The objectives of the proposed research and education program are: (1) to develop a viable technology for compliant substrates which can be used to grow defect-free heteroepitaxial materials of large (>15%) lattice mismatches and different lattice structures, and (2) to understand the underlining physics of compliant substrates and to establish a physical model to quantitatively describe the phenomenon of substrate compliance. In brief, this program aims to establish the theory and technology of compliant universal substrates. As a result of this research, one or two types of substrates, perhaps GaAs or Si, will be sufficient to accommodate a large variety of compound semiconductor epitaxial materials, including those having no proper conventional substrates on which to grow. The proposed compliant universal substrate is essentially made of an ultra thin (10 A to 100A) single crystal (e.g. GaAs or Si) bonded to a GaAs or Si bulk crystal with a large (> 10 degrees) twist angle. It is believed that the microstructure of the twist boundary and the extremely thin bonded layer play a critical role in making the structure compliant to the heteroepitaxial overlayer. We conceive that the twist bonded thin portion of the bicrystal behaves somewhat similar to a free standing thin template to achieve its compliance. Our preliminary experimental results show that InGaP, GaSb, and InSb, with 1%, 8%, and 15% mismatch to GaAs, respectively, can be grown defect-free on the compliant universal substrates. This proposal brings together the expertise of Lo, who has developed the concept of the compliant universal substrate, and of Sass, who has carried out extensive studies of the structure of grain boundaries contained in bicrystals with the same geometry as in the compliant universal substrate. The research team made of Lo, Sass, 3 Ph.D. students and at least 4 undergraduates will perform three tasks: fundamental materials research, compliant substrate technology development, and material and device demonstrations. Through these efforts, the physical mechanisms, technologies, and applications of compliant universal substrates are anticipated to be established. Compliant universal substrates have been a dream for many decades for people working on semiconductor materials and devices. The realization of compliant universal substrates will remove one of the most serious road blocks in semiconductor research and significantly advance the technologies of microelectronics, optoelectronics, and the integration of both. The proposed research will contribute substantially to achieving this goal.
