Growth of α-(AlGa)₂O₃ alloy thin films on c-sapphire substrates by mist chemical vapor deposition using acetylacetonated Al and Ga solutions

Abstract

α-Ga2O3 is a semi-stable phase of Ga2O3 and is known as an ultra-wide-bandgap semiconductor material. α-(AlGa)2O3 alloys are important for their applications in electronic and optoelectronic devices.We investigated the growth mechanism and process of α-(AlGa)2O3 alloys by mist chemical vapor deposition using acetylacetonated Al and Ga aqueous solutions. The contribution of acetylacetonated Al ions to the epitaxial growth was investigated. The effect of the epitaixal growth mechanisms based on an anchoring mechanism on the mosaic spread were experimentally evaluated. Investigating 10-14 x-ray diffraction profiles, strain relaxation processes in film formations are discussed.

Control of Al composition of mist chemical vapor deposition grown α-(AlGa)2O3 alloy thin films by acetylacetonation of Al ion

“…This formation mechanism is also expected in the formation of a an Al-O bond associated with acetylacetonated Al ions. Based on this expectation, we have also reported growths of high-quality α-(AlGa) 2 O 3 alloy thin films with smaller mosaic spread value and higher Al composition relative to the Al supply ratio, 23) in comparing with other reports on α-(AlGa) 2 O 3 growth by mist-CVD. [24][25][26][27][28] The growth of α-(AlGa) 2 O 3 alloy thin films with high quality and controllability is important in terms of bandgap engineering; it is necessary for the realization of cladding layers for two-dimensional electron gas devices 29) and optical devices using α-Ga 2 O 3 material systems.…”

“…22) The preparation methods for the aqueous gallium chloride solutions [GaCl 3 (aq)] and aluminum chloride solutions [AlCl 3 (aq)] were also described in detail in our previous papers. 22,23) The composition of the standard source solution and the growth conditions are shown in Table I.…”

“…Acetylacetone (Hacac) was dissolved in DI water, and then AlCl 3 (aq) and GaCl 3 (aq) were dissolved in this to make the target composition, as shown in Table I. If control of the pH was required, 23) ammonia water [NH 3 (aq)] and/or hydrochloric acid [HCl(aq)] were introduced. The standard stirring time and temperature of the source solutions were 10-20 min and ∼50 °C, respectively.…”

“…In this work, we investigate the effect of acetylacetonated Al complexes on the Al composition of α-(AlGa) 2 O 3 alloy thin films by controlling the complexation state of Al ions. In particular, we systematically discuss the realization of thin film growth with high Al composition by promoting acetylacetonation through pH control in source solutions, which was realized in our previous report, 23) and the decrease in Al composition with growth temperature.…”

“…On the other hand, the mist-CVD method can continuously grow the metastable phase of α-(AlGa) 2 O 3 on sapphire substrates in the entire Al composition range due to its strong epitaxial growth properties, but it has the problem that the Al composition varies depending on the crystal growth conditions. [23][24][25][26][27][28] However, compositional control of α-(AlGa) 2 O 3 alloy thin films in mist-CVD has not been discussed in much detail based on crystal growth mechanisms.…”