Observation of a monovacancy in the metastable state of theEL2 defect in GaAs by positron annihilation

Abstract

A monovacancy defect is observed by positron-lifetime and Doppler-broadening experiments in semiinsulating GaAs after photoquenching the ELI defects. The monovacancy exhibits the same thermal and optical recoveries as the metastable state of EL2 and its concentration is proportional to that of the ELI defect. It is concluded that the metastable state of the ELI defect involves the monovacancy. The results indicate that the monovacancy or its immediate surroundings is negatively charged.

Defect identification in semiconductors with positron annihilation: Experiment and theory

“…Another metastable defect whose identification proved to be a challenging task (around the same time) was the so-called DX center (Mooney, 1990;Mäkinen et al, 1993) in Al 1Àx Ga x As that produces persistent photoconductivity. Figure 15 shows results of positron experiments where SI GaAs crystals with two different EL2 concentrations were cooled in darkness and illuminated in situ with 1.2 eV light (Krause, Saarinen et al, 1990). To check that the EL2 defects were photoquenched by the illumination, infrared absorption was also measured.…”

“…Arsenic vacancies are observed in unintentionally n-type as-grown GaAs crystals (Saarinen et al, 1991), while they coexist with Ga vacancies and EL2 defects in semiinsulating GaAs (Kuisma et al, 1996). The metastable EL2 and DX centers in arsenides have both been shown to have vacancy character (Krause, Saarinen et al, 1990;Mäkinen et al, 1993). Thermal annealing experiments have been performed to elucidate vacancy formation mechanisms and the role of copper in determining the vacancy distribution in GaAs crystals (Elsayed et al, 2008(Elsayed et al, , 2011.…”

Microscopic nature of thermally stimulated current and electrical compensation in semi-insulating GaAs

“…5,18 This Ga vacancy is slightly smaller than an isolated Ga vacancy due to the arsenic interstitial in its neighborhood. The positron lifetime at the metastable state of EL2 is (EL2*) ϭ 245 ps.…”

“…IV C͒, so there the three-trap model is not accurate. 4 However, above 60 K the metastable EL2* is unable to trap positrons, 5 and the trapping rate at the arsenic vacancies can be estimated there. In the calculation the positron lifetime of v ϭ257 ps at the As vacancy is used since this value is in agreement with the present and earlier 4 decompositions of the lifetime spectra in SI GaAs, and this value has also been determined for negative As vacancy in n-type GaAs.…”

“…The positron lifetime at the metastable state of EL2 is (EL2*) ϭ 245 ps. 5 In this work the arsenic antisite concentrations were determined by converting the EL2 defect completely into the metastable state with a long 1.15 eV illumination and then measuring the average positron lifetime as a function of the annealing temperature after the illumination. All the measurements were done at 30 K in darkness, and between the measurements the samples were annealed for 10 min at a higher temperature.…”