Aniol Vellvehí, Pierre Gallarday, Edgars Butanovs, Vincent Sallet, José Rebollo, Josep Montserrat, Edvards Strods, Martins Zubkins, Lauris Dimitrocenko, Corine Sartel, Ekaterine Chikoidze, Xavier Perpiña, Miquel Vellvehi, Amador Pérez-Tomás

Journal of Alloys and Compounds

In this work, the feasibility of Si ion-implantation channel engineering in metastable α-Ga₂O₃ is directly compared with the well-established implantation process used in β-Ga₂O₃ lateral MESFETs. Identical multi-energy Si implantation schemes (10–200 keV) and thermal annealing conditions were applied to both polymorphs in order to evaluate the compatibility of implantation-based doping with the thermal stability window of α-Ga₂O₃. For β-Ga₂O₃, Si implantation followed by high-temperature annealing (900–1100 °C) successfully enabled conductive channel and ohmic contact formation, leading to functional lateral MESFET operation with proper current modulation and saturation behaviour. In contrast, α-Ga₂O₃ layers grown on m-plane sapphire exhibited a strong limitation associated with their metastable nature. An ALD-deposited Al₂O₃ capping layer delayed the α→β phase transition up to approximately 700 °C, as confirmed by X-ray diffraction analysis. However, electrical measurements revealed no measurable channel conduction after annealing within this temperature range, suggesting that efficient electrical activation of the implanted Si donors was not achieved within the α‑Ga₂O₃ thermal stability window. At higher annealing temperatures, where dopant activation would normally be expected, the α-phase underwent complete reconstructive transformation into β-Ga₂O₃, accompanied by severe structural degradation and suppressed electrical transport. These results demonstrate that the thermal budget required for conventional implantation-based donor activation exceeds the metastability window of α-Ga₂O₃, even when thermal stabilization layers are employed. The study therefore identifies a fundamental technological limitation for ion-implantation-defined α-Ga₂O₃ power devices and highlights the need for alternative low-thermal-budget doping and device fabrication strategies..

Link DOI: 10.1016/j.jallcom.2026.191091