Numerical analysis of bulk diffusion length in thin-film c-Si solar cells

We propose a novel technique of determining relationship between effective and bulk diffusion length of single-crystalline Si (c-Si) thin-film solar cells using two-dimensional device simulator. In addition, bulk diffusion length was obtained using the result of the simulation. Effective diffusion length was measured by LBIC method in order to presume bulk diffusion length of c-Si thin film. We obtained 6.7 μm for effective diffusion length of c-Si thin-film solar cell whose thickness was about 7 μm. We compared the result of measurement and simulation, bulk diffusion length of c-Si thin film prepared by CVD method was estimated more than 30 μm and recombination velocity was presumed <10⁴ cm/s for front surface and 10³ cm/s for rear surface of the cell.     

Analysis of minority carrier diffusion length in SiC toward high quality epitaxial growth

Homoepitaxy of 4H-SiC grown by a horizontal hot-wall chemical vapor deposition and the minority carrier diffusion length were studied. With the addition of HCl during the etching and the epitaxy, an optimum growth window on the C face became wide. Minority carrier diffusion length in SiC epilayers was evaluated by a line-scanning electron-beam-induced current method.     

Comparative analysis of coauthorship networks of different domains: The growth and change of networks

Many studies have tried to describe patterns of research collaboration through observing coauthorship networks. Those studies mainly analyze static networks, and most of them do not consider the development of networks. In this study, we turn our attention to the development of personal collaboration networks. On the basis of an analysis from two viewpoints, i.e., growth in the number of collaborating partners and change in the relationship strength with partners, we describe and compare the characteristics of four different domains, i.e., electrical engineering, information processing, polymer science, and biochemistry. This revised version was published online in June 2006 with corrections to the Cover Date.     

An analysis of the connection between researchers’ productivity and their co-authors’ past attributions,including the importance in collaboration networks

Although many studies have analyzed the “synchronic” correlation of properties between authors and their co-authors, the “diachronic” correlation of properties, i.e., the correlation between their subsequent and precedent activity, has not yet been sufficiently studied using quantitative methods. This study pays attention not only to productivity but also the importance in the collaboration network as a measure of the researcher’s activity, and clarifies whether there is any connection between (i) the researcher’s activity subsequent to a collaboration and (ii) the collaborator’s precedent activity, aiming at deriving knowledge about the diachronic effect of collaborators.     

Effect of hydrogen plasma treatment on grain boundaries in polycrystalline silicon solar cell evaluated by laser-beam-induced current

Effects of hydrogen plasma treatment on minority carrier diffusion length and recombination velocity at grain boundaries in polycrystalline silicon solar cells have been evaluated by the scanned laser-beam-induced current technique. We have successfully evaluated the two-dimensional minority carrier diffusion length. On the basis of the evaluated diffusion length, the recombination velocity at the grain boundaries was obtained. The recombination velocity was improved by the hydrogen plasma treatment from 15,000—20,000 to 5000—10,000 cm/s. It was quantitatively confirmed that the hydrogen plasma treatment is very effective in both grains and grain boundaries.     

Multiple regression analysis of a patent’s citation frequency and quantitative characteristics: the case of Japanese patents

Although many studies have been conducted to clarify the factors that affect the citation frequency of “academic papers,” there are few studies where the citation frequency of “patents” has been predicted on the basis of statistical analysis, such as regression analysis. Assuming that a patent based on a variety of technological bases tends to be an important patent that is cited more often, this study examines the influence of the number of cited patents’ classifications and compares it with other factors, such as the numbers of inventors, classifications, pages, and claims. Multiple linear, logistic, and zero-inflated negative binomial regression analyses using these factors are performed. Significant positive correlations between the number of classifications of cited patents and the citation frequency are observed for all the models. Moreover, the multiple regression analyses demonstrate that the number of classifications of cited patents contributes more to the regression than do other factors. This implies that, if confounding between factors is taken into account, it is the diversity of classifications assigned to backward citations that more largely influences the number of forward citations.     

Real-space investigation of a transverse wave in a liquid system generated by a molecular-dynamics simulation

We have invented a simple intuitive method for describing the existence of microscopic transverse wave in a liquid system produced by molecular-dynamics simulations. The method is based on an idea of using a velocity field which is determined by the velocity of atoms in liquids. One of the significant advantages of our method over a conventional method is that the waves are investigated in real space rather than in wavenumber space. This will help to visualize microscopic waves by computer graphics. We have applied the method to liquid tin at three thermodynamic states generated by ab initio molecular-dynamics simulations and found that it can distinguish whether the liquids have transverse waves or not in the same way as the conventional method. We have also shown that the velocity autocorrelation function consists of the transverse and longitudinal parts.     

1.14 b/s/Hz spectrally efficient 50/spl times/85.4-Gb/s transmission over 300 km using copolarized RZ-DQPSK signals

1.14 b/s/Hz spectrally efficient 50/spl times/85.4-Gb/s copolarized return-to-zero differential quaternary phase-shift keying (RZ-DQPSK) signals have been transmitted over 300 km of nonzero dispersion-shifted fiber (NZ-DSF), using optical prefiltering and conventional C-band erbium-doped fiber amplifier (EDFA) repeaters. In this study, in order to enhance the spectral efficiency, the impact of optical prefiltering on the RZ-DQPSK signal was experimentally investigated in comparison to the DQPSK signal, and we found that the RZ-DQPSK signal had better sensitivity with almost the same nonlinear tolerance than the DQPSK signal even with 65-GHz bandwidth optical prefiltering.     

Diversity of fields in patent citations: synchronic and diachronic changes

While there is a large body of research analyzing the overall structure of citation relations for patents, there has been very little research seeking to clarify the characteristics of fields relating to the diffusion of technology through observing the citation network surrounding each patent individually and tracing its growth. This study focused on the classifications assigned to patents and examined the diversity of the fields of patents citing each patent from the following two perspectives: (1) expected values for growth in the number of citing fields, when regarding the observation period as being in a synchronic state and assuming that the strength of connections between each patent and citing fields is constant; and (2) empirical values for growth in the number of citing fields according to the increase in the cumulative number of citations over time. From the results, it was confirmed that the strength of potential connections between each patent and citing fields changes over time. Especially in the fields of “chemistry; metallurgy” and “physics,” the following change is considerable: a patent tends to receive citations repeatedly from a limited range of fields for a while, but later comes to be cited by various fields.     

Estimation of the compositional gradient in a PVC/PMMA graded blend prepared by the dissolution-diffusion method

We reported a new preparation method in the previous paper, by which an excellent graded polymer blend was simply prepared. In this report, we propose a new model for the dissolution-diffusion process. The model was derived by obeying Fick's second law for diffusion and by assuming that the evaporation of the solvent in PMMA solution during the diffusion could be neglected. We then proved that this model was applicable to the graded structure of a PVC/PMMA graded blend. Further, it was confirmed that the dissolution rate of PVC into PMMA solution remained constant during preparation. Thus, our model was found to be reliable. However, while the apparent diffusion coefficients (D_ABs) of PVC in 0.183 and 0.274 ml/cm² of the initial solution volumes were equal to each other, they were larger than the D_AB in 0.091 ml/cm² of the initial solution volume. Thus, the effects of PVC concentration dependency of D_AB and changing of PMMA concentration in the solution on D_AB were discussed, because all of the D_ABs should be equal to each other. Then, our model was modified as follows. We considered that PVC finished diffusing below a PMMA concentration of 0.18 g/ml, because the diffusion coefficient of PVC immediately increased at a higher PMMA concentration. Then, the solution layer was shrunk to about 1/6, in order to form a blend film. Thus, it was found that the D_AB in each of the initial solution volumes was 4.2 ± 0.25 × 10⁻⁸ cm²/s. Further, the D_ABs estimated by diffusion thickness method, were from 1.5 to 3.5 times larger than those estimated by our model. Therefore, it was proved that our modified model was applicable to the experimental data.