Investigations into (InxGa1-x)2O3 structures grown on c-plane sapphire using pulsed laser deposition
Date
2022-08
Authors
Saha, Jibesh Kanti
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Abstract
Alloys of Ga2O¬3 with In2O3, ternary (InxGa1–x)2O3 were grown for x ≤ 15% as a function of growth parameters such as substrate temperature (Ts), oxygen partial pressure (Po2), and laser power using Pulsed Laser Deposition (PLD) technique. The structural property of the as-grown layers was studied based on the growth parameters employing X-ray diffraction (XRD) analysis. Besides the monoclinic phase reflections of Ga2O¬3 and cubic bixbyite phase reflections of In2O3, an extra peak was observed for indium concentration, x ≥ 8% at specific growth conditions. The indium incorporation was reflected in a band gap reduction between 4.98 and 4.64 eV, as determined using UV-Vis analysis. Ellipsometry study showed a slight thickness variation due to evaporation of volatile Ga2O and In2O suboxides. X-ray photoelectron spectroscopy (XPS) analyses indicated that the (InxGa1–x)2O3 alloy contains a mixture of Ga and In cation valence states and oxygen vacancies that were reduced when the oxygen partial pressure during deposition was increased. During the analysis of the XRD spectra of the (In0.10Ga0.90)2O3 alloy, the observation of an extra peak led to the investigation of metastable polymorphs of (InxGa1–x)2O3. This polymorph, κ-(InxGa1–x)2O3 was confirmed through X-ray diffraction phi-scan of the {122} reflection representing the orthorhombic phase. The spontaneous polarization of κ-(InxGa1–x)2O3 makes it a promising candidate for 2DEG HEMT and ferroelectric devices. Detailed investigation of the impact of growth conditions in the κ-phase indicated that the appearance of this phase is due to specific growth conditions and does not depend on the nucleation process. The impact of PLD growth parameters such as laser power, substrate temperature, and oxygen partial pressure was investigated using XRD to establish a phase diagram for the κ-phase and β-phase of (InxGa1–x)2O3.
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Keywords
Pulsed laser deposition, Bandgap engineering, Indium gallium oxide, Polymorphs, κ-phase, β-phase, Substrate temperature, Laser power, Oxygen partial pressure
Citation
Saha, J. K. (2022). <i>Investigations into (InxGa1-x)2O3 structures grown on c-plane sapphire using pulsed laser deposition</i> (Unpublished thesis). Texas State University, San Marcos, Texas.