Low temperature photoluminescence from GaAs impinged by mass-separated low-energy C⁺ ion beams during molecular beam epitaxy

C-doped GaAs films were prepared by novely a developed, combined ion beam and molecular beam method (CIBMBE) as a function of hyperthermal (30-500 eV) energies (E_C(+)) of carbon ion (C⁺) beam. Ion beams of a fixed beam current density were impinged during molecular beam epitaxy growth of GaAs at substrate temperature of 550 °C. Low temperature (2 K) photoluminescence (PL) has been used to characterize the samples together with Hall effects measurements at room temperature. Through the spectral evolution of an emission denoted by [g-g]_β which is a specific emission relevant to acceptor-acceptor pairs, the activation rate was confirmed to increase with increasing E_C(+) for E_C(+) lower than 170 eV. It was explicitly demonstrated that the most effective E_C(+) to establish highest activation rate is located at approx.170 eV. This growing activation rate was suggested to be attributed to the enhanced migration of both impinged C and host constituent atoms with increasing E_C(+). This surmise was supported also by Hall effect measurements which revealed the maximum net hole concentration (| N_A-N_D |) for E_C(+)=170 eV. For E_C(+) higher than approx.170 eV, increasing E_C(+) was found to induce the reduction of activation rate. It was suggested that this observation is ascribed not to the formation of C donors but to the enhanced sputtering effect of impinged C⁺ ions with increasing E_C(+).