Engineering Interfaces in No-Common-Atom Heterostructures

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A one-year program of research is proposed on the synthesis and atomic level characterization of short period superlattices (SPS) in which the constituent layers do not share a common element. These no-common-atom systems, such as InAs/GaSb, have attracted significant interest for applications in infrared optoelectronics technology, offering the possibility to tune electronic band structure by manipulating the low-symmetry interface structure. The goal is to achieve understanding of the epitaxial growth conditions and processes required to synthesize no-common-atom SPS with well-defined interface structures. This calls for a high level of control over atomistic mechanisms of interface formation and the ability to characterize the interface structure with atomic resolution. A unique feature of the project is the use of a novel direct method to image buried interfaces using x-ray synchrotron radiation. This technique, Coherent Bragg Rod Analysis (COBRA), is capable of providing, non-destructively, a three-dimensional map of epitaxial thin-film structures with sub-Angstrom resolution of atomic positions. COBRA maps will be used to seek sufficiently detailed structural and compositional information to control growth conditions enabling specific interface structures with tailored optoelectronic properties. Theoretical predictions of the interface composition distributions are available with which experimentally determined interface structures can be compared. These kinetic models will serve as a useful guide for experiments. %%% The project addresses basic research issues in a topical area of electronic materials with high technological relevance. The tunability of electronic properties inherent in no-common-atom short period superlattices (SPS) systems may impact infrared device technology in areas where there are important societal needs, for example in health care, communications, and national security. An important element of the project is the integration of research and education through the training of students in a fundamental and technologically significant area. The project offers exciting research opportunities for graduate training and also for more junior students to become interested in science and engineering. A program of research activities which are integrated with the proposed research, but which are also accessible to less experienced students has been devised. The use of national research facilities (Advanced Photon Source) will expose students to forefront programs in materials research, and provide opportunities to network with a broad range of educational and training activities in different fields. The U. MI joint Beam Line Sector with Howard University at the Advanced Photon Source is a focal point for encouraging research participation of students from underrepresented groups. ***