K. Lischka

Universität Paderborn, Paderborn, North Rhine-Westphalia, Germany

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Publications (269)480.47 Total impact

  • [Show abstract] [Hide abstract]
    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.
    MRS Online Proceeding Library 01/2012; 595. DOI:10.1557/PROC-595-F99W3.40
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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.
    MRS Online Proceeding Library 01/2012; 595. DOI:10.1557/PROC-595-F99W3.81
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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.
    Semiconductor Science and Technology 09/2011; 26(10):105023. DOI:10.1088/0268-1242/26/10/105023 · 2.21 Impact Factor
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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.
    Physical Review B 05/2011; 83(19). DOI:10.1103/PhysRevB.83.195301 · 3.66 Impact Factor
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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.
    Journal of Crystal Growth 05/2011; 323(1):286. DOI:10.1016/j.jcrysgro.2010.12.043 · 1.69 Impact Factor
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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.
    Journal of Crystal Growth 05/2011; 323(1):84. DOI:10.1016/j.jcrysgro.2010.12.042 · 1.69 Impact Factor
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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.
    Journal of Crystal Growth 05/2011; 323(1):88-90. DOI:10.1016/j.jcrysgro.2010.12.044 · 1.69 Impact Factor
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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)
    physica status solidi (c) 04/2011; 8(5):1495 - 1498. DOI:10.1002/pssc.201000904
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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)
    physica status solidi (c) 04/2011; 8(4):1204 - 1207. DOI:10.1002/pssc.201000838
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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.
    Physical review. B, Condensed matter 03/2011; 83(11). DOI:10.1103/PhysRevB.83.115302 · 3.66 Impact Factor
  • MRS Online Proceeding Library 01/2011; 263. DOI:10.1557/PROC-263-461
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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.
    MRS Online Proceeding Library 01/2011; 831. DOI:10.1557/PROC-831-E8.15
  • MRS Online Proceeding Library 01/2011; 482. DOI:10.1557/PROC-482-661
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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.
    MRS Online Proceeding Library 01/2011; 639. DOI:10.1557/PROC-639-G5.9
  • MRS Online Proceeding Library 01/2011; 449. DOI:10.1557/PROC-449-615
  • MRS Online Proceeding Library 01/2011; 537. DOI:10.1557/PROC-537-G3.14
  • MRS Online Proceeding Library 01/2011; 537. DOI:10.1557/PROC-537-G3.24
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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.
    MRS Online Proceeding Library 01/2011; 1040. DOI:10.1557/PROC-1040-Q04-02
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    ABSTRACT: We report on carbon doping of cubic GaN by CBr4 using plasma-assisted molecular beam epitaxy on 3C-SiC (001) substrates. The samples consist of a 70 nm thick GaN buffer followed by a 550 nm thick GaN:C layer. Carbon doping is realized with a home-made carbon tetrabromide sublimation source. The CBr4 beam equivalent pressure was established by a needle valve and was varied between 2×10-9 mbar and 6×10-6 mbar. The growth was controlled by in-situ reflection high energy electron diffraction. The incorporated carbon concentration is obtained from secondary ion mass spectroscopy. Capacitance voltage characteristics were measured using metal-insulator-semiconductor structures. Capacitance voltage measurements on nominally undoped cubic GaN showed n-type conductivity with ND-NA = 1×1017 cm-3. With increasing CBr4 flux the conductivity type changes to p-type and for the highest CBr4 flux NA-ND = 4.5×1018 cm-3 was obtained.
    11/2010; DOI:10.1063/1.3518291
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    ABSTRACT: By the analysis of intra- and intersubband transitions in GaN∕AlN superlattices the band offset is determined experimentally. Superlattice structures with different period lengths were fabricated by plasma-assisted molecular beam epitaxy 3C-SiC substrates. The structural properties were studied by high resolution X-ray diffraction, revealing a high structural perfection of the superlattice region with several peaks in the X-ray spectra. Infrared absorbance spectroscopy revealed clear intrasubband transitions in the spectral region of 1.55 μm measured at room temperature. Clear intersubband transitions were observed by photoluminescence at room temperature. These transition energies were compared to calculated energies using a 1D Poisson Schro¨dinger solver. For the calculations standard parameters for cubic GaN and AlN were used, while the band offset between GaN and AlN was varied. Optimal agreement between experimental and theoretical data was obtained for a band offset ΔEC:Δ EV of 55:45.
    11/2010; DOI:10.1063/1.3518288

Publication Stats

3k Citations
480.47 Total Impact Points

Institutions

  • 1970–2014
    • Universität Paderborn
      • Department of Physics
      Paderborn, North Rhine-Westphalia, Germany
  • 2010
    • University of Havana
      La Habana, Ciudad de La Habana, Cuba
    • HRL Laboratories, LLC
      Malibu, California, United States
  • 2007
    • Ruhr-Universität Bochum
      Bochum, North Rhine-Westphalia, Germany
  • 2006
    • University of Arkansas
      • Department of Electrical Engineering
      Fayetteville, Arkansas, United States
    • Stanford University
      • E. L. Ginzton Laboratory
      Palo Alto, California, United States
  • 2004
    • University Joseph Fourier - Grenoble 1
      • Institut Néel
      Grenoble, Rhone-Alpes, France
  • 1975–2004
    • Johannes Kepler University Linz
      • • Institute of Semiconductor and Solid State Physics
      • • Institut für Experimentalphysik
      • • Institut für Mikroelektronik und Mikrosensorik
      • • Institute of Physics
      Linz, Upper Austria, Austria
  • 1996–2001
    • University of São Paulo
      • São Carlos Institute of Physics
      San Paulo, São Paulo, Brazil
    • Humboldt-Universität zu Berlin
      Berlín, Berlin, Germany
  • 2000
    • Technische Universität Ilmenau
      Stadt Ilmenau, Thuringia, Germany
    • 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
  • 1994
    • Tampere University of Technology
      • Department of Physics
      Tammerfors, Pirkanmaa, Finland
  • 1989
    • Philips
      Eindhoven, North Brabant, Netherlands