Silicon-doped \(\beta\)-Ga\(_2\)O\(_3\) films grown at 1 \(\mu\)m/h by suboxide molecular-beam epitaxy

We report the use of suboxide molecular-beam epitaxy (S-MBE) to grow \(\beta\)-Ga\(_2\)O\(_3\) at a growth rate of ~1 \({\mu}\)m/h with control of the silicon doping concentration from 5x10\(^{16}\) to 10\(^{19}\) cm\(^{-3}\). In S-MBE, pre-oxidized gallium in the form of a molecular beam that is 99.98\% Ga\(_2\)O, 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 \(\beta\)-Ga\(_2\)O\(_3\) by conventional MBE. As a result, a growth rate of ~1 \({\mu}\)m/h is readily achieved at a relatively low growth temperature (T\(_{sub}\) = 525 \(^\circ\)C), resulting in films with high structural perfection and smooth surfaces (rms roughness of < 2 nm on ~1 \({\mu}\)m thick films). Silicon-containing oxide sources (SiO and SiO\(_2\)) producing an SiO suboxide molecular beam are used to dope the \(\beta\)-Ga\(_2\)O\(_3\) layers. Temperature-dependent Hall effect measurements on a 1 \({\mu}\)m thick film with a mobile carrier concentration of 2.7x10\(^{17}\) cm\(^{-3}\) reveal a room-temperature mobility of 124 cm\(^2\) V\(^{-1}\) s\(^{-1}\) that increases to 627 cm\(^2\) 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 \(\beta\)-Ga\(_2\)O\(_3\) films grown by S-MBE at growth rates of ~1 \({\mu}\)m/h.