Showing papers on "Photodiode published in 1993"

Semiconducting polymer‐buckminsterfullerene heterojunctions: Diodes, photodiodes, and photovoltaic cells

Abstract: The characterization of rectifying heterojunctions (diodes) fabricated from a semiconducting polymer, a soluble derivative of poly(phenylene‐vinylene), and buckminsterfullerene, C60, are reported. Rectification ratios in the current versus voltage characteristics exceed 104. When illuminated, the devices exhibit a large photoresponse as a result of photoinduced electron transfer across the heterojunction interface from the semiconducting polymer (donor) onto C60 (acceptor). The photodiode and photovoltaic responses are characterized. Photoinduced electron transfer across the donor‐accepted rectifying heterojunction offers potential for photodetector and for solar cell applications.

Glare sensor for a vehicle

Abstract: A glare sensor includes a light condensing means for condensing light beams from the fore scene and photo sensing element for sensing the light beams from the light condensing means. The photo sensing element is constructed with photodiodes. Blue filters are selectively coupled with the photodiodes. With provision of the blue filters, the glare sensor is able to discriminate red light from white light or yellow light. The output signals of the photodiodes with the blue filters and the photodiodes with no filters are used for detecting the direction and color of the light coming from the fore scene. With this, the glare sensor is capable of detecting forerunning cars, oppositely running cars and traffic lights.

Photon counting techniques with silicon avalanche photodiodes.

Abstract: The properties of avalanche photodiodes and associated electronics required for photon counting in the Geiger and the sub-Geiger modes are reviewed. When the Geiger mode is used, there are significant improvements reported in overall photon detection efficiencies (approaching 70% at 633 nm), and a timing jitter (under 200 ps) is achieved with passive quenching at high overvoltages (20-30 V). The results obtained by using an active-mode fast quench circuit capable of switching overvoltages as high as 15 V (giving photon detection efficiencies in the 50% range) with a dead time of less than 50 ns are reported. Larger diodes (up to 1 mm in diameter) that are usable in the Geiger mode and that have quantum efficiencies over 80% in the 500-800-nm range are also reported.

LED light standard for photo- and videomicroscopy

Abstract: The invention relates to a light calibration system consisting of a compact LED source with feedback control of intensity. The source is positioned in the focal plane of the microscope objective and produces flat-field illumination of up to 31 microwatts. The source can be easily used to determine the performance of microscope optics and camera response. It can also be used as a standard light source for calibration of experimental systems. Selectable light intensities are produced by controlling the LED input power via a feedback circuit consisting of a photodiode that detects output light intensity. Spectral coverage extends between 550 nm and 670 nm using green, yellow and red LEDS mounted side-by-side and which are individually selected. The LED chips are encapsulated in plastic diffusers which homogenize the light, and a flat field of illumination is obtained through a thin 1 mm diameter aperture positioned directly over each chip. Provision is made for insertion of Ronchi rulings over the aperture to enable measurements of contrast modulation in a uniform field. The light can be pulse-modulated to assess camera response times and the device can be synchronized with video frames. Narrow bandpass interference filters can be placed between the objective lens and the LED source to produce monochromatic light without affecting the spacing of controlled light intensities since emission spectra do not appreciably shift over the range of LED powers chosen in this design.

Silicon carbide UV photodiodes

Abstract: SiC photodiodes were fabricated using 6 H single-crystal wafers. These devices have excellent UV responsivity characteristics and very low dark current even at elevated temperatures. The reproducibility is excellent and the characteristics agree with theoretical calculations for different device designs. The advantages of these diodes are that they will operate at high temperatures and are responsive between 200 and 400 nm and not responsive to longer wavelengths because of the wide 3-eV bandgap. The responsivity at 270 nm is between 70% and 85%. Dark-current levels have been measured as a function of temperature that are orders of magnitude below those previously reported. Thus, these diodes can be expected to have excellent performance characteristics for detection of low light level UV even at elevated temperatures. >

Single photon avalanche diode for single molecule detection

Abstract: A commercially available single photon avalanche photodiode in a passively quenched circuit is used with time‐correlated single photon counting modules to achieve subnanosecond time response together with high quantum efficiency and low dark noise. These characteristics are required for experiments in single molecule detection and spectroscopy in which time‐gated detection schemes are used. By tightly focusing the input light onto the active area, a quantum efficiency of over 50% and a single photon timing jitter of 168 ps full width at half‐maximum are achieved. In addition, the full width at one‐hundredth maximum, which is of greater importance for time gating, is 790 ps, comparable to that from a microchannel plate photomultiplier. Measurements of the detector dead time, and the quantum efficiency, dark counts, time response, and pulse height distribution for different operating conditions are also reported.

Thin-film, flat panel, pixelated detector array for real-time digital imaging and dosimetry of ionizing radiation

Abstract: A thin-film, flat panel, pixelated detector array serving as a real-time digital imager and dosimeter for diagnostic or megavoltage X rays or gamma rays, including a plurality of photodiodes (30) made of hydrogenated amorphous silicon arrayed in columns and rows upon a glass substrate (12). Each photodiode (30) is connected to a thin film field effect transistor (52) also located upon the glass or quartz substrate (12). Upper and lower metal contacts (38, 22) are located below and above the photodiodes (30) to provide the photodiodes (30) with a reverse bias. The capacitance of each photodiode (30) when multiplied by the resistance of the field effect transistor (52) to which it is connected yields an RC time constant sufficiently small to allow fluoroscopic or radiographic imaging in real time.

A Time-to-Frequency Converter for Measuring Picosecond Optical Pulses

Abstract: There are several techniques for directly measuring the shape of short optical pulses, such as detection with photodiodes and streak cameras. Current state of the ait is 1-2 ps time resolution. We report a new technique to measure the pulse width of a 1.064 µm Nd:YAG mode-locked pulse-train with 3 ps resolution. This technique is best described as time-to-frequency conversion: pulse amplitude is uniquely mapped from die time domain to frequency domain such that the pulse shape can be directly measured with a spectrometer. This work further demonstrates the elegant analogy between diffraction and dispersion1, and the power of the time-lens description of pulse manipulation2 where spatial variables are exchanged with time variables and spatial frequencies with temporal frequencies.

Blue LEDs, UV photodiodes and high-temperature rectifiers in 6H-SiC

Abstract: Single junction devices in silicon carbide have been developed for use as blue LEDs, UV photodiodes and high- temperature rectifiers. As a light emitter, 6H-SiC junctions can be tailored to emit light across the visible spectrum. The most widely commercialized device is the blue LED. Over the past two years, the quantum efficiency of the Cree blue LED has increased significantly. The devices emit light with a peak wavelength of 470 nm with a spectral halfwidth of ∼70 nm. The optical power output is typically between 12 and 18 μW for a forward current of 20 mA at 3 V. This represents a power efficiency of ∼0.02–0.03%. In addition to blue emission, the energy bandgap of ∼3.0 eV allows for inherently low dark currents and high quantum efficiencies for ultraviolet photodiode detectors made in 6H-SiC, even at high temperatures. These devices typically exhibit a quantum efficiency of 80–100% and peak response of ∼250–280 nm. These characteristics are maintained to at least 623 K. The dark current density at -1.0 V and 473 K is ∼10-11 A/cm2. This corresponds to an extrapolated room temperature current density of ∼2 × 10-17 A/cm2 at -1.0 V. Rectifiers with blocking voltages as high as ∼1400 V and a forward current rating of 400 mA at ∼3.0 V have been fabricated. For a 710 V rectifier, the reverse bias leakage current density at 200 V is shown to increase from ∼10-9 to ∼10-7 A/cm2 from 300 to 673 K, respectively. The reverse bias breakdown appears to occur via avalanche multiplication processes exhibiting a sharp knee at breakdown. For a ∼1400 V rectifier, the reverse bias leakage current at 1375 V is less than 1 μA at room temperature.

Device and method to control the output power of laser diodes

Abstract: A device for the control of the output power of laser diodes designed to be coupled to an optical fiber for the tranmission of data comprises a photodiode that can be used to acquire a characteristic signal of the power emitted by the laser diode; digital means to drive the laser diode comprising a central processing unit associated with servo-control computation program memorizing means to keep a constant output power whatever may be the drift and change of slope of the characteristic of the laser diode in response to ageing phenomena or to a change in temperature or to a loss of power due to the coupling of this diode with an optical fiber or to variations in the response of the photodiode as a function of the temperature. Application to digital transmission by optical fiber.

Planar p‐on‐n HgCdTe heterostructure photovoltaic detectors

Abstract: We report a process to fabricate planar Hg1−yCdyTe/Hg1−xCdxTe (x

High-frequency performance of separate absorption grading, charge, and multiplication InP/InGaAs avalanche photodiodes

Abstract: Planar separate absorption, grading, charge, and multiplication avalanche photodiodes that were fabricated on whole wafers are discussed. The high-frequency performance was investigated over a range of integrated charge (2.4-3.4*10/sup 12/ cm/sup -2/) and high field InP thickness (0.2-0.4 mu m). The bandwidth vs. gain dependence, gain-bandwidth product, minimum gain for useful bandwidth, and breakdown voltage are strongly correlated with the integrated charge and weakly correlated with the high field InP thickness. A very high gain-bandwidth product of 122 GHz was found. These observations are explained theoretically by considering ionization in the InGaAs. >

Semiconductor photodiode device with isolation region

Abstract: A dielectrically isolated photodiode having an increased p-n junction size with improved photo-carrier collection efficiency. The photodiode comprises a first layer of semiconductor material formed on the bottom and the walls of an isolation region; a second layer of semiconductor material formed on the first layer. The second layer forming a first p-n junction with the first layer and having opposite conductivity type compared to that of the first layer. The photodiode also comprises a third layer of semiconductor material formed on the second layer and electrically coupled to the first layer. The third layer having the same conductivity type as the first layer and forming a second p-n junction with the second layer. During operation, the first p-n junction functions to collect photo-generated carriers that extend to the bottom and walls of the isolation region, thereby increasing the active collecting p-n junction area per isolation region area to improve efficiency of the photodiode.

Lens array for photodiode device with an aperture having a lens region and a non-lens region

Abstract: In an image sensor using photodiodes, the structure is arranged so that a lens for each photodiode focuses light onto a first portion of the photodiode. Light from the scene directly illuminates a second portion of the photodiode.

Characterization of Photodiodes in the UV and Visible Spectral Region Based on Cryogenic Radiometry

Abstract: Different types of photodiode have been characterized with respect to uniformity, linearity, stability of responsivity and temperature coefficient at several wavelengths between 257 nm and 799 nm based on cryogenic radiometry and intensity stabilized lasers. The Hamamatsu S1337 photodiode was found to be the best suited for use as a high accuracy transfer standard for both the visible and UV spectral regions. For low-level radiant power measurement, this kind of photodiode can be calibrated via a cryogenic radiometer with a total uncertainty as low as ±0,02% in the visible and ±0,25% in the UV.

Single-photon optical-time-domain reflectometer at 1.3 Mum with 5-cm resolution and high sensitivity.

Abstract: We demonstrate an optical-time-domain reflectometer operating at λ = 1.3 μm. It features a spatial resolution of better than 5 cm and enough sensitivity to detect the Rayleigh scattering at the same resolution when operated with a low-power semiconductor laser. Field operation of the instrument is discussed.

MBE HgCdTe heterostructure p-on-n planar infrared photodiodes

Abstract: We recently succeeded in fabricating planar Hg1−yCdyTe/Hg1−xCdxTe (x

System for monitoring the growth of crystalline films on stationary substrates

Abstract: A system for monitoring the growth of crystalline films on stationary or rotating substrates includes a combination of some or all of the elements including a photodiode sensor for detecting the intensity of incoming light and converting it to a measurable current, a lens for focusing the RHEED pattern emanating from the phosphor screen onto the photodiode, an interference filter for filtering out light other than that which emanates from the phosphor screen, a current amplifier for amplifying and converting the current produced by the photodiode into a voltage, a computer for receiving the amplified photodiode current for RHEED data analysis, and a graphite impregnated triax cable for improving the signal to noise ratio obtained while sampling a stationary or rotating substrate. A rotating stage for supporting the substrate with diametrically positioned electron beam apertures and an optically encoded shaft can also be used to accommodate rotation of the substrate during measurement.

Intensity Calibration and Sensitivity Comparisons for CCD/Raman Spectrometers:

Abstract: A calibrated tungsten source combined with a fiber optic was used to correct Raman spectra for instrumental response. With the placement of the fiber output at the Raman sample position, the product of throughput, collection efficiency, quantum efficiency, and sampled area could be assessed. This product is related to a spectrometer figure of merit, which provides a quantitative comparison of spectrometer sensitivity and signal-to-noise ratio. Four spectrometer configurations were compared to illustrate the approach. An additional feature of the white light calibration is correction of relative Raman peak intensities. This issue is particularly important due to the substantial differences between CCD quantum efficiency curves and those of photomultipliers or intensified photodiode arrays.

Nonlinearity of p-i-n photodetectors

Abstract: At higher operating frequencies, the field dependence of the carrier velocity in p-i-n photodetectors generates harmonics and intermodulation products that can degrade the dynamic range of RF fiber-optic links. The authors present both a perturbational theory and measured harmonic data for a p-i-n photodiode operated at very high power densities which show that this and other detector nonlinear effects need not seriously compromise link performance. In particular, neither transit-time nor static nonlinearities in p-i-n photodiodes need limit the dynamic range of fiber-optic links operating below 5 GHz. The fact that the theoretical bandwidth of the photodiode, with all parasitic capacitance and inductance ideally removed, is 17 GHz, suggests that comparable spur-free performance should be achievable at X and Ku-band frequencies, once packaging parasitics are reduced. >

A Photomicrodynamic System with a Mechanical Resonator Monolithically Integrated with Laser Diodes on Gallium Arsenide

Abstract: A cantilever resonant microbeam, laser diodes, and a photodiode have been fabricated on the surface of a gallium arsenide substrate. The microbeam is excited photothermally by light from a laser diode. The vibration is detected with a photodiode as the variation in light output caused by the difference in optical length between the microbeam and another laser diode. A high carrier-to-noise ratio (45 decibels) is achieved with a short (3 micrometers) external cavity length. Such a small distance allows a lensless system, which increases the ease of fabrication. This work could lead to applications in which photomicrodynamic systems are monolithically integrated on a gallium arsenide substrate with surface micromachining technology.

Semiconductor laser device

Abstract: A semiconductor laser device in which a housing (8) having an optical fiber (6) inserted therein is integrally secured to a header (2) having a semiconductor laser chip (1A) mounted thereon, the light emitting surface of the semiconductor laser chip (1A) and the end surface of the optical fiber (6) being opposed to each other, and a photodiode chip (1B) for detecting the signal light emitted from the backside (rear end surface) of the light emitting surface of the semiconductor laser chip (1A), the photodiode chip (1B) including on the light detecting surface opposed to the rear end surface of the semiconductor laser chip (1A) a p-n junction for outputting a photocurrent in a detected signal and a region for capturing carriers generated in a peripheral area of the p-n junction The semiconductor laser device (1A) can operate stably, and the positioning of the photodiode can be made less strictly Furthermore, the photodiode can be easily mounted Because the charge capturing region covered with an antireflection film absorbs an unnecessary component of the signal light, the semiconductor laser device (1A) generating neither reflected light nor scattered light, which makes its operation unstable, can stably operate

A Miniaturized, No-Moving-Parts Raman Spectrometer

Abstract: A solid-state acousto-optic tunable filter (AOTF) is combined with krypton laser excitation (647 nm), holographic Raman filters, and photon-counting silicon avalanche photodiode (APD) detection to construct a miniaturized Raman spectrometer with no moving parts. The physically compact AOTF and the highly integrated APD provide a rugged, digitally controlled spectrometer of moderate spectral resolution and with a footprint comparable in size to a laboratory notebook. Instrument design details are considered and representative spectra are reported. Potential areas of application for this prototype Raman spectrometer are also discussed.

Dual function conducting polymer diodes

Abstract: Dual function diodes based on conjugated organic polymer active layers are disclosed. When positively biased the diodes function as light emitters. When negatively biased they are highly efficient photodiodes. Methods of preparation and use of these diodes in displays and input/output devices are also disclosed.

Circuit for detecting a paper at a desired position along a paper feed path with a one shot multivibrator actuating circuit

Abstract: A print paper detecting circuit for installation on a printer, to detect whether a print paper is supplied at a predetermined position along a paper path by using an optical sensor composed of a light emitting diode and phototransistor. The circuit detects the existence of the print paper according to the detection of light which is emitted from the light emitting diode, which is reflected from the print paper, and which arrives at the phototransistor. According to one embodiment, circuit has a current amplifier and a gain reducing circuit. The current amplifier feeds a pulse current which is greater than the normal constant current to the light emitting diode while the gain reducing circuit reduces the output of the output voltage. From the phototransistor during the time that the pulse current is supplied with this circuit arrangement any external light entering the printer does not affect the detection of the presence of the printer paper since the quantity of the light from the light emitting diode is greater than the quantity of the external light.

Photon‐assisted avalanche spreading in reach‐through photodiodes

Abstract: We have investigated the spreading of the avalanche process over the area of reach‐through avalanche photodiodes operated in Geiger mode. A comparison between the measurements and the results of a computer simulation suggests that photons emitted from hot carrier relaxations play the dominant role in the avalanche dynamics. It is the randomness of the photon‐assisted process which impairs the performance of these detectors in timing measurements.

High-speed and low-dark-current flip-chip InAlAs/InAlGaAs quaternary well superlattice APDs with 120 GHz gain-bandwidth product

Abstract: High-speed flip-chip InAlAs/InAlGaAs quaternary well superlattice avalanche photodiodes grown by gas-source molecular beam epitaxy have been achieved with 120-GHz gain-bandwidth product. These photodiodes exhibit a maximum bandwidth of 15 GHz, 0.34- mu A dark current at a multiplication factor of 20, a capacitance of 0.17 pF, 65% quantum efficiency, and a low breakdown voltage of about 20 V. A clear eye opening at a multiplication factor of 20 was obtained for 10-Gbs nonreturn to zero signals. This indicates that these devices have potential for high-speed, high-sensitivity and low-power-consumption, long-wavelength optical receivers. >

Solid state radiation detector

Abstract: A radiation detection device includes a plurality of pixels, each pixel includes a thin film transistor and a photodiode conductively connected to a gate of the thin film transistor with the photodiode generating a current when the pixel is exposed to x-rays.

Apparatus for driving a laser diode array

Abstract: An apparatus for driving a laser diode array of the present invention has a reference drive circuit for driving one of laser diodes, a photodiode for detecting an output light of the laser diode, and a control circuit. The reference drive circuit is supplied with input clock signals continuously. The control circuit controls all drive circuits in accordance with an output signal of the photodiode.

Light transmission module

Abstract: A light transmission module is disclosed, having a light receiving element module, in which a photodiode and a coupling portion between the photodiode and a first optical fiber are hermetically sealed, and a light emitting element module, in which a laser diode driven by an electric signal and a coupling portion between said laser diode and a second optical fiber are also hermetically sealed. A two-sided print board is provided, on the two sides of which electric circuits for a transmitting system and a receiving system are mounted. The electric circuits for the transmitting and receiving circuits are; isolated electrically from each other, and are sealed in one body by molds, and accommodated in cases, together with the light receiving element module and the light emitting element module.