Influence of copper contamination on recombination activity of misfit dislocations in SiGe/Si epilayers: Temperature dependence of activity as a marker characterizing the contamination level

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Abstract
The technique of electron-beam-induced current (EBIC) has been used to study the recombination activity of misfit dislocations in Si/SiGe epilayers. EBIC contrast measurements recorded as a function of temperature (T=80–300 K), c(T), were found to show a completely altered character following copper contamination of SiGe epilayers. In as-grown ‘‘clean’’ material the dislocations were found to exhibit a very small contrast at low temperature only. For a Cu contamination of about 1 ppb the contrast increased markedly at low temperatures but remained invisible near room temperature. This c(T) behavior can be attributed to shallow trap levels at the dislocations. For a Cu contamination around 15 ppb the majority of dislocations exhibited contrast in the whole temperature range, being a consequence of near-midgap centers at the dislocation. Hydrogen plasma treatment of these dislocations was observed to passivate the contrast near room temperature but did not show a pronounced effect on the contrast at low temperatures, so that the very small dislocation contrast found for clean material was not restored by hydrogen. A Cu contamination treatment in the ppm range resulted in a dramatic increase of the contrasts in the whole temperature range. Investigations by transmission electron microscopy (TEM) revealed in that material copper precipitates connected with the misfit dislocations. In contrast to the low-contaminated material no direct decoration of the dislocations could be observed. TEM images revealed that the EBIC dislocation line contrast corresponded to bundles of up to 15 individual dislocations.

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