Transition metal gettering studies and simulation for the optimization of silicon photovoltaic device processing

We use what is known about transition metal (TM) defect thermodynamic driving forces and kinetic responses to make predictive simulation of gettering during solar cell fabrication possible. We have developed a simulator to explore the impact of various device and process parameters on gettering effectiveness. The relevant heat treatments are ramps up in temperature, isothermal annealing, and cools from high temperature down to room temperature. We explore a range of surface conditions, density and size of heterogeneous nucleation sites in the bulk, and the degree of contamination in order to create a framework in which to examine these mechanisms acting in concert. Such simulations enable process optimization for gettering. For solar cell processing, segregation to an Al back contact layer is routine. We have estimated the segregation coefficient between a p-type Si wafer and a molten Al layer by the Calphad method and use these results to estimate the thermodynamic driving force for redistribution of Fe into the Al layer. We simulate gettering treatments of supersaturated levels of Fe contamination in Si samples with FeSi2 and Al contacts and compare these results with data at various temperatures. The gettering data for FeSi2 contacts follow a simple exponential decay and can be simulated with appropriate choice of internal gettering time constant. We recognize that radiative heating dominates the temperature ramp for samples in evacuated quartz ampoules and use reasonable parameters to include this effect in our simulations. Fitting parameters for [Fe] data taken from heat treatments at 755ʻC on samples with FeSi2 and Al contacts successfully predict the gettering data of Al coated samples treated at 810ʻC.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Materials Science and Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2002

Author dc:creator

• Smith, Aimée Louise, 1971-

Advisor dc:contributor.advisor

• Lionel C. Kimerling.

• Materials Science and Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/8431

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/8431