Evidence for identification of the divacancy-oxygen center in Si

Abstract

A deep level transient spectroscopy ͑DLTS͒ study of electronic defect levels in 15 MeV electron irradiated n-type float-zone Si samples with different oxygen contents has been performed. Heat treatment at 250°C results in a shift of both the singly negative and doubly negative divacancy (V 2 ) related DLTS peaks. This is due to annealing of V 2 and the formation of a new double acceptor center. The formation of the new center has a close one-to-one correlation with the annealing of V 2 . The annealing rate of V 2 and the formation rate of the new center are close to proportional with the oxygen content in the samples. The new center is identified as a divacancy-oxygen complex.Despite the tremendous amount of studies of defects in Si, little is known about electronic properties of multivacancyoxygen complexes, including the most basic of them-the divacancy-oxygen complex (V 2 O). Since oxygen is one of the main impurities in Si, the knowledge of the electronic properties of V 2 O is crucial for the understanding of defect interactions in Si. For example, the exact mechanisms for impurity-assisted annealing of the divacancy (V 2 ) are presently not known but can to a large extent involve the formation of V 2 O.From electron paramagnetic resonance ͑EPR͒ studies using heavily electron-irradiated samples it is established that V 2 O has at least three different charge states: singly negative, neutral, and singly positive. 1 The exact positions of the electronic levels in the band gap are unknown. Besides, theoretical studies of V 2 O predict that it can also have a doubly negative charge state, 2,3 and an experimental observation of V 2 O could confirm or disprove this prediction.Recently, there have been contradicting reports on possible observation of V 2 O. 4,5 In Ref. 4, the formation of a center with a midgap level (E c Ϫ0.545 eV, where E c is the conduction band edge͒ has been observed in high-dose irradiated float-zone ͑FZ͒ Si. A correlation between the oxygen content and the formation rate of the center has been found. In samples with less oxygen content, the formation of the center occurs at lower doses, while in samples with higher oxygen content, higher doses are needed in order to form a considerable amount of the centers. This phenomenon has been interpreted in terms of interaction between the radiation-induced monovacancies and oxygen. For low doses, the interaction between the monovacancies and the interstitial oxygen atoms, resulting in the formation of the vacancy-oxygen pair (VϩO i →VO), dominates. As the dose increases, the concentration of unpaired oxygen atoms decreases and the interaction VϩVO→V 2 O takes place with a higher probability. In the samples with lower oxygen content, the unpaired oxygen becomes exhausted already at a lower dose and the formation of V 2 O is enhanced, while in the samples with higher oxygen content, higher doses are needed for the interaction VϩVO→V 2 O to become probable. Later it has been shown that the midgap level has a second-order generation rate as a function o...

Radiation-induced point- and cluster-related defects with strong impact on damage properties of silicon detectors

“…The V 2 O is the only one defect generated by a second order process that was evidenced by Electron Paramagnetic Resonance [53,54] as direct result of irradiation. On the other hand, there are studies based on the annealing of V 2 at high temperatures of diodes irradiated with small dose values that revealed the transformation of V 2 into another defect X in oxygen rich silicon [55,56]. In these publications the X-defect was associated also with the V 2 O-complex.…”

Divacancy annealing in Si: Influence of hydrogen

“…This is due to recent reports on the observation of a double acceptor center identified as the divacancy-oxygen center (V 2 O). [1][2][3] These reports have considerably improved the understanding of the mechanisms of V 2 annealing and, at the same time, raised new questions concerning the origin of the dominant mechanism.…”

Donor levels of the divacancy-oxygen defect in silicon

“…In particular, oxygen atoms were found to be effective traps for V 2 , and the divacancy-oxygen interaction was shown to be the main mechanism of the V 2 elimination upon annealing of irradiated Czochralski-grown (Cz) Si crystals. 4,9,10,[13][14][15][16][17] An EPR Si-A14 signal and an absorption line at 833.4 cm À1 have been assigned to a complex incorporating the divacancy and an oxygen atom (V 2 O). 14,16 Deep level transient spectroscopy (DLTS) studies on irradiated and annealed n-type Si crystals have shown that the V 2 O center possesses two acceptor levels at E c À 0.23 eV and E c À 0.47 eV.…”

“…14,16 Deep level transient spectroscopy (DLTS) studies on irradiated and annealed n-type Si crystals have shown that the V 2 O center possesses two acceptor levels at E c À 0.23 eV and E c À 0.47 eV. 9,10,17 In p-type Si crystals a level at E v þ 0.24 eV, which appeared simultaneously with the disappearance of V 2 upon annealing, has been assigned to a donor level of the V 2 O complex. 15 We have argued in a recent work that in addition to the first donor level at E v þ 0.236 eV the V 2 O center possesses a second donor level at E v þ 0.087 eV.…”