Showing papers on "Responsivity published in 1992"

High-responsivity photoconductive ultraviolet sensors based on insulating single-crystal GaN epilayers

Abstract: We report on the fabrication and characterization of photoconductive ultraviolet detectors based on insulating single‐crystal GaN. The active layer (GaN) was deposited over basal‐plane sapphire substrates using a unique switched atomic‐layer‐epitaxy process. The sensors were measured to have a responsivity of 2000 A/W at a wavelength of 365 nm under a 5‐V bias. The responsivity remained nearly constant for wavelengths from 200 to 365 nm and dropped by three orders of magnitude within 10 nm of the band edge (by 375 nm). We estimate our sensors to have a gain of 6×103 (for wavelength 365 nm) and a bandwidth in excess of 2 kHz. The photosignal exhibited a linear behavior over five orders of incident optical power, thereby implying a very large dynamic range for these GaN‐based ultraviolet sensors.

Photoconductive gain mechanism of quantum‐well intersubband infrared detectors

Abstract: Taking into account the discrete nature of the quantum‐well intersubband infrared detectors, we construct a model to calculate the photoconductive gain. It is shown that the photoconductive gain is inversely proportional to the number of quantum wells and that the detector‐current responsivity is independent of the number of wells.

Photoexcited escape probability, optical gain, and noise in quantum well infrared photodetectors

Abstract: We present a detailed and thorough study of a wide variety of quantum well infrared photodetectors (QWIPs), which were chosen to have large differences in their optical and transport properties. Both n- and p-doped QWIPs, as well as intersubband transitions based on photoexcitation from bound-to-bound, bound-to-quasi-continuum, and bound-to-continuum quantum well states were investigated. The measurements and theoretical analysis included optical absorption, responsivity, dark current, current noise, optical gain, hot carrier mean free path; net quantum efficiency, quantum well escape probability, quantum well escape time, as well as detectivity. These results allow a better understanding of the optical and transport physics and thus a better optimization of the QWIP performance.

High responsivity ultraviolet gallium nitride detector

Abstract: The invention is an Al x Ga 1-x N ultraviolet detector with extremely high responsivity at over 200 to 365 nanometers and a very sharp long wavelength cutoff. The active layer for the sensors is a single crystal Al x Ga 1-x N preferably deposited over a basal plane sapphire substrate using a switched atomic layer epitaxy process.

High-performance back-illuminated InGaAs/InAlAs MSM photodetector with a record responsivity of 0.96 A/W

Abstract: A high-performance back-illuminated In/sub 0.53/Ga/sub 0.47/As/In/sub 0.52/Al/sub 0.48/As/InP metal-semiconductor-metal (MSM) detector is reported. A record responsivity of 0.96 A/W at 1.3- mu m wavelength, corresponding to a quantum efficiency of 92%, was measured at 5 V and showed virtually no internal gain at 20 V. Packaged devices with 150- mu m-diameter large detection area showed a 3-dB bandwidth of 4 GHz at 5 V with fiber pigtail butt-coupled package and 3.5 GHz with fiber pigtail silicon V-grooved package. Switching to front-illumination improves the bandwidth by 30-40% with 45-50% reduction of responsivity. Planar and mesa devices both show a low capacitance per unit area of 3.0 nF/cm/sup 2/ and dark current density of 5.6*10/sup -5/ A/cm/sup 2/ at 5 V. Preliminary reliability test results show that the detector biased at 5 V survived temperature cycling of -35 degrees C to 200 degrees C, high-temperature burn-in at 125 degrees C for 168 h and subsequent short-term accelerated aging at 200 degrees C for 120 h without degradation. >

Double wavelength selective GaAs/AlGaAs infrared detector device

Abstract: We demonstrate the first GaAs/AlGaAs multiquantum well infrared detector device with double wavelength selectivity and high wavelength resolution. By applying an efficient light coupling mechanism, which is based upon the excitation and emission of surface plasmons, we have achieved a responsivity R of 2.20 A/W and a detectivity D* of 2.2×1011 cm √Hz/W for λ=7.38 μm at a temperature T=5 K for a 300 K background irradiance and a 90° field of view, which are one of the highest values reported to date.

Broadband (8-14 μm), normal incidence, pseudomorphic GexSi1-x/Si strained-layer infrared photodetector operating between 20 and 77 K

Abstract: Performance characteristics of a pseudomorphic p‐type, normal incidence, Ge0.25Si0.75/Si strained‐layer quantum well infrared photodetector on (001) Si is described for 20≤T≤77 K. The device shows broadband photoresponse (8–14 μm) which is attributed to strain and quantum confinement induced mixing of heavy, light, and split‐off hole bands. Typical device responsivity at λ=10.8 μm is ∼0.04 A/W over the 20–77 K temperature range. A detectivity D*λ=3.3×109 cm √Hz/W was measured at a bias of −2.4 V for a temperature of 77 K at λ=10.8 μm and no cold shield. Room temperature FTIR measurements yield a quantum efficiency η≊3.1% at λp≊8 μm at 300 K.

Si:Sb blocked impurity band detectors for infrared astronomy

Abstract: We discuss the characteristics of impurity band conduction detectors prepared from epitaxial Si:Sb. These detectors are sensitive to infrared light at wavelengths between 2.5 and 40 μm and outperform the current state‐of‐the‐art Ge:Be photoconductors for this wavelength range by a combination of a peak responsivity R=32 A/W, low noise equivalent power (NEP) =1.1×10−15 W/Hz1/2 (at a flux of 1012 ph/cm2 s), inherently low sensitivity to cosmic ray particles, and freedom from the anomalous behavior observed in photoconductors.

Lattice‐matched InGaAsP/InP long‐wavelength quantum well infrared photodetectors

Abstract: We demonstrate the first long‐wavelength quantum well infrared photodetector using the lattice‐matched n‐doped InGaAsP/InP materials system. A 45° prism coupled illumination responsivity of R=0.3 A/W and detectivity of D*λ=1.3×109 cm√Hz/W at T=50 K, for a cutoff wavelength λc=13.2 μm have been achieved.

Thin film pyroelectric imaging array.

Abstract: A thin film pyroelectric imaging array (N, M) fabricated as a Si wafer. A thin film (40) of PbTiO3 is deposited on a thermally isolated bridge (45). The bridge (45) suspends the PbTiO3 sensor (40) over a preferentially etched cavity (70) in the Si wafer (10). Improved thermal isolation increases the responsivity of the sensor (33) to incident radiation. The pyroelectric sensor (33) formed can operate effectively at room temperature.

Electrical tunability of infrared detectors using compositionally asymmetric GaAs/AlGaAs multiquantum wells

Abstract: For the first time, an electrically tunable infrared photoconductor is made with GaAs/AlGaAs asymmetric step multiquantum wells, using the linear Stark shift of the intersubband transition. An applied electric field excursion of ±40 kV/cm is sufficient to shift the peak responsivity wavelength from 8.5 to 13.5 μm. The photoresponse tunability is studied by comparing photocurrent and absorption spectra for different applied electric fields.

Characterization of an absolute cryogenic radiometer as a standard detector for radiant-power measurements.

Abstract: An active cavity radiometer of the electrical substitution type with a cone receiver that operates at 2-4 K has been developed for measuring radiant fluxes in the dynamic range of 20 nW to 100 microW within an uncertainty of +/-1% (2sigmalevel). It is a broadband absolute detector with a flat overall absorption efficiency that is >99% for radiation from the visible to long-wavelength IR. The system is designed based on thermal modeling and experimental measurements of concepts. It has been installed in the cryogenic chamber for low-background infrared radiation calibrations at the National Institute of Standards and Technology (NIST) for testing cryogenic blackbody sources, detectors, and optical components. Its time constant, responsivity, and nonequivalence error have been measured. They are in agreement with design predictions. Radiant power measurements of an amplitude-stabilized He-Ne laser beam with the radiometer and an industry standard photodiode detector, QED-200, have been intercompared and found to be in agreement. The intercomparison ratio of the measurements with the absolute cryogenic radiometer and QED-200 was 1.004 in the 75-100-microW range with an uncertainty of 0.5% (the 3sigma level).

An amorphous SiC/Si heterojunction p-i-n diode for low-noise and high-sensitivity UV detector

Abstract: The authors report the UV photoresponse of an a-SiC/a-Si heterojunction p-i-n diode with the structure of glass/TCO (transparent conducting oxide, SnO/sub 2/:F)/p-a-SiC:H/i-a-Si:H/n-a-Si:H/Al. The diode has been designed for a high-sensitivity and low-noise UV detector. The diode has its peak responsivity (0.254 A/W) and quantum efficiency (81.5%) at 385 nm. This structure possesses (1) the window effect by using the wide-bandgap a-SiC:H as the front layer (p-layer) and (2) the carrier confinement effect at the p-SiC:H/i-a-Si:H interface. Enhancements are proposed to raise UV response and suppress long-wave responsivity. The diode was designed to be operated under zero external bias to suppress the dark-current-induced noise. Results show a 200% higher UV sensitivity than a GaAsP Schottky photodiode in the 200-400-nm wavelength region. >

InGaAs/InP waveguide photodetector with high saturation intensity

Abstract: An InGaAs/InP rib-loaded waveguide pin, photodetector integrated with a microwave coplanar waveguide transmission line on a semi-insulating InP substrate is demonstrated. The detector has a 3 dB frequency response in excess of 20 GHz. The DC responsivity of the waveguide photo-detector remains constant at 0.21 A/W over a range of incident optical powers from 400 μW to 20 mW.

Influence of the number of wells in the performance of multiple quantum well intersubband infrared detectors

Abstract: We present the results of a systematic study of a series of intersubband multiple quantum well detector samples having 4, 8, 16, and 32 wells. We find that while the absorption increases with the number of wells in the device, the detector current responsivity is insensitive to the number of wells.

Up to 16 dB improvement in detected voltage using two-section semiconductor optical amplifier detector

Abstract: A semiconductor optical amplifier detector with an improved responsivity, obtained using two contacts is demonstrated. It is shown that up to 16dB improvement in detected output voltage may be obtained for a semiconductor optical amplifier with an internal gain of 30dB. Initial experimental results showing a 4dB improvement are presented.

A metal-amorphous silicon-germanium alloy Schottky barrier for infrared optoelectronic IC on glass substrate application

Abstract: The effects of material and structure parameters on an amorphous-silicon-germanium alloy Schottky barrier diode's responsivity have been investigated in detail. The effects contradict each other. A compromise is made in selecting parameters for construction of a Si/sub 1-x/Ge/sub x/:H Schottky barrier for an IR detector. The optimized amorphous-silicon-germanium alloy Schottky diode using x=0.43 alloy with a 900-nm-thick i-layer was found to have a peak at 850 nm with a responsivity of 0.6 A/W under -2-V bias. The diode also has a response time of 33 mu s and slight photodegradation. Thus, the diode becomes a candidate for manufacturing the infrared OEIC (optoelectronic integrated circuit) on glass substrate in applications which require size, reproducibility, and low cost more than sensitivity. >

Three-element stressed Ge:Ga photoconductor array for the infrared telescope in space.

Abstract: A stressed Ge:Ga photoconductor array with three elements applied to the Infrared Telescope in Space satellite was fabricated and tested in experiments at 2.0 K in very low-photon-influx conditions (~105 photons/s). Stress was applied to three Ge:Ga detectors in a series by a stable and compact stressing apparatus by using cone-disk springs. The cutoff wavelength was ~180 μm. Responsivity was ~100 A/W, and the product of quantum efficiency and photoconductive gain, ηG, was ~1 with a chopping frequency of 2 Hz. The noise equivalent power was <5 × 10−18 W/Hz1/2 when low-noise transimpedance amplifiers were used. A slow transient response and a nonlinear response that was dependent on the background photon influx were observed in the experiments. The latter showed that the ηG had a time constant τc that was proportional to Nph−1/2.

Design considerations of metal-film bolometer with micromachined floating membrane

Abstract: A metal-film microbolometer formed on a glass membrane suspended on a silicon substrate has been fabricated by the anisotropic etching technique. The rectangular glass membrane is supported by its four leads connected to the corners of an etched V-groove cavity. This structure allows flexible thermal management and sensitivity optimization of the bolometer for different kinds of application, with a trade-off between lead thermal impedance and device active area. Optimizations of the structure applied to both a focal-plane array and a single detector are interpreted. A thermal impedance as high as 4 × 10 5 °C/W with a response time of several milliseconds can be achieved. For a 320 μm x 320 μm detector, theoretical predictions give a responsivity and normalized detectivity of over 700 V/W and 10 9 cm √/Hz/W, respectively. For dimensions of 128 μm × 128 μm, suitable for a focal-plane-array detector, theory predicts a D * of 5.5 × 10 8 . A discrepancy exists between the experiment and the theory, which is also discussed.

Far infrared photoelectric thresholds of extrinsic semiconductor photocathodes

Abstract: Far infrared detection is demonstrated in forward biased Ge (out to 240 μm), Si (220 μm), and InGaAs (90 μm) p‐i‐n diodes with D up to 5×1010 cm Hz1/2/W at 4.2 K. For silicon detectors, this is the longest response wavelength ever reported. Estimates for the responsivity and the detectivity for unoptimized commercial samples are provided by comparison with a silicon composite bolometer. The variations observed in the long wavelength threshold (λt) suggest that if correlations with device processing parameters can be successfully established, this approach can be used to tailor detectors for different IR wavelength regions. Spectral response comparison with a single p‐i structure strongly supports the detection mechanism and opens the possibility of detector optimization using multilayered structures.

High-performance undoped InP/n-In/sub 0.53/Ga/sub 0.47/As MSM photodetectors grown by LP-MOVPE

Abstract: A new high-performance undoped In/sub 0.53/Ga/sub 0.47/As metal-semiconductor-metal photodetector (MSM-PD) with an undoped InP barrier-enhancement layer is reported. The layers were grown by the low-pressure metalorganic vapor-phase epitaxy (LP-MOVPE) technique. The main features of this device include: a very low dark current of less than 60 nA, (100*100) mu m/sup 2/, at 1.5 V; a short risetime of 30 ps at 6 V; and a high responsivity of 0.42 A/W for lambda =1.3 mu m. >

Quarter‐micrometer GaAs Schottky barrier diode with high video responsivity at 118 μm

Abstract: A quarter‐micrometer diameter Schottky barrier mixer diode has been fabricated on n+ GaAs using electron beam lithography and reactive ion etching (RIE). The anodes were formed using a Pt/Au electroplate technique. The diode zero‐bias capacitance of 0.25 fF and series resistance of about 25 Ω, measured at dc, correspond to a ‘‘figure‐of‐merit’’ cuttoff frequency of about 25 THz. The video responsivity at 118 μm (2540 GHz) was as high as 200 V/W, over three times higher than the best previously reported. The design, fabrication, and evaluation of this diode is described.

Influence of nonequivalent detector responsivity on FT-IR photometric accuracy

Abstract: Due to the temperature dependence of the detector responsivity, a photometric error mechanism exists in Fourier-transform infrared spectrometers, namely, nonequivalent detector responsivity. In this work, we analyze the mechanism theoretically and demonstrate experimentally how it affects FT-IR photometric accuracy.

Optoelectronic resonant cavity technology based on inversion channel devices

Abstract: In this paper the implementation of the inversion channel technology in a vertical cavity configuration is demonstrated. It is shown that by using a universal processing sequence a bistable surface emitting laser, a resonant cavity detector and a hetero-structure field effect transistor (H FET) can all be realized from a single epitaxial growth. The surface emitting double heterostructure opto-electronic switch (DOES) laser exhibits a pulsed threshold current of 10 mA for a 14 μm diameter device. The resonant cavity detector achieved a peak responsivity of 0.6 AW−1 in the H FET mode and 19 AW−1 when operated in phototransistor mode. The H FET had a peak transconductance of 40 mS mm−1 and a peak source to drain current density of 120 mA mm−1.

Irradiance responsivity and unequivocal type-1 phase responsivity of rat circadian activity rhythms

Abstract: Behavioral, neuropharmacological, and molecular studies of light-induced phase shifting of rodent circadian rhythms evaluate carefully the phase dependence of light responsivity. However, much less information is available regarding the dependence of such effects on the duration and irradiance of the photic stimulus used. In this study, very brief (5-min) white light pulses of 50 microW/cm2 (175 lux) administered to hooded rats elicited unequivocal type-1 phase responsivity, without significant changes in period, and with phase shift variability comparable to that in studies using longer, higher intensity pulses. Irradiance dependence was demonstrated in the phase-delay, phase-advance, and crossover portions of the phase-response curve, with minimal phase shifting seen during the dead zone even at very high irradiance. These results indicate that maximal phase-shifting magnitude may be achieved with shorter, less intense photic stimuli than are often used in studies of the neural mechanisms involved in light responsivity of rat circadian rhythms.

Time compression multiplex transmission system using a 1.3 mu m semiconductor laser as a transmitter and a receiver

Abstract: A bidirectional system using 1.3 mu m lasers as a transmitter and a receiver are investigated. The lasers considered are commercially available Fabry-Perot and distributed-feedback lasers. It is found that the poor performance of a laser receiver, compared to a PIN receiver, stems from three factors: low responsivity, high capacitance, and polarization dependence of responsivity, high capacitance, and polarization dependence of responsivity. The effect of each factor is evaluated. It has been clarified that the polarization dependence of sensitivity originates from the TE and TM modes dependence of both mode confinement factor and reflection at a facet. Using the measured parameters, 1.3- mu m laser receiver sensitivity for a 10/sup -9/ error rate is estimated. Burst data transmission experiments show that estimated sensitivities agree well with the measured values. Optical ping-pong transmission distance of narrowband services is determined based on estimated sensitivity. >

Bias dependence of responsivity and transport in asymmetric quantum well infrared detectors

Abstract: A new type of asymmetric stepped GaAs/AlGaAs multiquantum well infrared detector is reported. These asymmetric detectors utilize the usual bound‐to‐continuum transition. The current responsivity is remarkably asymmetric with regard to the voltage polarity. In contrast with rectangular wells, in which responsivity is saturated in both bias polarities, these wells exhibit saturation only for negative bias. The responsivity increases monotonously with positive electric field. This is attributed to changes induced by the field on the transport properties of the excited electrons. In particular, the bias affects the dwell time spent by the carrier wave packet in the well region. Employing this model, we achieve a very good fit with experimental data.

Light detector using intersub-valence band transitions with strained barriers

Abstract: An intersub-valence band quantum well detector (52), comprising alternating quantum wells (30') and barriers (32'), provided with differential strain permits obtaining hole mean free paths similar to the electron. Consequently, the gain and responsivity should dramatically increase. In addition, the absorption coefficient should increase, while the noise current should decrease; thus, the quantum efficiency and the detectivity (D*) should increase, compared to a detector without the added differential strain.

A 1550-nm millimeter-wave photodetector with a bandwidth-efficiency product of 2.4 THz

Abstract: The monolithic integration of an optical preamplifier and a waveguide p-i-n photodiode has resulted in a 1550-nm photodetector having an external quantum efficiency of 72 (a responsivity of 89 A/W) and an electrical bandwidth of 33.5 GHz. These figures combine to give a bandwidth efficiency product of 2.4 THz, which is approximately one hundred times higher than for any other type of millimeter-wave photodetector published to date. In addition, the preamplifier performance is supplemented by wide optical bandwidth (60 nm), low polarization sensitivity (1 dB), near traveling wave amplification (1-dB maximum gain ripple), and high saturated output power (+11 dBm). The principal advance over work reported earlier is the traveling wave operation of the monolithic optical preamplifier. >