Silicon-doped β-Ga2O3 films grown at 1 μm/h by suboxide molecular-beam epitaxy
Abstract
We report the use of suboxide molecular-beam epitaxy (S-MBE) to grow β-Ga2O3 at a growth rate of ~1 μm/h with control of the silicon doping concentration from 5x1016 to 1019 cm-3. In S-MBE, pre-oxidized gallium in the form of a molecular beam that is 99.98\% Ga2O, i.e., gallium suboxide, is supplied. Directly supplying Ga2O to the growth surface bypasses the rate-limiting first step of the two-step reaction mechanism involved in the growth of β-Ga2O3 by conventional MBE. As a result, a growth rate of ~1 μm/h is readily achieved at a relatively low growth temperature (Tsub = 525 ), resulting in films with high structural perfection and smooth surfaces (rms roughness of < 2 nm on ~1 μm thick films). Silicon-containing oxide sources (SiO and SiO2) producing an SiO suboxide molecular beam are used to dope the β-Ga2O3 layers. Temperature-dependent Hall effect measurements on a 1 μm thick film with a mobile carrier concentration of 2.7x1017 cm-3 reveal a room-temperature mobility of 124 cm2 V-1 s-1 that increases to 627 cm2 V-1 s-1 at 76 K; the silicon dopants are found to exhibit an activation energy of 27 meV. We also demonstrate working MESFETs made from these silicon-doped β-Ga2O3 films grown by S-MBE at growth rates of ~1 μm/h.
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