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

TL;DR

This paper demonstrates a rapid, controlled growth of high-quality silicon-doped $eta$-Ga$_2$O$_3$ films using suboxide molecular-beam epitaxy at 1 μm/h, enabling improved doping control and device fabrication.

Contribution

It introduces a novel S-MBE technique for fast, high-quality $eta$-Ga$_2$O$_3$ film growth with precise silicon doping control and demonstrates functional MESFET devices.

Findings

Achieved ~1 μm/h growth rate of $eta$-Ga$_2$O$_3$ films.

Controlled silicon doping from 5x10$^{16}$ to 10$^{19}$ cm$^{-3}$.

Demonstrated functional MESFETs from these films.

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.