Silicon implantation and annealing in β-Ga2O3: Role of ambient, temperature, and time

Optimizing thermal anneals of Si-implanted beta-Ga2O3 is critical for low resistance contacts and selective area doping. We report the impact of annealing ambient, temperature, and time on the activation of room temperature ion-implanted Si in beta-Ga2O3 at concentrations from 5 x 1018 to 1 x 1020 cm-3, demonstrating full activation (>80% activation, mobilities >70 cm2/V s) with contact resistances below 0.29 omega mm. Homoepitaxial beta-Ga2O3 films, grown by plasma-assisted molecular beam epitaxy on Fe-doped (010) substrates, were implanted at multiple energies to yield 100 nm box profiles of 5 x 1018, 5 x 1019, and 1 x 1020 cm-3. Anneals were performed in an ultra-high vacuum-compatible quartz furnace at 1 bar with well-controlled gas compositions. To maintain beta-Ga2O3 stability, pO2 must be greater than 10-9 bar. Anneals up to pO2 = 1 bar achieve full activation at 5 x 1018 cm-3, while 5 x 1019 cm-3 must be annealed with pO2 <= 10-4 bar, and 1 x 1020 cm-3 requires pO2 < 10-6 bar. Water vapor prevents activation and must be maintained below 10-8 bar. Activation is achieved for anneal temperatures as low as 850 degrees C with mobility increasing with anneal temperatures up to 1050 degrees C, though Si diffusion has been reported above 950 degrees C. At 950 degrees C, activation is maximized between 5 and 20 min with longer times resulting in decreased carrier activation (over-annealing). This over-annealing is significant for concentrations above 5 x 1019 cm-3 and occurs rapidly at 1 x 1020 cm-3. Rutherford backscattering spectrometry (channeling) suggests that damage recovery is seeded from remnant aligned beta-Ga2O3 that remains after implantation; this conclusion is also supported by scanning transmission electron microscopy showing retention of the beta-phase with inclusions that resemble the gamma-phase. (c) 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International (CC BY-NC-ND) license (https://creativecommons.org/licenses/by-nc-nd/4.0/).