C. A. Londos

Effect of tin doping on oxygen- and carbon-related defects in Czochralski silicon

Experimental and theoretical techniques are used to investigate the impact of tin doping on the formation and the thermal stability of oxygen- and carbon-related defects in electron-irradiated Czochralski silicon. The results verify previous reports that Sn doping reduces the formation of the VO defect and suppresses its conversion to the VO2 defect. Within experimental accuracy, a small delay in the growth of the VO2 defect is observed. Regarding carbon-related defects, it is determined that Sn doping leads to a reduction in the formation of the CiOi, CiCs, and CiOi(SiI) defects although an increase in their thermal stability is observed. The impact of strain induced in the lattice by the larger tin substitutional atoms, as well as their association with intrinsic defects and carbon impurities, can be considered as an explanation to account for the above observations. The density functional theory calculations are used to study the interaction of tin with lattice vacancies and oxygen- and carbon-related ...

ORIGIN OF INFRARED BANDS IN NEUTRON-IRRADIATED SILICON

Infrared absorption measurements were made of the localized vibrational modes due to defects produced in Czochralski-grown Si material after irradiation with fast neutrons and subsequent thermal treatments. The investigation was focused, in particular, on three satellite bands in the region of the A center, located at 839, 833 and 824 cm−1 respectively, the annealing behavior of which was carefully monitored. Correlation of our results with previous infrared, electron paramagnetic resonance and positron annihilation studies favors attributing these bands to the V2O, V3O2 and V2O2 defects respectively. In addition, semiempirical calculations were carried out for the vibrational frequencies of these defects, and the predicted values are in agreement with the above assignments.

Effect of germanium doping on the annealing characteristics of oxygen and carbon-related defects in Czochralski silicon

This paper is devoted to the annealing studies of defects produced in carbon-rich Ge-doped Czochralski-grown Si (Cz-Si) by 2 MeV electron irradiation. The annealing temperature of vacancy-oxygen (VO) complexes, carbon interstitial-oxygen interstitial (CiOi), and carbon interstitial-carbon substitutional (CiCs) pairs as well as the formation temperature of vacancy-two oxygen (VO2) complexes are monitored as a function of Ge concentration. It has been established that the annealing of CiOi and CiCs defects remains practically unaffected by the Ge presence, whereas the annealing temperature of VO defects and the formation temperature of VO2 complexes are substantially lowered at Ge concentrations larger than 1×1019u2002cm−3. The hydrostatic component of elastic strains introduced by Ge atoms in the Si crystal lattice was calculated. It appears to be very small, at least insufficient to exert a pronounced effect upon the annealing behavior of radiation-produced defects. This conclusion is in line with what is obs...

Defect engineering of the oxygen-vacancy clusters formation in electron irradiated silicon by isovalent doping: An infrared perspective

Infrared spectroscopy was used to study the production and evolution of oxygen–vacancy (VOn for nu2009=u20091, 2, 3 and VmO for mu2009=u20091, 2, 3) clusters, in electron-irradiated Czochralski silicon (Cz-Si) samples, doped with isovalent dopants. It was determined that the production of the VO pair is enhanced in Ge-doped Si but is suppressed in Sn and Pb-doped Si. The phenomenon is discussed in terms of the competition between isovalent dopants and oxygen atoms in capturing vacancies in the course of irradiation. In the case of Ge, only transient GeV pairs form, leading finally to an increase of the VO production. Conversely, for Sn and Pb the corresponding pairs with vacancies are stable, having an opposite impact on the formation of VO pairs. Regarding V2O and V3O clusters, our measurements indicate that Ge doping enhances their formation, although Sn and Pb dopants suppress it. Similar arguments as those for the VO pair could be put forward, based on the effect of isovalent impurities on the availability of vacancies. Additionally, it was found that the conversion ratio of VO to VO2 decreases as the covalent radius of the isovalent dopant increases. These results are discussed in terms of the local strains introduced by the isovalent dopants in the Si lattice. These local strains affect the balance of the intrinsic defects created as a result of irradiation, as well as the balance between the two main reactions (VOu2009+u2009Oiu2009→u2009VO2 and VOu2009+u2009SiIu2009→u2009Oi) participating in the VO annealing, leading finally to a decrease of the VO2 production. The larger the covalent radius of the isovalent dopant (rGeu2009<u2009rSnu2009<u2009rPb), the larger the introduced strains in the lattice and then the less the VO2 formation in accordance with our experimental results. Interestingly, an opposite trend was observed for the conversion ratio of VO2 to VO3. The phenomenon is attributed to the enhanced diffusivity of oxygen impurity as a result of the presence of isovalent dopants, leading to an enhanced formation of the VO3 cluster. The results indicate that isovalent doping of Si is an effective way to control the formation of the deleterious oxygen-vacancy clustering that can affect Si-based devices.Infrared spectroscopy was used to study the production and evolution of oxygen–vacancy (VOn for nu2009=u20091, 2, 3 and VmO for mu2009=u20091, 2, 3) clusters, in electron-irradiated Czochralski silicon (Cz-Si) samples, doped with isovalent dopants. It was determined that the production of the VO pair is enhanced in Ge-doped Si but is suppressed in Sn and Pb-doped Si. The phenomenon is discussed in terms of the competition between isovalent dopants and oxygen atoms in capturing vacancies in the course of irradiation. In the case of Ge, only transient GeV pairs form, leading finally to an increase of the VO production. Conversely, for Sn and Pb the corresponding pairs with vacancies are stable, having an opposite impact on the formation of VO pairs. Regarding V2O and V3O clusters, our measurements indicate that Ge doping enhances their formation, although Sn and Pb dopants suppress it. Similar arguments as those for the VO pair could be put forward, based on the effect of isovalent impurities on the availability of vacanci...

Impact of isovalent doping on radiation defects in silicon

Isovalent doping is an important process for the control of point defects in Si. Here, by means of infrared spectroscopy, we investigated the properties of the two main radiation-induced defects in Czochralski-Si (Cz-Si) the oxygen-vacancy (VO) and the carbon-oxygen (CiOi) centres. In particular, we investigated the effect of isovalent doping on the production, the thermal evolution, and the thermal stability of the VO and the CiOi defects. Additionally, we studied the reactions that participate upon annealing and the defects formed as a result of these reactions. Upon annealing VO is converted to VO2 defect although part of the CiOi is converted to CsO2i complexes. Thus, we studied the conversion ratios [VO2]/[VO] and [CsO2i]/[CiOi] with respect to the isovalent dopant. Additionally, the role of carbon in the above processes was discussed. A delay between the temperature characterizing the onset of the VO decay and the temperature characterizing the VO2 growth as well the further growth of VO2 after the ...

Isochronal Annealing Studies of the Oxygen–Vacancy Centres in Neutron-Irradiated Si

The infrared spectra of room-temperature, neutron-irradiated, Czochralski-grown Si were investigated. During annealing, the 827 cm -1 VO defect band decreases, and another band at 885 cm -1 generally attributed to the VO 2 centre increases. The kinetics of the evolution of these two defects was investigated. The decay of VO is dominated by a second-order reaction (VO + Si i → O i ) with an activation energy 1.70 eV. The growth of VO 2 exhibits two stages. Below 360 °C, a first-order reaction (VO+O i -VO 2 ) with an activating energy of 1.46eV or a second-order reaction (VO + VO → VO 2 + V) with an activation energy of 1.96 eV could fit the data. The two cases are considered and discussed. The analysis goes further taking into account the more realistic case that both reactions occur in parallel. Values of 2.1 and 2.0 eV were derived, respectively. Above 360 °C, the phenomenon is not well understood, as other factors might also be at work which manifest their presence more profoundly above this temperature.

Electrical properties of multiple-layer structures formed by implantation of nitrogen or oxygen and annealed under high pressure

Silicon-on-insulator-like structures formed in either oxygen- or nitrogen-implanted silicon during anneals under atmospheric and enhanced hydrostatic pressure are characterized by means of electrical techniques (current-voltage and capacitance-voltage measurements). It was found that the application of high pressure (∼1GPa) stimulates the formation of a perfect top silicon layer and results in the degradation of the properties of the buried insulator. The latter effect is caused by defect accumulation in the buried insulator and leads to a decrease in the effective thickness of the insulator layer as extracted from capacitance-voltage measurements. Pressure-stimulated formation of electrically active centers (donors and acceptors) in the top silicon layer and substrate was found. The fixed charge in the oxide was found to be independent on the pressure applied during anneals, whereas the negative charge in the nitride increased with pressure.

Investigation of two infrared bands at 1032 and 1043 cm−1 in neutron irradiated silicon

We report on infrared (IR) studies of defects in Czochralski-grown silicon (Cz-Si) subjected to fast neutron irradiation and subsequent thermal anneals. We focus mainly on the investigation of the VO4 defect which, in the literature, has been correlated with the pair of bands (1032 and 1043u2002cm−1) in neutron-irradiated Si and another pair of bands (983 and 1004u2002cm−1) in oxygen-implanted Si. Semiempirical calculations of the localized vibrational mode frequencies of the VO4 structure support its correlation with the second pair of bands. This correlation is consistent with the ascertainment that the zero point energy of each VOn (n=1,2,3,4) defect is smaller than the zero point energy of the constituent defects VOn−1, Oi, that is: EVOn

Production and evolution of defects in neutron-irradiated Si subjected to thermal pre-treatments under hydrostatic pressure

Thermal treatments of Czochralski-grown Si at T = 450, 600 and 650°C, under high hydrostatic pressure of P 11 kbar, introduce thermal donors and various structural defects, as for example oxygen precipitates. Neutron irradiation of such samples results first in the formation of oxygen-vacancy complexes, mostly VO defects. Upon annealing, the VO defects evolve in larger clusters via the accumulation of oxygen atoms and vacancies in the initial VO core, leading to the formation of V m O n defects. We focus on the study of the effect of pre-treatments on the production and evolution of the various V m O n defects upon isochronal annealing. The observed changes and variations in the IR spectra and the evolution curves in comparison with the corresponding ones of an initially untreated sample are discussed and some explanations are offered. The most important finding of this work is that the concentrations of the VO 2 and the VO 3 defects are reduced in the sample pre-treated at 450 °C, an indication of interaction between thermal donors and radiation-induced defects.

Impact of the germanium concentration in the stability of E-centers and A-centers in Si1−xGex

Electronic structure calculations are used to investigate the association of lattice vacancies and oxygen interstitials (known as A-centers) and compare them to vacancy-phosphorous atom pairs (known as E-centers) in silicon germanium (Si1−xGex) alloys. The local environment surrounding the A-centers and E-centers is described by the application of the special quasirandom structures approach. It is calculated that the stability of the A-centers and the E-centers is not linearly dependent upon the germanium concentration. The nearest neighbor environment will exert a strong influence upon the stability of these defects. These defect pairs will behave differently with respect to the Ge concentration as the oxygen interstitial (in the A-center) and the phosphorous atom (in the E-center) interact with the host lattice in a different manner. The results are discussed in view of recent theoretical and experimental investigations.