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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 1862-1867 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The defect energy levels in metalorganic chemical vapor deposition (MOCVD) grown GaxIn1−xP/InP:Fe and GaxIn1−xP/InP:S epilayers (x≤0.24) have been studied by photoluminescence (PL) and photoconductivity (PC) measurements. To understand the origin of the observed deep levels, we have determined the temperature dependence of the intensity and half-width of the dominant deep-level PL peaks. We find that (1) the dominant deep-level peaks of the samples grown on the same substrate are related to the epilayer composition, and move to higher energies with increasing gallium content; (2) the dominant deep-level peaks of the samples with the same epilayer composition grown on different substrates are different. They are attributed to the impurity in the substrate diffusing into the epilayer during MOCVD growth, forming an impurity-vacancy complex. The following tentative assignments are proposed: the dominant deep-level peaks in GaxIn1−xP/InP:Fe and GaxIn1−xP/InP:S are attributed to the emission of a (V)P-(Fe)III complex and a (V)III-(S)P complex, respectively. Comparing the deep level with the near-band-edge emission we show that (1) all deep levels are independent of the band edge as x is varied; (2) the composition dependences of the deep levels associated with such complexes depend on the site occupied by the impurity atom.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 4233-4235 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin TiN layers have been successfully produced by reactive evaporation combined with rapid thermal annealing. Their stoichiometry as a function of depth has been measured by elastic recoil detection combined with time-of-flight. It is shown that this technique is the most appropriate for stoichiometry determination of TiN layers.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 2321-2327 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Anisotropic optical, electrical, and structural properties have been observed in thick InxGa1−xAs/GaAs single heterostructures grown by low-pressure metal-organic vapor phase epitaxy on (001) and slightly misoriented GaAs substrates. The luminescence of the (001) samples is polarized and the electron mobility is higher along one of the 〈110〉 directions. Asymmetric distributions of surface ridges and misfit dislocations have been observed in secondary electron micrographs (SEMS) of the surfaces and in transmission electron micrographs. Strong anisotropy and a clear correlation between the anisotropic optical, electrical, and structural properties have been observed for samples grown on (001) oriented substrates. For (001) samples, the results indicate that the anisotropic properties are induced by nonuniform strain relaxation. For samples grown on misoriented substrates, SEM and micro-Raman spectroscopy indicate a better crystal quality. The anisotropic properties are found to be reversed and the degree of anisotropy is significantly reduced. The results suggest the improvement of interfacial coherency owing to the mechanism of nucleation on a substrate presenting a series of steps and ledges. The reduction of defects within the epilayer can be partly due to a faster strain relief in vicinal (001) epilayers.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 6803-6809 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photoluminescence (PL) and optical absorption spectra from samples containing InAsP/InP and InP/InGaP quantum well stacks reveal the presence of band tails in the excitonic density of states. At low temperature, radiative recombinations from these band-tail states contribute to the energy separation (redshift) between PL and optical absorption peaks for the fundamental transitions. This band-tail localization contribution is evaluated quantitatively by using a potential fluctuations model [developed by D. Ouadjaout and Y. Marfaing, Phys. Rev. B. 46, 7908 (1992)] to analyze the line shape of the low temperature PL peaks. The residual energy separation, after removing the band-tail localization component, arises from thermalization processes alone, demonstrating the validity of the model used to evaluate the band-tail induced redshift. We also found that the free excitons' effective temperature varies linearly with the optical absorption peak width, dominated by inhomogeneous broadening at low temperatures. This empirical relation suggests an explanation for the difference on the origin of the Stokes shift reported in the literature. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 9022-9028 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Samples of synthetic fused silica have been implanted at room temperature with silicon ions of energy 1.5 MeV. Fluences ranged from 1011 to 1013 cm−2. Samples were probed using variable-energy positron annihilation spectroscopy. The Doppler-broadening S parameter corresponding to the implanted region decreased with increasing fluence and saturated at a fluence of 1013 cm−2. It is shown that the decrease in the S parameter is due to the suppression of positronium (Ps) which is formed in the preimplanted material, due to the competing process of implantation-induced trapping of positrons. In order to satisfactorily model the positron data it was necessary to account for positron trapping due to defects created by both electronic and nuclear stopping of the implanted ions. Annealing of the 1013 cm−2 sample resulted in measurable recovery of the preimplanted S parameter spectrum at 350 °C and complete recovery to the preimplanted condition at 600 °C. Volume compaction was also observed after implantation. Upon annealing, the compaction was seen to decrease by 75%. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 1772-1778 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the low-temperature coplanar photoconductivity under pulsed and continuous illumination of n-InSb/GaAs heterostructures grown by metalorganic magnetron sputtering. The large lattice mismatch and the large difference in band gaps give rise respectively to a highly defective region at the interface and a high built-in field. The effect of these factors on the photoconductivity is then a function of the InSb film thickness. For photon energies above the InSb band gap, up to about 0.4 eV, we observe positive photoconductivity due to an increase in the electron density coupled with trapping of the excess minority carriers. As the film thickness is decreased from 2 to 0.2 μm, the photoconductivity gain per absorbed photon decreases and the decay time increases, indicating the presence of trapping or recombination centers near the interface. Illumination with photons of energy greater than 0.4 eV leads to the coexistence of a positive photoconductivity and a very slow transient negative photoconductivity which gives rise to high gains at low modulation frequencies. The negative photoconductivity increases with increasing photon energy and decreasing film thickness. Illumination at 0.9 eV from both sides of the heterostructure shows that the effect is related to diffusion and trapping of hot electrons at the interface. The onset of the saturation of the effect indicates a concentration of electron traps of about 1014 cm−2 at the interface, a value similar to the concentration of edge-type dislocations that predominantly accommodate the lattice mismatch in this heterostructure. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 2398-2405 
    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
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5921-5926 
    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
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 7612-7620 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: TiN layers prepared by reactive evaporation and rapid thermal annealing were tested as diffusion barrier between Al and Si. First, Rutherford backscattering spectroscopy (RBS) analysis of Al/Ti(N)/Ti/Si and Al/Ti(N)/Si multilayer structures showed that Si does not diffuse out up to a sintering temperature of 550 °C. However, as the temperature increases beyond 450 °C, Al starts to react with TiN. This reaction leaves less than half the TiN original thickness after a 30 min anneal at 550 °C. The RBS results indicate that TiN, crystallized at a temperature around 850 °C, forms a good barrier between Al and Si. Electrical measurements on various microelectronic devices were performed to verify this. Annealing of Ti(N) at 900 °C leads to a breakdown of p-MOS (metal–oxide–semiconductor) devices while n-MOS devices still work properly. Annealing at 800 °C gives good results on both MOS types except that the contact resistance of a p-type resistor is higher than desired. The electrical circuit failure is mainly due to dopant loss from the active area of the device into the titanium silicide which forms during the rapid thermal annealing at 800 or 900 °C of the deposited Ti(N) layers. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 2460-2465 
    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
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