Si-Induced AlGaAs/GaAs Superlaitce Disordering Using a Grown-In Impurity Source and the Effects of Annealing Ambient
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We show that it is possible to control the gap between the minibands of a superlattice by introducing positive barriers in the wells of the superlattice. An appropriate choice of the position, the width, and the height of these barriers achieved by standard methods can reduce or even close the minigaps of the superlattice.
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In this work, we present a detailed investigation of the low temperature emission properties of ZnSeO alloys by means of photoluminescence, micro-photoluminescence, and time-resolved photoluminescence. We show that the low temperature broad photoluminescence spectrum of ZnSeO attributed to the recombination of localized excitons is composed of sharp lines related to individual trapping states. Based on studies of photoluminescence thermal quenching from individual trapping states and photoluminescence dynamics, the mechanism of nonradiative recombination in ZnSeO alloys is discussed. Moreover, an unexpected decrease of the low temperature Stokes shift with increasing oxygen content is observed in contrast to what has been reported for GaAs based highly mismatched alloys. The possible origin of this effect is proposed.
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We examined the change in photoluminescence spectra of porous Si when it is oxidized then deoxidized chemically. After both steps, photoluminescence shifted to higher frequencies and increased in intensity. These shifts to higher frequencies indicate the photoluminescence is a result of the quantum size effect. Moreover, the increase in photoluminescence intensity after oxidation suggests that termination by hydrogen on the porous Si surface does not always play a key role in the photoluminescence mechanism.
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A disordered superlattice, a recently proposed artificially constructed material, is fabricated and photoluminescent properties and optical absorption are investigated. Disorder is intentionally introduced into the period of the superlattice in order to enhance its photoluminescence. The photoluminescent temperature dependences and the optical absorption spectra of Al0.5Ga0.5As bulk alloy, AlAs/GaAs ordered superlattice, and AlAs/GaAs disordered superlattice are studied and compared. The optical absorption spectra suggest that localized states are created in the band tail of the AlAs/GaAs disordered superlattice. The photoluminescence spectra of the disordered superlattice are strongly dependent on the localized states, and the temperature dependence of photoluminescence intensities obeys the same relation IPL∝[1+A exp(T/T0)]−1 as that reported for amorphous semiconductors.
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The superlattice unit-cell structure factors are calculated for the trapeziform model, which may be used for the epitaxically prepared one-dimensional superlattice crystals if the interdiffusion is taken into account. The particular cases of this model are: (1) the rectangular model, which describes the superlattice if the interdiffusion is negligible; (2) the triangular model, which describes the superlattice if the interdiffusion takes place all over the layer thickness. The change of satellite intensities during the interdiffusion is discussed. The results obtained may be used to interpret the X-ray diffraction patterns produced by superlattices.
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On the basis of the film structure of a Pt/AlN multilayer film which exhibits a superlattice peak after annealing, a disc-shaped nanocrystal model is proposed for simulating the diffraction line profile from a one-dimensional superlattice. The proposed model demonstrates that a superlattice peak can arise even from just two disc-shaped nanocrystals and even with a large misorientation (a few degrees), provided both the thickness and the in-plane crystal size of the nanocrystals are of the order of nanometres. Using the model, the superlattice peaks from Pt/AlN superlattices are analysed quantitatively and the effect of annealing on the film is discussed.
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In this work we investigate the excitonic properties of (4-FC6H4C2H4NH3)2PbI4 hybrid organic/inorganic thin films. We first use a standard point-by-point photoluminescence mapping. The maps formed using the photoluminescence intensity, line width, and broadening reveal the presence of structural defects. Using a statistical treatment of the data we found that the spatial fluctuations of the photoluminescence peak wavelengths are rather small compared to the photoluminescence line width. Moreover, we report the first direct observation of spatially resolved excitonic photoluminescence in this type of materials using dark-field imaging of white-light pumped photoluminescence. Owing to the rapid acquisition time of the dark-field images, their temperature dependence was studied, and the thermal behavior of the photoluminescence was investigated using this technique. We show that photoluminescence mapping combined with dark-field imaging and spectroscopy provides valuable information on the excitonic properties of hybrid organic/inorganic thin films.
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The theory of interactions between vacancies and impurities is formulated in terms of the pseudopotential method. It is shown that the interactions are given by the sums of three types of pair potentials, vacancy-vacancy, vacancy-impurity and impurity- impurity potentials. Some applications of the present formulae are also suggested.
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