Crystal Growth and Structure–Property Optimization of Thermally Annealed Nanocrystalline Ga₂O₃ Films

Abstract

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.

Heterogrowth of β-(AlxGa1–x)2O3 Thin Films on Sapphire Substrates

“…According to eqs and , , here D represents the grain size, k = 0.9 is a constant, β and ε represent the (−201) diffraction peak FWHM and microstrain, respectively, and θ and λ still represent the Bragg diffraction angle and X-ray wavelength, respectively. With the increasing TMAl flow rate, the FWHM and microstrain were increasing simultaneously, indicating that our analysis was reasonable.…”

Structural, Optical and Mechanical Properties of Nanocrystalline Molybdenum Thin Films Deposited under Variable Substrate Temperature

“…For polycrystalline metal and metal-oxide films, the optical constants are sensitive to the crystal structure, morphology, microstructure, defect structure and chemistry [50][51][52][53][54]. Most importantly, the surface/interface structure, crystal quality, packing density, lattice parameters, and defect structure of the deposited films strongly influence their optical parameters [50][51][52][53][54]. Thus, the observed changes noted for Mo films as a function of deposition temperature can be attributed to the microstructure and grain size variation.…”

A Comprehensive Study of Defects in Gallium Oxide by Density Functional Theory

“…High-temperature thermal annealing of β-Ga2O3 in an oxygen (O2) environment may increase the gallium vacancies (VGa) and oxygen interstitials (Oi), and reduce the oxygen vacancies (VO) in the thin films 47,48 .…”

“…The thickness of the sample is ~0. 47,48 . Raman spectra as shown in Figure 7 are acquired using a Horiba Raman spectroscope with a 638 nm red laser excitation passing through a 50x objective lens in backscattered mode with a spectral resolution of 0.5 cm −1 .…”