Residual ion damage in GaAs: C prepared by combined ion beam and molecular beam epitaxy

Ion-induced damage in the films grown by low-energy (30-30 000 eV) ion-beam doping method was investigated using the minority-carrier lifetime and temperature-dependent Hall-effect measurements. Minority-carrier lifetime measurement using scanning tunneling microscope stimulated time-resolved luminescence (STM-L) demonstrated the presence of residual ion damage in as-grown samples at C⁺-ion acceleration energy E_C+ = 240 and 350 eV, and annealed ones at E_C+ = 5, 10 and 30 keV. For E_C+= 30 eV, no ion damage was observed in as-grown condition. For E_C+ ≥ 5 keV, ion damage remains even after high-temperature annealing and degrades the activation of C atoms. In the temperature-dependent Hall-effect measurements, samples with E_C+ = 240 and 350 eV showed unusual characteristics in net hole carrier concentration (|N_A - N_D|) with decreasing temperature. For E_C+ = 10 and 30 keV, |N_A - N_D| in lower temperature regions indicates higher values than that obtained at room temperature. It was suggested that the conduction mechanisms of these two specimens are significantly affected by impurity conduction mainly due to ion damage.