Isotope-pure silicon layers grown by MBE

Molecular-beam epitaxy with a solid source was used to grow silicon layers enriched with ²⁸Si and ³⁰Si isotopes to 99.93 and 99.34%, respectively. Secondary-ion mass spectrometry and Raman scattering spectroscopy were applied to demonstrate the high isotopic purity and crystal perfection of the layers obtained.     

Effect of the Molecular Weight of Poly(ethylene glycol) on the Properties of Biocompatible Magnetic Fluids

The effect of the molecular weight of poly(ethylene glycol) (PEG) on the physical properties of water-based magnetic fluids with sodium oleate and PEG stabilization was investigated. The structure as well as magnetic, rheological, and thermal properties of the obtained samples were studied using transmission electron microscopy (TEM), photon cross correlation spectroscopy (PCCS), superconducting quantum interference device (SQUID), and differential scanning calorimetry (DSC) methods. The molecular weight of PEG had a strong effect on the rheological properties while the effect was rather insignificant on the particle size distribution and the self-heating of the studied magnetic fluids. The heating ability of the PEG-stabilized magnetic fluids was determined by calorimetric measurements of the specific absorption rate (SAR). The thickness of the PEG layer was calculated from the experimental data of the temperature rise rates as a function of the magnetic field strength using the Rosensweig theory.     

Capacitance-voltage profiling of Au/n-GaAs Schottky barrier structures containing a layer of self-organized InAs quantum dots

Capacitance-voltage measurements are used to obtain profiles of the free carrier distribution in Schottky barriers grown on uniformly doped n-GaAs hosts containing layers of self-organized InAs quantum dots. It is found that electrons accumulate at a depth of 0.54 μm, which corresponds to the depth of the quantum-dot layer. As the temperature drops below 90 K, a second peak appears in the concentration profile at 0.61 μm, which becomes dominant as the temperature continues to decrease. It is shown that the appearance of the second peak in the concentration profile is not due to electron density redistribution over the structure, but rather is observed when the rate of thermal emission of electrons from the quantum dots is slower than the angular frequency of the capacitance measurement signal. Fiz. Tekh. Poluprovodn. 32, 1229–1234 (October 1998)     

Quantum-dot injection heterolaser with 3.3 W output power

Continuous-wave lasing has been achieved via the ground state of composite vertically coupled InAlAs/InGaAs quantum dots in an AlGaAs matrix with a room temperature output power of 3.3W at both mirrors. Pis’ma Zh. Tekh. Fiz. 25, 41–46 (June 12, 1999)     

Mid-infrared (λ=2.775 µm) injection laser based on AlGaAsSb/InAs/CdMgSe hybrid double heterostructure grown by molecular-beam epitaxy

The lasing of an injection-pumped p-AlGaAsSb/n ⁰-InAs/n-CdMgSe double hybrid heterostructure in the mid-IR range is demonstrated for the first time. The lasing wavelength λ is 2.775 µm, and the threshold current density J _th=3–4 kA/cm² at T=77 K. The structure grown by two-stage molecular-beam epitaxy is characterized by extremely high (～1.5 eV) asymmetric potential barriers for electrons and holes in the InAs active region. The output power of spontaneous emission for round-mesa diodes at T=300 K was no less than 0.3 mW.     

ZnMnSe/ZnSSe Type-II semimagnetic superlattices: Growth and magnetoluminescence properties

A ZnSSe/ZnMnSe type-II semimagnetic superlattice was pseudomorphically grown via molecular beam epitaxy on a GaAs substrate. The superlattice-layer thicknesses and compositions were chosen so that compressive strains in the ZnMnSe layer compensated tensile strains in the ZnSSe layer. The photoluminescence spectra in an external magnetic field demonstrate the effect of “giant Zeeman splitting of an exciton”. Simulation of the luminescence-line shift in a magnetic field allowed us to determine more accurately the band offsets at the ZnSSe/ZnMnSe interface.     

Natural inactivation of phosphorus by aluminum in atmospherically acidified water bodies

Atmospheric acidification of catchment-lake ecosystems may provide natural conditions for the in-lake control of P cycling. This process is based on the elevated transport of aluminum from acidified soils and its subsequent precipitation in the water body and is described for strongly acidified forest lakes, acidified and circumneutral reservoirs, and a moderately acidified alpine lake. In water bodies with episodically or permanently acidified inflows a pH gradient develops between lake water and tributaries due to: (i) neutralization of acidic inflows after mixing with waters with undepleted carbonate buffering system, and/or (ii) the in-lake alkalinity generation dominated by biochemical removal of NO3- and SO4(2-). With the pH increasing towards neutrality, ionic Al species hydrolyze and form colloidal Al hydroxides (Al(part)) with large specific surfaces and strong ability to bind orthophosphate from the liquid phase. Moreover, Alpart settles and increases the P sorption capacity of the sediment. The presence of Al(part) on the bottom reduces orthophosphate release from sediments after its liberation from ferric oxyhydroxides during anoxia because Al(part) is not sensitive to redox changes. Consequently, the natural in-lake P inactivation may be expected in any water body with elevated Al input and a pH gradient between its inlet and outlet.     

A spatially single-mode laser for a range of 1.25–1.28 μm on the basis of InAs quantum dots on a GaAs substrate

Spatially single-mode lasing in the wavelength range of 1.25–1.28 μm was accomplished in injection lasers on GaAs substrates. The peak output power is 110 mW at room temperature, and the differential quantum efficiency amounts to 37%. The active region of the laser is formed by an array of self-organizing InAs quantum dots. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 34, No. 1, 2000, pp. 117–120. Original Russian Text Copyright ? 2000 by Mikhrin, Zhukov, Kovsh, Maleev, Ustinov, Shernyakov, Kayander, Kondrat’eva, Livshits, Tarasov, Maksimov, Tsatsul’nikov, Ledentsov, Kop’ev, Bimberg, Alferov.     

Electroluminescence of injection lasers based on vertically coupled quantum dots near the lasing threshold

Electroluminescence spectroscopy has been used in a wide range of temperatures (77–300 K) and driving current densities to study a laser heterostructure based on vertically coupled self-assembled InGaAs quantum dots (QD). It has been found that lasing occurs via the QD ground state in the entire temperature range. The temperature-independent position of the emission peak corresponding to the second excited state in QDs is explained.