Annealing Effects on the Electrical Activation of Si Dopants in InGaAs

There is a renewed interest in integrating high mobility III-V channel materials into sub 10 nm nMOS devices but the continued scaling of devices has resulted in the need to create contacts and source/drains with ultra low contact resistivities in order to reduce current losses. This study investigates thermal stability of Si dopants incorporated via MBE growth and ion implantation as potential methods to create heavily-doped, low resistance source/drain regions in III-V channel devices. For this study, the electrical activation and diffusion of Si active layers in In_0.53Ga_0.47As formed by a 10 keV, 5×10¹⁴ cm^-2 Si implant and MBE growth doping with a peak Si concentration of 7×10¹⁹ cm^-3 were investigated as a function of post growth and post-implant isochronal annealing.  While most previous studies conclude that MBE doping can achieve higher active Si concentrations than ion implantation, the results of this study show conclusively that electrically active Si concentrations above 1.4×10¹⁹ cm^-3 formed by MBE doping are prone to deactivation upon thermal treatment after growth whereas ion-implantation shows no metastable activation behavior.  Significant Si deactivation in MBE doped substrates is shown to occur before the onset of Si diffusion whereas saturated activation in ion implanted substrates does not occur until diffusion is observed.  Upon annealing at sufficiently high temperatures to cause Si diffusion, the electrical activation of Si in MBE doped substrates and ion implanted Si are shown to converge to a stable activation limit of 1.4×10¹⁹ cm^-3. The common activation limit upon Si profile motion for both Ion implanted and growth doped Si active layers after thermal annealing at 750°C suggests that the maximum stable electrical activation of Si is an intrinsic property of In_0.53Ga_0.47As. Si diffusivity has also been calculated from SIMS results in both ion-implanted substrates and growth-doped substrate and Si diffusion in MBE doped substrates was observed to be nearly three times as fast as ion implanted substrates presumably due to the observed concentration dependent diffusion effects. The mechanism of Si diffusion and its relation to the observed concentration dependent diffusion and electrical activation behavior in both materials are also discussed.