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2010
Conference Paper
Titel
Use of HCL gas gettering in the epitaxial wafer equivalent concept
Abstract
The concept of the epitaxial wafer equivalent (EpiWE) is pursued at the Fraunhofer ISE as an option to reduce the cost of silicon solar cells. Within this concept, only a small amount of the expensive high purity silicon is needed for the epitaxial deposition on a low-cost substrate made from low-quality silicon. A challenging task is the control of the impurity contents in the low-grade silicon substrate. Especially transition metals like Fe, Mn, and Cr act as recombination centres and degrade the minority carrier lifetime once they diffuse into the active layer. Gettering with HCl gas is an effective and fast method to reduce the metals mentioned above to an appropriate level and can be performed prior to the epitaxial deposition. This paper presents a reduction of metal impurity concentrations up to two orders of magnitude obtained by HCl gettering of metallurgical grade (MG) and upgraded metallurgical grade (UMG) silicon. Additionally, solar cell results are shown, demonstrating the improvement of EpiWE solar cells by HCl gas gettering.