Employing screen printing technology, aluminum is applied to the back side of the n-type silicon wafer to see the effect of the heat treatment parameters on the Voc of the solar cell. Heat treatment at 850℃ produces the highest Voc
among various heat treatment conditions. Heat treatment at the temperatures higher than 850℃ results in lower Voc, which is due to the destruction of the Al-Si alloy emitter layer. The destruction of Al-Si layer observed to be caused by the vigorous movement of silicon atoms toward aluminum layer during the heat treatment.
CaMoO₄crystals with ellipsoid, peanut, dumbbell, and notched sphere shapes were synthesized using a simple precipitation reaction. The morphology of CaMoO₄crystals evolved from ellipsoids, through peanut-like structures and dumbbells, to notched spheres with increasing the concentration of Ca²+ and MoO₄²- ions. This morphology evolution of
CaMoO₄crystals is attributed to a fractal mechanism. Branched crystal growth started at both ends of the ellipsoids. The peanut-like and dumbbell morphologies were formed by the first and second fractal growths, espectively. Finally, the notched spheres were formed by further fractal growth of dumbbells.
We will focus on the horizontal Bridgman growth system to analyze the transport phenomena numerically, because the simple furnace system and the confined growth environment allow for the precise understanding of the
transport phenomena in solidification process. In conventional melt growth process, the dopant concentration tends to vary significantly along the crystal. In this work, we propose the modification of crucible geometry for improving the productivity of silicon single-crystal growth by controlling axial specific resistivity distribution. Numerical analysis has been performed to study the transport phenomena of dopant impurities in conventional and proposed Bridgman silicon growth using the finite element method and implicit Euler time integration. It has been demonstrated using mathematical models
and by numerical analysis that proposed method is useful for obtaining crystals with superior uniformity along the growth direction at a lower cost than can be obtained by the conventional melt growth process.
Production of the silicon feedstock for the semiconductor industry cannot meet the requirement for the solar cell
industry because the production volume is too small and production cost is too high. This situation stimulates the solar cell
industry to try the lower grade silicon feedstock like UMG (Upgraded Metallurgical Grade) silicon of 5~6 N in purity.
However, this material contains around 1 ppma of dopant atoms like boron or phosphorous. Calculation of the composition
profile of these impurities using segregation coefficient during crystal growth makes us expect the change of the type from
p to n : boron rich area in the early solidified part and phosphorous rich area in the later solidified part of the silicon
ingot. It was expected that the change of the growth speed during the silicon crystal growth is effective in controlling the
amount of the metal impurities but not effective in reducing the amount of dopants.
Mechano Chemical Process (MCP) skips the calcinations steps at an intermediate temperature that is always required in the conventional solid-state reaction because forming phase from raw powder is activated by mechanical energy. In this study,we prepared (Pb, La)TiO₃nanopowder with perovskite structure by only high energy MCP. Especially, the PLT nanopowder was synthesized without any thermal treatment using oxides, not salts as raw powder. This process is also very simple due to dry milling method, unnecessary to dry of powder. The oxide powder was milled up to 12 hr at intervals of an hour using MCP and the pure PLT phase of perovskite structure was formed after milling time of 3 hr. And the average particle size was 20 nm with narrow distribution after milling time of 3 hr from raw powder of several μm with inhomogeneous distribution.
Pearl is the organic gemstone which does not come from mines but from the biomineralization inside mollusc. Mollusc with nacre on inner surface of the shell is inevitable to make pearl. In this paper we researched and analyzed the pearls cultured using Pen shell (Atrina pectinata) which is not used in pearl farming industry but has potential to make pearls because it has thick and beautiful nacre inside the shell. SEM analysis was conducted to reveal the pattern of nacre on the Atrina pectinata pearl. Specific characteristics as sea-water pearl are detected by further analysis with ED-XRF. Aragonite specific peaks such as 1083 cm-¹ and 705 cm-¹ were shown by Raman analysis. UV-Vis analysis of Atrina pectinata pearl showed different pattern of spectrum compared with Pinctada margaritifera pearl. The reason for this
discrepancy is assumed by the metabolic difference of each species.
The artificial lightweight aggregate (ALA) was manufactured in a rotary kiln at 1125℃ using green body formed by pelletizing the batch powder composing of coal bottom ash (CBA) produced from power plant, clay and dredged soil (DS). The TCLP (Toxicity characteristic leaching procedure) results showed that the dissolution concentration of heavy metal ions of ALA fabricated in this study was below the limitation defined by the enforcement regulations of
wastes management law in Korea. The ALA containing 60~70 wt% CBA had a bulk density of 1.45~1.49 and a water absorption of 17.2~18.5 %. The impact values for oven-dry state and saturated-surface dry state of ALA were 27.4 ± 1.3 and 23.4 ± 2.6 % respectively. The 28-days compressive strength of concrete made with various ALA was 22.7~27.8 N/mm². The slump of concrete with ALA containing CBA 60 and 70 wt% were 7.9 and 14.3 cm respectively. The unit weight of concrete made with any ALA fabricated in this study was satisfied with the standard specifications of lightweight concrete
for the civil engineering and construction presented by Korea as below 1.84 ton/m³.
A stoichiometric mixture of evaporating materials for ZnIn₂Se₄single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, ZnIn₂Se₄ mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the Hot Wall Epitaxy (HWE) system. The source and substrate temperatures were 630℃ and 400℃, respectively. The crystalline structure of the single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). The carrier density and mobility of ZnIn₂Se₄single crystal thin films measured from Hall effect by van der Pauw method are 9.41 × 1016 cm-³ and 292 cm²/v · s at 293 K, respectively. The temperature dependence of the energy band gap of the ZnIn₂Se₄obtained from the absorption spectra was well described by the Varshni’s relation, Eg(T) = 1.8622 eV − (5.23 × 10−4 eV/K)T2/(T + 775.5 K). The crystal field and the spinorbit splitting energies for the valence band of the ZnIn₂Se₄have been estimated to be 182.7 meV and 42.6 meV,respectively, by means of the photocurrent spectra and the Hopfield quasicubic model. These results indicate that the splitting of the Δso definitely exists in the Γ5 states of the valence band of the ZnIn₂Se₄/GaAs epilayer. The three photocurrent peaks observed at 10 K are ascribed to the A1-, B1-exciton for n = 1 and C27-exciton peaks for n = 27.