Rachel S. Goldman

Maria Goeppert Mayer Collegiate Professor


2094 H.H. Dow
T: (734) 647-6821




Research Facilities


Fundamental Phenomena in Semiconductors: Diffusion and Segregation

Sponsor: American Chemical Society-Petroleum Research Fund 34012-AC5, Air Force Office of Scientific Research F49620-00-0328
Direct measurements of diffusion and segregation lengths are generally limited by the inherent averaging that occurs in conventional characterization techniques. We are investigating the atomic-scale dynamics of these processes using a combination of annealing and cross-sectional scanning tunneling microscopy (XSTM). To date, we have studied these issues in a number of heterostructure systems, and have made several important contributions. For example, we used the "wetting layers" between InAs/GaAs quantum dots to directly measure In-Ga interdiffusion and In segregation lengths. To our knowledge, these XSTM studies represent the first direct atom-level measurements of both of these quantities. In addition, we report the first direct evidence for anti-site vacancy diffusion, originally predicted by Van Vechten more than 30 years ago. We are in the process of developing a further understanding of anti-site vacancy diffusion through XSTM studies a variety of mixed anion compound semiconductor heterostructures.
Highlights (Click an image for more information)
  • Direct Measurements of In-Ga Interdiffusion

    Diffusion and segregation are fundamental processes of critical importance for the design of a variety of electronic, photonic, and magnetic devices. Although many investigations of interfacial structure and chemistry have been undertaken, few have dealt with the dynamics of diffusion and segregation on the atomic scale. We are studying the atomic scale dynamics of diffusion in semiconductor structures, using a novel combination of annealing and cross-sectional scanning tunneling microscopy (XSTM). Our initial work includes studies of In-Ga interdiffusion within the wetting layers of InAs/GaAs quantum dot superlattices and Al-Ga interdiffusion in nonstoichiometric AlAs/GaAs superlattices. These experiments are providing further insight into the mechanisms of atomic diffusion in compound semiconductors, including direct measurement of diffusion coefficients for chemical species, on an atomic scale. The results obtained will be compared with existing diffusion-segregation models and Monte Carlo simulations of bulk diffusion in these systems. In addition, this method will be applied to the study of diffusion in optoelectronic devices consisting of layered semiconductors.