Growth and Characterization of (InxGa1-x)2O3, and NiO Heterostructures
In the recent past, ultra-wide bandgap β-Ga2O3 has drawn a significant amount of attention as an emerging wide bandgap semiconductor because of its promising material properties, for example, large bandgap (~ 4.9 eV), high electric breakdown field (~ 8 MVcm-1), hard radiation tolerance, physical and chemical stability in the harsh environment, as well as its suitability for mass production compared to their SiC and GaN counterparts. Pulsed laser deposited (PLD) NiO/ β-(InxGa1-x)2O3 heterostructure was investigated for p-n diode applications. Monoclinic structure of (InxGa1-x)2O3 grown on sapphire substrate at temperatures of 700ºC and oxygen partial pressure of 10-2 Torr was found for indium composition ≤10%. Theoretical calculations revealed that the addition of In in Ga2O3 increases the lattice constant and reduces the bandgap of the alloy. This was confirmed by measurements of the electrical properties of the grown layers. Primarily, heteroepitaxial thin films of NiO, β-Ga2O3, and β-(InxGa1-x)2O3 were grown on insulating c-plane (0001) sapphire (α-Al2O3) and improved crystallinity was observed at high deposition temperatures and pressures. RT measurement of β-(InxGa1-x)2O3 Schottky diodes and the Hall measurements correlated with each other with the alloy exhibited n-type conductivity with the resistivity, carrier concentration, and mobility value of ~ 0.6-50 Ω-cm, ~1017 - 1018 cm-3, and ~ 0.34 cm2V-1s-1, respectively. During the growth of Ga2O3 the use of, lanthanum aluminate (LAO) substrate and Sn dopant were used to stabilize single crystalline ε-Ga2O3 in a wide temperature range. In this study the stability of this ε- phase was investigated. Using temperature dependent XRD measurements it was found that at elevated temperature e.g. ≥ 800ºC an irreversible transition from ε- to the β- phase was observed resulting in changes in the structural and optical properties of the thin films with temperature. The properties of both NiO and β-(InxGa1-x)2O3 were investigated with oxygen plasma treatment. It was found that while there was an increased in the p-type conductivity in NiO by almost 3 orders of magnitude while increasing the presence of Ni3+ ions in the material, the conductivity of β-(InxGa1-x)2O3 was decreased. P-n diodes were fabricated after growing heterostructures comprising of NiO and β-(InxGa1-x)2O3 thin films. The layers in the heterostructure maintained a good epitaxial relationship without significant interfacial intermixing. A type-II staggered band alignment was observed with ΔEC and ΔEV of 1.54 and 2.38 eV, respectively. Finally, good ideality factor (~ 2.0) and breakdown voltages of the test devices of NiO/ β-(InxGa1-x)2O3 p-n diode of 9 - 16 V suggested dominant recombination process for forward bias conduction and demonstrated better performance than NiO/β-Ga2O3, consequently providing the feasibility of NiO/β-(InxGa1-x)2O3 in power applications.
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