Study on the Effect of Annealing on Ga$_2$O$_3$ Thin Films Deposited on Silicon by RF Sputtering

Abstract

Gallium oxide is an ultra-wide bandgap semiconductor with excellent opto-electronic properties, making it a highly promising material for a wide range of applications and devices. In this article, we report how the optical, morphological, structural, and compositional properties of $β$-Ga$_2$O$_3$ thin films deposited by RF sputtering on silicon substrates are affected by thermal treatments. Ellipsometric spectra recorded at multiple angles of incidence from several samples subjected to thermal annealing in the range of 550-1000 $^\circ$C were analyzed to extract the optical functions using appropriate multilayer models. This analysis is complemented by compositional, structural, and morphological characterization techniques. A significant increase of the refractive index was found after annealing at 1000 $^\circ$C, accompanied by a stark improvement in the samples' crystalline structure, as confirmed by complementary structural and compositional characterization techniques.

Figures (9)

• Figure 1: AFM images of the samples obtained (a) after deposition and after annealing at (b) 550, (c) 700, (d) 850, and (e) 1000 °C .
• Figure 2: RBS spectra and respective fits, for the samples as-grown and annealed at 550--1000 °C. The energies corresponding to the Ga and O at the surface, as well as the Si barrier from the substrate/SiO2, are marked. The data were vertically shifted for visual clarity and are from the detector placed at 165°.
• Figure 3: Schematic of the layer model used for the depth analysis.
• Figure 4: Density of the thin films, estimated from the RBS and ellipsometry thicknesses in Tables \ref{['rbs_fit_results']} and \ref{['ellipso']}, respectively.
• Figure 5: X-Ray diffractograms of the thin films as a function of annealing temperature, (a) in a 2$\theta$-$\omega$ scan with the most relevant substrate peaks marked in blue as well as the $400$ Ga2O3 reflection, (b) in a grazing incidence scan around the $400$ reflection, and (c) showing the full grazing incidence scan and the powder pattern ahman_reinvestigation_1996. The data were vertically shifted for visual clarity.