Hall effect and Raman analysis of residual damage and free electron concentration in Si-implanted GaAs: A quest for better doping efficiency
To tackle the problem of insufficient electrical activation of Si + dopant in GaAs, we have studied a series of heavily Si-implanted and thermally annealed GaAs samples (two different doses, each implanted at three different temperatures and with two implantation rates). A comparative analysis of electrical and optical measurements was done on the same set of samples and correlated with implantation parameters. By temperature dependent Hall-effect measurements carrier density and carrier mobility were determined over the 20-300 K range. The mobility data were analyzed taking into account different scattering mechanisms. The implantation-induced initial damage was determined by Rutherford backscattering, whereas the amount of residual damage present in the samples after thermal annealing was estimated by Raman spectroscopy. Additionally, scattering by LO phonon-plasmon coupled modes was used to study the properties of the free electron gas in the implanted layer, includi ng its depth distribution. Free carrier concentrations deduced from the analysis of the plasmon modes agree with the Hall-effect results. Multi-energy implantation in combination with higher implant temperature is suggested as a way to increase doping efficiency by reducing high local concentrations and lessen the probability of compensating defects formation.