Showing papers on "Photodiode published in 1975"

p−InP/n−CdS solar cells and photovoltaic detectors

Abstract: We have prepared p−InP/n−CdS heterodiode photovoltaic detectors with a uniform quantum efficiency of ∼70% for wavelengths between 550 and 910 nm. On a cloudy day in New Jersey, (53 mW/cm2) solar power conversion efficiencies of 12.5% have been measured on cells provided with antireflection coatings.

Semiconductor radiation wavelength detector

Abstract: A double-layer photodiode is created in an integral structure to form two diodes, the upper diode having a relatively thin active region and the lower diode a relatively thick active region. Light whose wavelength is to be measured is directed onto the upper diode. The thickness of the first diode is chosen so that, in the spectrum of light wavelengths being measured, the energy of the shortest wavelength is entirely absorbed therein. As the radiation wavelength increases, the absorption by the upper diode decreases exponentially, and the unabsorbed light is transmitted through the thin active region into the thick active region of the lower diode where it is absorbed. The thickness of the active region of the lower diode is chosen so that it absorbs substantially all of the energy of longest wavelength in the spectrum being measured. The absorption of the photon energy in each diode creates electron-hole pairs therein which produce in each diode a change in conductivity which is proportional to the absorbed energy. Therefore, since the difference in conductivities of the two diodes is a function of the wavelength of the incident light, as the wavelength changes, the difference between changes in the conductivity of the two diodes, divided by the sum of the changes in conductivity, is a function which is a single-valued function of the wavelength of the incident light and which is independent of the intensity of the incident light. A measuring circuit connected to the double-layer diode provides a direct reading of the wavelength. Furthermore, there is disclosed a method for fabricating a double-layer photodiode suitable for use in the wavelength detector.

Self-scanned digicon: a digital image tube for astronomical spectroscopy.

Abstract: We have successfully fabricated, tested, and operated a digital image tube consisting of a magnetically focused image intensifier tube in which a self-scanned linear array of 1024 silicon photodiodes operating in the EBS mode serves as the photoelectron image detector, amplifier, and intermediate image storage device. Integral on-chip MOS shift registers driven by an external clock sequentially interrogate the photodiodes through MOS FET multiplex switch arrays. Each output frame is a sequence of 256 analog pulses on each of four video lines. Laboratory and observing tests show that the output signal is photoelectron shot noise limited over at least a range of 1-100,000 detected photoelectrons per picture element, indicating that single photon detection is achieved. High-resolution astronomical spectroscopy has been carried out in the coude spectrograph of the 2.7-m telescope at McDonald Observatory. Examples are shown.

Planar InSb photodiodes fabricated by Be and Mg ion implantation

Abstract: Planar p−n junction photodiodes in InSb have been made by ion implantation of Be and Mg acceptors. Both ions were incorporated with a doping efficiency of about 50 per cent and each produced excellent photodiodes. At 77°K, 20-mil-dia. diodes have typical zero-bias resistances of 6 Mμ. At the wavelength peak of 5·3 μm, quantum efficiencies of 60–70 per cent and detectivities with a 77°K background of 2 × 10 12 cm Hz W were measured. Field plate guard rings were used to adjust the surface potential at the diode perimeters for optimum performance.

Heterojunction III—V alloy photodetectors for high-sensitivity 1.06-µm optical receivers

Abstract: A new type of 1.06-µm solid-state detector is discussed, the inverted hetrojunction III-V alloy mesa photodiode, which offers quantum efficiencies near 1.00 percent, extremely low capacitance and transit time, and low dark currents. The characterstics of these detectors allow their use in sensitive 1.06-µm optical receivers which promise better signal-to-noise ratios in a number of applications than any other available 1.06-µm photodetector. In particular, an optimization procedure for selecting photodiode and preamplifier parameters to give the best signal-to-noise ratio under signal conditions is discussed and this technique is applied to a proposed system application. It is shown that in this laser-illuminated airborne night imaging system, a small area heterojunction III-V alloy photodiode detector in an optimized receiver should be able to give signal-to-noise ratios much higher than any other 1.06-µm detector approach, even though the other 1.06-µm detectors may have lower noise equivalent power (NEP) values than this receiver. This is an illustration of the fact that such "magic numbers" for detector comparision as NEP are applicable only to comparing similar types of detectors in certain specific types of applications (such as comparing IR photoconductors in a high background application), and are of very little value in determining the relative performance of different types of detectors for a given system application (such as comparing photomultipliers, avalanche photodiodes, and low-noise photodiodes for this application).

Charge storage diode with graded defect density photocapacitive layer

Abstract: In a light actuated device such as an alternating current driven light valve or other display device requiring the photocapacitance of a light responsive layer in a photodiode to be modulated in response to changes in incident or writing light, sensitivity is an important factor, especially when a cathode ray tube phosphor image is the source of such light. This sensitivity can be improved by more than an order of magnitude by using a graded defect center (as defined hereinbelow) concentration, graded band gap layer in said diode which can produce a graded optical absorption coefficient between two regions of the layer so that most of the incident light is absorbed in the region near the semiconductor rectifying junction of the diode to store charge near this junction by this or any similar action. In one particular embodiment disclosed a cadmium sulfide photoconductor is used and the defect center density and hence the optical absorption coefficient for the incident light beam in the light sensitive region is graded from a low value on the light input side to a higher value near the junction forming interface with a cadmium telluride light blocking layer by varying the defect concentration in the cadmium sulfide during the film preparation by progressively lowering the temperature during sputter deposition. In a second embodiment this grading is accomplished by alloying cadmium sulfide with cadmium selenide near the cadmium telluride region thus introducing defect centers and lowering the absorption band edge. In both embodiments charge carriers are generated which are stored in the region adjacent to the junction interface and thereby change the photocapacitive depletion width adjacent to the junction to enhance the sensitivity of the diode.

Backside−illuminated Pb1−xSnxTe heterojunction photodiode

Abstract: The need for a long−wavelength infrared detector that makes more efficient use of the available radiation has led us to construct a backside−illuminated Pb1−xSnxTe heterojunction in which the radiation passes through a transparent substrate and is absorbed in the active region behind a p−n junction. This device permits a selectivity in the spectral bandwidth of the device due to the short−wavelength cut−on properties of the transparent PbTe substrate or an epitaxial Pb1−xSnxTe filter layer. Additionally, an effective increase in optical area is achieved because the radiation incident upon the sloping sides of the mesa is internally reflected into the junction region due to the index of refraction mismatch between air and PbTe; thus with this design the optical area which gives rise to the signal current is larger than the electrical area which is the source of noise. Laboratory measurements on devices of this construction verify these properties and show that a peak Dλ greater than 1011 cm Hz1/2 W−1 has b...

Silicon photodiode arrays

Abstract: A historical outline traces the development from the initial experiments using hybrid technologies to present day integrated arrays in volume production, and to the latest developments. The theory of operation of photodiode arrays is explained, showing how sensitive scanned arrays are made possible by the charge integration technique, and describing and comparing the various scanning methods which have been proposed and developed, including serial multiplexing, bucket brigades, CCD, CID etc. The optical and electrical characteristics of arrays are discussed, pointing out the effects of various main limiting factors on array performance. The main fields of application of arrays are presented, together with the considerations relevant to designing systems of various types.

Optical communications link

Abstract: The specification discloses a wireless optical communications link which includes a transmitter housing having circuitry for receiving electrical audio and video signals. A light emitting diode is mounted in the transmitter housing for generating a directional beam of light. Circuitry modulates the beam of light in accordance with the audio and video signals. A receiver housing is adapted to be located remote from the transmitter housing and includes an aspheric Fresnel lens for receiving and focusing the beam of light. A photodiode is mounted in the receiver housing for generating electrical output signals in response to the received beam of light. Circuitry is responsive to the electrical output signals for reconstructing the audio and video signals at the remote location.

Erbium laser ceilometer

Abstract: A laser rangefinder for clouds, fog, haze and precipitation including an erbium doped laser transmitter, a germanium photodiode monitor and a germanium avalanche photodiode detector. The germanium avalanche photodiode and an amplifier module is positioned at the focus of a parabolic reflector. The transmitter transmits light in a waveband with an optical center at 1.54 microns and is eye safe. A periscope system aligns the outgoing pulse with the returning light to reduce parallax. To reduce alignment problems when shifts in wavelengths occur, an optical circuit with only reflecting surfaces can be employed. To increase the efficiency of the laser transmitter, the clamps utilized to position the laser rod within the cavity are formed of the same material as the laser rod and the pump light reflector is a second surface mirror with a quartz substrate coated in succession with silver, copper and black paint.

Avalanche photodiodes with a gain‐bandwidth product of more than 200 GHz

Abstract: The design and characteristics of avalanche photodiodes with a gain‐bandwidth product in the range of 250 GHz are reported. The planar front‐illuminated silicon diodes are of the n+‐p‐π‐p+ reach‐through type.

Infrared Detectors: An Overview

Abstract: Infrared detectors are discussed in terms of an equivalent circuit consisting of a photocurrent generator in series with a gain mechanism, both shunted by the detector internal impedance. Detectivity, the usual measure of infrared detector sensitivity, is defined in terms of the parameters of this equivalent circuit. The properties and performance of the most common and best developed infrared sensitive photoconductors and photodiodes are then described in terms of these parameters. Both normal and low background performance are considered, with emphasis on maximum sensitivity in the low-to-moderate frequency region. Short discussions of the current status and recent developments in thermal detectors, high-speed detectors, and infrared detector arrays are included. The importance of preamplification is stressed throughout, and preamplifier principles and current practice for the various types of detector are separately discussed.

Optical radiation generator electrically controlled

Abstract: An optical radiation generator, controlled by an input current, comprising a light emissive diode optically coupled to an optical waveguide and a photodiode located close to the radiating surface of the emissive diode for picking off a part of the optical radiation and for delivering a feedback current which is used in a current negative feedback loop. The light emissive diode, the extremity of the waveguide and the photodiode are encased in a transparent material providing optical coupling and mechanical stability.

Automated Direct Current Arc Time Studies Using A Computer-Coupled Photodiode Array Spectrometer

Abstract: A hardware and software system has been developed which is capable of automatically acquiring and analyzing intensity-time data from a dc arc source. This system is based on a computer-coupled photodiode array spectrometer with which 260 A of continuous spectral information can be simultaneously measured and stored directly in a small computer. With the present system up to seven time sequential spectra, each representing the integral of the spectral intensity over times ranging from 1 to 10 sec, can be automatically obtained during a dc arc burn. The time interval spectra can then be analyzed under computer control and the intensity-time curves for any desired lines can be plotted on a computer terminal within about 2 min after termination of the are burn. The application of the system to some simple dc arc time studies is discussed and illustrated.

Electrically based spectral power measurements through use of a tunable cw laser

Abstract: A new approach to radiant power measurements is described. A continuously tunable cw dye laser was used to measure the absolute spectral response of a silicon photodiode and narrow band−pass filter by comparison with an electrically calibrated pyroelectric detector. The filtered photodetector was then used to measure the spectral power density from a standard lamp that had been calibrated by the classical technique. The agreement of better than 1% between the two measurements is well within the uncertainties identified with each measurement individually, of the order of 1%. A number of advantages in the new technique are identified.

Avalanche buildup time of silicon avalanche photodiodes

Abstract: The avalanche buildup time in silicon n+‐p avalanche photodiodes is studied by a shot noise investigation. The avalanche buildup time t is given by t∼5×10−13M sec, where M is the multiplication factor.

The Effect of Gamma Irradiation on Optical Isolators

Abstract: The effects of gamma radiation on optical isolators have been investigated. This study has included the simultaneous irradiation and measurement of the individual emitters and detectors making up the isolators. In this manner, the net effect of irradiation on the isolators could be attributed to the degradation of either the emitter or detector, or both. As expected, isolators containing photodiodes are more radiation resistant than those containing phototransistors. In the photodiode isolator the LED is responsible for essentially all the gamma-induced isolator degradation. The performance of phototransistor isolators depends strongly on the phototransistor bias, VCE, and the LED input current, ILED. At high ILED and low VCE where gamma-induced surface effects in the phototransistor are minimized, the degradation of the isolator is due primarily to the LED which is more sensitive than the LED in the photodiode isolator. In contrast, at low ILED and high VCE, gamma-induced surface damage in the phototransistor is the dominant effect and the isolator is quite sensitive to irradiation.

Remote vibration measurement of rough surfaces by laser interferometry.

Abstract: A He-Ne laser interferometer employing a focusing telescope is used remotely to measure transient longitudinal displacements of rough surfaces by monitoring the resulting Doppler shift of the backscattered light. The feasibility and accuracy of this technique are considered theoretically relative to laser output, range, telescope aperture, sensor efficiency, bandwidth, noise, surface characteristics, and coherence. The technique was successfully demonstrated on various test surfaces at distances up to 100 m using an unstabilized 4-mW laser, a 15-cm reflector telescope, and a PIN photodiode.

Opto-electronic sensor

Abstract: An instrument for giving electrical indications of the distance between two reference points includes a light source, a primary light-sensitive detector and a secondary light-sensitive control detector. Both detectors may be photodiodes. In one embodiment, the light from the source is reflected from a reference plane and is intercepted by the primary detector and by the secondary control detector. The secondary control detector is part of a control loop which adjusts the intensity of the light source in such a manner that the photo current through the secondary control detector remains constant, thus providing compensation for changes in brightness and sensitivity due to aging, soiling and other influences.

Solid state image modulator

Abstract: For use with a one- or two-dimensional charge-coupled photodiode array, apparatus for modulating an optical image formed on the photosensor portion of the array with a predetermined pattern of density variations and for causing the pattern to move in a predetermined manner with respect to the image.

Voltage isolated measurement of high voltage direct current - isolation provided by optical coupling

Abstract: An arrangement for the voltage-free measurement of the value of DC currents at high voltages, especially those of the traction motors of railway locomotive units, is suitable for the derivation of signals representing the actual current values for comparison with required values in an automatic control system, it operates by conversion of the current to a proportional pulse-width or frequency modulated pulse train which controls an optical coupling device connected to an output integrator; the coupler may contain a light emitting diode with a phototransistor to provide electrical isolation.

Electrical and Photovoltaic Properties of CdS-GaAs Junctions

Abstract: Heterojunction photodiodes were made by epitaxial growth of CdS on GaAs substrate using the close-spaced technique, and their photoelectric properties were examined as a function of the substrate temperature. Good rectification and photovoltaic properties were obtained on n–n CdS–GaAs junctions. The junction showed Schottky-diode like photoresponse. Since the carrier concentration in the CdS layers was much larger than that in the GaAs substrate, the depletion layer between these junctions extended mainly on the GaAs side. The diffusion of Cd into the GaAs substrate affected photoelectric properties of the diodes. The technical data for the optimum growth conditions for good characteristics are presented. The quantum efficiency of 69% from photon to electron for monochromatic light of 6328 A is obtained.

Ultraviolet radiation monitor

Abstract: A readily portable ultraviolet radiation monitor includes an ultraviolet radiation sensitive cell or transducer arranged in an electrical circuit to drive a digital voltmeter. The ultraviolet sensitive transducer includes a solar blind vacuum photodiode which is exposed to the area of interest through various ultraviolet filters to produce a desired predetermined transducer response characteristic. The monitor is generally T-shaped with the transducer located to view out of one arm of the T, while the meter display is viewed into the other arm. A dependent handle comprises the leg of the T.

Single electron recording by self-scanned diode arrays

Abstract: A unique multichannel photoelectron counting system can be made by using self-scanning semiconductor arrays in the electron bombardment induced mode provided the SNR in the self-scanning arrays permits the detection of single electrons. To investigate this in an experimental program, self-scanning light sensitive diode arrays were subjected to electron bombardment. In one experiment, a radioactive source Ni(63) was used to show that the 128 element (Reticon RL128L) self-scanned linear diode arrays were responsive to electrons, and good agreement could be derived between the high energy portion of the incident and -measured fluxes. In another experiment using an electron accelerator and 42-keV electrons, clear resolution of the pulse distribution peaks was obtained due to single, double, and triple incidences of electrons. The relative heights of the observed peaks obeyed a Poisson distribution as expected for random electron incidence. The incorporation of this device into a photoelectronic tube will result in a self-scanned photoelectronic detector closely approaching the theoretical performance limit.

Planar germanium photodiodes.

Abstract: Planar passivated germanium photodiodes have been developed whose useful response at 22°C extends from 0.6 μm to 1.85 μm at a nominal operating voltage of 20 V. Typical characteristics at 22°C are diode capacitance, 100 pF/cm2; rise and fall times, 10 nsec; leakage current, 2.5 mA/cm2; D*(1.54 μm) ∼2.5 × 1010 cm/W/√Hz with a 3-dB frequency of ∼45 MHz. Single and multiple element detectors ranging in size from 2 × 0.25-mm2 elements with 50-μm spacing between elements to 3-cm2 quadrant detectors have been made successfully for operation at temperatures from 77 K to room temperature.

Electro-optic system with expanded power range

Abstract: A Bragg cell spectrum analyzer in which the output of the Bragg cell is detected by a unique electro-optic system which allows the selection of any desired dynamic power detection range. As is known in the art, the output of a Bragg cell consists of a radiation spot or spots along a line in which the position of each spot along the line is related to the frequency of a component of the input signal to the Bragg cell, and the intensity of radiation of each spot is proportional to the strength of the component causing that spot. In the disclosed embodiment the output of the Bragg cell is directed upon a cylindrical lens system which expands each spot into a line of radiation. This results in a two dimensional pattern of lines with the position of each line being the same as the position of the radiation spot causing the line, and the intensity of radiation in each line being proportional to the intensity of radiation in the spot causing that line. The two dimensional pattern of radiation, consisting of spaced lines of radiation, is directed through a stepped density filter onto a two dimensional photodiode array. The photodiode array is utilized to detect the position of each line, which indicates the frequency of the input component causing that line, and is utilized to detect the number of photodiodes reaching saturation along the line, which indicates the strength of the component.

Image Sensors for Solid State Cameras

Abstract: Publisher Summary This chapter describes the various aspects of image sensors for solid state cameras. The function of an image sensor is to generate a time-varying video signal corresponding to the spatial variations in the incident optical image. The continuous photoconductive layer in a vidicon target can be represented as an array of isolated photoconductive elements each shunted by a capacitor. A major advance in image sensing occurred with the development of the silicon diode array target for the vidicon. Multiplexed scanning of solid state arrays is directly analogous to electron beam scanning in camera tubes. In each case, the picture charge at the element is discharged through a local switch into a common electrode connected to the output amplifier. The elemental capacitor shunting each diode should be large compared to the stray capacitance shunting the transistor. The elemental capacitor may consist largely of the depletion layer capacitance between photodiode and the substrate, or it may be formed of the oxide capacitance to an overlying electrode. It is found that although the derivation of video signal from the substrate permits a simplification of the scan generators and peripheral circuits, the relatively large capacitance of the output to the ground will degrade the signal-to-noise ratio at low light levels.

Optical timing receiver for the NASA laser ranging system. Part I. Constant-fraction discriminator

Abstract: Position-resolution capabilities of the NASA laser ranging system are essentially determined by time-resolution capabilities of its optical timing receiver. The optical timing receiver consists of a fast photoelectric device, primarily a standard of microchannel-plate-type photomultiplier or an avalanche photodiode detector, a timing discriminator, a high-precision time-interval digitizer, and a signal-processing system. The time-resolution capabilities of the receiver are determined by the photoelectron time spread of the photoelectric device, the time walk and resolution characteristics of the timing discriminator, and the time-interval digitizer. It is thus necessary to evaluate available fast photoelectronic devices with respect to their time-resolution capabilities, and to design a very low time walk timing discriminator and a high-precision time digitizer which will be used in the laser ranging system receiver. (auth)