Showing papers on "Photodiode published in 1998"

Photodiode detector with integrated noise shielding

Abstract: A photodiode has integrated shields for the rejection of noise-producing electromagnetic interference and ambient light. The electromagnetic shield forms a conductive matrix which covers the photodiode active area. The matrix is deposited as a metallization layer onto the photodiode and provides exposed portions of the active area for light detection. A pad is electrically connected to the shield to allow external termination of the shield. The ambient-light shield is in the form of a colored encapsulant surrounding the photodiode. The encapsulant provides a high-pass light transmission characteristic which passes signal light and rejects out-of-band ambient light. The photodiode is particularly advantageous for use in pulse oximetry probes.

Schottky barrier detectors for visible-blind ultraviolet detection

Abstract: The invention concerns the fabrication and characterization of vertical geometry transparent Schottky barrier ultraviolet detectors based on n- /n+ -GaN and AlGaN structures grown over sapphire substrates. Mesa geometry devices of different active areas were fabricated and characterized for spectral responsitivity, speed and noise characteristics. The invention also concerns the fabrication and characterization of an 8×8 Schottky barrier photodiode array on GaN with a pixel size of 200 μm by 200 μm.

Photovoltaic measurement of the built-in potential in organic light emitting diodes and photodiodes

Abstract: We measure the voltage at which the current under illumination in poly[2-methoxy, 5-(2-ethylhexoxy)-1,4-phenylene vinylene] based light emitting diodes is equal to the dark current. At low temperatures, this voltage, which we term the “compensation” voltage, is found to be equal to the built-in potential, as measured with electroabsorption on the same diode. Diffusion of thermally injected charges at room temperature, however, shifts the compensation voltage to lower values. A model explaining this behavior is developed and its implications for the operation of organic light emitting diodes and photovoltaic cells are briefly discussed.

Performance of InGaAs/InP avalanche photodiodes as gated-mode photon counters

Abstract: We investigate the performance of separate absorption multiplication InGaAs/InP avalanche photodiodes as single-photon detectors for 1.3- and 1.55-mum wavelengths. First we study afterpulses and choose experimental conditions to limit this effect. Then we compare the InGaAs/InP detector with a germanium avalanche photodiode; the former shows a lower dark-count rate. The effect of operating temperature is studied for both wavelengths. At 173 K and with a dark-count probability per gate of 10(-4), detection efficiencies of 16% for 1.3 mum and 7% for 1.55 mum are obtained. Finally, a timing resolution of less than200 ps is demonstrated.

High-quality germanium photodiodes integrated on silicon substrates using optimized relaxed graded buffers

Abstract: The integration of Ge photodetectors on silicon substrates is advantageous for various Si-based optoelectronics applications. We have fabricated integrated Ge photodiodes on a graded optimized relaxed SiGe buffer on Si. The dark current in the Ge mesa diodes, Js=0.15 mA/cm2, is close to the theoretical reverse saturation current and is a record low for Ge diodes integrated on Si substrates. Capacitance measurements indicate that the detectors are capable of operating at high frequencies (2.35 GHz). The photodiodes exhibit an external quantum efficiency of η=12.6% at λ=1.3 μm laser excitation in the photodiodes. The improvement in Ge materials quality and photodiode performance is derived from an optimized relaxed buffer process that includes a chemical mechanical polishing step within the dislocated epitaxial structure.

Reflection photodetector and biological information measuring instrument

Abstract: When the light from an LED (31) is incident to photodiodes (32 and 33) at illuminances (Pa and Pb), respectively, electric currents (ia and ib) corresponding to each illuminance are generated. When external light which arrives through the tissue of a finger is incident to the photodiodes (32 and 33) at an illuminance (Pc), an electric current (ic) is generated. The electric current (i1) (=ia+ic) generated in the photodiode (32) is added to the electric current (i2) (=-ib-ic) generated in the photodiode (33) at a node (X) and the electric current (ic) corresponding to the external light is offset. Since the photodiodes (32 and 33) are attached so that the distances from the LED (31) may be different from each other, the illuminance (Pb) is so extremely lowered that the electric current flowing into an operational amplifier (34) becomes the same as the current (ia) corresponding to the illuminance (Pa). The amplifier (34) generates a pulsating wave signal (Vm) through current-to-voltage conversion.

InP-InGaAs uni-traveling-carrier photodiode with improved 3-dB bandwidth of over 150 GHz

Abstract: Uni-traveling-carrier photodiodes (UTC-PD's) with ultrafast response and high-saturation output are reported. It is experimentally demonstrated that the photoresponse of UTC-PD's is improved by incorporating a step-like potential profile in the photoabsorption layer. The fabricated device shows a peak electrical 3-dB bandwidth of 152 GHz at a low reverse bias voltage of -1.5 V. The output voltage can be increased to as high as 1.9 V at higher reverse bias voltages with the 3-dB bandwidth staying at over three-quarters of the maximum value. To our knowledge, the obtained response is the fastest among those reported for 1.55-/spl mu/m wavelength photodiodes.

Partially pinned photodiode for solid state image sensors

Abstract: A pixelated image sensor having comprising a partially pinned photodiode which is formed a semiconductor of a first conductivity type formed on a surface of the sensor with at least one photodiode formed, within the semiconductor near the surface, the photodiode being formed from a second conductivity type opposite the first conductivity type; a pinning layer formed on the surface over at least a portion of the photodiode creating a pinned photodiode region, the pinning layer being formed from the first conductivity type; and an unpinned region formed near the surface in an area outside the portion used to form the pinning layer, the unpinned region is formed as a floating region that is employed as a capacitor. The partially pinned photodiode is useful in expanding the fill factor of photodetectors employing photodiode technology.

Mean energy required to produce an electron-hole pair in silicon for photons of energies between 50 and 1500 eV

Abstract: The photon energy dependence of the mean energy W required to produce an electron-hole pair in silicon for photons with energies between 50 and 1500 eV was determined from the spectral responsivity of selected silicon photodiodes. The spectral responsivity was measured with a relative uncertainty of less than 0.3% using monochromatized synchrotron radiation whose radiant power was measured with a cryogenic electrical substitution radiometer. In order to deduce W from the spectral responsivity of photodiodes with a relative uncertainty of about 1%, a method for the calculation of photon and electron escape losses from silicon photodiodes was developed and the model for the charge carrier recombination losses was improved. In contrast to recent theoretical and experimental results, a constant value W=(3.66±0.03) eV was obtained in the photon energy range from 50 to 1500 eV. The present experimental results are confirmed by calculation of the pair creation energy in silicon from data from the literature for ...

Vacuum ultraviolet spectroscopy

Abstract: Synchrotron Radiation Sources Configuration of a Typical Beamline Glow Discharges and Wall Stabilized Arcs Hollow Cathode, Penning, and Electron-Beam Excitation Sources Laser Produced Plasmas Transition Radiation Vacuum Ultraviolet Lasers Radiometric Characterization of VUV Sources Imaging Properties and Aberrations of Spherical Optics and Nonspherical Optics Reflectometers Reflectance Spectra of Single Materials Polarization Optical Properties of Materials Reflecting Optics: Multilayers Zone Plates Windows and Filters Diffraction Gratings Multilayer Gratings Crystal Optics Normal-Incidence Monochromators and Spectrometers Grazing-Incidence Monochromators for Third-Generation Synchrotron Radiation Sources Spectographs and Monochromators Using Varied Line Spacing Gratings Interferometric Spectrometers Gas Detectors Photodiode Detectors Amplifying and Position Sensitive Detectors Absolute Flux Measurements Vacuum Techniques Lithography X-Ray Spectromicroscopy Optical Spectroscopy in the VUV Region Soft X-Ray Fluorescence Spectroscopy

Three-dimensional second-harmonic generation imaging with femtosecond laser pulses.

Abstract: A three-dimensional reflectance scanning optical microscope based on the nonlinear optical phenomenon of second-harmonic generation is presented. A mode-locked Ti:sapphire laser producing <90-fs pulses at approximately 790 nm was used, and the images were constructed by scanning of an object, which possessed local second-order nonlinearity, relative to a focused spot from the laser. The second-harmonic light at approximately 395 nm generated by the specimen was separated from the fundamental beam by use of dichroic and interference filters and was detected by a photodiode. The technique was then used to characterize the distribution of second-order nonlinearity and microstructure of the nonlinear material lithium triborate.

Visible blind gan p-i-n photodiodes

Abstract: We present the growth and characterization of GaN p-i-n photodiodes with a very high degree of visible blindness. The thin films were grown by low-pressure metalorganic chemical vapor deposition. The room-temperature spectral response shows a high responsivity of 0.15 A/W up until 365 nm, above which the response decreases by six orders of magnitude. Current/voltage measurements supply us with a zero bias resistance of 1011 Ω. Lastly, the temporal response shows a rise and fall time of 2.5 μs measured at zero bias. This response time is limited by the measurement circuit.

Organic diodes with switchable photosensitivity

Abstract: Organic diode detectors (10) with switchable photosensitivity are achieved using organic photo layers (12) in the photodiodes and a detector circuit (15, 16) which applies a reverse or forward bias voltage across the diodes. These diodes can be arranged in matrices which function as high-performance, two-dimensional image sensors. These image sensors can achieve full color or selected color detection capability.

Adaptive power supply for avalanche photodiode

Abstract: An adaptive power supply for an avalanche photodiode (APD) is used to determine an optimum bias voltage. Without an optical signal input the adaptive power supply applies a swept voltage to the APD while monitoring the photodiode current. When breakdown occurs, the voltage is noted and the bias voltage from the adaptive power supply is set at a specified offset below the breakdown voltage. Where a source of optical digital data signal is present, it is coupled to the input of the APD via a programmable optical attenuator. The electrical digital signal output from the APD is input to a bit error rate counter, the output of which is monitored. For different optical power levels the APD bias voltage is swept by the adaptive power supply, determining a constant power level curve over which the bit error rate is virtually zero. This is repeated for a plurality of optical power levels, the resulting family of curves defining a region within the bit error rate is virtually zero. The adaptive power supply is set to a value that falls within the virtually zero bit error rate region for the expected optical power level input.

Fast-turnoff photodiodes with switched-gain preamplifiers in photoplethysmographic measurement instruments

Abstract: An improved photoplethysmographic measurement system is disclosed for use in ambient light. The system has two or more light emitters (20-23) each emitting light at different wavelengths and a detector photodiode (26) for detecting the intensity of light that has passed through a patient's tissue, e.g. a finger (24). The emitters are pulsed sequentially, consecutive pulses being separated by a dark time when no emitter is energised so that the detector measures the ambient light during the dark time. The signal from the detector (26) during the dark time is subtracted from the signal during one of the pulses to give a measure of the tissue transmission at the pulse wavelength. An error is introduced if the emitter does not turn off immediately at the end of a pulse since the light emitted boosts the dark time signal, particularly if the system uses switched-gain preamplifiers. According to the invention, a fast-turn-off photodiode is used in order to minimise the effect of "bleed-through" voltages on the dark time (ambient) light determination. A hardware method and a software method for determining whether a given photodiode has a sufficient decay time are also disclosed.

1 Gbit/s CMOS photoreceiver with integrated detector operating at 850 nm

Abstract: A fully integrated single-beam optical receiver is realised in a production 0.35 /spl mu/m CMOS process, which operates at 850 nm to 1 Gbit/s. The receiver integrates a photodiode, preamplifier, digital logic, and an off-chip driver. Pre-amplifier dissipation is <1.5 mW at 2.3 V, with an average optical power of -6.3 dBm required for 1 Gbit/s operation. Such a compact optical receiver may be of interest for short distance optical interconnects or local area networks.

A simple model to determine multiplication and noise in avalanche photodiodes

Abstract: Avalanche multiplication and noise in 1.0, 0.5, 0.1, and 0.05 μm GaAs p+-i-n+ diodes have been calculated for both electron and hole initiated multiplication using a simple model which incorporates a randomly-generated ionization path length (RPL) and a hard-threshold dead space. We find that the mean multiplication obtained using this RPL model is in excellent agreement, even for the shortest structure, with that obtained from an analytical-band structure Monte Carlo (MC) model, which incorporates soft-threshold effects. However, it predicts slightly lower avalanche noise in the shorter devices. This difference results from the narrower ionization path length probability distribution and larger dead space of the hard-threshold RPL model at high electric fields as compared to the more realistic distribution function associated with the relatively sophisticated MC model.

Back-illuminated GaN/AlGaN heterojunction photodiodes with high quantum efficiency and low noise

Abstract: Back-illuminated GaN/AlGaN ultraviolet (UV) heterojunction photodiodes with high quantum efficiencies are demonstrated. Photovoltaic (zero bias) responsivity of 0.2 A/W at 355 nm was achieved. The improved efficiencies primarily arise from the use of AlGaN/GaN heterojunction in which photons are absorbed within the p-n junction thus eliminates carrier losses due to surface recombination and diffusion processes in previously reported homojunction devices. Very high dark impedance and large visible rejection ratio were obtained. These results indicate high quality GaN/AlGaN interface and efficient photocarrier collection in the photodiode.

Thin multiplication region InAlAs homojunction avalanche photodiodes

Abstract: Low excess noise in avalanche photodetectors (APDs) is desired for improved sensitivity and high-frequency performance. Gain and noise characteristics are measured for InAlAs p-i-n homojunction APDs that were grown with varying i-region widths on InP by molecular beam epitaxy. The effective ionization ratio k (β/α) determined by noise measurements shows a dependence on multiplication region width, reducing from 0.31 to 0.18 for multiplication region thicknesses of 1600–200 nm. This trend follows previously shown results in AlGaAs-based APDs, which exhibit reduced excess noise due to nonlocal multiplication effects. These results show that this effect is a characteristic of thin avalanche regions and is not a material-specific phenomenon.

Energy resolution of scintillation detectors readout with large area avalanche photodiodes and photomultipliers

Abstract: The energy resolution of small NaI(Tl), CsI(Tl), BGO, GSO, YAP and LSO crystals has been studied using 16 mm diameter large area avalanche photodiodes (LAAPD) and a 52 mm diameter photomultiplier. The best result of 4.8% for 662 keV /spl gamma/-rays from a /sup 137/Cs source was obtained with a 9 mm in diameter by 9 mm high CsI(Tl) scintillator coupled to an LAAPD. Measuring the number of primary electron-hole pairs produced in the LAAPD and photoelectrons in the photomultiplier, as well as the noise contribution of the LAAPD, allowed a quantitative discussion of the results. The energy resolutions measured with LAAPDs are comparable to, or significantly better (at certain emission wavelengths) than, those obtained with the photomultiplier. At energies above 100 keV the energy resolution measured with the majority of crystals and the LAAPD was weakly affected by the photodiode noise contribution. The advantages and limitations of LAAPDs in energy spectrometry with scintillation detectors are also discussed.

Active pixel with a pinned photodiode

Abstract: An active pixel for use in an imaging array and formed in a semiconductor substrate having a first conductivity type. The active pixel comprises: a pinned photodiode formed in the semiconductor substrate; a transfer well having a second conductivity type formed in the substrate, the transfer well being adjacent to the pinned photodiode; a transfer gate adjacent the transfer well, the transfer gate for controlling the flow of a signal charge from the pinned photodiode through the transfer well and under the transfer gate; and an output well adjacent the transfer gate for receiving the signal charge and routing the signal charge to output circuitry.

Limited Geiger-mode silicon photodiode with very high gain

Abstract: The novel type of the Silicon Photodiode — Limited Geiger-mode Photodiode (LGP) has been produced and studied. The device consists of many ≈104 mm−2 independent cells ≈10 mkm size around n+ -“pins” located between p-substrate and thin SiC layer. Very high gain more than 104 for 0.67 mkm wave length light source and up to 6·105 for single electron have been achieved. The LGP photon detection efficiency at the level of one percent has been measured.

Image-recording apparatus

Abstract: PROBLEM TO BE SOLVED: To eliminate variations for every appliance and obtain a high-quality stable amount of light of a semiconductor laser, by setting a light amount- monitoring means for monitoring the amount of light emitted from the semiconductor laser, comparing an output of the means with a predetermined value and controlling to increase/decrease a pulse width of a PWM modulator based on the comparison. SOLUTION: Image data from a controller are input to a PWM modulation 1 which in turn outputs pulses with a pulse width corresponding to the image data. A laser driver 2, upon receipt of the pulses, drives a laser 4 to form a latent image on a photosensitive drum with the laser light. At this time, a part of the laser light by the laser 4 is detected at a light amount-monitoring photodiode 5, a received current is converted to a voltage by an I/V converter 6 and supplied to an integrating circuit 7. At the same time, the light is supplied to an APC circuit 3 to stabilize an emission amount of light. That is, an output of the integrating circuit 7 and a reference voltage 1 or 2 via a switch 9 are supplied to the comparator 8 and, the pulse width of the PWM modulator 1 is adjusted with an output of the comparator 8.

Low-frequency noise and performance of GaN p-n junction photodetectors

Abstract: We report on low-frequency noise characteristics of visible-blind GaN p-n junction photodetectors. Carrier hopping through defect states in the space charge region, believed to be associated with dislocations, is identified as the main mechanism responsible for the dark conductivity of the photodiodes. Under reverse bias, the dark current noise has the 1/f character and obeys the Hooge relation with α≈3. Under forward bias, we observe generation-recombination noise related to a trap level with the activation energy of 0.49 eV. Under illumination, detectivity is found to be shot noise limited. The noise equivalent power of a 200×200 μm2 photodetector is estimated at 6.6×10−15 W/Hz1/2 at a bias of −3 V.

Absolute silicon photodiodes for 160 nm to 254 nm photons

Abstract: Silicon n-on-p photodiodes with 100 % internal quantum efficiency have been studied in the 160 nm to 254 nm spectral range. Preliminary values have been determined for the quantum yield of silicon at these wavelengths. Using these values, a trap detector is presented for absolute flux measurement in this region. The stability under intense 193 nm irradiation, a property of importance in lithography and in photorefractive keratectomy, has been measured, and the diodes tested were found to be several orders of magnitude more stable than p-on-n diodes tested by other investigators at this wavelength. Spatial nonuniformities of the n-on-p diodes were found to be less than 1 % at wavelengths of 254 nm and 161 nm.

AlxGa1−xN:Si Schottky barrier photodiodes with fast response and high detectivity

Abstract: Gold and nickel Schottky barrier photovoltaic detectors have been fabricated on Si-doped AlxGa1−xN layers (0⩽x⩽0.22) grown on sapphire by metalorganic vapor phase epitaxy. Responsivity is independent of the Schottky metal or diode size, and also of the incident power in the range measured (10 mW/m2–2 kW/m2). A higher visible rejection has been observed in the spectral response of Au photodiodes (>103). Time response is resistance-capacitance limited, with time constants as short as 14 ns in Al0.22Ga0.78N diodes. Low frequency noise studies are also presented, and detectivities of 6.1×107 and 1.2×107 mHz1/2 W−1 are determined in GaN/Au and Al0.22Ga0.78N/Au detectors, at −2 V bias.

Performance of thin separate absorption, charge, and multiplication avalanche photodiodes

Abstract: Previously, it has been demonstrated that resonant-cavity-enhanced separate-absorption-and-multiplication (SAM) avalanche photodiodes (APDs) can achieve high bandwidths and high gain-bandwidth products while maintaining good quantum efficiency. In this paper, we describe a GaAs-based resonant-cavity-enhanced SAM APD that utilizes a thin charge layer for improved control of the electric field profile. These devices have shown RC-limited bandwidths above 30 GHz at low gains and gain-bandwidth products as high as 290 GHz. In order to gain insight into the performance of these APDs, homojunction APDs with thin multiplication regions were studied. It was found that the gain and noise have a dependence on the width of the multiplication region that is not predicted by conventional models. Calculations using width-dependent ionization coefficients provide good fits to the measured results. These calculations indicate that the gain-bandwidth product depends strongly on the charge layer doping and on the multiplication layer thickness and, further, that even higher gain-bandwidth products can be achieved with optimized structures.

Portable, Low-Cost, Solid-State Luminescence-Based O2 Sensor

Abstract: A novel sensor for quantifying molecular O2 based entirely on solidstate electronics is presented. The sensor is based on the luminescence quenching of tris(4,7-diphenyl-1, 10-phenanthroline)ruthenium(II) ([Ru(dpp)3]2+) by molecular O2. The sensor involves immobilizing the ruthenium complex within a porous sol-gel-processed glass film and casting this film directly onto the surface of a blue quantumwell light-emitting diode (LED). The ruthenium complex is excited by the LED, the [Ru(dpp)3]2+ emission is filtered from the excitation with a low-cost acrylic color filter, and the emission is detected with an inexpensive silicon photodiode. The sensor response to gaseous O2 and dissolved O2 in water is presented. The sensor exhibits fast response times and good reversibility, and detection limits are 0.5% , 0.02% , and 110 ppb, respectively, for O2 in the gaseous (linear Stern-Volmer and multi-site Stern-Volmer analysis) and aqueous phase. This sensor provides a cost-effective alternative to traditional electrochemical-based O2 sensing and also provides a platform for other optically based sensors.

A well to substrate photodiode for use in a cmos sensor on a salicide process

Abstract: An image sensor having a well (203)-to-substrate (200) diode as the photodetector. In a preferred embodiment, a modern salicided (CMOS) process is utilized to manufacture the image sensor. The field oxide region (207) above the diode junction is transparent to visible light, thus allowing the photodiode competitive quantum efficiency as compared to devices having source/drain diffusion-to-substrate photodiodes fabricated on a non-salicided process. The photodiode as part of a sensor array may be integrated with digital circuitry using a relatively unmodified digital CMOS fabrication process. Furthermore, the well-to-substrate structure allows the optical properties of the photodiode to be engineered by modifying the well without deleterious effects, to approximately a first order, on the characteristics of a FET built in another identical well.