Towards controllable Si-doping in oxide molecular beam epitaxy using a solid SiO source: Application to $\beta$-Ga2O3

Abstract

The oxidation-related issues in controlling Si doping from the Si source material in oxide molecular beam epitaxy (MBE) is addressed by using solid SiO as an alternative source material in a conventional effusion cell. Line-of-sight quadrupole mass spectrometry of the direct SiO-flux (${\Phi }_{SiO}$) from the source at different temperatures ($T_{SiO}$) confirmed SiO molecules to sublime with an activation energy of 3.3eV. The $T_{SiO}$-dependent ${\Phi }_{SiO}$ was measured in vacuum before and after subjecting the source material to an O${}_2$-background of $10^{-5}$ mbar (typical oxide MBE regime). The absence of a significant ${\Phi }_{SiO}$ difference indicates negligible source oxidation in molecular O${}_2$. Mounted in an oxygen plasma-assisted MBE, Si-doped $\beta$-Ga2O3 layers were grown using this source. The ${\Phi }_{SiO}$ at the substrate was evaluated [from 2.9x10${}^9$ cm${}^{-2}$s${}^{-1}$ ($T_{SiO}$=700°C) to 5.5x10${}^{13}$ cm${}^{-2}$s${}^{-1}$ (T${}_{SiO}$=1000°C)] and Si-concentration in the $\beta$-Ga2O3 layers measured by secondary ion mass spectrometry highlighting unprecedented control of continuous Si-doping for oxide MBE, i.e., $N_{Si}$ from 4x10${}^{17}$ cm${}^{-3}$ ($T_{SiO}$=700°C) up to 1.7x10${}^{20}$ cm${}^{-3}$ ($T_{SiO}$=900°C). For a homoepitaxial $\beta$-Ga2O3 layer an Hall charge carrier concentration of 3x10${}^{19}$ cm${}^{-3}$ in line with the provided ${\Phi }_{SiO}$ ($T_{SiO}$=800°C) is demonstrated. No SiO-incorporation difference was found between $\beta$-Ga2O3(010) layers homoepitaxially grown at 750°C and $\beta$-Ga2O3(-201) layers heteroepitaxially grown at 550°C. The presence of activated oxygen (plasma) resulted in partial source oxidation and related decrease of doping concentration (particularly at $T_{SiO}$<800°C) which has been tentatively explained with a simple model. Degassing the source at 1100°C reverted the oxidation.

References in corpus (6)

• Adsorption-Controlled Growth of Ga2O3 by Suboxide Molecular-Beam Epitaxy
• Offcut-related step-flow and growth rate enhancement during (100) $\beta$-Ga2O3 homoepitaxy by metal-exchange catalyzed molecular beam epitaxy (MEXCAT-MBE)
• Sr flux stability against oxidation in oxide-MBE environment: flux, geometry, and pressure dependence
• Crucible aperture: an effective way to reduce source oxidation in oxide molecular beam epitaxy process
• Simple self-gettering differential-pump for minimizing source oxidation in oxide-MBE environment
• Drastically enhanced cation incorporation in the epitaxy of oxides due to formation and evaporation of suboxides from elemental sources

Cited by in corpus (2)

• Phase-selective growth of $\kappa$- vs $\beta$-Ga${}_2$O${}_3$ and (In${}_x$Ga${}_{1-x}$)${}_2$O${}_3$ by In-mediated metal exchange catalysis in plasma-assisted molecular beam epitaxy
• Etching of elemental layers in oxide molecular beam epitaxy by O2-assisted formation and evaporation of their volatile suboxide: The examples of Ga and Ge