Silicon-doped <i>β</i>-Ga2O3 films grown at 1 <i>µ</i>m/h by suboxide molecular-beam epitaxy
Kathy Azizie, Felix V. E. Hensling, Cameron A. Gorsak, Yunjo Kim, Naomi Pieczulewski, Daniel M. Dryden, M. K. Indika Senevirathna, Selena Coye, Shun‐Li Shang, Jacob Steele, Patrick Vogt, Nicholas Parker, Yorick A. Birkhölzer, Jonathan P. McCandless, Debdeep Jena, Huili Grace Xing, Zi‐Kui Liu, M. D. Williams, Andrew J. Green, Kelson D. Chabak, David A. Muller, Adam T. Neal, Shin Mou, Michael O. Thompson, Hari P. Nair, Darrell G. Schlom
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 5 × 1016 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 °C), resulting in films with high structural perfection and smooth surfaces (rms roughness of &lt;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 2.7 × 1017 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 metal–semiconductor field-effect transistors made from these silicon-doped β-Ga2O3 films grown by S-MBE at growth rates of ∼1 µm/h.