Global axisymmetric and local 3D calculations have been performed for obtaining the melt convection and temperature field in Czochralski environment for growing silicon crystals. The influence of a travelling magnet field (TMF) on the melt flow is discussed with respect to the occurence of {110} facets during growth experiments in a TMF travelling down in the side heaters.
Conventionally grown Czochralski (Cz) silicon crystals for photovoltaic application are of unfavourable cylindrical shape leading to essential material loss during the wafer cutting process. Additionally, the typical high oxygen concentration promotes the solar cell degradation. In this paper the attemps to grow Cz silicon crystals with both quadratic cross section and relatively low as-grown oxygen content are summarized. A favourable technique is described wich allowed the pulling of 10 cm long rectangular Cz ingots with square coss section of 91×91 mm^2 and interstitial oxygen content of 7×10^<17>cm<-3> by {110} facetting along the [001] orientation. In order to obtain stable very low radial temperature gradient at the melt-solid periphery, as a prerequisit of pronounced facetting, travelling magnetic fields (TMF) have been applied. Such non-steady magnetic field is generated simultaneously within the heater around the crucible. It induces a very stable high-speed toroidal convection roll between crucible and growing crystal graduating the temperature distribution along the free melt surface that promotes the apperance of large {110} facet.
Si-faceted dendrites have unique crystal structures. The surface of dendrites is bounded by {111} facet planes, at least two parallel {111} twin boundaries exist at the center of the dendrites, and the preferential growth directions are <112> or <110>. Moreover, the growth velocity of dendrites is larger than equiaxed crystal grains. Such features can be applied in technology for growing multicrystalline Si (mc-Si) ingots for solar cells. We succeeded in observing the growth processes of Si <112> and <110> faceted dendrites by using originally developed in situ observation system. The growth scheme for the growth shape of the <112> and <110> dendrites were established based on our experimental evidence. The theoretical <112> and <110> dendrite growth velocities were calculated on the basis of the growth model established by our studies.
The third generation synchrotron radiation facilities allow us to perform time-resolve and in-situ observation of solidification for metallic alloys. The quantitative measurement of X-ray absorption coefficient intransmission images gives two-dimensional solute concentration profile. The solute profile will be helpful for verifying and validating solidification models. This paper presents preliminary results of solute profile around dendrites in Fe-Si alloys.
This paper discusses the determination factors of conversion efficiency in solar cells fabricated by silicon. The factors are impurity concentrations of light elements and heavy metals in a crystal, dislocation density and shape of a solid-liquid interface. A silicon multicrystal grown by a floating zone (FZ) method has about conversion efficiency with 80 to 90 percent of that in single crystalline silicon grown by FZ method. This result shows that the key point to obtain a high efficiency solar cell is to reduce impurity such as light elements and heavy metals, and dislocation.