M. Van Rossum

Intensity Distributions of Waves Transmitted through a Multiple Scattering Medium

The distributions of the angular transmission coefficient and of the total transmission are calculated for multiple scattered waves. The calculation is based on a mapping to the distribution of eigenvalues of the transmission matrix. The distributions depend on the profile of the incoming beam. The distribution function of the angular transmission has a stretched exponential decay. The total-transmission distribution grows log-normally whereas it decays exponentially.

Two new measurement methods for explicit determination of complex permittivity

This paper presents two new measurement methods for explicit determination of complex permittivity. For the first time, these methods combine the explicit algorithm with a simplified yet accurate error-correction technique. The combination is made possible by the use of one sample of single length and another of double length. For low-loss materials, one of the methods is valid for any sample length and independent of sample positions, but needs a prior estimate of the permittivity, while the other requires no such estimate, but avoidance of the single length being multiples of half-wavelength in the sample. For high-loss materials, both methods may need the estimate. Advantages of each method can be taken if both methods are used simultaneously. Experimental results from the proposed methods show excellent agreement with those from a recent iterative method. Errors arising from small deviations from the double length are also analyzed and presented. The validity, explicitness, and simple error-correction capability make the new methods very useful.

Zero‐dimensional states in submicron double‐barrier heterostructures laterally constricted by hydrogen plasma isolation

The lateral dimensions of resonant tunneling AlGaAs‐GaAs double barrier heterostructures have been restricted by hydrogen plasma exposure. Ohmic contacts to the submicron diodes have been made by solid phase epitaxial growth of Ge on GaAs. The current‐voltage characteristics show a fine structure splitting that is inversely proportional to the lateral size of the diode. The results are interpreted as resonant tunneling through zero‐dimensional states in the quantum box confined by the AlGaAs barriers and a harmonic lateral confining potential.

Consistent small-signal and large-signal extraction techniques for heterojunction FET's

A new method is reported to extract large-signal current and charge sources from the small-signal S-parameters of pseudomorphic heterojunction field effect transistors (PHFETs). This method produces a new intrinsic small-signal equivalent circuit topology with less constraints concerning the extraction of the large-signal current and charge sources. The main advantage of this new topology is charge conservation. The S-parameter measurements of a 0.2-/spl mu/m PHFET agrees well with the small-signal S-parameter data, obtained after evaluation of the new large-signal model at different bias points. >

Electrical-transport in (100)CoSi2/Si contacts.

A detailed investigation of the electrical transport in (100) CoSi2/Si contacts is presented. The transport properties of epitaxial CoSi2 films, obtained both by ion‐beam synthesis and by solid‐state reaction of a Ti/Co bimetallic layer, are compared with the transport properties of conventional polycrystalline CoSi2 layers. The electrical resistivity, the magnetoresistance, and the Hall effect are measured on Hall bars for temperatures ranging from 1.2 to 300 K and magnetic fields up to 5 T. Very high values of the order parameter kFL0 are observed, indicating that the investigated samples are of very high purity and crystalline order. In addition, the electric transport at the CoSi2/Si interface is studied by current‐voltage and capacitance‐voltage measurements on Schottky diode structures for temperatures ranging from 173 to 333 K. Ideality factors close to unity are observed for the highest temperatures, for the lower temperatures the ideality factors are found to increase with decreasing temperatures...

Quantum transport in a cylindrical sub-0.1 μm silicon-based MOSFET

Abstract A model is developed for a detailed investigation of the current flowing through a cylindrical sub-0.1 μm MOSFET with a closed gate electrode. The quantum mechanical features of the lateral charge transport are described by a Wigner distribution function which is explicitly dealing with electron scattering due to acoustic phonons and acceptor impurities. A numerical simulation is carried out to obtain a set of I – V characteristics for various channel lengths. It is demonstrated that inclusion of the collision term in the numerical simulation is important for low values of the source–drain voltage. The calculations have further shown that the scattering leads to an increase of the electron density in the channel thereby smoothing out the threshold kink in the I – V characteristics. An analysis of the electron phase-space distribution shows that scattering does not prevent electrons from flowing through the channel as a narrow stream, and that features of both ballistic and diffusive transport may be observed simultaneously.

Distribution of fields and charge carriers in cylindrical nanosize silicon-based metal-oxide-semiconductor structures

A quantum–mechanical description of charge carriers is presented for nanoscaled cylindrical metal–oxide–semiconductor structures. The Schrodinger and Poisson equations are solved self-consistently within the framework of the Hartree approximation and the profiles of the electrostatic field and the charge carrier densities are obtained.

Mössbauer study of the microscopic surrounding of co atoms implanted in si and ge below the full amorphization limit

Abstract Mossbauer spectroscopy on 57Co implanted into Si and Ge at doses between 1011 and 1015 atoms/cm2 supports the single track amorphization model. Calculations based on linear cascade theory do not give quantitative agreement with the experiment.

Rôle of a single scatterer in a multiple scattering medium

Abstract The influence of one extra static scatterer on multiple scattered classical waves is considered. It is shown how to connect two “diffusions” or “ladders”. Secondly, the interaction vertex of four diffusions (“Hikami box”) is generalized to non-static situations and the presence of absorption. Beyond the second order Born approximation, eight diagrams are relevant.

Migration of Si in molecular-beam epitaxial growth of δ-doped GaAs and Al0.25Ga0.75As

We have analyzed the incorporation of Si δ doping during the molecular‐beam epitaxial (MBE) growth of GaAs and Al0.25Ga0.75As using secondary‐ion mass spectroscopy. At high substrate temperatures (≥580 °C) a significant and asymmetric broadening is observed in both GaAs and Al0.25Ga0.75As. This is due to the combined effect of thermal diffusion and migration towards the surface during MBE growth. This study points out that a low substrate temperature (≤540 °C) and a short time are required during MBE crystal growth to achieve confined δ doping.