Page 183 - A Comprehensive Guide to Solar Energy Systems

Chapter 9 • Crystalline Silicon Solar Cell and Module Technology 185

FIGURE 9.3 A schematic process flow chart for preparing semiconductor silicon.

9.3.1 Crystalline Silicon Ingot Fabrication

The c-Si ingot can be a single-crystal or multicrystalline block of well-defined cross sec-
tion from which can be cut wafers of defined shape and thickness, suitable for solar cell
mass production.

9.3.1.1 Silicon Single-Crystal Ingot Fabrication
The Czochralski method is mostly used in the preparation of silicon single crystals. The
equipment consists of a chamber in which the feedstock material (poly c-Si pieces or resi-
dues from single crystals) is melted in a quartz crucible, doped with the proper concen-
tration of acceptors (to prepare P-type silicon) or donors (to prepare n-type silicon). A
seed of a single crystal of defined crystallographic orientation is first dipped into the melt,
and then the seed is slowly withdrawn vertically to the melt surface whereby the liquid
crystallizes on the seed surface. Then the pulling velocity is raised to the specific value at