Thursday, November 11, 2010: 2:40 PM
Seminar Theater (Hilton)
It is well known the properties of semiconductors are dramatically influenced by the presence of impurities (e.g. hydrogen, dopants) at concentrations as low as 1015-1018 atoms/cm3. Remarkably little is known about most impurities in semiconductor nanowires, despite their importance for realizing high performance optoelectronic devices. Studies that have focused on identifying the presence or location of dopants cannot provide chemical bonding information, have difficulty identifying mechanistic details, or are not sensitive to species at relevant concentrations. In a first step toward developing a chemical toolbox from which to effectively control nanowire optoelectronic properties, we have studied the incorporation of hydrogen in vapor-liquid-solid (VLS) grown Si nanowires with in-situ transmission infrared spectroscopy. Hydrogen is of critical fundamental and technological importance due to its role in defect passivation, dopant deactivation, and trapping phenomena. Au catalyst deposited in-situ onto a well-defined Si(111)-7x7 surface and exposed to disilane at pressures from 1 x 10-6 - 1 x 10-2 Torr and temperatures between 450oC and 600oC yield nanowires with diameters between 50 and 150 nm. Our experiments demonstrate that hydrogen is incorporated into the bulk and on the surface of nanowires during growth. Our results will be discussed within the context of achieving long carrier lifetimes for high efficiency nanowire-based photovoltaic devices. Preliminary results for hydrogen in Ge nanowires will also be presented.