Koichi Kamisako

Photoluminescence analysis of intragrain defects in multicrystalline silicon wafers for solar cells

Structures of intragrain defects were investigated by photoluminescence (PL) mapping tomography in multicrystalline silicon wafers for solar cells. PL dark patterns were observed in short minority carrier diffusion length regions, and we confirmed that the patterns came from the intragrain defects. The tomography revealed that the defects have planelike structures extended to the crystal growth direction. We also found that the growth conditions affect the structures of the defects: slower solidification leads to larger defects with lower density. Origins of the defects were analyzed by low-temperature PL spectroscopy, electron backscatter diffraction pattern measurement and etch-pit observation. We concluded that the defects are metal contaminated dislocation clusters which originate from small-angle grain boundaries.

Characterization of CVD-TiN films prepared with metalorganic source

This paper investigates the structural and electrical properties of TiN films prepared by metalorganic chemical vapor deposition (MOCVD) using a mixture of tetradimethylamino-titanium (Ti(N(CH3)2)4) and NH3 gases. The deposited films changed from a metallic gray to a gold color at a substrate temperature of 300~580°C. The film resistivity decreases with increasing substrate temperature to 8.4×102 µΩcm at 580°C. The preferred orientation was (111) at temperatures over 400°C.

Stress in Pulsed-Laser-Crystallized Silicon Films

Stress in pulsed-laser-crystallized silicon films was investigated using high-resolution Raman scattering measurements. Film stress was evaluated based on the peak shift of transverse optical (TO) phonon of crystalline silicon in Raman scattering spectra. The tensile stress in laser-crystallized 50-nm-thick silicon films on glass substrates increased from 3.5×108 Pa to 9.7×108 Pa as the film deposition temperature increased from 200°C to 480°C. The peak shift of laser-crystallized microcrystalline silicon (µc-Si) films revealed that the tensile stress introduced by laser irradiation was 2.3×108 Pa at most. These results indicate that the strong tensile stress is introduced by the silicon film deposition rather than by the pulsed-laser crystallization. Also, the authors demonstrate that pulsed-laser crystallization maintains the existing stress at the growth initiation sites in the bottom region of silicon films.

Evaluation of electric motor and gasoline engine hybrid car using solar cells

Abstract We evaluated the utility of a hybrid car in which both power sources of an electric motor and a gasoline engine are used and solar cells are settled on the roof and the bonnet. An array of 1.6 kW solar cells was installed on the top of a building to charge the batteries by solar energy. Though the capacities of the electric motor and batteries are half compared with conventional electric vehicles, we confirmed that this hybrid car has sufficient utility for practical use. The whole electric energy consumed in a day can be supplied by 1.6 kW solar cell system.

Conceptual considerations on PV systems composed of AC modules

AC module technology has become popular and a number of AC module types are commercially available. Although their specifications are clear, it seems that their technological meaning has not yet been well developed. Therefore, the authors tried to create the total concepts of PV systems composed of AC modules. They are abbreviated AC module-composed PV system or ACM-PV. In the paper, the possible structural configurations of simple AC modules and battery integrated ones are classified in principle. System categories are also classified to show their total concept. Necessary electrical terminals and interfaces, voltage matching method between inverter and PV part, and AC module testing methods are also discussed.

Residual Stress of a-Si1-xNx:H Films Prepared by Afterglow Plasma Chemical Vapor Deposition Technique

Relationships between residual stress and other film properties of amorphous silicon nitride films deposited by microwave afterglow plasma of NH3 and by photochemical vapor deposition have been studied. There are differences in the dependence of N-H and Si-H bond density and residual stress on the film composition between the films deposited by the two methods. The residual tensile stresses in both films, however, reach a maximum value of 7-9×109 dyn/cm2 when the N-H bond density is nearly equal to the Si-H bond density. The residual stress can be reduced by adjusting the N-H and Si-H bond density while maintaining the high breakdown field strength and high resistivity.

Effect on Al2O3 Doping Concentration of RF Magnetron Sputtered ZnO:Al Films for Solar Cell Applications

Al-doped ZnO (AZO) films were deposited onto glass substrates by RF magnetron sputtering for solar cell applications. The effects of the Al2O3 doping concentration on the structural, electrical, and optical properties of the AZO films were investigated. As the Al2O3 doping concentration was increased to 4.0 wt %, X-ray diffraction (XRD) showed a deterioration in the (002) peak intensity and a shift towards a higher angle. The best electrical properties (ρ= 9.8×10-4 Ω cm, µH = 22 cm2 V-1 s-1, and ne = 2.89×1020 cm-3) were obtained in the AZO sample containing 2 wt % Al2O3. Optical transmission >83% in the visible range was also observed and the optical bandgap was increased to 3.63 eV at an Al2O3 concentration of 4 wt %. For photoluminescence (PL) spectra, one UV emission peak at approximately 3.2 eV and a broad peak in the visible range from 2.3 to 2.7 eV were observed at Al2O3 doping concentrations ranging from 0–2.0 wt %. Blue emission at 2.67 eV, which indicates a non-stoichiometric structure, was only observed in the 4 wt % doped AZO films.

High-Rate Selective Etching of a-Si:H Using Hydrogen Radicals

A high-rate selective etching method of hydrogenated amorphous silicon (a-Si:H) using hydrogen radicals is presented. A very high etch rate of 2.7 µm/min was obtained at 50°C using a microwave hydrogen afterglow method. However, amorphous silicon nitride ( a-SiN1.2:H), silicon oxide ( SiO2), silicon carbide ( a-SiC0.5:H), and Al films were not etched under the same conditions. These results suggest that high-rate selective etching of a-Si:H can be achieved using hydrogen radicals. This method is suitable for the fabrication of large-area devices.

New generation of PV module rating by LED solar simulator - A novel approach and its capabilities

Authors have been proposing a novel approach by employing light emitting diodes (LED) as a light source with discrete-wavelength spectrum. LEDs have a number of practical advantages. Each of different color LED lights works as sampling wavelength for scanning the spectral sensitivity of PV module by modulating intensity of each spectral component in a sequential order. Even by a limited number of sampling wavelengths, full range spectral response can be estimated easily by newly developed fitting model. Then AM 1.5 spectrum of IEC 60904-3 is applied to obtained response curve to give STC rating. 3 types of experimental LED arrays have been developed since early 2003: i.e., Mk-1 to Mk-3. Under these experiments, spectral characteristic fitting model has been successfully developed. Nonuniformity of ±2% has been achieved by MK-2, satisfying Class A uniformity specification. The latest Mk-3 achieved 0.42 sun in October 2006. Its array consists of 2304 elements of high-brightness LEDs (HB-LED) in total provided with blue (473 nm), red (643 nm) and 2 elements of infrared (845 nm) for 1 unit. The following experimental results are presently attained for a one-cell module of 100 mm × 100 mm of single crystalline silicon with Pmax at STC of 1.553 W calibrated under Class A simulator: i.e., ISC=3.757 A (+0.080 %); VOC=0.601 V (−0.121 %); Pmax=1.660 W (+4.312 %); Ipmax=3.454 A (+2.493 %); Vpmax=0.469 V (+1.74 %); FF=71.74% (+4.73 %). Values in parentheses are corresponding to % errors for reference values. It is felt that present result has been already reaching practically usable level. If 6 LEDs allocation pattern is adopted, spectral response fitting formula will be very much improved.

Tantalum oxide films formed by UV photo-CVD using ozone and TaCl5

A new UV photo-CVD is developed to fabricate thin films of high-dielectric-constant Ta2O5. The significant features of the new photo-CVD are the UV 254 nm irradiation and the use of pure O3 as an oxidant source. The as-grown films obtained at a low deposition temperature of 300°C show very low leakage current and remarkably good step coverage. UV irradiation during CVD is essential to improve the resistivity and dielectric breakdown strength of the film. This CVD method and understanding of the related mechanism may be applicable to fabrication technology of future VLSIs.