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Hofstetter, Daniel

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Hofstetter, Daniel
Affiliation principale
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Ancien.ne collaborateur.trice
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https://libra.unine.ch/handle/123456789/472

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  • Publication
    Accès libre
    Lattice-Matched GaN–InAlN Waveguides at λ = 1.55 μm Grown by Metal–Organic Vapor Phase Epitaxy
    (2008)
    Lupu, A.
    ;
    Julien, François H.
    ;
    Golka, Sebastian
    ;
    Pozzovivo, G.
    ;
    Strasser, Gottfried
    ;
    Baumann, Esther
    ;
    Giorgetta, Fabrizio R.
    ;
    Hofstetter, Daniel 
    ;
    Nicolay, S.
    ;
    Mosca, M.
    ;
    Feltin, E.
    ;
    Carlin, J.-F.
    ;
    Grandjean, N.
    We report on the demonstration of low-loss, single-mode GaN-InAlN ridge waveguides (WGs) at fiber-optics telecommunication wavelengths. The structure grown by metal-organic vapor phase epitaxy contains AlInN cladding layers lattice-matched to GaN. For slab-like WGs propagation losses are below 3 dB/mm and independent of light polarization. For 2.6-μm-wide WGs the propagation losses in the 1.5- to 1.58-μm spectral region are as low as 1.8 and 4.9 dB/mm for transverse-electric- and transverse-magnetic-polarization, respectively. The losses are attributed to the sidewall roughness and can be further reduced by the optimization of the etching process.
  • Publication
    Accès libre
    MBE growth of nitride-based photovoltaic intersubband detectors
    (2006)
    Monroy, Eva
    ;
    Guillot, Fabien
    ;
    Leconte, Sylvain
    ;
    Bellet-Amalric, Edith
    ;
    Baumann, Esther
    ;
    Giorgetta, Fabrizio R.
    ;
    Hofstetter, Daniel 
    ;
    Nevou, Laurent
    ;
    Tchernycheva, Maria
    ;
    Doyennette, Laeticia
    ;
    Julien, François H.
    ;
    Remmele, T.
    ;
    Albrecht, M.
    In this work, we present the plasma-assisted molecular-beam epitaxial growth of quantum well infrared photodetector (QWIP) structures, including the Si-doped GaN/AlN short-period superlattice of the active region, conductive AlGaN claddings and integration of the final device. The growth of Si-doped GaN/AlN multiple quantum well (QW) structures is optimized by controlling substrate temperature, metal excess and growth interruptions. Structural characterization confirms a reduction of the interface roughness to the monolayer scale. P-polarized intersubband absorption peaks covering the 1.33–1.91 μm wavelength range are measured on samples with QW thickness varying from 1 to 2.5 nm. The absorption exhibits Lorentzian shape with a line width around 100 meV in QWs doped 5×1019 cm−3. To prevent partial depletion of the QWs owing to the internal electric field, we have developed highly-conductive Si-doped AlGaN cladding layers using In as a surfactant during growth. Complete ISB photodetectors with 40 periods of 1 nm-thick Si-doped GaN QWs with 2 nm-thick AlN barriers have been grown on conductive AlGaN claddings, the Al mole fraction of the cladding matching the average Al content of the active region. Temperature-dependent photovoltage measurements reveal a narrow (90 meV) detection peak at 1.39 μm.
  • Publication
    Accès libre
    Dry-etching and characterization of mirrors on III-nitride laser diodes from chemically assisted ion beam etching
    (1998)
    Kneissl, Michael
    ;
    Hofstetter, Daniel 
    ;
    Bour, David P.
    ;
    Donaldson, Rose M.
    ;
    Walker, J.
    ;
    Johnson, N. M.
    Vertical mirrors have been fabricated with chemically assisted ion beam etching (CAIBE) on OMVPE grown InGaN/AlGaN laser diode structures. AFM measurements show that smooth vertical sidewalls are obtained which exhibit a root mean squared (rms) roughness of only 40–60 Å. The inclination angle of the etched mirrors is within ±2° of vertical, as SEM studies indicate. Photopumping measurements reveal that the reflectivity of the etched mirrors corresponds to 60–70% of the value for an ideal GaN/air interface. The reduced reflectivity may be due to surface roughness, a slight tilt in the facet angle, and the excitation of higher-order transverse waveguide modes in the laser structure.