We have studied the annealing of vacancy defects in neutron-irradiated germanium. After irradiation, the Sb-doped samples ͓͑Sb͒ = 1.5ϫ 10 15 cm −3 ͔ were annealed at 473, 673, and 773 K for 30 min. The positron lifetime was measured as a function of temperature ͑30-295 K͒. A lifetime component of 330 ps with no temperature dependence is observed in as-irradiated samples, identified as the positron lifetime in a neutral divacancy and indicating that the divacancy is stable at room temperature ͑RT͒. Annealing at 673 K resulted in an increase in the average positron lifetime, and in addition, the annealed samples further showed a larger lifetime component of 430 ps at RT, which is due to larger vacancy clusters. The average positron lifetime in the samples annealed at 473 K has a definite temperature dependence, suggesting that the divacancies become negative as the crystal recovers and the Fermi level moves upwards in the band gap. Annealing at 673 K, reduces the average lifetime and intensity of the defect component 2 at RT, indicating that the vacancy clusters have started to anneal. Negative divacancies are still present in the samples after this anneal. Annealing at 773 K is enough to remove all observable vacancy defects.
We have found evidence of a second acceptor state of the E center in Si 1−x Ge x by using positron annihilation spectroscopy. To achieve this, we studied proton irradiated n-type Si 1−x Ge x with a Ge content of 10%-30% and a P dopant concentration of 10 18 cm −3 , in which the number of Ge atoms around irradiation induced E centers was increased by annealing. When measuring the Doppler broadening of the annihilation line, the shape parameter S starts to decreases at 150 K with decreasing measurement temperature. This indicates that a charge transition in the upper half of the Si 1−x Ge x band gap, above the well known ͑0/Ϫ͒ level, takes place. Hence, we suggest that the increased concentration of germanium around the E center pulls down the localized second acceptor state into the Si 1−x Ge x band gap, making the Ge decorated E center a more effective trap for conduction electrons.
Epitaxial thin film CuGaSe 2 and CuInSe 2 samples grown on GaAs substrates with varying [Cu]/[Ga,In] ratios were studied using positron annihilation Doppler-broadening spectroscopy and were compared to bulk crystals. We find both Cu monovacancies and Cu-Se divacancies in CuInSe 2 , whereas, in CuGaSe 2 , the only observed vacancy defect is the Cu-Se divacancy.
Concerted experiments and theoretical analysis are applied to conclusively demonstrate the vacancy generation during fast melting and regrowth of Si by laser irradiation. Experiments, based on the positron annihilation spectroscopy and designed to test the theoretical predictions, evidence a vacancy supersaturation after the laser process depending on the irradiation conditions. Stochastic atomistic simulations of the molten Si recrystallization show trapping of vacancies in the recrystallized region. Finally, continuum phase-field simulations of the full process, calibrated using the Monte Carlo results, show a defect evolution in close agreement with the experiments.
Thermal evolution of vacancy complexes was studied in P-doped ͓͑P͔ =10 18 cm −3 ͒ proton irradiated Si 1−x Ge x with Ge contents of 10%, 20%, and 30% in the range of 250-350°C using positron annihilation spectroscopy. The radiation damage recovers in the course of anneals but the final state differs from that in as-grown samples indicating the presence of small Ge clusters in the samples, contrary to the initially random Ge distribution. The activation energy for the annealing process was estimated to be 1.4Ϯ 0.3 eV and attributed to the dissociation energy of the vacancy-phosphorus-germanium ͑V-P-Ge͒ complex.
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