Modeling boron diffusion gettering of iron in silicon solar cells

In this paper, a model is presented for boron diffusion gettering of iron in silicon during thermal processing. In the model, both the segregation of iron due to high boron doping concentration and heterogeneous precipitation of iron to the surface of the wafer are taken into account. It is shown, by comparing simulated results with experimental ones, that this model can be used to estimate boron diffusion gettering efficiency of iron under a variety of processing conditions. Finally, the application of the model to phosphorus diffusion gettering is discussed.Peer reviewe

Modeling the effect of mobile ion contamination on the stability of a microelectromechanical resonator

We present a theoretical model for mobile ion contamination in a silicon microelectromechanical resonator. In the model both drift and diffusion of the mobile charge in dielectric films are taken into account. The model is verified through a comparison to existing experimental data. We show that the model can describe the frequency drift of resonators in a wide temperature range.Peer reviewe

Modeling phosphorus diffusion gettering of iron in single crystal silicon

We propose a quantitative model for phosphorus diffusion gettering (PDG) of iron in silicon, which is based on a special fitting procedure to experimental data. We discuss the possibilities of the underlying physics of the segregation coefficient. Finally, we show that the proposed PDG model allows quantitative analysis of gettering efficiency of iron at various processing conditions.Peer reviewe

Experimental and theoretical study of heterogeneous iron precipitation in silicon

Heterogeneous iron precipitation in silicon was studied experimentally by measuring the gettering efficiency of oxide precipitate density of 1×10exp10cm−3. The wafers were contaminated with varying iron concentrations, and the gettering efficiency was studied using isothermal annealing in the temperature range from 300 to 780°C. It was found that iron precipitation obeys the so called s-curve behavior: if iron precipitation occurs, nearly all iron is gettered. For example, after 30 min annealing at 700°C, the highest initial iron concentration of 8×10exp13cm−3 drops to 3×10exp12cm−3, where as two lower initial iron concentrations of 5×10exp12 and 2×10exp13cm−3 remain nearly constant. This means that the level of supersaturation plays a significant role in the final gettering efficiency, and a rather high level of supersaturation is required before iron precipitation occurs at all. In addition, a model is presented for the growth and dissolution of iron precipitates at oxygen-related defects in silicon during thermal processing. The heterogeneous nucleation of iron is taken into account by special growth and dissolution rates, which are inserted into the Fokker-Planck equation. Comparison of simulated results to experimental ones proves that this model can be used to estimate internal gettering efficiency of iron under a variety of processing conditions.Peer reviewe

Improved stability of black silicon detectors using aluminum oxide surface passivation

Publisher Copyright: © 2021 ESA and CNESWe have studied how high-energy electron irradiation (12 MeV, total dose 66 krad(Si)) and long term humidity exposure (75%, 75 °C, 500 hours) influence the induced junction black silicon or planar photodiode characteristics. In our case, the induced junction is formed using n-type silicon and atomic-layer deposited aluminum oxide (Al2O3), which contains a large negative fixed charge. We compare the results with corresponding planar pn-junction detectors passivated with either with silicon dioxide (SiO2) or Al2O3. The results show that the induced junction detectors remain stable as their responsivity remains nearly unaffected during the electron beam irradiation. On the other hand, the SiO2 passivated counterparts that included conventional pn-junction degrade heavily, which is seen as strongly reduced UV response. Similarly, after humidity test the response of the induced junction detector remains unaffected, while the pn-junction detectors passivated with SiO2 degrade significantly, for instance, the response at 200 nm reduces to 50% from the original value. Interestingly, the pn-junction detectors passivated with Al2O3 exhibit no degradation of UV response, indicating that the surface passivation properties of Al2O3 are more stable than SiO2 under the studied conditions. This phenomenon is further confirmed with PC1D simulations suggesting that the UV degradation results from increased surface recombination velocity. To conclude, the results presented here suggest that black silicon photodiodes containing Al2O3-based induced junction are highly promising alternatives for applications that require the best performance and long-term stability under ionizing and humid conditions.Peer reviewe

Quantitative copper measurement in oxidized p-type silicon wafers using microwave photoconductivity decay

We propose a method to measure trace copper contamination in p-type silicon using the microwave photoconductivity decay (μ-PCD) technique. The method is based on the precipitation of interstitial copper, activated by high-intensity light, which results in enhanced minority carrier recombination activity. We show that there is a quantitative correlation between the enhanced recombination rate and the Cu concentration by comparing μ-PCD measurements with transient ion drift and total reflection x-ray fluorescence measurements. The results indicate that the method is capable of measuring Cu concentrations down to 10exp10cm−3. There are no limitations to wafer storage time if corona charge is used on the oxidized wafer surfaces as the charge prevents copper outdiffusion. We briefly discuss the role of oxide precipitates both in the copperprecipitation and in the charge carrier recombination processes.Peer reviewe

Effect of thermal history on iron precipitation in crystalline silicon

We have studied the effect of thermal history on iron precipitation behavior in intentionally contaminated Czochralski silicon wafers that contain well-defined precipitation sites for iron, oxide precipitates. Iron precipitation was studied at a temperature range between 600°C and 700°C for various times. The results indicate that iron precipitation is strongly affected by the thermal history of the wafers. Our results also explain the disagreement observed previously in iron precipitation behavior at low temperature anneals. Finally, we discuss how the results can be applied to gettering in multicrystalline silicon.Peer reviewe

Analysis of simultaneous boron and phosphorus diffusion gettering in silicon

We studied the simultaneous phosphorus and boron diffusion gettering (BDG) of iron in silicon by physical modeling. We present improvements to the previously used models for BDG and phosphorus diffusion gettering (PDG). We show that the improved model is suitable for analyzing the gettering efficiency in advanced solar cell structures with phosphorus doped (n+) and boron doped (p+) layers by comparing simulations with experimental results. The simulations indicate that during a low temperature step with high iron concentration, an additional p+ layer reduces the time needed for an effective gettering, whereas under low supersaturation segregation to the n+ layer is the dominating gettering mechanism