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  • 2000-2004  (11)
  • 1995-1999  (23)
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  • 1
    Digitale Medien
    Digitale Medien
    Far-infrared electroluminescence from parabolic quantum well superlattices excited by resonant tunneling injection (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 172-177 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We present an investigation of intersubband emission at far-infrared wavelengths from semiconductor superlattices with parabolically graded quantum wells. Light emission is produced by sequential resonant tunneling injection of electrons into higher energy levels of the quantum wells and subsequent radiative decay. The current versus voltage curves of these devices exhibit negative differential resistances characteristic of the sequential resonant tunneling injection. A single, narrow emission peak is observed from the superlattices with parabolic quantum wells demonstrating radiative decay through multiple evenly spaced energy levels. When a chirped superlattice acting as an electron energy filter replaces the barrier in each period of the structure, clearer resonances are observed in the current–voltage characteristics and more efficient injection is achieved. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.373638
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  • 2
    Digitale Medien
    Digitale Medien
    A two-dimensional ultrahigh vacuum positioner for scanning tunneling microscopy (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 1403-1405 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A two-dimensional ultrahigh vacuum compatible positioner is presented. The positioner uses two piezoelectric inchworms which allow for motions of up to 1 cm with a precision of 4 nm mounted at right angles to each other in order to give two dimensions of motion. Images of three-dimensional In0.3Ga0.7As islands in cross section are presented to demonstrate the functionality of the positioner. It is found that motion towards the tip is smooth, while motion in the perpendicular direction is less smooth. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1148773
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  • 3
    Digitale Medien
    Digitale Medien
    Fabrication and characterization of 100-nm-thick GaAs cantilevers (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 3591-3593 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: We describe a new process for making submicron, micromechanical cantilevers out of GaAs epilayers grown by molecular beam epitaxy. The extremely high aspect ratios of these cantilevers (typically 100 nm thick and 100 μm long) give spring constants as low as 10−4 N/m. We present characterizations of the cantilevers' resonant frequencies, quality factors, and spring constants. The ability to fabricate III–V GaAs-based mechanical microstructures offers new opportunities for integration with electronics for strain-sensitive force detection. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1147250
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  • 4
    Digitale Medien
    Digitale Medien
    Electrical and optical properties of infrared photodiodes using the InAs/Ga1−xInxSb superlattice in heterojunctions with GaSb (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 1116-1127 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The InAs/Ga1−xInxSb strained-layer superlattice (SLS) holds promise as an alternative III–V semiconductor system for long wavelength infrared detectors. In this article, we present the first investigation, to the best of our knowledge, of heterojunction photodiodes using this new material. The devices were grown by molecular beam epitaxy on GaSb substrates, and are comprised of a 38 A(ring) InAs/16 A(ring) Ga0.64In0.36Sb SLS used in double heterojunctions with GaSb contact layers. The structures were designed to optimize the quantum efficiency while minimizing transport barriers at the heterointerfaces. The photodiodes are assessed through the correlation of their performance with the SLS material quality and the detector design. X-ray diffraction, absorption, and Hall measurements are used to determine the SLS material properties. The electrical and optical properties of the photodiodes are determined using current–voltage and spectral responsivity measurements. At 78 K, these devices exhibit rectifying electrical behavior and photoresponse out to a wavelength of 10.6 μm corresponding to the SLS energy gap. The responsivity and resistance in these thin-layered (0.75 μm), unpassivated photodiodes result in a detectivity of 1×1010 cm (square root of)Hz/W at 8.8 μm and 78 K. Based upon the performance of these devices, we conclude that high-sensitivity operation of long-wavelength photovoltaic detectors at temperatures well in excess of conventional III–V band gap-engineered systems, and potentially in excess of HgCdTe, is feasible using this material system. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.362849
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  • 5
    Digitale Medien
    Digitale Medien
    Tunneling induced transparency: Fano interference in intersubband transitions (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 3455-3457 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report the observation of tunneling induced transparency in asymmetric double quantum well structures. Resonant tunneling through a thin barrier is used to coherently couple the two upper states in a three level system of electronic subbands in a GaAs/AlGaAs structure. This creates Fano-type interferences for the collective intersubband excitations in the absorption from the ground state, analogous to electromagnetically induced transparency (EIT) in atomic systems. We observe a 50% reduction in absorption between the subband resonances which can be explained by taking into account the coherent coupling of the upper states. We analyze the bias dependent absorption spectra and determine the relevant lifetime broadening and dephasing rates for the transitions. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.119199
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  • 6
    Digitale Medien
    Digitale Medien
    Cryogenic scanning probe characterization of semiconductor nanostructures (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 671-673 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We demonstrate the use of a scanned probe microscope (SPM) at 4 Kelvin to study electron transport through a ballistic point contact in the two-dimensional electron gas inside a GaAs/AlGaAs heterostructure. The electron gas density profile is locally perturbed by the charged SPM tip providing information about the electron flow through the point contact. As the tip is scanned, one obtains a spatial image of the ballistic electron flux as well as the topographic profile of the structure. Calculations indicate the spatial resolution is comparable to the electron gas depth. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.117801
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  • 7
    Digitale Medien
    Digitale Medien
    Far-infrared emission from parabolically graded quantum wells (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 3522-3524 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have observed grating coupled far infrared (FIR) emission from parabolically graded quantum wells (PQWs) by the application of an in-plane electric field. The peak emission frequency from different wells matches the designed harmonic oscillator frequency for each well, as determined by the curvature of the PQWs. This is a confirmation that the generalized Kohn theorem applies for emission of FIR radiation. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.117232
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  • 8
    Digitale Medien
    Digitale Medien
    Imaging and magnetometry of switching in nanometer-scale iron particles (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 3269-3271 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The reversal mechanisms in arrays of nanometer-scale (〈40 nm diameter) iron particles are studied by low-temperature Hall magnetometry and room-temperature magnetic force microscopy. Rotation of the net array magnetization at low temperatures (20 K) occurs by both reversible and irreversible modes, the latter revealed by Barkhausen jumps. Spatially resolved measurements at room temperature show the particles to be single domain with remanence and coercivity indicating they are not superparamagnetic. Individual particles are observed to switch irreversibly over a small field range (〈10 Oe) between preferred magnetic directions parallel to the growth direction of the particles. Scaling of the arrays offers the possibility of magnetic storage at the 45 Gbit/in.2 level, nearly 50 times greater than current technology. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.118032
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  • 9
    Digitale Medien
    Digitale Medien
    Far-infrared pump-probe measurements of the intersubband lifetime in an AlGaAs/GaAs coupled-quantum well (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 3019-3021 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report pump-and-probe measurements of the electron intersubband lifetime (T1) in an AlGaAs/GaAs heterostructure using a picosecond pulsed far-infrared laser. The subband spacing (11 meV) is less than the optical-phonon energy. Time-resolved measurements yield intersubband lifetimes ranging from T1=1.1±0.2 ns to T1=0.4±0.1 ns depending on measurement conditions. Results are in agreement with previous lifetime measurements on the same sample using continuous excitation at intensities ≤1 W/cm2. The steady-state measurements yielded shorter lifetimes at high excitation intensities, possibly due to carrier heating leading to intersubband scattering by optical phonon emission. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.116683
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  • 10
    Digitale Medien
    Digitale Medien
    Photon-assisted tunneling in a resonant tunneling diode: Stimulated emission and absorption in the THz range (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 2816-2818 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The dc I–V characteristic of a triple-barrier resonant tunneling diode (RTD) integrated in a bowtie antenna and driven by THz radiation displays up to five additional resonant tunneling channels. These channels appear as additional peaks in the I–V characteristic whose voltage positions vary linearly with frequency in the investigated range between ν=1.0 and 3.4 THz. We attribute these peaks to photon-assisted tunneling processes corresponding to absorption and stimulated emission of up to three photons. The experiments suggest that such a device can be utilized to detect and generate THz radiation. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.114794
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