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  • 1
    Electronic Resource
    Electronic Resource
    Experimental study of the electron density and discharge dynamics in a XeCl excimer laser (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 3838-3843 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The temporal variation of the electron and current densities as well as the discharge voltage in a XeCl excimer laser discharge is studied as function of gas pressure and HCl+Xe concentration. The results show that independent of pressure and gas mix composition the electron drift velocity is a constant of vd=(1.2±0.2)×106 cm s−1. While in discharges containing only helium the current and electron density are independent of pressure P, both quantities vary as P0.6 once Xe and HCl have been added. The results are examined considering the most important atomic reaction rates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346268
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  • 2
    Electronic Resource
    Electronic Resource
    Normal-incidence electroabsorption in Ga1−xAlxSb/AlSb L-valley quantum wells for 3–5 μm optical modulation (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 2810-2812 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Theoretical investigations are presented of the electric-field dependence of normal-incidence interconduction subband absorption in Ga1−xAlxSb/AlSb L-valley quantum wells. Under an applied electric field of 50 kV/cm, a blue shift of the absorption peak from 4.94 to 4.82 μm was found in a Ga0.7Al0.3Sb/AlSb structure with well width of 25 A(ring). The ability to absorb normally incident light and to achieve significant Stark shifts with bias makes the Ga1−xAlxSb/AlSb L-valley system an attractive choice for the 3–5 μm vertical optical modulators.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354630
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  • 3
    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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  • 4
    Electronic Resource
    Electronic Resource
    Anisotropic screening and ionized impurity scattering in semiconductor superlattices and multiple quantum wells (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 6676-6685 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a general theoretical treatment of ionized impurity scattering in semiconductor superlattices. Employing an extension of the quasi-two-dimensional calculations of Stern and Howard to multi-well structures, we explicitly account for nonuniformity of the wavefunction distribution function, arbitrary dispersion relations, scattering by impurities in neighboring periods, and screening by electrons in neighboring wells. Interperiod phenomena are found to be quite significant whenever the screening length is comparable to or longer than the distance between the quantum wells. Calculated results are compared with recent data for modulation-doped and setback-modulation-doped HgTe-CdTe superlattices. However, the discussion emphasizes general aspects of the problem rather than features specific to a particular system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355338
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  • 5
    Electronic Resource
    Electronic Resource
    Enhancement of intersubband Stark effects in L-valley step quantum wells for infrared modulation and voltage tunable detection (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 1195-1198 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We propose a new type of optical modulator employing two-step Ga1−xAlxSb/Ga1−yAlySb/Ga1−zAlzSb L-valley quantum wells to enhance the Stark shifts of the intersubband transition energy and therefore to achieve large absorption spectral changes with applied bias. Due to the effective-mass anisotropy of electrons in the L-valleys and the tilted growth direction with respect to the valleys, this novel structure can intrinsically absorb normal incidence light. Under an electric field of 50 kV/cm, a blue shift of the absorption peak from 10.9 to 9.8 μm was found from our calculations in a Ga0.7Al0.3Sb/Ga0.5Al0.5Sb/Ga0.4Al0.6Sb structure with a Ga0.7Al0.3Sb well width of 25 A(ring) and a Ga0.5Al0.5Sb step width of 25 A(ring). The ability to absorb normally incident light and to achieve significant Stark effects with bias makes this structure an attractive choice for such high-speed optoelectronic devices as vertical infrared light modulators and voltage tunable photodetectors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354920
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  • 6
    Electronic Resource
    Electronic Resource
    Auger recombination in HgCdTe quantum wires and quantum boxes (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 3394-3398 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Quantum-wire and quantum-box structures for narrow-gap materials with small effective masses, such as HgCdTe, can readily be fabricated using current lithographic techniques. In this article, we calculate the Auger-recombination carrier lifetimes in HgCdTe quantum-wire and quantum-box structures, with band gaps in the 2–5 μm wavelength range. Quantum confinement is generally believed to increase the carrier lifetimes. However, we find the Auger recombination lifetime in a HgCdTe quantum wire is shorter than that in a quantum well, and it decreases as the wire width decreases because of the corresponding increase in the density of states. On the other hand, band-to-band Auger recombination is zero in a quantum box because the overlap functions vanish and because of the discrete nature of the energy levels. Therefore, within the confines of our model, we can expect improved temperature performance from long-wavelength quantum-box lasers but not from quantum-wire lasers. Furthermore, these conclusions are applicable for all types of band-to-band Auger processes and semiconductor materials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350935
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  • 7
    Electronic Resource
    Electronic Resource
    High Rydberg states of methyl iodide perturbed by nitrogen: A mutual cancellation of shift terms (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 7885-7889 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dependence of the positions of both prethreshold and autoionizing high Rydberg states of CH3I on the density ρ of the perturber N2 was measured at room temperature, using synchrotron radiation. Up to ρ=2.2×1020 cm−3 no pressure shift was observed, showing that the scattering shift by the valence electron is compensated by the polarization shift due to the core. From the results, the value A=(1.9±0.3)×10−9 cm was found for the scattering length, in good accord with previous pressure shift and swarm results. The wide range of useful applications of the photocurrent excitation spectra to the study of perturbed transitions is stressed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462341
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  • 8
    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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  • 9
    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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  • 10
    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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