Open Access. Powered by Scholars. Published by Universities.®
Articles 1 - 15 of 15
Full-Text Articles in Physics
Dark Current Modeling With A Moving Depletion Edge, Justin Charles Dunlap, Morley M. Blouke, Erik Bodegom, Ralf Widenhorn
Dark Current Modeling With A Moving Depletion Edge, Justin Charles Dunlap, Morley M. Blouke, Erik Bodegom, Ralf Widenhorn
Physics Faculty Publications and Presentations
Within a pixel in a digital imager, generally either a chargecoupled device or complementary metal oxide semiconductor device, doping of the semiconductor substrate and application of gate voltages create a region free of mobile carriers called the depletion region. This region fills with charge after incoming photons or thermal energy raise the charges from the valence to the conduction energy band. As the signal charge fills the depletion region, the electric field generating the region is altered, and the size of the region is reduced. We present a model that describes how this dynamic depletion region, along with the location …
Dynamic Ccd Pixel Depletion Edge Model And The Effects On Dark Current Production, Justin Charles Dunlap, Morley M. Blouke, Erik Bodegom, Ralf Widenhorn
Dynamic Ccd Pixel Depletion Edge Model And The Effects On Dark Current Production, Justin Charles Dunlap, Morley M. Blouke, Erik Bodegom, Ralf Widenhorn
Physics Faculty Publications and Presentations
The depletion edge in Charge-Coupled Devices (CCD) pixels is dependent upon the amount of signal charge located within the depletion region. A model is presented that describes the movement of the depletion edge with increasing signal charge. This dynamic depletion edge is shown to have an effect on the amount of dark current produced by some pixels. Modeling the dark current behavior of pixels both with and without impurities over an entire imager demonstrates that this moving depletion edge has a significant effect on a subset of the pixels. Dark current collected by these pixels is shown to behave nonlinearly …
Computational Approach To Dark Current Spectroscopy In Ccds As Complex Systems. Ii. Numerical Analysis Of The Uniqueness Parameters Evaluation, Ionel Tunaru, Ralf Widenhorn, Dan A. Iordache, Erik Bodegom
Computational Approach To Dark Current Spectroscopy In Ccds As Complex Systems. Ii. Numerical Analysis Of The Uniqueness Parameters Evaluation, Ionel Tunaru, Ralf Widenhorn, Dan A. Iordache, Erik Bodegom
Physics Faculty Publications and Presentations
The evaluation of the uniqueness parameters of the temperature dependence in CCDs is difficult to the considerable number of input parameters and to the strongly nonlinear (exponential) theoretical relations. For this reason, the elaborated computer programs are very sensitive to the choice of the zero-order approximations of the effective (Si) energy gap, and of the weights associated to the experimentally determined dark current. The main goal of this work was to study the rather narrow stability domains of the zero-order approximations, which lead to attractors with physical meaning. It was found that the stability domains are surrounded by (usually in …
Nonlinear Time Dependence Of Dark Current In Charge-Coupled Devices, Justin Charles Dunlap, Erik Bodegom, Ralf Widenhorn
Nonlinear Time Dependence Of Dark Current In Charge-Coupled Devices, Justin Charles Dunlap, Erik Bodegom, Ralf Widenhorn
Physics Faculty Publications and Presentations
It is generally assumed that charge-coupled device (CCD) imagers produce a linear response of dark current versus exposure time except near saturation. We found a large number of pixels with nonlinear dark current response to exposure time to be present in two scientific CCD imagers. These pixels are found to exhibit distinguishable behavior with other analogous pixels and therefore can be characterized in groupings. Data from two Kodak CCD sensors are presented for exposure times from a few seconds up to two hours. Linear behavior is traditionally taken for granted when carrying out dark current correction and as a result, …
Dark Current In An Active Pixel Complementary Metal-Oxide-Semiconductor Sensor, Justin Charles Dunlap, William Christian Porter, Erik Bodegom, Ralf Widenhorn
Dark Current In An Active Pixel Complementary Metal-Oxide-Semiconductor Sensor, Justin Charles Dunlap, William Christian Porter, Erik Bodegom, Ralf Widenhorn
Physics Faculty Publications and Presentations
We present an analysis of dark current from a complementary metal?oxide?semiconductor (CMOS) active pixels sensor with global shutter. The presence of two sources of dark current, one within the collection area of the pixel and another within the sense node, present complications to correction of the dark current. The two sources are shown to generate unique and characteristic dark current behavior with respect to varying exposure time, temperature, and/or frame rate. In particular, a pixel with storage time in the sense node will show a dark current dependence on frame rate and the appearance of being a ?stuck pixel? with …
Charge Diffusion In The Field-Free Region Of Charge-Coupled Devices, Ralf Widenhorn, Alexander Weber-Bargioni, Morley M. Blouke, Albert J. Bae, Erik Bodegom
Charge Diffusion In The Field-Free Region Of Charge-Coupled Devices, Ralf Widenhorn, Alexander Weber-Bargioni, Morley M. Blouke, Albert J. Bae, Erik Bodegom
Physics Faculty Publications and Presentations
The potential well in back-illuminated charge-coupled devices (CCDs) does not reach all the way to the back surface. Hence, light that is absorbed in the field-free region generates electrons that can diffuse into neighboring pixels and thus decreases the spatial resolution of the sensor. We present data for the charge diffusion from a near point source by measuring the response of a back-illuminated CCD to light emitted from a submicron diameter glass fiber tip. The diffusion of electrons into neighboring pixels is analyzed for different wavelengths of light ranging from 430 to 780 nm. To find out how the charge …
Correction Of Dark Current In Consumer Cameras, Justin Charles Dunlap, Erik Bodegom, Ralf Widenhorn
Correction Of Dark Current In Consumer Cameras, Justin Charles Dunlap, Erik Bodegom, Ralf Widenhorn
Physics Faculty Publications and Presentations
A study of dark current in digital imagers in digital singlelens reflex (DSLR) and compact consumer-grade digital cameras is presented. Dark current is shown to vary with temperature, exposure time, and ISO setting. Further, dark current is shown to increase in successive images during a series of images. DSLR and compact consumer cameras are often designed such that they are contained within a densely packed camera body, and therefore the digital imagers within the camera frame are prone to heat generated by the sensor as well as nearby elements within the camera body. It is the scope of this work …
Study Of The Numerical Modeling Of The Temperature Dependence Of The Dark Current In Charge Coupled Devices, Ralf Widenhorn, Ionel Tunaru, Erik Bodegom, Dan A. Iordache
Study Of The Numerical Modeling Of The Temperature Dependence Of The Dark Current In Charge Coupled Devices, Ralf Widenhorn, Ionel Tunaru, Erik Bodegom, Dan A. Iordache
Physics Faculty Publications and Presentations
As it is well known, the classical works of the Dark Current Spectroscopy method allow - using some not too accurate theoretical relations, but huge numbers of dark current values for thousands of pixels - the evaluation of a reduced number of basic impurities parameters. Unlike these works, this paper tries to obtain--by means of some better approximations of the Shockley-Read-Hall (SRH) model--more information about the studied impurities, as well as the study of the compatibility of the used theoretical model SRH relative to the experimental data. In this manner, both the compatibility SRH model with the studied experimental data …
Influence Of Illumination On Dark Current In Charge-Coupled Device Imagers, Ralf Widenhorn, Ines Hartwig, Justin Charles Dunlap, Erik Bodegom
Influence Of Illumination On Dark Current In Charge-Coupled Device Imagers, Ralf Widenhorn, Ines Hartwig, Justin Charles Dunlap, Erik Bodegom
Physics Faculty Publications and Presentations
Thermal excitation of electrons is a major source of noise in charge-coupled-device (CCD) imagers. Those electrons are generated even in the absence of light, hence, the name dark current. Dark current is particularly important for long exposure times and elevated temperatures. The standard procedure to correct for dark current is to take several pictures under the same condition as the real image, except with the shutter closed. The resulting dark frame is later subtracted from the exposed image. We address the question of whether the dark current produced in an image taken with a closed shutter is identical to the …
Dark Current Behavior In Dslr Cameras, Justin Charles Dunlap, Oleg Sostin, Ralf Widenhorn, Erik Bodegom
Dark Current Behavior In Dslr Cameras, Justin Charles Dunlap, Oleg Sostin, Ralf Widenhorn, Erik Bodegom
Physics Faculty Publications and Presentations
Digital single-lens reflex (DSLR) cameras are examined and their dark current behavior is presented. We examine the influence of varying temperature, exposure time, and gain setting on dark current. Dark current behavior unique to sensors within such cameras is observed. In particular, heat is trapped within the camera body resulting in higher internal temperatures and an increase in dark current after successive images. We look at the possibility of correcting for the dark current, based on previous work done for scientific grade imagers, where hot pixels are used as indicators for the entire chip?s dark current behavior. Standard methods of …
Measurements Of Dark Current In A Ccd Imager During Light Exposures, Ralf Widenhorn, Ines Hartwig, Justin Charles Dunlap, Erik Bodegom
Measurements Of Dark Current In A Ccd Imager During Light Exposures, Ralf Widenhorn, Ines Hartwig, Justin Charles Dunlap, Erik Bodegom
Physics Faculty Publications and Presentations
Thermal excitation of electrons is a major source of noise in Charge-Coupled Device (CCD) imagers. Those electrons are generated even in the absence of light, hence the name dark current. Dark current is particularly important for long exposure times and elevated temperatures. The standard procedure to correct for dark current is to take several pictures under the same condition as the real image, except with the shutter closed. The resulting dark frame is later subtracted from the exposed image. We address the question of whether the dark current produced in an image taken with a closed shutter is identical to …
Infrared Response Of Charge-Coupled Devices, Matthias Loch, Ralf Widenhorn, Erik Bodegom
Infrared Response Of Charge-Coupled Devices, Matthias Loch, Ralf Widenhorn, Erik Bodegom
Physics Faculty Publications and Presentations
With a band gap of silicon of 1.1eV, the largest wavelength that can excite electrons from the valence to the conduction band is roughly 1100nm. As a consequence, in, for instance, a charge-coupled device, the quantum efficiency (QE) for wavelengths larger than 1100nm is assumed to be zero. We found that there is a response at those longer wavelengths and that the response decreases with increasing wavelength. The QE increases with increasing chip temperature which suggests a thermally activated process. Impurities in the silicon provide the energy levels in the band gap, from which electrons can be excited either thermally …
Psf Measurements On Back-Illuminated Ccds, Ralf Widenhorn, Alexander Weber, Morley M. Blouke, Albert J. Bae, Erik Bodegom
Psf Measurements On Back-Illuminated Ccds, Ralf Widenhorn, Alexander Weber, Morley M. Blouke, Albert J. Bae, Erik Bodegom
Physics Faculty Publications and Presentations
The spatial resolution of an optical device is generally characterized by either the Point Spread Function (PSF) or the Modulation Transfer Function (MTF). To directly obtain the PSF one needs to measure the response of an optical system to a point light source. We present data that show the response of a back-illuminated CCD to light emitted from a sub-micron diameter glass fiber tip. The potential well in back-illuminated CCD"s does not reach all the way to the back surface. Hence, light that is absorbed in the field-free region generates electrons that can diffuse into other pixels. We analyzed the …
Residual Images In Charged-Coupled Device Detectors, Armin Rest, Lars Mündermann, Ralf Widenhorn, Erik Bodegom, T. C. Mcglinn
Residual Images In Charged-Coupled Device Detectors, Armin Rest, Lars Mündermann, Ralf Widenhorn, Erik Bodegom, T. C. Mcglinn
Physics Faculty Publications and Presentations
We present results of a systematic study of persistent, or residual, images that occur in charged-coupled device (CCD) detectors. A phenomenological model for these residual images, also known as "ghosting," is introduced. This model relates the excess dark current in a CCD after exposure to the number of filled impurity sites which is tested for various temperatures and exposure times. We experimentally derive values for the cross section, density, and characteristic energy of the impurity sites responsible for the residual images.
Temperature Dependence Of Dark Current In A Ccd, Ralf Widenhorn, Morley M. Blouke, Alexander Weber, Armin Rest, Erik Bodegom
Temperature Dependence Of Dark Current In A Ccd, Ralf Widenhorn, Morley M. Blouke, Alexander Weber, Armin Rest, Erik Bodegom
Physics Faculty Publications and Presentations
We present data for dark current of a back-illuminated CCD over the temperature range of 222 to 291 K. Using an Arrhenius law, we found that the analysis of the data leads to the relation between the prefactor and the apparent activation energy as described by the Meyer-Neldel rule. However, a more detailed analysis shows that the activation energy for the dark current changes in the temperature range investigated. This transition can be explained by the larger relative importance at high temperatures of the diffusion dark current and at low temperatures by the depletion dark current. The diffusion dark current, …