Defect control in As-rich GaAs

The incorporation of excess As in GaAs, grown by MBE at low tempertures, produces native defects such as As antisites (As_Ga), As interstitials (As_i) or Ga vacancies (V_Ga). These point defects dilate the lattice. Their concentrations increase with decreasing growth temperature and can be well reproduced by a careful control of the substrate temperature and the As/Ga flux ratio. The ionized [As_Ga⁺] equals three times the [V_Ga]. Therefore, V_Ga triple acceptors are the dominant native acceptors in LT-GaAs. The ultrafast electron trapping time, measured in LT-GaAs (< 1ps below T_G=230°C) was reported to correlate to [As_Ga⁺]. In undoped LT-GaAs, however, the [As_Ga⁺] does not exceed 10% of the total concentration of As_Ga. We studied high p-doping with Be acceptors in order to achieve a larger ionization fraction of the As_Ga. As a result we developed thermally stable, non-stoichiometric GaAs with subpicosecond trapping times, grown at T=275°C. The ratio [As_Ga⁺]/[As_Ga] was found to exceed 50%. However, in LT-GaAs:Be carrier capture at As_Ga⁺ is not the only trapping mechanism, it's concentration is neither correlated to the [Be] nor to the measured trapping times.It is suggested that additional carrier capture by doubly ionized As_Ga⁺⁺, is taking place, caused by the lowered Fermi level due to Be-doping. The strain compensation of the large As_Ga defects with the small Be_Ga acceptors enhances the thermal stability of the native point defects. Therefore, the thermally more stable LT-GaAs:Be offers new prospects for the application of As-rich GaAs in ultrafast optoelectronics. non-stoichiometric GaAs,.