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High temperature Hall effect measurements in CdTe〈Cl〉 single crystals grown by THM and Bridgman techniques at 200–900 °C under well defined Cd and Te vapor pressure were made. Associates decay at heating from 500 to 700 °C in THM grown samples was observed. Cd vapour pressure influence on electron concentration [e–] in all samples was established. The main point defects present in crystals were: at T 700 °C - chlorine donors, Cd vacancies and Cd interstitials. Bridgman grown CdTe〈Cl〉 crystals had [e–] similar to undoped CdTe and differed in Cd vapor pressure dependencies by line slopes. Under Te vapor pressure the samples demonstrated p-type conductivity up to 550 °C. In this case the hole density changed from [h+] = 1016 cm–3 to 3 × 1017 cm–3 and did not depend on Te vapor pressure. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The peculiarities of the melting and crystallization processes of CdTe, Cd 0.95 Zn 0.05 Te and Cd 0.9 Zn 0.1 Te were monitored by dynamic viscosity measurements at temperatures up to 1403 K. Heating/cooling rates of between 10 and 20 K/h were used. The non-isothermal nature of the melting process of all investigated samples was observed. The results revealed the differences in structural changes of the molten binary and ternary compounds both on heating and cooling.

CdTe detectors (3 × 5 mm2 electrode area and 1 mm thick), mounted in a back-to-back configuration with common anode, have been characterized, aiming at determining the actual regions of these devices giving the best and almost constant spectroscopic performance. This configuration ensures that the maximum paths of the charge carriers correspond to the inter-electrode distances and consequently the spectroscopic performance is essentially the same as for the single coupled detectors, but allows one: • to double the useful absorbing thickness when irradiated in the classical planar parallel field geometry; • to double the pixel area when irradiated in the planar transverse field (PTF) geometry, while the absorbing thickness can be freely adjusted according to the experimental requirements. The tests were performed in PTF geometry by using well collimated photon beams (10–300 keV energy range) obtained by a 20 mm thick tungsten collimator having a 0.1 × 1 or a 0.3 × 1 mm2 collimating channel. Experimental results concerning the spectroscopic behaviour of the coupled detectors have been compared with those obtained by single devices having the same thickness as the single components or the same total thickness as the coupled device. The results show that the back-to-back configuration does not introduce further significant noise with respect to 1 mm thick single detectors and their spectroscopic performance is similar or better than the one shown by 2 mm thick single devices for fine and wide collimator measurements, and mostly in the uncollimated case.

An experimental investigation of the radiation damage induced on CdTe and CdZnTe semiconductor detectors has been performed by exposing a set of samples to increasing doses of 2 MeV protons produced by a 1.7 MV Tandetron accelerator. The modifications in the detector performances have been studied through the dark current measurements and spectroscopic response analyses at low and medium energies. The deep levels of the materials have been investigated by means of Photo Induced Current Transient Spectroscopy analyses. The evolution of some important parameters (energy resolution, charge collection efficiency, leakage current, activation energies and capture cross-section of deep level defects) have been monitored with respect to increasing proton exposures and the results obtained give us some important indications on the modifications of the material properties as well as on the performances degradation of the detectors.

CdTe array detectors are being investigated for use in a variety of applications, ranging from medical diagnosis to high-energy astronomy. Herein, we present a study of the spatial resolution of several prototype CdTe arrays of varying thickness as a function of energy and angle of the incident radiation. These measurements were performed at the European Synchrotron Research Facility at Grenoble, France in the first week of July 2002. The energy range employed was between 100 and 500 keV, while the detectors consisted of a set of CdTe arrays containing elements of thicknesses between 3 and 8 mm. The spatial response of the detectors was measured using single site events, while the possibility of using this type of array detector also for measuring the degree of polarisation of the radiation was investigated using multi-site interactions.

The performance of room temperature CdTe and CdZnTe detectors exposed to a radiation source can be strongly altered by the interaction of the ionizing particles and the material. Up to now, few experimental data are available on the response of II–VI compound detectors to different types of radiation sources. We have carried out a thorough investigation on the effects of γ-rays, neutrons and electron irradiation both on CdTe : Cl and Cd0.9Zn0.1Te detectors. We have studied the detector response after radiation exposure by means of dark current measurements and of quantitative spectroscopic analyses at low and medium energies. The deep traps present in the material have been characterized by means of PICTS (photo-induced current transient spectroscopy) analyses, which allow to determine the trap apparent activation energy and capture cross-section. The evolution of the trap parameters with increasing irradiation doses has been monitored for all the different types of radiation sources. A comparison of the results obtained for CdTe : Cl and Cd0.9Zn0.1Te detectors allows to deepen our understanding of the detectors’ properties and performance.

Coded Imager and Polarimeter for High Energy Radiation (CIPHER) is a hard X- and soft gamma- ray spectroscopic and polarimetric coded mask telescope based on an array of Cadmium telluride microspectrometers. The position sensitive detector (PSD) will be arranged in 4 modules of 32 x 32 crystals, each of 2 x 2 mm(2) cross-section and 10 mm thickness giving a total active area of about 160 cm(2), operating over a wide energy range (similar to10 keV to 1 MeV). Each PSD module is obtained by aligning 32 linear arrays of micro-detectors each also containing the integrated analog front end electronics on a thin ceramic layer. The CIPHER instrument will be proposed for a balloon experiment, both in order to assess the performance of such an instrumental concept for a small/medium size satellite (or an external ISS-alpha payload) survey mission and to perform an innovative high energy polarisation measurement. Herein we describe the CIPHER position sensitive spectrometer design, together with current development on CdTe detectors array and on a low noise and low power consumption ASIC for the analog front end electronics. Furthermore we present the expected performance in terms of image and spectral quality (spatial and energy resolution) and polarimetric capabilities for such a detector. (C) 2002 Elsevier Science B.V. All rights reserved.

Thin CdTe detectors (3×5 mm 2 electrode area and 0.5 mm thick) mounted in a back-to-back configuration with a common anode, have been characterized. The goal was to determine the dimensions of the detector region offering good spectroscopic performance. The detector size was chosen on the basis of previous studies performed on various detectors which have shown that the width of this “best spectroscopy region” assumes a constant value of about 0.4 mm in the device thickness range 1.0– 2.5 mm , while it is largely reduced when using a smaller electrode area (2×2 mm 2 ) and 0.5 mm thick devices. The tests were performed by irradiating the detectors with a well collimated E X =122 keV photon beam. The results show that the edge effects observed in smaller detectors with the same configurations are significantly reduced, giving a better energy resolution, but not a wider region with good spectroscopic performance; at lower energies the effects of larger electrodes (increased electric capacitance and leakage current) result in a higher noise and an increased detection threshold.

A brief review of different aspects of In atoms in the CdTe lattice behavior, necessary for scientific preparation of radiation-sensitive material is presented. Data concerning the CdTe–In T – x phase diagram, In segregation, diffusion and solubility as function of stoichiometric relations in CdTe and temperature are included. Low- and high-temperature electrical measurements results are discussed in the framework of compensation phenomena. A short review concerning the manufacture of In-doped CdTe crystals as well as their practical use is included.

The performance of room-temperature CdTe and CdZnTe detectors exposed to a radiation source can be strongly altered by the interaction of the ionizing particles and the material. Up to now few experimental data are available on the response of II–VI compound detectors to different types of radiation sources. We have focussed our attention on the effects of γ-rays and neutron irradiation and we have investigated the exposed detectors by means of dark current measurements and of quantitative spectroscopic analyses at low and medium energies. The deep traps present in the material have been characterized by means of photo-induced current transient spectroscopy analyses, which allow for the determination of the trap apparent activation energy and capture cross-section. The evolution of the trap parameters with increasing irradiation doses has been monitored for both types of radiation sources. The comparison of the results obtained for CdTe and CdZnTe detectors allows us to deepen our understanding of the detectors’ properties and performance.

An analysis of the variation in size of good spectroscopy region as a function of the inter-electrode distance for planar CdTe detectors operated at room temperature is reported. Four detectors with inter-electrode distance ranging from 1.0 to 2.5 mm, in steps of 0.5 mm, were investigated. The measurements were carried out by scanning the detectors, in the configuration with the electric field perpendicular to the incoming radiation, Planar Transverse Field (PTF), with a narrow beam of 122 keV photons, obtained by using a 20 mm thick tungsten collimator having a 0.2×2 mm 2 collimating channel. A “best charge collection region” has been identified, close to the cathode and ∼0.4 mm wide, almost independent of the detector thickness in the above range, in which the photopeak amplitude and the energy resolution assume the best and sufficiently constant values. Outside this region, both these parameters rapidly worse, with a behavior well described by the Hecht's relationship. These characteristics appear essentially in the energy range 30 E x

The knowledge of a detector response to different types of radiation sources is becoming a key issue for its employment in many medical, space and scientific applications. Nevertheless, a clear understanding of the effects of irradiation on the material properties is still a long way ahead and, therefore, we have started a thorough investigation of room temperature CdTe and CdZnTe detectors exposed to γ-ray irradiation. As-grown detectors have been exposed to increasing γ-ray doses, up to the virtual death of the detector, which occurs at a dose of 30 kGy. The modifications in the detector performance have been investigated by dark-current measurements and quantitative spectroscopic analyses at low and medium energies. The deep levels present in the material have been identified by means of Photo-Induced Current Transient Spectroscopy (PICTS) analyses. The evolution of the trap parameters with increasing irradiation dose has been monitored and a comparison of the results obtained from CdTe and CdZnTe detectors allows to achieve a better insight into the modifications of the material properties and performances after γ-ray exposure.

The shear viscosity of the molten CdTe with near stoichiometric initial composition was measured by using an oscillating cup viscometer up to 1403 K. The viscosity values hysteresis was obtained on heating and cooling curves. The viscosity increases from the melting point „ . up to „ . #22 K, followed by a reduction in a narrow temperature range (2}3 K) during heating with a rate of 0.5 K/min. The reached value of the viscosity „ . #25$1 K slightly decreases up to 1403 K and monotonically increases during the next cooling with the same rate. It was concluded that the solid defect structure is in#uenced by the liquid CdTe viscosity dependence on temperature. The melt holding at „ . #2 K during 112 min and at „ . #40 K during 41 min led to the viscosity quasi-harmonic oscillation with a period of about 5 min. ( 2000 Elsevier Science B.V. All rights reserved.

We report deep level characterization on CdZnTe nuclear detectors grown by the high pressure Bridgman method. Three CdZnTe samples taken from the top, middle and tail of the same ingot were investigated using photo-induced current transient spectroscopy and thermoelectric-effect spectroscopy. Three major traps are detected and their influence on the nuclear detection properties are discussed.

Defects and the relations with the levels introduced in the gap are among the toughest remaining problems in II–VI semiconductors. Up to now, more than 30 levels have been detected without any clear identification and assignation for most of them. PICTS, TEES and TSC are well suited for such investigation, but not complete. A very useful complement is provided by numerical simulation of some properties and the comparison between calculation and experimental results. We have used a simple existing model using the neutrality equation and the Fermi–Dirac distributions. This model was improved to introduce more than three levels which is largely our case (30 levels, 5–6 bands). Carrier concentration and resistivity are then deduced. PICTS results are used as model input. Results and compensation processes are discussed.

Il est bien connu que tous les materiaux presentent pour les rayons X un indice de refraction voisin de 1. Il s'en suit que toute optique pour rayons X est impossible. Neanmoins, pour des angles rasants (a ≤ 3 mrd dans le cas du verre), il y a reflexion totale des rayons X. On peut ainsi, en utilisant des capillaires de forme appropriee, produire un certain nombre de reflexions sur les parois et obtenir en sortie de ce capillaire une densite de photons plus importante, ce qui equivaut a une reelle focalisation; ce dispositif permet donc d'obtenir des faisceaux fins (echelle micrometrique) et de forte densite.

Cd x Zn 1− x Te crystals grown by high-pressure Bridgman are promising for nuclear detection and are already widely used and studied for this application. Phase precipitation is identified for the first time in such HPB grown crystals, more or less pronounced depending on the samples studied. TEM images and electron diffraction patterns are presented. The possible relationships with nuclear detection performance and defect energy levels are discussed in the light of nuclear spectrometry, PICTS, TSC and TEES.

A mercuric iodide detector, having an electrode surface 5 × 5 mm2 and a thickness of about 500 μm, was irradiated with a photon beam of 511 keV impinging perpendicularly to the direction of the detector polarisation electric field, that is parallel to the electrodes. In this way the useful thickness for absorption is 5 mm, about ten times greater than in the planar irradiation configuration, where the detector is irradiated through the electrodes along the direction of the electric field. The use of the detector in this configuration allows to achieve a better absorption efficiency for energies up to several hundred keV, without affecting the charge collection efficiency, contrary to the situation when the detector is irradiated in usual configuration (i.e. through the electrodes).

We present electro-optical characterization (by deep level transient spectroscopy, deep level optical spectroscopy and photo-induced current transient spectroscopy) on vanadium doped CdTe and CdZnTe crystals prepared by the vertical Bridgman method for photorefractive applications. Two main electron traps at 0.95 and 0.78 eV were detected and characterized. These levels are strongly involved in the photorefractive effect of CdTe doped with V, and led to distinguish two classes of crystals.

Recent studies of the photorefractive characteristics of CdTe:V compound have demonstrated this material to provide high two wave mixing gain in the 1–1.5 μm wavelength range. However due to its high figure of merit, larger two wave mixing gain could be expected. We present some results about the influence of the zinc content in these materials which could explain such a reduction. In particular, we show that crystals can be ranked in two different classes following their photorefractive properties. This classification is essentially based on the absence (or existence) of a resonant intensity-temperature effect with the crystals with zinc (respectively without zinc). We also present some physico-chemical parameters obtained on these crystals by secondary ionic mass spectroscopy (SIMS) and electron paramagnetic resonance (EPR) experiments. The difference of photorefractive properties between the two classes would imply an evolution in the V 2+ V 3+ ratio which is not compatible with the EPR results. As to clarify this problem we will propose a new model of two deep levels in the gap of the material.

Cd 1− x Zn x Te single crystals doped with IV group elements (Ge, Pb) were grown by the Bridgman method. The equilibrium characteristics of specimens were determined by deep levels: E v +(0.62±0.04) eV (Ge impurity) and E v +(0.36±0.04) eV (Pb impurity). Measurements of magnetic susceptibility ( χ ) have shown the increase of paramagnetic constituent χ p compared with undoped CdTe and the absence of its temperature dependence. The results obtained are explained by the formation of complex associates containing intrinsic defects and impurity atoms.

Rapid thermal annealing (RTA) was investigated for curing doped and undoped spin-on glass films deposited onto silicon substrates. The annealed undoped spin-on glass (SOG) films present an important densification of the layers as a function of temperature and a reduction in the interfacial state density. The possibility of using rapid thermally annealed spin-on doped glass (SOD) films as a doping source as well as a surface passivation layer was investigated. The results show that the combination of spin-on film (after dilution of the solution with methanol) deposition and RTA can produce shallow lightly doped emitters. Sheet resistances lower than 150 Ω/□ are easily reached. Moreover, the minority-carrier diffusion length is improved owing to the gettering effect induced by phosphorus diffusion. The use as a passivation layer of the SOG or the remaining SOD oxide film makes this technique favourable for applications such as the fabrication of solar cells.

Deep level characterization by photoinduced current transient spectroscopy, deep level transient spectroscopy and deep level optical spectroscopy is presented on vanadium doped CdTe crystals grown for photorefractive applications. A main electron trap at 0.95 eV, connected with V doping, is proposed to be the main deep level involved in the photorefractive effect of CdTe:V on the bases of the σn0 and σp0 ionization cross-sections measurements as compared to spectroscopic results of the electron-hole competition factor obtained on CdTe:V.

The photorefractive properties of two CdTe:V crystals are compared in the infrared range. For both crystals, an increase of the electron–hole competition factor (from electrons to holes) is measured when the operating wavelength increases. The values of the wavelength where the sign of the dominating carriers changes are different. In the high wavelength range, high TWM gains are obtained by applying a square-shaped electric field at an optimum frequency. This frequency dependence can be explained by considering the effect of a second deep level. In the low wavelength range, a resonant intensity-temperature effect, as in InP:Fe, is demonstrated for the first time in this material. The difference between the two crystals is assumed to be particularly sensitive to the compensation – or not – of the cadmium losses during the crystal growth.

We present a prototype of an X- and γ-ray camera based on a semiconductor crystal of mercuric iodide (HgI 2 ) having a cross-sectional area of 10 × 10 mm 2 and a thickness of 0.5 mm. Two orthogonal sets of 20 charge-collecting μstrips are deposited on the two opposite surfaces of the detector giving a pixel size of 0.5 × 0.5 mm 2 . Using commercial hybrid preamplifiers several experimental tests have been performed in order to assess the performance of this device. Preliminary results on the spectroscopic capabilities together with an evaluation of the attainable spatial resolution are presented.

Generation and recombination lifetimes have been theoretically studied for the case of high‐resistivity silicon on the basis of the Shockley–Read–Hall model. Thanks to the high resistivity of silicon, it has been possible to take into account only the generation‐recombination levels which are situated between the Fermi level EF and the level E’F symmetrical to EF with regard to the midgap. First, a simple approach based on the presence of a single generation‐recombination level in the band gap has been considered; however, its validity is fair because chemical analyses of high‐resistivity silicon show that several levels with energy close to midgap or to the boundaries EF–E’F are generally present. This means that levels which are located at different positions in the gap may influence the generation and recombination lifetimes τg and τr but are not taken into account by such a model. In order to overcome this difficulty, a two‐level model has been developed. The main result is that the ratio of τg/τr sho...

Rapid thermal processing can offer many advantages, such as small overall thermal budget and low power and time consumption, in a strategy focused on cost-effective techniques for the preparation of solar cells in a continuous way. We show here that this very short duration (a few tens of seconds) of isothermal heating performed in a lamp furnace can be used for many thermal steps of silicon solar cell processing. Rapid thermal processing was applied to form the p-n junction from a phosphorus-doped spin-on silica film deposted on (100) silicon substrates at typical processing temperatures between 800 and 1100°C. the solar cells showed conversion efficiencies as good as those processed in a conventional way.

3C‐SiC, the only polytype which can be heteroepitaxially grown on large diameter silicon substrates, is a promising material to achieve power Schottky diodes. To carry out such diodes, high quality ohmic contacts are required. In this work, ohmic contacts were investigated on in situ highly n‐doped 3C‐SiC epilayers grown on (100) cheap silicon substrates. Different metals such as nickel, titanium, aluminum and gold were used to carry out the contacts. Classical circular Transfert Length Method (c‐TLM) structures were prepared to evaluate the specific contact resistance. Ni and Ti‐Ni contacts were annealed between 950° C and 1050° C while Al and Ti‐Au contacts were annealed between 300° C and 600° C. The specific contact resistance was then determined by using c‐TLM patterns. For each investigated contact, the best specific contact resistance values obtained are lower than 2×10−5Ω⋅cm2, even consecutively to a low temperature annealing.

The magnetic properties of ZnSe:Fe, ZnSe:Mn and ZnSe:Cr crystals are investigated. It is established that magnetic properties of ZnSe:Fe differ from magnetic properties of ZnSe doped with other transition metals, for example Cr2+ or Mn2+, because of Fe2+ ions ground state has a permanent magnetic moment. For ZnSe crystals doped from Zn+Fe the two subsystems are observed: paramagnetic and anti‐ferromagnetic with TC = −130 K (B = 67 G). It is shown that ZnSe:Fe magnetic properties are sensible to the crystals doping technique. We proposed a model, that explains formation of the few magnetic phases (paramagnetic, antiferromagnetic and “spin‐glass” phase) in ZnSe:Fe as result of nonuniform doping and formation of the impurity clusters in crystal. It is shown that the most uniform crystal doping may be obtained in case of doping during the growth process or at thermal annealing in Bi melt.

In this work we investigated the influence of the Si substrate misorientation and 3C‐SiC film thickness on the density of Anti‐Phase Boundaries, in order to better understand the mechanism of antiphase domain annihilation. The two highlights in our work are the utilization of [001] orientated Si on‐axis wafer with spherical dimples, which gave us access to a continuum of off‐cut angles (0° to ∼11°) and directions, and the deposition of elongated silicon islands on the surface of 3C‐SiC epilayers, which improved the detection of APDs by analysis of Scanning Electron Microscopy images. We found that for a given layer thickness the relative surface occupation of one domain increases with the off‐cut angle value, leading to single domain film up to a certain angle. This critical value is reduced as the film is thickened.

Zinc‐blende GaN quantum dots were grown on 3C‐AlN(001) by two different methods in a molecular beam epitaxy system. The quantum dots in method A were fabricated by the Stranski‐Krastanov growth process. The quantum dots in method B were fabricated by droplet epitaxy, a vapor‐liquid‐solid process. The density of the quantum dots was controllable in a range of 108 cm−2 to 1012 cm−2. Reflection high energy electron diffraction analysis confirmed the zinc‐blende crystal structure of the QDs. Photoluminescence spectroscopy revealed the optical activity of the QDs, the emission energy was in agreement with the exciton ground state transition energy of theoretical calculations.

By the analysis of intra‐ and intersubband transitions in GaN/AlN superlattices the band offset is determined experimentally. Superlattice structures with different period lengths were fabricated by plasma‐assisted molecular beam epitaxy 3C‐SiC substrates. The structural properties were studied by high resolution X‐ray diffraction, revealing a high structural perfection of the superlattice region with several peaks in the X‐ray spectra. Infrared absorbance spectroscopy revealed clear intrasubband transitions in the spectral region of 1.55 μm measured at room temperature. Clear intersubband transitions were observed by photoluminescence at room temperature. These transition energies were compared to calculated energies using a 1D Poisson Schrodinger solver. For the calculations standard parameters for cubic GaN and AlN were used, while the band offset between GaN and AlN was varied. Optimal agreement between experimental and theoretical data was obtained for a band offset ΔEC:Δ EV of 55:45.

The chemical evolutions of iridium surfaces induced by different bias voltages applied during BEN were followed using X‐ray Photoelectron Spectroscopy (XPS). This sequential study was carried out in an UHV set‐up connected to a MPCVD reactor. First, results clearly demonstrate the formation of a carbon overlayer with comparable equivalent thickness (2.5–2.8 nm) whatever the bias voltage during BEN. To confirm that diamond nucleation has occurred during BEN, a CH4/H2 plasma was then performed. XPS surface analysis and ex situ FEG‐SEM investigations well emphasise the existence of a bias voltage window leading to diamond nucleation.

Although the growth of 6H and 4H‐SiC polytypes seem to be almost solved, it is somewhat different for the cubic 3C‐SiC polytype. This latter still is a highly challenging and exciting scientific issue, mainly because of the discrepancy between the stability range of this polytype and the operating conditions of the available bulk growth processes. Despite many previous attempts along the last decades, it is only very recently that some works have paved the way to a real 3C‐SiC bulk growth development. Among the key results is the demonstration of 3C‐SiC growth using a variant of the sublimation method, thereby demonstrating that the high temperatures are not necessarily a lock to the growth of 3C. Another example is the achievement of a stable growth front over a very long time in a top seeded solution growth process. Both approaches have shown a real potential for growing high structural quality 3C‐SiC crystals. The current state of the art of these two processes will be presented and compared with respect to the problems of size or density of extended defects. Their respective strengths will also be discussed considering their future development.

In this work we have analyzed the possibility of upscaling the growth of 3C‐SiC. The growth was done at different temperatures to find limiting mechanisms of the growth rate and to examine the morphology of grown layers. Coverage by 3C‐SiC increases when increasing temperature, however more twins appeared. Activation energy of the growth is 130 kcal/mol—showing that growth rate limiting mechanism is sublimation of the source. We discuss the influence of large area 6H‐SiC wafers on the formation of 3C‐SiC, in which the change in basal plane orientation could also influence the growth of 3C‐SiC.

In the present work homoepitaxial (111) 3C‐SiC layers, grown by Chemical Vapour Deposition (CVD) on top of 3C‐SiC seeds grown by the Vapour Liquid Solid (VLS) mechanism on Si‐face on‐axis (0001) 6H‐SiC substrates, are investigated by means of Transmission Electron Microscopy (TEM). The CVD process was performed at constant C/Si ratio and the growth temperature was varied from 1450° C to 1650° C. The main defects in the VLS seeds which are directly nucleated on the interface with the 6H‐SiC substrate are microtwins, dislocations and stacking faults (SFs). Within the CVD layers, the main defects appearing are also SFs together with multiple twin complexes which consist of two Σ3 and one Σ9 boundaries. Systematic analysis revealed that the multiple twin complexes disappear with increasing temperature while the trend for SFs is more difficult to follow. Some 3C to 6H polytypic transformation was found to occur at CVD growth temperature above 1550° C.

We report the results of a low temperature photoluminescence investigation of 3C‐SiC samples grown by chemical vapor deposition on vapor‐liquid‐solid seeds. The main parameters tested in this series of samples were i°) the effects of changing the C/Si ratio and ii°) the growth temperature on the final growth product. On the first series the C/Si ratio varied from 1 to 14 for a constant growth temperature of 1550° C. For the second series, the growth temperature varied from 1450 to 1650° C by steps of 50° C with a constant C/Si ratio equal to 3. According to this work, the best results (minimum incorporation of impurities and best crystal quality) were obtained when using a C/Si ratio of 3 at 1650° C.

Heteroepitaxial junctions formed by p‐type strontium doped lanthanum manganite and n‐type cobalt doped titanium dioxide were fabricated on LaAlO3 (100) substrates by pulsed laser deposition. The La0.7Sr0.3MnO3 (LSMO) layers were grown at 650° C and under 150 mTorr ambient oxygen pressure. They showed room temperature ferromagnetism and metallic‐like electrical conduction with a resistivity of 0.015 ohm cm at 300 K. The CoxTi1−xO2[x = 0.05 and 0.1] (CTO), which, at anatase phase, was reported as a wide‐band‐gap dilute magnetic semiconductor, was deposited on the LSMO film surface at 600° C with an ambient oxygen pressure of 20 mTorr. The as‐grown CTO films exhibited pure anatase crystalline phase and semiconductor‐like conduction. Under optimized fabrication conditions the CTO/LSMO junction revealed a heteroepitaxial relationship of (004)CTO‖‖(001)LSMO‖‖(001)LAO. Electrical characterization of these p‐n junctions yielded excellent rectifying characteristics with a current rectifying ratio over 1000 at room...

Epitaxial p‐type 3C‐SiC layers have been grown on 6H‐SiC substrates by means of the sublimation epitaxy method. The growth process was conducted at a source temperature of 2000° C under vacuum conditions (

In present work we report on the study of microstructure and quality of 3C‐SiC layers grown by Vapor‐Liquid‐Solid mechanism using Si‐Ga melt on 6H‐SiC substrates. We aim to investigate the influence of the Ga concentration in the SiGa melt on the density and type of structural defects appearing in the layers. Transmission Electron Microscopy study was carried out on 3C‐SiC layers which were grown using three different Si50Ga50, Si25Ga75 and Si10Ga90 melts. Main defects in the layers were microtwins and stacking faults. The microtwins were always formed at the interface with the 6H‐SiC. By increasing the Ga concentration from 50% to 75% the stacking fault density is slightly increased, but the amount of microtwinned islands at the interface is much higher as compared to the layer grown in the lowest Ga content in the melt. Further increasing the Ga content deteriorates the quality of the layer in terms of stacking fault concentration. The defect density is rapidly increased and almost all of the stacking f...

Since their first synthesis, cubic boron nitride (c‐BN) and diamond thin films have triggered a vivid interest in these wide band gap materials for many different applications. Because of superior properties, c‐BN and diamond can be applied in optic, electronic and acoustic for high performances devices. In this discussion, we first describe briefly the properties of c‐BN and diamond and we review both the growth techniques and the progresses achieved in the synthesis of c‐BN and diamond, and in a second part, characteristics of new c‐BN and diamond UV detectors for solar observation are reported. These photo‐detectors present extremely low dark current, high breakdown voltage, high responsivity and stability under UV irradiation. Finally, diamond based acoustic devices and sensors are presented. High frequency acoustic wave devices can be design for high frequency filtering or sensing applications. Diamond/AlN micro‐cantilevers are excellent platform for sensor applications.

In this paper, a new deep submicron double‐gate (DG) GaN‐MESFET structure and its 2‐D numerical model have been proposed, investigated and expected to suppress the short‐ channel‐effects (SCEs) and improve the subthreshold behavior for deep submicron GaN‐MESFET‐based applications. The models have been used to predict and compare the performances of downscaled DG and conventional GaN‐MESFETs, where the comparison of device architectures shows that the proposed DG GaN‐Based MESFET exhibits a superior performance with respect to the conventional MESFET both in terms of threshold voltage and DIBL (Drain Induced Barrier Lowering) effect in deep submicron domain. The obtained results make (DG) GaN‐MESFET a promising candidate for future MESFET‐based circuits.

The electrical properties of post‐oxidized PECVD oxides in wet oxygen based on 3C‐SiC(111) epilayers grown by Vapor‐Liquid‐Solid and Chemical‐Vapor‐Deposition mechanisms on 6H‐SiC(0001) have been studied. Different 6H‐SiC(0001) samples exhibiting diverse crystal orientations (on‐axis, 2° off‐axis) and growth conditions were regarded. A comparative study of oxide qualities has been carried out via capacitance and conductance measurements (C‐G‐V). Achieved interface traps densities and effective oxide charges were compared for the different samples. Reliability issues have been considered via current measurements (I–V and TZDB) and statistical data treatment techniques (Weibull plots). Oxides based on 3C‐SiC layer grown by a process combining VLS and CVD methods demonstrated low interface states densities Dit of 1.2×1010 eV−1cm−2 at 0.63 eV below the conduction band and fixed oxide charges Qeff/q estimated to −0.1×1011 cm−2.

For high-power and high-voltage applications, silicon is by far the dominant semiconductor material. However, silicon has many limitations, e.g. a relatively low thermal conductivity, electric breakdown occurs at relatively low fields and the bandgap is 1.1 eV which effectively limits operation to temperatures below 175 deg.n C. Wide-bandgap materials, such as silicon carbide (SiC), gallium nitride (GaN) and diamond offer the potential to overcome both the temperature and power handling limitations of silicon. Diamond is the most extreme in this class of materials. By the fundamental material properties alone, diamond offers the largest benefits as a semiconductor material for power electronic applications. On the other hand, diamond has a problem with a large carrier activation energy of available dopants which necessitates specialised device concepts to allow room temperature (RT) operation. In addition, the role of common defects on the charge transport properties of diamond is poorly understood. Notwithstanding this, many proof-of-principle two-terminal and three-terminal devices have been made and tested. Two-terminal electronic diamond devices described in the literature include: p-n diodes, p-i-n diodes, various types of radiation detectors, Schottky diodes and photoconductive or electron beam triggered switches. Three terminal devices include e.g. MISFETs and JFETs. However, the development of diamondmore » devices poses great challenges for the future. A particularly interesting way to overcome the doping problem, for which there has been some recent progress, is to make so-called delta doped (or pulse-doped) devices. Such devices utilise very thin ({approx}1 nm) doped layers in order to achieve high RT activation.« less

Epitaxial formation of SiC nanocrystals has been investigated on single crystal silicon surfaces. A simple and cheap method using reactive annealing in CO has been developed and patented by our group (BME AFT and MTA MFA). By this technique epitaxial 3C‐SiC nanocrystals can be grown at the Si side of a SiO2/Si interface without void formation at the SiC/Si interface. CO diffusion and SiC nanocrystal formation on different silicon based systems (SiO2/Si, Si3N4/3Si and SiO2/LPCVD poly‐Si) after CO treatment at 105 Pa at elevated temperatures (T>1000° C) will be presented. By optimizing the annealing time a thin continuous nanocrystalline SiC layer has been formed. Applying a patterned Si3N4 capping layer as a barrier layer against CO diffusion, SiC nanocrystal formation at the Si3N4/Si interface is inhibited. We will present the selective growth of SiC nanocrystals using the before mentioned technique.

Raman microscopy has been used to study the carrier concentration and mobility in n‐doped 3C‐SiC epilayers grown on different silicon substrates, namely (100) Si and (111) Si on axis and off‐axis towards the [110] direction. By analyzing the longitudinal optical phonon‐plasmon coupled mode (LOPC), we were able to estimate the 3C‐SiC electron bulk mobility (μ) within the range between 5 and 500 cm2/Vs. The carrier concentration (n) was ranging from 2×1016 to 6×1018 cm−3. The observed trend shows a reduction in the electron mobility as the carrier concentration increases for films grown on any substrate considered, accordingly to the existent theory. For equal values of doping concentration, 3C‐SiC epitaxial films grown on (100) Si substrates show a higher mobility than films grown on (111) Si counterparts. This could be ascribed to a higher defect density in (111) Si samples. A deeper characterization by performing Raman maps shows a broadening and a splitting of the 3C‐SiC transverse optical (TO) peaks fo...

Residual stress and carrier lifetime variation have been measured in free‐standing n‐type 3C‐SiC wafer grown on undulated Si substrate. We identify extended regions of residual stress that lie parallel to epilayer surfaces. The opposite polarity of stress is identified toward the interface and toward the top surface. Integrated carrier lifetime has been determined by random defect density distribution which is enhanced in the areas of double‐positioning boundary defects. It is shown that carrier lifetimes are severely reduced by the presence of residual stress towards epilayer surfaces. In this way lifetime depth‐distribution can be mistakenly attributed to enhanced surface recombination.

The electrical properties of SiO2/3C‐SiC structures fabricated by rapid thermal processing (RTP) using oxynitridation and hydrogenation processes have been examined. It is shown that the growth of the SiO2 films in a RTP chamber is one order of magnitude faster than in a conventional furnace. As well as being fast, this process leads to oxide films with quality comparable or even better than the one grown in classical furnaces. It is revealed that with respect to oxides grown in N2O gas, without any pre‐annealing step, hydrogenation by H2 surface pre‐treatment reduces the density of interface traps and effective oxide charge in SiO2 layers. The improvement in the quality of the SiO2/3C‐SiC interface by H2 pre‐oxidation annealing is discussed.

Aiming at the growth of diamond nanowires on carbon nanotubes we have studied carbon nanotubes for treatment in pure hydrogen in Hot‐Filament assisted chemical vapour deposition reactor (HFCVD). Purified multiwalled carbon nanotubes were dispersed onto silicon substrates, and annealed in pure hydrogen in HFCVD reactor. Important parameters were substrate temperature (650 to 870° C), nanotube density, annealing time (1 to 4 hours), hot‐filament temperature (HFVCD, 1900 to 2350° C), and gas pressure (30 to 70 Torr). No catalyst was used, and no methane was introduced in the chamber. Annealed samples were studied by Field Emission SEM and EDX analysis. Results show that for a filament temperature of 2000 to 2350° C, carbon nanotubes are rather stable in atomic hydrogen environment. For higher filament temperatures (>2350° C) nanotubes are converted into microcrystalline graphite, and for lower temperatures (1900–1950° C) nanotubes are etched away. In the conditions in which nanotubes are stable, growth of na...