A center from the family of "fourfold coordinated ͑FFC͒ defects", previously predicted theoretically, has been experimentally identified in crystalline silicon. It is shown that the trivacancy ͑V 3 ͒ in Si is a bistable center in the neutral charge state, with a FFC configuration lower in energy than the ͑110͒ planar one. V 3 in the planar configuration gives rise to two acceptor levels at 0.36 and 0.46 eV below the conduction band edge ͑E c ͒ in the gap, while in the FFC configuration it has trigonal symmetry and an acceptor level at E c − 0.075 eV. From annealing experiments in oxygen-rich samples, we also conclude that O atoms are efficient traps for mobile V 3 centers. Their interaction results in the formation of V 3 O complexes with the first and second acceptor levels at E c − 0.46 eV and E c − 0.34 eV. The overall picture, including structural details, relative stability, and electrical levels, is accompanied and supported by ab initio modeling studies.

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The trivacancy (V 3) in silicon has been recently shown to be a bistable center in the neutral charge state, with a fourfold-coordinated configuration, V 3[FFC], lower in energy than the (110) planar one. Transformations of the V 3 defect between different configurations, its diffusion, and disappearance upon isochronal and isothermal annealing of electron-irradiated Si:O crystals are reported from joint deep level transient spectroscopy measurements and first-principles density-functional calculations. Activation energies and respective mechanisms for V 3 transformation from the (110) planar configuration to the fourfold-coordinated structure have been determined. The annealing studies demonstrate that V 3 is mobile in Si at T>200C and in oxygen-rich material can be trapped by interstitial oxygen atoms so resulting in the appearance of V 3O complexes. The calculations suggest that V 3 motion takes place via consecutive FFC/planar transformation steps. The activation energy for the long-range diffusion of the V 3 center has been derived and agrees with atomic motion barrier from the calculations. © 2012 American Physical Society

Local vibrational mode (LVM) spectroscopy has been used to study the evolution of vacancy-oxygen-related defects (VOn) in the temperature range 300-700°C in carbon-lean Cz-Si samples irradiated with MeV electrons or neutrons. New experimental data confirming an attribution of the absorption bands at 910, 976 and 1105 cm-1 to the VO3 complex are obtained. In particular, a correlated generation of VO3 and the oxygen trimer is observed upon irradiation of Cz- Si crystals in the temperature range 300-400°C. Strong evidence for the assignment of the bands at 991 and 1014 cm-1 to a VO4 defect is presented. The lines are found to develop very efficiently in the VO2 containing materials enriched with the oxygen dimer. In such materials the formation of VO4 is enhanced due to occurrence of the reaction O2i+VO2 ⇒ VO4. Annealing of the VO3 and VO4 defects at T ≥ 550C °C is found to result in the appearance of new defects giving rise to a number of O-related LVM bands in the range 990-1110 cm-1. These bands are suggested to arise from VO5 and/or VO6 defects. Similar bands also appear upon the annihilation of oxygen-related thermal double donors at 650°C in Cz-Si crystals pre-annealed at 450°C.

It is argued that the vacancy–oxygen (VO) complex (A center) in Ge has three charge states: double negative, single negative, and neutral. Corresponding energy levels are located at Ec−0.21 eV (VO−−/−) and Ev+0.27 eV (VO−/0). An absorption line at 716 cm−1 has been assigned to the asymmetrical stretching vibration mode of the doubly negatively charged VO complex.

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The elimination of divacancies (V 2 ) upon isochronal and isothermal annealing has been studied in oxygen-rich p-type silicon by means of deep level transient spectroscopy (DLTS) and high resolution Laplace DLTS. Divacancies were introduced into the crystals by irradiation with 4 or 6 MeV electrons. The temperature range of the divacancy disappearance was found to be 225-300 C upon 30 min isochronal annealing in the samples studied. A clear anti-correlation between the disappearance of V 2 and the appearance of two hole traps with activation energies for hole emission of 0.23 eV and 0.08 eV was observed. It is argued that these traps are related to the first and second donor levels of the divacancy-oxygen (V 2 O) complex, respectively. Significant electric field enhancement of the hole emission from the second donor level of the V 2 O center occurred in the diodes studied. It is shown that in the range of electric field from 4 Â 10 3 to 1.2 Â 10 4 V/cm the emission enhancement is associated with phonon-assisted tunnelling. V C 2014 AIP Publishing LLC. [http://dx.