Silicon float-zoned crystal growth for high minority charge-carrier lifetime material applications

Abstract

The performance of a number of electronic devices such as solar cells, power devices, and transistors is strongly influenced by minority charge-carrier lifetimes in the semi-conductor material. The conditions for float-zone growth of silicon crystals for these devices can be adjusted to achieve charge-carrier lifetimes as long as 20 ms. Low impurity levels are of course necessary, and the material must be free of dislocations and grain boundaries. Microdefects such as swirl defects (A- or B-type) and frozen-in defects are also carrier recombination centers, and thus must be controlled during crystal growth. The type and density of defects can be altered by changing the growth conditions. Long minority charge-carrier lifetimes are achieved at moderately high growth rates and low thermal gradients during crystal growth.