K. Lischka

Universität Paderborn, Paderborn, North Rhine-Westphalia, Germany

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Publications (288)491.95 Total impact

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    ABSTRACT: It has been shown that the excitons bound to individual donors in epitaxially grown ZnMgSe/ZnSe quantum-well (QW) nanostructures provide suitable single-photon sources and optically controllable qubits for quantum information technology. Here we demonstrate ion implantation as an alternative fluorine doping method for ZnMgSe/ZnSe QWs. Photoluminescence measurements of F-implanted ZnSe QWs show the correlation between the number of sharp recombination peaks of F-donor bound excitons and the implantation dose as well as the saturation of the luminescence intensity related to a donor. The magnetospectroscopy results confirm the presence of two doubly connected Λ systems in the same way as for epitaxially grown and F-doped ZnSe QWs. If special techniques such as selective implantation through a mask and registration of single-ion impacts are applied on micro- and nanocavities, the ion implantation can be an attractive alternative fluorine doping method for quantum information technology based on fluorine impurities in ZnSe.
    No preview · Article · Feb 2012 · Physical review. B, Condensed matter
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    ABSTRACT: Here we demonstrate the ion-implantation of fluorine as an alternative doping method for ZnMgSe/ZnSe QWs. The photoluminescence measurements of F-implanted ZnSe QWs show the correlation between the number of sharp recombination peaks of F-donor bound-excitons and the implantation dose as well as the saturation of the luminescence intensity related to a donor. When special techniques such as selective implantation through a mask and registration of single ion impacts are applied on micro-, nano-cavities, the ion implantation can be an attractive alternative fluorine doping method for quantum information technology based on fluorine impurities in ZnSe.
    No preview · Article · Feb 2012 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: Carrier concentration and mobility were measured for intrinsic cubic InN and GaN, and for Si-doped cubic GaN as a function of temperature. Metallic n-type conductivity was found for the InN, while background p-type conductivity was observed for the intrinsic GaN layer. Doping the cubic GaN with Si two regimes were observed. For low Si-doping concentrations, the samples remain p-type. Increasing the Si-doping level, the background acceptors are compensated and the samples became highly degenerated n-type. From the carrier concentration dependence on temperature, the activation energy of the donor and acceptor levels was determined. Attempts were made to determine the scattering mechanisms responsible for the behavior of the mobility as a function of temperature.
    Full-text · Article · Jan 2012 · MRS Online Proceeding Library
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    ABSTRACT: Si-doping of cubic GaN epilayers grown by an rf plasma-assisted molecular beam epitaxy on semi-insulating GaAs (001) substrates is investigated by secondary ion mass spectroscopy (SIMS), photoluminescence (PL) and by Hall-effect measurements. SIMS measurements show a homogeneous incorporation of Si in cubic GaN epilayers up to concentrations of 5*1019 cm−3. PL shows a clear shift of the donor-acceptor emission to higher energies with increasing Si-doping. Above a Si-flux of 1*1011cm−2s−1 the near band edge lines merge to one broad band due to band gap renormalization and conduction band filling effects. The influence of the high dislocation density (≈1011cm−2) in c-GaN:Si on the electrical properties is reflected in the dependence of the electron mobility on the free carrier concentration. We find that dislocations in cubic GaN act as acceptors and are electrically active.
    No preview · Article · Jan 2012 · MRS Online Proceeding Library
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    ABSTRACT: Laser irradiation damage in ZnTe epilayers was analyzed in situ by power-density-dependent and time-resolved micro-Raman spectroscopy. Damage by ablation or compound decomposition on the sample surface was revealed by the decrease of the ZnTe–nLO mode intensity with the increase of laser power density. The appearance of the peaks associated with the stronger crystalline-tellurium modes, tellurium aggregates and second-order Raman scattering at room temperature μ-Raman spectra was observed for higher power densities than 4.4 × 105 W cm−2. The Raman signal time transients of ZnTe–nLO and crystalline-tellurium modes reveal an exponential evolution of the laser irradiation damage and a fast formation of crystalline tellurium aggregates on the layer surface.
    Full-text · Article · Sep 2011 · Semiconductor Science and Technology
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    ABSTRACT: Vapor–liquid–solid condensation was utilized to fabricate zinc-blende GaN quantum dots on 3C-AlN (0 0 1) in a molecular beam epitaxy system. By adjustment of deposition parameters and nitridation procedure the density of the quantum dots was controllable in the range of 5e8–5e12 cm−2. The quantum dots in the range of 8e10–5e12 cm−2 have shown strong optical activity in photoluminescence spectroscopy. Furthermore we have demonstrated that vapor–liquid–solid condensation is suitable to tune the emission energy of zinc-blende GaN quantum dots in the range of 3.55–3.81 eV.
    No preview · Article · May 2011 · Journal of Crystal Growth
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    ABSTRACT: Non-polar relaxed cubic GaN was grown by molecular beam epitaxy (MBE) on nano-patterned 3C-SiC/Si (0 0 1) substrates with negligible hexagonal content and less defect density than in planar cubic GaN layers. Nano-patterning of 3C-SiC/Si (0 0 1) is achieved by self-ordered colloidal masks for the first time. The method presented here offers the possibility to create nano-patterned cubic GaN without the need for a GaN etching process and thus is a potential alternative to the conventional top–down fabrication techniques.
    No preview · Article · May 2011 · Journal of Crystal Growth
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    ABSTRACT: The presently unknown band offset in nonpolar cubic GaN/AlN superlattices is investigated by inter-sub-band and interband spectroscopies as well as ab initio calculations. On one hand, the conduction-band offset (CBO) has been determined from the comparison of the measured transition energies with model calculations within the effective mass approximation. On the other hand, the valence-band offset (VBO) and the CBO are accurately simulated by calculating many-body corrections within the GW approximation on top of hybrid-functional density functional theory calculations. Thus, a CBO of (1.4±0.1) eV and a VBO of (0.5±0.1) eV is obtained as a result of both approaches.
    No preview · Article · May 2011 · Physical Review B
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    A. Zado · E. Tschumak · J. W. Gerlach · K. Lischka · D. J. As
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    ABSTRACT: We report on carbon doping of cubic GaN by CBr4 using plasma-assisted molecular beam epitaxy. Cubic GaN:C samples were doped at different CBr4 beam equivalent pressures between 2×10−9 and 6×10−6 mbar. The incorporated carbon concentration of up to 1×1020 cm−3 was achieved in c-GaN:C as measured by secondary ion mass spectroscopy. The net donor/acceptor concentration was obtained by evaluation of capacitance-voltage data. Capacitance-voltage measurements on nominally undoped cubic GaN showed n-type conductivity. With an increase in CBr4 flux the conductivity type changed to p-type and for highest CBr4 flux an acceptor surplus of 1×1019 cm−3 was obtained. The electrical properties of the c-GaN:C layers were investigated by current–voltage measurements and a decrease in the serial conductance by two orders of magnitude was demonstrated in c-GaN:C. A blue shift of the 2 K donor–acceptor pair luminescence with an increase in carbon concentration was obtained.
    Full-text · Article · May 2011 · Journal of Crystal Growth
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    ABSTRACT: Zinc-blende GaN/AlN quantum dots were grown in a molecular beam epitaxy system by two alternative methods. In method A the quantum dots were formed by the Stranski-Krastanov process, whereas in method B the quantum dots were created by a vapor-liquid-solid process, respectively. The density of the Stranski-Krastanov quantum dots was adjustable in a range of 5 x 109 cm-2 to 5 x 1012 cm-2. The density of the quantum dots grown by method B was controllable in the range of 5 x 108 cm-2 to 5 x 1012 cm-2. For both methods the samples with a high density of quantum dots have shown strong optical activity in photoluminescence spectroscopy. The emission energy of the quantum dots was tuneable in a range of 3.5 eV to 3.9 eV by alteration of the quantum dot height. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    Full-text · Article · May 2011 · physica status solidi (c)
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    ABSTRACT: We report the growth of cubic GaN/AlN superlattices by plasma-assisted molecular beam epitaxy on 3C-SiC substrates. The samples consist of 100 nm thick unintentionally doped GaN buffer and 20-40 period superlattices of silicon doped GaN quantum wells embedded in undoped AlN barriers. The thickness of the AlN barriers is varied between 1.5 nm-3.2 nm, while the thickness of the GaN well varies between 1.5 nm-12.5 nm. The growth was controlled by in situ reflection high energy electron diffraction. The structural properties of our samples were studied by high resolution x-ray diffraction. Two superlattice satellite peaks in the x-ray spectra reveal a high structural perfection of the active region. Clear evidence for inter- and intrasubband transitions was observed in photoluminescence, absorbance and photoconductivity spectra measured at room temperature. Model calculations show the possibility to fabricate devices for the near- and far infrared region. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    Full-text · Article · Apr 2011 · physica status solidi (c)
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    ABSTRACT: Exciton states have been studied experimentally in strained ZnSe/(Zn,Mg)Se quantum well structures with a Mg content of only 3.6% by means of magnetoreflectivity and ultrafast piezospectroscopy. The small intrinsic band gap difference and the built-in strain in barriers and quantum wells lead to a shallow confinement potential for heavy holes which is smaller than the Coulomb electron-hole interaction. An exciton state formed by a confined electron and heavy-hole continuum states is identified. The experimental findings are supported by numerical model calculations.
    No preview · Article · Mar 2011 · Physical review. B, Condensed matter
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    ABSTRACT: The misfit dislocation structure of vicinal InP-on-GaAs heterostructures is studied by transmission electron microscopy (TEM). An island type growth is identified. The misfit stress is not fully relaxed at the interface. X-ray measurements on strain relaxation and epilayer misorientation are also reported, and the latter results are explained with the asymmetric introduction of 6Ø° dislocations at island edges. Comparing the results, it is concluded that x-ray data supply additional, although indirect, information on initial growth which is hardly detectable by TEM.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    ABSTRACT: Cubic InGaN/GaN double heterostructures and multi-quantum-wells have been grown by Molecular Beam Epitaxy on cubic 3C-SiC. We find that the room temperature photoluminescence spectra of our samples has two emission peaks at 2.4 eV and 2.6 eV, respectively. The intensity of the 2.6 eV decreases and that of the 2.4 eV peak increases when the In mol ratio is varied between x = 0.04 and 0.16. However, for all samples the peak energy is far below the bandgap energy measured by photoluminescence excitation spectra, revealing a large Stokes-like shift of the InGaN emission. The temperature variation of the photoluminescence intensity yields an activation energy of 21 meV of the 2.6 eV emission and 67 meV of the 2.4 eV emission, respectively. The room temperature photoluminescence of fully strained multi quantum wells (x = 0.16) is a single line with a peak wavelength at about 510 nm.
    Full-text · Article · Jan 2011 · MRS Online Proceeding Library
  • D. J. As · C. Wang · B. Schöttker · D. Schikora · K. Lischka

    No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    ABSTRACT: Temperature dependent Hall-Effect-measurements on unintentionally doped cubic GaN epilayers grown by molecular beam epitaxy (MBE) are reported. The cubic GaN layers have been deposited on semiinsulating (001) GaAs-substrates under N-stabilized growth conditions which were controlled by in-situ reflection high energy electron diffraction (RHEED) measurements. GaN-layers, which were fabricated under N-stabilized conditions have a (2×2) surface reconstruction during growth and show p-type conductivity. At room temperature the measured hole concentrations and mobilities are p = 9.7* 1012 cm-3, μp ≅ 350 cm2/Vs, respectively. Temperature dependent measurements of the carrier concentration yield an acceptor activation energy of EA = 0.445 eV. The nature of these defects will be discussed in view of intrinsic defects proposed by theoretical calculations already published in literature. The temperature dependence of the mobility is dominated by polar optical phonon scattering in the investigated temperature range.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    ABSTRACT: Cubic Al y Ga 1-y N/GaN heterostructures on GaAs(001) substrates were grown by radio-frequency plasma-assisted molecular beam epitaxy. High resolution X-ray diffraction, spectroscopic ellipsometry and cathodoluminescence were used to characterize the structural and optical properties of the alloy epilayers. X-ray diffraction reciprocal space maps demonstrate the good crystal quality of the cubic Al y Ga 1-y N films. Both SE as well as room temperature CL of the Al y Ga 1-y N epilayer show a linear increase of the band gap with increasing Al-content. A pseudomorphically strained cubic 10 x (2.4 nm GaN/ 4.8 nm Al 0.12 Ga 0.88 N) multi-quantum well (MQW) structure has been realized. Cathodoluminescence clearly demonstrates strong radiative recombination due to quantized states in the GaN well layer at a photon energy of 3.323 eV.
    Full-text · Article · Jan 2011 · MRS Online Proceeding Library
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    ABSTRACT: Nominally undoped cubic GaN epilayers deposited by rf-plasma assisted molecular beam epitaxy on semi-insulating GaAs substrates were investigated by electric and photoelectric spectroscopical methods. As a consequence of the existence of deep levels in the GaAs-substrate itself, special care has to be taken to separate the contributions of the substrate from that of the cubic GaN epilayer in the various spectra. Two different contact configurations (coplanar and sandwich structures) were successfully used to perform this separation, In the cubic GaN epilayer a trap with a thermal activation energy of (85+/-20)meV was found by thermal admittance spectroscopy and thermal stimulated currents. Optical admittance spectroscopy and photocurrent measurements furthermore revealed defects at E-G-(0.04-0.13) eV, E-G-(0.21-0.82) eV and two additional deeper defects at 1.91 Ev and 2.1 eV, respectively. These defect related transitions are very similar to those observed in hexagonal GaN.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    ABSTRACT: Cubic AlxGa1-xN films were grown by molecular beam epitaxy on freestanding 3C-SiC (001) substrates with an Al mole fraction of x=0 to 0.74. Using the intensity of a reflected high energy electron beam as a probe we find optimum growth conditions of c-AlGaN when a one-monolayer gallium coverage is formed at the growing surface. Clear reflection high energy electron diffraction oscillations during the initial growth of AlxGa1-xN/GaN layers were observed. The growth rate was about 177 nm/h. We find that the aluminium mole fraction is only determined by the aluminium flux, and that the AlxGa1-xN growth rate is independent on the aluminium content. Atomic force microscopy exhibits smooth surfaces with a RMS roughness of about 5 nm on 5×5 µm2 areas. Cathodoluminescence spectroscopy revealed clear band edge emission up to an aluminium mole fraction of x=0.52, showing a linear relation between the band gap energy and the Al composition.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    ABSTRACT: P-type doping with Mg and n-type doping with Si of cubic GaN (c-GaN) epilayers is reported. Cubic GaN films are grown by rf-plasma assisted MBE on semi-insulating GaAs (001) substrates at a substrate temperature of 720°C. Elemental Mg and Si are evaporated from thermal effusions cells. Secondary ion mass spectroscopy (SIMS), low temperature photoluminescence (PL) and temperature dependent Hall-effect measurements are used to study the incorporation, optical and electrical properties. A Mg related shallow donor-acceptor transiton at 3.04 eV with an acceptor activation energy of EA=0.230 eV is observed by low temperature PL. At Mg concentrations above 1018 cm-3 the dominance of a broad blue band indicates that also in c-GaN Mg is incorporated at different lattice sites or forms complexes. Si-doped c-GaN epilayers are n-type with electron concentrations up to 5*1019 cm-3. The incorporation of Si follows exactly the vapor pressure curve of Si, indicating a sticking coefficient of 1 for Si in c-GaN. With increasing Si-concentration the intensity of the near-band luminescence continuously increases and broadens.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library

Publication Stats

4k Citations
491.95 Total Impact Points

Institutions

  • 1970-2014
    • Universität Paderborn
      • Department of Physics
      Paderborn, North Rhine-Westphalia, Germany
  • 2011
    • Otto-von-Guericke-Universität Magdeburg
      • Institute of Experimental Physics (IEP)
      Magdeburg, Saxony-Anhalt, Germany
  • 1998
    • Charles University in Prague
      • Ústav částicové a jaderné fyziky
      Praha, Hlavni mesto Praha, Czech Republic
  • 1975-1998
    • Johannes Kepler University Linz
      • • Institut für Experimentalphysik
      • • Institut für Mikroelektronik und Mikrosensorik
      • • Institute of Semiconductor and Solid State Physics
      • • Institute of Physics
      Linz, Upper Austria, Austria
  • 1994
    • Masaryk University
      Brünn, South Moravian, Czech Republic