AVS 52nd International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP23
Step Edge Diffusion in Strained Compound Semiconductors

Tuesday, November 1, 2005, 4:00 pm, Room Exhibit Hall C&D

Session: Surface Science Poster Session
Presenter: C. Pearson, University of Michigan-Flint
Authors: C. Pearson, University of Michigan-Flint
J. Mirecki Millunchick, University of Michigan
Correspondent: Click to Email
Understanding the growth of strained alloys films is an enduring problem in surface science. Models of strained film growth based on elastic strain energy predict unique morphologies for different strain: islands upon large terraces for compressive films and mesas separated by trenches for tensile films. Using a combined MBE-STM system, we have imaged 2 ML thick films both in compression (InAs or GaSb) and in tension (GaAs or AlAs) grown on InP(001) near T=480°C using a group III growth rate of ~0.2 ML/s with an approximate group V/III ratio of 5. A roughness analysis reveals that the skewness of the height distribution for InAs is positive, which is indicative of a morphology dominated by islands while for AlAs the skewness is negative, which is indicative of a morphology dominated by holes. These results agree with the previously described morphologies predicted using elastic strain energy considerations. The Ga containing compounds also follow this strain energy trend, except the terraces or mesas have significantly rougher steps and higher surface anisotropies. These observations suggest that in addition to the sign of the misfit strain, factors such as step edge diffusion contribute to surface roughness. From an analysis of the images we compute the step edge density (step edge length per unit area) versus deposition flux and use a recent level set model@footnote 1@ to extract values of step edge diffusion. These results may explain the variety of microstructures observed in short period superlattice structures of these compounds that exhibit lateral composition modulation. @FootnoteText@ @footnote 1@ C. Ratsch, J. Garcia, and R. E. Caflisch, submitted to Applied Physics Letters.