17 research outputs found

    Andreev reflection in Si-engineered Al/InGaAs hybrid junctions

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    Andreev-reflection dominated transport is demonstrated in Al/n-In0.38Ga0.62As superconductor-semiconductor junctions grown by molecular beam epitaxy on GaAs(001). High junction transparency was achieved in low-doped devices by exploiting Si interface bilayers to suppress the native Schottky barrier. It is argued that this technique is ideally suited for the fabrication of ballistic transport hybrid microstructures.Comment: 9 REVTEX pages + 3 postscript figures, to be published in APL 73, (28dec98

    Reflectionless tunneling in planar Nb/GaAs hybrid junctions

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    Reflectionless-tunneling was observed in Nb/GaAs superconductor/semiconductor junctions fabricated through a two-step procedure. First, periodic őī\delta-doped layers were grown by molecular beam epitaxy near the GaAs surface, followed by an As cap layer to protect the surface during {\it ex-situ} transfer. Second, Nb was deposited by dc-magnetron sputtering onto the GaAs(001) 2 √ó\times 4 surface {\it in-situ} after thermal desorption of the cap layer. The magnetotransport behavior of the resulting hybrid junctions was successfully analyzed within the random matrix theory of phase-coherent Andreev transport. The impact of junction morphology on reflectionless tunneling and the applicability of the fabrication technique to the realization of complex superconductor/semiconductor mesoscopic systems are discussed.Comment: 10 pages, 3 figures, to be published in Appl. Phys. Let

    Excitons and electron-hole plasma in ZnCdSe/ZnSe quantum wells

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    We report the results of pump and probe transmission and magneto- stimulated emission experiments performed in ZnCdSe/ZnSe multiple quantum wells of different well width and composition. The pumping conditions for the excitonic bleaching and the stimulated emission are directly correlated to the exciton stability in different samples. A transition from excitonic to free carrier lasing is observed by finely tuning the injection rate around the exciton ionization threshold.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only

    1.26 őľ\mum intersubband transitions in In0.3_{0.3}Ga0.7_{0.7}As/AlAs quantum wells

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    We observed room-temperature intersubband transitions at 1.26 microns in n-doped type-II In0.3_{0.3}Ga0.7_{0.7}As/AlAs strained quantum wells. An improved tight-binding model was used to optimize the structure parameters in order to obtain the shortest wavelength intersubband transition ever achieved in a semiconductor system. The corresponding transitions occur between the first confined electronic levels of the well following mid-infrared optical pumping of electrons from the barrier X-valley into the well ground state.Comment: To appear in Applied Physics Letter

    Electronic materials: a new era in materials science

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    Microscopic Mechanisms of Self-compensation in Si d-doped GaAs

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    We combined systematic cross-sectional scanning tunneling microscopy and spectroscopy investigations with Hall measurements on single Si \u3b4-doped layers, as well as Si \u3b4-doped superlattices in GaAs. We found that Si self-compensation involves nucleation and growth of electrically neutral Si precipitates at the expense of the conventional donor Si phase

    Novel materials for optoelectronics

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    Heterovalent semiconductor heterostructures, unlike isovalent semiconductor heterostructures, exhibit electronic properties strongly dependent on the detail of the interface atomic structure. Heterojunction band offsets, and therefore carrier injection and confinement, can in principle be modified by acting on the growth protocol and interface composition profile. The authors discuss examples of III-V/IV/III-V single and multiple quantum well structures (with IV = Si, Ge and III-V = GaAs, AlAs) as well as II-VI/III-V and II-VI/IV/III-V heterostructures grown by molecular beam epitaxy and examined by a variety of in-situ and ex-situ characterization techniques. Large deviations from the commutativity and transitivity rules of heterojunction band offsets in these systems are related to the establishment of inequivalent local interface environments. Such deviations are likely to be exploited first in a variety of optoelectronic devices to tune the band alignment

    A Roadmap for Controlled and Efficient n-Type Doping of Self-Assisted GaAs Nanowires Grown by Molecular Beam Epitaxy

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    N\u2010type doping of GaAs nanowires has proven to be difficult because the amphoteric character of silicon impurities is enhanced by the nanowire growth mechanism and growth conditions. The controllable growth of n\u2010type GaAs nanowires with carrier density as high as 1020 electron cm 123 by self\u2010assisted molecular beam epitaxy using Te donors is demonstrated here. Carrier density and electron mobility of highly doped nanowires are extracted through a combination of transport measurement and Kelvin probe force microscopy analysis in single\u2010wire field\u2010effect devices. Low\u2010temperature photoluminescence is used to characterize the Te\u2010doped nanowires over several orders of magnitude of the impurity concentration. The combined use of those techniques allows the precise definition of the growth conditions required for effective Te incorporation
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