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Effect of lights with various wavelength on the defect generation in reactive plasma deposition (RPD) process is studied using capacitance–voltage analysis. Indium-tin oxide (ITO) deposition by RPD dramatically decreases the minority carrier lifetime and deteriorates the solar cell performances. The wavelength of light which arrives at the SiO2/Si interface and Si crystal is controlled by varying the SiO2 thickness in SiO2/Si samples. Thick SiO2 layer with above 10 nm prevents the penetration of many ions into the SiO2/Si interface layer, and the only effects of light wavelength on the defect formation are obtained. When SiO2 thickness are 10–600 nm, a large number of defects of the order of 1012 eV−1 cm−2, mid gap energy of Si, are generated by ITO-RPD independent of SiO2 thickness. These defects are expected to be recombination centers. These SiO2 thicknesses are enough thick to completely absorb the light below-110-nm-wavelength. The results suggest that the light of longer wavelength than 110 nm mainly contributes to the defect formation in RPD process. On the other hand, in the case of 500 µm thick SiO2, the generated defects are significantly decreased by one order of magnitude (or decreased to the order of 1010 eV−1 cm−2) small amount of defect is generated. This thick SiO2 prevents the penetration of light with below 180 nm wavelength into the Si. Therefore, the light with around 110–180 nm wavelength, which are generated by Ar and/or O2 plasma in RPD process, mainly forms the recombination-active defects.

This paper presents analytical results for improving crystalline Si solar cells, analyzed using our knowledge in radiation-induced defects in Si. This study suggests that key issues for realizing higher performance Si solar cells are decrease in carbon concentration of less than 1 × 1014 cm−3. Defect introduction rates of Bi–O2i center induced by light illumination are compared with those of Bi–Oi center induced by 1-MeV electron irradiations in this study. Surface recombination velocity degradation of Si solar cells due to 1-MeV electron irradiations is compared with surface degradation of Si solar cells under light illumination by considering Pb center generation.

The behavior of oxide precipitates during solar cell fabrication processes and the resulting effect on device performance have been investigated by transmission electron microscopy (TEM) observation. Samples were prepared with different carbon concentration and under different crystal growth conditions, namely using the conventional and an advanced process. The density of oxide precipitates increased monotonically with the carbon concentration, while the cell efficiency improved with decreasing oxygen precipitate density. When the carbon concentration was reduced to below 1016 cm−3, the oxide precipitates grew largely and dislocations were introduced. TEM observations confirmed that the morphology of the oxide precipitates clearly differed depending on the crystal growth conditions. Precipitates grown in platelet form introduced high density dislocations in their surroundings, while the dislocation density was relatively lower around polyhedral-type precipitates. These results thus reveal that oxygen precipitation can be controlled by varying the crystal growth conditions, possibly contributing to the production of high-efficiency solar cells.

We have investigated the chemical and electrical properties of a thin SiO2/TiO2 stacking layer deposited on n-Si and heavily phosphorus-doped n++ Si substrates to elucidate effects of phosphorus doping of Si absorbers on the band alignment and electrical performance of a SiO2/TiO2 stack-based electron-selective contact deposited on the differently doped Si substrates. From our XPS study, we show a shift of the TiO2 energy levels up to ~0.13 eV with respect to those of Si as the doping level of Si substrates changes. We also show that the conduction band offset of the SiO2/TiO2 stacking layer at the interface with the n++ Si substrate seems to smaller than that of the SiO2/TiO2 stacking layer at the interface with n-Si substrate. Finally, from our electrical transport measurements, we could conclude that the thinner tunneling barrier, the increased electron density in front of the SiO2 layer in the n++ Si surface, and/or the reduced barrier height by heavy doping, seem to enhance the majority electron transport property of the SiO2/TiO2/n++ Si samples compared to that of the SiO2/TiO2/n-Si samples.

Efficiency potential of crystalline Si solar cells is analyzed by considering external radiative efficiency (ERE), voltage, and fill factor losses. Crystalline Si solar cells have an efficiency potential of more than 28.5% by realizing ERE of 20% from about 5% and normalized resistance of less than 0.05 from around 0.1. Nonradiative recombination losses in single-crystalline and multicrystalline Si solar cells are also discussed. Especially, nonrecombination and resistance losses in multicrystalline Si solar cells are shown to be higher than those of single-crystalline cells. Importance of further improvement of minority-carrier lifetime in crystalline Si solar cells is suggested for further improvement of crystalline Si solar cells. High efficiency of more than 28.5% will be realized by realizing high minority-carrier lifetime of more than 30 ms. Key issues for those ends are reduction in carbon concentration of less than 1 × 1014 cm−3, oxygen precipitated and dislocations even in single-crystalline Si solar cells, and reduction in dislocation density of less than 3 × 103 cm−2 in multicrystalline Si solar cells.

The electron-beam-induced-current (EBIC) technique using scanning transmission electron microscopy (STEM) has been applied to the observation of grain boundaries in polycrystalline Si. It was shown that defects in thin regions can disappear or give bright contrast in EBIC images, but are distinct in STEM images. For the sample with a high carrier concentration, the surface effect was shown to dominate the EBIC current for a thin region. The bright contrast of the defects observed for the sample with a low carrier concentration can be attributed to the combination of the diffraction effect and the built-in electric field induced by the depletion of the entire thickness.

We review recent progresses on in-situ observation of lattice relaxation of III-V lattice-mismatched system and analyses of defect properties in III-V-N solar cell materials. We found that there were five phases during the InGaAs growth on GaAs substrate. The transition point of the dominant dislocation behavior could be determined precisely. We also found that compositionally step-graded InGaAs/GaAs(001) buffers with overshooting (OS) layers were effective to control the strain of the top layer from tensile to compression. To understand the defect properties that dominate the electrical property of CBE-grown GaAsN films, we characterized deep levels in CBE-grown GaAsN films by DLTS. In this characterization, a well-known electron trap E1 (Ec-0.33eV) center in n-GaAsN and p-GaAsN was confirmed to be non-radiative recombination center by using double-carrier pulse DLTS.

III-V compound multi-junction solar cells have high efficiency potential of more than 50% due to wide photo response, while limiting efficiencies of single-junction solar cells are 31-32%. In order to realize high efficiency III-V compound multi-junction solar cells, understanding and controlling imperfections (defects) are very important. This paper reviews fundamentals of defects and defect management for III-V compound materials, single-junction, multi-junction, space and concentrator solar cells.

Microscopic and spectroscopic photoluminescence (PL) mapping was performed on a region including intra-grain defects in multicrystalline silicon wafers in the temperature range between 15 and 300 K, and the temperature dependence of PL spectra from the region was studied. We confirmed that the origin of deep-level emission with an intensity maximum at 0.78 eV at room temperature was different from that of dislocation-related lines at low temperature. We believe that the 0.78 eV emission is associated with oxygen precipitation, and that the intra-grain defects are dislocation clusters decorated with not only heavy-metal but also oxygen impurities.

The in situ X-ray reciprocal space mapping (in situ RSM) of symmetric diffraction measurements during lattice-mismatched InGaAs/GaAs(001) growth were performed to investigate the strain relaxation mechanisms. The evolution of the residual strain and crystal quality were obtained as a function of InGaAs film thickness. Based on the results, the correlation between the strain relaxation and the dislocations during the film growth were evaluated. As a result, film thickness ranges with different relaxation mechanisms were classified, and dominant dislocation behavior in each phase were deduced. From the data obtained in in situ measurements, the quantitative strain relaxation models were proposed based on a dislocation kinetic model developed by Dodson and Tsao. Good agreement between the in situ data and the model ensured the validity of the dominant dislocation behavior deduced from the present study.

The amount of residual carbon in the GaAsN film deposited by chemical beam epitaxy (CBE) is decreased by the flow rate modulation growth method (FM-CBE). The number of carbon atoms remained in the grown film increases as the growth temperature decreases. At low temperatures below 440°C, the carbon atoms are mainly originated from the nitrogen source gas mono-methylhydrazine. However, increasing the substrate temperature during the growth causes the deterioration of film qualities and the high growth temperature is not the solution for reducing the impurities. On the other hand, by intermitting the supply of gallium source triethylgallium while the arsenic and nitrogen sources are continuously supplied, the carbon concentration drastically decreases as compared with that grown by the conventional CBE growth. The results of temperature programmed desorption and ab initio calculations suggest that the desorption of adsorbates that contain C atom, such as, NHCH3, is enhanced by the FM-CBE growth, resulting in the decrease of the residual C concentration.

Physical properties of multiple-energy B-ion implanted C60 thin films were investigated for various doses. Fourier Transform Infra-red Spectroscopy (FTIR) results indicate the structural transformation of C60 to amorphous carbon phase during implantation. The conductivity type of the implanted films is found to be p-type and the conductivity measurements reveal a dramatic increase in the conductivity with ion implantation. Temperature dependent conductivity shows the semiconducting nature of the B-ion implanted films. The optical absorption coefficient and optical gap of the implanted films have been observed as a function of B-ion dose. Measurements on implanted films subjected to thermal annealing indicate the removal of the defects caused during the implantation. Ion implantation-induced defects are found to partially annihilate with the annealing temperature. Electrical conductivity and optical gap are determined in the post-implanted films. The observation of the systematic increase in the conductivity of the annealed films is due to the removal of the defects and the formation of defect free boron impurity acceptor.

The important intermediates in the Ti plasma-enhanced CVD using TiCl4/Ar/H2 are investigated by ab initio molecular orbital (MO) calculations. From the experimental point of view, it is pointed out that'TiCls is a key species for the Ti deposition reaction. So, its reactivity with the Si and SiO2 substrates is estimated theoretically from the stabilization energy. The difference of the stabilization energies of TiCl3 between them, which is 12.3kcal/mol in Hartree-Fock level calculations with using the on-top deposition reaction model, indicates a longer existing time by the factor of 102 on SiO2 than on Si. In addition to these calculations, the stabilization energies on the suicide substrates are also calculated and compared with the results on the Si and Si02 substrates. But other reaction paths may have to be considered because the growth rates of Ti thin films onto between Si and SiO2 don't necessarily coincide with the tendency of calculated results.

Copper films are etched at a low temperature of 60 °C using a Cl2 plasma etching method with IR light irradiation. The etch rate is as high as 1 μm/min. The anisotropic Cu line patterns are obtained independent of the Cl2 gas flow rate and the etching pressure conditions. Moreover, there is no corrosion on the etched sample.

Role of in-situ heavy As doping in Si selective growth is studied using the SiH2Cl2/H2/HCl/AsH3 gas system. By increasing AsH3 flow rate, the growth rate decreases in proportion to In (AsH3 flow rate). This result is explained well using a Frumkin-Temkin adsorption model. The As concentrations in grown films depend on surface orientation. Moreover, the maximum As concentration is about ten times lower than the solubility limit at a given temperature. These results are able to be explained qualitatively, if equilibrium concentrations of impurities at the Si(100), the Si(111), and the bulk are assumed to be different from one another, and that the concentration at the surface is frozen in the grown film.

β -SiC is grown on a Si(100) substrate by chemical vapor deposition method under reduced pressure using SiH2 Cl2/C3H8/HCl/H2 gas system. The addition of HCI to SiH2 Cl2/C3H8/HCl/H2 gas system makes it possible to obtain a stoichiometric β -SiC film with a mirror surface at low growth temperature of 900°C. Moreover, β -SiC selective growth on Si(100) surface, with no nucleation on SiO2 surface, is achieved. According to the increase of the HCI flow rate, the density of SiC nucleation on SiO2 surface is greatly decreased. Perfect selective β -SiC film is obtained for HCI concentrations greater than 1.2%.

Silicon vapor phase epitaxial growth with SiH2Cl2 is theoretically studied. The optimized geometries and total energigs of the species, generated from SiH2Cl2, are calculated by using ab initio molecular orbital method. As the intgraction between silicon surface and SiCl2 the charge transfer is considered. Based on the computational result that SiCl2 - has the lower total energy than SiCl2, a new adsorption mechanism, named, charge transfer adsorption, is p~oposed. By using this charge transfer adsorption followed by the surface reaction at the hollow bridge site, the epitaxial growths on the silicon (001), (111), and (110) surfaces are discussed.