Showing papers on "Responsivity published in 1994"

Improved performance of quantum well infrared photodetectors using random scattering optical coupling

Abstract: We demonstrate that a random scattering reflector on top of a quantum well infrared photodetector increases the optical coupling (i.e., increases the infrared absorption, responsivity, and detectivity) by an order of magnitude compared with a one‐dimensional grating or 45° angle of incidence geometry.

Photoresponse characteristics of n‐type tetrahedral amorphous carbon/p‐type Si heterojunction diodes

Abstract: The photovoltaic behavior and spectral response of n‐type (nitrogen‐doped) tetrahedral amorphous carbon (ta‐C)/p‐type crystalline silicon heterojunction photodiodes are reported. Abrupt step junction type characteristics are observed with ta‐C films ranging in thickness from 40 to 160 nm. The photovoltage increases and the prominent peak in responsivity shifts from 800 nm to longer wavelengths of 1000 nm as the doping in the ta‐C films is increased, indicative of a widening of the depletion region in the Si. Use of the responsivity vs wavelength data with the Donnelly and Milnes model for an abrupt heterojunction is successful in predicting the depletion width in the Si and the doping level in the higher doped ta‐C. The latter value coupled with the x‐ray photoemission spectroscopy derived N concentration in the ta‐C films enables an estimation of the doping efficiency. Secondary ion mass spectroscopy studies also confirm the abrupt nature of the junctions.

Antenna‐coupled high‐Tc air‐bridge microbolometer on silicon

Abstract: An antenna‐coupled high‐Tc superconducting microbolometer on a silicon substrate, operating at infrared wavelengths, is described. This detector incorporates a silicon‐micromachined yttria‐stabilized zirconia air bridge at the feed of a planar lithographic antenna to simultaneously minimize the thermal conductance and the heat capacity of the bolometer. At an operating temperature of 87.4 K, the optical responsivity measured using a 300‐K blackbody source over a 0.2–2.9 THz bandwidth is 2900 V/W, the optical noise‐equivalent power (NEP) is 9×10−12 W/Hz1/2, and the time constant is <10 μs. This NEP is nearly a factor of 2 lower than the previous record for a liquid‐nitrogen‐cooled thermal detector, and the time constant is several orders of magnitude shorter.

In0.53Ga0.47As metal‐semiconductor‐metal photodiodes with transparent cadmium tin oxide Schottky contacts

Abstract: A metal‐semiconductor‐metal (MSM) In0.53Ga0.47As photodiode using a transparent cadmium tin oxide (CTO) layer for the interdigitated electrodes was investigated. The transparent contact prevents shadowing of the active layer by the electrodes, thus allowing greater collection of incident light. The barrier height (φBn) of CTO on i‐In0.52Al0.48As was determined to be 0.47 eV, while the Ti/Au barrier height was 0.595 eV. The reduced barrier height for CTO is caused by tunneling through the sputter‐damaged cap layer. Responsivity for 1.3 μm incident light was 0.49 and 0.28 A/W, respectively, for the CTO and Ti/Au MSM photodiodes. No antireflection (AR) coating was utilized over the bare semiconductor surface. The CTO MSM photodiode shows a factor of almost two improvement in responsivity over conventional Ti/Au MSM photodiodes.

Optimization of two dimensional gratings for very long wavelength quantum well infrared photodetectors

Abstract: We have performed a detailed study of two‐dimensional grating coupling for quantum well infrared photodetectors in the very long wavelength spectral region λ∼16–17 μm. Using calculations based on the modal expansion method we quantitatively explain the double peaked responsivity spectrum. By optimizing the grating parameters we achieve a normal incidence responsivity and detectivity which are three times larger than the 45° angle of incidence geometry.

Strained InGaAs/AlGaAs quantum well infrared detectors at 4.5 μm

Abstract: We demonstrate midinfrared photodetection at λ=4.5 μm in a multi‐quantum well detector using a strained InGaAs/AlGaAs alloy grown on a GaAs substrate. The detector shows very low dark current of a few pA, a peak unpolarized light responsivity R=12 mA/W for an external 45° angle of incidence, and a background‐limited detectivity D*BL=4×1010 cm Hz1/2/W at temperatures up to 95 K in the same conditions. This opens the way to high performance 3–5 and 8–12 μm GaAs‐based multispectral detectors

Transient resistive photoresponse of YBa2Cu3O7−δ films using low power 0.8 and 10.6 μm laser radiation

Abstract: Thin YBa2Cu3O7−δ laser deposited films were patterned into devices consisting of ten parallel 1 μm wide strips. Nonequilibrium picosecond and bolometric photoresponses were studied by the use of 17 ps full width at half‐maximum laser pulses and amplitude modulated radiation from an AlGaAs laser up to 10 GHz and from a CO2 laser up to 1 GHz. The time and frequency domain measurements were in agreement. The fast response can be explained by electron heating. The use of low optical power and a sensitive measurement system excluded any nonlinear transient processes and kinetic inductance changes in the superconducting state. At 1 GHz modulation frequency, the responsivity was ∼1.2 V/W both for 0.8 and 10.6 μm wavelengths. The sensitivity of a fast and spectrally broadband infrared detector is discussed.

Improved device technology for epitaxial Hg1-xCdxTe infrared photoconductor arrays

Abstract: The performance of Hg1-xCdxTe infrared photoconductors is strongly dependent on the semiconductor surface conditions and, in particular, the degree to which the surface contributes to recombination of photogenerated excess carriers. Although published photoconductor fabrication processes based on bulk Hg1-xCdxTe address this issue by fully passivating both major surfaces (i.e. front and back) with anodically grown native oxide, passivation of the sidewalls is neglected. In this paper it is shown both theoretically and experimentally that leaving the sidewalls unpassivated can result in approximately a factor of two reduction in responsivity for long-wavelength infrared (LWIR) detectors used in high-resolution thermal imaging systems. Detector arrays are typically fabricated on x=0.23 Hg1-xCdxTe representing a cut-off wavelength of 9.4 mu m and use individual element sizes of approximately 50*50 mu m2. We describe in detail for the first time a device technology which enables the fabrication of Hg1-xCdxTe photoconductor arrays such that the entire surface of the semiconductor is effectively passivated, including the sidewalls. Of particular interest is the fact that this improved device technology is compatible with present-day Hg1-xCdxTe epitaxial growth processes. This is in contrast to current photoconductor technology which is primarily based on bulk Hg1-xCdxTe. Experimental results are presented which compare device performance of LWIR detectors fabricated using the improved photoconductor technology with current published photoconductor technology. These results clearly indicate that detectors fabricated on liquid phase epitaxially (LPE) grown x=0.23 Hg1-xCdxTe material using the improved photoconductor device technology achieve much higher responsivities and detectivities. Furthermore, it is shown that only a fully passivated device structure is capable of exploiting any future improvements in bulk minority carrier lifetime as it approaches the Auger recombination limit.

Design and performance of very long-wavelength GaAs/Al(x)Ga(1-x)As quantum-well infrared photodetectors

Abstract: We present an extensive and detailed study of very long wavelength quantum well infrared photodetectors covering the spectral region between 14 and 20 micrometers. Measurements were made on seven different molecular beam epitaxy grown samples having different well widths and barrier heights. In this study we combine experimental results with theoretical analysis and focus on the relationship between the quantum well structure and detector performance, i.e., responsivity, dark current, dynamic resistance, noise current, optical-gain, and detectivity. These results provide the basis for further optimization, and the detector parameters needed for the design of the readout circuit for focal plane arrays.

CMOS photodetectors for industrial position sensing

Abstract: The properties of a CMOS-compatible pn-photodiode, phototransistor, and one-dimensional lateral-effect photodiode (LEP) for position-sensing applications are characterized. The photodiode and phototransistor seem to have properties that are comparable to typical commercial photodetectors despite the relatively large variations in their spatial and spectral responses and the lower responsivity in the near-infrared band. In addition to the above properties the LEP's show excellent linearity, but 3-4 times larger NEP than corresponding commercial LEP's due to low resistance of the current dividing layer. The responsivity variations have no effect on the linearity of the LEP, and the slightly lower responsivity at near-infrared has only a negligible effect on the achievable resolution (SNR). These properties, usually considered as weak points of CMOS-compatible photodetectors, are believed to have little or no effect on the properties of a position sensor, if the diameter of the light spot is small ( >

Noise and photoconductive gain in AlGaAs/GaAs quantum well intersubband infrared photodetectors

Abstract: We reevaluate the current model of noise gain and photoconductive gain for AlGaAs/GaAs quantum well infrared photodetectors. An experimental study is carried out on samples covering different types of intersubband transitions, i.e., bound‐to‐continuum, bound‐to‐quasibound, and bound‐ to‐bound cases. A general difference between gains measured by dark current noise and by responsivity was found for all three cases, while agreement between them was found within some ranges of bias voltages for the bound‐to‐quasibound and bound‐to‐continuum samples. The thermal noise contribution to the total white noise is explicitly modeled and discussed.

Postgrowth tuning of quantum‐well infrared detectors by rapid thermal annealing

Abstract: The peak detection wavelength of an operational quantum‐well infrared photodetector structure has been red shifted using rapid thermal annealing to partially intermix the well and barrier layers. Successive anneals at 850 °C were used to tune an 8.13 μm detector continuously out to 9.13 μm. All of the fabricated detectors were operational in spite of very long annealing times of up to 300 s. The peak spectral responsivity at a device current of 10 μA dropped from 0.62 to 0.12 A/W after the longest anneal time, but the broadband responsivity only dropped by a factor of 3 due to a simultaneous increase in the detection spectral bandwidth.

High-{Tc} superconducting antenna-coupled microbolometer on silicon

Abstract: Boulder, Colorado, 80303ABSTRACTA process is described for fabricating antenna-coupled resistive-edge microbolometers based onthe high-Ta superconductor YBaCu3O7 (YBCO) on silicon. The YBCO and a buffer layer of yttria-stabilized zirconia (YSZ) were grown epitaxially on silicon to minimize excess electrical noise. A silicon-micromachined YBCO/YSZ air-bridge was incorporated to minimize the thermal conductance and the heatcapacity. The thermal conductance of the air-bridge was measured to be 3 x 10 W/K at a temperatureof 100 K. At an operating temperature of 89 K, the detector is estimated to have a response time of 2us, a responsivity in the 1000 VJW range, and a noise-equivalent power (NEP) in the 1012 W/Hz"2 rangeat 1000 Hz.1. INTRODUCTIONOne of the most straightforward applications of the high-Ta superconductor YBaCu3O7 (YBCO)is as resistive-edge bolometers for detection of infrared and millimeter-wave radiation. Such detectors mayoffer performance advantages over current technology in applications such as long-wavelength infraredimaging and as detectors for FTIR spectrometers.' Much of the research to date has been on surface-absorbing bolometers, in which a surface that absorbs well over the spectral region of interest is in goodthermal contact with the YBCO, but is thermally isolated from the surroundings."2' The typical response

A GaAs/AlAs/AlGaAs and GaAs/AlGaAs stacked quantum well infrared photodetector for 3–5 and 8–14 μm detection

Abstract: A new two‐color n‐type GaAs/AlAs/AlGaAs double barrier quantum well (DBQW) and bound‐to‐miniband GaAs/AlGaAs quantum well infrared photodetector (QWIP) with photovoltaic (PV) and photoconductive (PC) dual‐mode operation in the 3–5 and 8–14 μm atmospheric spectral windows has been demonstrated in this work. It consists of a stack of the midwavelength infrared (MWIR) QWIP and the long‐wavelength infrared (LWIR) QWIP. The PV detection scheme uses transition from the ground bound state to the first quasi‐bound excited state for the MWIR‐QWIP. The PC detection scheme has two different transitions, one identical to the PV mode detection scheme while the other uses transition from the ground bound state to the miniband state of the superlattice barrier LWIR‐QWIP. The peak responsivity for the PV mode was found to be 17 mA/W at λp=4.1 μm and T=50 K with a bandwidth Δλ/λp=15%. The peak responsivities for the PC mode were found to be 25 mA/W at λp=4.1 μm, Vb=1.0 V, and 0.12 A/W at λp=11.6 μm, Vb=3.2 V, and at T=50 ...

Nonlinear effects in high‐temperature superconducting bolometers

Abstract: In this paper deviations from ideal behavior of high‐temperature superconducting bolometers are analyzed. Formulas include corrections to the bolometric parameters for electrical nonlinearity. A simple empirical model for the resistive transition together with the standard bolometer theory are used to calculate the electrical and thermal parameters. It is shown that the standard method used to derive the detector responsivity would lead to wrong results. A new criterion for deducing the responsivity from electrical measurements in the presence of nonlinear effects is illustrated.

Theoretical study of the effect of an AlGaAs double heterostructure on metal-semiconductor-metal photodetector performance

Abstract: The impulse and square-wave input response of different GaAs metal-semiconductor-metal photodetector (MSM) designs are theoretically examined using a two dimensional drift-diffusion numerical calculation with a thermionic-field emission boundary condition model for the heterojunctions. The rise time and the fall time of the output signal current are calculated for a simple GaAs, epitaxially grown, MSM device as well as for various double-heterostructure barrier devices. The double heterostructure devices consist of an AlGaAs layer sandwiched between the top GaAs active absorption layer and the bottom GaAs substrate. The effect of the depth of the AlGaAs layer on the speed and responsivity of the MSM devices is examined. It is found that there is an optimal depth, at fixed applied bias, of the AlGaAs layer within the structure that provides maximum responsivity at minimal compromise in speed. >

Voltage tunable three‐color quantum well infrared photodetector

Abstract: A voltage tunable three‐color quantum well infrared photodetector (QWIP) consisting of asymmetric GaAs/AlGaAs double quantum wells has been demonstrated. The detector uses electron intersubband transitions in a coupled asymmetric double quantum well superlattice. The infrared photocurrent spectrum characterized using a blackbody monochromator source shows three prominent peaks appearing at 8.4 μm, 9.6 μm, and 10.3 μm under different biases. The three detection peaks are well resolved and can be independently selected by tuning the applied voltage. The responsivity and the detectivity of the detector at different biases and operating temperatures are characterized and found to be sufficient for detector operation at temperatures ∼60 K.

InAs/GaSb infrared photovoltaic detector at 77 K

Abstract: The characterisation of an 8 mu m infrared photovoltaic detector based on InAs/GaSb superlattices is carried out at 77 K for the first time. The built-in field is established by the Fermi level difference between the superlattice surface and the InAs buffer layer. The photocurrent is from photoexcited carriers traversing through the superlattice conduction miniband. A current responsivity of 0.07 A/W has been obtained, implying that one out of 10 photoexcited electrons has been collected.

Two‐photon intersubband transitions in quantum well infrared photoconductors

Abstract: We demonstrate that a symmetric GaAs/GaAlAs quantum well photodetector with a peak responsivity centered at 8.1 μm shows a significant quadratic power response at 10.6 μm. This is due to intersubband two‐photon transitions from the ground level to continuum states. The two‐photon responsivity agrees with a theoretical prediction based on a perturbative approach and photoconductive gain estimations.

InAlAs/InGaAs metal‐semiconductor‐metal photodiodes heteroepitaxially grown on Si substrates

Abstract: To study performance and reproducibility of photodiodes (PDs) on Si in the long‐wavelength region, InAlAs/InGaAs metal‐semiconductor‐metal PDs were fabricated on high‐quality heteroepitaxial InP layers on Si substrates. A dark current of 0.5–2×10−8 A and a responsivity of 0.05–0.15 A/W were reproducibly obtained, at least at one of the ±5 V bias voltages. These dark currents and responsivity are similar to those of PDs with the same structure fabricated on InP substrates. The PDs on Si have pulse responses with full widths at half‐maximum of 150–600 ps.

Internal photovoltaic effect in microwave devices

Abstract: This paper is concerned with the internal photovoltaic effect in microwave MODFETs and MESFETs. Characteristic of the photovoltaic effect are the large gain and logarithmic variation of the photoresponse with light intensity. Although the basic photodetection mechanisms are different for the two types of devices, in each case the incident light acts as an additional terminal, an "optical gate". The optimization of the photoresponse and the photodetection performance of these devices, with respect to responsivity and bandwidth, are also discussed. >

Spectral response of a photodiode using 3C-SiC single crystalline film

Abstract: 3C-SiC/Si heterojunction photodiodes and 3C-SiC homojunction photodiodes have been fabricated by atmospheric chemical vapor deposition. The maximum quantum efficiency of heterojunction photodiodes with a window layer of 10 μm thick is 80% at 550 nm. An increase in the thickness of the SiC layer reduces the responsivity in wavelength regions shorter and longer than 500–550 nm. 3C-SiC self supported films of 20 μm thick, epitaxially grown on Si, have been used as substrates for homojunction photodiodes. The responsivity of the homojunction photodiode with a window layer thickness of 0.5 μm is 72 mA/W at 250 nm with a quantum efficiency of 36%. When the thickness of the window layer is decreased, the peak responsivity increases and the peak wavelength shifts to a shorter wavelength. These spectral responsivities are discussed together with the results of calculations using a one-dimensional model.

A fully CMOS-compatible infrared sensor fabricated on SIMOX substrates

Abstract: We report on the use of SIMOX substrates for fabrication of IR radiation thermopiles by CMOS technology. SIMOX technology enables the fabrication of single-crystal leads on thin silicon or silicon oxide membranes. Two p-type silicon/aluminium thermopiles on different membranes are presented. A thermopile with a 4 μm thick, epitaxially grown silicon membrane has a responsivity of 18 V/W and a time constant of 3 ms. Using a 2.5 μm thick silicon oxide membrane, a responsivity of 150 V/W and a time constant of 25 ms are achieved. In addition, the fabrication and properties of an IR absorber made in CMOS technology are presented.

WDM receiver chip with high responsivity

Abstract: A semiconductor optical amplifier, a grating demultiplexer and a photodiode array were integrated in InGaAsP/InP to form a WDM receiver chip. 10 wavelength channels (TE or TM polarisation) in the 1.54 mu m wavelength region with a channel spacing of 2 nm were detected with a crosstalk of less than -20 dB and a responsivity of up to 8 A/W.

Monolithically integrated silicon nMOS pin photoreceiver

Abstract: A monolithic Si optical receiver is reported that consists of an Si nMOS preamplifier and a novel lateral Si pin photodiode. The Si photodiode has a bandwidth of 900 MHz and a responsivity of 0.48 A/W at 870 nm. The optical receiver has demonstrated open-eye operation to 370 Mbit/s with 3 mu A of signal photocurrent.

Quantum well photodetector with pseudo-random reflection

Abstract: Quantum well infrared photodetectors (QWIPs) according to the invention have a surface that provides pseudo-random reflection of the radiation that is incident thereon, resulting in an increase in the effective number of passes of the radiation through the quantum well region, and hence in increased responsivity of the QWIPs, as compared to corresponding prior art grating QWIPs. A convenient approach to forming the pseudo-random reflecting surface is disclosed.

Detectivity of a three-level quantum-well detector

Abstract: We have calculated the noise properties of a three-level metastable photocapacitive intersubband quantum-well detector. It is shown that while a large gain in responsivity is obtainable by using a three-level system, a good detectivity requires a very effective blocking of the tunneling relaxation from the metastable state to the ground state. >

Pyroelectric ir detectors using periodic inverted domains of litao3

Abstract: In this paper, a new-structure pyroelectric infrared detector is proposed, which consists of interdigital electrodes deposited on periodic inverted domains of ferroelectric crystal. Since only a shallow region close to the crystal surface is pyroelectrically active in this structure, the surface charges are quickly induced in response to IR irradiation and this structure therefore provides us with a high responsivity. A pyroelectric detector fabricated using periodic antipolar domains formed by selective proton exchange and subsequent heat treatment of LiTaO3 crystal is experimentally demonstrated to exhibit a high current responsivity in high frequency range of IR power modulation.

Normal state YBa2Cu3Ox films: A new fast thermal detector for far infrared laser radiation with a uniform wavelength response

Abstract: Room temperature YBa2Cu3Ox films, epitaxially grown on oriented substrates, are shown to be effective detectors of far infrared laser pulses. The photovoltage arises due to an anisotropic material thermopower subject to the thermal gradient arising from the radiation heating. For a 40 nm thick film we have measured a responsivity of (5±2)×10−7 V/W, independent of frequency in the range from 20 to 110 cm−1. The response time is limited by thermal diffusion, giving a 200 MHz detector bandwidth and a noise equivalent power of 3.6×10−3 W(Hz)−1/2 for this film thickness. Due to their large area (1 cm2) and uniform spectral response, such films may be useful replacements for pyroelectric power/energy meters.