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• 1. [Article] Temperature dependence of dark current in a CCD

  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 ...

  Citation × Citation Citation Abstract Copy Title: Temperature dependence of dark current in a CCD Author: Widenhorn, Ralf, Blouke, Morley M., Weber, Alexander, Rest, Armin, Bodegom, Erik Year: 2002 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, characterized by the band gap of silicon, is uniform for all pixels. At low temperatures, the depletion dark current, characterized by half the band gap, prevails, but it varies for different pixels. Dark current spikes are pronounced at low temperatures and can be explained by large concentrations of deep level impurities in those particular pixels. We show that fitting the data with the impurity concentration as the only variable can explain the dark current characteristics of all the pixels on the chip. Title: Temperature dependence of dark current in a CCD Author: Widenhorn, Ralf, Blouke, Morley M., Weber, Alexander, Rest, Armin, Bodegom, Erik Year: 2002 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, characterized by the band gap of silicon, is uniform for all pixels. At low temperatures, the depletion dark current, characterized by half the band gap, prevails, but it varies for different pixels. Dark current spikes are pronounced at low temperatures and can be explained by large concentrations of deep level impurities in those particular pixels. We show that fitting the data with the impurity concentration as the only variable can explain the dark current characteristics of all the pixels on the chip. Close

• 2. [Article] Computation of dark frames in digital imagers

  Dark current is caused by electrons that are thermally exited into the conduction band. These electrons are collected by the well of the CCD and add a false signal to the chip. We will present an algorithm ...

  Citation × Citation Citation Abstract Copy Title: Computation of dark frames in digital imagers Author: Widenhorn, Ralf, Rest, Armin, Blouke, Morley M., Berry, Richard L., Bodegom, Erik Year: 2007 Dark current is caused by electrons that are thermally exited into the conduction band. These electrons are collected by the well of the CCD and add a false signal to the chip. We will present an algorithm that automatically corrects for dark current. It uses a calibration protocol to characterize the image sensor for different temperatures. For a given exposure time, the dark current of every pixel is characteristic of a specific temperature. The dark current of every pixel can therefore be used as an indicator of the temperature. Hot pixels have the highest signal-to-noise ratio and are the best temperature sensors. We use the dark current of a several hundred hot pixels to sense the chip temperature and predict the dark current of all pixels on the chip. Dark current computation is not a new concept, but our approach is unique. Some advantages of our method include applicability for poorly temperature-controlled camera systems and the possibility of ex post facto dark current correction. Title: Computation of dark frames in digital imagers Author: Widenhorn, Ralf, Rest, Armin, Blouke, Morley M., Berry, Richard L., Bodegom, Erik Year: 2007 Dark current is caused by electrons that are thermally exited into the conduction band. These electrons are collected by the well of the CCD and add a false signal to the chip. We will present an algorithm that automatically corrects for dark current. It uses a calibration protocol to characterize the image sensor for different temperatures. For a given exposure time, the dark current of every pixel is characteristic of a specific temperature. The dark current of every pixel can therefore be used as an indicator of the temperature. Hot pixels have the highest signal-to-noise ratio and are the best temperature sensors. We use the dark current of a several hundred hot pixels to sense the chip temperature and predict the dark current of all pixels on the chip. Dark current computation is not a new concept, but our approach is unique. Some advantages of our method include applicability for poorly temperature-controlled camera systems and the possibility of ex post facto dark current correction. Close

• 3. [Article] Meyer-Neldel rule for dark current in charge-coupled devices

  We present the results of a systematic study of the dark current in each pixel of a charged-coupled device chip. It was found that the Arrhenius plot, at temperatures between 222 and 291 K, deviated from ...

  Citation × Citation Citation Abstract Copy Title: Meyer-Neldel rule for dark current in charge-coupled devices Author: Widenhorn, Ralf, Mündermann, Lars, Rest, Armin, Bodegom, Erik Year: 2001 We present the results of a systematic study of the dark current in each pixel of a charged-coupled device chip. It was found that the Arrhenius plot, at temperatures between 222 and 291 K, deviated from a linear behavior in the form of continuous bending. However, as a first approximation, the dark current, D, can be expressed as: D=Dₒ exp(−ΔE/kT),where ΔE is the activation energy, k is Boltzmann’s constant, and T the absolute temperature. It was found that ΔE and the exponential prefactor Dₒ follow the Meyer–Neldel rule (MNR) for all of the more than 222,000 investigated pixels. The isokinetic temperature, Tₒ, for the process was found as 294 K. However, measurements at 313 K did not show the predicted inversion in the dark current. It was found that the dark current for different pixels merged at temperatures higher than Tₒ. A model is presented which explains the nonlinearity and the merging of the dark current for different pixels with increasing temperature. Possible implications of this finding regarding the MNR are discussed. Title: Meyer-Neldel rule for dark current in charge-coupled devices Author: Widenhorn, Ralf, Mündermann, Lars, Rest, Armin, Bodegom, Erik Year: 2001 We present the results of a systematic study of the dark current in each pixel of a charged-coupled device chip. It was found that the Arrhenius plot, at temperatures between 222 and 291 K, deviated from a linear behavior in the form of continuous bending. However, as a first approximation, the dark current, D, can be expressed as: D=Dₒ exp(−ΔE/kT),where ΔE is the activation energy, k is Boltzmann’s constant, and T the absolute temperature. It was found that ΔE and the exponential prefactor Dₒ follow the Meyer–Neldel rule (MNR) for all of the more than 222,000 investigated pixels. The isokinetic temperature, Tₒ, for the process was found as 294 K. However, measurements at 313 K did not show the predicted inversion in the dark current. It was found that the dark current for different pixels merged at temperatures higher than Tₒ. A model is presented which explains the nonlinearity and the merging of the dark current for different pixels with increasing temperature. Possible implications of this finding regarding the MNR are discussed. Close

• 4. [Article] Dark current behavior in DSLR cameras

  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 ...

  Citation × Citation Citation Abstract Copy Title: Dark current behavior in DSLR cameras Author: Dunlap, Justin Charles, Sostin, Oleg, Widenhorn, Ralf, Bodegom, Erik Year: 2009 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 dark current correction are compared to computed dark frames. Dark current is a concern for DSLR cameras as optimum conditions for limiting dark current, such as cooling the imager, are not easily obtained in the typical use of such imagers. Title: Dark current behavior in DSLR cameras Author: Dunlap, Justin Charles, Sostin, Oleg, Widenhorn, Ralf, Bodegom, Erik Year: 2009 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 dark current correction are compared to computed dark frames. Dark current is a concern for DSLR cameras as optimum conditions for limiting dark current, such as cooling the imager, are not easily obtained in the typical use of such imagers. Close

• 5. [Article] Infrared response of charge-coupled devices

  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, ...

  Citation × Citation Citation Abstract Copy Title: Infrared response of charge-coupled devices Author: Loch, Matthias, Widenhorn, Ralf, Bodegom, Erik Year: 2005 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 or by absorption of a photon. It is these impurities that contribute to the infrared response. We characterized the response at chip temperatures of 248 K to 293 K for wavelengths from 1200 nm to 1600 nm and calculated the activation energies at these wavelengths. We found that hot pixels, i.e., pixels with extraordinary high counts in a dark frame, tend to respond stronger to infrared light than normal pixels. This correlation gets stronger for longer wavelengths. It is argued that this response can be used for probing the impurities present in the silicon bulk of the sensors Title: Infrared response of charge-coupled devices Author: Loch, Matthias, Widenhorn, Ralf, Bodegom, Erik Year: 2005 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 or by absorption of a photon. It is these impurities that contribute to the infrared response. We characterized the response at chip temperatures of 248 K to 293 K for wavelengths from 1200 nm to 1600 nm and calculated the activation energies at these wavelengths. We found that hot pixels, i.e., pixels with extraordinary high counts in a dark frame, tend to respond stronger to infrared light than normal pixels. This correlation gets stronger for longer wavelengths. It is argued that this response can be used for probing the impurities present in the silicon bulk of the sensors Close

• 6. [Article] Residual images in charged-coupled device detectors

  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," ...

  Citation × Citation Citation Abstract Copy Title: Residual images in charged-coupled device detectors Author: Rest, Armin, Mündermann, Lars, Widenhorn, Ralf, Bodegom, Erik, McGlinn, T. C. Year: 2002 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. Title: Residual images in charged-coupled device detectors Author: Rest, Armin, Mündermann, Lars, Widenhorn, Ralf, Bodegom, Erik, McGlinn, T. C. Year: 2002 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. Close

• 7. [Article] Study of the numerical modeling of the temperature dependence of the dark current in Charge Coupled Devices

  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 ...

  Citation × Citation Citation Abstract Copy Title: Study of the numerical modeling of the temperature dependence of the dark current in Charge Coupled Devices Author: Widenhorn, Ralf, Tunaru, Ionel, Bodegom, Erik, Iordache, Dan A. Year: 2010 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 was checked up, as well as the values of some additional physical parameters of the impurified semiconductor (the logarithms of the pre-exponential factors lnDiff, lnDep, the effective value of the energy gap Eg) and of the separate capture cross-sections of the free electrons, and holes, respectively, by the studied deep-level contaminants, were evaluated. Title: Study of the numerical modeling of the temperature dependence of the dark current in Charge Coupled Devices Author: Widenhorn, Ralf, Tunaru, Ionel, Bodegom, Erik, Iordache, Dan A. Year: 2010 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 was checked up, as well as the values of some additional physical parameters of the impurified semiconductor (the logarithms of the pre-exponential factors lnDiff, lnDep, the effective value of the energy gap Eg) and of the separate capture cross-sections of the free electrons, and holes, respectively, by the studied deep-level contaminants, were evaluated. Close

• 8. [Article] Dark Current Measurements in a CMOS Imager

  We present data for the dark current of a commercially available CMOS image sensor for different gain settings and bias offsets over the temperature range of 295 to 340 K and exposure times of 0 to 500 ...

  Citation × Citation Citation Abstract Copy Title: Dark Current Measurements in a CMOS Imager Author: Porter, William C., Kopp, Bradley, Dunlap, Justin Charles, Widenhorn, Ralf, Bodegom, Erik Year: 2008 We present data for the dark current of a commercially available CMOS image sensor for different gain settings and bias offsets over the temperature range of 295 to 340 K and exposure times of 0 to 500 ms. The analysis of hot pixels shows two different sources of dark current. One source results in hot pixels with high but constant count for exposure times smaller than the frame time. Other hot pixels exhibit a linear increase with exposure time. We discuss how these hot pixels can be used to calculate the dark current for all pixels. Finally, we show that for low bias settings with universally zero counts for the dark frame one still needs to correct for dark current. The correction of thermal noise can therefore result in dark frames with negative pixel values. We show how one can calculate dark frames with negative pixel count. Title: Dark Current Measurements in a CMOS Imager Author: Porter, William C., Kopp, Bradley, Dunlap, Justin Charles, Widenhorn, Ralf, Bodegom, Erik Year: 2008 We present data for the dark current of a commercially available CMOS image sensor for different gain settings and bias offsets over the temperature range of 295 to 340 K and exposure times of 0 to 500 ms. The analysis of hot pixels shows two different sources of dark current. One source results in hot pixels with high but constant count for exposure times smaller than the frame time. Other hot pixels exhibit a linear increase with exposure time. We discuss how these hot pixels can be used to calculate the dark current for all pixels. Finally, we show that for low bias settings with universally zero counts for the dark frame one still needs to correct for dark current. The correction of thermal noise can therefore result in dark frames with negative pixel values. We show how one can calculate dark frames with negative pixel count. Close

• 9. [Article] Measurements of dark current in a CCD imager during light exposures

  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 ...

  Citation × Citation Citation Abstract Copy Title: Measurements of dark current in a CCD imager during light exposures Author: Widenhorn, Ralf, Hartwig, Ines, Dunlap, Justin Charles, Bodegom, Erik Year: 2008 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 produced in an exposure in the presence of light. In our investigation, we illuminated two different CCD chips to different intensities of light and measured the dark current generation. A surprising conclusion of this study is that some pixels produce a different amount of dark current under illumination. Finally, we discuss the implications that this has for dark frame image correction. Title: Measurements of dark current in a CCD imager during light exposures Author: Widenhorn, Ralf, Hartwig, Ines, Dunlap, Justin Charles, Bodegom, Erik Year: 2008 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 produced in an exposure in the presence of light. In our investigation, we illuminated two different CCD chips to different intensities of light and measured the dark current generation. A surprising conclusion of this study is that some pixels produce a different amount of dark current under illumination. Finally, we discuss the implications that this has for dark frame image correction. Close

• 10. [Article] Characterization and correction of dark current in compact consumer cameras

  A study of dark current in digital imagers within consumer grade digital cameras is presented. Dark current is shown to vary with temperature, exposure time, and ISO setting. Further, dark current is shown ...

  Citation × Citation Citation Abstract Copy Title: Characterization and correction of dark current in compact consumer cameras Author: Dunlap, Justin Charles, Bodegom, Erik, Widenhorn, Ralf Year: 2010 A study of dark current in digital imagers within 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. Consumer cameras are often designed to be as compact as possible and therefore the digital imagers within the camera frame are prone to heat generated by nearby elements within the camera body. It is the scope of this work to characterize the dark current in such cameras and to show that the dark current, in part due to heat generated by the camera itself, can be corrected for by using hot pixels on the imager. This method generates computed dark frames based on the dark current indicator value of the hottest pixels on the chip. We compare this method to standard methods of dark current correction. Title: Characterization and correction of dark current in compact consumer cameras Author: Dunlap, Justin Charles, Bodegom, Erik, Widenhorn, Ralf Year: 2010 A study of dark current in digital imagers within 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. Consumer cameras are often designed to be as compact as possible and therefore the digital imagers within the camera frame are prone to heat generated by nearby elements within the camera body. It is the scope of this work to characterize the dark current in such cameras and to show that the dark current, in part due to heat generated by the camera itself, can be corrected for by using hot pixels on the imager. This method generates computed dark frames based on the dark current indicator value of the hottest pixels on the chip. We compare this method to standard methods of dark current correction. Close