Special Colloquium, February 19, 2004

Stress-Driven Processes & Nanostructure Formation in Compound Semiconductor Films

Rachel S. Goldman

Department of Materials Science and Engineering
University of Michigan

Recently, low-dimensional semiconductor structures have been achieved in variety of heteroepitaxial thin film systems. Arrays of self-assembled semiconductor nanostructures are easily produced in systems AB, where A and B have different atomic sizes. An example is a semiconductor quantum dot, which may be produced by the controlled coarsening of a film of A deposited on a substrate B. Repetition of this process leads to the vertical alignment, or “stacking”, of the resulting islands of A. A related semiconductor nanostructure is one formed by the decomposition of an alloy film. For example, in an alloy film AB or a superlattice A/B/A/B, spontaneous lateral phase separation leads to the formation of lateral superlattices consisting of alternating A-rich and B-rich layers. Although the formation of these nanostructure arrays is generally driven by elastic relaxation of stress, their perfection and stability are often determined by additional processes, such as diffusion and segregation, occurring during epitaxial growth and subsequent thermal annealing. In this talk, I will discuss the formation and stability of a variety of semiconductor nanostructure arrays, including self-assembled InAs/GaAs quantum dots, and phase separated InAlAs and GaP/InP alloys. I will present new mechanisms for nanostructure formation, which are likely to be applicable to a wide range of heteroepitaxial thin film systems.

This work is supported in part by the Department of Energy, through the National Renewable Energy Laboratory Photovoltaics Beyond the Horizon Program, the National Science Foundation, the Air Force Office of Scientific Research, the Army Research Office, the Office of Naval Research, the TRW Foundation, and NASA-Lewis.

9:00 a.m., Smith Laboratory, Room 1094

Refreshments served in Smith 1094 at 8:30 a.m.