Front Surface Recombination Velocity Research Articles

An Investigation of The J-V Curve for N-AlGaAs/p-GaAs Heterojunction Solar Cell Due to Influence of Surface Recombination Velocity

Theoretical analysis can substantially reduce the time and costs required for developing a specific device such as solar cell, by allowing the designer to take a suitable geometry and doping profile prior to the fabrication stage. In this paper, theoretical analysis of electric field and electric potential within depletion layer of N-AlGaAS/p-GaAs has been made by solving Poisson's equation numerically using finite difference method (FDM) with Fortran program. Continuity equations of charge carriers in quasi- nature regions in N and p-layers were solved numerically to obtain the current density curve (J-V curve). Boundary conditions related to surface recombination velocity were implemented in this analysis. The effect of front and back surface recombination velocity on the excess minority carriers distribution and photocurrent have been studied. The aim of this work is to find the influence of surface recombination velocity in the output of N-AlGaAs/p-GaAs heterojunction solar cell. The analysis showed that, the low surface recombination velocity produce high efficient solar cell.

Numerical and Experimental Study of the Front Surface Recombination Velocities and Base Widths Effect in Multi-Crystalline Silicon Solar Cell Quantum Efficiency

Photovoltaic research activities are related to material innovation that can be obtained at a comparatively low cost. Semiconductor p-type multi-crystalline Czochralskyc (CZ)-grown silicon wafers were used in this study. The effects of front surface recombination velocities and base thickness in solar cells’ quantum efficiency are theoretically calculated. The results denote that both the surface recombination velocities and the base widths significantly impact the quantum efficiency. The results are of universal technical importance in designing solar cells and their surface structures. The main goal of this paper was to confirm the validity of the above theoretical calculations; for this purpose, silicon solar cells with front-thin porous silicon and rear interdigitated contact have been produced. A good agreement was obtained between experimentally obtained solar cells’ quantum efficiency data and the theoretical results. Therefore, the quantum efficiency of the mc-Si solar cells with porous silicon and rear interdigitated contact was enhanced up to 25% at 580–1100 nm wavelength range and up to 50% at short wavelength (400–570 nm), compared to reference mc-Si solar cells. The obtained results indicate that the rear interdigitated contact maximizes the surface area of the metal contact and improves the current collection. At the same time, the porous silicon layer passivates the front surface and reduces recombination losses.

Machine learning for enhanced semiconductor characterization from time-resolved photoluminescence

<h2>Summary</h2> To enhance the accuracy and effectiveness of optoelectronic characterization, Bayesian inference has been applied to the statistical analysis of time-resolved photoluminescence (TRPL) data with large-scale graphics-processing unit (GPU)-based simulations of electron dynamics. A simulated TRPL dataset, derived from a CH₃NH₃PbI_3-xCl_x perovskite absorber, was used as a case study. From a power scan, Bayesian inference extracts values of the (ambipolar) carrier mobility, free-carrier density, radiative recombination rate, and the overall lifetime of the nonradiative recombination processes. Analysis of the experimental TRPL data yields similar parameter values. The independent contributions of bulk and surface recombination can be distinguished via the introduction of an additional sample thickness. Further experiments separate the front and back surface recombination velocities and can distinguish the electron and hole mobilities. Ultimately, Bayesian inference enables a significant increase in the information yield from TRPL measurements.

Surface recombination property of silicon wafers determined accurately by self-normalized photocarrier radiometry

Surface recombination has a great impact on the performance of solar cells and photodetectors, and thus is necessary to be accurately determined. In this paper, a self-normalized photocarrier radiometry (PCR) with mean square variance graph is employed to improve the determination accuracy of the surface recombination velocities of silicon wafers and to reduce the influence of initial values on multi-parameter estimations. In this method data obtained from both the illuminated front surface and the illuminated rear surface are employed. The uncertainties of the estimated carrier recombination parameters, especially for the surface recombination velocities are improved significantly. Moreover, the influence of instrumental frequency response (IFR) on the multi-parameter estimation is totally eliminated. Theoretical simulations and experiments are performed to confirm the theoretical predictions. The estimated average uncertainties of the front and back surface recombination velocities for the sample used are approximately ± 7.60% and ± 5.71% by the proposed method, which are much improved than ± 13.65% and >±50% by the conventional method.

Impact of different parameters on the performance of GaAs solar cell using PC1D simulation

In this work, GaAs solar cell has been analyzed by using PC1D simulation software. Optimization of thickness and doping concentration of emitter and absorber layer of solar cell is done. Effect of front and rear surface recombination velocity is analyzed in this work. When surface recombination velocity increases, the value of efficiency decreases due to increase in recombination process. The optimum value of surface recombination velocity are Sn = Sp = 102 cm/s. Front surface reflection is minimized by the use of TiO2 single layer ARC and double layer LiF/HfO2 ARC. Increase in efficiency around 2.71% is achieved as compared to cell without ARC after applying anti-reflection coating of optimum thickness. Simulation results shows GaAs solar cell with efficiency of 26.68%.

Uniqueness of parameter estimates obtained from fitting free carrier absorption data of silicon wafers

In this paper, a data processing method is employed to improve the uniqueness of the electronic transport parameters (the carrier lifetime, carrier diffusion coefficient, and front and rear surface recombination velocities) obtained from fitting free carrier absorption data of silicon wafers. By employing the mean square variance graph or map, the influence of initial values on multi-parameter estimation greatly decreases. Theoretical simulations are performed to investigate the dependence of the uniqueness of the estimated parameters on the number of free parameters by choosing different initial values during multi-parameter fitting. Simulation and experimental results show that the proposed method can significantly improve the uniqueness of the fitted electronic transport parameters.

Carrier Transmission Mechanism-Based Analysis of Front Surface Field Effects on Simplified Industrially Feasible Interdigitated Back Contact Solar Cells

Interdigitated back contact (IBC) n-type silicon solar cells with a different front surface layer doping concentration were fabricated and studied and the influence of the front surface doping level was analyzed via simulation (PC1D). The IBC cells were processed by industrially feasible technologies including laser ablation and screen printing; photolithography was not used. A maximum efficiency of up to 20.88% was achieved at an optimal front surface field (FSF) peak doping concentration of 4.8 × 1019 cm−3 with a sheet resistance of approximately 95 Ω/square, corresponding to Jsc = 40.05 mA/cm2, Voc = 671 mV and a fill factor of 77.70%. The effects of the front surface doping level were studied in detail by analyzing parameters related to carrier transmission mechanisms such as minority carrier concentration, minority carrier lifetime and the saturation current density of the FSF (J0e). The influence of the front surface recombination velocity (FSRV) on the performance of IBC solar cells with different FSF layer doping concentrations was also investigated and was verified by examining the variation in the minority carrier density as a function of the distance from the front surface. In particular, the impact of the FSF doping concentration on the Jsc of the IBC cells was clarified by considering carrier transmission mechanisms and the charge-collection probability. The trends revealed in the simulations agreed with the corresponding experimental data obtained from the fabricated IBC solar cells. This study not only verifies that the presented simulation is a reasonable and reliable guide for choosing the optimal front surface doping concentration in industrial IBC solar cells but also provides a deeper physical understanding of the impact that front surface layer doping has on the IBC solar cell performance considering carrier transmission mechanisms and the charge-collection probability.

Dependence of the Optimization of the Front Grid Design in Passivated Emitter and Rear Contact c-Si Solar Cells on the Finger Width and the Aspect Ratio

In this research, modeling was performed to optimize the grid of the front surface of a solar cell with the passivated emitter and rear contact (PERC) structure by considering the recombination characteristics. The front surface recombination velocity can be reduced in two main ways. The first method is to reduce the emitter Auger recombination by lowering the surface doping concentration during emitter formation, and the second method is to reduce the recombination that occurs at the surface when the electrode and the silicon are in contact, which is called metal-induced recombination and is represented by J0.metal. Because J0.metal increases in proportion to the area of the front electrode, minimizing the finger width and number by optimizing the electrode design is important. Therefore, the front electrode grid should be designed considering the emitter characteristics, J0.metal, according to the number of fingers and the resistance. In this research, the front grid of the solar cell was optimized via modeling using equations to calculate the number of fingers and the resistance. According to the finger width, the number of busbars, the sheet resistance, the aspect ratio, and the number of fingers corresponding to the maximum efficiency were identified. As a result, this modeling enabled us to optimize the front grid to the desired conditions, and we found that an increase in the number of busbars plays an important role in improving the efficiency of solar cells. In addition, the efficiency change with increasing number of busbars can be seen to be affected by the width of the finger and the resolution of the printed finger rather than the aspect ratio.

Electronic transport characterization of B+ ion-implanted silicon wafers with nonlinear photocarrier radiometry

A nonlinear photocarrier radiometry (PCR) based quantitative defect characterization method is applied to determine the electronic transport parameters of the implantation layer of B+ ion-implanted silicon wafers with different implantation doses. A rigorous two-layer nonlinear PCR model is employed to fit the experimental modulation frequency dependences of PCR amplitude and phase to determine the transport parameters, that is, the carrier lifetime, carrier diffusion coefficient, and front surface recombination velocity of the implantation layer via multiparameter fitting. In the multiparameter fitting, the effects of the implantation layer thickness determination on the extraction of the electronic transport properties of the implantation layer are discussed via setting the thickness as a free parameter in the multiparameter fitting and fixed parameters determined by Monte Carlo based TRIM calculation. The fitted implantation layer thicknesses are in good agreement with that determined via TRIM calculation with a modified electronic damage threshold. Monotonic dependences of the transport properties of the implantation layers on the implantation dose are observed, and the effects of impurity density on the transport properties of the implantation layers are discussed. Good agreements between the experimental implantation dose dependence of the nonlinearity coefficient and corresponding theoretical calculations with the determined transport parameters are obtained. These results show that the two-layer nonlinear PCR model is accurate for quantitatively characterizing the transport properties and thickness of the ion-implantation layers of silicon wafers, and the nonlinear PCR technique is appropriate for precise defect characterization in the semiconductor manufacturing processes.

Comparative study of different silicon oxides used as interfacial passivation layer (SiNy:H / SiOx /n+-Si) in industrial monocrystalline silicon solar cells

Ultrathin silicon oxide (SiOx) is used as a passivating and tunneling layer in high efficiency passivated contact silicon (Si) wafer solar cells. In this work, the emitter surface passivation quality using a low-cost, low-temperature (40 °C), non-acidic and safe chemical oxide passivation process (named as NCPRE-oxide) grown using sodium hypochlorite solution is compared with other existing oxide growth or deposition processes such as dry thermal oxide, Radio Corporation of America standard clean-2 (RCA-2) chemical oxide, nitric acid based oxide, sulphuric acid based (Piranha) oxide, ozone based oxide and deposited oxide by plasma enhanced chemical vapour deposition on standard 6-inch textured Si wafers. All the oxides layers are capped with hydrogenated amorphous silicon nitride (SiNy:H) improve passivation of the n+-type Si surface. There is a substantial improvement in the effective minority carrier lifetime (τeff) for SiOx/SiNy:H stack on the phosphorous diffused pyramidal textured Si surface. Further, to compare the influence of NCPRE-oxide process with other oxide processes on the electrical performance of the final device, these different processes were included in the fabrication of large area industrial aluminum-back surface field (Al-BSF) solar cells. A comprehensive analysis based on ellipsometry for film thickness measurement, τeff measurement, cell current-voltage characteristics, photoluminescence imaging, internal quantum efficiency mapping, and front surface recombination velocity measurement is presented. The NCPRE-oxide process resulted in a similar improvement in passivation and cell efficiency as other oxide processes for Al-BSF cells. In addition, its low-cost, low thermal budget, easy waste disposal, and single-component nature make it viable for industrial scale implementation.

26.1%‐efficient POLO‐IBC cells: Quantification of electrical and optical loss mechanisms

AbstractWe present experimental results for interdigitated back contacted (IBC) solar cells with passivating POLO contacts for both polarities with a nominal intrinsic poly‐Si region between them. We reach efficiencies of 26.1% and 24.9% on a 1.3 Ω cm and 80 Ω cm p‐type FZ wafer and 24.6% on a 2 Ω cm n‐type Cz wafer, respectively. The initially measured implied efficiency potentials of the cells after passivating the surfaces are very similar, namely, 26.8%, 26.8%, and 26.4%, respectively. We attribute the difference between the efficiency potential and the final current‐voltage measurement to degradation, perimeter, and series and shunt resistance losses, which we quantify by lifetime measurements. With these measurements in combination with a finite element simulation, we determine the surface recombination velocity in the nominal intrinsic poly‐Si region to be in the range from 13 to 21 cm s−1. Using the same approach, we analyze the increase of the front surface recombination velocity during cell processing from 2 to 10 cm s−1 for the 1.3 Ω cm and from 0.5 to 2.3 cm s−1 for the 80 Ω cm. This leads to the fact that cells fabricated on lowly doped bulk material are more vulnerable to a process‐induced degradation of the surface passivation quality. We further determine the theoretical limits of the cells by firstly idealizing the recombination (28% for 1.3 Ω cm and 28.2% for 80 Ω cm) and secondly also idealizing the optics of the solar cells (29.4% and 29.5%).

Theoretical study on influence of photon reabsorption on photocarrier radiometric characteristics of silicon wafers

In microelectronic and photovoltaic industry, semiconductors are the base materials in which impurities or defects have a serious influence on the properties of semiconductor-based devices. The determination of the electronic transport properties, i.e., the carrier bulk lifetime (&lt;inline-formula&gt;&lt;tex-math id="M41"&gt;\begin{document}$\tau $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20181889_M41.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20181889_M41.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;), diffusion coefficient (&lt;i&gt;D&lt;/i&gt;) and front surface recombination velocity (&lt;i&gt;S&lt;/i&gt;&lt;sub&gt;1&lt;/sub&gt;), is important in the evaluation of semiconductor materials. In this paper, the influence of reabsorption of spontaneously emitted photons within silicon wafers on conventional frequency domain photocarrier radiometric (PCR) is theoretically analyzed. The model with photon reabsorption, proposed by our previous paper, in which both band-to-band absorption and free carrier absorption are taken into account, is used. It is shown that the influence strongly depends on not only the doping level, but also the excess carrier density and its distribution, which are sensitive to the electronic transport properties. The influences of photon reabsorption on PCR amplitude and phase increase with doping level and carrier lifetime increasing. While, as the diffusion coefficient and the front surface recombination velocity increase, the influence of photon reabsorption on PCR amplitude decreases but on PCR phase increases. If photon reabsorption is ignored in the determination of the electronic transport parameters for high-doping silicon wafers via multi-parameter fitting, there are large errors for the fitted results. For a sample with &lt;inline-formula&gt;&lt;tex-math id="M42"&gt;\begin{document}$\tau $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20181889_M42.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20181889_M42.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; = 50 μs, &lt;i&gt;D&lt;/i&gt; = 20 cm&lt;sup&gt;2&lt;/sup&gt;/s, and &lt;i&gt;S&lt;/i&gt;&lt;sub&gt;1&lt;/sub&gt; = 10 m/s, if the effect of photon reabsorption is ignored, the fitting results with conventional PCR model are 55.66 μs, 19.98 cm&lt;sup&gt;2&lt;/sup&gt;/s, and 11.94 m/s, and the corresponding deviations from the true value are 11.33%, 0.10%, and 19.40%, respectively. In addition, simulation results show the effect of photon reabsorption can be greatly reduced with a suitable filter in front of the detector, while still enabling the majority of the emitted signal to be captured. For example, with a 1100 nm long-pass filter, the fitted results for the same sample above are 51.43 μs, 20.19 cm&lt;sup&gt;2&lt;/sup&gt;/s, and 9.88 m/s with the relative errors of 2.86%, 0.95%, and 1.23%, respectively. It should be pointed out that an infinitely steep cut-on edge of the long-pass filter is assumed in our simulations, while in fact the influences of the filter on PCR signal and the fitted results should be further considered.

Superiority of random inverted nanopyramid as efficient light trapping structure in ultrathin flexible c-Si solar cell

Abstract In this work, random inverted nanopyramids (INPs) are fabricated as light trapping structures on ultrathin c-Si through a simple and cost-effective wet chemical method, followed by a systematic investigation of the photo-capturing properties of INPs combining experiments and simulations. In comprehensive consideration of thickness loss and light trapping performance, random INPs are applied onto 45 μm ultrathin c-Si solar cell and a high short-current density (Jsc) (36.6 mA/cm2) and energy-conversion efficiency (17.0%) are achieved, which are 0.3 mA/cm2 and 0.13% respectively higher than that in micro pyramid textured one, and our electrical simulation also demonstrates that the advantages of INPs are more obvious on thinner c-Si compared with conventional micro pyramids. Finally, through electrical simulation, INPs textured 45 μm c-Si solar cell is expected to have a large improvement room for efficiency by controlling the front and rear surface recombination velocity. All the findings not only offer additional insight into the light-trapping mechanism in the random INPs but also provide controllable and efficient broadband light harvesters for next-generation cost effective flexible photovoltaics.

3D simulations of interdigitated back-contacted crystalline silicon solar cells on thin substrates

Interdigitated back contact technology is a promising candidate to be applied to thin crystalline silicon solar cells because of its simpler one-side interconnection while allowing a more flexible front surface treatment. This work explores the efficiency potential of IBC c-Si solar cells applied to thin c-Si substrates through 3D device simulations. In particular, we explore the impact of substrate thickness and front surface recombination velocity on cell performance with special attention to the different behavior in carrier collection of two different rear-surface doping structures. Firstly, the model is validated by comparing simulation results to a fabricated device on 280 µm-thick substrates with stripe-like p+ and n+ diffusions. It is revealed that efficiencies of 16–17% are reachable for substrates on the 10–15 µm range without changing the technology developed for thick ones. Next, the rear doping structure is modified leading to doped regions just under the metal contacts. This type of structure is expected in solar cells where high-temperature diffusions are replaced by point-like laser doped contacts, which is a feasible alternative to be applied to thin substrates. Simulation results show that diffusion length requirements for those locally-doped structures are more demanding due to the reduction of emitter regions. As a result, very well passivated front and rear surfaces are required to maintain short-circuit current densities to reasonable values. Finally, for both structures open-circuit voltage is kept almost constant with reduced thickness, despite the strong reduction in short-circuit current. Simulations show a reduction of dark saturation current density with substrate thinning due to the redistribution of dark current densities that flow parallel to the device surface.

Estimating various losses in c-Si solar cells subjected to partial shading: insights into J–V performance reduction

This article reports the effect of partial shading (PS) on the electrical output of a solar cell using the two-diode model. The reduction in electrical performance parameters induced by various recombination losses has been explained for c-Si solar cells under the effect of PS. The PS mainly affects the short-circuit current density $$({J}_{\mathrm{SC}})$$ and efficiency $$(\eta )$$ of the solar cells. $${J}_{\mathrm{SC }}$$ and $$\eta $$ decrease from 37.84 to 5.48 mA $$\hbox {cm}^{-2}$$ and from 18.31 to 2%, respectively. Among all the energy losses encountered for PS, spatial relaxation and recombination losses are the dominating factors responsible for the reduction in $${J}_{\mathrm{SC}}$$ . PC1D and Griddler simulations have been performed to evaluate the effect of front surface and bulk recombination. The PC1D simulated external quantum efficiency is governed by the front and back surface recombination velocity and carrier life time of the charge carriers under PS. The power loss ( $${P}_{\mathrm{e}}$$ ) of $${\sim }$$ 34% from the emitter region has been determined by resistance analysis in correlation with the recombination in the emitter region of the solar cells under PS.

Determination of carrier bulk lifetime and surface recombination velocity in semiconductor from double-wavelength free carrier absorption

In microelectronic and photovoltaic industry, semiconductors are the basic materials in which impurities or defects have a serious influence on the properties of semiconductor-based devices. The determination of the electronic transport properties, i.e., the carrier bulk lifetime (τ) and the front surface recombination velocity (S1), is important for evaluating the semiconductor material. In this paper, a method of simultaneously measuring the bulk lifetime and the front surface recombination rate of semiconductor material by using double-wavelength free carrier absorption technique is presented. The effect of the carrier bulk lifetime and the front surface recombination rate on the modulated free carrier absorption signal (Ampratio and Phadiff) are qualitatively analyzed. The process of extracting the bulk lifetime and the front surface recombination rate by the proposed double-wavelength free carrier absorption method are also given. At the same time, the uncertainties of the parameters extracted by this method are calculated and compared with those obtained by the traditional frequency-scan free carrier absorption technique. The results show that the proposed method can significantly reduce the uncertainties of the measurement parameters, especially for the samples with higher surface recombination rate. For the sample with a lower front surface recombination rate (S1=102 m/s), the uncertainty of the carrier bulk lifetime and the front surface recombination velocity obtained by the proposed method are almost in agreement with those obtained by the conventional frequency-scan method. On the contrary, for the samples with higher front surface recombination rate (S1 ≥ 103 m/s), the uncertainties of the carrier transport parameters are much smaller than those from the conventional frequency-scan method. For example, the estimated uncertainty of the carrier bulk lifetime and the front surface recombination velocity for the sample with τ=10 μs and S1=103 m/s are approximately ±5.55% and ±2.83% by the proposed method, which are more improved than ±18.50% and ±31.46% by the conventional frequency-scan method with a wavelength of 405 nm. Finally, we explain the above phenomenon by analyzing the distribution of excess carrier concentration at different pump wavelengths. As the pump wavelength decreases, the more excess carriers are excited near the surface of the sample due to the greater absorption coefficient, and the influence of the surface recombination by the impurities and defects on the signal is more obvious. Therefore, the measurement accuracy of the front surface recombination rate can be improved effectively by using double wavelength pumping.

Simulation and Fabrication of HfO2 Thin Films Passivating Si from a Numerical Computer and Remote Plasma ALD

Recombination of charge carriers at silicon surfaces is one of the biggest loss mechanisms in crystalline silicon (c-Si) solar cells. Hafnium oxide (HfO2) has attracted much attention as a passivation layer for n-type c-Si because of its positive fixed charges and thermal stability. In this study, HfO2 films are deposited on n-type c-Si using remote plasma atomic layer deposition (RP-ALD). Post-annealing is performed using a rapid thermal processing system at different temperatures in nitrogen ambient for 10 min. The effects of post-annealing temperature on the passivation properties of the HfO2 films on c-Si are investigated. Personal computer one dimension numerical simulation for the passivated emitter and rear contact (PERC) solar cells with the HfO2 passivation layer is also presented. By means of modeling and numerical computer simulation, the influence of different front surface recombination velocity (SRV) and rear SRV on n-type silicon solar cell performance was investigated. Simulation results show that the n-type PERC solar cell with HfO2 single layer can have a conversion efficiency of 22.1%. The PERC using silicon nitride/HfO2 stacked passivation layer can further increase efficiency to 23.02% with an open-circuit voltage of 689 mV.

Theoretical study on the influence of photon reabsorption on spatially resolved photocarrier radiometric imaging of silicon wafers

The influence of reabsorption of spontaneously emitted photons within silicon wafers on spatially resolved steady-state photocarrier radiometric (PCR) imaging is theoretically analyzed. A new PCR model with photon reabsorption, in which both band-to-band absorption and free carrier absorption are taken into account, is introduced. It is shown that the influences strongly depend on both the excess carrier density and its distribution, which are sensitive to the doping level, electronic transport properties, sample thickness, and surface topography. If photon reabsorption is ignored in the determination of the electronic transport parameters for high-doping double polished silicon wafers via multi-parameter fitting, the relative errors of the fitted minority carrier lifetime, diffusion coefficient, and front surface recombination velocity could reach 38%, 9.5%, and 24%, respectively.

Pre-wetted treatment for optimized multicrystalline Si wafer texturing and its solar cell efficiency improvement

We report a simple way to optimize texturing of multi-crystalline Si (mc-Si) wafer by pre-wetted surface in the wet etching. In the range of 300–1200 nm, a better texturing surface was achieved with average reflectivity 40 mA) and efficiency (0.1% absolute) has been achieved compared with control cell without deterioration of other performance parameters (such as open circuit voltage and fill factor). Internal quantum efficiency measurement also proves the lower front surface recombination velocity of pre-wetted based solar cell. We believe that the improved wetting surface property of multi-crystalline Si prior to etching is important for optimizing texturing process, and pre-wetted treatment is easy integrated for industrial mass production.

Accurate determination of electronic transport properties of silicon wafers by nonlinear photocarrier radiometry with multiple pump beam sizes

In this paper, photocarrier radiometry (PCR) technique with multiple pump beam sizes is employed to determine simultaneously the electronic transport parameters (the carrier lifetime, the carrier diffusion coefficient, and the front surface recombination velocity) of silicon wafers. By employing the multiple pump beam sizes, the influence of instrumental frequency response on the multi-parameter estimation is totally eliminated. A nonlinear PCR model is developed to interpret the PCR signal. Theoretical simulations are performed to investigate the uncertainties of the estimated parameter values by investigating the dependence of a mean square variance on the corresponding transport parameters and compared to that obtained by the conventional frequency-scan method, in which only the frequency dependences of the PCR amplitude and phase are recorded at single pump beam size. Simulation results show that the proposed multiple-pump-beam-size method can improve significantly the accuracy of the determination of the electronic transport parameters. Comparative experiments with a p-type silicon wafer with resistivity 0.1–0.2 Ω·cm are performed, and the electronic transport properties are determined simultaneously. The estimated uncertainties of the carrier lifetime, diffusion coefficient, and front surface recombination velocity are approximately ±10.7%, ±8.6%, and ±35.4% by the proposed multiple-pump-beam-size method, which is much improved than ±15.9%, ±29.1%, and &amp;gt;±50% by the conventional frequency-scan method. The transport parameters determined by the proposed multiple-pump-beam-size PCR method are in good agreement with that obtained by a steady-state PCR imaging technique.