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  • 1
    Electronic Resource
    Electronic Resource
    Spectroscopic ellipsometry characterization of strained and relaxed Si1−xGex epitaxial layers (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 239-250 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Spectroscopic ellipsometry has been used to study thick, relaxed and thin, strained epilayers of Si1−xGex on Si in the range 0.1〈x〈0.25. Dielectric functions of relaxed Si0.87Ge0.13 and Si0.8Ge0.2 have been obtained and long-wavelength absorption coefficient values, required for interference fringe fitting, shown to be higher than measured previously. The dielectric function of strained Si0.78Ge0.22 has been measured for the first time and the effects of strain on the critical points shown to be consistent with deformation potential theory. An interpolation procedure has been developed for the fitting of layer composition and thickness, and excellent agreement with conventional techniques obtained for a series of uncapped single epilayers. The surface roughness of Si1−xGex epilayers has been studied as a function of time and deposition temperature and shown to play an important role in the modeling. The application of the technique to the characterization of buried strained layers is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353896
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  • 2
    Electronic Resource
    Electronic Resource
    Spectroscopic ellipsometry of Si1−xGex epilayers of arbitrary composition 0≤x≤0.255 (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 1114-1116 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Critical point (CP) transition energies have been calculated for strained Si1−xGex (0≤x≤0.255) between 2.5 and 3.5 eV from Lorentzian fits to the second differential of reference dielectric function spectra. E1 and E'0 transition energies are similar to those of the relaxed alloy. Comparison with deformation potential theory shows E1+Δ1 to be coincident with E'0 due to a strain-induced up shift in the former's transition energy. The reference spectra and CP transition energies are used in an interpolation procedure to analyze spectroscopic ellipsometry spectra of both uncapped and buried layers of strained Si1−xGex. Compositions and thicknesses are obtained in good agreement with alternative techniques.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.110823
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  • 3
    Electronic Resource
    Electronic Resource
    Analysis and modeling of the base currents of Si/Si1−xGex heterojunction bipolar transistors fabricated in high and low oxygen content material (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 2823-2829 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A comparison is made of the dc electrical characteristics of Si/Si1−xGex heterojunction bipolar transistors (HBTs) fabricated on high oxygen content material grown using molecular beam epitaxy and low oxygen content material grown using chemical vapor deposition. The base currents of Si/Si0.85Ge0.15 HBTs with a high oxygen content are significantly higher than those of comparable devices with a low oxygen content and the base currents of both are higher than those of silicon homojunction devices. In addition the base current in the low oxygen content devices increases significantly when the germanium concentration is increased from 15% to 23%. The roles of the lifetime in the base and the out-diffusion of the boron from the Si1−xGex base are investigated using a two-dimensional drift-diffusion device simulator. It is shown that the increased base currents in the HBTs are caused by recombination in the neutral base, and that the lifetime in the Si1−xGex is an important parameter in determining the base current. Modelling of the measured base currents indicates that the lifetime in the high oxygen content Si0.85Ge0.15 is reduced by a factor of approximately 15 compared with silicon, but in the low oxygen content Si0.77Ge0.23 by a smaller factor of approximately 4. Boron out-diffusion from the base is present in both the high and low oxygen content HBTs, but it appears to be significantly less in the former. A high oxygen content in Si1−xGex HBTs therefore has the disadvantage of decreasing the lifetime, but the advantage of decreasing the boron out-diffusion from the base. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360082
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  • 4
    Electronic Resource
    Electronic Resource
    A model for heterogeneous growth of Si1−xGex films from hydrides (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 3729-3732 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Growth rates for Si1−xGex films (0≤x≤0.19) have been measured between 610–750 °C using low pressure H2/SiH4/GeH4 mixtures and at different temperatures these rates show different dependencies on composition x. A model attributes this complex behavior to competition between an increasing rate for desorption of surface hydrogen and a decreasing sticking probability for the reactive hydrides as x increases. The latter effect is explicitly reported for the first time. GeH4 is found to be ∼4.7 times more reactive than SiH4, and relative surface hydrogen coverages on Si and Si0.87Ge0.13 films measured by secondary ion mass spectroscopy are compared with the model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348466
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  • 5
    Electronic Resource
    Electronic Resource
    Atmospheric impregnation of porous silicon at room temperature (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 422-431 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Microporous and mesoporous Si layers contain a very large surface area that affects both their optical and electrical properties. Secondary ion mass spectroscopy (SIMS) analysis is used for the first time to simultaneously monitor all the major impurities on that surface. SIMS data on a microporous layer demonstrate that its chemical composition changes dramatically with time during ambient air exposure. Similar trends are observed for mesoporous layers. Extended storage in air at room temperature converts the hydride surface of freshly anodized layers to that of a contaminated native oxide. Characterization techniques need to take the metastability of the hydride surface into account since the structural, optical, and electrical properties of porous Si can consequently change with time upon exposure to ambient air. Low-temperature photoluminescence and spectroscopic ellipsometry data on freshly anodized and "aged'' microporous and mesoporous layers are chosen to illustrate typical changes in optical properties and the timescales involved. Spreading resistance analysis is also shown for the first time to provide depth information on the resistivities of porous layers and their variation with extended exposure to air. Implications for other characterization techniques are briefly discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350293
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  • 6
    Electronic Resource
    Electronic Resource
    Efficient visible electroluminescence from highly porous silicon under cathodic bias (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 2563-2565 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Visible electroluminescence (EL) has been obtained from porous silicon cathodically biased in an aqueous electrolyte containing either the persulphate or the peroxide ion. EL efficiencies of up to 0.1% have been obtained from porous silicon formed on both n-type and p-type substrates for the application of only a few volts bias. In subdued lighting, the EL is easily visible to the naked eye at excitation densities of 0.1 W cm−2. EL is obtained only from porous silicon capable of giving photoluminescence (PL); the EL and PL spectra are broadly similar in width and peak wavelength. The EL spectra are reversibly shifted to shorter wavelengths as the magnitude of the bias is increased. In contrast with the previously reported EL under anodic conditions, this cathodic EL process does not irreversibly oxidize the porous silicon skeleton.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.108127
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  • 7
    Electronic Resource
    Electronic Resource
    Electroluminescence from a pseudomorphic Si0.8Ge0.2 alloy (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 1350-1352 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electroluminescence due to recombination of electrons and holes at the band edges of strained Si1−xGex alloy is reported for the first time. This is demonstrated by comparison of the luminescence energy with the photoconductivity threshold of a p-i-n diode incorporating Si0.8Ge0.2, and with the calculated energy gap for the pseudomorphic alloy. The luminescence is strong at low temperature and persists to 220 K. The high intensity of the no-phonon line relative to the momentum-conserving phonon replica in the spectrum shows the scattering in the random alloy is a practical and effective mechanism for enhancing the recombination probability in this indirect semiconductor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105305
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  • 8
    Electronic Resource
    Electronic Resource
    Long-wavelength SiGe/Si resonant cavity infrared detector using a bonded silicon-on-oxide reflector (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 544-546 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Resonant-enhanced detection of long wavelength infrared radiation using a SiGe/Si multiquantum well device grown on a bonded silicon-on-insulator substrate reflector is reported. A low refractive index in the wavelength region below the 9.2 μm absorption peak in SiO2 gives high Si/SiO2 reflectivities between 7 and 9 μm. Comparison with a control device grown on a p+-Si substrate shows a fivefold enhancement in the peak responsivity at 7.2 μm, which is the resonant wavelength of the cavity formed between the buried Si/SiO2 and the Si/air interfaces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116394
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  • 9
    Electronic Resource
    Electronic Resource
    Absorption in p-Si1−xGex quantum well detectors (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 1512-1514 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The normal incidence absorption between 2 and 14 μm in a pseudomorphic p-Si0.81Ge0.19/Si multiple quantum well sample with doping 5×1012 cm−2 per well is described by a Drude conductivity characteristic of free carriers, with an in-plane mobility of 32 cm2/V s and a relaxation time of 5.5 fs at 77 K. When the absorption is scaled with dopant concentration these parameters predict quantum efficiencies for quantum well infrared photodetectors in reasonable agreement with experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113630
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  • 10
    Electronic Resource
    Electronic Resource
    Spectroscopic ellipsometry of epitaxial Si {100} surfaces (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 1304-1306 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dielectric spectra of Si {111} and Si {100} orientations are shown to be equivalent using ex situ spectroscopic ellipsometry on clean epitaxial surfaces. The peak values for the real and imaginary parts (εr,i) of the dielectric function exceed those previously reported, values of εi (at 4.25 eV)≥47 being obtained. Surface features with lateral scales of ≈0.5–2 μm, do not affect the dielectric spectra significantly. The high dielectric function peaks indicate that the nanometer lateral-scale roughness on these epitaxial surfaces is very small.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.107573
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