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The space charge analysis within depletion layers in semiconductors containing deep trap levels is reconsidered. A simple approach to the frequency dependence of the admittance ofp+/n junctions is properly generalized in order to deal with the effect of interface states at heterojunctions and Schottky barriers, as well as with a special case for the space distribution of the trap density. The density of interface states atp-Ge/CdS heterojunctions is so derived. Approximate analytical solutions accounting for a spatially distributed time constant are obtained for the admittance ofp+/n junctions with a single trap state. A comparison with experimental data is given and discussed.

Abstract: Some physical properties of CdS/p-Ge heterojunctions made by chemical vapour deposition of single crystal CdS epitaxial layers on (111)p-type nearly degenerate Ge substrates are reported. the equilibrium energy band diagram is discussed in the light of junction capacitance measurements as a function of frequency and of the reverse bias. The presence of interface states in the CdS band gap, with a density maximum at 1.1 eV below the equilibrium Fermi level has been shown. A model for the acceptor nature of the electronic states of misfit dislocations in CdS is suggested. The temperature dependence of theI-V characteristics has been measured in the temperature range 77–300 K. Models for the current flow in both direct and reverse bias conditions are discussed, taking into account the tunneling-recombination or generation-tunneling mechanisms throgh interface states.

Positron lifetime spectra in V2O3have been recorded in the temperature range (80÷300) °K in which the transition to the metal state occurs. The occurrence of a complex positron time annihilation spectrum is ascribed to annihilations taking place in different positron band states. The positron lifetimesτ1=1.94·10−10s andτ2=4.74·10−10s are found to be constant in the explored temperature range. This is explained in terms of localization of positron and electron wave functions. The observed behaviour with temperature of the intensities of the decay components is discussed as being due to the screening effect of the conduction electrons on the repulsive action of the V3+lattice ions. Spettri temporali di decadimento dei positoni nel V2O3sono stati registrati in un intervallo di temperature ((80÷300) °K) comprendente la temperatura di transizione allo stato metallico. La comparsa di uno spettro di annichilazione complesso si suppone dovuta a positoni che occupano bande diverse. Si è trovato che le vite medie dei positoniτ1=1.94·10−10s eτ2=4.74·10−10s si mantengono costanti nell’intervallo di temperature esplorato. Ciò è stato spiegato considerando la localizzazione delle funzioni d’onda elettroniche e positoniche. Il comportamento con la temperatura delle intensità delle componenti di decadimento può essere assegnato all’effetto di schermo degli elettroni di conduzione sull’azione repulsiva degli ioni V3+del reticolo. Были иэмерены спектры времени жиэни поэитрона в V2O3в области температур (80÷300)°K, при которых имеет место переход в металлическое состояние. Наличие сложного спектра для времени аннигиляции поэитрона приписывается аннигиляциям, которые происходят в раэличных поэитронных эонных состояниях. Обнаружено, что времена жиэниτ1=1.94·10−10сек иτ2=4.74·10−10сек являются постоянными в исследованной области температур. Это общясняется на основе локалиэации поэитронных и злектронных волновых функций. Обсуждается, что наблюденная эависимость от температуры интенсивностей компонент распада обусловлена зффектом зкранирования злектронов проводимости на основании отталкивания ионов рещетки V3+.

Positron-decay curves in commercially available metal hydrides have been measured, using a delayed coincidence system with 0.37 ns (FWHM) prompt time resolution. Evidence was found that the annihilation is complex, with two exponential decays of comparable intensities. In alkali-metal hydrides as in alkaline-earth hydrides, the annihilation ratesΓ1andΓ2are found to increase with molecular densities. The experimental results are against the crude application of the simple decay model of the positron bound to a single H−ion of the lattice. This model seems realistic only in the limit of very low molecular densities. Positron lifetimes in TiH2and ZrH2are found to be considerably shorter than lifetimes in divalent alkaline earth hydrides, probably owing to the presence of the highly polarizable electrons in the conduction band. Le vite medie dei positoni negli idruri metallici commercialmente disponibili sono state misurate mediante un sistema di coincidenza ritardata avente una risoluzione di 0.37 ns (FWHM). L’annichilamento è risultato essere complesso con due componenti di decadimento esponenziali aventi intensità paragonabili. Sia negli idruri dei metalli alcalini che in quelli dei metalli alcalino terrosi si è trovato che le probabilità di annichilimentogT1egT2aumentano con le densità molecolari. I risultati sperimentali sono contrari alla applicazione del semplice modello di decadimento del positone legato ad un singolo ione H−. Questo modello sembra plausibile solo nel limite di densità molecolari molto basse. Le vite medie dei positoni in TiH2e ZrH2sono risultate considerevolmente più brevi di quelle riscontrate negli idruri dei metalli alcalino terrosi: ciò è probabilmente dovuto al contributo degli elettroni di conduzione. Были иэмерены кривые распада поэитронов в имеюшихся с продаже металлических гидридах, испольэуя эапаэдываюшую систему совпадений с 0.37 нсек (FWHM) мгновенным временным раэрещением. Найдено подтверждение, что аннигиляция является сложной, с двумя зкспоненциальными распадами, со сравнимыми интенсивностями. В шелочных металлических гидридах, подобных шелочноэемельным гидридам, получено, что скорости аннигиляции Γ1и Γ2увеличиваются с увеличением молекулярных плотностей. Экспериментальные реэультаты противоречат непосредственному применению простой модели распада, которая рассматривает поэитрон, свяэанным с отдельным ионом Н- в рещетке. Эта модель окаэывается реалистичной только в пределе очень ниэких молекулярных плотностей. Получено, что времена жиэни поэитронов в TiH2и ZrH2эначительно короче, чем времена жиэни в двухвалентных шелочно-эемельных гидридах, что, вероятно, обусловлено наличием сильно поляриэуемых злектронов в эоне проводимости.

EEPN (Enea Extented Petri Nets) is a prototyping environment for real-time process control system requirements specification. Its major components are : a specification model based on Extended Petri Nets, a graphical editor for net construction and a simulator with animation support. The environment, implemented in an object-oriented programming language, is available on IBM-PC.

Abstract: Cd1−x Zn x S/p-GaAs heterojunctions for solar cell applications have been prepared by growing single crystal Cd1−x Zn x S epitaxial layers on (111)GaAs substrates through a vapour phase chemical transport method using the close-spaced geometry and H2 as a transport agent. Electrical and photovoltaic properties of the heterojunctions have been investigated and discussed in connection with the main features of the growth technique. AM1 power conversion efficiencies up to 6.2% have been measured and possible improvements have been examined.

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In order to study metabolic modifications induced by short term fasting and their consequences on the uptake and intracellular fate of fatty acids iodine labelled in omega position, rats undergo a 36h fasting. Hearts are perfused in a Langendorff system with a glucose (11 mM) perfusion medium; [123I] hexadecenoic acid (IHA) is injected as a bolus. A comparison between time-activity curves p.i. demonstrates a much faster activity decrease for the hearts fasted animals. The intracellular analysis shows that short fasting did not significantly increase the myocardial uptake of fatty acids, but decreased the storage and increased the degradation of the fatty acids taken up. Mathematical analysis of the myocardial time-activity curves obtained by external detection provided results comparable to those of intracellular analysis. The coefficients of correlation between the values of the aqueous phases, organic phases and free fatty acids measured by intracellular analysis and calculated with the compart-mental model are consistently higher than 0.97. Consequently, this experimental model combined with mathematical analysis of the time-course of myocardial radioactivity after 123IHA administration appears to be very promising method for studying the effects of drugs or variations of energy substrate availability on myocardial fatty-acid metabolism.

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Capacitance DLTS measurements have been performed in VPE GaAs MESFETs prepared on Bridgman Cr-doped and LEC undoped semi-insulating substrates. A band of electron traps not intrinsically related to the VPE growth process and accumulating near the metal (gate) — semiconductor interface was detected in all the samples. Deeper regions into the channel were free from any detectable trap. Near pinch-off conditions, a positive capacitance signal was found to dominate the DLTS spectra only in the case of samples prepared on Cr-doped substrates. The hypothesis of this positive transient being related to changes in the occupation of surface states in the ungated surface access regions has been checked by comparing experimental and calculated dependencies of the signal amplitude on reverse gate voltage. Unexplained discrepancies, together with the absence of positive signal in MESFETs prepared on LEC undoped substrates, suggest the possibility of hole emission from hole traps within the bulk of the device.

The 14.4 keV (λ=0.8602 Å)γ-rays from a57Co source were scattered by the (444) and (555) planes of a perfect silicon crystal and the inelastic contribution to the total scattering was determined by means of the Mössbauer effect. It was found that the thermal diffuse scattering has intensity maxima under the Bragg peak, as expected on the basis of the lattice wave theory of the X-ray diffuse scattering. The ratio between the integrated intensities of the thermal diffuse and the total scatterings was equal to 0.47 and 0.55 for the (444) and (555) reflections respectively, the geometry of the experiment being similar to those commonly used for studies of diffuse scattering. The integrated Bragg intensities of the above reflections were compared with those calculated by using the formulae of the dynamical theory of diffraction. A comparison was also made between the intensities of the thermal scattering at the Bragg angle and those calculated by using some simplifying assumptions for the numerical evaluation of the formulae of the theory. A satisfactory agreement between experimental and calculated values was found for both the Bragg and the thermal diffuse scatterings. Mediante l’effetto Mössbauer si è determinato il contributo anelastico allo scattering della radiazioneγdi 14.4 keV (λ=0.8602 Å) diffratta dai piani (444) e (555) di un cristallo perfetto di silicio. Come previsto dalla teoria dello scattering dei raggi X dalle vibrazioni reticolari, si è trovato che i massimi di intensità dello scattering anelastico coincidono con le posizioni di Bragg. In una geometria di diffrazione simile a quella usata comunemente per studiare lo scattering termico, si è trovato un rapporto fra l’intensità integrata di quest’ultimo e quella dello scattering totale pari a 0.47 ed a 0.55 per le riflessioni (444) e (555) rispettivamente. Le intensità integrate dello scattering di Bragg sono state confrontate con quelle calcolate per mezzo della teoria dinamica della diffrazione; le intensità dello scattering termico in posizione di Bragg sono state confrontate con quelle calcolate mediante alcune ipotesi semplificative. In entrambi i casi si è trovato un accordo soddisfacente fra i valori sperimentali e quelli teorici. γ-лучи с знергией 14.4 кзВ (λ=0.8602 Å) от источника57Co рассеивались плоскостями (444) и (555) в идеальном кристалле кремния, и определялся неупругий вклад в полное рассеяние с помошью зффекта Мëссбаузра. Было обнаружено, что тепловое диффуэное рассеяние имеет максимальную интенсивность в пике Брзгга, как и ожидалось на основе рещеточной вплновой теории диффуэного рассеяния Х-лучей. Отнощение между проинтегрированными интенсивностями теплового диффуэного и полного рассеяния составило 0.47 и 0.55 для отражения от плоскостей (444) и (555), соответственно, причем, геометрия зксперимента является аналогичной обычно испольэуемым геометриям при иэучении диффуэного рассеяния. Проинтегрированные интенсивности Брзгга для выщеупомянутых отражений сравнивались с вычисленными с испольэованием формул динамической теории диффракции. Также проводилось сравнение между интенсивностями теплового рассеяния на угол Брзгга и интенсивностями, вычисленными с испольэованием некоторых упрошаюших предположений для численных оценок формул теории. Получается удовлетворительное согласие между зкспериментальными и вычисленными величинами и для рассеяния Брзгга и для теплового диффуэного рассеяния.

Absolute measurements of integrated intensities, diffracted in anomalous transmission through perfect single crystals of Ge were done in the temperature interval (80÷500) °K. The intensities of the transmitted and reflected beams were measured for the {220} reflection with MoKα(μ0t≈ 38) and CuKαradiations (μ0t≈ 44). By comparing the plots of the logarithm of the measured intensitiesvs.temperature with those calculated for different Debye temperatures,Θwas found to be (283±3) °K with both X-ray wavelengths. The independence ofΘon the wavelength can be considered as a proof that theKandLelectrons of the atom vibrate as a rigid body. The absolute integrated intensities measured with CuKαradiation give a value ofε0(the ratio between the imaginary parts of the form factor for the scattering and forward directions) equal to 0.994±0.0015 which is in very good agreement with the calculated value. Si sono eseguite misure assolute delle intensità integrate, diffratte in trasmissione anomala attraverso cristalli perfetti di germanio, nell’intervallo di temperatura da 80 a 500oK. Si sono misurate le intensità sia del fascio riflesso che di quello trasmesso per la riflessione {220}, con le radiazioni MoKα(μot≈38) e CuKα(μ0t≈44). La temperatura di DebyeΘdel cristallo, ottenuta paragonando le curve sperimentali del logaritmo dell’intensità in funzione della temperatura con quelle calcolate per diverse temperatureΘ, è uguale a (283±3)oK per ambedue le radiazioni usate. L’indipendenza diΘdalla lunghezza d’onda della radiazione dimostra che gli elettroniKeLdell’atomo vibrano come un corpo rigido. Le intensità integrate assolute misurate con la radiazione CuKαdànno un valore diε0(il rapporto fra le parti immaginarie dei fattori di forma nelle direzioni del fascio incidente e diffratto) uguale a 0.994±0.0015 in ottimo accordo con il valore calcolato. Проводились абсолютные иэмерения интегральных интенсивностей, диффрагированных при аномальном прохождении череэ идеальные многокристаллы Gе в интервале температур (80÷500) °К. Иэмерялись интенсивности прощедщих и отраженных пучков для отражения {220} при иэлучении МоKα(μ0t≈38) иKα(μ0t≈44). Сравнивая кривые для логарифма иэмеренных интенсивностей в эависимости от температуры с расчитанными интенсивностями для раэличных температур Дебая, было найдено, что & равна (283±3)°К для обеих длин волн рентгеновских лучей. Можно рассматривать эависимостьΘот длины волны, как докаэательство, чтоKиLатомные злектроны колеблются, как твердое тело. Абсолютные интегральные интенсивности, иэмеренные при иэлученииKαдают величинуε0(отнощение между мнимыми частями форм-фактора для рассеянного направления и направления вперед) равную 0.994±0.0015, которая находится в очень хорощем согласии с вычисленной величиной.

X-ray topography was employed in order to study the nucleation of dislocation lines at surface heterogeneities in (111) Si wafers during phosphorus diffusion. Star-like patterns of 60° dislocations nucleated at phosphorus decorated surface defects were observed and were proved to be localized within the diffused layer. The analysis of the X-ray contrast and the results of some heating experiments suggested a mechanism of growth of the dislocation lines which was based on climb processes.

High-quality, unintentionally doped GaSb layers were grown by molecular beam epitaxy (MBE) and by atomic layer MBE (ALMBE) to study the influence of growth conditions on their transport and photoluminescence properties. While the hole mobility μ is only slightly dependent on the growth conditions, the 77 K hole concentration p shows minima at growth temperatures of ∼ 450°C and for Sb 4 /Ga beam equivalent pressure ratios (BEPRs) of ∼ 8; the concentrations of singly and of doubly ionizable acceptors and of a compensating donor have been obtained by simultaneously fitting the temperature dependence of μ and p in the 40-300 K range; from these results we show that the existence of minima of p can be related to an increased electrical compensation due to a reduced incorporation of acceptors. The 15 K photoluminescence spectra are generally dominated by the donor-acceptor pair transition (A, 779 meV) involving the neutral state of the native acceptor, except when the growth is carried out at relatively low temperatures with low BEPRs. Under the latter conditions: (i) a peak (788 meV) shows at an energy 25 meV below the band-gap energy and (ii) exciton related transitions have intensities comparable to that of the A recombination.

Admittance measurements have been performed to reveal trap levels within the space charge region of CdZnS/ p-GaAs heterojunctions prepared by chemical vapour deposition in the close-spaced geometry. The presence, between GaAs and the CdZnS layer, of a transition region containing a high concentration of acceptor-like traps is hypothesized. Taking into account electric field effects, a ionization energy greater than 0.28 eV is estimated for the trap state. [ABSTRACT FROM AUTHOR]

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Copyright of Acta Endoscopica is the property of Lavoisier and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Acta Endoscopica is the property of Lavoisier and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)