α-Ga2O3 grown by low temperature atomic layer deposition on sapphire

Abstract

-Ga2O3 is a metastable phase of Ga2O3 of interest for wide bandgap engineering since it is isostructural with -In2O3 and -Al2O3. -Ga2O3 is generally synthesised under high pressure (several GPa) or relatively high temperature (~500 o C). In this study, we report the growth of -Ga2O3 by low temperature atomic layer deposition (ALD) on sapphire substrate. The film was grown at a rate of 0.48 Å/cycle, and predominantly consists of -Ga2O3 in the form of (0001)-oriented columns originating from the interface with the substrate. Some inclusions were also present, typically at the tips of the -phase columns and most likely comprising -Ga2O3. The remainder of the Ga2O3 filmi.e. nearer the surface and between the -Ga2O3 columns, was amorphous. The film was found to be highly resistive, as is expected for undoped material. This study demonstrates that -Ga2O3 films can be grown by low temperature ALD and suggests the possibility of a new range of ultraviolet optoelectronic and power devices grown by ALD. The study also shows that scanning electron diffraction is a powerful technique to identify the different polymorphs of Ga2O3 present in multiphase samples.

Low temperature growth and optical properties of α-Ga2O3 deposited on sapphire by plasma enhanced atomic layer deposition

“…From our XRD results (Figure 1(B)), the film is dominantly α-Ga2O3. The structure of this film, that is, α phase columns, agrees well with our earlier report 33 . It can be seen that in comparison with Figure 3(A), there is a slight increase in surface roughness related to the grain boundaries where α-Ga2O3 columns touch.…”

“…The XRD peaks seen in Figure 1 In our previous study of 130 nm thick Ga2O3 films, we observed by SED that the ca. 70 nm of Ga2O3 material adjacent to the substrate was dominantly α phase columns with a diameter of 2-23 nm 33 . Since the films shown here are approximately 30 nm thick, we expect that the grain-like structure observed here by AFM corresponds to the termination of the α phase columns.…”

“…Most Ga2O3 atomic layer deposition (ALD) papers using a variety of deposition temperatures, chemical precursors and substrates report deposition of amorphous material [26][27][28][29][30][31][32] . However, in a recent study we reported that α-Ga2O3 could be deposited by plasma enhanced ALD (PEALD) onto sapphire (α-Al2O3) substrates 33 . Here, we investigate the impact of several growth parameters (substrate temperature, plasma power and O2 flow) on Ga2O3 thin films deposited by PEALD on sapphire.…”

Atomic layer deposited α-Ga2O3 solar-blind photodetectors

“…To better understand the origin of this variation, TEM imaging of the as-grown sample, of the sample annealed in oxygen, and of the forming gas annealed sample was conducted. As illustrated in Figure 5, all three samples are nearly identical; they exhibit a columnar structure of α-Ga2O3 separated by amorphous Ga2O3 [21] and the columns have visually similar width and height. It appears that all the annealed samples A c c e p t e d M a n u s c r i p t exhibit a columnar structure (from TEM observations); a comparable α phase volume fraction or crystallite size (from XRD 2θ-ω scans); and similar strain state (from XRD RSMs).…”

“…Using atomic layer deposition (ALD), most studies have reported the deposition of amorphous Ga2O3 films [14][15][16][17][18][19][20]. However, it has been recently demonstrated that α-Ga2O3 could also be synthesized using plasma-enhanced ALD at temperatures as low as 250 o C [21]. To date, the body of work on this material has focused on growth aspects, and only a limited number of studies have reported the application of the grown materials in devices.…”