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

Abstract

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.

19 pages, 7 figures, 2 tables, 2 pages supplementary materials