Nuclear Magnetic Resonance Studies of Impurities in Semiconductors

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9623299 Warren Impurity-species nuclear magnetic resonance (NMR) will be used to investigate the local atomic and electronic structure of impurities in crystalline semiconductors. Our previous variable-temperature studies of the donor and acceptor bands in Si(P) and Si(B) in the range 100 - 500 K will be extended to liquid helium temperatures. The group III impurities Ga and In in II-VI materials will be studied by conventional impurity-nucleus NMR in the presence of persistent photoconductivity at low temperatures. An attempt will be made to observe optical nuclear polarization in ZnO and related II-VI materials. The effect of optical excitation on the local atomic structure of impurities such as Ga in CdTe will be examined as a test of the "DX model" of these materials. %%% Impurity atoms play a critical role in technologically important semiconducting crystals since they introduce the charged carriers necessary for the materials to conduct electricity. Despite their importance, the atomic-scale environments of many important impurities are still poorly understood. Nuclear magnetic resonance (NMR) provides a highly local, chemically-specific probe which will be used in this research to investigate the structural and electronic environments of selected impurities in materials such as CdTe and Si. The state of atoms such as Ga and In in CdTe and related materials will receive particular attention in an attempt to understand why these impurities, contrary to conventional behavior, do not introduce carriers. In Si, NMR will be used to clarify the way in which interactions between P or B impurities influence the carrier mobility and hence, the performance of silicon-based devices. ***