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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 1 (1982), S. 751-777 
    ISSN: 0392-6737
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Sono stati misurati gli spettri di termoriflettanza tra 3 e 9 eV per una serie di cristalli misti GaSxSe1−x. I campioni erano lastrine monocristalline cresciute dalla fase vapore con il metodo del trasporto chimico. Le misure sono state effettuate con radiazione non polarizzata propagantesi all'incirca lungo l'asse di anisotropia dei cristalli, mentre la modulazione in temperatura è stata eseguita attorno a 65 K. Molte strutture degli spettri di riflettività sono state analizzate nella loro dipendenza dalla concentrazione di zolfo nei cristalli misti. Su questa base si è data una approfondita discussion degli spettri ottici di GaS e GaSe oltre la soglia fondamentale, e si sono ottenute nuove informazioni riguardanti i livelli elettronici di energia sia per questi composti che per l'InSe, che ha struttura cristallina analoga.
    Abstract: Резюме Были измерены спектры термоотражения в области между 3 и 9 эВ для ряда смешанных GaS x Se x−1 кристаллов. Образцы представляют монокристал-лические пластинки, вырращенные из пара химическнм методом. Измерения проведены с неполяризованным светвым пучком, распространяющимся приблизителщимся приблизительно рдоль оси анизотропии кристалла. Температура модулируется вблизи 65 К. Анализи-руются некоторы в спектрах отражения в зависимости от концентрации серы в смешанных кристаллах. Прородится подробное обсуждение оптических спектров в GaS и GaSe ниже основного края. Получается новая информадия об электронных энергетических уровнях для указанных соединений и для InSe, которые имеют аналогичную кристаллическую структуру.
    Notes: Summary The thermoreflectance spectra between 3 and 9 eV have been measured for a series of GaSxSe1−x mixed crystals. The samples were single-crystal platelets grown from the vapour by the chemical-transport method. The measurements were performed with a nonpolarized light beam propagating approximately along the anisotropy crystal axis and the temperature was modulated around 65 K. Many structures in the reflectance spectra have been analysed in their dependence on the sulphur concentration in the mixed crystals. On this basis a detailed discussion of the optical spectra in GaS and in GaSe beyond the fundamental edge is given, and new information concerning the electronic energy levels is obtained both for these compounds and for InSe, which has an analogous crystal structure.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 10 (1988), S. 57-69 
    ISSN: 0392-6737
    Keywords: Thin-film growth ; structure and epitaxy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Films di solfuro di cadmio sono stati cresciuti su substrati di tellururo di cadmio, mediante la tecnica della deposizione chimica da fase vapore in tubo aperto. La crescita è stata realizzata in un reattore di tipo orizzontale, usando come sorgente grani policristallini di CdS e idrogeno come agente trasportatore. Le temperature della zona sorgente e della zona substrato sono state variate nell'intervallo (700÷900)°C e (400÷800)°C, rispettivamente. I valori sperimentali della velocità di crescita sono stati paragonati a quelli calcolati assumendo un modello di crescita in condizioni di quasi equilibrio. Il confronto mostra che il processo di crescita può essere adeguatamente descritto da tale modello in un piccolo intervallo di temperatura attorno a 700°C. A temperature inferiori o superiori le cinetiche superficiali limitano la crescita. I films cresciuti a 700°C mostrano inoltre la migliore morfologia. Misure di diffrazione X e di fotoluminescenza evidenziano inoltre che i films cresciuti in queste condizioni hanno una buona qualità strutturale.
    Abstract: Резюме Метод химического напыления в открытой тпубке испольэуется для выращивания эпитаксиальных CdS пленок на CdTe подложках. Выращивание проиэводится в гориэонтальном реакторе, испольэуя поликристаллический CdS в качестве материала источника и водород, как транспортный гаэ. Температуры эоны источника и эоны подложки иэменяются соответсвенно в интервалаш (700÷900)°C и (400÷800)°C. Экспериментальные значения напыления сравниваются с вычисленными значениями, предполагая квази-равновесныю модель. Сравнение показывает, что выращивания мжет быть адекватно описан с помощью такой модели в небодьшой области температур вблиэи 700°C. При меньших и больших температурах поверхностная кинетика ограничивает процесс роста. Пленки, выращенные при 700°C, также овнаруживает наилучшую морфологию. Иэмерения рентгеновской дифракции и фотолюминиесценции подтверждают, что пленки, выращенные в этих условиях, имеУт высокое качество структуры.
    Notes: Summary The open-tube chemical vapour deposition has been used to grow epitaxial CdS films on CdTe substrates. The growth has been performed in a horizontal reactor, using polycristalline CdS as source material and hydrogen as transporting gas. The deposition and the source temperatures have been varied in the range (400÷800)°C and (700÷900)°C, respectively. The experimental values of the deposition rate have been compared with those calculated assuming a quasi-equilibrium model. The comparison shows that the growth process can be adequately described by such a model in a small-temperature region around 700°C. At lower or higher temperatures the surface kinetics becomes the limiting mechanism. Films grown at 700°C show also the best morphology. X-ray diffraction and photoluminescence measurements evidence that films grown in these conditions have a good structural quality.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 13 (1991), S. 233-245 
    ISSN: 0392-6737
    Keywords: Specific structure of inorganic compounds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary A systematic investigation of the structural modifications of GaSe crystals, grown from the melt by different doping elements, has been performed by convergent-beam electron diffraction technique, in order to analyse the dependence of the structure on the doping atoms. Iodine-doped crystals have shown the ɛ-2H hexagonal and γ-3R rhombohedral polytypes. The structure of crystals doped either by silver, or copper, or cadmium, or zinc, or arsenic has been proved a mixture of the ɛ-2H hexagonal and of γ, 9 R, 12 R, 15 R rhombohedral phases. Ingots doped either by zinc or arsenic have shown the ɛ polytype prevailing in some zones and the γ structure in the other ones. The ɛ modification is dominant in ingots doped by the remaining atoms.
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 359-361 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Stransky–Krastanow metalorganic vapor phase epitaxy growth of self-organized ZnTe islands on homoepitaxial (001)GaAs is demonstrated. The −7.4% lattice mismatch of the ZnTe/GaAs heterostructure leads to a strain-driven distribution of nanoscale ZnTe islands on top of a two-dimensionally (2D) grown wetting layer. Atomic force microscopy and Rutherford backscattering spectrometry are used to determine the island dimensions and the thickness of the wetting layer. The density of the islands, their average diameter, and aspect ratio turn out to be about 520 μm−2, 13.6 nm, and 0.20, respectively, for a 1.2 ML thick 2D layer. Furthermore, the average aspect ratio of the islands decreases by increasing the thickness of the wetting layer, as expected by the progressive extinction of the strain-driven island nucleation. © 1998 American Institute of Physics.
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  • 5
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The metalorganic vapor phase epitaxy growth of ZnTe by di-isopropyl-telluride and di-methyl-zinc (Me2Zn) precursors is investigated by studying the epilayer growth rate as a function of both growth temperature and precursor transport rates. The ZnTe growth is a thermally activated process involving the heterogeneous pyrolysis of both Zn and Te alkyls onto the ZnTe surface. The growth rate dependence on growth conditions is explained in terms of surface adsorption-desorption reactions, assuming that the incorporation of Zn and Te atoms into ZnTe takes place through their selective adsorption on different surface lattice sites. There is also evidence that the occurrence of a competitive species for the surface adsorption of Zn atoms, which is identified as the CH3⋅ (methyl) radical, is produced by the pyrolysis of Me2Zn. Photoluminescence (PL) and absorption measurements performed on ZnTe allow to identify two new donor-acceptor pair (DAP) bands, originated from the recombination of a Ga donor with two acceptor centers, whose ionization energies are 56 meV for the higher energy band and around 140–150 meV for the lower energy one. Hall measurements show that the 56 meV acceptor is responsible of the p-type conductivity of the layers. The nature of the impurities originating such PL features is discussed with the support of secondary ion mass spectrometry. It is shown that Ga, Si, and C are dominant impurities in the layers, whereas Cu does not occur in our ZnTe. Unintentional C doping occurs in ZnTe as a consequence of the strong methyl and iso-propyl radical surface adsorption. We show that C is incorporated as an acceptor in ZnTe, originating the DAP bands observed in the PL spectra. Within this view, the 56 meV ionization energy acceptor is tentatively assigned to substitutional C atoms on Te lattice sites. © 1997 American Institute of Physics.
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  • 6
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The structural characterization of ZnTe epilayers grown on (100)GaAs by metalorganic vapor-phase epitaxy is reported. A detailed study of the ZnTe/GaAs heterostructure based on both high-resolution and conventional electron microscopy and ion channeling Rutherford backscattering spectrometry allows correlation of the type and spatial distribution of the extended defects occurring at or close to the ZnTe/GaAs interface with the amount of residual lattice strain into the ZnTe epilayers. Both pure edge Lomer and 60°-mixed misfit dislocations were identified at the interface along with partial dislocations bounding stacking faults, their overall density and distance distribution indicating the occurrence of a residual compressive strain at the heterostructure interface. By comparing this interface strain to the corresponding surface value of the same samples the occurrence of an inhomogeneous strain relaxation along the growth direction is clearly demonstrated. It is shown that such a strain gradient should be entirely ascribed to threading dislocations occurring into the ZnTe epilayers, their distribution being strictly correlated to the amount of residual strain along the epilayer growth direction. The conclusions are further supported by the analysis of the ZnTe surface strain, whose dependence on the epilayer thickness is consistent with that expected on the basis of a phenomenological model for the epilayer residual strain relaxation by threading dislocations. © 1995 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 2041-2045 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the structural characterization by Rutherford backscattering spectrometry in channeling geometry of CdS epitaxial layers grown on the highly lattice-mismatched CdTe substrates by chemical vapor deposition. The overall layer quality has been investigated for different CdS thicknesses, as well as the occurrence of small misalignments of the crystallographic directions from point-to-point in the layers. A crystallographic study of the hexagonal (wurtzite) lattice is also presented: two principal planes parallel to the c axis have been determined experimentally, i.e., (101¯0) and (112¯0), together with their in-plane axial directions. This allows investigation of the occurrence of 30° rotation effects in the crystal lattice as observed by scanning electron microscopy.
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  • 9
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the direct measurements of surface lattice strain in ZnTe epitaxial layers on {100}GaAs substrates by ion channeling Rutherford backscattering spectrometry and low-temperature (10 K) reflectance spectroscopy measurements. The measured ZnTe strain is the superposition of the expected thermal (tensile) strain and a thickness-dependent residual compressive strain. Our data indicate that the removal of this residual strain is slower than the rate predicted by the equilibrium theory, following an apparent h−1/2 power-law dependence on the epilayer thickness h, above ∼100 nm.
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  • 10
    ISSN: 1573-482X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The Stranski–Krastanow (SK) growth by atmospheric pressure metalorganic vapour phase epitaxy of self-organized ZnTe nanoislands on homoepitaxial (0 0 1)GaAs is demonstrated. The −7.4% lattice mismatch of the ZnTe/GaAs heterostructure leads to a strain driven distribution of nanoscale ZnTe islands on top of a two-dimensionally (2D) grown wetting layer. Atomic force microscopy and Rutherford backscattering spectrometry are used to determine the island dimensions, the ZnTe mean coverage and the thickness of the 2D wetting layer. The island average density and diameter, as well as their aspect ratio are about 520 μm-2, 13.6 nm and 0.20, respectively, in the case of a 1.20 monolayer (ML) thick wetting layer and a growth rate of 0.074 ML s-1. Preliminary data on the effects of different growth rates on the island average densities are also reported. © 1998 Chapman & Hall
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