Hall mobility in undoped microcrystalline Si:H,Cl films.

The Hall mobility in undoped microcrystalline Si:H, Cl films has been measured in the temperature range 130<T<300K. The dependence of μH on the temperature clearly evidences two different transport mechanisms. Above T0=200 K, the Hall mobility has an activation energy of about 0.3 eV, while below T0 it is practically temperature independent

Hall mobility in doped Si:H,Cl films.

The Hall mobility μH in phosphorus- and boron-doped Si:H, Cl films was measured in the temperature range 130–300 K. The conductivity is markedly influenced by the doping, and the activation energies of both the Hall mobility and the conductivity as functions of the temperature are much lower in doped samples than in undoped samples. The process tends to become unactivated at higher doping levels

Optical characterization of CdSxSe1-x films grown on quartz substrate by pulsed laser ablation technique

CdSxSe1-x alloys have been deposited on quartz substrates by means of pulsed laser ablation, a relatively new technique for growing semiconductor films. We obtained high quality polycrystalline films which present photoluminescence efficiency up to at room temperature. The dependence of the band gap on the x composition, measured by absorption spectra at 10 K, shows an upwards band gap bowing. The real part of the refractive index in the transparent region at room temperature is well described by the Sellmeier relation. (C) 1999 Published by Elsevier Science S.A. All rights reserved

Controlling semiconductor/metal junction barriers by incomplete, nonideal molecular monolayers

We study how partial monolayers of molecular dipoles at semiconductor/metal interfaces can affect electrical transport across these interfaces, using a series of molecules with systematically varying dipole moment, adsorbed on n-GaAs, prior to Au or Pd metal contact deposition, by indirect evaporation or as "ready-made" pads. From analyses of the molecularly modified surfaces, we find that molecular coverage is poorer on low-than on high-doped n-GaAs. Electrical charge transport across the resulting interfaces was studied by current-voltage-temperature, internal photoemission, and capacitance-voltage measurements. The data were analyzed and compared with numerical simulations of interfaces that present inhomogeneous barriers for electron transport across them. For high-doped GaAs, we confirm that only the former, molecular dipole-dependent barrier is found. Although no clear molecular effects appear to exist with low-doped n-GaAs, those data are well explained by two coexisting barriers for electron transport, one with clear systematic dependence on molecular dipole (molecule-controlled regions) and a constant one (molecule-free regions, pinholes). This explains why directly observable molecular control over the barrier height is found with high-doped GaAs: there, the monolayer pinholes are small enough for their electronic effect not to be felt (they are "pinched off"). We conclude that molecules can control and tailor electronic devices need not form high-quality monolayers, bind chemically to both electrodes, or form multilayers to achieve complete surface coverage. Furthermore, the problem of stability during electron transport is significantly alleviated with molecular control via partial molecule coverage, as most current flows now between, rather than via, the molecules

Contacting organic molecules by metal evaporation

Reproducible electrical contacts to organic molecules are created non-destructively by indirect electron beam evaporation of Pd onto molecular films on cooled substrates. In contrast, directly evaporated contacts damage the molecules seriously. Our conclusions are based on correlating trends in properties of a series of molecules with systematically varying, exposed functional groups, with trends in the electrical behaviour of Pd/molecule/GaAs junctions, where these same molecules are part of the junctions