IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Semiconductors Tuesday Sessions
       Session SC-TuA

Paper SC-TuA9
Nanoscale Dislocation Patterning in PbTe/PbSe (001) Lattice-mismatched Heteroepitaxy

Tuesday, October 30, 2001, 4:40 pm, Room 124

Session: Semiconductor Heterojunctions
Presenter: K. Wiesauer, University of Linz, Austria
Authors: G. Springholz, University of Linz, Austria
K. Wiesauer, University of Linz, Austria
Correspondent: Click to Email
Molecular beam epitaxy of PbTe on 5.2% lattice-mismatched PbSe (100) is studied using scanning tunneling microscopy. It is found that at a critical thickness of 0.8 monolayers, pure edge type misfit dislocations are formed at the layer/substrate interface. In the STM images these misfit dislocations appear as dark lines that run over the epitaxial surface along the four-fold <011> directions. From atomically resolved lattice images, the dislocation Burgers vector is found to be ½<001> parallel to the interface. This unusual misfit dislocation configuration is explained by the fact that the dislocation are formed by climb rather than glide processes. From detailed investigations of the early relaxation stages, we find that all misfit dislocations are all injected from monolayer step edges on the surface, which greatly reduces the nucleation barrier of dislocation half loops. As the layer thickness increases, the dislocation density drastically increases and a nearly perfect quadratic grid of dislocations with an average spacing of 10 nm is formed, indicating that at 10 ML more than 90% of the misfit strain is relaxed. In addition, the course of strain relaxation is found to be in well agreement with the Frank-van-der-Merwe model. This surprising result is explained by the reduction of the dislocation nucleation barrier by the edge injection mechanism. The remarkable uniformity of the dislocation array is evidenced by the appearance of satellite peaks in the FFT power spectra of the STM images due to the dislocation superstructure. From a statistical analysis we find a variation of the lateral dislocation spacing of only 12%, which is better than the typical size uniformity of self-assembled quantum dots. Thus, these structures could serve as templates for the deposition of self-organized ordered nanostructures.