40 research outputs found
Schottky barrier heights at polar metal/semiconductor interfaces
Using a first-principle pseudopotential approach, we have investigated the
Schottky barrier heights of abrupt Al/Ge, Al/GaAs, Al/AlAs, and Al/ZnSe (100)
junctions, and their dependence on the semiconductor chemical composition and
surface termination. A model based on linear-response theory is developed,
which provides a simple, yet accurate description of the barrier-height
variations with the chemical composition of the semiconductor. The larger
barrier values found for the anion- than for the cation-terminated surfaces are
explained in terms of the screened charge of the polar semiconductor surface
and its image charge at the metal surface. Atomic scale computations show how
the classical image charge concept, valid for charges placed at large distances
from the metal, extends to distances shorter than the decay length of the
metal-induced-gap states.Comment: REVTeX 4, 11 pages, 6 EPS figure
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UV FEL light source for industrial processing
Short wavelength UV light is strongly absorbed by most materials, creating the opportunity to drive near-surface thermal or chemical processes. The resulting modifications have a wide range of prospective applications, but few have been developed because of the low capacity and high unit cost of light from present sources. We analyze the light source requirements for large-scale applications to polymers and metals. We describe meeting them with free electron laser whose design is described in a companion paper in this session. This machine will deliver 1.0 to 2.5 kW between 190nm and 350nm with options in the visible and IR, and serve to further develop FEL technology for much higher powered machines. We gratefully acknowledge support for this work from the Commonwealth of Virginia Center for Innovative Technologies and the U.S. Department of Energy
Thermal process dependence of Li configuration and electrical properties of Li-doped ZnO
We used depth-resolved cathodoluminescence spectroscopy (DRCLS) to describe the strong dependence of Li acceptor formation on thermal treatment in Li-doped ZnO. Within a 500-600 °C annealing temperature range, subsequent quenching ZnO leaves Li as interstitial donors, resulting in low room temperature resistivity, while slow cooling in air allows these interstitials to fill Zn vacancies forming Li acceptors 3.0 eV below the conduction band edge. DRCLS reveals an inverse relationship between the optical emission densities of lithium on zinc sites versus zinc vacancy sites, demonstrating the time dependence of Li interstitials to combine with zinc vacancies in order to form substitutional Li acceptors.
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