Jen Teh College

Taiwan

Jen Teh College

Taiwan

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Teng Y.-Y.,Chung Shan Institute of Science and Technology | Chen J.-C.,National Central University | Lu C.-W.,Jen Teh College | Chen C.-Y.,Sino American Silicon Products Inc.
Journal of Crystal Growth | Year: 2012

Oxygen is one of the most important types of impurities that can cause thermal donor or light-induced degradation in mc-Si solar cells. The objective of this study is to investigate the effect that installing a gas flow guidance device in a mc-Si crystal-growth furnace would have on the oxygen impurity distribution in the melt during the growth process. The installation of such a gas flow guidance device can enhance the gas flow near the free surface, which would allow the argon to carry a greater amount of evaporated SiO gas outside the furnace. Furthermore, the enhanced motion of the gas flow also improves heat transfer near the free surface, which would make the melt vortex separate more easily. The separated melt vortex, which is located near the central region of the melt-crystal interface, directs any oxygen impurity towards the central region of the melt-crystal interface. This is why the oxygen concentration can be reduced by installing the gas flow guidance device. The effectiveness of the gas flow guidance device depends on the vertical distance between it and the free surface (h) as well as the gap between the crucible sidewall and the tip of the device (d). The effect on the oxygen concentration in the melt is significant when smaller values for h and d are adopted. © 2011 Elsevier B.V.


Teng Y.-Y.,National Central University | Chen J.-C.,National Central University | Lu C.-W.,Jen Teh College | Chen H.-I.,National Central University | And 2 more authors.
Journal of Crystal Growth | Year: 2011

Oxygen impurities can reduce the carrier lifetime of mc-Si solar cells. In this study, simulations of the transient temperature, velocity and concentrations of oxygen and silicon oxide are carried out in order to clarify the transport mechanism of oxygen impurities in the silicon melt and silicon oxide through argon gas, in a directional solidification system (DSS) furnace. As the solidification fraction enlarges, the oxygen concentration in the melt diminishes, because of the reduction in the amount of crucible surface immersed below the silicon melt. When the solidification fraction is small, two pairs of vortices appear in the melt. Oxygen originating from the crucible is carried towards the free surface by the upper vortex. Oxygen concentration is higher with a higher furnace pressure rather than with a lower one due to the low SiO evaporation at the free surface. When the solidification fraction increases, the upper vortex gradually disappears. The lower vortex occupies almost the whole of the melt, with the exception of a small upper central region where a small vortex forms because of the cooling effect of the argon gas. Oxygen impurities carried by the lower vortex along the crystallization front towards the central region are obstructed by this small vortex. The size of the small vortex increases as the solidification fraction increases. Since the small vortex is stronger when the furnace pressure is higher, the concentration is lower around the central region. This means that the oxygen concentration is smaller when the furnace pressure is higher rather than lower. The simulation results agree well with the experimental results. © 2010 Elsevier B.V. All rights reserved.


Chen J.-C.,National Central University | Teng Y.-Y.,National Central University | Wun W.-T.,National Central University | Lu C.-W.,Jen Teh College | And 3 more authors.
Journal of Crystal Growth | Year: 2011

In this study, the effect of the flow motion and heat transfer generated by the crystal and crucible rotation on the oxygen distribution inside the melt during Czochralski silicon crystal growth is investigated. When the crucible rotates in a direction opposite to the crystal rotation, TaylorProundman vortices appear in the region below the crystal. The diffusion of oxygen impurity from the crucible wall to the crystalmelt interface is suppressed by these TaylorProundman vortices, while heat transport from the crucible wall to the crystalmelt interface is blocked by the TaylorProundman vortices. With a higher crucible rotation rate, the size of the TaylorProundman vortices increases and the size of the buoyancythermocapillary vortices decreases. This causes the temperature at the crucible wall to rise and the evaporation of oxygen impurity on the free surface to decrease. Hence, the amount of oxygen impurity that diffuses into the melt towards the crystalmelt interface increases. The suppression from the TaylorProundman vortices is dominant for the smaller crucible rotation rate, while the enhancement from the oxygen impurity diffusion prevails for the higher crucible rotation rate. Therefore, there is an optimum combination of crucible and crystal rotation for obtaining the lowest oxygen concentration. © 2010 Elsevier B.V. All rights reserved.


Teng Y.-Y.,Chung Shan Institute of Science and Technology | Chen J.-C.,National Central University | Lu C.-W.,Jen Teh College | Huang C.-C.,National Central University | And 4 more authors.
International Journal of Photoenergy | Year: 2012

We perform numerical simulations to analyze the effect of the position of the heater on the thermal and flow fields and the oxygen concentration distribution during the industrial Cz silicon crystal growth process. The amount of oxygen released from the silica crucible to the silicon melt during the growth process can be lowered by adjusting the heater position to decrease the temperature on the crucible wall. During growth of the crystal body, there is a significant decrease in the gradient of the oxygen concentration along the melt-crystal interface due to the stronger Taylor-Proudman vortex, which is generated by the crucible and crystal rotation. There is a significant reduction in the average oxygen concentration at the melt-crystal interface for longer crystal lengths because of the lower wall temperature, smaller contact surface between the crucible wall and the melt and the stronger Taylor-Proudman vortex. Copyright 2012 Ying-Yang Teng et al.


Teng Y.-Y.,National Central University | Chen J.-C.,National Central University | Lu C.-W.,Jen Teh College | Chen C.-Y.,Sino American Silicon Products Inc.
Journal of Crystal Growth | Year: 2010

In this study, we performed a numerical simulation of the growth of multicrystalline silicon ingots using the DSS method and compared the results with the experiments. The thermal flow field and the carbon concentration distribution during the growth process were analyzed under the same operating conditions. The carbon concentration distribution in the grown ingots was measured and the results compared with that of the simulation predictions. The simulation results are in good agreement with the experimental ones. The simulation shows that in a directional solidification furnace carbon impurities accumulate easily in the melt near the central region of the melt/crystal interface due to convection. This is the main reason for the non-uniformity of the carbon concentration in ingots grown in the DSS furnace. In order to improve the uniformity of carbon distribution in the melt, a higher convexity of crystalline front interface in the central region needs to be maintained during the growth process to reduce the strength of melt convection around the crystalline front interface. © 2009 Elsevier B.V. All rights reserved.

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