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  • 1
    Electronic Resource
    Electronic Resource
    Effects of energy gap and band structure on free-carrier nonlinear susceptibilities in semiconductors (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4317-4321 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using dispersion relations from the Kane band model, we obtain limiting forms for the third-order nonlinear susceptibilities due to nonparabolicity, thermal-carrier generation, and nonequilibrium optical-carrier generation. We show that whereas χ(3)'s for all three processes increase with decreasing energy gap, there is no further benefit once Eg becomes smaller than either the Fermi or thermal energies. In fact, simultaneous optimization of both the magnitude of χ(3) and the saturation properties favors materials with a large direct gap and large effective mass, coupled with a smaller thermal gap which may be indirect in either real or momentum space.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349110
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  • 2
    Electronic Resource
    Electronic Resource
    Electron scattering in dense CO2 gas: Photoionization spectra of CH3I perturbed by CO2 (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 4070-4073 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A photoionization study of CH3I in the presence of dense CO2 (density range: 1.6–10.0×1019 cm−3 ) revealed the prethreshold 2E3/2 Rydberg transitions of methyl iodide perturbed by CO2. From the measured pressure shift of the nd Rydbergs (n=11,12,13,14) the scattering length of CO2 was deduced as A=−0.224 nm, in accord with cross-section data. The vibrational structure of CO2 above 9.54 eV was found to be superimposed on the CH3I absorber photoionization spectrum, yielding a spectrum more detailed than absorption spectra of pure CO2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460762
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  • 3
    Electronic Resource
    Electronic Resource
    Autoionization spectra of CH3I in dense gaseous methane, ethane, and propane observed by photoconduction (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 1820-1824 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The influence of light alkane perturbers (up to densities 5×1020 cm−3 for methane and ethane and 2×1020 cm−3 for propane, respectively) on the autoionization spectrum of CH3I nd'(2E1/2) Rydberg series was investigated by photoconductivity excitation spectroscopy. In the experiments, we recorded photocurrents due to electronic transitions from the absorber molecule to the conduction state of each perturber. The absorption maxima of the perturbed autoionization Rydberg states appeared as maxima in the photocurrent spectrum. The asymptotic pressure shift of the Rydberg lines equals the shift of the second vertical ionization potential I(2E1/2) of the perturbed absorber. The energy shift also provides the electron scattering length A in methane, ethane, and propane. The data obtained are compared with results in the literature on photoinjection, electron beam, and swarm experiments in pure alkanes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459956
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  • 4
    Electronic Resource
    Electronic Resource
    Noise and the Kelvin method (1991)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 62 (1991), S. 1326-1332 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The Kelvin probe, used to measure changes in work function (wf), has proved particularly useful as a UHV surface analysis technique, having applications in the study of thin films, adsorption kinetics, surface photovoltage spectroscopy, surface topographies, etc. However the Kelvin circuit is plagued by noise problems, which are considerably enhanced by long connecting wires and the nonideal UHV environment. Careful shielding is essential in order to improve the signal-to-noise (S/N) ratio, especially at backing potentials close to the null condition. Although lock-in-amplifier (LIA) based automatic compensation systems are available they operate on low signal levels and are prone to electromagnetic pickup from the driving element and mechanical instabilities of the vibrating capacitor. We discuss the general noise spectrum and describe an alternative "off-null'' approach utilizing a data-acquisition-system (DAS) based measuring system that features an active suspension system (ASS), automatic set-up, and software elimination of driver talkover. This system has applications where very high resolution (〈0.1 meV) is required, or if low S/N ratios caused by reduced probe dimensions or a high noise background would otherwise prejudice the measurement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142494
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  • 5
    Electronic Resource
    Electronic Resource
    Infrared electroabsorption modulation at normal incidence in asymmetrically stepped AlSb/InAs/GaSb/AlSb quantum wells (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 92-96 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A normal-incidence modulation mechanism is proposed which uses the Stark effect to induce Γ-L transitions in asymmetrically stepped AlSb/InAs/GaSb/AlSb quantum wells (QWs). A significant feature of this structure is the unusual band alignments which localize two deep wells for the Γ and L bands in adjacent layers, i.e., the Γ-valley minimum is in the InAs while the L-valley minimum is in the GaSb. In contrast to a square QW, where the Stark shifts for both Γ and L subbands are in the same direction, the two step wells for Γ and L valleys in the proposed structure are oppositely biased in the presence of an electric field. Therefore, the first Γ and L subbands move toward each other, making the Γ-L crossover occur more efficiently. Near this point, most of the Γ electrons transfer to the L valleys, where they are allowed to make intersubband transitions under normally incident radiation. As a result, the device switches from being transparent to normal-incidence light to strongly absorbing it. The calculations indicate that excellent on/off ratios can be achieved in this structure operating at T≤150 K with electric fields on the order of ∼100 kV/cm for any infrared wavelength within the range of 3–20 μm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357065
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  • 6
    Electronic Resource
    Electronic Resource
    Interface roughness limited electron mobility in HgTe-CdTe superlattices (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 2523-2525 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We demonstrate that interface roughness is the dominant low-temperature scattering mechanism for electrons in HgTe-CdTe superlattices with thin wells. Not only do the experimental mobilities follow the expected d6W dependence, but the observed temperature dependence is accurately reproduced by theory when the treatment of interface roughness scattering is generalized for narrow-gap superlattices. The fits to data yield roughness correlation lengths in the range 60–200 A(ring).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104840
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  • 7
    Electronic Resource
    Electronic Resource
    Subpicosecond reflection switching of 10 μm radiation using semiconductor surfaces (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 1940-1942 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electromagnetic wave equations for P-polarized 10 μm radiation in a semiconductor with a free-carrier density decreasing exponentially from the surface are solved numerically. The infrared (IR) reflectivity for Brewster angle incidence is then calculated as a function of free-carrier surface density n0. This reflectivity shows a minimum of zero just below and a sharp peak at the value where n0 reaches its critical value. The features are explained with the help of a simple model. The results suggest the feasibility of a subpicosecond IR reflection switch for the case when the surface is irradiated by a 100 fs visible laser pulse. Solutions to the diffusion equation show that ensuing reflectivity decreases to zero in times shorter than 0.5 ps.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105240
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  • 8
    Electronic Resource
    Electronic Resource
    Monolayer thickness fluctuations in infrared photoluminescence for [211]-oriented HgTe-CdTe superlattices (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 545-547 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the observation of multiple photoluminescence peaks due to monolayer thickness fluctuations in HgTe-CdTe superlattices. The spectra for seven different [211]-oriented superlattices with band gaps varying from 133 to 495 meV exhibit double peaks, and in nearly all cases the energy splitting corresponds to a difference of ≈1.5 ML in the quantum well thickness.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111098
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  • 9
    Electronic Resource
    Electronic Resource
    Étalon enhancement of nonlinear optical response in Bi1−xSbx (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 756-758 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Measurements of the nondegenerate four-wave mixing of CO2 laser beams in a Bi1−xSbx film have yielded the largest high-power third-order nonlinear susceptibilities ever reported at that wavelength (χ(3)(approximately-greater-than)6×10−4 esu at P0(approximately-greater-than)2×105 W/cm2). Furthermore, an étalon effect resulting from the high reflectivity of the Bi1−xSbx films at both the air and substrate interfaces leads to an additional enhancement of the four-wave signal by as much as a factor of 30. A theoretical model based on optical modulation of the free-carrier susceptibility gives results which are in excellent agreement with the data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105333
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  • 10
    Electronic Resource
    Electronic Resource
    Normal incidence second-harmonic generation in L-valley AlSb/GaSb/Ga1−xAlxSb/AlSb stepped quantum wells (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 2048-2050 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A novel mechanism is proposed for surface-emitting second-harmonic generation at normal incidence using L-valley intersubband transitions in AlSb/GaSb/Ga1−xAlxSb/AlSb stepped quantum wells. The calculations indicate that second-harmonic susceptibilities of at least 9×10−8 m/V should be achievable under double resonance conditions, which is comparable to the best obtainable in GaAs/Ga1−xAlxAs systems for realistic propagation angles (e.g., 45°). Besides the advantage of normal-incidence geometry, the large L-valley conduction band offset between GaSb and AlSb enables doubling to frequencies spanning the entire midwave infrared spectral region. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112789
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