W. van der Vleuten

Technische Universiteit Eindhoven, Eindhoven, North Brabant, Netherlands

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Publications (38)54.92 Total impact

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    ABSTRACT: The phonon bottleneck in self-assembled InAs/GaAs quantum dots (SAD's) is observed directly in continuous-wave photoluminescence experiments when exciting one GaAs longitudinal optical (LO)-phonon energy above the ground level of the smallest dot. To overcome the phonon bottleneck, selective photoluminescence (PL) experiments are performed and multiple phonon-assisted radiative bands are observed. We found that no real crystal states are involved in the experimentally observed phonon emission. Under nonresonant excitation at 5 K, the SAD's photoluminescence band is centered at 1.315 eV. As proven by our photoluminescence experiments at high excitation densities, there are no excited states in such small dots. We interpret the phonon-assisted PL as being due to enhanced Fröhlich interaction between strain-induced polarized excitons in the SAD's and LO phonons. Further experimental support for this model is found from the cleaved-side PL measurements. A light-hole ground state is observed, instead of the theoretically predicted heavy-hole one.
    Physical Review B 02/2001; · 3.77 Impact Factor
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    ABSTRACT: We present experimental evidence that asymmetric current injection in intracavity contacted vertical-cavity surface-emitting lasers (VCSELs) stabilizes the polarization of the emitted light. Anisotropies in the gain and loss mechanisms introduced by asymmetric current injection are considered to explain this effect. The design scheme opens perspectives to obtain actual polarization control in VCSELs.
    IEEE Photonics Technology Letters 09/2000; · 2.04 Impact Factor
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    ABSTRACT: The carrier capture into ultrathin InAs layers embedded in a GaAs matrix has been investigated by time-resolved two-wavelength pump-probe phototransmission at 4.2 K. Using an InAs thickness of 1.2 monolayers, we observe switching of the carrier relaxation from optical to acoustic phonon emission. At the light-hole (lh) exciton transition we find a constant capture time of 20 ps. In contrast, the capture time decreases abruptly from 50 ps to 22 ps within the heavy-hole (hh) exciton transition as the energy separation between lh and hh states exceeds the threshold for GaAs LO phonon emission. The combination of both characteristics provides strong evidence for a two-step capture process of the holes. First the holes are captured by the weakly confined lh state and then they cool down to the hh state. We calculated the transient bleaching of the excitonic absorption considering both phase-space filling and exciton screening. The calculations show in agreement with the measurements that the phototransmission transients directly reflect the population of the confined InAs states only at excitation densities below 3×108 cm-2. At larger excitation densities, the phototransmission rise time becomes significantly smaller than the capture times whereas its decay time appears longer than the carrier lifetime.
    Physical Review B 06/2000; 61(24):1475387-16840. · 3.77 Impact Factor
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    ABSTRACT: We have experimentally determined the band offsets at a highly strained InAs/GaAs interface by means of coupling between two ultrathin InAs layers embedded in a GaAs matrix. When both InAs layers are separated by a 32-ML barrier, the confined electron and light-hole (lh) states are split into symmetric and antisymmetric states, whereas the heavy-hole (hh) level is not split yet. Consequently, the splitting between the hh exciton transitions, which is measured by photoluminescence excitation spectroscopy, is solely determined by the conduction-band offset ΔEc. Knowing ΔEc, the hh and lh band offsets ΔEhh and ΔElh were subsequently determined from the coupling-induced shift and splitting in samples with 16-, 8-, and 4-ML barriers. We find a conduction-band offset of 535 meV, a conduction-band offset ratio of Qc=0.58, and a strain-induced splitting between the hh and lh levels of 160 meV. This method for the direct determination of band offsets is explicitly sensitive to the band-offset ratio, and its application is not restricted to particular type-I semiconductor heterostructures as long as the effective-mass-band-offset product for the conduction and valence bands differs by at least a factor of 2.
    Physical Review B 04/1999; 59(15):1061211-10326. · 3.77 Impact Factor
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    ABSTRACT: A low-confinement asymmetric GaAs-AlGaAs double-quantum-well molecular-beam-epitaxy grown laser diode structure with optical trap layer is characterized, The value of the internal absorption coefficient is as low as 1.4 cm/sup -1/, while keeping the series resistance at values comparable cm with symmetrical quantum-well gradient index structures in the same material system. Uncoated devices show COD values of 35 mW//spl mu/m. If coated, this should scale to about 90 mW//spl mu/m. The threshold current density is about 1000 A/cm/sup 2/ for 2-mm-long devices and a considerable part of it is probably due to recombination in the optical trap layer. Fundamental mode operation is limited to 120-180 mW for 6.5-/spl mu/m-wide ridge waveguide uncoated devices and to 200-300 mW for 13.5-/spl mu/m-wide ones, because of thermal waveguiding effects. These values are measured under pulsed conditions, 10 /spl mu/s/l ms.
    IEEE Photonics Technology Letters 03/1999; · 2.04 Impact Factor
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    ABSTRACT: The authors report on temperature-dependent Hall effect measurements on Si delta-doped GaAs samples grown by MBE at 480 °C, 530 °C and 620 °C. In the best sample grown at 480 °C the mobility is 6760 cm2 V-1 s-1 at 4.2 K. To the authors' knowledge this is the highest mobility ever reported in a delta-doped structure. From subband population measurements the spreading of the donors in the samples grown at low temperature is determined to be 20 Å. On these high-mobility samples they were able to perform the first reported cyclotron resonance measurements. The electron effective mass is found to be considerably higher than that at the Gamma-conduction band minimum in GaAs.
    Semiconductor Science and Technology 12/1998; 5(8):861. · 1.92 Impact Factor
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    ABSTRACT: A photoluminescence (PL) study is made of (001) oriented GaAs samples containing a single delta doping layer of silicon. Depending on the growth temperature several novel narrow spectral features are observed that are related to the delta doping procedure, but cannot be attributed to transitions involving conduction electron subbands. The nature of one specific PL feature at 1.4977 eV is explored in detail. It is present in delta-doped samples grown at low temperatures (480 degrees C) and shows all the characteristics of a bound exciton recombination. Its most conspicuous properties are a strong linear polarization along (110) and a (001) axially symmetric spin splitting in high magnetic fields. The whole of the spectroscopic data leads to a model in which an exciton is bound to a Si-As-Si complex, aligned along the (110) direction.
    Semiconductor Science and Technology 12/1998; 6(11):1079. · 1.92 Impact Factor
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    F. Karouta, E. Smalbrugge, W.C. van der Vleuten, S. Gaillard, G.A. Acket
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    ABSTRACT: A versatile fabrication technique for GaAs-AlGaAs wet-etched mirror lasers is presented. This technique works independently of the Al concentration in the cladding layers up to a value of 70%, and it requires four photolithography steps. Ridge waveguide lasers have been successfully processed using a double heterostructure (DHS) as well as graded index separate confinement heterostructures (GRINSCH) having different quantum-well (QW) active layers. This technique is used to fabricate short-cavity lasers in GRINSCH structures having GaAs multiple-quantum-well (MQW) or bulk active layers. Laser operation was obtained in a 29-μm-long device using a 5-QW structure. Short lasers with QW active layers show a complex spectral behavior. These lasers operate at higher current densities (~20 kA/cm<sup>2</sup>) and emit light at more than one wavelength. This implies that higher order transitions are involved which is not the case when using a bulk GaAs active layer. Besides the two peaks corresponding to the n=1 and n=2 transitions, we found an intermediate peak which corresponds presumably to the forbidden transition E1-HH2
    IEEE Journal of Quantum Electronics 09/1998; · 1.83 Impact Factor
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    ABSTRACT: High in-plane magnetic field gradients are used to control the lateral motion of excitons in an InGaAs quantum well. The gradients, as large as 6.104 T/m, are produced by positioning a thin magnetized stripe of dysprosium on top of the quantum well. By measuring the exciton photoluminescence energy and intensity, spatially resolved with μm resolution, it is shown that the diamagnetic excitons are forced to regions of low magnetic field, because of the interaction of their magnetic moment with the inhomogeneous field. These results show the possibility to magnetically confine excitons to a limited region of space, which opens the way for the realization of the first magnetic trap in solids.
    Physica B Condensed Matter 01/1998; · 1.33 Impact Factor
  • F. Karouta, H.A. Langeler, E. Smalbrugge, W.C. van der Vleuten
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    ABSTRACT: Etched mirror lasers offer the possibility of being integrable in Opto-Electronic Integrated Circuits (OEIC). A versatile processing technique of GaAs/AlGaAs Wet Chemically Etched Mirror Lasers (WCEML) has been developed previously. It is applicable to all laser structures in the InGaAs/AlGaAs/GaAs system. A special set of masks allowed us to vary the cavity lengths of ridge waveguide type devices from 750 μm down to 11 μm and ridge widths of 4, 6 and 10 μm. The processing requires four photolithography steps. In this paper we report on the results obtained from four different GRINSCH laser structures: one having a bulk GaAs active layer (50 nm thick) while the others have 2, 3 and 5 QWs of 7 nm GaAs as an active layer respectively
    Lasers and Electro-Optics Society Annual Meeting, 1997. LEOS '97 10th Annual Meeting. Conference Proceedings., IEEE; 12/1997
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    ABSTRACT: Three terminal (3T) Double Barrier Resonant Tunneling (DBRT) devices having the base contact to the quantum well have been fabricated from GaAs/AlAs material system. The technological solution is based on high selective etching processes to reach the plane of the very thin quantum well on which, subsequently, a Schottky base contact is obtained using a nonalloyed Ti/Pt/Au metallization scheme. DC and AC electrical measurements demonstrate that the base contact lies on the quantum well of the DBRT structure and the base voltage modulates the collector current. It is shown that the electrical characteristics of these devices enlarge the possibilities of investigations on DBRT structures and suggest important applications in high-speed electronics
    Semiconductor Conference, 1997. CAS '97 Proceedings., 1997 International; 11/1997
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    ABSTRACT: Accurate microwave measurements up to 40 GHz have been carried out on GaAs/AlAs Double Barrier Resonant Tunneling (DBRT) diodes over the whole bias range of its DC characteristic. The resulting small-signal scattering parameters (S-parameters) have been analysed afterwards in terms of equivalent circuits. The analysis demonstrates that the most suitable equivalent circuit of the DBRT structure has to include, apart from the circuit elements used to model the Esaki tunnel diode, an intrinsic inductance which is related to the life time of the quantum well quasi-state involved in the tunneling process. The bias dependency of the equivalent circuit parameters and the maximum oscillation frequency of the DBRT device have been obtained
    Semiconductor Conference, 1997. CAS '97 Proceedings., 1997 International; 11/1997
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    ABSTRACT: The small-signal intrinsic impedance of GaAs/AlAs based resonant tunnelling diodes with thin barriers has been measured at room temperature over the full 0-2 V bias-voltage and 0.05-40.05 GHz frequency ranges, on stable, non-oscillating devices. The classical Esaki and the quantum-inductance equivalent circuits were used to model the impedance for CAD purposes. Information about the quasibound-state lifetime against bias-voltage was extracted
    Electronics Letters 10/1997; · 1.04 Impact Factor
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    ABSTRACT: This paper reports experimental results on single quantum-well separate confinement heterostructures (SQW SCH) with low-confinement factor, designed for very high-power operation. The maximum power output for AR/HR coated 3-mm-long devices, measured in very short pulsed conditions (100 ns/1 kHz), from 10-μm-wide stripes was as high as 6.4 W before catastrophic optical degradation. If scaled to continuous-wave (CW) conditions, this value would be 800-1100 MW, which would mean a factor of 22.7 times more than reported for the best devices with normal design for threshold minimization. The absorption coefficient for the symmetrical structure is as low as 1.1 cm<sup>-1</sup>, in spite of the low trapping efficiency of carriers in the quantum well (QW). The maximum differential efficiency is 40% (both faces, uncoated devices) for symmetrical structure and 33% for the asymmetrical one (all measurements in pulsed conditions). Threshold current densities were 800 A/cm<sup>2</sup> for 5-mm-long devices in the symmetrical case and 2200 A/cm<sup>2</sup> in the asymmetrical one. The effects of inefficient carrier trapping in the QW on the threshold current densities and differential efficiency are discussed
    IEEE Journal of Selected Topics in Quantum Electronics 05/1997; · 4.08 Impact Factor
  • F. Karouta, J.S. Wellen, O. Abu-Zeid, G.A. Acket, W.C. van der Vleuten
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    ABSTRACT: Very short wet chemically etched mirror lasers reveal that devices show laser operation down till 29 μm of cavity length at a threshold current of 70 mA, exhibiting an output power of 0.5 mW. These devices lase simultaneously at two or three different wavelengths namely around 855, 830 and 805 nm. The number of peaks is related to the current
    Optoelectronic and Microelectronic Materials And Devices Proceedings, 1996 Conference on; 01/1997
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    ABSTRACT: High in-plane magnetic field gradients, as large as 6×104 T/m, produced with a magnetized thin dysprosium stripe, are used to control the lateral motion of excitons in a 8 nm In0.2Ga0.8As quantum well. By measuring the exciton photoluminescence (PL) energy and intensity, spatially resolved with m resolution, it is shown that diamagnetic excitons are forced to regions of low magnetic field, due to the interaction of the magnetic moment with the non-homogeneous field.
    physica status solidi (a) 01/1997; 164(1):591-594. · 1.21 Impact Factor
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    ABSTRACT: The donor-acceptor transition in the photoluminescence (PL) spectra of δ-doped n-i-p structures in GaAs is studied in detail. Unpolarized PL spectra exhibit an unexpected large linewidth; p-polarized PL spectra reveal that this line broadening is due to electron-phonon coupling. Raman data suggest that the 25-meV phonon involved belongs to the edge of the first Brillouin zone. The Huang-Rhys figure (S), which measures the electron-phonon coupling, shows a remarkable dependence both on the effective dopant charge density eNu=e(NA-+ND+)/2 as well as on the interplanar distance R0. Since under strong irradiation Nu→(NA-ND)/2, both the S value and the Stark shift Δ can be used to determine the magnitude of the miscompensation in these samples. A theoretical model will be presented that explains the observed dependences S(Nu) and S(R0) in a qualitative way. © 1996 The American Physical Society.
    Physical review. B, Condensed matter 06/1996; 53(23).
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    ABSTRACT: A single‐electron tunneling transistor has been directly coupled on‐chip to a high electron mobility transistor. The high electron mobility transistor (HEMT) is used as an impedance matching circuit with a gain close to unity. The HEMT transformed the 1.4 MΩ output impedance of the single electron tunneling (SET) transistor by two orders of magnitude down to 5 kΩ, increasing its bandwidth to 50 kHz. This circuit makes it possible to observe the motion of individual electrons at high frequencies. The requirements for the bandwidth in high frequency applications is discussed. © 1996 American Institute of Physics.
    Applied Physics Letters 03/1996; 68(14):2014-2016. · 3.79 Impact Factor
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    ABSTRACT: A program has been developed that can model the static characteristics of Double Barrier Resonant Tunneling (DBRT) diodes. This device can be considered to consist of the actual barrier structure and two reservoirs from which electrons can tunnel. Under bias one reservoir will be accumulated, the other one depleted and electrons will tunnel mainly from the former to the latter. The accumulation region provides the supply of tunneling electrons while the depletion region absorbs most of the bias voltage, so both regions have a strong influence on the device characteristics. A major problem in modeling DBRTs is the connection of the reservoirs to the barrier structure, another one is modeling the reservoirs themselves, in particular the accumulation region. Here part of the electrons is in three-dimensional states and part is confined in two-dimensional subbands. Tunneling can be partly incoherent due to interface roughness and phonon scattering. It is also important to include the charge in the well because it has a noticeable effect on the I-V and C-V characteristics as well as the noise properties. In this program all these considerations are taken into account. The model enables one also to model the static I-V and C-V characteristics of different structures. From these also the microwave noise and small-signal impedance can be calculated. The frequency range is limited to the frequency where quantum-mechanical tunneling times start to play a role.
    Solid State Device Research Conference, 1995. ESSDERC '95. Proceedings of the 25th European; 10/1995

Publication Stats

65 Citations
89 Downloads
915 Views
54.92 Total Impact Points

Institutions

  • 1993–1997
    • Technische Universiteit Eindhoven
      • • Department of Electrical Engineering
      • • Department of Applied Physics
      Eindhoven, North Brabant, Netherlands
    • Delft University of Technology
      • Applied Geophysics and Petrophysics
      Delft, South Holland, Netherlands
  • 1995
    • University of Essex
      • School of Computer Science and Electronic Engineering
      Colchester, England, United Kingdom