Durability and the performance of pavement depend mainly on the characteristics of materials which change over time like all other organic substances. They are subject to significant changes due to environmental conditions during the different phases of use. In the present work we investigated experimentally the influence of the association of ethyl vinyl acetate polymer (EVA) with an industrial waste, acrylonitrile-butadiene rubber (NBR) on the modification of bitumen AC 35-50 and its rheological behavior. The incorporation of NBR and EVA in the bitumen improved its intrinsic characteristics (softening point, penetration and ductility). In addition to improving the characteristics of bituminous binders that will affect the durability of bituminous structures, the environment will be preserved by the recycling of industrial waste.

The defect energy levels in metalorganic chemical vapor deposition (MOCVD) grown Ga,Int -,P/InP:Fe and Ga,Int -,P/InP:S epilayers (~~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 Ga,Int _p/InP:Fe and Ga,Ini--$/InP:S are attributed to the emission of a ( V),-( Fe)ru complex and a ( V)m-( 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.

We have observed differential reflection dynamics in In0.518Ga0.492As/InP multiple quantum wells, using the pump–probe technique, and examined the photoluminescence spectra to determine the interface quality for the samples studied. Our results show that the interface quality and well width of the quantum wells (QWs) strongly influence the differential reflection dynamics. The experimental results provide a direct evidence to demonstrate that photoexcited carrier diffusion in cap layer and barriers along the direction perpendicular to sample surface plays a dominant role in determining the differential reflection dynamics of the QWs.

Strained-layer multiple quantum wells InAsP/InP and InAsP/InGaP optical modulators based on the quantum-confined Stark effect have been fabricated from layers grown by metalorganic vapor phase epitaxy on InP(001). The device layers have been characterized by complementary high resolution x-ray diffraction, transmission electron microscopy, optical absorption and photoluminescence analyses. The structural properties of the layers were deduced from the above data and an accurate determination of the band alignment of the heterostructures was made by performing multiple transition fits to the optical absorption spectra using the Marzin–Bastard envelope function model for strained-layer superlattices. The electric field-dependent redshift of the fundamental electron-heavy hole transition was measured by a photocurrent method and found to be enhanced for structures with lower valence band barrier heights. This observation leads directly to the conclusion that the overall performance of high speed, low drive voltage optical modulators may be improved by engineering the band alignment of the multiple quantum well stack towards structures with disproportionately large conduction band offsets. An optimization of the band alignment will permit more efficient optical modulation by reducing the drive field required to operate the device, which, in turn, can have direct effects upon the drive voltage, device capacitance, attenuation coefficient, and optical coupling and propagation losses.

We report on optical absorption of the interband transitions in zero-net strained multiple quantum wells (MQW) grown by low-pressure metalorganic vapour phase epitaxy (LP-MOVPE), using tertiarybutylarsine as a group V source. Sharp interfaces are obtained using a growth interruption procedure. Analysis of this procedure with different interruption times leads to the same optimal times as those obtained for InP/InAsP superlattices grown in the same reactor. We have achieved the growth of modulation-free strain-balanced heterostructures, as indicated by cross-sectional transmission electron microscopy. High-resolution x-ray diffraction and optical absorption analysis demonstrate the high crystallographic and optical quality of these structures. The absorption spectrum of an x = 0.06, y = 0.14 sample was accurately fitted using the Bastard/Marzin model, and a strained conduction band offset of was deduced. This corresponds to about of the total strained bandgap difference.

Strained-layer multiple quantum well (MQW) InAsP/InP optical modulators have been fabricated from layers grown by metal-organic vapor phase epitaxy. The devices are a series of p-i(MQW)-n photodiodes in which the active core regions consist nominally of 25 periods of 10 nm InAsP quantum wells of 4.4%, 10.0%, 15.6%, and 26.4% As composition separated by 10 nm InP barriers. Structural parameters for the samples were obtained using high-resolution x-ray diffraction rocking curves and transmission electron microscopy. The series contains samples with both coherently strained and partially relaxed multi-layers where the relaxation is characterized by misfit dislocations. The band offsets for the heterostructures were determined by fitting the energy positions of the optical absorption peaks with those computed using the Marzin–Bastard model for strained-layer superlattices [as in M. Beaudoin et al., Phys. Rev. B 53, 1990 (1996)]. The conduction band discontinuities thus obtained are linear in the As composition (7.56±0.08 meV per As % in the InAsP layer) at low and room temperature for As concentrations up to 39%, and up to 17% average relaxation. Comparisons between the coherently strained and partially relaxed samples demonstrated a broadening of optical transition linewidths due to relaxation which appears to be of minor consequence for optical modulator devices as the essential optical and electrical properties remain intact. The electric field-dependent red-shift of the n=1 electron-heavy hole transition was measured by a photocurrent method and found to be enhanced in structures with lower barrier heights.

The evolution of an unique interface control layer (ICL) SiNx /lnP/InGaAs Heterojunction Insulated Gate (HIG)FET technology is described from its inception. An In-S monolayer ICL, formed by a novel photoelectrochemical process, is used to reduce and control trap states at the SiNx/InP interface. Buried channel insulated gate ICL HIGFETs fabricated using this approach operate over a large gate voltage range (Vgs=±8 V) with very low gate leakage (10 nA@V gs=±5 V) and Ids(sat) of 250 mA/mm. Undoped channel ICL HIGFETs exhibit transconductance (gm) of 40 mS/mm that is limited by conduction through the buffer layer. A 3 to 4 fold improvement in gm (140-150 mS/mm) is achieved by using a doped InGaAs channel and eliminating parallel conduction paths through the device. The doped channel HIGFETs show ft of 5-6 GHz (Lg=3 μm) and fmax of 10-12 GHz with a power gain of 14.2 dB at 3 GHz. The ICL HIGFET technology has been used to construct simple circuits such as buffer amplifiers with a gain of 7-10 dB at 3 GHz and recently, high frequency sample and hold ICL HIGFET circuits that operate at frequencies of 2 GHz

Epitaxial In0.75Ga0.25P/Ag Schottky contacts were fabricated by electron beam evaporation of Ag on an epitaxial thin film of In0.75Ga0.25P grown on highly doped n‐InP substrate by MOCVD. The diode showed non‐ideal behavior with an ideality factor of 1.3 and is thought to have a metal‐interface layer‐semiconductor (MIS) structure. The room temperature small signal ac capacitance (Cm) was measured as a function of applied voltage (Va), in the frequency (f ) range 0.5 KHz and 1 MHz. Under forward bias, the large frequency dispersion in Cm was attributed to the interface states in equilibrium with the semiconductor (In0.75Ga0.25P). From Cm, the interface states capacitance Cp was extracted. The experimental Cp−f data fitted well to Lehovec’s model of an interface state continuum with a single time constant and provided the values of the interface states energy density (Nss), relaxation time (τ) and capture cross‐section (σn) for forward bias (Va) voltages between 0.0 V and 0.4 V. Over the forward bias range 0...

Low- and room-temperature optical absorption spectra are presented for a series of InAsxP1-x/InP strained-layer multiple quantum well structures (0.11 less than or equal to x less than or equal to 0.35) grown by low-pressure metal-organic vapor phase epitaxy using trimethylindium, tertiarybutylarsine, and phosphine as precursors. The well widths and compositions in these structures are exactly determined from the use of both high-resolution x-ray diffraction and transmission electron microscopy on the same samples. The absorption spectra are then analyzed by self-consistently fitting, for the five samples, the excitonic peak energy positions with transition energies determined from a solution to the Schrodinger equation in the envelope function formalism using the well-known Bastard/Marzin model [J. Y. Martin et al., in Semiconductors and Semimetals, edited by Thomas P. Pearsall, (Academic, New York, 1990), Vol. 32, p. 56]. From these self-consistent fits, both the bowing parameter of bulk unstrained InAsxP1-x and the band offsets of the heterostructures are deduced self-consistently. The conduction-band offsets thus determined represent 75%+/-3% of the total strained band-gap differences at both low (liquid He) and room temperatures. These values of the band offsets are consistent with the predictions of the quantum dipole model [J. Tersoff, Phys. Rev. B 30, 4874 (1984)]. The values determined for the bowing parameters are found to differ slightly between 0.10+/-0.01 eV at low temperature and 0.12+/-0.01 eV at room temperature.

We have determined the origin of the spatial luminescence fluctuations observed between the dark line defects present in tensile strained GaxIn1-xP/In1-xP/n(+)-InP heterostructures (Part I [F. Cleton et al. J. Appl. Phys. 80, 827 (1996)]). For that purpose, we have undertaken semi-quantitative and spectroscopic cathodoluminescence (CL) measurements on various specimens in areas exhibiting CL contrasts which could be as large as 80%. The analysis of the variation of the CL polychromatic signal with electron beam energy allowed us to get information on the diffusion-recombination (DR) parameters of the areas under study. From the correlation between the local relaxation level of these areas and their DR parameters, we can conclude that the variation of the misfit dislocations density at the GaxIn1-xP/InP interface is at the origin of the luminescence heterogeneities. We also demonstrate that recycling, by the GaxIn1-xP epilayer, of the photons originating from the heavily doped InP substrate, enhances the CL contrast between areas exhibiting different relaxation levels. (C) 1996 American Institute of Physics.

We have investigated the optical and structural properties of tensile-strained GaxIn1−xP/InP heterojunctions by cathodoluminescence (CL) in the scanning electron microscope and by transmission electron microscopy (TEM). The lattice mismatch of the samples is ranging from 0.4% (x=5.5%) to 0.84% (x=11.8%). We show, in agreement with previous studies, that the relaxation of tensile-strained epilayers occurs by the emission of partial and perfect dislocations. The numerous twins and stacking faults which are found in the epilayers act as efficient recombination centers for electron-hole pairs and appear as dark line defects (DLDs) in CL images. ‘‘Ladderlike’’ configurations of these defects are found both by TEM and CL in samples with a lattice mismatch larger than 0.5%. We also demonstrate that DLDs are contaminated by impurities. Areas with networks of perfect dislocations are found between the DLDs. The analysis of the dislocation types allows us to suggest that the growth of low-mismatched samples is two dimensional, and that it is three dimensional in highly mismatched samples. Finally, the spatial variations of the strain relaxation throughout the samples are studied by 77-K CL spectroscopic measurements and it is shown that these variations can be correlated with the various types of structural defects.

Two tensile-strained GaxIn1-xP / InP (001) heterostructures (with x = 6.5% and x = 11.2%) have been studied by TEM and cathodoluminescence. In both structures stacking faults and twins, located in the epilayer, have been found preferably along the [(1) over bar 10] direction whereas perfect misfit dislocations have been observed at the interface in the [110] and [(1) over bar 10] directions. The two types of structures differ about the nature of the misfit dislocations and about the thickness of the twins and this is thought to be due to the different stress relaxation amounts in these structures.

Two tensile-strained GaxIn1-xP / InP (001) heterostructures (with x = 6.5% and x = 11.2%) have been studied by TEM and cathodoluminescence. In both structures stacking faults and twins, located in the epilayer, have been found preferably along the [(1) over bar 10] direction whereas perfect misfit dislocations have been observed at the interface in the [110] and [(1) over bar 10] directions. The two types of structures differ about the nature of the misfit dislocations and about the thickness of the twins and this is thought to be due to the different stress relaxation amounts in these structures.

A detailed investigation of the structural and optoelectronic properties of thick GaInP epilayers on sulfur-doped InP substrates is reported. Significant variations of the optical absorption and photoluminescence transition energies from light- and heavy-hole states are observed as a function of the epilayer composition as well as of the degree of relaxation of the misfit strain. High-resolution x-ray measurements were used to determine the Ga concentrations and the strains and indicate significant anisotropic relaxation in several films. Even small relaxations result in a significant increase in the optical linewidths and a rapid drop in the transition intensities. A model with no free parameters based on the strain Hamiltonian of Pikus and Bir provides excellent agreement with the transition energies and serves to identify unambiguously the transitions observed in the optical spectra. Within this model, isotropic in-plane relaxation produces a shift of both light- and heavy-hole energies whereas anisotropic in-plane relaxation contributes only negligibly.

We characterize sulfur diffusion from heavily doped (n/spl sim/10/sup 19/ cm/sup -3/) InP:S (001) substrates into nominally undoped Ga/sub x/In/sub 1-x/P (0/spl les/x/spl les/0.2) epilayers during growth by low-pressure MOCVD. The composition, relaxation and dislocation density of the samples have been studied by high resolution X-ray diffraction and in-depth doping profiles have been obtained using a C-V electrochemical profiler. The analysis of these profiles shows that as the Ga content of these thick (/spl sim/1 /spl mu/m) samples is increased, a rapid enhancement of the sulfur diffusion from the substrate is observed. This enhancement is a consequence of the generation of an increasing number of dislocations initially caused by the mismatch. The structural defects act as pipes inside which the diffusion coefficient (D/sub d/) of sulfur atoms is calculated to be 6 orders of magnitude higher than that of the undislocated material (D/sub l/). Value of D/sub lspl sim/2/spl times/10/sup -17/ cm/sup 2s at the growth temperature of 640/spl deg/C have been deduced.<>