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  • 1
    Digitale Medien
    Digitale Medien
    Thermally induced optical bistability in ZnSe epilayers grown by molecular-beam epitaxy (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 2532-2534 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: For the first time, ZnSe epitaxial layers grown by molecular-beam epitaxy are shown to exhibit large contrast, low power, and extremely long-term stable thermally induced absorptive optical bistability. It is observed over a wide temperature range between 169 K and RT, with a strongly variable loop width and a switch-back adjustable to be less than 50% of the respective switch-down value. Critical slowing down as well as switch-down times are studied in dependence of the excess over the switch-down intensity values.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.346475
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  • 2
    Digitale Medien
    Digitale Medien
    Comparative optical investigations of ZnSe/GaAs epilayers grown by molecular beam and hot-wall epitaxy (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 5630-5635 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Comparative photoluminescence and excitation spectra of ZnSe/GaAs epilayers grown by molecular beam epitaxy (MBE) and hot-wall epitaxy (HWE) show likewise features in the exciton energy regime. Two strain-split components of the free exciton are observed, as well as characteristic sets of transitions from or into ground and excited states of acceptor- and donor-bound excitons. However, all respective lines are shifted to lower energies in the HWE samples, due to the increased thermally induced strain as a consequence of the substrate temperatures being enhanced compared to the MBE growth. Whereas the dominant donors are of the same nature in both kinds of samples, specific acceptor centers are incorporated in the HWE films. Although the MBE-grown layers are of superior quality, it is shown that HWE under optimized growth conditions is a cheap and useful alternative to obtain ZnSe epilayers of reliable properties.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.346975
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  • 3
    Digitale Medien
    Digitale Medien
    Electroabsorption studies on quasi-three-dimensional and quasi-two-dimensional excitons in (Zn,Cd)Se/Zn(S,Se) structures (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 4360-4364 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The electro-optical properties of (Zn,Cd)Se/Zn(S,Se) quantum well structures grown on GaAs substrates have been studied with differential electroabsorption spectroscopy at room temperature and compared to model calculations. (Zn,Cd)Se wells of 20, 10, and 4×5 nm are investigated, corresponding to well widths of four, two, and one times the exciton Bohr radius in this material system, respectively. We observe the quantum confined Stark effect for the 4×5 nm sample and find a Stark shift of 18 meV in the heavy-hole exciton peak for an electric field change from 82 to 175 kV/cm. In contrast, the 10 nm sample shows a rather weak and more Franz–Keldysh-like signal. We show that the 20-nm-thick quantum-well sample behaves like bulk material, i.e., the electro-absorption signal is well described by Franz–Keldysh oscillations. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.371370
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  • 4
    Digitale Medien
    Digitale Medien
    Quantum beats of excitons in Zn1−xCdxSe/ZnSe multiple quantum well structures (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 4145-4147 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We investigate the coherent dynamics of excitons in Zn1−xCdxSe/ZnSe multiple quantum wells by means of spectrally integrated and spectrally resolved transient four-wave mixing. When simultaneously exciting the heavy- and light-hole exciton resonance, a beating of the spectrally integrated four-wave mixing signal is observed. The measured beating period does not exactly correspond to the energetic split of the involved free-exciton resonances. By including a bound-exciton state in the calculation of the four-wave mixing signal, quite a reasonable fit can be achieved yielding the dephasing times of the excitonic transitions. The spectrally resolved signal allows to determine the origin of the oscillation as a quantum beat between the light- and heavy-hole exciton. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.359505
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  • 5
    Digitale Medien
    Digitale Medien
    Calorimetric absorption spectroscopy of free and bound excitons in CdS at millikelvin temperatures (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 455-457 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: It is shown for the first time that the recently developed calorimetric absorption spectroscopy (CAS) is most fruitfully applicable as a direct measure of nonradiative decay of excitonic systems even concerning their fine structure properties if experiments are performed in the mK range achieved in a 3He/4He-dilution refrigerator. CAS gives hints on different scattering and relaxation processes of longitudinal AL and triplet AF excitons in CdS, and directly evidences nonradiative decay ratios of different bound-exciton complexes. Even TA-phonon-assisted recombination of such systems leads to well measurable CAS signal enhancement.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.103664
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  • 6
    Digitale Medien
    Digitale Medien
    Picosecond lasing dynamics of gain-switched (Zn,Cd)Se/Zn(S,Se)/(Zn,Mg)(S,Se) quantum well lasers (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 548-551 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We present the temporal and spectral evolution of stimulated emission from (Zn,Cd)Se/Zn(S,Se)/(Zn,Mg)(S,Se) multiple quantum well lasers at 2 K after picosecond optical excitation. For pumping well above the threshold, ultrahigh-frequency oscillations of up to 100 GHz are observed. These oscillations are generated by a multimode emission through mode beating caused by the coherent superposition of longitudinal ground modes and higher lateral modes. The modelling of the experimental results shows that the modes are coupled to some extent. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.365613
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  • 7
    Digitale Medien
    Digitale Medien
    Intensity-dependent energy and line shape variation of donor–acceptor-pair bands in ZnSe:N at different compensation levels (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 1914-1916 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We show that energy position and line shape of donor–acceptor-pair luminescence bands in ZnSe:N/GaAs epilayers depend very sensitively on excitation density and compensation. A continuous development from structureless red-shifted broad to well structured donor–acceptor-pair (DAP) bands is observed for increasing excitation density. The red shift is explained by the fluctuating potential affecting the bands and impurity levels and is caused by random distribution of charged impurities in highly compensated samples. The shift is reduced when these charge fluctuations are diminished due to an increasing number of impurities being neutralized via light-induced carrier excitation. These effects have not been taken into account in previous work concerning doped II-VI materials; however, they have to be considered when evaluating the frequently used hypothesis of a deep donor in ZnSe:N as an explanation of low-energy broadband DAP emission. The influence of band fluctuations on the behavior of the DAP luminescence and excitation spectra is qualitatively discussed. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.114566
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  • 8
    Digitale Medien
    Digitale Medien
    Quantum confined Stark effect of II-VI heterostructures suitable as modulators in the blue–green spectral region (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 3320-3322 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We present a systematic and quantitative investigation of the quantum confined Stark effect in (Zn, Cd)Se/Zn(S,Se) quantum well structures at room temperature. For this purpose, differential transmission spectroscopy is performed on two samples with different thicknesses of the active layers (4×5 nm and 10 nm) and compared to model calculations. We observe a Stark shift of 18 meV in the heavy-hole exciton peak for an electric-field change from 82 to 175 kV/cm for the 4×5 nm sample. In contrast, the 10 nm sample shows a rather weak and more Franz–Keldysh-like signal. Furthermore, we have analyzed the spectral behavior of the linewidth enhancement factor αH. Values between 5.1 and 0.2 are found at the energy of absolute maximum of the absorption change for the 4×5 nm sample. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.121637
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  • 9
    Digitale Medien
    Digitale Medien
    Influence of the barrier height on carrier recombination and transparency density in GaN-based laser structures (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 755-757 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Using temperature-dependent and gain measurements, we have examined the laser threshold density of (In,Ga)N/GaN/(Al,Ga)N laser structures with various well widths and different In contents in the active layer. Thermal activation energies, obtained by temperature-dependent photoluminescence measurements at low excitation densities, yield information on the nonradiative recombination channels and demonstrate the existence of two different activation processes. One of them may be related to thermal activation of localized carriers into quasifree states and subsequent nonradiative recombination. The other is attributed to thermal emission of carriers into the barriers. The influence of the barrier height is also reflected by the dependence of the threshold densities required on the temperature. © 2002 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1434305
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  • 10
    Digitale Medien
    Digitale Medien
    Optical gain and saturation in nitride-based laser structures (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 1763-1765 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have performed systematic studies of the optical gain and its saturation in (In, Ga)N/GaN/(Al, Ga)N laser structures that depend on the excitation density and number of quantum wells. The unsaturated gain factor which was obtained by the variable stripe-length method increases with excitation power, i.e., increasing modal gain. The gain factor also increases with a decreasing number of quantum wells, as is shown by the investigation of a series of laser structures with 3, 4, 5, and 10 quantum wells for fixed modal gain. Values up to 40 dB at 300 K were measured. Thermal activation energies obtained by temperature dependent photoluminescence measurements yield information on the influence of nonradiative recombination processes on optical gain saturation. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1401780
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