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  • 1
    Electronic Resource
    Electronic Resource
    HIV-1 neutralization and tumor cell proliferation inhibition in vitro by simplified analogs of pyrido[4,3,2-mn]thiazolo[5,4-b]acridine marine alkaloids (1992)
    s.l. : American Chemical Society
    Journal of medicinal chemistry 35 (1992), S. 2744-2752 
    Details
    ISSN: 1520-4804
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/jm00093a005
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  • 2
    Electronic Resource
    Electronic Resource
    Competition between band gap and yellow luminescence in GaN and its relevance for optoelectronic devices (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 4615-4620 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The competition between band gap and the 2.2 eV (yellow) luminescence of epitaxial GaN is studied for excitation densities ranging from 5×10−6 to 50 W/cm2. The ratio of the peak intensities of the band gap-to-yellow luminescence changes from 4:1 to 3000:1 as the excitation density is increased by 7 orders of magnitude. At room temperature, the band gap luminescence linewidth is 2.3kT, close to the theoretical minimum of 1.8kT. A model is developed describing the intensity of the two radiative transitions as a function of the excitation density. This model is based on bimolecular rate equations and takes into account shallow impurities, deep levels, and continuum states. The theoretically predicted dependences of the two different luminescence channels follow power laws with exponents of 1/2, 1 and 3/2. Thus the intensity of the yellow luminescence does not saturate at high excitation densities. These dependences are in excellent agreement with experimental results. The relevance of the results for optoelectronic GaN devices is discussed. It is shown that the peak intensity of the yellow luminescence line is negligibly small at typical injection currents of light-emitting diodes and lasers. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363443
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  • 3
    Electronic Resource
    Electronic Resource
    Low-temperature photoluminescence of epitaxial InAs (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 6416-6424 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photoluminescence studies as well as reflectance and transmittance measurements were performed on high-purity epitaxial InAs grown by metal-organic chemical-vapor deposition. We report the optical identification of excitonic, donor, and acceptor impurity related transitions at a temperature of 1.4 K. Measurements at higher temperature and in the presence of magnetic fields up to 7 T support these identifications. We find the excitonic band gap at 415.65±0.01 meV according to the minimum in the polariton reflectance feature. The donor–acceptor-pair and acceptor-bound exciton transitions for three different acceptors are observed by photoluminescence, and we tentatively associate one of them to a double acceptor formed by a Ga impurity on an As lattice site. A donor-bound exciton transition is observed with a binding energy of 0.42 meV. The magnetic field dependence yields values of the electron effective mass and g factor of (0.026±0.002)m0 and −15.3±0.2, respectively, in good agreement with values obtained by other techniques. Furthermore, we report a deep luminescence band of unknown origin at ∼375 meV, related to drastic temporal changes in the band-edge photoluminescence intensity. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363660
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  • 4
    Electronic Resource
    Electronic Resource
    Strain effects in high-purity InP epilayers grown on slightly mismatched substrates (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 2460-2465 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The growth of high-purity InP on various As-, S-, and Fe-doped InP substrates has been investigated using high-resolution photoluminescence spectroscopy (PL) and high-resolution x-ray diffractometry. Substrate induced strains of −7×10−5 or less have been observed using low-temperature PL. In this way information about the strain dependence of the electronic excited states of the donor bound excitons in InP was obtained. In addition, it was shown that the assessment of variations in substrate lattice parameter can be determined with a resolution of at least 5×10−6 by PL techniques.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356271
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  • 5
    Electronic Resource
    Electronic Resource
    Atomic layer epitaxy and structural characterization of InP and InAs/InP heterostructures (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 2398-2405 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the growth and structural properties of InP, InAs/InP strained single quantum wells and short-period InAs/InP strained layer superlattices by atomic layer epitaxy. A self-limiting growth close to 1 monolayer/cycle has been obtained for InP and for InAs with low substrate temperatures between 350 and 360 °C. The samples were grown on InP (001) substrates and characterized by high resolution x-ray diffraction, grazing-incidence x-ray reflectometry, and Raman spectroscopy. The interference of x-ray wave fields in the grown structures observed by both types of x-ray measurements can be used to measure nondestructively the thickness of the deposited films with relatively high precision. High resolution x-ray diffraction and grazing-incidence x-ray reflectometry of the InAs/InP superlattices confirm the periodicity of the structures in agreement with theoretical predictions. Raman spectroscopy shows doublets of folded acoustic modes as well as InAs-like and InP-like confined longitudinal optical phonons in the InAs/InP superlattices. Results indicate that, despite the 3.2% lattice mismatch, atomic layer epitaxy is a powerful method for fabricating highly strained structures with atomically controlled heterointerfaces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356261
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  • 6
    Electronic Resource
    Electronic Resource
    Temperature dependence of photoluminescence in InAsP/InP strained multiple quantum wells (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5921-5926 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The photoluminescence spectra of InAsP/InP strained multiple quantum wells have been experimentally determined in the temperature range 7–300 K. In order to understand the temperature behavior of the photoluminescence, a theoretical calculation is presented that takes into account the temperature-induced variations in band gap, carrier effective mass, biaxial strain, and exciton binding energy. The results show that the energy of the transition E1H between the n=1 electron subband and the n=1 heavy-hole subband changes as a function of temperature, and depends mainly on the evolution of the strained band gap of the InAsP layers. This is because in the temperature range 7–300 K the variations of the electron subband energy and the exciton binding energy are much less than those of the strained band gap, while the variation of the heavy-hole subband energy can be neglected. These results also explain why, for a lattice-matched quantum well, the variation of exciton peak energies with temperature follows that of the forbidden energy gap of the bulk material in the well.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358481
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  • 7
    Electronic Resource
    Electronic Resource
    In situ observation of indium segregation by reflectance difference spectroscopy in single monolayer heterostructures grown by atomic layer epitaxy (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 1576-1578 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Single monolayers of InAs in GaAs and GaAs in InAs have been grown by atomic layer epitaxy (ALE) at 50 Torr. In situ reflectance difference spectroscopy monitoring of the surface during each stage of the growth showed a strong asymmetry in the surface behavior between the two systems. Following insertion of an InAs monolayer in GaAs, approximately 20 ML of GaAs are required to recover an In-free, As-stabilized GaAs surface at 390 °C. On the other hand, following the insertion of 1 ML of GaAs in InAs, the spectrum returns to a Ga-free, As-stabilized InAs surface after only 1 ML of InAs deposition. This behavior shows clear evidence of the presence of segregation caused by thermodynamic factors even at the very low growth temperatures used for ALE. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.114944
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of strain on confined optic phonons of highly strained InAs/InP superlattices (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 4983-4989 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have measured Raman scattering and high-resolution x-ray diffraction from highly strained [(InAs)4(InP)4]N short-period superlattices grown on InP substrates by atomic layer epitaxy at 355 °C. The InAs and InP confined phonons are observed in these highly strained short-period superlattices. The energy of the InAs confined longitudinal-optical phonon (LO) modes of a fully strained superlattice (with N=8) is blue shifted by about 10 cm−1 compared to the LO phonon of bulk InAs. This effect is explained by the large biaxial strain existing in the InAs layers. The observed frequency shift agrees with the lattice-mismatch strain given by elasticity theory and independently measured by high-resolution x-ray diffraction. No evidence of a frequency shift of the InP confined LO modes in the N=8 fully strained superlattice is observed, indicating that the strain is confined to the InAs layers. We show that in a partially relaxed superlattice (with N=20), the InAs layers are in compression, while the InP layers are in tension. In this case the InP confined LO1 phonons are red shifted by about 3 cm−1 compared to the InP LO1 phonons of the N=8 fully strained superlattice, and the shift of the InAs confined LO phonons with respect to the LO phonons of bulk InAs is also reduced.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354303
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  • 9
    Electronic Resource
    Electronic Resource
    Inductively coupled plasma etching of GaN (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 1119-1121 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Inductively coupled plasma (ICP) etch rates for GaN are reported as a function of plasma pressure, plasma chemistry, rf power, and ICP power. Using a Cl2/H2/Ar plasma chemistry, GaN etch rates as high as 6875 A(ring)/min are reported. The GaN surface morphology remains smooth over a wide range of plasma conditions as quantified using atomic force microscopy. Several etch conditions yield highly anisotropic profiles with smooth sidewalls. These results have direct application to the fabrication of group-III nitride etched laser facets. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117077
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  • 10
    Electronic Resource
    Electronic Resource
    Characterization of 3C–SiC crystals grown by thermal decomposition of methyltrichlorosilane (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 3824-3826 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Single crystal 3C–SiC platelets, formed by thermal decomposition of methyltrichlorosilane at 1650–1750 °C, have been characterized in terms of structure and morphology. The platelets are ∼3–5 mm in length and 1–1.5 mm in thickness. The (111) C face of the crystal, which has an effective zero growth rate, presents a large, mirrorlike surface in the as-grown 3C crystals. Atomic force microscopy indicates that these as-grown surfaces are extraordinarily flat and uniform, with a mean surface roughness of 1–2 A(ring). This value is comparable with the roughness of state-of-art polished Si wafers. X-ray rocking curves of the 〈111〉 peak were obtained with a linewidth of 12.3 arcsec. This is the smallest value reported to date for any polytype of SiC. Raman spectroscopy at 300 K reveals a very sharp TO–phonon peak at 797.8 cm−1, with a linewidth of 2.1 cm−1. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117117
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