Showing papers on "Responsivity published in 1986"

A silicon-thermopile-based infrared sensing array for use in automated manufacturing

Abstract: This paper describes a new low-cost infrared detector array that has been realized using standard silicon MOS process technology and micromachining. This array uses thermopiles as infrared detecting elements and multiple layers of silicon oxide and silicon nitride for diaphragm windows measuring 0.4 mm × 0.7 mm × 1.3 µm. Each thermopile consists of 40 polysilicon-gold thermocouples. A high fill factor for this array structure has been achieved by using the boron etch-stop technique to provide 20-µm thick silicon support rims. The array shows a response time of less than 10 ms, a responsivity of 12 V/ W; and a broad-band input spectral sensitivity. The process is compatible with silicon MOS devices, and a 16 × 2 staggered array with on-chip multiplexers has been designed for applications in process monitoring. The array theoretically achieves an NETD of 0.9°C and an MRTD of 1.4°C at a spatial frequency of 0.2 Hz/mrad in a typical imaging system.

Design and performance of blocked-impurity-band detector focal plane arrays

Abstract: Blocked-Impurity-Band (BIB) extrinsic silicon (Si:As) detectors have demonstrated high sensitivity and quantum efficiency in the long wavelength infrared (LWIR) spectral region (to 28 microns) as well as wide frequency response, low optical crosstalk, nuclear radiation hardness, and stable, predictable performance. Furthermore, it has been demonstrated that SWItched mosFET (SWIFET) multiplexers provide a low noise readout approach for use with BIB detectors. This paper describes the state-of-the-art of multiplexed BIB detector hybrid focal plane arrays (HFPAs). The principle of operation and performance of optimized BIB and Back Illuminated BIB (BIBIB) detectors are presented. The SWIFET multiplexer, including necessary circuitry for BIBIB detector readout, has been designed and fabricated using a newly developed process for cryogenic (<20K) MOS electronics which avoids anomalies (lack of device isolation, excess noise, and long time constants) associated with conventional silicon processes. A description of the design and operation of this multiplexer is given. A number of uniform, highly responsive, 500 element HFPAs have been fabricated and their performance evaluated. The characterization measurements, to be described in the paper, include evaluation of detector dark current, responsivity, noise for various operating conditions, and uniformity of array characteristics. The results obtained and presented demonstrate that focal plane arrays with excellent, unprecedented, LWIR performance have been realized with Blocked-Impurity-Band detector technology.

Gate‐controlled Hg1−xCdxTe photodiodes passivated with native sulfides

Abstract: The properties of ion‐implanted junctions in Hg1−xCdxTe with x=0.22, passivated by a novel native sulfide technique, are described. The junctions are typically operated at 77 K, with 50% responsivity at a wavelength of 10.5 μm. To study the effects of the passivated surface on the diode properties, special gate‐controlled diodes were processed, including both nickel and titanium gate metals. In addition, a novel enhancement mode metal–insulator–semiconductor field‐effect transistor (MISFET) is presented. The measured dc properties and noise current spectral densities of various diodes as a function of reverse bias and gate control voltage show that close to background limited devices may be realized with the above surface passivation. In particular, such diodes exhibit good 1/f noise performance at low frequency, with reverse bias of close to 200 mV, without requiring a special gate electrode.

Multiple field of view sensor

Abstract: Images of two fields of view of one or two scenes in a radiation sensor are generated by use of a single detector and common signal process circuitry. The two imaged fields of view, typically a narrow view and a wide view, are provided by two independent telescopes (18, 20), and are combined by use of a field-of-view switch (32) comprising a chopper wheel (34) or an optical switch in synchronized operation with a mirror scanner (22). The same field-of-view switch is employed in performing detector non-uniformity correction functions, such as automatic responsivity control and direct current restoration. Folding optics couples scanned radiation from the scanner to the switch. An additional field of view may be introduced by displacing a folding mirror of the folding optics. Also, a portion of a reflecting surface of the switch may be tilted to admit a reference beam of radiation useful in performing the functions of responsivity control and D.C. restoration.

Capacitive bolometer with improved responsivity

Abstract: The capacitive bolometer comprises a detection capacitor having a first-order phase transition ferroelectric material between two electrodes. The detection capacitor operates during a detection step and a subsequent readout step. During the detection step, a preselected electric field is applied to the detection capacitor to maximize its sensitivity to temperature. A second electric field is applied to the capacitor during the readout step in order to increase responsivity of the detection cell. The detection cells according to the invention can be assembled into disclosed detection arrays.

Optical efficiency of far-infrared photoconductors

Abstract: The present optimization of the geometry of far-IR photoconductive detectors with diffraction-limited throughput, on the basis of experimental and theoretical results, gives attention to the internal optical path relative to measured absorption length, photoconductive gain, uniformity of illumination, cosmic ray cross section, and design compatibility with the requirements of one- and two-dimensional arrays. It is demonstrated that a rod-shaped, square cross section detector geometry, having lateral face electrodes and a beveled backface with which to trap the radiation by total internal reflection, exhibits responsivity commensurate with that of the best available detectors in integrating cavities.

Millimetre-waveguide-mounted InGaAs photodetectors

Abstract: We describe the design and characteristics of InGaAs PIN photodetectors mounted in microwave waveguides for use in transmission of millimetre-wave modulation signals on optical carriers. For an experimental device operating to 60 GHz (5 mm wavelength), we show the wavelength dependence of responsivity, the spatial uniformity of response and the bias dependence of modulation bandwidth.

Design of an ultraviolet radiometer. 1: Detector electrical characteristics.

Abstract: An ultraviolet radiometer has been designed to the exacting standards required for use in a space simulation facility. In this paper the electrical characteristics, photocurrent linearity, and noise performance (when used with high quality operational amplifiers) of available photodetectors are examined. A combined experimental and theoretical assessment shows that GaAsP Schottky barrier photodiodes are superior to both diffused-junction and inversion-type silicon photodetectors in both high current linearity and noise performance. This results in GaAsP devices having an increased dynamic range at room temperature, a significant radiometric advantage. The superiority of the GaAsP diodes is further increased at higher operating temperatures. The following paper discusses UV stability and responsivity/filtering requirements of both types of device.

Analysis of InSb Photodiode Low Temperature Characteristics

Abstract: The quantum efficiencies of front and back illuminated indium antimonide photodiodes have been calculated with the aid of a computer model. This model describes the photodiode quantum efficiency, resistance, capacitance and responsivity for any given doping profile and temperature. The calculations show that front and back illuminated devices optimized for high resistance-area products at 77K have low quantum efficiencies when operated at 4.2K. These photodiodes are fabricated diffusion or ion implantation of a p-type layer in an n-type base with ~1 x 1015 cm-3 donors. The mechanism limiting the quantum efficiencies of these "normal" InSb photodiodes at low temperatures is reduced minority carrier diffusion lengths in the base layer. This effect is minimized by reducing the donor concentrations of the n-type base layer to ~ 1 x 1014 cm-3, thereby increasing the depletion layer width, carrier lifetimes and diffusion lengths of photogenerated minority carriers. High quantum efficiencies from 1-5 microns can then be achieved at 4.2K with front illuminated photodiodes provided that the p-type layer thickness < 2 microns. High quantum efficiencies may also be achieved at low temperature with back illuminated devices fabricated from high purity base layers as thick as ~10 microns provided that the surface recombination velocity < 102 cm/sec. or the base layer is depleted by reverse biasing the photodiode.

Recent Developments on a 128 x 128 Indium Antimonide/FET Switch Hybrid Imager For Low-Background Applications

Abstract: By combining high-quality mesa photovoltaic indium antimonide detector material with a silicon x-y FET switch multiplexer, a useful infrared area detector has been developed. This device is intended for low-background applications, where high sensitivity is required. Initial characterization of the detector at 80 K showed a KTC limited read noise of less than 1000 electrons, good dark current, responsivity uniformity, and a maximum readout rate of 10 MHz. The hybrid mating technology has sufficient precision to allow expansion to a 256 x 256 format. The dark current in the detector material is sufficiently low to allow full-frame integration, even with arrays as large as 256 x 256 elements.

Monolithic HgCdTe MIS IR detectors with a floating-diode sense mechanism

Abstract: Monolithic charge-transfer devices for use as electronic focal planes in infrared imaging systems have been tested under varying conditions to assess their operating limitations. These devices employ the charge imaging matrix [1] concept (CIM), which uses the potential change on a floating diode for charge detection. Unlike a charge injection device, the CIM READ operation does not involve the recombination of charge carriers. Charge is integrated in a metal-insulator-semiconductor well and then transferred to the sense diode. This allows for very fast READ operations and potentially high (2 MHz) data rates. The responsivity, charge transfer, crosstalk, uniformity, and noise characteristics have been evaluated using small arrays of up to 9 × 8 pixels having diode areas formed by ion implantation with boron. HgCdTe with optical cutoff wavelengths from 9 to 9.5 µm were used, and tests were conducted at liquid-nitrogen temperature.

Effect of light attenuation on the responsivity and detectivity of transverse and longitudinal detectors

Abstract: It is shown that when account is taken of the attenuation of incident radiation into the bulk of a photoconductor, as a result of the absorption, the expressions for the responsivity and detectivity are modified. An earlier derivation [Infrared Phys. 20, 385 (1980)] attributed the difference in the operation of the detectors in the transverse and longitudinal geometries to carefully defined ‘‘effective’’ quantum efficiencies. Here we show that a more physically motivated view attributes the difference to the different photoconductive gains for the two geometries. It is shown that the appropriate gains for the responsivity and detectivity are not the same.

Low dark current GaAs/AlAs graded-parameter superlattice PIN photodetector

Abstract: Preliminary measurements of the photoresponse of a GaAs p-n junction containing an undoped asymmetric GaAs/AlAs superlattice are presented. Very low reverse-bias dark currents (<6×10?8 A/cm2 at 3 V) are measured, while still retaining the speed and spectral response of a conventional GaAs PIN diode. The ?3 dB bandwidth is found to be greater than 1 GHz, and the responsivity is 0.1 A/W.

Three-dimensional analytical model for photovoltaic detector arrays

Abstract: Decreasing dimensions along with increasing number of elements in imaging photodiode arrays result in degradation of spatial resolution and sensitivity due to lateral transport(1-5). This effect is modelled using a novel 3-D analytical solution of the continuity equation. The model enables the full 3-D analysis of lateral transport as manifested in excess carrier distribution photocurrent, self and cross responsivities. Three detector structures are investigated: semi-infinite substrate, perfectly collecting, and perfectly reflecting backside. Front and rear illuminations are treated. Calculated results for the 3-D case deviate fundamentally from those predicted by the 1-D model. The 3-D model succeeds in explaining measured reduced quantum efficiency of small area detectors. It also predicts the observed limited effect of diffusion length on self responsivity and cutoff wavelength. Calculated spectral responses fit extremely well data measured on InSb and HgCdTe test arrays.

An infrared hygrometer witH on-line temperature compensation

Abstract: A single-beam infrared absorption hygrometer for measuring fluctuations in atmospheric water vapour and suitable for use in eddy correlation studies of evatranspiration is described. This instrument differs from previously described devices since it incorporates a method for monitoring detector responsivity and correcting for temperature-induced changes in this responsivity. Without such a correction, changes in the hygrometer calibration coefficient, due to instrument temperature effects, can be as large as 30% during energy balance studies over grassland.

Surface effects and grain‐boundary domination in thin‐film Zn3P2 photoconductivity

Abstract: Photoconductivity spectral response, linearity, and response time measurement indicate that surface effects and intergrain boundaries can play important roles in the characteristics of thin‐film Zn3P2. Response time of the order of a few seconds and the dependence of the spectral response on vacuum operation indicate the existence of long‐lived states at the surface. Photoconductivity response was found to be a maximum at a wavelength of 400 nm. Vacuum operation and heat treatment were observed to improve responsivity, shift the peak responsivity wavelength towards longer wavelengths, and increase the spectral width of maximum responsivity. The photoconductivity spectral dependence and the response times were found to be light–intensity dependent. It is proposed that effects of the barrier heights at the surface and at the intergrain junctions are light‐illumination dependent. The properties of the surface and the grain boundary depend on chemisorption or chemical reactions due to adsorbed gases or impuri...

Spin-on diffused GaSb mesa photodiode with high breakdown voltages

Abstract: GaSb mesa photodiodes have been fabricated by Zn diffusion from spin-on film sources For the first time, breakdown voltages up to 30 V are reported on diffused GaSb diodes Broadband responsivity with an external quantum efficiency of 60% at 17 μm has been obtained without antireflection coating

Measurement Techniques for Planar High-Frequency Circuits (Short Paper)

Abstract: Planar bismuth bolometers can be used as measuring elements in planar millimeter-wave circuits. These devices are easy to fabricate and calibrate; moreover, their responsivity is thought to be nearly independent of frequency throughout the millimeter-wave regime. Furthermore, they are inherently linear detectors over as much as seven orders of magnitude. Noise-equivalent powers of 2x 10/sup-10/ W/Hz/sup 1/2/ can be attained. The high sensitivity of these devices makes them suitable for use in probes. Techniques for measurement of current and reflection coefficient are proposed. Trial measurements, using simulation at 1 GHz, are described.

Hg1−x−yMnxCdyTe Alloys for 1.3−1.8 μm Photodiode Applications

Abstract: HgMnCdTe/CdTe photodiodes with responsivity cutoffs of up to 1.54 pm have been fabricated by liquid phase epitaxy (LPE). The mesa device structure consists of a boron-implanted mosaic fabricated on a p-type Hg1−x−yMnxCdyTe layer grown on a CdTe substrate. A reverse breakdown voltage (VB) of 50 V and a leakage current density of 1.5 × 10−4 A/cm2 at V = −10 V was measured at room temperature (295K). A 0.75 pF capacitance was also measured under a 5 V reverse bias at room temperature. This device performance based on the quaternary HgMnCdTe shows both theoretical and practical promise of superior performance for wavelengths in the range 1.3 to 1.8 μm for fiber optic applications.

Photoresponsive measurements on InAs0·3Sb0·7 infrared detector

Abstract: This paper presents a study of responsivity of InAs0·3Sb0·7 infrared detector. Thin films of InAs0·3Sb0·7 semiconducting compound were prepared by vacuum evaporation on glass and mica substrates held at 473° K under a pressure of 10−6 torr with deposition rate of 20 A°/sec. The isothermal annealing process was employed to improve the quality of the films. The responsivity variation with blackbody temperature (333° K to 673° K), detector temperature (80° K to 303° K) and frequency (10 Hz to 10 kHz) was measured. The experimental set-up and the results are presented and discussed.

A broadband photon drag detector for pulsed, high-power radiation detection

Abstract: A broadband detector based on the photon drag effect in semiconductors has been used for radiation detection from 600 μm to 1 cm wavelengths. The measured responsivity of the detector at the longer wavelengths is ∼3 μV/W.

A Two-Dimensional HgCdTe IRCCD with Increased Cell Capacity

Abstract: A new chip organization for CCD multiplexers to increase the cell capacity is discussed. The chip uses the interlaced readout scheme, the MCCD and the storage/transfer common electrode configuration. These three techniques triple the conventional cell capacity. The CCD multiplexer is source-coupled with a 64 x 64 element HgCdTe photovoltaic array for 3-5 μm spectral region. The cell size of the CCD is 100 x 50 μm. The detector element pitch is 50 μm. The multiplexer has the charge handling capability of 1.1 x 107 electrons/cell. A 50 dB dynamic range is obtained for all 64 x 64 elements with 8% offset variation against 300 K background radiation and 14% responsivity variation. The mean detectivity D*λρ is 1.8 x 1011 cmHz1/2/W at peak wavelength of 4.7 μm. This IRCCD realizes wide dynamic range without sacrificing detectivity.

An analysis algorithm for thermal detectors of radiation

Abstract: The response of a thermal detector to an input signal is characterized by an exponential approach to the steady-state level. Moreover, since this device is rather sensitive to external conditions, the measured signal is perturbed by noise and thermal drift. An algorithm, based on optimization techniques, is presented for determining the responsivity of the detector (calibration stage) or the input radiant power (actual measurement) from the measured data. Some examples on the algorithm performances are carried out in different experimental situations.

Responsivity of ion-implanted p-n junction in a GaAs electroabsorption avalanche detector

Abstract: The performance characteristics of an ion-implanted p-n junction electroabsorption avalanche detector (EAD) are reported. Wtih avalanche-assisted multiplication, the optical gain reaches value of over 500 and the devices achieved a peak responsibility of 200 A/W at a wavelength of 0.88 µm. Owing to the combination of the Franz-Keldysh effect with avalanche multiplication, a narrowband, i.e., self-filtering, response of 50 nm full-width half-magnitude was demonstrated. With a 50-Ω load the pulse response of this large-area EAD, i.e., 1.6 × 10-2cm2, is about 5-10 ns and is RC time constant limited.

Far-infrared detection by GaAs-IREDs and GaAs0.6P0.4-LEDs

Abstract: In GaAs-IREDs and GaAs0.6P0.4-LEDs a photoconductive and a bolometric FIR response has been observed at low temperatures by applying different pulsed optically pumped FIR lasers. The short circuit current responsivity peaks at λ=400 μm being about 1.5 mA/W. By monitoring the rapid modulation of the FIR radiation due to mode beating of the pump laser, an upper limit of 1 ns was established to the time constant of the photoconductive signal.