Search

Negative temperature coefficient thermistors have been prepared with nickel-copper-manganite spinels, Mn 7/3- x -Ni 2/3 Cu x O 4 . These devices are very sensitive, but unstable with time and storage temperature. The addition of Ba to these ceramics decreases this instability from 15% to less than 2%. To study this change in the electrical properties of the ceramics we used R ( T ), I ( V ) and thermopower measurements. The correlation of ionic distribution and the results obtained from Seebeck measurements allowed us to propound the transfer of Cu 2+ between tetrahedral and octahedral sites to explain this phenomenon. We also assume that the Cu 2+ ions in the octahedral site contribute to the electrical conductivity.

Liquid-phase sintering (LPS) of ceramics issued from powders of bismuth-titanium-doped zinc oxide, made of spherical grains constituted of small crystallites, were studied by dilatometry. A correlation can be established between the shape of the shrinkage curves and the microstructure of the ceramics. During sintering the spherical grains are destroyed as soon as the liquid phase appears and the rearrangement proceeds directly between crystallites. Systematic studies were carried out on bismuth-titanium-doped ZnO. For small Bi contents, the beginning of a solid-phase sintering process occurs. For 1 at % Bi in the binary system Bi-doped ZnO, rapid shrinkage leads to a well-densified ceramic with a grain size of 70 μm on average. The influence of the amount of titanium iny% Ti-1% Bi-doped ZnO is discussed. Whatever the amount of Ti, LPS is observed. The shrinkage curves depend greatly on the amount of Ti: only a Ti content ofy=0.6 % leads to an increase in grain size (100 μm on average).

Nd3+‐doped CaF2 monocrystalline films have been grown by molecular‐beam epitaxy using CaF2 and NdF3 evaporation on CaF2 (100) substrates. Auger electron spectrometry and high‐energy electron diffraction have been used as in situ techniques to characterize the grown layers. No degradation of crystallinity was observed even for the highest levels of doping considered. The effect of Nd3+ concentration is studied by means of the photoluminescence signal of Nd3+ ions. The results can be compared favorably with those of bulk CaF2:Nd crystals. For a given Nd3+ concentration a lower quantity of Nd3+ aggregate centers is observed. Nd3+ ions can, therefore, be efficiently incorporated in isolated Nd3+‐F− centers up to concentrations of 3.7 wt % Nd3+ without emission quenching of the associated line at 1.0457 μm. The results are related to the thermodynamic conditions imposed by the molecular‐beam epitaxy technique.

The IR absorption spectra of tetragonal copper manganite CuxMn3−x O4 spinels (O 0.60 in conformity with that recorded by our previous measurements and have warranted the existence of a more complex cation distribution than that proposed earlier. It has been concluded from this study that the ionic configuration for x 0.60 to (Cux−y+Mn1−x+y2+)A(Cuy2+Mn2−x−y3+Mnx4+)BO42−, where y represents a low value (less than 0.20). When the oxidation of Mn2+ and Cu+ ions is achieved below 450 °C, IR absorption measurements confirm the formation of a cation-deficient metastable spinel phase Cu1.5Mn1.5O4+δ with a 1:3 octahedral superstructure.

In the present work, the oxidation mechanism and cationic distribution of the single phase copper manganite spinels CuxMn3−xO4 (0 < x < 1) prepared by thermal processing of copper-manganese-coprecipitated hydroxide precursors have been investigated in the temperature range 300–900°C. Thermogravimetry measurements and infrared spectrometry have enabled us to propose copper and manganese ion distributions in the spinel lattice which are given by the formula (Cu+xMn2+1−x)A(Mn3+2−xMn4+)BO2−4 when the oxidation temperature is lower for Cu+ ions than that for Mn2+ ions. Further, isothermal oxidations achieved below 450°C showed, for composition x & 0.70, the formation of cation-deficient spinels with oxidation kinetics controlled by a diffusion law. With decreasing of copper content, the kinetic curves become sigmoidal according to nucleation growth-mechanism induced by the formation of α-Mn2O3.

The electrical conductivity and thermoelectric power of single-phase copper manganite spinels CuxMn3−xO4 with 0 > x > 1 are measured as a function of temperature at low oxygen partial pressure (10−3 Pa for x > 0.50 and 1 Pa for x > 0.50). For x > 0.70, electrical conduction is explained by the small polaron hopping of electron holes (p-type) between Mn4+ and Mn3+ ions on octahedral sites, yielding a hopping energy EH that varies between 0.23 eV for x = 0.96 to 0.26 eV for x = 0.75. Over the composition range 0 > x > 0.75, the electrical conductivity drops by three (x = 0.45) to ten (x = 0) orders of magnitude with a concurrent increase in the activation energy which suggests a band-type conduction rather than hopping conduction. The different electrical behaviour at high oxygen pressure (105 Pa) is found to arise from the presence of two phases α-Mn2O3 and Cu1.5Mn1.5O4. La conductivite electrique et l'Effet thermoelectrique des manganites de cuivre de structure spinelle CuxMn3−xO4 pour 0 > x > 1 sont etudies en fonction de la temperature sous faible pression partielle d'oxygene (10−3 Pa pour x > 0,50 and 1 Pa pour x > 0,50). Pour x > 0,70 la conductivite electrique est expliquee par un mecanisme de sauts entre les ions Mn4+ et les ions Mn3+ sur les sites octaedriques ou les porteurs de charge sont des trous avec une energie d'activation EH qui varie de 0,23 eV pour x = 0,96 a 0,26 eV pour x = 0,75. Pour les compositions x > 0,75, la conductivite electrique diminue fortement (d'un ordre de grandeur de trois a dix quand la composition varie de x = 0,45 a x = 0) avec pour consequence une importante augmentation de l'energie d'activation. Ce comportement suggere un mecanisme de conduction par bande plutot que par sauts. En presence d'oxygene (105 Pa) la conductivite electrique est influencee par la presence de deux phases α-Mn2O3 et Cu1.5Mn1.5O4 de structure spinelle.

The electrical conductivity and thermoelectric power of single-phase cubic nickel manganite spinels NixMn3−xO4 with 0.57

PSi microcavity (PSiMc) is characterized by a narrow resonance peak in the optical spectrum that is very sensitive to small changes in the refractive index. We report that the resonant optical cavities of PSi structures can be used to enhance the detection of labeled fluorescent biomolecules. Various PSi configurations were tested in order to compare the optical response of the PSi devices to the capture of organic molecules. Morphological and topographical analyses were performed on PSiMc using Atomic Force (AFM) and Scanning Electron (SEM) microscopies. The heterogeneity in pores lengths resulting from etching process assures a better penetration of larger molecules into the pores and sensor sensitivity depends on the pore size. Molecular detection is monitored by the successive red shifts in the reflectance spectra after the stabilization of PSiMc with 3-aminopropyltriethoxysilane (APTES). The glucose oxidase was crosslinked into the PSiMc structures following a silane-glutaraldehyde (GTA) chemistry.

Single-phase nickel manganite spinels, NixMn3−xO4, with 0.5 ⩽x ⩽ 1, were prepared by a careful thermal processing of nickel-manganese coprecipitated oxalate precursors. Powder X-ray diffraction analysis of the spinel revealed the presence of cubic single spinel phase with parametera which decreases with nickel content. The lattice parameter variation can be explained in terms of the distribution of Ni2+ ions on the octahedral sites. Therefore, a fine analysis of data shows that some Ni2+ ions (forx>0.56) are located in tetrahedral sites. The percentage of nickel in A-sites increases with nickel content (x) following the relation % Ni2+ in A sites =P = − 82.1x2+192.4x−81.5 and thus the general formula for cation distribution is $${\text{Mn}}_{{\text{1 - }}y}^{{\text{2 + }}} {\text{Ni}}_y^{{\text{2 + }}} [{\text{Ni}}_{x{\text{ - }}y}^{{\text{2 + }}} {\text{Mn}}_{{\text{2 - 2(}}x - y)}^{{\text{3 + }}} {\text{Mn}}_{x{\text{ - }}y}^{{\text{4 + }}} ]{\text{O}}_{\text{4}}^{{\text{2 - }}} $$ withy=xP/100

We have investigated the temperature dependence of the fundamental absorption edge of a series of Hg1−xCdxTe alloys (with composition x ranging from 0.5 to 1). Analyzing our data in the light of the three‐dimensional theory of direct‐allowed excitons, we find precise values for the fundamental Γ8‐Γ6 interband transition energy in a temperature range extending from 0 to 300 K. All experimental results, including previous data for HgTe and mercury‐rich Hg1−xCdxTe alloys, are well accounted for using a simple empirical formula: Eg (eV)=−0.303(1−x)+1.606x−0.132x(1−x)+[6.3(1−x) −3.25x −5.92x(1−x)]10−4T2/[11(1−x)+78.7x+T]. This expression, which is valid for all compositions 0≤x≤1 and temperatures 0≤T≤500 K, predicts an alloy composition such that the band‐gap energy is temperature independent: We find x=0.505. Finally, it can be used for technological application purpose (far‐infrared detection as well as optical‐fiber communications performed at realistic values of the temperature) and gives accurate values f...

Porous silicon (PSi) nanostructures have remarkable optical properties that can be used for biosensing applications. In this paper we report first on the fabrication of heavily doped p-type PSi with pore diameters in the range of 400-4000 nm. The nonspecific and specific binding of the Glucose Oxidase protein (GOX) was then studied onto the PSi mirrorlike substrate. Adsorption of GOX was tuned by the pH of the protein solution (pI = 4.2) depending of the surface charge. PSi matrixes were first stabilized by thermal oxidation and GOX adsorption was performed once directly on the oxidized PSi surface, and also on previously functionalized PSi surfaces. In the latter case the GOX was coupled to the PSi via the S-H group of the 3-(mercaptopropyl)trimethoxysilane (MPTS). The silane-GOX and GOX interactions on the PSi surface were monitored by the Fourier Transformed Infrared spectra that display characteristic bands of the linked molecules. The interference spectrum shows a large blue shift in the Fabry- Perot interference pattern caused by the change in the refractive index of the medium implying a decrease in the effective optical thickness. Quantitative analysis shows that chemically modified PSi samples admit approximately 24% of GOX. Activity assay proved that the protein preserves its catalyst properties under these adsorption conditions.

A novel optical waveguide exhibiting a layered core region is proposed. Owing to the original design of the core stack and form birefringence in the multilayer, a waveguide supporting both TE and TM lowest-order modes with high confinement has been obtained. It has been designed, fabricated, and characterized and presents a modal birefringence greater than 0.01, which is in good agreement with the calculated values.

Investigations of polarizations effects in second-harmonic generation of a one-dimensional photonic crystal based on gallium nitride were performed for the fundamental beam incident on the surface of the photonic crystal. The angle of incidence, the azimuthal rotation angle of the photonic crystal, the frequency, and the polarization behaviour for strongly enhanced second-harmonic generation agree well with the identified position and polarization of the resonant Bloch modes. Along the direction, giant enhancements of 7500 times in the second-harmonic conversion have been obtained in the one-dimensional photonic crystal by comparison with the unpatterned GaN layer. The combined role of the resonant coupling of the fundamental field and of the second-harmonic field has been observed as the polarization of the fundamental beam is rotated.

The second-harmonic field generated has been measured in reflection from the surface of one-dimensional and two-dimensional photonic crystals etched into a GaN layer. A very large second-harmonic enhancement is observed when simultaneously the incident beam at the fundamental frequency w excites a resonant Bloch mode and the second-harmonic field generated is coupled into a resonant Bloch mode at 2w. A smaller, but still substantially enhanced, second-harmonic generation level was also observed when the fundamental field was coupled into a resonant mode, while the second-harmonic field was not. By using calculated and experimental equifrequency surfaces, it is possible to identify the geometrical configurations that will allow quasi-phase matching to be satisfied - and observed experimentally in the available wavelength tuning range of the laser. The extended transparency window of III-nitride wide-bandgap semiconductors, coupled with large non linearities, is an appealing feature pointing towards the control and manipulation of light in photonic structures.

This paper reports measurements of the the giant second harmonic generation (SHG) enhancement of a 1D thin-film GaN-based photonic structure. The extraordinary enhancement has been obtained in specular reflection when the angular configuration satisfies the quasi-phase-matching (QPM) conditions, i.e. when both the fundamental and SH fields are resonant with radiative Bloch modes.

The equifrequency surface plot is demonstrated as a powerful tool in obtaining the angular geometries that maintain quasi-phase matched (QPM) conditions for enhanced SHG with extended tuning range. These results are promising for the practical realisation of nonlinear frequency conversion devices based on GaN and related materials.

We established the angular conditions that maintain the quasi-phase matching conditions for enhanced second-harmonic generation. To do that, we investigated the equifrequency surfaces of the resonant Bloch modes of a two-dimensional periodic, hole-array photonic crystal etched into a GaN/sapphire epitaxial structure. The equifrequency surfaces exhibit remarkable shapes, in contrast to the simpler surfaces of a one-dimensional structure. The observed anisotropy agrees well with the surfaces calculated by a scattering matrix method. The equifrequency surfaces at fundamental and second-harmonic frequencies provide the values of polar and azimuthal angles that maintain quasi-phase matching conditions for enhanced second-harmonic generation over an extended tuning range. The predicted values for quasi phase-matching conditions show that frequency tuning for the two-dimensional case covers an about two times larger fractional bandwidth relative to the one-dimensional case.

We have performed investigations of resonance effects inside a gallium nitride one-dimensional photonic crystal slab in order to enhance the second-harmonic generated from an beam incident on the surface of the slab. Convenient conditions on the incident beam propagation direction and polarization are first identified by experimental or theoretical linear optical studies. Giant enhancements in the second-harmonic conversion have been obtained by comparison with the unpatterned GaN layer. The combined role of the resonant coupling of the fundamental field and of the second-harmonic field has been observed by rotating the polarization of the fundamental beam.

International audience; Highly accurate layer thicknesses are required for multilayers involved in photonic devices, such as Bragg reflectors. In this letter, we demonstrate that precise, real-time monitoring of molecular beam epitaxy growing layers can be achieved by near-normal incidence dynamic reflectometry with a tunable sapphire-titanium laser used as a source. The advantage of this new technique lies in the possibility of synchronizing the material changes and the reflectivity extrema by selecting adequate analysis wavelengths. This technique is shown to provide 885 nm GaAs-AlAs Bragg reflectors with a layer thickness accuracy in excess of 1%.

The temporal and spectral response of bulk GaAs Fabry-Perot microcavities have been investigated in the subpicosecond regime at room temperature. Time resolved reflectivity measurements show a strong reshaping of a Gaussian fs-pulse after reflection from a microcavity caused by group velocity dispersion. The pulse distortion agrees fairly well with model calculations using Fourier transform analysis. Time integrated degenerate four-wave mixing experiments show that response times of the cavity as short as 300 fs were achieved.

International audience; Photonic crystals are a new class of materials where photonic band gaps, large dispersion and anisotropy occur. By exploiting these properties GaN photonic crystals should have important potential for optoelectronic applications, principally in the areas of high-efficiency light emitters and second-harmonic generators. We present measurements of the equifrequency surfaces of the radiative Bloch modes for a photonic crystal etched in a GaN/sapphire film. The photonic band structure is calculated by using a scattering matrix method that reproduces well the anisotropy of the equifrequency surfaces exhibited by the photonic crystal. (C) 2002 Elsevier Science B.V. All rights reserved.

The cation distribution has been determined in the nickel manganites NiMn2O4 and Ni0.8Mn2.2O4 from powder neutron diffraction studies. It strongly depends upon the thermal history of the specimens. Additional information given by Mn2+ thermogravimetric oxidation experiments, has established the oxidation states of cations on the tetrahedral and octahedral sites of the cubic spinel structure. The magnetic structures determined at 1.5. K are in good agreement with the weak values of the spontaneous magnetization.

Un cas clinique de fracture bilaterale du col du radius chez un adulte est rapporte par les auteurs. L'embrochage centro-medullaire ascendant, derive de la technique de Metaizeau decrite chez l'enfant, parait particulierement indiquee dans les fractures sous-capitales engrenees de l'extremite superieure du radius, resultant d'un traumatisme par mecanisme de compression et tassement.

The electrical conductivity of manganite spinels such as CuxMn3−xO4, Co0.4CuxMn2.6−xO4 and Nix Mn3−xO4 has been investigated versus composition x. For these three spinels the conductivity is described by a “hopping mechanism” between Mn3+ and Mn4+ ions on octahedral sites of the spinel lattice and reaches a maximum when the number of Mn3+ ions is equal to the number of Mn4+ ions.

The need for aeration of microcosms during mineralization of 14C-labeled compounds in high oxygen demand environments was assessed using active compost-soil mixtures as the model system. Rapid mineralization of 14C-hexadecane occurred in continuously aerated microcosms while no mineralization occurred in unaerated microcosms. Daily flushing with air also yielded no mineralization. Mineralization of 14C-glucose was much less dependent on aeration. The alkaline solution volume and number of CO2 traps required for continuous aeration were calculated and tested experimentally.

We examine the classical indications for thoracoscopy in case of pneumothorax and recall the therapeutic modalities of thoracoscopic treatment. We then discuss the long-term incidence of this approach, examining outcome in terms of post-operative pain, respiratory function, cost and complications. A comparison of these parameters after thoracoscopy with those observed after classical surgery would favor thoracoscopic management.

Molecular beam epitaxy of Nd3+‐doped CaF2 monocrystalline layers on CaF2 substrates is demonstrated. Nd concentration is controlled by the temperature of an evaporation cell containing NdF3. Photoluminescence spectra of the samples show emissions from Nd3+ centers in tetragonal symmetry sites as a consequence of the charge compensation mechanism provided by interstitial F− ions.

Tibial periostitis frequently occurs in athletes. We present our experience with MRI in a series of 7 patients (11 legs) with this condition. The clinical presentation and scintigraphic scanning suggested the diagnosis. MRI exploration of 11 legs demonstrated a high band-like juxta-osseous signal enhancement of SE and IR T2 weighted sequences in 6 cases, a signal enhancement after i.v. contrast administration in 4. Tibial periostitis is a clinical diagnosis and MRI and scintigraphic findings can be used to assure the differential diagnosis in difficult cases with stress fracture. MRI can visualize juxta-osseous edematous and inflammatory reactions and an increased signal would appear to be characteristic when the band-like image is fixed to the periosteum.

We describe a case of unilateral and spontaneous adrenal hematoma. Initial and follow up MRI examinations showed serial modifications typical of hematoma and allowed to exclude a preexisting non hyperfunctioning tumor. MRI findings modified the therapeutic attitude, a voiding surgery.

International audience; In situ molecular beam epitaxy control of III-V optoelectronic device growth has been achieved by dynamic optical reflectometry with tunable excitation wavelength, through the use of a titanium:sapphire laser light source. This new multi-wavelength reflectometry method was used to determine the values of the AlAs and GaAs refractive indices at growth temperature (600 °C). Index dispersion between 760 and 960 nm is presented and found to be in good agreement with the existing models.

Authors report a case of parathyroid adenoma as lateral palpable cervical mass, with serious hypercalcemia. MRI and ultrasound investigations were performed preoperatively. No other pathological parathyroid gland was found. Surgical treatment did not include the exploration of the four parathyroid glands. Long term follow-up is necessary.

Molecular beam epitaxy of CaF 2 monocrystalline layers Er 3+ doped up to a concentration of 50 mol% is demonstrated on CaF 2 substrates. Separated effusion cells containing CaF 2 and ErF 3 have been used. The photoluminescence spectra of these thin layers exhibit emissions from centers which were found to correspond to those already reported for CaF 2 :Er 3+ bulk crystals. The influence of growth temperature and Er concentration on the spectroscopic properties of these layers was investigated. The 1.54 μm emission of interest was shown to behave as aggregate centers, and the integrated luminescence was only quenched for concentrations higher than 35 mol%. The trends observed evidence that molecular beam epitaxy is a powerful technique for growing thin Er-doped fluoride layers

We have studied the birth weights, obstetrics data and anthropometrical data from 1.157 full-term newborns who were delivered in the Hospital del Insalud-Cruz Roja in Ceuta (Spain). Of these newborns, 489 were of arabic origin and 668 of hispanic origin. Arabic newborns were heavier (3.248 +/- 473 g versus 3.280 +/- 431 g, p0.001) and longer (50.2 +/- 1.8 cm versus 49.6 +/- 1.8 cm, p0.001) than their hispanic counterparts. These differences were not due to a disproportion in sex or gestational age between the groups. Furthermore, the differences were still present after adjustments were made for maternal age, parity and the mother's smoking habit. Thus, this difference in size at birth between arabic and hispanic newborns could be, at least in part, ethnically related.

Nd3+ doped CaF2 monocrystalline films have been grown by molecular beam epitaxy using CaF2 and NdF3 evaporation on CaF2 substrates. The effect of Nd3+ concentration is studied by means of the photoluminescence signal of ~ d 3 + ions. The results can be compared favourably with those obtained on CaF2:Nd bulk crystals. For a given Nd3+ concentration a lower quantity of Nd3+ aggregate centers is observed. ~ d 3 + ions can therefore be efficiently incorporated as isolated Nd3+-~centers up to a concentration of 6 wt % ~ d 3 + without emission quenching of their associated line at 1045.7 nm.

Pneumatosis cystoides intestinalis is most frequently characterised by the presence of gaseous cysts, in the intra-parietal, subserous or sub-mucous zones of the colon. This complaint, with symptoms of non specific colic and the cause of chronic pain, generally progresses favourably but can be responsible for surgical complications. Characteristic signs are detected on an plain abdominal X-ray and by colonoscopy. The diagnosis can be established by CT or by ultrasonography but needs carefully trained operators. CT remains the most successful technique for the initial diagnosis and subsequent follow-up. Ultrasonography can also be used for follow-up. As the lesions regress rapidly, the diagnosis must established rapidly, otherwise the disorder might easily be incorrectly diagnosed.

Various inflammatory reactions can be induced by different crystals responsible for various arthropathies. The aim of this work was to study modifications induced in the rat, locally and at distance, by intrapleural injection of 3 forms of pyrophosphate crystals (CaPP dihydrated monoclinic (M), CaPP dihydrated triclinic (T) and CaPP anhydrous (β)). The data presented here show that the structure of irritants plays a decisive role in the kinetics of inflammatory reactions from a local and systemic point of view. CaPP crystals / pleurisies / polymorphonuclear / macrophages.

The authors present room temperature four-wave mixing experiments on a subpicosecond timescale at the band edge of bulk GaAs integrated into microcavities. In the cavity, the diffraction efficiency η ≃ 8 × 10-3 is enhanced by approximately a factor of 20 at 890 nm compared to bulk GaAs without cavity. This result shows the potential capability of microcavities for reducing the switch energy of many all-optical devices.

CoFe2O4 and Co1.80Mn0.15Fe1.05O4 spinels were prepared as thin films. The as-deposited films were crystallized by conventional treatment (CT) and by rapid thermal annealing (RTA). The magneto-optical (MO) properties of oxides films were studied in relation with their thermal history. Between 600 and 800 nm the Faraday effect of RTA samples were different from those of CT films because the RTA process modified the cationic distribution of oxides and particularly the distribution of Co2+ ions on the sites of the spinel structure. We put the structural changes to advantage in order to optimize the MO properties of Mn-Fe cobaltites at 690 nm.

The influence of alloy disorder on exciton luminescence is studied in CdxHg1-xTe alloys as a function of composition. For compositions x > 0.85, the low temperature luminescence is dominated at high energy by the recombination of intrinsic excitons trapped in the tail states associated with potential fluctuations. For compositions richer in mercury (0.5 < × < 0.85) the low temperature spectra only show extrinsic excitons bound to some defects. In this case the line broadening is well described by binomial statistics. However as the temperature rises these extrinsic excitons are quenched for the benefit of the tail intrinsic excitons.

In a case of CPPD crystal deposition disease of the pseudorheumatoid type and of long duration, calcified constrictive pericarditis developed and was surgically treated. Analysis of the calcium deposit in the pericardium was carefully made by infrared absorption, x-ray diffraction, and thermogravimetry. It revealed that the deposit was composed of B-type carbonated apatite. Previously, both calcium pyrophosphate dihydrate (CPPD) and apatite crystals, either in the same place or in different tissues, have been reported in the same patient. These observations raise the possibility that the same metabolic error might lead to both types of crystal deposition.

We have studied the photoluminescence (PL) emission of various Cd-rich Hg 1- x Cd x Te crystals, including the 1.3 μm alloy composition ( x ⋍ 0.7). They were either bulk crystals grown and purified by the travelling heater method or layers grown by liquid phase epitaxy on CdTe substrates. In undoped materials, the low temperature luminescence of each sample (1.3 μm range) consists of one set of bands: a high energy band, labelled “A”, followed by LO phonon replicas. We have analysed the PL spectra of a series of alloys with x ranging between 1 and 0.7; using a new revised relationship for the variation E g ( x , T ) in this composition range, we are led to assign the “A” band to a mixing of excitonic lines broadened by the effects of disorder. We have also measured the PL spectrum of In-doped Hg 0.3 Ce 0.7 Te crystals grown by THM and presenting a low electronic concentration ( n 300 = 2×10 14 cm -3 ). In this case, we observed clearly, and for the first time for this composition, emission arising from excitons and from donor-acceptor pairs transitions. This result confirms our conclusion on the excitonic nature of the “A” band.

Ion implantation of In, Ar and Xe was carried out on p-type Cd x Hg 1- x Te ( x = 0.7) and followed by both furnace annealing (FA) in the presence of Hg vapour and rapid thermal annealing (RTA) on encapsulated crystals. Rutherford backscattering spectroscopy and photoluminescence experiments show that the implantation damage is removed by FA at 400°C for 1 h or RTA at 380°C for 10 s. The In-implanted profile obtained by SIMS exhibits a diffusion broadening following FA, while the In atomic distribution is very little affected by RTA. Sheet Hall-effect measurements indicate that following FA at 300 and 400°C electron conductivity appears and is associated with some activation of the In and with implantation-induced defects. RTA, which removes the defects very well, does not lead to any n-type conversion that could be related to the absence of a Hg external phase.

GaAs layers grown by organometallic chemical vapor deposition (OMCVD) on Si substrates oriented 2° off (100) toward [011] have been studied by 10‐K filtered cathodoluminescence, deep‐level transient spectroscopy (DLTS), electron‐beam‐induced current (EBIC), and secondary ion mass spectrometry (SIMS) measurements. The mapping of the near‐band‐edge emission intensity shows the existence of zones of lower defect density, whose relative volume increases with the layer thickness. Four deep‐level energy peaks have been characterized at 1.33, 1.20, 1.15, and 1.02 eV. The 1.33 and 1.20 eV energy peaks are attributed to Si in GaAs. Strong inhomogeneities in the intensity of these two emissions have been observed with depth of the layers, and this behavior has been related to the silicon distribution. From measurements on structures grown with different buffer layers, we show that a GaAs/AlAs supperlattice located at 1 μm from the Si substrate is efficient in decreasing the width of a highly Si‐doped interface regi...