Papers by Keyword: Carbon Impurity

Abstract: We have proposed single seed cast Si growth and developed a furnace for 50 cm square ingots. By optimizing growth parameters, improving gas condition, coating, the quality of mono Si ingot has improved. Namely, dislocation density, the concentrations of substitutional carbon and interstitial oxygen have been significantly reduced. The conversion efficiency of cast Si solar cells has become comparable with those of CZ Si wafers.

Abstract: The spectrum of defects produced by 5 MeV electron irradiation at room temperature in the oxygen-lean p-type silicon strongly contaminated with interstitial copper (Cu_i) is studied using the deep-level transient spectroscopy. It is observed that the interstitial carbon defects (C_i), which are abundant in irradiated copper-free samples, are not detected directly after irradiation. The phenomenon is attributed to the formation of a {Cu_i, C_i} complexes which exhibit no deep levels in the lower half of the band gap. The complexes are shown to dissociate under anneals at 300-340 K resulting in the appearance of the C_i species.

Abstract: Reducing the carbon concentration in Czochralski (CZ) silicon crystals is crucial in order to improve the properties of high-power devices, such as on-resistance and carrier lifetime. To achieve carbon concentration reduction, it is necessary to reduce carbon monoxide (CO) contamination from the CZ furnace graphite components and to remove the carbon impurities originating from the starting material. In this study, suppressing the chemical reaction between silicon monoxide (SiO) and the graphite heater effectively reduced the CO contamination rate. Furthermore, we attempted to promote CO evaporation during the CZ process in order to remove carbon impurities from the melt. Increasing the Ar gas flow velocity above the melt surface was found to be effective in increasing the CO evaporation rate during both the melting and growth processes. The CO evaporation rate during the melting process of 8-inch CZ silicon was calculated as being of the order of 10^-2 μg/s. Owing to the effects of the CO evaporation, 8-inch CZ silicon crystals with carbon concentrations lower than 2.0 × 10¹⁴ atoms/cm³ at a solidified fraction of 0.85 were grown.

Abstract: Carbon impurity concentration and dislocation density were investigated with optical microscopy and Fourier transform infrared absorption spectrometer in radial direction of large diameter (6-inch) undoped semi-insulating Gallium Arsenide (SI-GaAs) grown by liquid encapsulated Czochralski (LEC). The experimental results showed that their distributions are both “W”-shaped along wafer diameter, which is relatively higher on the center and lower near the center, but highest on the edge of the wafer. The nonuniformity distribution of thermal stress from growth process leads to the “W”-shaped distribution of dislocations in radial direction. The adsorption of matrix elastic strain field around dislocations induces the “W”-shaped distribution of carbon impurity. Dislocations adsorb carbon impurity and carbon impurity decorates dislocations. Dislocation density distribution affects carbon behavior.

Abstract: Silicon wafers with different carbon contents have been characterized by Fourier transform infrared spectroscopy technique. An infrared absorption band at 1207cm-1 can be newly observed in the case of carbon content being above 1.7×1017/cm3, whose intensity increases with an increase of carbon concentration in silicon crystal. More interestingly, the 1207cm-1 band cannot be influenced by the long-time annealing in the temperature range of 450-1250oC, suggesting the high thermal stability of this carbon-related defect, which might be related to the presence of silicon carbide in silicon crystals.

Abstract: The evolution of radiation-induced carbon-related defects in low temperature irradiated oxygen containing silicon has been studied by means of Fourier transform infrared absorption spectroscopy (FTIR) and deep level transient spectroscopy (DLTS). FTIR measurements have shown that annealing of interstitial carbon atom Ci, occurring in the temperature interval 260-300 K, results in a gradual appearance of a number of new absorption bands along with the well known bands related to the CiOi complex. The new bands are positioned at 812, 910.2, 942.6, 967.4 and 1086 cm-1. It has been found that the pair of bands at 910 and 942 cm-1 as well as another set of the bands at 812, 967.4 and 1086 cm-1 display identical behavior upon isochronal annealing, i.e. the bands in both groups appear and disappear simultaneously. The disappearance of the first group occurs at T = 285-300 K while the second group anneals out at T = 310-340 K. These processes are accompanied by an increase in intensity of the bands related to CiOi. It is suggested that intermediate states (precursors) are formed upon the transformation from a single (isolated) Ci atom to a stable CiOi defect. The results obtained in DLTS studies are in agreement with the FTIR data and show unambiguously the formation of CiOi precursors with slightly lower activation energy for the hole emission as compare to that for the main CiOi state.