Effects of hyperthermal carbon subimplantation doping on the Raman spectra of GaAs

The structural effects of low-energy (30-500 eV), mass separated C¹² Ion doping of GaAs simultaneous with conventional solid source MBE growth have been studied using room-temperature raman scattering, Hall-effect, transmission electron microscopy and 2 K photoluminesence measurements for GaAs epitaxy temperatures of 550°C. Results indicate good acceptor activation without detectable residual damage is achieved for ion energies ≤ 240 eV, while at E_Ion = 500 eV, residual damage is present with a corresponding reduction in electrical activation. Low-energy TRIM calculations indicate that the damage is related to the increased depth distribution of vacancies and interstitials created during the higher (500 eV) implantation process which can not be annealed out at growth temperatures. Constant energy (100 eV) film growth experiments for a range of implantation currents (45 pA/cm² - 45 nA/cm²) and growth temperatures of 550 and 550 °C, show LO Raman peak broadening and mode hardening for currents ≥ 15 nA while maintaining very high C acceptor activation. This is interpreted as residual stress due to small amounts of interstitial C in the highest doped films. Both Hall mobility measurements and photoluminesence show no evidence of C dopant compensation.