3,222 research outputs found
Low temperature reflectivity study of ZnO/(Zn,Mg)O quantum wells grown on M-plane ZnO substrates
We report growth of high quality ZnO/Zn0.8Mg0.2O quantum well on M-plane
oriented ZnO substrates. The optical properties of these quantum wells are
studied by using reflectance spectroscopy. The optical spectra reveal strong
in-plane optical anisotropies, as predicted by group theory, and marked
reflectance structures, as an evidence of good interface morphologies.
Signatures ofc onfined excitons built from the spin-orbit split-off valence
band, the analog of exciton C in bulk ZnO are detected in normal incidence
reflectivity experiments using a photon polarized along the c axis of the
wurtzite lattice. Experiments performed in the context of an orthogonal photon
polarization, at 90^{\circ}; of this axis, reveal confined states analogs of A
and B bulk excitons. Envelope function calculations which include excitonic
interaction nicely account for the experimental report
Structural properties of GaAsN/GaAs quantum wells studied at the atomic scale by cross-sectional scanning tunnelling microscopy
The nitrogen distribution in GaAsNGaAs quantum wells _QWs_ grown by molecular beam epitaxy is studied on the atomic scale by cross-sectional scanning tunneling microscopy. No nitrogen clustering is observed in the range of N contents studied _between 1.0% and 2.5%, as measured by counting the individual N atoms inside the QW_. Nevertheless, the upper interface roughness increases with the amount of N. A residual N concentration in the GaAs barriers is found, which strongly increases with the amount of N in the QW
Electrical Characterization of a Thin Edgeless N-on-p Planar Pixel Sensors For ATLAS Upgrades
In view of the LHC upgrade phases towards the High Luminosity LHC (HL-LHC),
the ATLAS experiment plans to upgrade the Inner Detector with an all-silicon
system. Because of its radiation hardness and cost effectiveness, the n-on-p
silicon technology is a promising candidate for a large area pixel detector.
The paper reports on the joint development, by LPNHE and FBK of novel n-on-p
edgeless planar pixel sensors, making use of the active trench concept for the
reduction of the dead area at the periphery of the device. After discussing the
sensor technology, and presenting some sensors' simulation results, a complete
overview of the electrical characterization of the produced devices will be
given.Comment: 9 pages, 9 figures, to appear in the proceedings of the 15th
International Workshops on Radiation Imaging Detector
Novel Silicon n-on-p Edgeless Planar Pixel Sensors for the ATLAS upgrade
In view of the LHC upgrade phases towards HL-LHC, the ATLAS experiment plans
to upgrade the Inner Detector with an all-silicon system. The n-on-p silicon
technology is a promising candidate for the pixel upgrade thanks to its
radiation hardness and cost effectiveness, that allow for enlarging the area
instrumented with pixel detectors. We report on the development of novel n-in-p
edgeless planar pixel sensors fabricated at FBK (Trento, Italy), making use of
the "active edge" concept for the reduction of the dead area at the periphery
of the device. After discussing the sensor technology and fabrication process,
we present device simulations (pre- and post-irradiation) performed for
different sensor configurations. First preliminary results obtained with the
test-structures of the production are shown.Comment: 6 pages, 5 figures, to appear in the proceedings of the 9th
International Conference on Radiation Effects on Semiconductor Materials
Detectors and Device
Development of Edgeless n-on-p Planar Pixel Sensors for future ATLAS Upgrades
The development of n-on-p "edgeless" planar pixel sensors being fabricated at
FBK (Trento, Italy), aimed at the upgrade of the ATLAS Inner Detector for the
High Luminosity phase of the Large Hadron Collider (HL-LHC), is reported. A
characterizing feature of the devices is the reduced dead area at the edge,
achieved by adopting the "active edge" technology, based on a deep etched
trench, suitably doped to make an ohmic contact to the substrate. The project
is presented, along with the active edge process, the sensor design for this
first n-on-p production and a selection of simulation results, including the
expected charge collection efficiency after radiation fluence of comparable to those expected at HL-LHC (about
ten years of running, with an integrated luminosity of 3000 fb) for the
outer pixel layers. We show that, after irradiation and at a bias voltage of
500 V, more than 50% of the signal should be collected in the edge region; this
confirms the validity of the active edge approach.Comment: 20 pages, 9 figures, submitted to Nucl. Instr. and Meth.
Performance of Irradiated Thin Edgeless N-on-P Planar Pixel Sensors for ATLAS Upgrades
In view of the LHC upgrade phases towards the High Luminosity LHC (HL-LHC),
the ATLAS experiment plans to upgrade the Inner Detector with an all-silicon
system. Because of its radiation hardness and cost effectiveness, the n-on-p
silicon technology is a promising candidate for a large area pixel detector.
The paper reports on the joint development, by LPNHE and FBK of novel n-on-p
edgeless planar pixel sensors, making use of the active trench concept for the
reduction of the dead area at the periphery of the device. After discussing the
sensor technology, a complete overview of the electrical characterization of
several irradiated samples will be discussed. Some comments about detector
modules being assembled will be made and eventually some plans will be
outlined.Comment: 6 pages, 13 figures, to appear in the proceedings of the 2013 Nuclear
Science Symposium and Medical Imaging Conference. arXiv admin note: text
overlap with arXiv:1311.162
Deep levels in a-plane, high Mg-content MgxZn1-xO epitaxial layers grown by molecular beam epitaxy
Deep level defects in n-type unintentionally doped a-plane MgxZn1−xO, grown by molecular beam epitaxy on r-plane sapphire were fully characterized using deep level optical spectroscopy (DLOS) and related methods. Four compositions of MgxZn1−xO were examined with x = 0.31, 0.44, 0.52, and 0.56 together with a control ZnO sample. DLOS measurements revealed the presence of five deep levels in each Mg-containing sample, having energy levels of Ec − 1.4 eV, 2.1 eV, 2.6 V, and Ev + 0.3 eV and 0.6 eV. For all Mg compositions, the activation energies of the first three states were constant with respect to the conduction band edge, whereas the latter two revealed constant activation energies with respect to the valence band edge. In contrast to the ternary materials, only three levels, at Ec − 2.1 eV, Ev + 0.3 eV, and 0.6 eV, were observed for the ZnO control sample in this systematically grown series of samples. Substantially higher concentrations of the deep levels at Ev + 0.3 eV and Ec − 2.1 eV were observed in ZnO compared to the Mg alloyed samples. Moreover, there is a general invariance of trap concentration of the Ev + 0.3 eV and 0.6 eV levels on Mg content, while at least and order of magnitude dependency of the Ec − 1.4 eV and Ec − 2.6 eV levels in Mg alloyed samples
Single phase a-plane MgZnO epilayers for UV optoelectronics: substitutional behaviour of Mg at large contents
High quality 1 μm thick a-plane MgxZn1−xO layers were produced by molecular beam epitaxy with Mg contents higher than 50%. Resonant Rutherford backscattering spectrometry combined with ion channeling revealed a uniform growth in both composition and atomic order. The lattice-site location of Mg, Zn and O elements was determined independently, proving the substitutional behaviour of Mg in Zn-sites of the wurtzite lattice. X-Ray diffraction pole figure analysis also confirms the absence of phase separation. Optical properties at such high Mg contents were studied in Schottky photodiodes
Analysis of Clean Transition Metal Surfaces by Core Level Spectroscopy
The shifts in the binding energy of core electrons detected by high resolution X-ray photoelectron spectroscopy are a very sensitive probe of the chemical bonding of the excited atom. Since the surface atoms have their geometrical environment perturbed, their core levels are shifted from their bulk positions. A very large number of experiments have been performed on the 4f core level positions of tantalum and tungsten for various orientations of the surface plane. Systematic trends have been put forward and explained by theoretical models. Furthermore, the analysis of the angular variation of the core level line intensities gives structural information when compared with theoretical calculations. In the case of W(100) a single scattering theory is sufficient to reproduce experimental data. Finally we show that, in some particular cases, the core level lineshapes may differ strongly from a Doniach Sunjic model. The temperature dependence of their widths due to core hole-phonon coupling can be reproduced within the independent boson theory
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