the best results. Schottky barrier heights calculated from current–voltage (I-V) and capacitance–voltage (C-V) measurements of the five selected metals were typically in the range of 1.0–1.3 and 1.6–2.0 eV, respectively, and showed little dependence on the metal work function. Several diodes also displayed inhomogeneous Schottky barrier behavior at room temperature. The results indicate that bulk or near-surface defects and/or unpassivated surface states may have a more dominant effect on the electrical behavior of these diodes compared to the choice of Schottky metal and its work function.
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