Lifetimes of positrons trapped at Si vacancies

Saito, Mineo; Oshiyama, Atsushi

doi:10.1103/physrevb.53.7810

Cited by 83 publications

(74 citation statements)

References 29 publications

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“…A positron lifetime of ϳ400 ps in a semiconductor indicates a vacancy cluster of ϳ10 missing atoms in size. [26][27][28] This indicates that the smaller irradiation-induced defects form bigger clusters during the annealing. The intensity of the higher lifetime component drops during the annealing at 673 K, suggesting that most of the cluster defects start to anneal.…”

Section: Brief Reports Physical Review B 78 033202 ͑2008͒mentioning

confidence: 99%

Divacancy clustering in neutron-irradiated and annealedn-type germanium

et al. 2008

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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.

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Section: Brief Reports Physical Review B 78 033202 ͑2008͒mentioning

confidence: 99%

Divacancy clustering in neutron-irradiated and annealedn-type germanium

et al. 2008

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“…As in defect spectroscopy it is often necessary to perform large series of measurements, e.g., as a function of temperature or detection depth, and Doppler broadening spectroscopy has been the method of choice. ACAR and 2D-ACAR have been used in defect studies much less (Saito, Oshiyama, and Tanigawa, 1991;Ambigapathy et al, 1994). The typical resolution of a HPGe detector is around 1-1.5 keV at 511 keV.…”

Section: Methodsmentioning

confidence: 99%

Defect identification in semiconductors with positron annihilation: Experiment and theory

2013

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Positron annihilation spectroscopy is particularly suitable for studying vacancy-type defects in semiconductors. Combining state-of-the-art experimental and theoretical methods allows for detailed identification of the defects and their chemical surroundings. Also charge states and defect levels in the band gap are accessible. In this review the main experimental and theoretical analysis techniques are described. The usage of these methods is illustrated through examples in technologically important elemental and compound semiconductors. Future challenges include the analysis of noncrystalline materials and of transient defect-related phenomena.

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“…Previously, Saito and Oshiyama 48 and Makhov and Lewis 45 have studied vacancies in Si within the twocomponent scheme by Gilgien et al 11 including the effects of forces due to the positron. Their lifetimes for the monovacancy are reasonable but the relative W parameter of 0.28 estimated from Saito and Oshiyama's data is very low in comparison with our result, which is 0.72 ͑both evaluated using calculated annihilation rates as in Ref.…”

Section: Neutral Monovacancy In Simentioning

confidence: 99%

Modeling the momentum distributions of annihilating electron-positron pairs in solids

2006

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Measuring the Doppler broadening of the positron annihilation radiation or the angular correlation between the two annihilation gamma quanta reflects the momentum distribution of electrons seen by positrons in the material. Vacancy-type defects in solids localize positrons and the measured spectra are sensitive to the detailed chemical and geometric environments of the defects. However, the measured information is indirect and when using it in defect identification comparisons with theoretically predicted spectra is indispensable. In this article we present a computational scheme for calculating momentum distributions of electron-positron pairs annihilating in solids. Valence electron states and their interaction with ion cores are described using the all-electron projector augmented-wave method, and atomic orbitals are used to describe the core states. We apply our numerical scheme to selected systems and compare three different enhancement ͑electron-positron correlation͒ schemes previously used in the calculation of momentum distributions of annihilating electron-positron pairs within the density-functional theory. We show that the use of a state-dependent enhancement scheme leads to better results than a position-dependent enhancement factor in the case of ratios of Doppler spectra between different systems. Further, we demonstrate the applicability of our scheme for studying vacancy-type defects in metals and semiconductors. Especially we study the effect of forces due to a positron localized at a vacancytype defect on the ionic relaxations.

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Lifetimes of positrons trapped at Si vacancies

Cited by 83 publications

References 29 publications

Divacancy clustering in neutron-irradiated and annealedn-type germanium

Divacancy clustering in neutron-irradiated and annealedn-type germanium

Defect identification in semiconductors with positron annihilation: Experiment and theory

Modeling the momentum distributions of annihilating electron-positron pairs in solids

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