Photoelectric properties of the GeSi/Si heterostructures with self-assembled nanoclusters grown by sublimation molecular beam epitaxy in a GeH4 medium

The photosensitivity (PS) spectra of the GeSi/Si(001) heterostructures with self-assembled nanoclusters grown by sublimation molecular beam epitaxy in a GeH₄ medium have been studied by photo-emf spectroscopy at the semiconductor/electrolyte junction (PSE) and by photo-emf and photocurrent spectroscopy of Schottky barriers including the temperature dependence of the PS spectra in the temperature range of 10–300 K. The bands related to the phonon assisted and phonon-less interband of spatially indirect optical transitions in the GeSi nanoclusters have been observed in the PS spectra even at 300 K. The scatter effect of the GeSi nanoclusters in size and/or in composition on the PS spectrum’s edge shape has been theoretically considered. The emission theory of the photoexcited carriers from the quantum wells of the GeSi/Si nanoclusters built-in to a Schottky barrier (p-tn junction, semiconductor/electrolyte junction) has been developed.     

Crystal lattice defects and Hall mobility of electrons in Si: Er/Si layers grown by sublimation molecular-beam epitaxy

The density of crystal lattice defects in Si: Er layers grown through sublimation molecular-beam epitaxy at temperatures ranging from 520 to 580°C is investigated by a metallographic method, and the Hall mobility of electrons in these layers is determined. It is found that the introduction of erbium at a concentration of up to ～5 × 10¹⁸ cm^?3 into silicon layers is not accompanied by an increase in the density of crystal lattice defects but leads to a considerable decrease in the electron mobility.     

Effect of growth conditions on photoluminescence of erbium-doped silicon layers grown using sublimation molecular-beam epitaxy

Erbium-doped epitaxial silicon layers were grown using two different growth techniques, namely, commonly used molecular-beam epitaxy (MBE) and solid-phase epitaxy (SPE). It is shown that an erbium-doped silicon epitaxial layer deposited through SPE on a cold substrate and subsequently annealed displays amore intense photoluminescence at a wavelength of 1.54 μm than do MBE-grown layers. __________ Translated from Fizika Tverdogo Tela, Vol. 46, No. 1, 2004, pp. 102–104. Original Russian Text Copyright ? 2004 by Shengurov, Svetlov, Chalkov, Andreev, Krasil’nik, Kryzhkov.     

High-temperature photoluminescence of CdHgTe solid solutions grown by molecular-beam epitaxy

The spectra of the high-temperature (up to 300 K) photoluminescence of the heteroepitaxial structures based on the CdHgTe solid solutions that are grown using molecular-beam epitaxy and emit at room temperature in the wavelength interval λ = 1.5–4.3 μm are analyzed. It is demonstrated that the observed photoluminescence of the CdHgTe narrow-gap semiconductor at high temperatures and the specific features of the high-temperature spectra can be interpreted using the disorder of the solid solution as in the case of the solid solutions of the group-III nitrides.     

Thickness uniformity of silicon layers grown from a sublimation source by molecular-beam epitaxy

The thickness distributions of epitaxial layers over the substrate area are experimentally and theoretically studied for deposition from a molecular beam formed by a sublimation source in vacuum. The calculated data agree well with the experimental results for the molecular-beam epitaxy of silicon.     

Vibrational spectra of monoisotopic SiH<Subscript>4</Subscript> and GeH<Subscript>4</Subscript> in low-temperature matrices

IR absorption spectra of monoisotopic ²⁸SiH₄ and ⁷⁶GeH₄ are studied in Ar and N₂ matrices at 10 K. It is shown that the absorption spectra of silane and germane are similar in the regions of the stretching ν₃ and bending ν₄ vibrations. Four groups of bands can be separated out in the spectra of each molecule: (1) narrow bands characteristic of the matrix isolation studies, (2) broad bands, (3) diffuse absorption with a large value of the spectral moment M ₂^* the intensity of which increases upon annealing, and (4) bands of dimers the intensity of which increases quadratically with concentration. The spectra of ²⁸SiH₄ and ⁷⁶GeH₄ in nitrogen matrices contain a triplet in the stretching region and a doublet in the bending region, which is explained by the change in the molecular symmetry from T _d to C _3V on passage from the gas phase to solid nitrogen.     

Peculiarities of photoluminescence of erbium in silicon structures prepared by the sublimation molecular-beam epitaxy method

The photoluminescence of semiconducting structures Si: Er: O/Si grown by the molecular-beam epitaxy method is studied. The dependences of Er photoluminescence intensity on the intensity of pumping are measured at the liquid helium temperature. An analysis of the experimental results on the basis of the exciton model of excitation of Er ions in a crystalline silicon matrix reveals the significant role played by an alternative channel of free-exciton trapping (apart from the donor energy levels of erbium-oxygen complexes), as well as that played by the nonradiative channel in the recombination of excitons, bound to erbium donors, without the excitation of erbium. The ratio of the concentration of optically active centers of erbium luminescence to the total concentration of introduced erbium is estimated.     

Photoluminescence of Si/Ge nanostructures grown by molecular-beam epitaxy at low temperatures

Multilayer Si/Ge nanostructures grown by molecular-beam epitaxy at low temperatures (250–300°C) of germanium deposition are studied using photoluminescence and atomic-force microscopy (AFM). It is assumed that, upon low-temperature epitaxy, the wetting layer is formed through the intergrowth of two-dimensional (2D) and three-dimensional (3D) nanoislands.     

Low-energy photoluminescence of structures with GeSi/Si(001) self-assembled nanoislands

The photoluminescence spectra of structures with self-assembled GeSi/Si(001) islands are investigated as functions of the growth temperature. It is shown that the shift of the peak of photoluminescence from islands toward lower energies on decreasing the growth temperature is due to the suppression of Si diffusion into islands and an increase in the fraction of Ge in islands. A photoluminescence signal from the GeSi islands is found in the region of energies down to 0.6 eV, which is considerably smaller than the band-gap width in bulk Ge. The position of the peak of photoluminescence from islands is described well by the model of a real-space indirect optical transition with account of the real composition and elastic strains of the islands. Mono-and multilayer structures are obtained with self-assembled GeSi/Si(001) nanoislands exhibiting a photoluminescence signal in the region 1.3–2 μm at room temperature.     

Photoelectric properties and electroluminescence of <Emphasis Type="Italic">p-i-n</Emphasis> diodes based on GeSi/Si heterostructures with self-assembled nanoclusters

This paper reports on the results of investigations into the photoelectric properties and electroluminescence of p-i-n diodes based on GeSi/Si heterostructures with GeSi self-assembled nanoclusters embedded in the i region. The p-i-n diodes are grown through sublimation molecular-beam epitaxy using a vapor-phase source of germanium. The photovoltage spectra of the p-i-n diodes measured at a temperature of 300 K exhibit a photosensitivity band attributed to interband optical transitions in the GeSi nanoclusters. A new approach to analyzing the photosensitivity spectra of the heterostructures containing GeSi thin layers is proposed, and the energy at the edge of the photosensitivity bands assigned to these layers is determined. The electroluminescence observed in the p-i-n diodes at 77 K is associated with the radiative interband optical transitions in GeSi nanoclusters.     

Effective excitation cross section and lifetime of Er<Superscript>3+</Superscript> ions in Si: Er light-emitting diodes fabricated by sublimation molecular-beam epitaxy

A series of Si: Er electroluminescent diode structures is fabricated by sublimation molecular-beam epitaxy. The diode structures efficiently emit at a wavelength of 1.5 μm under conditions of p-n junction breakdown at room temperature. The effective cross section of excitation of Er³⁺ ions with hot carriers heated by the electric field of a reverse-biased p-n junction and the lifetime of Er³⁺ ions in the first excited state ⁴I_13/2 are determined for structures that emit in a mixed breakdown mode and are characterized by the maximum intensity and excitation efficiency of the Er³⁺ electroluminescence.     

Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> nanosquaresheets grown on Si substrate

A novel morphology of Bi₂O₃ nanomaterial (nanosquaresheets) has been successfully synthesized in large area by thermal evaporation of commercial Bi₂O₃ powder at high temperatures. The Bi₂O₃ nanosquaresheets (NSSs) are perfect regular squares and have sharp, uniform edges. The typical length of the sides is in the range of 200–600 nm. The thickness varies from 30 to 100 nm. Electron microscopy observations show that the Bi₂O₃ NSSs are single crystalline. The growth of Bi₂O₃ NSSs is probably controlled by a vapor–solid mechanism. The dominate growth directions are [2̄10] and [1̄2̄2] within the (245) planes. PACS 81.05.Hd; 81.10.Bk; 81.16.Be     

Formation of self-assembled InGaAsN/GaP quantum dots by molecular-beam epitaxy

We have grown self-assembled InGaAsN/GaP quantum dots (QDs) with an In composition of 50% via the Stranski–Krastanov growth mode of molecular-beam epitaxy, obtaining high-density InGaAsN islands of 8×10¹⁰ cm⁻². When the InGaAsN islands are directly exposed to the P₂ beam, we observe a quantum-well-like hetero-interface using cross-sectional transmission electron microscopy (XTEM). This result indicates that the InGaAsN island density is remarkably reduced by As/P exchange reactions. To suppress these exchange reactions, we deposit Ga corresponding to 1 monolayer on the InGaAsN islands. When the Ga deposition sequence is finished, we use XTEM to detect InGaAsN islands embedded in GaP, which indicates that As/P exchange reactions can be suppressed by Ga deposition. Subsequently, we grow a multiple-stacked InGaAsN/GaP 5QDs using the Ga deposition sequence and report their room-temperature photoluminescence spectra.     

Ion implantation into heteroepitaxial Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Hg<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>Te grown by molecular-beam epitaxy

The results of investigations into the electrophysical properties of heteroepitaxial semiconductor material CdHgTe (CMT) grown by molecular-beam epitaxy (MBE) after ion implantation are reported. The major factors responsible for the differences between ion implantation in bulk CMT crystals and heteroepitaxial MBE CMT are determined. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 5–18, October, 2008.     

Ferroelectric and dielectric properties of SrBi<Subscript>4</Subscript>Ti<Subscript>4</Subscript>O<Subscript>15</Subscript> thin films grown on Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> film layer

Ferroelectric and dielectric properties of bilayered ferroelectric thin films, SrBi₄Ti₄O₁₅ grown on Bi₄Ti₃O₁₂, were investigated. The thin films were annealed at 700°C under oxygen atmosphere. The bilayered thin films were prepared on a Pt(111)/Ti/SiO₂/Si substrate by a chemical solution deposition method. The dielectric constant and dielectric loss of the bilayered thin films were 645 and 0.09, respectively, at 100 kHz. The value of remnant polarization (2P _r) measured from the ferroelectric thin film capacitors was 60.5 μC/cm² at electric field of 200 kV/cm. The remnant polarization was reduced by 22% of the initial value after 10¹⁰ switching cycles. The results showed that the ferroelectric and dielectric properties of the SrBi₄Ti₄O₁₅ on Bi₄Ti₃O₁₂ ferroelectric thin films were better than those of the SrBi₄Ti₄O₁₅ grown on a Pt-coated Si substrate suggesting that the improved properties may be due to the different nucleation and growth kinetics of SrBi₄Ti₄O₁₅ on the c-axis-oriented Bi₄Ti₃O₁₂ layer or on the Pt-coated Si substrate.