Recombination lifetime analysis of deep levels in silicon

By the addition of selected impurities to silicon it is possible to affect its physical, optical and electrical properties to a remarkable extent.

Of great technological importance are the elements of groups III and V which introduce shallow acceptor and donor levels and control the equilibrium charge density. These levels have been studied extensively and are well understood.

However, other impurities and structural defects are known to introduce deep levels. These levels may act as acceptors or donors in the traditional sense but they can also control the recombination of non-equilibrium charge carriers.

The properties of these recombination levels reflect the processes of energy exchange and provide information on the defect structure and energy spectrum and are thus of physical interest. Also since they control the excess carrier lifetime which is a critical parameter in many semiconductor devices they are of interest to the technologist.

The major difficulty in analyzing these levels arises from the catalytic nature of the recombination centers which allows an extremely low density of centers to significantly affect the recombination lifetime.

Most bulk single crystal silicon techniques applied to date use activation processes with high resistivity, high recombination center density samples. This severely limits the range and sensitivity of analysis.

In this dissertation is detailed a new approach to more accurately determine lifetime parameters in conjunction with a phenomenological model which describes the recombination using a set of characterizing parameters. The technique is used to characterize the levels responsible for recombination in single crystal silicon after controlled heat treatments and, also, in gamma irradiated and impurity containing silicon.