Silicon Implantation and Annealing in $β$-Ga$_2$O$_3$: Role of Ambient, Temperature, and Time

K. R. Gann; N. Pieczulewski1; C. A. Gorsak; K. Heinselman; T. J. Asel; B. A. Noesges; K. T. Smith; D. M. Dryden; H. G. Xing; H. P. Nair; D. A. Muller; M. O. Thompson

arXiv · 2311.00821

Silicon Implantation and Annealing in $β$-Ga$_2$O$_3$: Role of Ambient, Temperature, and Time

K. R. Gann·N. Pieczulewski1·C. A. Gorsak·K. Heinselman·T. J. Asel·B. A. Noesges·K. T. Smith·D. M. Dryden·H. G. Xing·H. P. Nair·D. A. Muller·M. O. Thompson

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Abstract

Optimizing thermal anneals of Si-implanted $β$-Ga$_2$O$_3$ is critical for low resistance contacts and selective area doping. We report the impact of annealing ambient, temperature, and time on activation of room temperature ion-implanted Si in $β$-Ga$_2$O$_3$ at concentrations from 5x10$^{18}$ to 1x10$^{20}$ cm$^{-3}$, demonstrating full activation (>80% activation, mobilities >70 cm$^{2}$/Vs) with contact resistances below 0.29 $Ω$-mm. Homoepitaxial $β$-Ga$_2$O$_3$ films, grown by plasma assisted MBE on Fe-doped (010) substrates, were implanted at multiple energies to yield 100 nm box profiles of 5x10$^{18}$, 5x10$^{19}$, and 1x10$^{20}$ cm$^{-3}$. Anneals were performed in a UHV-compatible quartz furnace at 1 bar with well-controlled gas composition. To maintain $β$-Ga$_2$O$_3$ stability, $p_{O2}$ must be greater than 10$^{-9}$ bar. Anneals up to $p_{O2}$ = 1 bar achieve full activation at 5x10$^{18}$ cm$^{-3}$, while 5x10$^{19}$ cm$^{-3}$ must be annealed with $p_{O2}$ <10$^{-4}$ bar and 1x10$^{20}$ cm$^{-3}$ requires $p_{O2}$ <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 °C with mobility increasing with anneal temperature up to 1050 °C, though Si diffusion has been reported above 950 °C. At 950 °C, activation is maximized between 5 and 20 minutes with longer times resulting in decreased carrier activation (over-annealing). This over-annealing is significant for concentrations above 5x10$^{19}$ cm$^{-3}$ and occurs rapidly at 1x10$^{20}$ cm$^{-3}$. RBS (channeling) suggests damage recovery is seeded from remnant aligned $β$-Ga$_2$O$_3$ that remains after implantation; this conclusion is also supported by STEM showing retention of the $β$-phase with inclusions that resemble the $γ$-phase.

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K. R. Gann, N. Pieczulewski1, C. A. Gorsak, K. Heinselman, T. J. Asel, B. A. Noesges, K. T. Smith, D. M. Dryden, H. G. Xing, H. P. Nair, D. A. Muller, M. O. Thompson. 2023-11-01. Silicon Implantation and Annealing in $β$-Ga$_2$O$_3$: Role of Ambient, Temperature, and Time. https://arxiv.org/abs/2311.00821

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