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1
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EN
The anti-Stokes luminescence is a mechanism of the optical refrigeration in semiconductor light sources. The heavily doped semiconductors are considered as a material for the laser cooling. The limitation of this mechanism appears to be connected with a transition from the non-degenerate to degenerate occupation. This transition occurs at higher pumping rate (along with the transition to the optical gain and lasing) and at lower temperature. Thus, the limit for the laser cooling can be indicated. The minimal obtainable temperature is about 60–120 K depending on the doping level. The laser cooling of a semiconductor is impeded by the difficulty of extracting the spontaneous emission from a radiating body that is characterized by large angle of the total internal reflection.
EN
In the present research paper, we investigated spin polarized electronic, magnetic, thermodynamic, and transport properties of thallium gadolinium dichalcogenides TlGdX₂ (X = S, Se, Te) using density functional theory. Electronic structure reveals that all the three compounds are wide band gap semiconductors which are beneficial for good thermoelectric performance. Calculated magnetic moment of TlGdX₂ is found to be in good agreement with available experimental values and mainly dominant by Gd³⁺ ions. Semiclassical Boltzmann transport theory has been used to calculate the Seebeck coefficient and electrical conductivity for the proposed dichalcogenides. Calculated values of the Seebeck coefficient and electrical conductivity are found to be consistent with available experimental values in literature. Thermodynamic properties of TlGdX₂ have also been estimated for the first time and explained on the basic facts.
PL
Ciągły trend w kierunku miniaturyzacji sprzętu elektronicznego zapoczątkowany wprowadzeniem technologii powierzchniowego montażu oraz rosnącą liczbą wejść/wyjść osiągnęły punkt, w którym nowe rozwiązanie jakim jest bezpośredni montaż struktury półprzewodnikowej na płytce stało się niezbędne. Rozwój tanich technik formowania kontaktów podwyższonych, postęp w tworzeniu połączeń techniką lutowania rozpływowego, termokompresji lub za pomocą klejów przewodzących oraz wprowadzenie na rynek płytek drukowanych o bardzo dużej gęstości upakowania ścieżek stworzyły warunki do szerokiego wykorzystania technologii „flip chip" w różnych obszarach zastosowań. W Instytucie Inżynierii Precyzyjnej i Biomedycznej Wydziału Mechatroniki PW podjęto prace zakresie badań podstawowych, prób technologicznych oraz badań prototypowych technologii „flip-chip" planuje się skonstruowanie laboratoryjnego stanowiska badawczego. Projekt, realizowany w ramach grantu przyznanego przez KBN, jest wykonywany we współpracy z ITR. Zasady technologii „flip chip" oraz podstawowe założenia opracowywanego projektu stanowiska badawczego zostały przedstawione w artykule.
EN
Systematic miniaturisation of electronic assemblies after introduction of SMT and growing number of the chip outputs achieved the level in which new solutions as direct chip mounting on PC boards are necessary. The development of low cost bumping methods, progress in interconnection technology by reflow soldering, thermocompression or adhesive bonding and miniaturisation of PCB layout offer favourable conditions for wide application area of the Flip Chip technology. Implementations of Flip Chip interconnections is at present one of the most expanding research areas in electronic packaging technology. Some work in this area are planned in Institute of Precision and Biomedical Engineering of Warsaw University of Technology. For essential investigations, tests and prototyping a laboratory stand is planned. The project sponsored by State Committee of Scientific Research will be realised in cooperation with Tele & Radio Researcg Institute. The bases of Flip Chip technology and some assumptions for the elaborated project are presented.
Open Physics
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2011
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tom 9
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nr 6
1488-1492
EN
First-principles calculations of Na2Ti3O7 have been carried out with density-functional theory (DFT) and ultrasoft pseudopotentials. The electronic structure and bonding properties in layered Na2Ti3O7 have been studied through calculating band structure, density of states, electron density, electron density difference and Mulliken bond populations. The calculated results reveal that Na2Ti3O7 is a semiconductor with an indirect gap and exhibits both ionic and covalent characters. The stability of the (Ti3O7)2− layers is attributed to the covalent bonding of strong interactions between O 2p and Ti 3d orbitals. Furthermore, the O atoms located in the innerlayers interact more strongly with the neighboring Ti atoms than those in the interlayer regions. The ion-exchange property is due to the ionic bonding between the Na+ and (Ti3O7)2− layers, which can stabilize the interlayers of layered Na2Ti3O7 structure.
EN
The structure of chalcogenide glassy semiconductors in three-component systems of Ge-As-Se and As-Sb-Se has been studied by means of both NQR (nuclear quadrupole resonance) and EPR (electron paramagnetic resonance) spectroscopy. It is investigated that in the glasses of both systems the value of the electric field gradient at the resonating nuclei grows with increasing concentration of the clusters As2Se3 and Sb2Se3, thereby increasing the NQR resonance frequencies. It appears that for the Ge-As-Se system the structural transition from a two-dimensional to three-dimensional structure occurs at average coordination number $\bar r$ = 2.45. The EPR spectral parameters of glasses depend on the composition, the average coordination number and the temperature, and these are discussed. The effect of ”ageing” for CGS (chalcogenide glassy semiconductors) of As-Sb-Se system due to partial crystallization of the sample is observed from the EPR spectra.
EN
The paper presents results of computations of the energy efficiency of the cobalt luminescence in ZnSe:Co determined by the photoacoustic method. The transmission spectra, photoacoustic experimental and theoretical spectra, and the frequency dependence on the photoacoustic amplitude characteristics are presented. From them, the energy efficiency of Co²⁺ the near infrared luminescence (3200 nm) was computed in the frame of new proposed photoacoustic model of computations of the luminescence energy efficiency.
7
Content available remote Electronic parameters of MIS Schottky diodes with DNA biopolymer interlayer
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EN
In this work, we prepared an ideal Cu/DNA/n-InP biopolymer-inorganic Schottky sandwich device formed by coating a n-InP semiconductor wafer with a biopolymer DNA. The Cu/DNA/n-InP contact showed a good rectifying behavior. The ideality factor value of 1.08 and the barrier height (Φb) value of 0.70 eV for the Cu/DNA/n-InP device were determined from the forward bias I-V characteristics. It was seen that the Φb value of 0.70 eV obtained for the Cu/DNA/n-InP contact was significantly larger than the value of 0.48 eV of conventional Cu/n-InP Schottky diodes. Modification of the interfacial potential barrier of Cu/n-InP diode was achieved using a thin interlayer of DNA biopolymer. This was attributed to the fact that DNA biopolymer interlayer increased the effective barrier height by influencing the space charge region of InP.
EN
DFT analyses of electronic and optical spectra of barium cadmium chalcogenides (Ba2CdX3, X = S, Se, Te) have been carried out. The study of electronic spectra has been made in terms of band structure and density of states using full potential linear augmented plane wave plus local orbital method. Band structure calculations have been carried out under the approximations PBE-GGA, PBE-Sol, LDA and TB-mBJ. Band structures of these materials show that Ba2CdS3, Ba2CdSe3 and Ba2CdTe3 crystals possess a band gap less than 1 eV, underestimated relative to the experimental/theoretical literature values. Optical spectra of these chalcogenides have been analyzed in terms of real and imaginary parts of dielectric function, reflectivity, refractive index, extinction coefficient, absorption coefficient, optical conductivity and electron energy loss. Optical results show large anisotropy along different directions. These results provide a physical basis of barium cadmium chalcogenides for potential application in optoelectronic devices.
EN
In situ detection and dynamics of laser-induced melting in different semiconductor crystals (CdTe, CdHgTe, GaAs, InSb and SiC) were performed by the time-resolved reflectivity (TRR). The samples were subjected to irradiation with 20 ns pulses of KrF excimer or ruby laser with energy density varied in a wide range. The surface morphology of the crystals was monitored using optical microscopy and time dependences of the temperature of the crystal surface as a function of laser pulse energy density was also calculated. The melting and ablation threshold values were determined and specific features of the laser-induced phase transitions in the surface region of the semiconductors were analyzed.
10
Content available remote Ultrasonic study of CuxAg1-xInTe2 bulk material
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EN
Longitudinal and shear ultrasonic wave velocities were measured in the quaternary compounds CuxAg1¡xInTe2 (0 · x · 1) using pulse echo technique. Measurements were carried out at 4 MHz frequency and at room temperature. Elastic moduli and acoustic impedance have been calculated. Results indicated that these parameters are influenced by the increased addition of copper from x = 0 to 1.
EN
We report on the effect of rapid thermal annealing (RTA) on GaAs1-x-Nx layers, grown by molecular beam epitaxy (MBE), using room temperature spectroscopic ellipsometry (SE). A comparative study was carried out on a set of GaAs1-x-Nx as-grown and the RTA samples with small nitrogen content (x = 0.1%, 0.5% and 1.5%). Thanks to the standard critical point model parameterization of the GaAs1-x-Nx extracted dielectric functions, we have determined the RTA effect, and its nitrogen dependence. We have found that RTA affects more samples with high nitrogen content. In addition, RTA is found to decrease the E1 energy nitrogen blueshift and increase the broadening parameters of E1, E1+?1, E'0 and E2 critical points.
EN
The paper presents results of photoacoustic studies of thermal and transport properties of silicon samples. It shows for the first time the influence of plasma waves on the Sf/Sr and phase-lag frequency photoacoustic characteristics and describes a procedure leading to the determination of both thermal diffusivity and the life time or the diffusion length of excess carriers from those characteristics.
EN
The US-Taiwan Technology, Trade and Investment Collaboration framework is one of the American responses to the semiconductor Global Value Chains pandemic disruptions. It calls for closer economic and technological cooperation in the microchip industry including two-way investment. The aim of the study is to determine the potential positive and negative effects of TTIC within the context of complex Sino-American relations, and new approaches to globalisation with a special focus on its friend-shoring features. As the outcome of the analysis of the secondary data from research papers or reports and the descriptive research method conducted in this paper, TTIC appears as a balanced means of addressing the supply chain disruptions in the key sectors of the economy.
15
Content available History of Semiconductors
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EN
The history of semiconductors is presented beginning with the first documented observation of a semiconductor effect (Faraday), through the development of the first devices (point-contact rectifiers and transistors, early field-effect transistors) and the theory of semiconductors up to the contemporary devices (SOI and multigate devices).
EN
We are presenting a study of damage distribution in GaAs irradiated with 84Kr ions of energy EKr = 394 MeV up to the fluence of 5 × 1012 ion/cm-2. The distribution of damage along the projected range of 84Kr ions in GaAs was investigated using selective chemical etching of a single crystal cleaved perpendicularly to the irradiated surface. The damage zone located under the Bragg peak of 84Kr ions was observed. Explanation of the observed effects based on possible processes of channeling of knocked target atoms (Ga and As) is proposed.
EN
A TiO2/CdS coupled system was prepared by mixing the TiO2 P25 with CdS synthesized by means of the precipitation method. It was found that the specific surface area (SSA) of both components is extremely different and equals 49.5 for TiO2 and 145.4 m2·g-1 for CdS. The comparison of particle size distribution and images obtained by means of transmission electron microscopy (TEM) showed agglomeration of nanocomposites. X-ray diffraction (XRD) patterns suggest that CdS crystallizes in a mixture of cubic and hexagonal phases. Optical reflectance spectra revealed a gradual shift of the fundamental absorption edge towards longer wavelengths with increasing CdS molar fraction, which indicates an extension of the absorption spectrum of TiO2. The photocatalytic activity in UV and UV-vis was tested with the use of methyl orange (MO). The Langmuir–Hinshelwood model described well the photodegradation process of MO. The results showed that the photocatalytic behaviour of the TiO2/CdS mixture is significantly better than that of pure nanopowders.
18
Content available remote Thermally activated defect transformations in III-V compound semiconductors
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EN
Defect properties are usually studied by the analysis of their thermally activated transformations. In this paper the results of the first RBS/channeling study of the simple defect behavior in the GaAs single crystals and AlxGa1-xAs epitaxial layers irradiated at 77K and annealed at temperatures ranging from 77 to 650K are presented. Two important recovery stages at 280 and 450K were revealed. They were attributed to the defect mobility in the Ga- and As-sublattice, respectively. The structure of defects and their properties are discussed and the comparison with findings obtained using other analytical techniques is made.
PL
Własności defektów strukturalnych są zazwyczaj badane na drodze analizy ich termicznie aktywowanych przemian. W artykule przedstawiono wyniki pomiarów własności defektów prostych w monokryształach GaAs i warstwach epitaksjalnych AlGaAs bombardowanych jonami azotu w temperaturze 77K i wygrzewanych w przedziale temperatur od 77K do 650K. Zaobserwowano dwie granice ruchliwości defektów w temperaturach 280K i 450K. Zostały one przyporządkowane ruchliwości defektów odpowiednio w podsieci Ga i As. Przedstawiono hipotezy odnośnie struktury tych defektów i porównano je z obserwacjami uzyskanymi za pomocą innych metod pomiarowych.
EN
Investigation of the reciprocal system CuInSe2+2CdTeUCuInTe2+2CdSe was performed using XRD and differential thermal analysis. The isothermal section at 870 K, the liquidus surface projection, several vertical sections and a spatial diagram were constructed. The existence of a large homogeneity region of the sphalerite modifications of the compounds was established.
20
Content available remote Evidence for metastable behavior of Ga-doped CdTe
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EN
In this paper, we report for the first time on persistent photoeffects in gallium doped CdTe. Persistent photoconductivity and photoinduced persistent absorption were observed at 77 K. Both effects quenched above 120 K. The photoeffects have been attributed to the metastable behavior of gallium in CdTe.
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