Joanna Millunchick

Closed-loop experiment-simulation approach to designer materials: GaAsSbBi for optoelectronics

Sponsor: National Science Foundation
There is a strong national need for efficient optoelectronic devices that operate in the infrared and far infrared regime. Applications for infrared sources and detectors include night vision and surveillance, wireless communication, and chemical and biological sensing. Most current infrared applications rely on expensive and hazardous materials. Bismuth containing III-V semiconductors are non-toxic and may be directly integrated into existing fabrication lines, further reducing cost. However, growing these materials is nontrivial due to the complex interactions of Bi with the other elements in these compounds. In this work, the growth and optical properties of Bi-containing compound semiconductors are examined with an eye on infrared detector applications. The mode in which this research is performed is also important, because it marries experimental and computational methods to speed the pace of discovery. The novelty of this research is in coupling experiments with computations when studying an unknown and highly complex alloy system. Using a calculate-verify cycle to establish the growth parameters to obtain films that have the desired lattice parameter and band structure. ab initio statistical mechanics combines Density Functional Theory, cluster expansions, and statistical Monte-Carlo to calculate the equilibrium properties (including band structure) of the GaAsSbBi alloy. In tandem, growth modeling based on kinetic Monte Carlo is used to understand deviations from equilibrium behavior. Robust experimental methods for the growth (Molecular Beam Epitaxy) and atomic-scale characterization (Atom Probe Tomography, X-Ray Diffraction, Rutherford Backscattering, etc) are also used. Using experiments coupled with computation greatly reduces parameter space and speed the path to optimization of this new class of materials suitable for infrared devices.