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- Vines, L, et al.
(författare)
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Effect spatial defect distribution on the electrical behavior of prominent vacancy points defects in swift-ion implanted Si
- 2009
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 79:7, s. 075206-
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Tidskriftsartikel (refereegranskat)abstract
- Samples of epitaxially grown n-type silicon have been implanted at room temperature with low doses (10(6)-10(9) cm(-2)) of He, C, Si, and I ions using energies from 2.75 to 46 MeV. Deep level transient spectroscopy studies reveal that the generation of divacancy (V-2) and vacancy-oxygen (VO) pairs has a distinct ion mass dependence. Especially, the doubly negative charge state of the divacancy, V-2(=/-), decreases in intensity with increasing ion mass compared to that of the singly negative charge state of the divacancy, V-2(-/0). In addition, the measurements show also a decrease in the intensity of the level assigned to VO compared to that of V-2(-/0) with increasing ion mass. Carrier capture cross-section measurements demonstrate a reduction in the electron capture rate with increasing ion mass for all the three levels V-2(-/0), V-2(=/-), and VO; but a gradual recovery occurs with annealing. Concurrently, the strength of the V-2(-/0) level decreases in a wide temperature range starting from below 200 degrees C, accompanied by an increase in the amplitudes of both the VO and V-2(=/-) peaks. In order to account for these results a model is introduced where local carrier compensation is a key feature and where two modes of V-2 are considered: (1) V-2 centers located in regions with a high defect density around the ion track (V-2(dense)) and (2) V-2 centers located in regions with a low defect density (V-2(dilute)). The V-2(dense) fraction does not give any contribution to the V-2(=/-) signal due to local carrier compensation, and the amplitude of the V-2(=/-) level is determined by the V-2(dilute) fraction only. The spatial distributions of defects generated by single-ion impacts were simulated by Monte Carlo calculations in the binary collision approximation, and to distinguish between the regions with V-2(dense) and V-2(dilute) a threshold for the defect generation rate was introduced. The model is shown to give good quantitative agreement with the experimentally observed ion mass dependence for the ratio between the amplitudes of the V-2(=/-) and V-2(-/0) peaks. In particular, the threshold value for the defect generation rate remains constant (similar to 1.2 vacancies/ion/A) irrespective of the type of ion used, which provides strong evidence for the validity of the model. Annealing at temperatures above similar to 300 degrees C is found to reduce the spatial localization of the defects and migration of V-2 occurs with subsequent trapping by interstitial oxygen atoms and formation of divacancy-oxygen pairs.
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- Vines, L, et al.
(författare)
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Formation and annealing behavior of prominent point defects in MeV ion implanted n-type epitaxial Si
- 2009
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Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5107 .- 1873-4944. ; 159-160, s. 177-181
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Tidskriftsartikel (refereegranskat)abstract
- Samples of epitaxially grown n-type Si have been implanted with low doses (< 1 x 10(9) cm(-1)) of He, C, Si, and I ions using energies from 2.75 to 48 MeV. Deep level transient spectroscopy (DLTS) analysis of the implanted samples reveals a stronger signal for the signature of the singly negative charge state of the divacancy (V-2(-/0)) as compared to that of the doubly negative charge state of the divacancy (V-2(=/-)). Isochronal annealing for 20 min ranging from 150 to 400 degrees C results in a gradual decrease ill the DLTS peak amplitude of the V-2(-/0) signature, accompanied by an increase in the peak amplitudes of both the vacancy oxygen pair (VO) and the V-2(=/-) levels, as well as an increase in the carrier Capture rates for the levels. A model based on local compensation of charge carriers front individual ion tracks is proposed in order to explain the results, involving two fractions of V-2: (1) V-2 centers localized in regions with high defect density around the ion track (V-2(dense)) and (2) V-2 centers located in regions with a low defect density (V-2(dilute)).
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- Vines, L., et al.
(författare)
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Scanning probe microscopy of single Au ion implants in Si
- 2006
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Ingår i: Materials science & engineering. C, biomimetic materials, sensors and systems. - : Elsevier BV. - 0928-4931 .- 1873-0191. ; 26:07-maj, s. 782-787
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Tidskriftsartikel (refereegranskat)abstract
- We have studied 5 MeV Au2+ ion implantation with fluences between 7 x 10(7) and 2 x 10(8) cm(-2) in Si by deep level transient spectroscopy (DLTS) and scanning capacitance microscopy (SCM). The DLTS measurements show formation of electrically active defects such as the two negative charge states of the divacancy (V-2(=/-) and V-2(-/0)) and the vacancy-oxygen (VO) center. It is observed that the intensity of the V-2(=/-) peak is lower compared to that of V-2(-/0) by a factor of 5. This has been attributed to a highly localized distribution of the defects along the ion tracks, which results in trapping of the carriers at V-2(-/0) and incomplete occupancy of V-2(=/-). The SCM measurements obtained in a plan view show a random pattern of regions with a reduced SCM signal for the samples implanted with fluence above 2 x 10(8) cm(-2). The reduced SCM signal is attributed to extra charges associated with acceptor states, such as V-2(-/0), formed along the ion tracks in the bulk Si. Indeed, the electron emission rate from the V-2(-/0) state is in the range of 10 kHz at room temperature, which is well below the probing frequency of the SCM measurements, resulting in freezing of electrons at V-2(-/0).
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- Vines, L., et al.
(författare)
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Visualization of MeV ion impacts in Si using scanning capacitance microscopy
- 2006
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 73:8
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Tidskriftsartikel (refereegranskat)abstract
- Scanning capacitance microscopy (SCM) of 3 MeV Au2+ ion implanted Si have been performed for doses between 2x10(8) and 5x10(9) cm(-2). The measurements show a random pattern of reduced SCM signal (charge trapping) correlated with the ion impacts. These features have a lateral dimension of 150-600 nm and reveal a pronounced dose dependence. It is argued that the Fermi level near the impacts and along the ion tracks is modified (pinned) due to deep acceptor states formed by the penetrating ions. Substantial evidence for this argument is provided by SCM images obtained at different temperatures, where a strong correlation is revealed between the probing frequency and the emission rate of the single negative acceptor level of divacancy. To the best of our knowledge, this is a direct observation of signatures for individual ion impacts in Si by an electrical scanning technique.
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