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ABSTRACT: The optical properties of wurtzite GaN nanowires containing single AlGaN/GaN quantum discs of different thickness have been investigated. The dependence of the photoluminescence (PL) transition energy on the quantum disc thickness and the thickness of a lateral AlGaN shell has been simulated in the framework of a three-dimensional effective mass model, accounting for the presence of a lateral AlGaN shell, strain state and the piezoelectric and spontaneous polarization. The predicted transition energies are in good agreement with the statistics realized on more than 40 single nanowire emission spectra and PL spectra of ensembles of nanowires. The emission spectra of the single quantum discs exhibit a Lorentzian shape with a homogeneous line width as low as 3 meV. Finally, we discuss the dependence of the interband transition energy on diameter.
Nanotechnology 03/2013; 24(12):125201. · 3.98 Impact Factor
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G Jacopin,
L Rigutti,
S Bellei,
P Lavenus, F H Julien,
A V Davydov,
D Tsvetkov,
K A Bertness,
N A Sanford,
J B Schlager,
M Tchernycheva
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ABSTRACT: The optical polarization properties of GaN/AlGaN core/shell nanowire (NW) heterostructures have been investigated using polarization resolved micro-photoluminescence (μ-PL) and interpreted in terms of a strain-dependent 6 × 6 k·p theoretical model. The NW heterostructures were fabricated in two steps: the Si-doped n-type c-axis GaN NW cores were grown by molecular beam epitaxy (MBE) and then epitaxially overgrown using halide vapor phase epitaxy (HVPE) to form Mg-doped AlGaN shells. The emission of the uncoated strain-free GaN NW core is found to be polarized perpendicular to the c-axis, while the GaN core compressively strained by the AlGaN shell exhibits a polarization parallel to the NW c-axis. The luminescence of the AlGaN shell is weakly polarized perpendicular to the c-axis due to the tensile axial strain in the shell.
Nanotechnology 07/2012; 23(32):325701. · 3.98 Impact Factor
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M Tchernycheva,
L Rigutti,
G Jacopin,
A de Luna Bugallo,
P Lavenus, F H Julien,
M Timofeeva,
A D Bouravleuv,
G E Cirlin,
V Dhaka,
H Lipsanen,
L Largeau
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ABSTRACT: We report on the growth and electro-optical studies of photovoltaic properties of GaAsP nanowires. Low density GaAsP nanowires were grown by Au assisted MOVPE on Si(001) substrates using a two step procedure to form a radial p-n junction. The STEM analyses show that the nanowires have cubic structure with the alloy composition GaAs₀.₈₈P₀.₁₂ in the nanowire core and GaAs₀.₇₆P₀.₂₄ in the shell. The nanowire ensembles were processed in the form of sub-millimeter size mesas. The photovoltaic properties were characterized by optical beam induced current (OBIC) and electronic beam induced current (EBIC) maps. Both OBIC and EBIC maps show that the photovoltage is generated by the nanowires; however, a strong signal variation from wire to wire is observed. Only one out of six connected nanowires produce a measurable signal. These strong fluctuations can be tentatively explained by the variation of the resistance of the nanowire-to-substrate connection, which is highly sensitive to the quality of the Si-GaAsP interface. This study demonstrates the importance of the spatially resolved charge collection microscopy techniques for the diagnosis of failures in nanowire photovoltaic devices.
Nanotechnology 07/2012; 23(26):265402. · 3.98 Impact Factor
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ABSTRACT: The aim of the present paper was to determine the index variation in the GaN/AlN heterostructures related to the population/depletion of the quantum well fundamental state leading to the absorption variation in the spectral domain around 1.5 µm. The variation of the refractive index was deduced from the shift of the position of the beating interference maxima of different order modes in a guided wave configuration. The obtained index variation with bias from complete depletion to full population of the quantum wells is around -5 × 10(-3). This value is similar to the typical index variation achieved in InP and is an order of magnitude higher than the index variation obtained in silicon.
Optics Express 05/2012; 20(11):12541-9. · 3.59 Impact Factor
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Applied Physics Express 01/2012; 5(5):052203. · 3.01 Impact Factor
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S Sakr,
M Tchernycheva,
J Mangeney,
E Warde,
N Isac,
L Rigutti,
R Colombelli,
A Lupu,
L Vivien, F H Julien,
others
Proceedings of SPIE. 01/2012; 8262:82621Q.
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ABSTRACT: The effect of the temperature on the electrical characteristics in GaN-based resonant tunneling diodes is studied both theoretically and experimentally. At room temperature, the current-voltage measurements show reproducible negative differential resistances and a current hysteresis. However these features disappear when the temperature is decreased down to 100 K. In addition, the current exhibits transients over a few tenths of seconds which effect disappears at low temperatures. Based on these results, we conclude that the observed negative differential resistance at room temperature is not due to electron resonant tunneling but to trap charging and release.
Applied Physics Letters 10/2011; 99(14):142103-142103-3. · 3.84 Impact Factor
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ABSTRACT: We present a letter on single-wire photodetectors based on radial n-i-n multiquantum well (QW) junctions. The devices are realized from GaN wires grown by catalyst-free metalorganic vapor phase epitaxy coated at their top by five nonpolar In0.16Ga0.84N/GaN undoped radial QWs, and are sensitive to light with energy E>2.6 eV. Their photoconductive gain is as high as 2×103. The scanning photocurrent microscopy maps evidence that the detector response is localized at the extremity containing the QWs for both below (at λ = 488 nm) and above GaN band gap (at λ = 244 nm) excitation. This confirms that the device operates as a radial n-i-n junction.
Applied Physics Letters 06/2011; 98(23):233107-233107-3. · 3.84 Impact Factor
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ABSTRACT: In this work we theoretically study the vertical transport in GaN/AlGaN resonant tunneling diodes in the ballistic regime. Heterostructures based on III-nitride compounds are characterized by a large conduction band discontinuity and a presence of an internal electric field, both of which have important effects on the electronic transport. Using the transfer matrix formalism, we investigate the effect of the energetic barrier height on the resonant current. Our calculations show an increase in the peak to valley ratio (PVR) with increasing Al content of the barriers which arises from the large decrease in the valley current. Furthermore, we show that the current resonances are different for positive and negative applied voltages. We also demonstrate that, due to the asymmetry of the conduction band profile, only one current direction leads to a significant PVR. Finally, we present an approach to achieve large PVR in both current directions by reducing the asymmetry induced by the internal field.
Journal of Applied Physics 02/2011; · 2.17 Impact Factor
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ABSTRACT: The intersubband absorption of cubic GaN/Al(Ga)N quantum wells is studied experimentally and theoretically over a wide spectral range. By changing the quantum well thickness it is possible to tune the intersubband absorption peak wavelength from 1.4 μm (214 THz) to 63 μm (4.76 THz). Comparing the experimental results with simulations based on the effective-mass model we demonstrate that the GaN/AlN conduction-band offset is higher than 1.2 eV. The best fit with the experimental data is achieved for a conduction-band offset of 1.4 eV and for a GaN effective mass of 0.11m 0 .
PHYSICAL REVIEW B. 01/2011; 83(075313).
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ABSTRACT: We demonstrate terahertz intersubband absorptions at frequencies of 2.1 THz (λ ≈ 143 μm) and 4.2 THz (λ ≈ 70 μm) in nitride-based semiconductor quantum wells. The structures consist of a 3 nm thick GaN well, an Al0.05Ga0.95N step barrier, and a 3 nm thick Al0.1Ga0.9N barrier. The absorption is detected at 4.7 K. The structure design has been optimized to approach a flat-band potential in the wells to allow for an intersubband absorption in the terahertz frequency range and to maximize the optical dipole moments.
Applied Physics Letters 11/2010; 97(19):191101-191101-3. · 3.84 Impact Factor
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ABSTRACT: We report the demonstration of single-nanowire photodetectors relying on carrier generation in GaN/AlN QDiscs. Two nanowire samples containing QDiscs of different thicknesses are analyzed and compared to a reference binary n-i-n GaN nanowire sample. The responsivity of a single wire QDisc detector is as high as 2 x 10(3) A/W at lambda = 300 nm at room temperature. We show that the insertion of an axial heterostructure drastically reduces the dark current with respect to the binary nanowires and enhances the photosensitivity factor (i.e., the ratio between the photocurrent and the dark current) up to 5 x 10(2) for an incoming light intensity of 5 mW/cm(2). Photocurrent spectroscopy allows identification of the spectral contribution related to carriers generated within large QDiscs, which lies below the GaN band gap due to the quantum confined Stark effect.
Nano Letters 08/2010; 10(8):2939-43. · 13.20 Impact Factor
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Nano Letters 08/2010; · 13.20 Impact Factor
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M. Tchernycheva,
H. Macchadani,
L. Nevou,
J. Mangeney, F. H. Julien,
P. K. Kandaswamy,
A. Wirthmüller,
E. Monroy,
A. Vardi,
S. Schacham,
G. Bahir
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ABSTRACT: We have investigated intraband absorptions in GaN/AlN QDs for ultrafast all-optical switching applications at telecommunication wavelengths. Using time-resolved pump-probe experiments the electron lifetime in the excited state of the QDs is measured to be 165 fs. Intraband absorption saturation experiments reveal a record low switching energy. We then investigate quantum cascade ISB photodetectors based on GaN/AlGaN QWs and show that mesa devices with 17 × 17 µm2 size provide a frequency response above 10 GHz at 1.5 µm wavelength.
Physica Status Solidi (A) Applications and Materials 05/2010; 207(6):1421 - 1424. · 1.46 Impact Factor
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ABSTRACT: In this paper we review the recent achievements in terms of GaN/AlGaN-based intersubband (ISB) physics and devices. We first discuss the design issues and in particular the band bending effect and its influence on the ISB absorption. We then illustrate recent achievements in terms of III-nitride ISB devices with special emphasis on electro-optical modulator and a quantum cascade detector operating in the near-infrared. We show that these devices offer high frequency response at telecommunication wavelengths.
physica status solidi (b) 05/2010; 247(7):1622 - 1627. · 1.32 Impact Factor
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ABSTRACT: We report on the effect of Si doping on the mid-infrared intersubband absorption in GaN/AlGaN superlattices. For increasing doping levels, interband luminescence displays a blueshift and a broadening of the band edge caused by the screening of the internal electric field and band-filling effects. The intersubband absorption energy is mainly governed by many-body effects like exchange interaction and depolarization shift, which increase the e1–e2 subband separation. The ISB blueshift induced by many-body effects can be more than 50% of the e1–e2 transition energy.
Applied Physics Letters 04/2010; 96(14):141903-141903-3. · 3.84 Impact Factor
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G. Cywinski,
M. Gladysiewicz,
R. Kudrawiec,
M. Kry s ko,
A. Feduniewicz-Zmuda,
M. Siekacz,
M. Sawicka,
P. Wolny,
J. Smalc-Koziorowska,
L. Nevou,
M. Tchernycheva, F. H. Julien,
J. Misiewicz,
C. Skierbiszewski
J ournal of Vac cum Sci ence and Technol ogy B. 01/2010; 28(3):C3B17-C3B21.
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Proceedings of SPIE. 01/2010; 7602:76021A.
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Applied Physics Letters. 01/2010; 97:061903.
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H Machhadani,
P Kandaswamy,
S Sakr,
A Vardi,
A Wirtmüller,
L Nevou,
F Guillot,
G Pozzovivo,
M Tchernycheva,
A Lupu,
L Vivien,
P Crozat,
E Warde,
C Bougerol,
S Schacham,
G Strasser,
G Bahir,
E Monroy, F H Julien
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ABSTRACT: This paper reviews recent progress toward intersubband (ISB) devices based on III-nitride quantum wells (QWs). First, we discuss the specific features of ISB active region design using GaN/AlGaN materials, and show that the ISB wavelength can be tailored in a wide spectral range from near- to long infrared wavelengths by engineering the internal electric field and layer thicknesses. We then describe recent results for electro-optical waveguide modulator devices exhibiting a modulation depth as large as 14 dB at telecommunication wavelengths. Finally, we address a new concept of III-nitride QW detectors based on the quantum cascade scheme, and show that these photodetectors offer the prospect of high-speed devices at telecommunication wavelengths.
New Journal of Physics 12/2009; 11(12):125023. · 4.18 Impact Factor
