An investigation of photo-quenching properties of LEC GaAs by using optical and electrical techniques

Optical processes related to arsenic vacancies in semi-insulating GaAs studied by positron spectroscopy

“…The latter transition gives a microscopic explanation for the nearband-edge absorption observed in GaAs. 5 The detected vacancy concentrations of 10 15 -10 16 cm Ϫ3 are close to those of residual impurities and EL2 defects, indicating that the native vacancies have a role in the compensation of SI GaAs.…”

“…However, absorption near the band edge at hу1.4 eV has been reported even when the EL2 is in the metastable state. 5,27 According to the experiments of this work, the negative As vacancy is observed under illumination with the photon energy hу1.4 eV and the flux у1ϫ10 15 cm Ϫ2 s Ϫ1 when the EL2 defect is in the metastable state. As explained above, the optical process leading to the population of the negative V As in this case is different from the one taking place when the EL2 defect is in the stable state.…”

“…This transition gives a microscopic explanation for the near-bandedge absorption seen in the previous optical experiments in undoped semi-insulating GaAs. 5,35 The observed concentrations of the Ga and As vacancies are typically ͑5-10͒ϫ10 15 cm Ϫ3 . This is roughly one order of magnitude less than the As vacancy concentrations observed in n-type GaAs, 10 but comparable to the concentrations of the residual impurities and of the EL2 defects in high-purity GaAs.…”

“…10 In optical experiments on bulk GaAs a strong absorption of monochromatic light within 50 meV of the conduction band edge is observed below 150 K. 5,35 This near-band-edge absorption has been attributed to an unidentified point defect, but it is not associated with the EL2 defect. 5 Due to the spatial anticorrelation of E g Ϫ50 meV absorption and the EL2 concentrations this absorption process is called the reverse contrast ͑RC͒. Other studies have shown that the defects giving rise to the RC absorption are the main nonradiative recombination centers in SI GaAs.…”

Near-band-edge absorption and positron trapping under illumination in semi-insulating GaAs: Role of As vacancies

“…1 On the other hand, an ionization energy of approximately E g Ϫ50 meV is involved in a near-band-edge absorption process called reverse contrast ͑RC͒, which is observed in samples cooled below about 140 K. 2,3 Reverse contrast is so called because it spatially anticorrelates with the absorption of the midgap donor EL2 in as-grown LEC GaAs. [3][4][5] It is important to control concentrations of RC defects for device applications and consequently to identify their nature. We give here strong evidence that these RC defects are related to As vacancies by showing a correlation between their respective concentrations in SI GaAs.…”