P. Van Mieghem

Band-gap narrowing in highly doped n- and p-type GaAs studied by photoluminescence spectroscopy

Band‐gap narrowing of GaAs as a function of doping concentration has been measured using photoluminescence spectroscopy on samples grown by molecular beam epitaxy. Both n‐ (Si) and p‐ (Be) doped samples with concentrations varying from 3×1017 to 3×1018 cm−3 have been measured. The experimental results obtained from a line‐shape analysis of the spectra taking tailing effects into account are in good agreement with recent theoretical calculations. A simple expression for the band‐gap narrowing as a function of concentration for both n‐and p‐doped GaAs is given.

Stress relaxation in laterally small strained semiconductor epilayers

The stress field in laterally small strained semiconductor epilayers has been studied by the finite element method. The reaction of the epilayer on the substrate and the bulging‐out effect caused by shear forces in the side wall boundaries play an important role. Analytical approximate methods are shown to be deficient. The normal stresses relax faster than a simple exponential with height z and virtually complete relaxation occurs at a height heff≊ √ab/2 (where a and b are the width and length, respectively, of the parallellopipidial epilayer) which is in good agreement with recent experiments. An equivalent lattice spacing fm as a function of z/√ab is defined and calculated.

Theory of the junction capacitance of an abrupt diode

A new theory for the junction capacitance of mathematically abrupt diodes is presented. In contrast with previous theories, Fermi–Dirac statistics are applied, and instead of using a parabolic density of states, a more appropriate function can be taken into account as this is required for heavily doped material. The main approximation is that of constant quasi‐Fermi levels. Besides the study of symmetrical junctions, the behavior of asymmetrical abrupt junctions is both analyzed and explained. Anomalies resulting from the calculations are shown to be due to the mathematical discontinuity.

Optical characterization of Si‐doped InAs1−xSbx grown on GaAs and GaAs‐coated Si by molecular‐beam epitaxy

Epitaxial layers of Si‐doped InAs1−xSbx have been grown by molecular‐beam epitaxy on GaAs and GaAs‐coated Si substrates. The absorption coefficient was measured in the 3–12 μm wavelength range and the experimental data was fit using an analytical expression that was derived from the Kane band model. The fitted value of the Fermi level was used to calculate the electron concentration and the results were compared with doping levels obtained from secondary ion mass spectroscopy and Hall measurements.

A Geometrical Strategy for the Identification of State Space Models of Linear Multivariable Systems with Singular Value Decomposition

Abstract In this paper, some geometrically inspired concepts are studied for the identification of models for multivariable linear time invariant systems from noisy input - output observations. Starting from a fundamental highly structured input-output matrix equation, it is shown how the singular value decomposition allows to estimate the order of the observable part of the system and its state space model matrices. Moreover, conditions for persistance of excitation of the inputs and the behavior of the algorithm when the data are perturbed by noise, can easily be studied from a geometrical point of view . The singular values allow to quantify these concepts. An example of an industrial plant identification is presented.

INFLUENCE OF MAJORITY CARRIER BANDTAILS ON THE PERFORMANCE OF SEMICONDUCTOR DEVICES

Abstract A model for bandtailing is built into the 1-D device simulator SEDAN. The influence of bandtails on the current gain of a state-of-the-art bipolar transistor is examined. It is shown that for transistors with high emitter doping, bandtail effects decrease the current gain significantly. This reduction in current gain is more pronounced at low temperature.

Band offsets in heavily doped p type GeSi/Si(100) strained layers: Applications to design of Long Wave-length InfraRed (LWIR) detectors

We show that the effect of heavy B doping modifies considerably the valence band offsets of the layers as well as the calculated cut-off wave-lengths of LWIR detectors.

Effects of bandgap narrowing on the capacitance of silicon and GaAs pn junctions

The effect of heavy doping on the capacitance-voltage relation of abrupt and linearly-graded p-n junctions is studied by computer simulations. An estimate of bandgap narrowing in compensated silicon is given for linearly-graded junctions. Capacitance-voltage curves of abrupt p-n GaAs junctions grown by MBE are investigated and compared to the theoretical curves.<<ETX>>