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  • Two inch GaN substrates fabricated by the near equilibrium ammonothermal (NEAT) method

    2019-08-19

    This paper reports two inch gallium nitride (GaN) substrates fabricated from bulk GaN crystals grown in the near equilibrium ammonothermal method. 2'' GaN wafers sliced from bulk GaN crystals have a full width half maximum of the 002 X-ray rocking curve of 50 arcsec or less, a dislocation density of mid-105 cm−2 or less, and an electron density of about 2 × 1019 cm−3. The high electron density is attributed to an oxygen impurity in the crystal. Through extensive surface preparation, the Ga surface of the wafer shows an atomic step structure. Additionally, removal of subsurface damage was confirmed with grazing angle X-ray rocking curve measurements from the 114 diffraction. High-power p–n diode structures were grown with metalorganic chemical vapor deposition. The fabricated devices showed a breakdown voltage of over 1200 V with sufficiently low series resistance. Source:IOPscience For more information, please visit our website: www.semiconductorwafers.net, send us email at sales@powerwaywafer.com or powerwaymaterial@gmail.com

  • Enhancement of the quality of InAsSb epilayers using InAsSb graded and InSb buffer layers grown by hot wall epitaxy

    2019-08-12

    We have investigated the structural and electrical properties of InAsxSb1−x epilayers grown on GaAs(0 0 1) substrates by hot wall epitaxy. The epilayers were grown on an InAsSb graded layer and an InSb buffer layer. The arsenic composition (x) of the InAsxSb1−x epilayer was calculated using x-ray diffraction and found to be 0.5. The graded layers were grown with As temperature gradients of 2 and 0.5 °C min−1. The three-dimensional (3D) island growth due to the large lattice mismatch between InAsSb and GaAs was observed by scanning electron microscopy. As the thicknesses of the InAsSb graded layer and the InSb buffer layer are increased, a transition from 3D island growth to two-dimensional plateau-like growth is observed. The x-ray rocking curve measurements indicate that full-width at half-maximum values of the epilayers were decreased by using the graded and buffer layers. A dramatic enhancement of the electron mobility of the grown layers was observed by Hall effect measurements. Source:IOPscience For more information, please visit our website: www.semiconductorwafers.net, send us email at sales@powerwaywafer.com or powerwaymaterial@gmail.com

  • Quality Variation of ZnSe Heteroepitaxial Layers Correlated with Nonuniformity in the GaAs Substrate Wafer

    2019-08-06

    ZnSe layers are grown heteroepitaxially on substrates cut from a LEC-grown, undoped semi-insulating GaAs(100) wafer along the diameter parallel to the [001] axis. The intensities of free-exciton photoluminescence and X-ray diffraction from the ZnSe layers show an M-shaped profile along the GaAs wafer diameter, and are inversely correlated with the etch-pit-density distribution of the GaAs wafer. This observation gives, for the first time, experimental evidence that the quality of ZnSe heteroepitaxial layers grown by recent epitaxial techniques can be limited by the quality of GaAs substrates. Source:IOPscience For more information, please visit our website: www.semiconductorwafers.net, send us email at sales@powerwaywafer.com or powerwaymaterial@gmail.com

  • Highly boron-doped germanium layers on Si(001) grown by carbon-mediated epitaxy

    2019-07-29

    Smooth and fully relaxed highly boron-doped germanium layers were grown directly on Si(001) substrates using carbon-mediated epitaxy. A doping level of  was measured by several methods. Using high-resolution x-ray diffraction we observed different lattice parameters for intrinsic and highly boron-doped samples. A lattice parameter of a Ge:B = 5.653 Å was calculated using the results obtained by reciprocal space mapping around the (113) reflection and the model of tetragonal distortion. The observed lattice contraction was adapted and brought in accordance with a theoretical model developed for ultra-highly boron-doped silicon. Raman spectroscopy was performed on the intrinsic and doped samples. A shift in the first order phonon scattering peak was observed and attributed to the high doping level. A doping level of  was calculated by comparison with literature. We also observed a difference between the intrinsic and doped sample in the range of second order phonon scattering. Here, an intense peak is visible at  for the doped samples. This peak was attributed to the bond between germanium and the boron isotope 11B. Source:IOPscience For more information, please visit our website: www.semiconductorwafers.net, send us email at sales@powerwaywafer.com or powerwaymaterial@gmail.com

  • Epitaxial CdS Layers Deposited on InP Substrates

    2019-07-22

    The CdS layers were deposited on InP substrates by using the (H2–CdS) vapor growth technique. The single crystal layers of hexagonal CdS were obtained on InP (111), (110) and (100) with the following heteroepitaxial relationships; (0001) CdS//(111) InP and [bar 12bar 10] CdS//[01bar 1] InP, (01bar 13) CdS//(110) InP and [bar 2110] CdS//[bar 110] InP, (30bar 34) CdS//(100) InP and [bar 12bar 10] CdS//[01bar 1] InP. The CdS layers deposited on InP (bar 1bar 1bar 1) were identfied in terms of the twinned hexagonal crystals, twin planes of which were nearly parallel to (30bar 3bar 4) and its crystallographic equivalents. The compositional gradients were observed at the interface of the deposits and the substrates. Source:IOPscience For more information, please visit our website: www.semiconductorwafers.net, send us email at sales@powerwaywafer.com or powerwaymaterial@gmail.com

  • Absorption and dispersion in undoped epitaxial GaSb layer

    2019-07-16

    In this paper, we present the results of a theoretical and experimental investigation into the refractive index and absorption, at room temperature, of a 4 μm-thick undoped epitaxial layer of GaSb deposited on a GaAs substrate. A theoretical formula for optical transmission through an etalon was derived, taking into account the finite coherence length of the light. This formula was used to analyse the measured transmission spectra. The refractive index was determined in a wide spectral range, between 0.105 eV and 0.715 eV. The absorption was determined for photon energies between 0.28 eV and 0.95 eV. An Urbach tail was observed in the absorption spectrum, as well as a constant increase in absorption in the spectral region above the band gap. Source:IOPscience For more information, please visit our website: www.semiconductorwafers.net, send us email at sales@powerwaywafer.com or powerwaymaterial@gmail.com

  • Study on Cd vacancy in CdZnTe Crystal by Positron Annihilation Technology

    2019-07-08

    Cd vacancies in cadmium zinc telluride(CdZnTe) crystals have an important effect on the crystal properties. In this paper, position distribution and concentration change of Cd vacancy in CdZnTe crystal grown by the temperature gradient solution growth (TGSG) were investigated by positron annihilation technology (PAT), which was based on the potential energy distribution and probability density of the positron in the crystal. The results showed that, the density of Cd vacancy increased obviously from the first-to-freeze to stable growth of the ingots, while decreased along the radial direction of the ingots. Source:IOPscience For more information, please visit our website: www.semiconductorwafers.net, send us email at sales@powerwaywafer.com or powerwaymaterial@gmail.com

  • GaN substrate and GaN homo-epitaxy for LEDs: Progress and challenges

    2019-07-03

    After a brief review on the progresses in GaN substrates by ammonothermal method and Na-flux method and hydride vapor phase epitaxy (HVPE) technology, our research results of growing GaN thick layer by a gas flow-modulated HVPE, removing the GaN layer through an efficient self-separation process from sapphire substrate, and modifying the uniformity of multiple wafer growth are presented. The effects of surface morphology and defect behaviors on the GaN homo-epitaxial growth on free standing substrate are also discussed, and followed by the advances of LEDs on GaN substrates and prospects of their applications in solid state lighting. Source:IOPscience For more information, please visit our website: www.semiconductorwafers.net, send us email at sales@powerwaywafer.com or powerwaymaterial@gmail.com

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