Development of low cost production technologies for polycrystalline silicon solar cells

To develop a technology of forming grooves for low cost cell production, a multi-blade wheel grinding method was investigated. The process time of groove formation on the surface of 10 × 10 cm² polycrystalline silicon substrate was reduced to 30 s by a newly developed high-speed groove formation machine. Simultaneous formation of junction and anti-reflection coating by atmospheric pressure chemical vapor deposition (APCVD) technique was also investigated. For electrodes formation process, single firing method for both side electrodes made possible to simplify the firing process and to speed up from a conventional speed of 400 mm/min to 5000 mm/min.     

Influence of the substrate's surface structure on the mechanism and kinetics of the electrochemical UPD formation of a copper monolayer on gold

The copper electrodeposition process was studied onto different gold substrates, single crystal (1 1 1) and polycrystalline, using electrochemical techniques. It was found, from the analysis of the experimental current density transients, that the potentiostatic formation of a full copper monolayer onto the gold electrode under UPD conditions follows the same mechanism, regardless of the crystallinity of the substrate. The mechanism involved the simultaneous presence of an adsorption process and of two 2D nucleation processes, progressive and instantaneous, respectively.     

Effect of polycrystalline mullite fibers on the properties of vitrified bond and vitrified CBN composites

The effect of polycrystalline mullite fibers (PMFs) on the properties of vitreous bonds and vitrified CBN composites was investigated. The results show that the addition of PMFs can increase the porosity of composites and reduce the fluidity of binders. The vitrified composites incorporating 6.4 wt% PMFs display excellent mechanical strength, which is enhanced by 21.2% compared with that of composites without PMFs sintered at the optimal sintering temperature. Meanwhile the thermal expansion coefficient of vitrified bond reduces from 6.256×10⁻⁶ °C⁻¹ to 4.805×10⁻⁶ °C⁻¹ with increasing fraction of PMFs. The improvement of mechanical strength is associated with the change of cracking mechanisms of the composites with fibrous crystals and the existence of several observed mechanisms, including fiber pull-out, fiber bridging and rupture.     

人造金刚石聚晶粘结剂的研究

对Ｓｉ－Ｔｉ－Ｂ、Ｓｉ－Ｎｉ－Ｂ,Ｓｉ（Ｎｉ－Ｔｉ）－Ｂ三种金刚石聚晶粘结剂进行了结比性研究。分析了各种元素和粘结中入量对聚晶性能的影响,探讨了成分、组织、结构对人造金刚石聚晶性能的影响。     

Preparation of high quality polycrystalline silicon thin films by aluminum-induced crystallization

High quality polycrystalline silicon (poly-Si) thin films without Si islands were prepared by using aluminum-induced crystallization on glass substrates. Al and amorphous silicon films were deposited by vacuum thermal evaporation and radio frequency magnetron sputtering, respectively. The samples were annealed at 500 °C for 7 h and then Al was removed by wet etching. Scanning electron microscopy shows that there are two layers in the thin films. After the upper layer was peeled off, the lower poly-Si thin film was found to be of high crystalline quality. It presented a Raman peak at 521 cm^− 1 with full width at a half maximum of 5.23 cm^− 1, which is similar to c-Si wafer.     

Precursor Cat-CVD a-Si films for the formation of high-quality poly-Si films on glass substrates by flash lamp annealing

Amorphous Si (a-Si) films with lower hydrogen contents show better adhesion to glass during flash lamp annealing (FLA). The 2.0 µm-thick a-Si films deposited by plasma-enhanced chemical vapor deposition (PECVD), containing 10% hydrogen, start to peel off even at a lamp irradiance lower than that required for crystallization, whereas a-Si films deposited by catalytic CVD (Cat-CVD) partially adhere even after crystallization. Dehydrogenated Cat-CVD a-Si films show much better adhesion to glass, and are converted to polycrystalline Si (poly-Si) without serious peeling, but are accompanied by the generation of crack-like structures. These facts demonstrate the superiority of as-deposited Cat-CVD a-Si films as a precursor material for micrometer-thick poly-Si formed by FLA.     

Chemical vapor deposition of boron- and nitrogen-containing graphene thin films

Boron and nitrogen-incorporated graphene thin films were grown on polycrystalline Ni substrates by thermal chemical vapor deposition using separate boron- and nitrogen-containing feedstocks. Boron and nitrogen atoms were incorporated in the film in almost equal amounts and the total content reached ∼28%. The film predominantly consisted of separate graphene and boron nitride domains. Carrier concentration in the graphene domains was estimated to be about 1 × 10⁻³ e/atom (3.8 × 10¹² cm⁻²) from G band shift in Raman spectra.     

Structural and electrical properties of polycrystalline silicon films deposited by low pressure chemical vapor deposition with and without plasma enhancement

Silicon thin films prepared by chemical vapor deposition of silane at very low pressures (4 mTorr) in an experimental reactor that allows deposition with and without plasma enhancement have been characterized. The temperature range of the substrates on which the films were deposited was varied from 500 to 800° C for plasma-enhanced depositions and 600 to 800° C for nonplasma depositions. Conductivity measurements as a function of temperature as well as average grain size and crystallographic texture measurements were performed. The results indicate that the films deposited with the assistance of a plasma were amorphous at deposition temperatures of 650° C and below and polycrystalline at deposition temperatures of 700° C and above. In the temperature regime investigated, this amorphous-to-crystalline transition was not observed in films deposited without the assistance of a plasma. Furthermore, all the films deposited at temperatures of 650° C and below have been found to have significantly different properties from the similarly prepared films deposited at higher temperatures.     

Tensile cracks in polycrystalline ice under transient creep: Part II — Numerical simulations

This paper discusses predictions of a numerical model presented in the companion paper (Nanthikesan and Shyam Sunder, 1995) to analyze tensile cracks in polycrystalline ice undergoing transient creep. The numerical model is based on the internal state variable constitutive theory of transient creep in ice developed by Shyam Sunder and Wu (1989a,b, 1990). The finite element model uses the boundary layer approach of Rice (1968), in conjunction with a mid-point crack-tip element and reduced integration, to simulate the asymptotic stress and deformation fields in the vicinity of the crack tip, including incompressible creep deformations.

The problem of a stationary, traction-free, tensile (mode I) crack is analyzed to predict the size, shape and time evolution of the creep-dominated fracture process zone surrounding the crack-tip. The numerical simulations quantify the effects of transient creep, material strain hardening, fabric anisotropy, loading rate, temperature, and finite fracture test-specimen boundary on the development of the creep zone. A range of stress-intensity rates from 1 to 100 kPa s⁻¹ and temperatures from −5° to −25°C is considered in the simulations.

The results from a comprehensive numerical simulation study show that: (i) transient creep increases the creep zone size by more than an order of magnitude over that for a power-law creeping material, i.e., about 40 times for the isotropic, equiaxed granular ice tested by Jacka (1984); (ii) material strain hardening significantly affects the creep zone size, i.e., the creep zone for the transversely-isotropic columnar-grained ice tested by Sinha (1978), with the crack loaded in the plane of isotropy, is about 4 times smaller than that for the granular isotropic ice; (iii) fabric anisotropy increases the size of the creep zone by a factor of at least two for cracks in the transversely-isotropic, columnar-grained ice loaded in the plane of isotropy; (iv) the Riedel and Rice (1980) equation, which was derived for an isotropic power-law creeping material subjected to a suddenly applied constant stress-intensity, overestimates the creep zone size by a factor of 4.2 for a constant stress-intensity rate loading; and (v) as the crack size increases, linear elastic fracture mechanics becomes increasingly applicable at lower loading rates and higher temperatures.     

Thin CdS films prepared by metalorganic chemical vapor deposition

Polycrystalline CdS thin films have been deposited on borosilicate glass substrates coated with ITO film by metalorganic chemical vapor deposition using dimethyl cadmium and diethyl sulfide as source materials. The growth of CdS film occurred at substrate temperatures within the range of 280–360°C. The deposition rate increased with increasing VI/II molar ratio at any substrate temperature and showed a maximum value at the VI/II molar ratio of 4. The grain size of as-deposited CdS film prepared at substrate temperatures from 300°C to 360°C was about 0.1 μm. The CdS films consist of hexagonal form with a preferential orientation of the (0 0 2) plane parallel to the substrate. Thin CdS film with high optical transmittance was prepared at 350°C with the VI/II molar ratio of 4. The CdS film deposited by MOCVD may be used as a window layer for CdS/CdTe solar cell.