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Showing papers on "Photodiode published in 1999"


Journal ArticleDOI
TL;DR: The addition of the axial information offers true three‐dimensional position detection in solution, creating, together with a position control, a photonic force microscope with nanometer spatial and microsecond temporal resolution.
Abstract: A quadrant photodiode placed in the back-focal plane of the microscope of a laser trap provides a high-resolution position sensor. We show that in addition to the lateral displacement of a trapped sphere, its axial position can be measured by the ratio of the intensity of scattered laser light to the total amount of the light reaching the detector. The addition of the axial information offers true three-dimensional position detection in solution, creating, together with a position control, a photonic force microscope with nanometer spatial and microsecond temporal resolution. The measured position signals are explained as interference of the unscattered trapping laser beam with the laser light scattered by the trapped bead. Our model explains experimental data for trapped particles in the Rayleigh regime (radius a , 0.2l) for displacements up to the focal dimensions. The cross-talk between the signals in the three directions is explained and it is shown that this cross-talk can be neglected for lateral displacements smaller than 75 nm and axial displacements below 150 nm. The advantages of three-dimensional single-particle tracking over conventional video-tracking are shown through the example of the diffusion of the GPI-anchored membrane protein Thy1.1 on a neurite. Microsc. Res. Tech. 44:378-386, 1999. r 1999 Wiley-Liss, Inc.

376 citations


Journal ArticleDOI
TL;DR: In this article, two main trends in the progress of ultrawide-band/high-frequency photodetectors (PD's), improving the bandwidth-efficiency product and obtaining a high saturation current, are reviewed.
Abstract: The two main trends in the progress of ultrawide-band/high-frequency photodetectors (PD's), improving the bandwidth-efficiency product and obtaining a high saturation current, are reviewed. With respect to achieving large bandwidth-efficiency, the limiting factors and potentials of edge-coupled (waveguide, waveguide-fed, traveling-wave, periodic-traveling-wave), resonant-cavity, and refracting-facet photodiodes, as well as the avalanche photodiode are discussed. Regarding high-saturation current, the author estimated how much the space-charge effect limits the saturation current and two ways to reduce the space-charge effect are outlined. One way is to distribute the photocarriers along the edge-coupled PD's and the other is to increase the carrier velocity using a uni-traveling carrier structure. The waveguide-photodiode-based technologies that we have developed are also presented; namely the design and fabrication of a 100-GHz waveguide photodiode (WGPD), uni-traveling carrier WGPD, 60-GHz packaging, and a 20-GHz large-core WGPD for planar lightwave circuit integration. A 50-Gb/s receiver opto-electronic integrated circuit technology based on the WGPD is also presented.

346 citations


Journal ArticleDOI
TL;DR: In this paper, solar-blind ultraviolet photodiodes with a band-edge wavelength of 285 nm were fabricated on laterally epitaxially overgrown GaN grown by metalorganic chemical vapor deposition.
Abstract: Solar-blind ultraviolet photodiodes with a band-edge wavelength of 285 nm were fabricated on laterally epitaxially overgrown GaN grown by metalorganic chemical vapor deposition. Current–voltage measurements of the diodes exhibited dark current densities as low as 10 nA/cm2 at −5 V. Spectral response measurements revealed peak responsivities of up to 0.05 A/W. Response times for these diodes were measured to be as low as 4.5 ns for 90%-to-10% fall time. For comparison, diodes were fabricated using the same p–i–n structure deposited on dislocated GaN. These diodes had dark current densities many orders of magnitude higher, as well as a less sharp cutoff, and a significant slow tail under impulse excitation.

319 citations


Journal ArticleDOI
TL;DR: In this article, a strain-balance multiquantum well (MQW) was used to enhance the GaAs solar cell efficiency using a p-i-n diode structure.
Abstract: A strain-balance multiquantum well (MQW) approach to enhance the GaAs solar cell efficiency is reported. Using a p-i-n diode structure, the strain-balanced GaAsP/InGaAs MQW is grown on a GaAs substrate and equals a good GaAs cell in terms of power conversion efficiency. The cell design is presented together with measurements of the forward bias dark current density, quantum efficiency, and 3000 K light-IV response. Cell efficiencies under standard air mass (AM) 1.5 and AM 0 illumination are projected from experimental data and the suitability of this cell for enhancing GaInP/GaAs tandem cell efficiencies is discussed.

270 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the capability of simultaneous detection of two photons generated by parametric down conversion and presented a high quantum efficiency (∼47%) detection with good time resolution.
Abstract: Visible light photon counters feature noise-free avalanche multiplication and narrow pulse height distribution for single photon detection events. Such a well-defined pulse height distribution for a single photon detection event, combined with the fact that the avalanche multiplication is confined to a small area of the whole detector, opens up the possibility for the simultaneous detection of two photons. In this letter, we investigated this capability using twin photons generated by parametric down conversion, and present a high quantum efficiency (∼47%) detection of two photons with good time resolution (∼2 ns), which can be distinguished from a single-photon incidence with a small bit-error rate (∼0.63%).

261 citations


Book
01 Jan 1999
TL;DR: In this paper, the authors present a detailed overview of Optoelectronic pn-Junction devices and their application in the field of device fabrication and packaging, and their reliability.
Abstract: Basics of Optoelectronic pn-Junction Devices. Light-Emitting Diodes. Laser Diodes. Photodiodes. Optical Modulators. Device Fabrication and Packaging. Reliability. Application of Optoelectronic pn-Junction Devices. Index.

203 citations


Patent
14 May 1999
TL;DR: In this paper, an image processing system for capturing and compressing images into a digital format is described, which consists of an array of imaging pixel elements which consist of two photodiode detectors.
Abstract: An image processing system for capturing and compressing images into a digital format is disclosed. The system has an array of imaging pixel elements which consist of two photodiode detectors. One photodiode detector is a capture detector while the other detector is a reference detector. The capture detector has an anode electrically coupled to the cathode of the reference detector. The cathode of the capture detector is electrically coupled to the anode of the reference detector. An image may be compared to a reference image detected by the reference detector. Different levels of light between the captured image and the reference image change the electrical output of the opsistor. Image compression is facilitated since only pixel elements which change from frame to frame need be stored. Additionally, a processing and compression circuit may use column and row scans to eliminate unchanged pixels and store only pixels with different light levels between images.

192 citations


Journal ArticleDOI
TL;DR: In this article, the design considerations for gigahertz-bandwidth, high-current p-i-n photodiodes utilizing InGaAs absorbers are discussed.
Abstract: This paper outlines the design considerations for gigahertz-bandwidth, high-current p-i-n photodiodes utilizing InGaAs absorbers. The factors being investigated are photodetector intrinsic region length, intrinsic region doping density, temperature effects, illumination spot size, illumination wavelength, frequency, and illumination direction. Space-charge calculations are used to determine optimal device geometry and conditions which maximize saturation photocurrent. A thermal model is developed to study the effects of temperature on high-current photodetector performance. The thermal and space-charge model results are combined to emphasize the importance of thin intrinsic region lengths to obtain high current. Finally, a comparison between surface-illuminated p-i-n structures and waveguide structures is made to differentiate between the problems associated with achieving high current in each structure and to outline techniques to achieve maximum performance.

183 citations


Journal ArticleDOI
TL;DR: In this paper, the fabrication and characterization of AlxGa1−xN p-i-n photodiodes (0.15) grown on sapphire by low-pressure metalorganic chemical vapor deposition was described.
Abstract: We report the fabrication and characterization of AlxGa1−xN p-i-n photodiodes (0⩽x⩽0.15) grown on sapphire by low-pressure metalorganic chemical vapor deposition. The devices present a visible rejection of six orders of magnitude with a cutoff wavelength that shifts from 365 to 338 nm. Photocurrent decays are exponential for high load resistances, with a time constant that corresponds to the RC product of the system. For low load resistances, the transient response becomes non-exponential, with a decay time longer than the RC constant. This behavior is justified by the strong frequency dependence of the device capacitance. By an admittance analysis, we conclude that speed is not limited by deep levels, but by substitutional Mg capture and emission time.

144 citations


Journal ArticleDOI
TL;DR: In this article, the authors measured the saturation of photodetectors in the time domain using optical pulses of different duration and in the frequency domain using amplitude-modulated optical carriers.
Abstract: Saturation of photodetectors is measured in the time domain using optical pulses of different duration and in the frequency domain using amplitude-modulated optical carriers. In the time domain, saturation is characterized by a reduction in peak photocurrent and growth of a pulse tail indicating that significant carrier velocity reduction is occurring as the opposing space-charge field persists. In the frequency domain, saturation is characterized by a reduction in response to a sinusoidal signal. The time-domain saturation measurements are shown to result in substantially larger 1-dB compression currents than frequency-domain measurements for the same photodiode. Transient space-charge calculations and a spectral analysis based on Gaussian pulses are shown to help to explain the apparent differences and to correlate the measured results from the time and frequency domains.

133 citations


Patent
27 Oct 1999
TL;DR: In this paper, an active matrix pixel within a display includes a photodiode that is optically connected to a light emitting diode within the pixel in order to detect a portion of the luminous flux that is generated by the diode.
Abstract: An active matrix pixel within an active matrix display includes a photodiode that is optically connected to a light emitting diode within the pixel in order to detect a portion of the luminous flux that is generated by the light emitting diode. The photodiode discharges excess charge within the pixel in response to the detected portion of luminous flux. Once the excess charge is discharged, the light emitting diode stops emitting light. In an embodiment, the gate of a drive transistor is controlled by the charge on a storage node. If the charge on the storage node sets a voltage that exceeds the threshold voltage of the drive transistor then the drive transistor conducts. The amount of charge on the storage node above that which is needed to set the threshold voltage is referred to as the excess charge.

Journal ArticleDOI
TL;DR: In this paper, metal-semiconductor-metal photodetectors based on epitaxial pure-Ge grown on silicon by chemical vapor deposition were designed and tested.
Abstract: We review our recent results on Ge-based near-infrared photodetectors grown on silicon. We fabricated metal-semiconductor-metal photodetectors based on epitaxial pure-Ge grown on silicon by chemical vapor deposition. Material characterization and device performances are illustrated and discussed. Exploiting a novel approach based on evaporation of polycrystalline-Ge on silicon, we also realized efficient near-infrared photodiodes with good speed and sensitivity. Finally, multiple-element devices were designed, fabricated, and tested, such as a voltage-tunable wavelength-selective photodetector based on a SiGe superlattice and a linear array of 16 photodetectors in poly-Ge on Si.

Journal ArticleDOI
TL;DR: In this article, the first examination of the use of active matrix flat-panel arrays for dosimetry in radiotherapy is reported, where an array consisting of 512 x 512 pixels with a pixel pitch of 508 microm giving an area of 26 x 26 cm2 is used.
Abstract: The first examination of the use of active matrix flat-panel arrays for dosimetry in radiotherapy is reported. Such arrays are under widespread development for diagnostic and radiotherapy imaging. In the current study, an array consisting of 512 x 512 pixels with a pixel pitch of 508 microm giving an area of 26 x 26 cm2 has been used. Each pixel consists of a light sensitive amorphous silicon (a-Si:H) photodiode coupled to an a-Si:H thin-film transistor. Data was obtained from the array using a dedicated electronics system allowing real-time data acquisition. In order to examine the potential of such arrays as quality assurance devices for radiotherapy beams, field profile data at photon energies of 6 and 15 MV were obtained as a function of field size and thickness of overlying absorbing material (solid water). Two detection configurations using the array were considered: a configuration (similar to the imaging configuration) in which an overlying phosphor screen is used to convert incident radiation to visible light photons which are detected by the photodiodes; and a configuration without the screen where radiation is directly sensed by the photodiodes. Compared to relative dosimetry data obtained with an ion chamber, data taken using the former configuration exhibited significant differences whereas data obtained using the latter configuration was generally found to be in close agreement. Basic signal properties, which are pertinent to dosimetry, have been investigated through measurements of individual pixel response for fluoroscopic and radiographic array operation. For signal levels acquired within the first 25% of pixel charge capacity, the degree of linear response with dose was found to be better than 99%. The independence of signal on dose rate was demonstrated by means of stability of pixel response over the range of dose rates allowed by the radiation source (80-400 MU/min). Finally, excellent long-term stability in pixel response, extending over a 2 month period, was observed.

Journal ArticleDOI
TL;DR: In this article, a brief review of classification, application and sources of near-ultraviolet (UV) radiation the methods for fabricating UV photodetectors and characteristics of the photoconductive cells, p-n junction structure and Schottky barrier photodiodes are discussed.
Abstract: After a brief review of classification, application and sources of near-ultraviolet (UV) radiation the methods for fabricating UV photodetectors and characteristics of the photoconductive cells, p-n junction structure and Schottky barrier photodiodes are discussed. Characteristics of some light filters used in photodetectors and measuring devices are also reported. Now Si p-n structures are commonly used but Schottky diodes based on wide-gap (GaAsP, GaP, GaN, AlGaN, SiC) semiconductors are very attractive. They are insensitive to the infrared radiation and if necessary simple glass filters can be used for correcting the spectrum in such way that it covers just the near-UV region.

Journal ArticleDOI
TL;DR: In this paper, the fabrication and characterization of AlGaN metal-semiconductor-metal photodiodes with sharp cutoff wavelengths from 365 to 310 nm was described, with an ultraviolet/visible contrast of about 4 orders of magnitude.
Abstract: We report on the fabrication and characterization of AlGaN metal–semiconductor–metal photodiodes with sharp cutoff wavelengths from 365 to 310 nm. The detectors are visible blind, with an ultraviolet/visible contrast of about 4 orders of magnitude. The photocurrent scales linearly with optical power for photon energies both over and below the band gap, supporting the absence of photoconductive gain related to space-charge regions. No persistent photoconductivity effects have been detected. Time response is limited by the RC product of the measurement system, the transit time of the device being far below 10 ns. The normalized noise equivalent power at 28 V bias is lower than 17 pW/Hz1/2 in GaN detectors, and about 24 pW/Hz1/2 in Al0.25Ga0.75N photodiodes.

Journal ArticleDOI
TL;DR: The use of photodiodes instead of photomultiplier tubes gives a better stability response and offers the possibility to perform absolute dosimetry.
Abstract: In planning stereotactic radiosurgerytreatments, depth dose curves, profiles, and dose rate of treatment beams are difficult to obtain with conventional detectors because of loss of lateral electronic equilibrium and volume averaging. A scintillating detector with high spatial resolution and good reliability has been developed to overcome this problem. The miniature dosimeter consists of two identical radiation-resistant 10 m long silica optical fibers, each connected to an independent silicon photodiode. A small cylindrical polystyrene scintillator (3.9 mm3) is optically glued to the detection fiber. The light seen by the photodiode connected to this fiber arises from fluorescence of the scintillator and from the Cerenkov effect produced in silica. The reference signal produced by the fiber without scintillator is used to subtract the Cerenkov light contribution from the raw detector response. The sensitive volume of the scintillating detector is nearly water-equivalent and thus minimizes dose distribution perturbation in water. The miniature dosimeter has a spatial resolution comparable to the film-densitometer system. Profiles of 1 cm diam, 6 MV photon beam measured with both systems show very similar shapes. Furthermore, the use of photodiodes instead of photomultiplier tubes gives a better stability response and offers the possibility to perform absolute dosimetry.

Patent
12 Oct 1999
TL;DR: In this article, a microelectronic method is described for optimizing the fabrication of optical and semiconductor array structures for high efficiency color image formation in solid-state cameras, which is an ordered fabrication sequence in which microlens formation precedes color filter layer formation to enable increased image light collection efficiency.
Abstract: A microelectronic method is described for optimizing the fabrication of optical and semiconductor array structures for high efficiency color image formation in solid-state cameras Disclosed is an ordered fabrication sequence in which microlens formation precedes color filter layer formation to enable increased image light collection efficiency, to encapsulate and protect the microlens elements from chemical and thermal processing damage, to minimize topographical underlayer variations which would axially misalign or otherwise aberrate microlens elements formed on non-planar surfaces, and, to complete the most difficult steps early in the process to minimize rework and scrap A CMOS, CID, or CCD optoelectronic configuration is formed by photolithographically patterning a planar-array of photodiodes on a Silicon or other III-V, II-VI, or compound semiconductor substrate The photodiode array is provided with metal photoshields, passivated, planarized, and, a first convex microlens array of high curvature or other suitable lenses are formed thereon A transparent encapsulant is deposited to planarize the microlens layer and provide a spacer for the successive deposition(s) of one or more color filter layers The microlens array may be formed from positive photoresists and the spacer from negative resist, with close attention to matching the index of refraction at layer interfaces A final surface layer comprising a color filter completes the solid-state color image-forming device

Journal ArticleDOI
TL;DR: In this article, a resonant cavity Si photodiode grown by merged epitaxial lateral overgrowth was reported, and the dark current was 2.7 pA and the bandwidth exceeded 34 GHz.
Abstract: We report a resonant cavity Si photodiode grown by merged epitaxial lateral overgrowth. At a reverse bias of 5 V, the dark current was 2.7 pA and the bandwidth exceeded 34 GHz. The peak quantum efficiencies ranged from 42% at 704 nm to 31% at 836 nm. This is the highest speed reported for a Si p-i-n photodiode and the highest bandwidth-efficiency product for any Si-based photodetector.

Journal ArticleDOI
TL;DR: A visible-blind camera based on a 32 × 32 array of backside-illuminated GaN/AlGaN p-i-n photodiodes has been successfully demonstrated as mentioned in this paper.
Abstract: A visible-blind UV camera based on a 32 × 32 array of backside-illuminated GaN/AlGaN p-i-n photodiodes has been successfully demonstrated. Each of the 1024 photodiodes in the array consists of a base n-type layer of AlGaN (~20%) onto which an undoped GaN layer followed by a p-type GaN layer is deposited by metallorganic vapor phase epitaxy. Double-side polished sapphire wafers are used as transparent substrates. Standard photolithographic, etching, and metallization procedures were employed to obtain fully-processed devices. The photodiode array was hybridized to a silicon readout integrated circuit using In bump bonds. Output from the UV camera was recorded at room temperature at a frame rate of 30 Hz. This new type of visible-blind digital camera is sensitive to radiation from 320 nm to 365 nm in the UV spectral region.

Journal ArticleDOI
TL;DR: A novel absorption detection method for highly multiplexed capillary electrophoresis and for micellar electrokinetic chromatography using a linear photodiode array on which a capillary array is imaged by a camera lens.
Abstract: A novel absorption detection method for highly multiplexed capillary electrophoresis is presented for zone electrophoresis and for micellar electrokinetic chromatography. The approach involves the use of a linear photodiode array on which a capillary array is imaged by a camera lens. Either a tungsten lamp or a mercury lamp can be used as the light source such that all common wavelengths for absorption detection are accessible by simply interchanging narrow-band filters. Each capillary spans several diodes in the photodiode array for absorption measurements. Over 100 densely packed capillaries can be monitored by a single photodiode array element with 1024 diodes. The detection limit for rhodamine 6G for each capillary in the multiplexed array is ∼1.8 × 10-8 M injected (S/N = 2). The cross-talk between adjacent capillaries is less than 0.2%. Simultaneous analysis of 96 samples is demonstrated.

Patent
26 Feb 1999
TL;DR: In this paper, a low-voltage photodiode which is fully depleted at a bias of 1.2-4.5V is described, where the P0 region has the same potential as the P-epi layer.
Abstract: A CMOS image sensor according to the present invention has a low-voltage photodiode which is fully depleted at a bias of 1.2-4.5V. The photodiode comprises: a P-epi layer; a field oxide layer dividing the P-epi layer into a field region and an active region; a N− region formed within the P-epi layer, wherein the first impurity region is apart from the isolation layer; and a P0 region of the conductive type formed beneath a surface of the P-epi layer and on the N− region, wherein a width of the P0 region is wider than that of the N− region so that a portion of the P0 region is formed on the P-epi layer, whereby the P0 region has the same potential as the P-epi layer.

Journal ArticleDOI
TL;DR: Avalanche photodiodes have been demonstrated utilizing GaN grown by hydride vapor-phase epitaxy as discussed by the authors, and the external quantum efficiency at unity gain is measured to be 35%.
Abstract: Avalanche photodiodes have been demonstrated utilizing GaN grown by hydride vapor-phase epitaxy. Spatially uniform gain regions were achieved in devices fabricated on low-defect-density GaN layers that exhibit no microplasma behavior. A uniform multiplication gain up to 10 has been measured in the 320–360 nm wavelength range. The external quantum efficiency at unity gain is measured to be 35%. The electric field in the avalanche region has been determined from high-voltage C–V measurements to be ∼1.6 MV/cm at the onset of the multiplication gain. Electric fields as high as 4 MV/cm have been measured in these devices. Response times are found to be less than 5 μs, limited by the measurement system.

Journal ArticleDOI
Y.P Tan1, Isabel Llano1, A Hopt1, F Würriehausen1, Erwin Neher1 
TL;DR: A method for scanning small regions of interest with line repetition rates two to four times higher than conventional ones and a duty cycle of 70%, and found the optimum choice to depend strongly on the photon flux during a given application.

Journal ArticleDOI
TL;DR: A three-wavelength-based passive quadrature digital phase-demodulation scheme has been developed for readout of fiber-optic extrinsic Fabry-Perot interferometer vibration, acoustic, and strain sensors, resulting in significant improvement of the linearity of the sensor characteristics.
Abstract: A three-wavelength-based passive quadrature digital phase-demodulation scheme has been developed for readout of fiber-optic extrinsic Fabry–Perot interferometer vibration, acoustic, and strain sensors. This scheme uses a superluminescent diode light source with interference filters in front of the photodiodes and real-time arctan calculation. Quasi-static strain and dynamic vibration sensing with up to an 80-kHz sampling rate is demonstrated. Periodic nonlinearities owing to dephasing with increasing fringe number are corrected for with a suitable algorithm, resulting in significant improvement of the linearity of the sensor characteristics.

Patent
28 May 1999
TL;DR: In this article, a reverse bias is applied to the peripheral electrode for making a wide depletion layer beneath the peripheral pn-junction, where extra carriers generated by peripherally-incidence rays are fully absorbed by the peripheral depletion layer.
Abstract: Besides the central pn-junction and the central electrode, a PD chip has a peripheral pn-junction and a peripheral electrode which do not appear on the sides. The ends of the peripheral pn-junction are covered with a protection layer for preventing self-shortcircuit. A reverse bias is applied to the peripheral electrode for making a wide depletion layer beneath the peripheral pn-junction. Extra carriers generated by peripherally-incidence rays are fully absorbed by the peripheral depletion layer and annihilated by the reverse bias.

Journal ArticleDOI
TL;DR: In this paper, a compact optical signal quality monitor suitable for WDM linear repeaters which use a semiconductor arrayed waveguide grating filter (AWG) is proposed.
Abstract: A compact optical signal quality monitor suitable for WDM linear repeaters which use a semiconductor arrayed waveguide grating filter (AWG) is proposed. Implemented with semiconductor AWG module monolithically integrated with eight photodiodes, an optical signal-to-noise ratio measurement is carried out.

Journal ArticleDOI
TL;DR: It is argued that the secondary quantum sink of optical photons imposed by the optical chain leads to a significant degradation of the signal-to-noise ratio at spatial frequencies which are most important for successful registration of portal images.
Abstract: The imaging performance of metal plate/phosphor screens which are used for the creation of portal images in radiotherapy is investigated by using Monte Carlo simulations. To this end the modulation transfer function, the noise power spectrum and the detective quantum efficiency [DQE(f)] are calculated for different metals and phosphors and different thicknesses of metal and phosphor for a range of spatial resolutions. The interaction of x-rays with the metal plate/phosphor screen is modeled with the EGS4 electron gamma shower code. Optical transport in the phosphor is modeled by simulating scattering and reabsorption events of individual optical photons. It is shown that metals with a high atomic number perform better than lighter metals in maximizing the DQE(f). It is furthermore shown that the DQE(f) for the metal plate/phosphor screen alone is nearly x-ray quantum absorption limited up to spatial frequencies of 0.4 cycles/mm. In addition, it is argued that the secondary quantum sink of optical photons imposed by the optical chain (mirror, lenses and video camera) leads to a significant degradation of the signal-to-noise ratio at spatial frequencies which are most important for successful registration of portal images. Therefore, the conclusion is that a replacement of the optical chain by a flat array of photodiodes placed directly under the phosphor will lead to a substantial improvement in image quality of portal images.

Journal ArticleDOI
TL;DR: In this article, the performance of a GaN p-i-n photodiode as a nonlinear sensor for second and third-order femtosecond pulse autocorrelation measurements in the visible and near-infrared regimes, respectively, is characterized.
Abstract: We characterize the performance of a GaN p-i-n photodiode as a nonlinear sensor for second- and third-order femtosecond pulse autocorrelation measurements in the visible and near-infrared regimes, respectively. The two- and three-photon absorption coefficients for GaN are also determined.

Journal ArticleDOI
TL;DR: An improved version of a recently developed "Buried Junction" avalanche photodiode (APD), designed for use with scintillators, is described and characterized in this paper, where the electrical and optical characteristics of this device are described and measurements of energy and timing resolution of the device with several SCI devices of potential interest in high-energy physics and PET imaging systems are presented.
Abstract: An improved version of a recently developed “Buried Junction” avalanche photodiode (APD), designed for use with scintillators, is described and characterized. This device, also called the “Reverse APD”, is designed to have a wide depletion layer and thus low capacitance, but to have high gain only for e–h pairs generated within the first few microns of the depletion layer. Thus it has high gain for light from scintillators emitting in the 400–600 nm range, with relatively low dark current noise and it is relatively insensitive to minimum ionizing particles (MIPs). An additional feature is that the metallurgical junction is at the back of the wafer, leaving the front surface free to be coupled to a scintillator without fear of junction contamination. The modifications made in this device, as compared with the earlier diode, have resulted in a lower excess noise factor, lower dark current, and much-reduced trapping. The electrical and optical characteristics of this device are described and measurements of energy and timing resolution of this device with several scintillators (BGO, LSO and GSO) of potential interest in high-energy physics and PET imaging systems are presented.

Patent
11 Jun 1999
TL;DR: In this paper, an active pixel sensor includes a photodiode for capturing photocharge, a reset transistor for resetting the photode to a reset potential, and a readout transistor.
Abstract: In a first embodiment an active pixel sensor includes a photodiode for capturing photocharge, a reset transistor for resetting the photodiode to a reset potential, and a readout transistor, and in a second embodiment an active pixel sensor includes a photodiode for capturing photocharge, a reset transistor for resetting the photodiode to a reset potential, a transfer transistor for transferring captured photocharge, and a readout transistor. In both embodiments, the readout transistor has a drain that is coupled to a first supply voltage during integration of photocharge and a second supply voltage during readout of the photocharge. Accordingly, the sensitivity of an active pixel sensor is increased by increasing the fill factor, the noise of an active pixel sensor is reduced by increasing the relative side of the readout transistor, and the gain is compressive as the relative light intensity in an active pixel sensor increases.