Optimized Annealing for Activation of Implanted Si in β-Ga₂O₃

Ion implantation for selective area doping is important for device structures and lowering contact resistance in Ga₂O₃. While there are reports of implant and activation of Si under N₂, little has been done to narrow down the optimal time, temperature, and ambient conditions for annealing as well as the impact of a capping layer during implantation and annealing. To form a 100 nm box implant with a target concentration of 5x10¹⁹ cm^-3, Si was implanted at three energies (16-120 keV) with a total dose 7x10¹⁴ cm^-2 into MBE grown UID β-Ga₂O₃ films on Fe-doped semi-insulating β -Ga₂O₃ substrates. A wide variety of annealing conditions was used for dopant activation and lattice recovery (with the best conditions yielding 88% activation with R_s= 130 Ω/sq and μ = 72 cm²/Vs) using an ultrahigh vacuum quartz tube furnace with precise gas control and an extra drying step. Anneal times varied from 10 minutes to two hours and temperatures ranged from 850 to 1000 °C. Hall measurements showed that shorter times were optimal for activation and longer times resulted in “over annealing” and deactivation of the Si dopants. Highest activation was achieved between 900 and 950 °C with lower temperatures showing reduced mobility and higher temperatures showing reduced carriers as well as increased redistribution of Si, seen in Secondary Ion Mass Spectrometry profiles. While previous studies have shown a N₂ ambient to yield higher activation and reduced redistribution compared to O₂ conditions, by annealing under dried forming gas (4% H₂/N₂) and vacuum with poorer results, it is clear that a non-zero pO₂ and pH₂O are needed for optimized electrical activity, and this processing window was identified using controlled gas mixtures. Recovery of Photoluminescence signal was found to be correlated with increased sheet resistance values and lattice recovery was gauged with Cathodoluminescence and Transmission Electron Microscopy.