Modelling of microdefect in single crystal germanium

Aim of project
Dislocation-free germanium crystals, used to produce wafers for optoelectronic and electronic applications, are grown by the Czochralski crystal growth technique. In order to enhance the applicability of germanium wafers for micro- and nano-electronic applications, it is important to minimize the defects on the wafer surface. Experimental evidence shows that at least part of the defects on the wafer surface originate from grown-in defects formed during the crystal growth process. Based upon analogies with the problem of defects in Czochralski- grown silicon crystals, the current belief is that these microdefects are the result of aggregation of point defects, which are formed at the crystal/melt boundary during the solidifi cation process. Hence, in order to control and minimize the distribution and/or size of these grown-in microdefects, one needs to understand the mechanisms responsible for their formation. In contrast to the case of silicon crystal growth, there is no (recent) literature available on the formation of grown-in defects in germanium.

Expected results
In this project, it is expected to develop:
A physical model which gives insight into the formation of grown-in defects in Czochralski-grown germanium crystals, and its experimental verifi cation;

A method and software code, based on the physical model, which can be used to describe and predict the distribution of these defects in terms of crystal growth conditions (e.g. temperature distribution in the growing crystal, dynamics at the crystal/melt boundary).

For the development of the physical model, it will be necessary to obtain satisfactory estimations of certain physical material parameters. One of the tasks in this project will be determination of these parameters from ab initio (fi rst principles) and molecular dynamics calculations. Afterwards, the calculated results will be correlated to experimental defect distributions, and to recent experimental data from other academic sources working on germanium characterization.