Offcut-related step-flow and growth rate enhancement during (100) β-Ga₂O₃ homoepitaxy by metal-exchange catalyzed molecular beam epitaxy (MEXCAT-MBE)

Homoepitaxial β-Ga₂O₃ layers grown via molecular beam epitaxy (MBE) have exhibited prohibitively low growth rates on (100) oriented substrates in the past. In this work, we investigate the possibility to employ indium-assisted metal exchange catalyzed (MEXCAT) MBE to overcome this limit. We demonstrate that the fine tuning of the MEXCAT growth parameters and the choice of a proper substrate offcut allow for the deposition of thin films with high structural quality via the step-flow growth mechanism at relatively high growth rates for β-Ga₂O₃ homoepitaxy (i.e., around 1.5 nm/min, ≈ 45% incorporation of the incoming Ga flux), making MBE growth in this orientation feasible. Moreover, through the employment of the four investigated different (100) substrate offcuts along the $[001¯]$ direction (i.e., 0°, 2°, 4°, and 6°), we give experimental evidence on the fundamental role of the $(2¯01)$ step edges as nucleation sites in the growth of (100)-oriented Ga₂O₃ films by MBE.