Solid state theory research
Dynamic processes at surfaces/defects in semiconductors
The nature of the atomic-scale defects in semiconductors often determines the optical, electronic, and structural properties of these materials, and how these properties change with time, heating, pressure, and application of fields. Our research group investigates the properties of the important defects and defect complexes occurring in various semiconductors.
In order to be able to identify the defects responsible for particular experimental properties (and suggest how to optimize these properties as desired for particular applications), we use first-principles quantum molecular dynamics calculations to search for low energy defect structures, characterize the electronic and optical properties of these low-energy defects, and compare these properties with the experimental observations.
We also determine whether these energetically favorable defects have metastable higher energy configurations, and investigate their motion and interactions. Since these calculations are very demanding, they are supported by grants of supercomputing time from the Air Force Office of Scientific Research at ERDC, NAVO, and other national supercomputing centers.
There is currently a lot of interest in producing nanoscale devices and low-dimensional structures, such as quantum dots, in order to achieve faster response times, and the possibility of modifying the properties as desired by changing the geometrical dimensions. While changing the conditions during growth and processing can affect the quality of surfaces and interfaces and the concentrations of various defects remaining in important regions in larger devices as well, this can produce particularly dramatic changes in the properties of low-dimensional or very small structures. Therefore a better understanding of semiconductor growth at the atomic level is needed.
Our research group is currently investigating how growth and processing under different conditions can lead to different concentrations of structural defects at the surface, and different concentrations of various defects remaining in the material after growth. In order to address these questions, we use first-principles calculations to study the dynamics and energetics of the microscopic processes occurring at the growing semiconductor surfaces, as well as the defects which can occur at the growing surface.
References and an overview of some of the first-principles methods we use, including codes written and maintained by our long-term collaborators at the Fritz-Haber-Institut der Max-Planck-Gesellschaft and a manual on how to do these calculations coauthored by us, is available at FHI98md.
First-Principles Study of As Interstitials in GaAs: Convergence, Relaxation, and Formation Energy, J. T. Schick, C. G. Morgan, and P. Papoulias, Physical Review B66 195302 (2002).
Optical and Electrical Properties of Low to Highly Degenerate InN Films, D. B. Haddad et al., Mat Res. Soc. Symp. Proc. 798 Y12.7.1-Y12.7.6 (2004).