S. Figge

University of Bremen

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D. Hommel

Łukasiewicz Research Network – PORT Polish Center for Technology Development

130

C. Kruse

University of Bremen

Christian Tessarek

University of Bremen

S. Einfeldt

Ferdinand-Braun-Institut

T. Böttcher

Karlsruhe Institute of Technology

T. Aschenbrenner

University of Bremen

K. Sebald

University of Bremen

Andreas Rosenauer

University of Bremen

T. Paskova

Linköping University

J. Gutowski

University of Bremen

Cooperative Institutions

University of Bremen

110

Polish Academy of Sciences

Institute of Physics

Centre National de la Recherche Scientifique

University of California, Santa Barbara

Linköping University

Czech Academy of Sciences, Institute of Physics

University of Stuttgart

Technische Universität Berlin

Max Planck Society

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Improved capping layer growth towards increased stability of InGaN quantum dots

Physica status solidi. C, Conferences and critical reviews/Physica status solidi. C, Current topics in solid state physics (2009)

Christian Tessarek Tomohiro Yamaguchi S. Figge D. Hommel

Abstract Improvements in GaN capping layer growth towards increased stability of InGaN quantum dots (QDs) will be presented. Surface quality is enhanced with changing the carrier gas during GaN capping layer growth from nitrogen to hydrogen. Without a dissolution of QDs it is possible to increase the temperature to 1050 °C applying a temperature ramp during growth of GaN. Dot stacks with an uniform and up to room temperature bright photoluminescence emission spectra is reported qualifying the structure to be incorporated into LED and laser structures. Finally, the evolution of the nucleation layer into flat and broad island‐like structures will be explained by the spinodal decomposition model (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Spinodal decomposition

10.1002/pssc.200880913

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Citations (17)

Anti-diffusion barriers for gold-based metallization to GaN

MRS Proceedings (2005)

Anna Piotrowska E. Kamińska M. Guziewicz E. Dynowska A. Stonert

Diffusion barrier

Ohmic contact

Overlayer

Barrier layer

Metallizing

10.1557/proc-0892-ff14-05

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Citations (1)

In-depth and in-plane profiling of light emission properties of InGaN-based laser diode

physica status solidi (a) (2004)

M. Godlewski Ewa M. Goldys Matthew R. Phillips T. B�ttcher S. Figge

We employ cathodoluminescence (CL) technique for evaluation of in-depth and in-plane instabilities of light emission in laser diode structure. We study light emission properties from laser structure and their relation to microstructure details. Large in-plane instabilities of light emission are also present for excitation densities, larger than the threshold densities for the stimulated emission, i.e., potential fluctuations are not fully screened in the active region of the laser even at large excitation densities. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Cathodoluminescence

Laser diode

Light emission

10.1002/pssa.200303902

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Citations (0)

Photoluminescence of a ‐plane GaN: comparison between MOCVD and HVPE grown layers

Physica status solidi. C, Conferences and critical reviews/Physica status solidi. C, Current topics in solid state physics (2006)

T. Paskova R. Schifano T. Malinauskas T. Paskova J. P. Bergman

Abstract We report on the emission properties of nonpolar a ‐plane GaN layers grown by metalorganic chemical vapor deposition (MOCVD) and hydride vapor phase epitaxy (HVPE). Together with the typical band edge exciton emission, the low‐temperature photoluminescence spectra reveal several emission bands in the spectral range 3.29‐3.42 eV. These emissions appear with different intensities in layers grown by different techniques and show different thermal quenching and recombination dynamics. The 3.42 eV and 3.35 eV emissions are found to be of an intrinsic origin and are associated with carriers localized at stacking faults. The emission at 3.29 eV, which is present only in MOCVD layers, shows a donor‐acceptor pair behavior suggesting that impurities attached to structural defects are involved. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Acceptor

10.1002/pssc.200565416

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Citations (9)

Phase diagram and critical behavior of the random ferromagnet Ga1−xMnxN

Physical Review B (2013)

S. Stefanowicz G. Kunert Constantinos Simserides Jacek A. Majewski W. Stefanowicz

Molecular beam epitaxy has been employed to obtain Ga${}_{1\ensuremath{-}x}$Mn${}_{x}$N films with $x$ up to 10% and Curie temperatures ${T}_{\text{C}}$ up to 13 K. The magnitudes of ${T}_{\text{C}}$ and their dependence on $x$, ${T}_{\text{C}}(x)\ensuremath{\propto}{x}^{m}$, where $m=2.2\ifmmode\pm\else\textpm\fi{}0.2$, are quantitatively described by a tight-binding model of superexchange interactions and Monte Carlo simulations of ${T}_{\text{C}}$. The critical behavior of this dilute magnetic insulator shows strong deviations from the magnetically clean case ($x=1$), in particular, (i) an apparent breakdown of the Harris criterion, (ii) a nonmonotonic crossover in the values of the susceptibility critical exponent ${\ensuremath{\gamma}}_{\text{eff}}$ between the high temperature and critical regimes, and (iii) a smearing of the critical region, which can be explained either by the Griffiths effects or by macroscopic inhomogeneities in the spin distribution with a variance $\ensuremath{\Delta}x=(0.2\ifmmode\pm\else\textpm\fi{}0.1)$%.

Superexchange

Exponent

10.1103/physrevb.88.081201

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Citations (57)

The dominant shallow 0.225 eV acceptor in GaN

physica status solidi (b) (2006)

B. Ḿonemar T. Paskova J. P. Bergman T. Paskova S. Figge

Abstract We have studied the optical signatures of the Mg acceptor in GaN, using samples that are doped with Mg during MOCVD growth. In order to reduce the defect density in the material and thus achieve narrow linewidths in optical spectra we have used thick HVPE grown GaN layers as templates in the MOCVD growth. The photoluminescence (PL) spectra show two acceptor‐related bound exciton peaks at 3.466 eV and 3.455 eV respectively. In the lower photon energy range the 3.27 eV emission with its LO‐phonon replicas is dominant, riding on a broad background emission peaking at about 3.1 eV. These results, together with previous data in the literature, indicate that there are two acceptors in Mg‐doped GaN, one dominating the optical spectra (the 3.466 eV and the 3.27 eV emissions) and another related to the 3.455 eV and the 3.1 eV emissions. We suggest that the latter is related to the Mg acceptor, while the former is a H‐related complex, not necessarily involving Mg. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Acceptor

10.1002/pssb.200565425

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Citations (20)

Direct MOVPE‐ and MBE‐growth of a‐plane GaN on r‐plane sapphire

Physica status solidi. C, Conferences and critical reviews/Physica status solidi. C, Current topics in solid state physics (2008)

T. Aschenbrenner K. Goepel C. Kruse S. Figge D. Hommel

Abstract We report on the growth of pit‐free a‐plane GaN on (1 $ \bar 1 $ 02) sapphire (r‐plane) substrates by metal organic vapor phase epitaxy (MOVPE) using a three step growth method without low temperature nucleation layer. X‐ray diffraction ω ‐scans of the symmetric GaN (11‐20) reflex revealed for 1.2 μm thick crack‐ and pit‐free GaN layers low FWHM of 885 arcsec and 2484 arcsec measured by inclination in c‐ and m‐direction, respectively. To analyze the evolution growth was stopped at different stages and the samples were measured with AFM, SEM, and XRD. Furthermore, we discuss the overgrowth of MOVPE GaN layer with molecular beam epitaxy (MBE). For smooth MOVPE templates with closed surfaces the morphology was reproduced, whereas for not coalesced thinner layers a different growth mode and a smoothening of the layers occurred. We will discuss SEM‐ and AFMdata in detail to examine this overgrowth procedure. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Morphology

10.1002/pssc.200778690

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Citations (8)

Emission properties of a-plane GaN grown by metal-organic chemical-vapor deposition

Journal of Applied Physics (2005)

T. Paskova R. Schifano B. Monemar T. Paskova S. Figge

We report on the emission properties of nonpolar a-plane GaN layers grown on r-plane sapphire. Temperature-, excitation-density-, and polarization-dependent photoluminescences and spatially resolved microphotoluminescence and cathodoluminescence are employed in order to clarify the nature of the different emission bands in the 3.0–3.5eV spectral range. In the near band-edge region the emission lines of the donor-bound excitons (3.472eV) and free excitons (3.478eV) are resolved in the polarized low-temperature spectra, indicating a good quality of the layers. At low energies two other emissions bands with intensity and shape varying with the excited area are observed. The 3.42eV emission commonly attributed to the excitons bound to basal plane stacking faults shows thermal quenching with two activation energies (7 and 30meV) and an S-shaped temperature dependence of the peak position. This behavior is analyzed in terms of hole localization in the vicinity of the stacking faults. The emission band that peaked at 3.29eV is found to blueshift and saturate with increasing excitation intensity. The spatially resolved cathodoluminesence measurements show that the emission is asymmetrically distributed around the triangular-shaped pits occurring at the surface. The 3.29eV emission is suggested to involve impurities, which decorate the partial dislocation terminating the basal stacking faults.

Cathodoluminescence

Wide-bandgap semiconductor

10.1063/1.2128496

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Citations (192)

OT6.260 - Characterization of an Integrated Pt Counter Electrode on GaN/AlGaN-ISFET Wheatstone Bridge pH-sensors

Lectures (2024)

Alexander Hinz G. Steingelb Christian Habben S. Figge Martin Eickhoff

Wheatstone bridge

ISFET

Characterization

Bridge (graph theory)

10.5162/eurosensorsxxxvi/ot6.260

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Citations (0)

Heat generation and dissipation in GaN-based light emitting devices

physica status solidi (a) (2003)

S. Figge T. Böttcher D. Hommel Christoph Zellweger M. Ilegems

InGaN laser diodes were been grown by metalorganic vapor phase depositions on sapphire substrates. These lasers were processed as gain guided structures and showed lasing in pulsed mode operation with duty cycles up to 2% at a wavelength of 401 nm. We determined the activation energy of the carriers in the active region by temperature dependent electroluminescence measurements during LED operation. By this means we estimated the temperature evolution inside the quantum wells by recording the transients of the output intensity during a single pulse. To verify the correlation of light output power and heating of the active region we performed simulations of the heat distribution in laser diodes on a two-dimensional mesh, which contained the laser structure including the substrate. With the help of these simulations we were able to reconstructed the temperature evolution within the active region in good agreement with the experiment and determined the heat generation to be the limiting factor of the lasers driving conditions. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Duty cycle

10.1002/pssa.200303492

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Citations (21)