Гетероструктура квантово-каскадного детектора частотного диапазона 2.5 ТГц

The design of the heterostructure of a 2.5 THz range quantum-cascade detector is proposed and heterostructure is grown by molecular-beam epitaxy technique. To optimize the thicknesses of the layers of the heterostructure cascades, a numerical method for iterative solution of the Schrodinger ¨ −Poisson equation in the k · p formalism was used. The grown heterostructure of the quantum-cascade detector showed a high structural perfection, confirmed by the small values of the average FWHM of the high-order satellite peaks on the X-ray diffraction rocking curves, which were (8.3 ± 0.5)′′. Analysis of dark-field images obtained by transmission electron microscopy showed that the total thickness of the layers in the cascade is (137.3 ± 6.9) nm, which corresponds to the calculated thickness of the layers in the cascade of the heterostructure of the quantum-cascade detector.

Growth-sector dependence of morphological, structural and optical features in boron-doped HPHT diamond crystals

Semiconducting boron-doped diamond single crystals of cubo-octahedral habit with prevalent development of octahedron {111} faces and insignificant area of cube {001}, rhombo-dodecahedron {110} and tetragon-trioctahedron {311} faces were obtained using solution-melt crystallization at high pressure 6.5 GPa and temperatures 1380…1420 °C. Using the Fe-Al solvent, which allows controlled incorporation of boron dopant between 2·10–4…10–2 at.% made it possible to vary the electro-physical properties of the crystals. Methods of micro-photogrammetry, atomic force microscopy, and micro-Raman spectroscopy were applied to reveal sectorial inhomogeneity of impurity composition and morphology of different crystal faces. The obtained crystals were shown to have high structural perfection and boron concentration ranging approximately from 1·1017 up to 7·1018 cm–3. An increase in boron concentration increases the area of {111} faces relatively to the total crystal area. Nanoscale morphological features like growth terraces, step-bunching, dendrite-like nanostructures, columnar substructures, negative growth pyramids on different crystal faces are shown to reflect peculiarities of carbon dissolution at high pressures and temperatures. The changes in the crystals’ habit and surface morphology are discussed in relation to inhomogeneous variation of thermodynamic conditions of crystal growth and dissolution at different boron concentrations.

Dynamical X-ray diffraction imaging of voids in dislocation-free high-purity germanium single crystals

White-beam X-ray topography has been performed to provide direct evidence of micro-voids in dislocation-free high-purity germanium single crystals. The voids are visible because of a dynamical diffraction contrast. It is shown that voids occur only in dislocation-free parts of the crystal and do not show up in regions with homogeneous and moderate dislocation density. It is further suggested that the voids originate from clustering of vacancies during the growth process. A general method is proposed to verify the presence of voids for any crystalline material of high structural perfection.

Favourable growth conditions for the preparation of bulk AlN single crystals by PVT

A high seed temperature (2251 °C) reveals the highest deep UV transparency (α265nm = 27 cm−1), a high structural perfection (EPD = 9 × 103 cm−2) and a suitable growth rate (R = 200 μm h−1).

Stability and Degradation Mechanismof Si-based Photocathodes for Water Splitting with Ultrathin TiO2 Protection Layer

Using transmission and scanning electron microscopy, we study mechanisms which determine the stability of Silicon photocathodes for solar driven water splitting. Such tandem or triple devices can show a promising stability as photocathodes if the semiconductor surface is protected by an ultrathin TiO2 protection layer. Using atomic layer deposition (ALD) with Cl-precursors, 4–7 nm thick TiO2 layers can be grown with high structural perfection. The layer can be electrochemically covered by Pt nanoparticels serving as electro-catalysts. However, Cl-remnants which are typically present in such layers due to incomplete oxidation, are the origin of an electrochemical degradation process. After 1 h AM1.5G illumination in alkaline media, circular shaped corrosion craters appear in the topmost Si layer, although the TiO2 layer is intact in most parts of the crater. The crater development is stopped at local inhomogenities with a higher Pt coverage. The observations suggests that reduced Titanium species due to Cl−/O2− substitution are nucleation sites of the initial corrosion steps due to enhanced solubility of reduced Ti in the electrolyte. This process is followed by electrochemical dissolution of Si, after direct contact between the electrolyte and the top Si layer surface. To increase the stability of TiO2 protected photocathodes, formation of reduced Ti species must be avoided.

Влияние висмута на структурное совершенство и люминесцентные свойства тонкопленочных упругонапряженных гетероструктур Al-=SUB=-x-=/SUB=-In-=SUB=-y-=/SUB=-Ga-=SUB=-1-x-y-=/SUB=-Bi-=SUB=-z-=/SUB=-Sb-=SUB=-1-z-=/SUB=-/GaSb

The effect of bismuth on the structural perfection and the luminescent properties of Al_ x In_ y Ga_1– x – y Bi_ z Sb_1– z /GaSb heterostructures has been studied. The optimal parameters of the process of zone recrystallization with temperature gradient at which epitaxial AlInGaBiSb layers have the minimum roughness and high structural perfection have been revealed: temperature gradient 1 ≤ G ≤ 30 K/cm, the liquid zone thickness 60 ≤ l ≤ 100 μm, the temperature range 773 K ≤ T ≤ 873 K, and bismuth concentration 0.3–0.4 mol fraction.

Эпитаксиальный рост пленок селенида кадмия на кремнии с буферным слоем карбида кремния

An epitaxial cubic 350-nm-thick cadmium selenide has been grown on silicon for the first time by the method of evaporation and condensation in a quasi-closed volume. It is revealed that, in this method, the optimum substrate temperature is 590°C, the evaporator temperature is 660°C, and the growth time is 2 s. To avoid silicon etching by selenium with formation of amorphous SiSe_2, a high-quality ~100-nm-thick buffer silicon carbide layer has been synthesized on the silicon surface by substituting atoms. The powder diffraction pattern and the Raman spectrum unambiguously correspond to cubic cadmium selenide crystal. The ellipsometric, Raman, and electron diffraction analyses demonstrate high structural perfection of the cadmium selenide layer and the absence of a polycrystalline phase.