Pseudomorphic growth of Si-doped α-(AlGa)₂O₃ on m-plane α-Al₂O₃ substrates by molecular beam epitaxy

Abstract

α-(AlGa)2O3 is an attractive material for high-power devices and vacuum UV optoelectronics. However, α-(AlGa)2O3 on sapphire substrates suffers from lattice relaxation and phase transformation. Here, we investigated the effect of controlling the Al composition and thickness of Si-doped α-(AlGa)2O3 layers pseudomorphically grown on α-Al2O3 (10 1 ¯ 0) substrates by MBE. We found that the critical layer thicknesses of α-(AlGa)2O3 layers with Al compositions of 58%, 66%, and 79% were around 13, 18, and 44 nm, respectively. We also found that a 9.0 nm thick α-(Al0.65Ga0.35)2O3/3.5 nm thick Al2O3 multilayer with 20 periods grew almost pseudomorphically and formed α-(Al0.90Ga0.10)2O3 alloy after post-thermal annealing at 1400 °C.

Si-doped (AlGa)2O3 growth on a-, m- and r-plane α-Al2O3 substrates by molecular beam epitaxy

“…Under the assumption of fully-relaxed (AlGa) 2 O 3 layers, the Al composition was calculated by using a XRD symmetrical 2θ-ω measurement. Comparison with previous results reveals that (AlGa) 2 O 3 layers with lower Al composition were obtained by increasing the BEP Ga from 3.0 × 10 −7 Pa to 1.6 × 10 −6 Pa. 23) The XRD peak position of (112 ¯0) and (101 ¯0) (AlGa) 2 O 3 layers increased with increasing the BEP Al (supplementary data) due to the increased Al compositions. At the same BEP Al (>1 × 10 −6 Pa), the estimated Al compositions in the (101 ¯0) (AlGa) 2 O 3 layers were slightly higher than those in the (112 ¯0) (AlGa) 2 O 3 layers.…”

“…Under the assumption that the relative sensitivity factor used for SIMS analysis of α-(AlGa) 2 O 3 remains constant despite the Al composition ranging from 58% to 100%, the Si concentrations in the (101 ¯0) α-(AlGa) 2 O 3 layers were independent of the Al composition. 23) For (AlGa) 2 O 3 growth, only the BEP Al was changed while fixing the BEP Ga at 1.6 × 10 −6 Pa, providing an oxygen-rich regime. The BEP Al , Al composition, [Si], and thickness (d) for (AlGa) 2 O 3 growth are listed in supplementary data.…”

“…The Al composition of the (AlGa) 2 O 3 layers was determined by high-resolution X-ray diffraction (XRD) using Co Kα1 radiation with the wavelength (λ) of 0.1789 nm at room temperature. 23) From the out-of-plane lattice constant (d f ) of fully relaxed (Al x Ga 1−x ) 2 O 3 layers, x is calculated using Vegard's law, as follows = + -…”

“…Using m-plane (101 ¯0) α-Al 2 O 3 substrates, the (AlGa) 2 O 3 layers can have the α single phase for the whole Al composition range. 5,13,16,23) For α-(AlGa) 2 O 3 , Si, Ge, and Sn atoms are available as donors. 24,25) The Sn-doped α-Ga 2 O 3 layers on (101 ¯0) α-Al 2 O 3 substrates had a higher electron mobility than those on (0001) α-Al 2 O 3 substrates.…”

MOCVD growth of Si-doped α-(AlGa)2O3 on m-plane α-Al2O3 substrates

“…20,24) Common (AlGa) 2 O 3 /Ga 2 O 3 MODFETs consist of a donordoped (AlGa) 2 O 3 barrier layer and an undoped Ga 2 O 3 channel layer. (AlGa) 2 O 3 layers have been grown by using MBE, 21,22,25) pulse-laser deposition (PLD), [26][27][28] MOCVD, 23) and mist CVD. [29][30][31][32][33] High-quality α-(AlGa) 2 O 3 growth favors m-plane (10_10) sapphire substrates.…”