Solid State Phenomena Vols. 156-158

Abstract: We have investigated the gettering efficiency at the interface of Si (110) and Si (100) directly bonded (DSB) substrates. DSB substrates were prepared by conventional bonding and grinding back methods. DSB substrates were intentionally contaminated with 3d transition metals (Fe, Ni, Cu) and then annealed at 1000 oC. The dependence of metal concentrations on the depth was evaluated by a secondary ionization mass spectrometer (SIMS). Furthermore, we observed the interface of DSB by transmission electron microscope (TEM), and characterized the form of the gettered metals.

Abstract: Implantation of 18O into highly B-doped and undoped silicon provides the possibility to investigate the effect of B-doping and to distinguish the processes of in-diffusion and out-diffusion of oxygen by profiling of 16O and 18O, respectively. The simultaneous in- and outdiffusion of oxygen was observed at 1000°C under oxidizing conditions. For silicon, heavily Bdoped to concentrations of 􀀀 1019 B cm-3, oxygen tends to diffuse out toward the surface. Moreover, a fraction of the oxygen from both sources, implanted 18O and in-diffused 16O, also migrates deep into the substrate and is trapped far beyond the mean ion range RP in the depth of x
3RP at the so-called trans-RP gettering peak. In undoped silicon oxygen accumulation only takes place at vacancy-type defects introduced by ion implantation at a position shallower than RP. The mobility of oxygen implanted into B-doped Si is higher than for implantation into undoped Si. Highly mobile defects are suggested to be formed in B-doped silicon beside the common mobile interstitial oxygen, Oi, and the immobile SiOX precipitates. These I OXBY defects may involve selfinterstitials, I, and O and B atoms. The trans-RP peak appears due to the decay of these defects and the segregation of their constituents.

Abstract: We investigated the impact of using low quality feedstock such as recycled silicon and simplified pulling condition on the performance of CZ silicon solar cells. Groups of wafers carefully chosen from different ingots were analyzed after different solar cell process steps by minority carrier lifetime measurements, by measurements of the interstitial iron content and by measurements of the total impurity content using NAA. Our results show that the main electronic properties of the ingots, namely the carrier lifetime, interstitial iron content and base resistivity are strongly affected by feedstock quality. Surprisingly, high solar cell efficiencies were achieved using highly contaminated silicon. These positive results are due to the beneficial effect of impurity segregation gettering by phosphorous diffusion and aluminum alloying. Post-diffusion gettering by an additional annealing step was demonstrated to enhance the charge carrier lifetime.

Abstract: The eect of slow cooling after dierent high temperature treatments on the in- terstitial iron concentration and on the electron lifetime of p-type mc-Si wafers has been in- vestigated. The respective impacts of internal relaxation gettering and external segregation gettering of metal impurities during an extended phosphorous diusion gettering are studied. It is shown that the enhanced reduction of interstitial Fe during extended P-gettering is due to an enhanced segregation gettering while faster impurities like Cu and Ni are possibly reduced due to an internal gettering eect.

Abstract: Low temperature boron and phosphorous diffusion gettering (BDG and PDG) of iron in Czochralski-grown silicon were experimentally studied. Differences and similarities between the gettering techniques were clarified by using intentionally iron contaminated wafers emphasizing especially the effect of oxygen. Experiments showed that the surprisingly high gettering effects of BDG could be explained by B-Si precipitates. Oxygen precipitation was seen to decrease minority carrier diffusion length after long gettering at low temperatures in both BDG and PDG. In the case of BDG oxygen precipitation affected more as a higher thermal budget was needed to obtain similar sheet resistance to that of PDG. According to experiments the efficiency of BDG can not be concluded from the sheet resistance, whereas the efficiency of PDG can. This has practical influences in a process control environment.

Abstract: Defects distribution in 6H-SiC implanted with Bi ions was investigated with the local cathodoluminescence. There are two typical areas with radiation defects found in implanted samples. Implanted layer was about 27 micrometers depth. Far-action area with radiation defects was observed for the first time. Thickness of this area varies from few tens up to hundreds micrometers. This effect depended on concentration of defects i.e. irradiation fluence. Radiation defects at this area disappeared after annealing the sample if fluence is not to high.

Abstract: Iron concentration imaging has been proven to be a very valuable analysis technique for silicon material characterization. We applied this method to determine the influence of a low temperature annealing after surface passivation on the interstitial iron concentration. The influence of hydrogen passivation induced by silicon nitride passivation is estimated by comparison of silicon nitride and aluminum oxide passivation. The second part of this work deals with systematic errors inherent to the iron concentration technique. Simulations show under which conditions errors occur due to the non-uniformity of carrier profiles.

Abstract: The relatively new “thin-film polycrystalline-silicon (pc-Si) (grain size of 0.1-100 µm) solar cell on foreign substrate” technology aims at low-cost devices with energy conversion efficiencies above 12 %. A very promising technique to obtain thin pc-Si layers is aluminum-induced crystallization (AIC). Solar cell absorber layers can be made by epitaxial thickening of these AIC seed layers. So far, we have reached energy conversion efficiencies of up to 8% with this approach. In contrast to what is expected a performance independent of the grain size is found which is explained by the presence of intragrain defects. In this paper the electrical activity of both the intragrain defects as well as the grain boundaries is investigated with electron beam induced current (EBIC) measurements before and after hydrogen plasma passivation. Metal-insulator-semiconductor contacts were used as collecting junction to eliminate the interference of the junction shape with the EBIC measurement as found when diffused emitters where used. It is shown that both grain boundaries and intragrain defects are electrically active before and after hydrogen plasma passivation. Finally we argue that Leff,mono, the diffusion length inside the grains, is probably much closer to 1µm in our layers than equal to 100µm as often expected in the literature.

Abstract: Electrical and structural properties of thin-film photovoltaic (PV) material fabricated using Crystal Silicon on Glass (CSG) technology was investigated applying photoluminescence (PL) and Raman spectroscopy (RS). The obtained results and their correlation with the PV properties of the cells prepared from the same material showed that PL is applicable for in-line characterization of the material before the electrical contact fabrication processes. The results obtained using RS gave useful information on crystallization grade of the material during the fabrication process.

Abstract: The Czochralski-grown silicon crystals plastically deformed at 680±C to the residual strain of 5% and subsequently annealed in the temperature range of 650{850±C were studied by the IR absorption and DLTS techniques. The formation and disappearance kinetics were investigated for several weak IR absorption lines around the 1000 cm¡1 wave number, which were previously related to the deformation-induced defects of non-dislocation nature in the dislocation trails. In parallel, the spectrum and concentrations of the deep-level centers in the upper half of the gap were measured by DLTS. It is found that the deep-level centers and op- tically active defects exhibit a common behavior during the post-deformation heat treatments. However, a direct correspondence between the IR and DLTS features cannot be established be- cause of the higher concentration of the deep-level centers as compared to the optically active defects.