[en] Short communication

No abstract available

[en] The formation of GaSb quantum dots in a GaAs matrix in the Stranski--Krastanow growth mode under metalorganic chemical vapor deposition conditions is investigated. Transmission electron microscopical images and photoluminescence measurements show the islands to nucleate during the GaSb deposition and to grow subsequently by mass transfer from the two-dimensional wetting layer. The evolving surface morphology indicates local equilibria between quantum dots and the surrounding wetting layer regions. Copyright 2001 American Institute of Physics

[en] In recent years the calorimetric absorption spectroscopy has been developed to a powerful tool of semiconductor spectroscopy based on the detection of nonradiative relaxation processes. Calorimetric absorption spectroscopy is an ultra sensitive quantitative absorption technique. Recent investigations of Fe in III-V semiconductors and InAs/GaAS quantum dots are presented here to illustrate the potential of the method. Sharp absorption lines have been observed at the low energy onset of the Fe^3+/2+ charge transfer band in III-V semiconductors. Calorimetric absorption spectroscopy demonstrates ground state absorption coinciding in energy with luminescence for self-organized InAs/GaAs quantum dot structures grown by MBE. Transitions to excited hole states are resolved and a comparison to photoluminescence excitation spectroscopy is presented. (author)

[en] The aim of an implantation of iodine seeds into the prostate controlled by ultrasound is reached by means of the equipment presented in this paper. The method, allowing to implant the seeds according to the therapy plan, has been developed above all in order to reduce the radiation exposure to the physicist, the radiotherapist and the surgeon. (orig.)

[en] The interaction between point defects in the matrix and excitons localized in self-organized InGaAs/GaAs quantum dots is investigated for structures irradiated by protons. The exciton ground state is demonstrated to be unaffected by radiation doses up to 10¹⁴ p/cm². The close proximity of radiation-induced defects leads to a strong nonmonotonous temperature dependence of the luminescence yield: Carriers are lost via tunneling from excited quantum dot states to irradiation-induced defects below ∼100 K, whereas at higher temperatures, carriers escape to the barrier and are captured by defects

[en] An effective method for controlling the position and number of self-assembled quantum dots (QDs) grown by molecular-beam epitaxy has been developed. Epitaxially grown shadow masks are used to realize selective area growth, which exploits different incidence angles of the molecular beams. We applied this method to control the position and number of self-assembled CdSe QDs in a ZnSe matrix. Bright cathodoluminescence shows the presence of regularly distributed ensembles of QDs and that single QDs can be reliably grown

[en] We present a method which increases the versatility of molecular beam epitaxy through multiple application of a stationary shadow mask. The method is based on selected area growth in the overlap of the incidence regions of two molecular beams impinging through different apertures of the mask. The width of the overlap depends on the incidence angles of the beams which can be adjusted in situ. Size-control of CdZnSe quantum-well (QW) islands with a precision of 20 nm by varying the distance between the apertures can be obtained. Without Se beam, a minor quantity of Cd is incorporated in the matrix modulating the band-gap energy by just 5 meV. Cathodoluminescence (CL) of nanoscale QW islands shows dot-like behavior, i.e., sharp emission lines that are attributed to different excited states and a blueshift of the CL on reducing the island dimensions

[en] We present a versatile method for in situ lateral growth control of optically efficient quantum structures. The method is based on molecular-beam epitaxy through an epitaxial shadow mask. Lateral control is achieved by selective area growth of short period superlattices. We demonstrate how the method can be applied to both lattice-matched and unmatched material systems. In the former, selective growth is employed in the formation of quantum wires. In the latter, this growth concept was also successfully applied to control the self-assembly of quantum dots within selected areas. The excellent quality of the quantum structures is demonstrated by their bright cathodoluminescence at room temperature

[en] Strain-driven decomposition of an alloy layer is investigated as a means to control the structural and electronic properties of self-organized quantum dots. Coherent InASGaAs islands overgrown with an InGa(Al)As alloy layer serve as a model system. Cross-section and plan-view transmission electron microscopy as well as photoluminescence (PL) studies consistently indicate an increase in height and width of the island with increasing indium content and/or thickness of the alloy layer. The increasing island size is attributed to the phase separation of the alloy layer driven by the surface strain introduced by the initial InAs islands. The decomposition is enhanced by the addition of aluminum to the alloy layer. The ground-state transition energy in such quantum dots is significantly (up to 200 meV) redshifted compared to the original InASGaAs quantum dots, allowing to reach the 1.3 μm spectral region maintaining the high PL efficiency and the low defect density typical for Stranski-Krastanow growth. The possibility of degradation less stacking of such quantum dot layers enables injection lasing on the ground-state transition with a differential efficiency of 57% and a continuous-wave output power of 2.7 W