A. Andrianakis

Radiation-induced defects in Czochralski-grown silicon containing carbon and germanium

Formation processes of vacancy-oxygen (VO) and carbon interstitial-oxygen interstitial (CiOi) complexes in electron-irradiated Czochralski-grown Si crystals (Cz–Si), also doped with Ge, are investigated. IR spectroscopy measurements are employed to monitor the production of these defects. In Cz–Si with carbon concentrations [Cs] up to 1 × 1017 cm−3 and Ge concentrations [Ge] up to 1 × 1020 cm−3 the production rate of VO defects as well as the rate of oxygen loss show a slight growth of about 10% with the increasing Ge concentration. At high concentrations of carbon [Cs] around 2 × 1017 cm−3 the production rate of VO defects is getting larger by ~40% in Cz–Si:Ge at Ge concentrations around 1 × 1019 cm−3 and then at [Ge] ≈ 2 × 1020 cm−3 this enlargement drops to ~13%, thus approaching the values characteristic of lesser concentrations of carbon. A similar behavior against Ge concentration displays the production rate of CiOi complexes. The same trend is also observed for the rate of carbon loss, whereas the trend for the rate of oxygen loss is opposite. The behavior of Ge atoms is different at low and high concentrations of this isoelectronic impurity in Cz–Si. At low concentrations most isolated Ge atoms serve as temporary traps for vacancies preventing them from indirect annihilation with self-interstitials. At high concentrations Ge atoms are prone to form clusters. The latter ones are traps for vacancies and self-interstitials due to the strain fields, increasing the importance of indirect annihilation of intrinsic point defects. Such a model allows one to give a plausible explanation for the obtained results. A new band at 994 cm−1 seen only in irradiated Ge-doped Cz–Si is also studied. Interestingly, its annealing behavior was found to be very similar to that of VO complexes.

Radiation effects on the behavior of carbon and oxygen impurities and the role of Ge in Czochralski grown Si upon annealing

The annealing behavior of the oxygen and carbon impurities in Czochralski grown silicon (Cz-Si) was investigated in electron- and neutron-irradiated materials. The irradiated samples were subjected to isochronal anneals of up to ∼1000 °C, and the evolution of oxygen and carbon concentrations was monitored by means of infrared spectroscopy from the amplitudes of the 1106 and 605 cm−1 bands of the two impurities correspondingly. It was found that the electron irradiation does not affect the temperature of annealing of oxygen, although in the neutron-irradiated samples the oxygen band begins to decay in the spectra at a lower temperature than that in the nonirradiated samples. This behavior could be determined by supersaturation of vacancies mainly liberated from disordered regions in the latter material. This assists the oxygen aggregation process. Regarding carbon evolution, it was found that in the irradiated samples the annealing out of the 605 cm−1 band occurs at a lower temperature than that of the non...

IR studies of the impact of Ge doping on the successive conversion of VOn defects in Czochralski-Si containing carbon

We report infrared absorption studies of oxygen-related defects in electron-irradiated Ge-doped Czochralski-Si. Our investigation was mainly focused on the reaction channel leading to the formation of VOn (1≤n≤6) defects. The VOn defects form mainly upon annealing, as a result of the successive aggregation of oxygen atoms in the initial VO defect produced by the irradiation: (VO+Oi→VO2+Oi→VO3+Oi→VO4,…). It was found that the ratio of the conversion of VOn to VOn+1 defects is sensitive to the Ge content of the material. In particular, the ratio of the conversion of the VO to the VO2 defects was found to decrease with the increase in Ge concentration of the samples, although the opposite trend was observed for the VO3 to VO4 conversion. However, the VO2 to VO3 conversion changes only slightly with Ge content, being practically unaffected for Ge concentrations up to 2×1020 cm−3. In the case of VO2 formation, the phenomenon was attributed to the elastic strains induced in the lattice due to the Ge presence wh...

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 1×1019 cm−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...

Production of vacancy-oxygen defect in electron irradiated silicon in the presence of self-interstitial-trapping impurities

The enhancement by carbon of vacancy-oxygen (VO) defect formation in electron irradiated silicon was investigated using many samples of various carbon contents. The effect of carbon is well described by a simple analytical model of competing trapping of self-interstitials by VO and by carbon (and by emerging carbon-related defects like CiOi and ICiOi). The trapping ratio by Cs and by VO was determined to be about 0.9, and the optical calibration coefficients for CiOi and ICiOi were deduced. In crystals containing a high concentration of Ge, germanium also acts as a self-interstitial trapping impurity and, thus, enhances VO production. The trapping efficiency of Ge is 1000 times less than that of carbon.

Production and evolution of A-centers in n-type Si1−xGex

The vacancy-oxygen pair (VO or A-center) in n-type Si1−xGex crystals (x = 0, 0.025, 0.055) has been studied using infrared (IR) spectroscopy. It is determined that the VO production is suppressed in the case of n-type Si1−xGex as compared to Si. It is observed that the annealing temperature of the VO defect in Si1−xGex is substantially lower as compared to Si. The decay of the VO (830 cm−1) band, in the course of 20 min isochronal anneals, shows two stages: The onset of the first stage is at ∼180 °C and the decrease of the VO signal is accompanied in the spectra by the increase of the intensity of two bands at ∼834 and 839 cm−1. These bands appear in the spectra immediately after irradiation and were previously correlated with (VO-Ge) structures. The onset of the second stage occurs at ∼250 °C were the 830 cm−1 band of VO and the above two bands of (VO-Ge) decrease together in the spectra accompanied by the simultaneous growth of the 885 cm−1 band of the VO2 defect. Interestingly, the percentage of the VO...

Oxygen aggregation kinetics, thermal donors and carbon-oxygen defect formation in silicon containing carbon and tin

Localized vibrational mode spectroscopy measurements on Czochralski silicon (Cz-Si) samples subjected to isothermal annealing at 450 °C are reported. First, we studied the effect of carbon (C) and tin (Sn) isovalent dopants on the aggregation kinetics of oxygen. It is determined that the reduction rate of oxygen is described by the Johnson-Mehl-Avrami equation in accordance with previous reports. The activation energy related with the reaction rate constant of the process is calculated to increase from Cz-Si, to C-doped Cz-Si (CCz-Si), to Sn-doped Cz-Si contained C (SnCz-Si). This is attributed to the presence of the isovalent dopants that may impact both the kinetics of the oxygen atoms and also may lead to the formation of other oxygen-related clusters. Second, we studied the effect of Sn on the formation and evolution of carbon-oxygen (C-O) defects. It was determined that the presence of Sn suppresses the formation of the C-O defects as indicated by the reduction in the strength of the 683, 626, and 58...

IR Studies on VON, CIOI and CICS Defects in Ge-Doped Cz-Si

This paper reports experimental results on the production and annealing of oxygen-vacancy related (VOn, 1<n<5) and carbon-related (CiOi, CiOiI, and CiCs) defects in Ge-doped Czochralski-grown silicon (Cz-Si) materials containing carbon. The samples were irradiated by 2 MeV fast electrons and the behavior of radiation-produced defects is studied by means of infrared (IR) spectroscopy, monitoring the relevant bands in spectra. Regarding the VOn family, it was found that the presence of Ge affects the annealing temperature of VO defects as well as their fraction that is converted to VO2 defects. Both effects are discussed in relation with an impact of Ge on the concentration of self-interstitials that take part in the annealing of VO defects via two reaction paths VO + I → Oi and VO + Oi → VO2. Furthermore, two bands at 1037 and 1051 cm-1 are attributed to the VO5 defect, although three other bands at 762, 967 and 1005 cm-1 are believed to be associated with VnOm clusters containing carbon, most likely having a VOnCs structure. Regarding carbon-related complexes, it has been established that the annealing of the 862 cm-1 band belonging to the CiOi defect is accompanied by the emergence of the 1048 cm-1 band previously assigned to the CsO2i center. The evolution of the CiCs and the CiOiI bands is monitored and the identification of bands at 947, 967 and 1020 cm-1 making their appearance in IR spectra over the temperature range where CiCs and CiOiI defects are annealed out is discussed.