Growth of Si Crystals in Rectangular Shape for the Solar Cell Application(<Special Issue>Square-shaped Si Crystals for Solar Cell use)

Abstract

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.