Isotopically Controlled Semiconductors: Diffusion and Nanocrystals

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This project addresses (1) the physics of atomic diffusion in crystalline thin film multilayer structures and (2) the properties of nano-particles composed of isotopically controlled semiconductors. Self-diffusion (i.e., isotope inter-diffusion) and dopant diffusion will be studied directly and simultaneously for the first time in strained and relaxed silicon-germanium (SiGe) multi-layer structures. The studies are designed to reveal the physics underlying the various diffusion mechanisms. The expected results will expand the fundamental solid-state knowledge base, may lead to the discovery of new diffusion processes, and will be of direct use to the designers of future SiGe electronic devices. The proposal further addresses the properties of isotopically pure germanium nano-crystals. Selective Neutron Transmutation Doping (NTD) will be used to form acceptors (70Ge) or donors (74Ge). The NTD process looks promising because it occurs at temperatures sufficiently low for the newly formed dopant atoms to remain inside the nanocrystal. Choice of the isotopic composition also allows selection of isotopes with or without nuclear spin. Semiconductors with controlled nuclear spin distribution are of great current interest to the rapidly emerging field of "spintronics." The proposed research offers graduate and undergraduate students training in cutting-edge research in several fields of science and technology.This project addresses (1) the study of diffusion in crystalline thin film multilayer structures and (2) the properties of nano-particles composed of enriched isotopes of the semiconductor elements silicon and germanium. Atom self-diffusion and dopant diffusion are used in several of the key processes used to fabricate modern semiconductor devices ("chips"). The present studies are designed to reveal the atomic-level diffusion mechanisms in mixtures of silicon and germanium. The results will expand the fundamental solid-state knowledge base, and may lead to the discovery of new diffusion processes. The latter will be of direct use to the designers of future very high-speed electronic devices. The proposal further addresses the properties of isotopically pure germanium nano-crystals that have been doped using selective nuclear techniques. Choice of the isotopic composition also allows selection of isotopes with nuclear spin that are of great current interest to the rapidly emerging field of "spintronics." The proposed research offers graduate and undergraduate students training in cutting-edge research in several fields of science and technology.