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 accepters are the dominant native accepters in LT-GaAs. The ultrafast electron trapping time, measured in LT-GaAs (< 1 ps below T-G=230 degrees 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 accepters 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 degrees 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 accepters 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.