Realization and optimization of the tunable/enhanced optical properties are critical to further advancing the fields of optoelectronics, photonics, and nanoelectronics. In this context, here, we demonstrate green-emission characteristics with a ∼30-fold enhancement in selectively engineered nanocrystalline Ga 2 O 3 with control over the size, phase, and interface nanostructure. Pulsed-laserdeposited β-phase Ga 2 O 3 films with an average crystallite size of ∼9 nm along with a highly dense, close-compact nanocolumnar structure with the lowest possible defect density facilitate the 30-fold enhancement in the photoluminescence (PL) intensity in the green region. Enhanced PL emission in the optimized, engineered nanoarchitecture sheds light on the design of Ga 2 O 3 materials for promising future optoelectronic/ photocatalytic applications.
The effects of thermal annealing on the crystal chemistry, crystallization process, index of refraction, mechanical properties, and electrical characteristics of nanocrystalline Ga 2 O 3 films was evaluated. Ga 2 O 3 thin films were sputtered onto Si(100) substrates at 500 °C utilizing a Ga 2 O 3 ceramic target, while postdeposition thermal annealing was performed between a range of 500−900 °C. Both structural quality and packing density of the Ga 2 O 3 films was improved by the thermal annealing as indicated by the X-ray diffraction and ellipsometry studies. The atomic force microscopy analysis indicates that the annealing temperature has a dramatic effect on surface roughness, especially when the annealing temperature exceeds 700 °C. Corroborating with structure and morphology changes, the high values of hardness and elastic modulus are noted for Ga 2 O 3 films annealed at higher temperatures (800−900 °C). Index of refraction (n) and extinction coefficient (k) results, and their dispersion profiles indicate that the annealing temperature strongly influences the optical properties. The refractive index values vary in the range of 1.78−1.84 (632 nm) because of the gradual improvement of structural quality, texturing, and packing density upon thermal annealing. A correlation between annealing temperature, optical characteristics, and electrical characteristics in Ga 2 O 3 films is established.
Gallium oxide (Ga2O3) thin films were deposited onto Si(100) substrates at 500°C by sputtering the Ga2O3 ceramic target. The effect of thermal annealing in the temperature range of 500–900°C on the crystal structure, chemical bonding, electronic structure, and bandgap of polycrystalline Ga2O3 films was evaluated. Thermal annealing induced improvement in the structural quality and packing density of the Ga2O3 films as evident from X-ray diffraction and Raman spectroscopic analyses. X-ray photoelectron spectroscopic (XPS) analyses indicate the binding energies (BE) of the Ga 2p doublet i.e., the Ga 2p3/2 and Ga 2p1/2 peaks, are located at 1118.0 and 1145.0 eV, respectively, characterizing gallium in its highest chemical oxidation state (Ga3+) in the as-deposited films. The core level XPS spectra of O 1s indicate that the peak is centered at a BE∼531 eV, which is also characteristic of Ga-O bonds in the Ga2O3 phase. No significant changes were seen in the electronic structure, especially in terms of chemical valence of Ga ions and Ga-O bonds, as function of thermal annealing in the entire temperature range of 500–900°C. However, the presence of carbonyl functional groups become evident in XPS for samples under thermal annealing. Raman analysis also reveals an obvious blueshift for the high-frequency stretching and bending of the GaO4 tetrahedra, which structurally form the β-Ga2O3, with confinement. The bandgap determined from spectrophotometry measurements varies in the range of 4.94–4.78 eV for a variation in annealing temperature in the range of 500–900°C. A correlation between annealing temperature, electronic structure, chemical bonding and bandgap in Ga2O3 films is established.
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