Silicon Implantation and Annealing in ..beta..-Ga2O3: Role of Ambient, Temperature, and Time: Article No. 015302

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 10^18 to 1 x 10^20 cm-3, demonstrating full activation (>80% activation, mobilities >70 cm2/V s) with contact resistances below 0.29 O 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 10^18, 5 x 10^19, and 1 x 10^20 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 10^18 cm-3, while 5 x 10^19 cm-3 must be annealed with pO2 = 10-4 bar, and 1 x 10^20 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 10^19 cm-3 and occurs rapidly at 1 x 10^20 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.