Growth and Characterization of (InxGa1-x)2O3 Thin Films Grown by Pulsed Laser Deposition

Abstract

Silicon has been an important material in the integrated circuit (IC) technology and is a commonly used elemental semiconductor. However, silicon has limitations in its operating voltage, temperature and switching frequency. Furthermore, being an indirect bandgap semiconductor, it is unsuitable for optoelectronic device applications. Wide bandgap semiconductors that include GaN and SiC is being used for power application but their breakdown field is limited. A new generation of power semiconductor devices based on materials having a larger breakdown field will help increase the efficiency of alternative electric energy transmission and generation. Due to its excellent thermal and chemical stability, beta-gallium oxide (β-Ga2O3) is a promising material for high breakdown, high-power devices. It’s large direct bandgap of 4.9 eV is predicted to have a high breakdown electric field of 8 MV/cm for fabricated electronic devices. The large bandgap of β-Ga2O3 makes it transparent from the visible to UV wavelengths and can be alloyed with In2O3 to provide tunable bandgaps.

The growth of (InxGa1-x)2O3 with varying indium content (x) on sapphire (0001) substrates using pulsed laser deposition was demonstrated. X-ray diffraction (XRD) measurements revealed an increase in the lattice parameter as In content was increased as expected for an increase in lattice constant. The films were found to exhibit a predominantly monoclinic crystal structure for an In content x=0.1 grown at 650°C with a small amount of polycrystalline cubic structure present. As the indium content increased from x=0.1 to x=0.4, the cubic structure of films became dominant. The optical constants (n, k) were determined using spectroscopic ellipsometry and found to vary with In content x=0.1 to 0.4 ranging between 1.8 to 2 for n while the k values range between 0.0002 to 0.0005 at a wavelength of 632 nm. The small value of k is expected since the bandgap of the material is large.

The percentage transmittance of the films is determined by ultraviolet visible spectroscopy with the films exhibiting large transmittance values in the visible region. The extracted bandgap was found to decrease with increase in indium content as expected.