Publications de Marc Ilegems | EPFL Graph Search

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An original method for the extraction of FET parameters at low drain bias is presented. It is based on a simple linear charge-control model and on a power-law dependence (with an exponent k > 0 for GaAs/AlGaAs MODFET's and k < 0 for Si-MOSFET's) of the low-field mobility-mu on the two-dimensional electron gas (2DEG) concentration n(S), valid in a certain range of gate voltages. Simple analytical expressions for the transfer characteristics I(ds)-V(gs) and g(m)-V(gs) at low drain bias are combined to extract

In this paper, we present a systematic study of the effect of growth parameters on the structural and optical properties of InAs quantum dot (QD) grown under Stranski-Krastanov mode by molecular beam epitaxy. The dot density is significantly reduced from 1.9x10(10) to 0.6x10(10) cm(-2) as the growth rate decreases from 0.075 to 0.019 ML/s, while the island size becomes larger. Correspondingly, the emission wavelength shifts to the longer side. By increasing the indium fraction in the InGaAs capping layer, t

Low-frequency noise measurements have been performed in the linear range of the I-V characteristics of pseudomorphic Al0.3Ga0.7As/In0.25Ga0.75As/GaAs high electron mobility transistors (HEMTs) grown by molecular beam epitaxy with different channel thicknesses. The results obtained show that the 1/f noise in such devices depends greatly on channel thickness. It is controlled by the penetration of the electron wavefunction into the barrier as well as by Coulombic effects for thin channels and by the increase

The molecular-beam epitaxial growth conditions of (N + 1)(InAs)m/N(GaAs)n short period superlattices (SPSs) on GaAs substrates have been optimized. Hall electrical properties measured by the van der Pauw method were compared to low-temperature photoluminescence (77 K PL) spectra of GaAs/SPS/AlGaAs modulation-doped field-effect transistor-type heterostructures. By using these two characterization methods, the influences of the growth temperature T(s), of the SPS channel thickness d(ch) and of its average ind

Low-frequency drain-current noise in lattice-matched InAlAs/InGaAs/InP HEMTs has been studied at low drain bias in a temperature range of 77 to 350 K. The 1/f noise was found to be strongly dependent on gate-source bias , which can be interpreted by taking into account the role played by the series resistance. The Hooge's parameter for 1/f noise were extrcated to be 1.5x10-3 for the InGaAs channel and 7x10-4 for the series resistance. Noise spectra analysis reveals two generation-recombination (G-R) noise c

We present a comparative study, at 300 K and at low longitudinal field, of the DC characteristics and the low-frequency noise in the drain current of GaAs/AlGaAs MODFETs which, ideally, differ only by the doping mode of the AlGaAs layer. The higher 1/f-like noise in the δ-doped structure is consistent with our previous suggestion that charge fluctuations under the gate contribute significantly to the 1/f-like noise. This work further indicates that the charge centers are related to the Si dopants under the

Hall electrical properties measured by the van der Pauw method and low-temperature photoluminescence (77 K PL) spectra of pseudomorphic GaAs/InyGa1-yAs/AlGaAs modulation-doped field-effect transistor-type heterostructures grown by molecular-beam epitaxy were compared. By using these two characterization methods, the influences of the growth temperature T(s), the InGaAs quantum-well channel thickness d(ch), and its indium composition y were studied. Interesting correlations were established between their 77

We report on the realization of InGaAs-lnGaAsP separate confinement heterostructure multiple quantum well lasers grown by chemical beam epitaxy. We discuss key growth parameters and characterization by secondary-ion mass spectroscopy, transmission electron microscopy, electron-beam-induced current, and x-ray diffraction. Threshold current densities as low as 450 A/cm(2) are obtained on lasers with five strained InGaAs quantum wells, along with internal quantum efficiencies of 90% and optical losses of 5 cm(

High-efficiency top-emitting InGaAs/AlGaAs microcavity light-emitting diodes (MCLEDs) have been optimized and fabricated. The structures were grown using molecular beam epitaxy on GaAs substrates. They consist of a three-period Be-doped distributed Bragg reflector (DBR) centred at 950 nm wavelength, a cavity containing three InGaAs quantum wells and a 15-period Si-doped DBR. Different values for the wavelength detuning between the spontaneous emission line and Fabry-Perot cavity mode were explored, between

Quantitative Secondary Ion Mass Spectrometry (SIMS) determination of oxygen incorporation in epitaxial AlGaAs/GaAs layers is strongly affected by the presence of oxygen adsorbed on the surface. By flooding the sample with oxygen isotope O18 during the analysis, one can account and correct for the influence of the adsorbed oxygen O16 species. After the background subtraction, the oxygen content can be determined from the measured ratio of AlO to Al or O to Al signals, knowing the relative sensitivity factors

We studied the formation of buried heterostructures obtained in a single growth step over nonplanar substrates patterned with ridges. When the ridge dimensions are large enough, the growth on the mesa top is similar to that on a planar substrate. In contrast, ridge spacings below almost-equal-to 10 mum influence the composition of the alloys grown on the ridge as well as those grown in the valley centre. The possible surface mechanisms which may explain this behaviour are discussed.

We studied the influence of the indium composition y, growth temperature T(s) and InGaAs quantum-well channel thickness d(ch) on the 300 and 77 K Hall electrical properties of pseudomorphic modulation doped field effect transistor (MODFET)-type heterostructures grown by molecular-beam epitaxy. In agreement with Nguyen et al., we find an optimum channel thickness of 90 angstrom for an indium composition y = 0.25 of the channel. Significant improvements in sheet resistivity rho(s) and in carrier concentration

We demonstrate edge-emitting lasers based on self-assembled InAs quantum dots (QDs) on GaAs substrates. The InAs QDs are embedded in an InGaAs quantum well (QW) to red-shift the lasing transition. The lasers emit at lambda=1.2 mum with threshold current densities approximate to100 A/cm(2). Maximum modal gains on the order of 5 cm(-1) are deduced for a single QD sheet.

The coherent dynamics of cavity-polaritons are investigated using the four-wave-mixing technique. A series of experiments on four samples operating in both the weak and strong coupling regimes were performed to study the influence of strong coupling on the interaction of cavity-polaritons with other cavity-polaritons, free carriers and acoustic phonons. Due to Rabi splitting a larger number of free carriers are created in the strong coupling sample compared with the weak coupling sample. This has a signific

Low-frequency drain-current noise in pseudomorphic InAlAs/InGaAs/InP HEMTs has been studied at low drain bias as a function of the InGaAs pseudomorphic channel thickness. The 1/f noise at 77 K, quantified through the Kooge's empirical parameter alpha(ch), was found to be strongly dependent on the 2DEG concentration n(s) and correlated to the reciprocal mobility 1/mu. alpha(ch) was found to strongly increase at high channel thicknesses. Noise spectra analysis as a function of temperature reveals two traps wi

We discuss the growth of lattice matched GaInAs, GaInAsP and GaInAsP/GaInAs multiple quantum well structures for high speed laser applications. Optical cavities, including five 90 angstrom GaInAs quantum wells with GaInAsP barriers and waveguides showed a 4 K photoluminescence line width of 8.7 meV. Transmission electron microscopy and X-ray diffraction confirm the good control over the growth of these structures.

A measurement system has been developed to determine the resistance of integer quantum Hall plateaux relative to a room-temperature reference resistor network of nominally the same values. Silicon MOSFET and GaAs-AlGaAs samples have been successfully fabricated and measured. The results confirm that the integer quantum Hall effect (QHE) may be used to monitor a group of standard resistors comprising the laboratory unit of resistance. They demonstrate the feasibility of defining the laboratory unit of resist

Regular periodic structures with large refractive index contrast are often called photonic crystals and may exhibit photonic bandgap behaviour. Planar waveguide 2D and 1D periodic microstructures exhibiting photonic bandgap behaviour are likely to be useful in realising the devices and connecting structures required for compact forms of integrated optical circuit.

We used optical pumping by the Vanderbilt free-electron laser and the technique of internal photoemission to measure with high accuracy the conduction-band discontinuity of semiconductor heterojunction interfaces. The experiment is the first application to our knowledge of a free-electron laser to interface research.

A reproducible and robust techique of contacting GaAs/GaAlAs heterostructures using an evaporated AuGeNi alloy has been developed. The behavior of the electrical contacts to the two-dimensional electron gas has been studied in the quantum Hall regime. Contact resistance values of typically 10-50 m-OMEGA are obtained which are stable with time and thermal cycling. This type of contact is therefore well suited to be used for precision measurements of the quantized Hall resistance.

Marc Ilegems

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Extraction of FET parameters at low drain bias by taking into account the dependence of mobility on 2D electron gas concentration

Tuning InAs/GaAs quantum dot properties under Stranski-Krastanov growth mode for 1.3 mu m applications

Low-Frequency Noise Measurements of Alxga1-Xas/Inyga1-Y as/Gaas High-Electron-Mobility Transistors

Molecular-beam epitaxial growth and characterization of modulation-doped field-effect transistor heterostructures using InAs/GaAs superlattice channels

Low-frequency Noise in Lattice-matched In0.52Al0.48As/In0.53Ga0.47As/InP HEMTs

DC characterization and low-frequency noise in delta-doped, pulse-doped and uniformly-doped GaAs/AlGaAs MODFETs

Photoluminescence and Hall characterization of pseudomorphic GaAs/InGaAs/AlGaAs heterostructures grown by molecular-beam epitaxy

Chemical Beam Epitaxy of 1.55-Mu-M Separate-Confinement Heterostructure Multiple-Quantum-Well Laser-Diodes

Design and characterization of top-emitting microcavity light-emitting diodes

Determination of oxygen content in MBE AlGaAs layers

One-Step Growth of Buried Heterostructures by Chemical Beam Epitaxy over Patterned InP Substrates

Electrical characterization of pseudomorphic GaAs/InGaAs/AlGaAs and AlGaAs/InGaAs/AlGaAs modulation doped field effect transistor-type heterostructures grown by molecular-beam epitaxy

Long-wavelength edge-emitting lasers on gallium arsenide using InAs quantum dots embedded in InGaAs

Dephasing of strongly coupled exciton-photon systems

Low-frequency noise in pseudomorphically grown In0.52Al0.48As/In0.7Ga0.3As/InP HEMTS as a function of channel thickness

Growth of Gainas(P) and Gainasp/Gainas Mqw Structures by Cbe

The quantum Hall effect as a standard to define the laboratory unit of resistance

Waveguide photonic crystals and microstructures

Interface Measurements of Heterojunction Band Lineups with the Vanderbilt Free-Electron Laser

Properties of alloyed AuGeNi-contacts on GaAs/Ga/AlAs-heterostructures