An SEM EBIC study of the electronic properties of dislocations in silicon

Individual, well structurally characterised dislocations present in n-type silicon have been studied using the electron beam induced current (EBIC) mode of an SEM.An EBIC system has been designed and constructed which includes i) phase sensitive detection, ii) computerised control of the experimental equipment and data capture and iii) a variable temperature SEM specimen stage. With this system measurements have been made of the EBIC contrast of individual segments of deformation induced dislocations produced by two stage compressive deformation at 850°C and 420°C.An experimental and theoretical analysis of EBIC signal generation in the Schottky barrier specimens used in this work is presented. This shows that the EBIC contrast measurements made may be directly correlated to the dislocation recombination strength.Contrast measurements have been made at temperatures in the range 120K to 370K and for electron beam currents from 6 x 10-12A to 2 x 10-9A. Several new effects have been observed. Minority carrier diffusion length measurements have also been performed in silicon containing dislocations. These show that the value obtained may depend upon experimental parameters used in a hitherto undetected manner.A new theory describing recombination of carriers at charged dislocations has been developed and this has been extended to provide a description of the variation of the EBIC contrast of dislocations with temperature, electron beam current and also the transient response of the EBIC contrast. Comparison of the theoretical predictions with the results gained experimentally shows full agreement for low temperatures or large beam currents. At high temperatures and small beam currents the theory shows the EBIC contrast will behave differently depending on the density of dislocation states present.Interpretation of the experimental results in terms of this theory allows some new insight to be gained for recombination at dislocations, and values for some of the parameters controlling recombination have been obtained.