407 research outputs found
Study of the depletion depth in a frontside biased CMOS pixel sensors
Depletion of the sensitive volume for semiconductor based detectors is a key to achieve high performance. It is for instance required for charged particle detection in highly radiative environment and for X-ray spectroscopy.
PIPPER-2 is a CMOS pixel sensor featuring an architecture that allows the application of the reverse bias of the pn junction from the frontside (cathode), on the electronic side, without process modification. Biasing voltages up to 45 V have been applied to sensor prototypes fabricated on two different high resistivity substrates: a thin epitaxial layer (1 kΩ cm) and a 40 μm thick bulk substrate (600 Ω cm).
Calculations from a simplified analytical model and 3D-TCAD simulations were conducted to predict the evolution of the depletion depth with the bias voltage. These expectations were compared to measurements of PIPPER-2 illuminated with two X-ray energies.
We conclude that the frontside biasing method allows the full-depletion of the thin epitaxial layer. In contrast, depletion of the bulk substrate reaches about half-depth but X-rays are still detected over the full depth
Characterisation of a novel reverse-biased PPD CMOS image sensor
A new pinned photodiode (PPD) CMOS image sensor (CIS) has been developed and characterised. The sensor can be fully depleted by means of reverse bias applied to the substrate, and the principle of operation is applicable to very thick sensitive volumes. Additional n-type implants under the pixel p-wells, called Deep Depletion Extension (DDE), have been added in order to eliminate the large parasitic substrate current that would otherwise be present in a normal device. The first prototype has been manufactured on a 18 μm thick, 1000 Ω .cm epitaxial silicon wafers using 180 nm PPD image sensor process at TowerJazz Semiconductor. The chip contains arrays of 10 μm and 5.4 μm pixels, with variations of the shape, size and the depth of the DDE implant. Back-side illuminated (BSI) devices were manufactured in collaboration with Teledyne e2v, and characterised together with the front-side illuminated (FSI) variants. The presented results show that the devices could be reverse-biased without parasitic leakage currents, in good agreement with simulations. The new 10 μm pixels in both BSI and FSI variants exhibit nearly identical photo response to the reference non-modified pixels, as characterised with the photon transfer curve. Different techniques were used to measure the depletion depth in FSI and BSI chips, and the results are consistent with the expected full depletion
Self-consistent model of unipolar transport in organic semiconductor diodes: accounting for a realistic density-of-states distribution
A self-consistent, mean-field model of charge-carrier injection and unipolar
transport in an organic semiconductor diode is developed utilizing the
effective transport energy concept and taking into account a realistic
density-of-states distribution as well as the presence of trap states in an
organic material. The consequences resulting from the model are discussed
exemplarily on the basis of an indium tin oxide/organic semiconductor/metallic
conductor structure. A comparison of the theory to experimental data of a
unipolar indium tin oxide/poly-3-hexyl-thiophene/Al device is presented.Comment: 6 pages, 2 figures; to be published in Journal of Applied Physic
Scaling analysis of electron transport through metal-semiconducting carbon nanotube interfaces: Evolution from the molecular limit to the bulk limit
We present a scaling analysis of electronic and transport properties of
metal-semiconducting carbon nanotube interfaces as a function of the nanotube
length within the coherent transport regime, which takes fully into account
atomic-scale electronic structure and three-dimensional electrostatics of the
metal-nanotube interface using a real-space Green's function based
self-consistent tight-binding theory. As the first example, we examine devices
formed by attaching finite-size single-wall carbon nanotubes (SWNT) to both
high- and low- work function metallic electrodes through the dangling bonds at
the end. We analyze the nature of Schottky barrier formation at the
metal-nanotube interface by examining the electrostatics, the band lineup and
the conductance of the metal-SWNT molecule-metal junction as a function of the
SWNT molecule length and metal-SWNT coupling strength. We show that the
confined cylindrical geometry and the atomistic nature of electronic processes
across the metal-SWNT interface leads to a different physical picture of band
alignment from that of the planar metal-semiconductor interface. We analyze the
temperature and length dependence of the conductance of the SWNT junctions,
which shows a transition from tunneling- to thermal activation-dominated
transport with increasing nanotube length. The temperature dependence of the
conductance is much weaker than that of the planar metal-semiconductor
interface due to the finite number of conduction channels within the SWNT
junctions. We find that the current-voltage characteristics of the metal-SWNT
molecule-metal junctions are sensitive to models of the potential response to
the applied source/drain bias voltages.Comment: Minor revision to appear in Phys. Rev. B. Color figures available in
the online PRB version or upon request to: [email protected]
Electron-multiplying CCDs for future soft X-ray spectrometers
CCDs have been used in several high resolution soft X-ray spectrometers for both space and terrestrial applications such as the Reflection Grating Spectrometer on XMM-Newton and the Super Advanced X-ray Emission Spectrometer at the Paul Scherrer Institut in Switzerland. However, with their ability to use multiplication gain to amplify signal and suppress readout noise, EM-CCDs are being considered instead of CCDs for future soft X-ray spectrometers. When detecting low energy X-rays, EM-CCDs are able to increase the Signal-to-Noise ratio of the device, making the X-rays much easier to detect. If the signal is also significantly split between neighbouring pixels, the increase in the size of the signal will make complete charge collection and techniques such as centroiding easier to accomplish. However, multiplication gain from an EM-CCD does cause a degradation of the energy resolution of the device and there are questions about how the high field region in an EM-CCD will behave over time in high radiation environments. This paper analyses the possible advantages and disadvantages of using EM-CCDs for high resolution soft X-ray spectroscopy and suggests in which situations using them would not only be possible, but also beneficial to the instrument
Design and modeling of a transistor vertical-cavity surface-emitting laser
A multiple quantum well (MQW) transistor vertical-cavity surface-emitting
laser (T-VCSEL) is designed and numerically modeled. The important physical
models and parameters are discussed and validated by modeling a conventional
VCSEL and comparing the results with the experiment. The quantum capture/escape
process is simulated using the quantum-trap model and shows a significant
effect on the electrical output of the T-VCSEL. The parameters extracted from
the numerical simulation are imported into the analytic modeling to predict the
frequency response and simulate the large-signal modulation up to 40 Gbps
Multi-dimensional modeling and simulation of semiconductor nanophotonic devices
Self-consistent modeling and multi-dimensional simulation of semiconductor nanophotonic devices is an important tool in the development of future integrated light sources and quantum devices. Simulations can guide important technological decisions by revealing performance bottlenecks in new device concepts, contribute to their understanding and help to theoretically explore their optimization potential. The efficient implementation of multi-dimensional numerical simulations for computer-aided design tasks requires sophisticated numerical methods and modeling techniques. We review recent advances in device-scale modeling of quantum dot based single-photon sources and laser diodes by self-consistently coupling the optical Maxwell equations with semiclassical carrier transport models using semi-classical and fully quantum mechanical descriptions of the optically active region, respectively. For the simulation of realistic devices with complex, multi-dimensional geometries, we have developed a novel hp-adaptive finite element approach for the optical Maxwell equations, using mixed meshes adapted to the multi-scale properties of the photonic structures. For electrically driven devices, we introduced novel discretization and parameter-embedding techniques to solve the drift-diffusion system for strongly degenerate semiconductors at cryogenic temperature. Our methodical advances are demonstrated on various applications, including vertical-cavity surface-emitting lasers, grating couplers and single-photon sources
No evidence that protein truncating variants in BRIP1 are associated with breast cancer risk: implications for gene panel testing.
BACKGROUND: BRCA1 interacting protein C-terminal helicase 1 (BRIP1) is one of the Fanconi Anaemia Complementation (FANC) group family of DNA repair proteins. Biallelic mutations in BRIP1 are responsible for FANC group J, and previous studies have also suggested that rare protein truncating variants in BRIP1 are associated with an increased risk of breast cancer. These studies have led to inclusion of BRIP1 on targeted sequencing panels for breast cancer risk prediction. METHODS: We evaluated a truncating variant, p.Arg798Ter (rs137852986), and 10 missense variants of BRIP1, in 48 144 cases and 43 607 controls of European origin, drawn from 41 studies participating in the Breast Cancer Association Consortium (BCAC). Additionally, we sequenced the coding regions of BRIP1 in 13 213 cases and 5242 controls from the UK, 1313 cases and 1123 controls from three population-based studies as part of the Breast Cancer Family Registry, and 1853 familial cases and 2001 controls from Australia. RESULTS: The rare truncating allele of rs137852986 was observed in 23 cases and 18 controls in Europeans in BCAC (OR 1.09, 95% CI 0.58 to 2.03, p=0.79). Truncating variants were found in the sequencing studies in 34 cases (0.21%) and 19 controls (0.23%) (combined OR 0.90, 95% CI 0.48 to 1.70, p=0.75). CONCLUSIONS: These results suggest that truncating variants in BRIP1, and in particular p.Arg798Ter, are not associated with a substantial increase in breast cancer risk. Such observations have important implications for the reporting of results from breast cancer screening panels.The COGS project is funded through a European Commission's Seventh Framework Programme grant
(agreement number 223175 - HEALTH-F2-2009-223175). BCAC is funded by Cancer Research UK
[C1287/A10118, C1287/A12014] and by the European Community´s Seventh Framework Programme under
grant agreement number 223175 (grant number HEALTH-F2-2009-223175) (COGS). Funding for the iCOGS
infrastructure came from: the European Community's Seventh Framework Programme under grant agreement
n° 223175 (HEALTH-F2-2009-223175) (COGS), Cancer Research UK (C1287/A10118, C1287/A 10710,
C12292/A11174, C1281/A12014, C5047/A8384, C5047/A15007, C5047/A10692, C8197/A16565), the
National Institutes of Health (CA128978) and Post-Cancer GWAS initiative (1U19 CA148537, 1U19
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CA148065 and 1U19 CA148112 - the GAME-ON initiative), the Department of Defense (W81XWH-10-1-
0341), the Canadian Institutes of Health Research (CIHR) for the CIHR Team in Familial Risks of Breast
Cancer, Komen Foundation for the Cure, the Breast Cancer Research Foundation, and the Ovarian Cancer
Research Fund. This study made use of data generated by the Wellcome Trust Case Control consortium.
Funding for the project was provided by the Wellcome Trust under award 076113. The results published here
are in part based upon data generated by The Cancer Genome Atlas Project established by the National Cancer
Institute and National Human Genome Research Institute.This is the author accepted manuscript. The final version is available from BMJ Group at http://dx.doi.org/10.1136/jmedgenet-2015-103529
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