This paper reports the results of a systematic study on the kinetics of dissociation and formation of iron-boron (FeB) pairs in boron-doped Czochralski silicon after phosphorus implantation gettering of iron at different temperatures. The aim of this study is threefold: (i) investigation of the dissociation kinetics of the FeB pairs by a standardized illumination as a function of the iron concentration after gettering process, (ii) study of the kinetics of their association, and (iii) extraction of the characteristic parameters of these two phenomena for gettered samples, in particular the effective time constants of dissociation and association as well as the constant of material, which describes the dissociation rate well in the absence of other recombination channels.
Control of detrimental metal impurities is crucial to silicon solar cell performance. Traditional silicon solar cell emitters are diffused in an infinite-source regime and are known to cause strong point defect segregation towards the emitter and thus enhance bulk minority carrier diffusion length. With the advent of ion-implantation and chemical vapor deposition (CVD) glasses, finite-source diffused emitters are attracting interest. This contribution aims to increase their adoption by elucidating the dominant gettering mechanisms present in finite-source diffused emitters. Our findings indicate that infinite-source diffusion is critical for effective segregation gettering, but that high enough surface phosphorus concentration can activate segregation gettering via finite-source diffusion as well. In the case of ionimplanted emitters, the traditional segregation gettering may be considerably enhanced by impurity precipitation in the implanted layer.
We have investigated in this work the effect of the temperature profile during homogeneous phosphorous diffusion gettering (PDG) on multicrystalline (mc-Si) silicon p-type wafers destined for photovoltaic solar cells. Temperatures were varied from 800 • C due probably to a partial dissolution of the metallic precipitates, especially at the grain boundaries and in the dislocations vicinity. The related τCr-Impurity lifetime value of about 8.5 µs is extracted, which is the result of interstitial Cri or CriBs pairs, proving their strongest recombination activity in silicon.
Boron-doped hydrogenated amorphous silicon (a-Si:H(B)) thin films have been prepared by DC magnetron sputtering technique under argon and hydrogen mixture. The films were deposited at various hydrogen pressures between 0 and 9 10-5 mbar. The boron concentration estimated from Secondary Ion Mass Spectrometry (SIMS) analysis was found to be around 1.5 1021 cm-3 for all samples. Their physico-chemical, optical and electrical properties are investigated. The physico-chemical properties were studied by infrared absorption measurements. The bonded hydrogen content in the films is then determined using the absorption band of stretching mode. The optical transmission measurements show an increase of the static refractive index and a decrease of optical gap value when hydrogen pressure increases. The dark-conductivity and the photo-conductivity measurements according to the temperature are also reported. We have observed the decreasing of dark-conductivity when hydrogen pressure increases. A slight sensitivity of light was observed for the film deposited at the highest hydrogen pressure. The dark-conductivity was affected by annealing temperature for the whole of the films through its increase in the annealing temperature region 200-350°C.
The vanadotungstate K 7 V 5 W 8 O 40 •12H 2 O synthesized by hydrothermal route at 453 K was reported for the first time. The compound crystallizing in a Keggin type structure was characterized by powder X-ray diffraction, FTIR spectroscopy and UV-Vis diffuse reflectance; it was successfully tested for the removal of Rhodamine B (Rh B). The effects of contact time, initial concentration and pH were investigated. The adsorption capacity reached ~ 40% in aqueous solution within 16 h. Pseudo-first-order, pseudo-second-order, Elovich and intra-particle diffusion models were applied to fit the experimental data. The pseudo-second-order was the best to describe the adsorption. The equilibrium isotherms were also analyzed by different models. Negative free enthalpy (ΔG) suggested that adsorption Rh B is spontaneous. The positive enthalpy (ΔH) entropy (ΔS) indicated endothermic process with an increase in the randomness of the solid/liquid interface. The compound showed 42% degradation of the remaining concentration after 4 h exposure to solar radiation.
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