Showing papers on "Responsivity published in 2005"

Visible and near-infrared responsivity of femtosecond-laser microstructured silicon photodiodes.

Abstract: We investigated the current-voltage characteristics and responsivity of photodiodes fabricated with silicon that was microstructured by use of femtosecond-laser pulses in a sulfur-containing atmosphere. The photodiodes that we fabricated have a broad spectral response ranging from the visible to the near infrared (400-1600 nm). The responsivity depends on substrate doping, microstructuring fluence, and annealing temperature. We obtained room-temperature responsivities as high as 100 A/W at 1064 nm, 2 orders of magnitude higher than for standard silicon photodiodes. For wavelengths below the bandgap we obtained responsivities as high as 50 mA/W at 1330 nm and 35 mA/W at 1550 nm.

Enhanced functionality of cantilever based mass sensors using higher modes

Abstract: By positioning a single gold particle at different locations along the length axis on a cantilever based mass sensor, we have investigated the effect of mass position on the mass responsivity and compared the results to simulations. A significant improvement in quality factor and responsivity was achieved by operating the cantilever in the fourth bending mode thereby increasing the intrinsic sensitivity. It is shown that the use of higher bending modes grants a spatial resolution and thereby enhances the functionality of the cantilever based mass sensor.

Tensile strained Ge p-i-n photodetectors on Si platform for C and L band telecommunications

Abstract: We demonstrate a 0.25% tensile strained Ge p-i-n photodetector on Si platform that effectively covers both C and L bands in telecommunications. The direct band edge of the Ge film has been pushed from 1550 to 1623 nm with 0.25% tensile strain, enabling effective photon detection in the whole L band. The responsivities of the device at 1310, 1550, and 1620 nm are 600, 520, and 100mA∕W under 0 V bias, which can be further improved to 980, 810, and 150mA∕W with antireflection coating based on calculations. Therefore, the device covers the whole wavelength range used in telecommunications. The responsivities at 1310 and 1550 nm are comparable to InGaAs photodetectors currently used in telecommunications. In the spectrum range of 1300–1650 nm, maximum responsivity was already achieved at 0 V bias because carrier transit time is much shorter than carrier recombination life time, leading to ∼100% collection efficiency even at 0 V bias. This is a desirable feature for low voltage operation. The absorption coeffic...

Characteristics of a tunneling quantum-dot infrared photodetector operating at room temperature

Abstract: We report high-temperature (240–300K) operation of a tunneling quantum-dot infrared photodetector. The device displays two-color characteristics with photoresponse peaks at ∼6μm and 17μm. The extremely low dark current density of 1.55A∕cm2 at 300K for 1V bias is made possible by the tunnel filter. For the 17μm absorption, the measured peak responsivity is 0.16A∕W (300K) for a bias of 2V and the specific detectivity D* is 1.5×107cmHz1∕2∕W (280K) for a bias of 1V. Excellent performance characteristics are also measured for the 6μm photoresponse.

Quantum dots-in-a-well infrared photodetectors

Abstract: Novel InAs/InGaAs quantum dots-in-a-well (DWELL) infrared photodetectors are reviewed. These detectors, in which the active region consists of InAs quantum dots (QDs) embedded in an InGaAs quantum well, represent a hybrid between a conventional quantum well infrared photodetector (QWIP) and a QD infrared photodetector (QDIP). Like QDIPs, DWELL detectors display normal incidence operation without gratings or optocouplers while demonstrating reproducible 'dial-in recipes' for control over the operating wavelength, like QWIPs. Using femtosecond spectroscopy, long carrier lifetimes have been observed in DWELL heterostructures, suggesting their potential for high temperature operation. Moreover, DWELL detectors have also demonstrated bias-tunability and multicolour operation in the mid-wave infrared (3–5 µm), long-wave infrared (LWIR, 8–12 µm) and very long-wave infrared (>14 µm) regimes. We have recently developed LWIR 320 × 256 focal plane arrays operating at liquid nitrogen temperatures. One of the potential problems with these detectors is the low quantum efficiency, which translates into low responsivity and detectivity. Some solutions for mitigating these problems are suggested at the end of this paper.

High-performance mid-infrared quantum dot infrared photodetectors

Abstract: Quantum dot infrared photodetectors (QDIPs) have emerged as attractive devices for sensing long wavelength radiation. Their principle of operation is based on intersublevel transitions in quantum dots (QDs). Three-dimensional quantum confinement offers the advantages of normal incidence operation, low dark currents and high-temperature operation. The performance characteristics of mid-infrared devices with three kinds of novel heterostructures in the active region are described here. These are a device with upto 70 QD layers, a device with a superlattice in the active region, and a tunnel QDIP. Low dark currents (1.59 A cm−2 at 300 K), large responsivity (2.5 A W−1 at 78 K) and large specific detectivity (1011 cm Hz1/2 W−1 at 100 K) are measured in these devices. It is evident that QDIPs will find application in the design of high-temperature focal plane arrays. Imaging with small QD detector arrays using the raster scanning technique is also demonstrated.

Uncooled operation of type-II InAs∕GaSb superlattice photodiodes in the midwavelength infrared range

Abstract: We report high performance uncooled midwavelength infrared photodiodes based on interface-engineered InAs∕GaSb superlattice. Two distinct superlattices were designed with a cutoff wavelength around 5μm for room temperature and 77 K. The device quantum efficiency reached more than 25% with responsivity around 1A∕W. Detectivity was measured around 109cmHz1∕2∕W at room temperature and 1.5×1013cmHz1∕2∕W at 77 K under zero bias. The devices were without antireflective coating. The device quantum efficiency stays at nearly the same level within this temperature range. Additionally, Wannier–Stark oscillations in the Zener tunneling current were observed up to room temperature.

A 3-Gb/s optical detector in standard CMOS for 850-nm optical communication

Abstract: This paper presents a monolithic optical detector, consisting of an integrated photodiode and a preamplifier in a standard 0.18-/spl mu/m CMOS technology. A data rate of 3 Gb/s at BER <10/sup -11/ was achieved for /spl lambda/=850 nm with 25-/spl mu/W peak-peak optical power. This data rate is more than four times than that of current state-of-the-art optical detectors in standard CMOS reported so far. High-speed operation is achieved without reducing circuit responsivity by using an inherently robust analog equalizer that compensates (in gain and phase) for the photodiode roll-off over more than three decades. The presented solution is applicable to various photodiode structures, wavelengths, and CMOS generations.

Silicon waveguide-integrated optical power monitor with enhanced sensitivity at 1550nm

Abstract: We describe the fabrication and operation of an optical power monitor, monolithically integrated with a silicon-on-insulator rib waveguide. The device consists of a p+‐v‐n+ structure with a detection volume coincident with the single-mode supporting waveguide. Detection of optical signals at wavelengths around 1550nm is significantly enhanced by the introduction of midband-gap generation centers, which provide partial absorption of the infrared light. The most efficient device extracted 19% of optical power from the waveguide and showed a responsivity of 3mA∕W. These devices are fabricated using current standard processing technology and are fully compatible with silicon waveguide technology and integrated operational amplifier circuits.

Thermally stable visible-blind diamond photodiode using tungsten carbide Schottky contact

Abstract: We have developed a thermally stable, deep-ultraviolet (DUV) photodiode using tungsten carbide (WC) Schottky and Ti/WC ohmic contacts for a boron-doped homoepitaxial p-diamond epilayer. Effects of thermal annealing in an argon ambient on the electrical and photoresponse properties were investigated. Annealing at temperatures up to 550°C improves the rectifying current-voltage characteristics, resulting in a dramatic enhancement of DUV responsivity at 220nm by a factor of 4×103. A blind ratio as large as 105 between DUV and visible light has been achieved at a reverse bias as small as 1V. Development of the thermally stable WC-based Schottky and ohmic contacts provides a route for stable operation of a diamond photodetector at high temperatures.

High-speed, high-responsivity, and high-power performance of near-ballistic uni-traveling-carrier photodiode at 1.55-/spl mu/m wavelength

Abstract: In this letter, we demonstrate a novel photodiode at a 1.55-/spl mu/m wavelength: the near-ballistic uni-traveling-carrier photodiode (UTC-PD). After a p/sup +/ delta-doped layer was inserted into the collector of a UTC-PD, near-ballistic transport of photogenerated electrons under high reverse bias voltage (-5 V) and a high output photocurrent (/spl sim/30 mA) was observed. The demonstrated device has been combined with an evanescently coupled optical waveguide to attain high responsivity and high saturation power performance. Extremely high responsivity (1.14 A/W), a high electrical bandwidth (around 40 GHz), and a high saturation current-bandwidth product (over 1280 mA/spl middot/GHz, at 40 GHz) with high saturation radio-frequency power (over 12 dBm at 40 GHz) have been achieved simultaneously at a 1.55-/spl mu/m wavelength.

Quantum dot infrared photodetectors: Comparison of experiment and theory

Abstract: We present data and calculations and examine the factors that determine the detectivities in self-assembled InAs and InGaAs based quantum dot infrared photodetectors (QDIPs). We investigate a class of devices that combine good wavelength selectivity with ``high detectivity.'' We study the factors that limit the temperature performance of quantum dot detectors. For this we develop a formalism to evaluate the optical absorption and the electron transport properties. We examine the performance limiting factors and compare theory with experimental data. We find that the notion of a phonon bottleneck does not apply to large-diameter lenslike quantum dots, which have many closely spaced energy levels. The observed strong decrease of responsivity with temperature is ultimately due to a rapid thermal cascade back into the ground states. High temperature performance is improved by engineering the excited state to be near the continuum. The good low temperature $(77\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ performance in strongly bound QDIPs is shown to be due to the high gain and the low noise achievable in these micron size devices.

Single-wall carbon nanotube coating on a pyroelectric detector.

Abstract: Carbon single-wall nanotubes (SWNTs) are studied as the thermal-absorption coating on a large area pyroelectric detector. The SWNTs were produced by a laser vaporization method and dispersed onto the detector surface by use of a simple airbrush technique. The detector was based on a 1-cm-diameter, 60-μm-thick lithium tantalate disk having nickel electrodes. We report the spectral responsivity of the detector ranging from 600 to 1800 nm, as well as the spatial and directional uniformity at 850 nm. Using Drude and Lorentzian dielectric functions and an effective medium approximation to obtain the indices of refraction of semiconductor and metallic SWNTs, we compared the expected theoretical relative responsivity for the two types of tube with the measured relative responsivity of the detector. Values of thermal conductivity, specific heat, and damage threshold obtained from the literature are compared with properties of alternatives for thermal coatings such as gold-black and carbon-based paint.

Interband cascade detectors with room temperature photovoltaic operation

Abstract: We investigated mid-infrared interband cascade laser structures as photodetectors, which are sensitive to normal incidence and operate in photovoltaic mode at room temperature. The proposed operation principle of these interband cascade detectors is based on the unique combination of interband photoexcitation and the much faster intersubband relaxation as well as interband tunneling recombination, which allows for the efficient collection of the photoexcited carriers. Peak responsivity and detectivity of 21 mA/W and 7.1×108cmHz1∕2∕W at λ=4.0μm are obtained for a device with cutoff wavelength of 4.4μm. Peak responsivity and detectivity of 46 mA/W and 1.4×109cmHz1∕2∕W at λ=3.0μm are obtained for another device with cutoff wavelength of 3.3μm. These detectors exhibit low noise (4.8×10−13A∕Hz1∕2) and a large product of the differential resistance and active area (19Ωcm2) at room temperature.

Single-wall Carbon Nanotube Coating on a Pyroelectric Detector

Abstract: Carbon single-wall nanotubes (SWNTs) are studied as the thermal-absorption coating on a large area pyroelectric detector. The SWNTs were produced by a laser vaporization method and dispersed onto the detector surface by use of a simple airbrush technique. The detector was based on a 1-cm-diameter, 60-μm-thick lithium tantalate disk having nickel electrodes. We report the spectral responsivity of the detector ranging from 600 to 1800 nm, as well as the spatial and directional uniformity at 850 nm. Using Drude and Lorentzian dielectric functions and an effective medium approximation to obtain the indices of refraction of semiconductor and metallic SWNTs, we compared the expected theoretical relative responsivity for the two types of tube with the measured relative responsivity of the detector. Values of thermal conductivity, specific heat, and damage threshold obtained from the literature are compared with properties of alternatives for thermal coatings such as gold-black and carbon-based paint.

Miniaturized waveguide-integrated p-i-n photodetector with 120-GHz bandwidth and high responsivity

Abstract: A low-capacitance waveguide-integrated photodiode on InP with a minimized absorber length is presented. In order to maintain a high quantum efficiency, an optical matching layer exploiting mode beating effects is employed. Its optimization leads to a twofold enhanced external responsivity of 0.5 A/W at 1.55-/spl mu/m wavelength in accordance with simulation. The reduced p-n junction capacitance enables 3-dB bandwidths up to 120 GHz mainly limited due to carrier transit time effects.

High-performance evanescently edge coupled photodiodes with partially p-doped photoabsorption layer at 1.55-/spl mu/m wavelength

Abstract: In this letter, we demonstrate a high-performance evanescently coupled photodiode (ECPD) with the partially p-doped photoabsorption layer. As compared to the control ECPD with the traditional intrinsic photoabsorption layer, the demonstrated device can exhibit much higher output saturation current (power) and electrical bandwidth without sacrificing the quantum efficiency performance. By properly designing the geometry size and epilayer structures of the partially p-doped ECPD, very high responsivity (1.01 A/W), high electrical bandwidth (around 50 GHz), and high saturation current bandwidth product (920 mA/spl middot/GHz, at 40 GHz) have been achieved simultaneously at 1.55-/spl mu/m wavelength.

Characterization of uncooled bolometer with vanadium tungsten oxide infrared active layer

Abstract: A surface micromachining uncooled infrared detector with an optimized vanadium alloy oxide layer is fabricated, based on low temperature annealing of V–W alloy oxide layer. Vanadium oxide is a promising material for an uncooled bolometer, due to its high temperature coefficient of resistance at room temperature. An infrared active layer is needed to be with the reflective layer to enhance its IR absorption. Test bolometers are successfully fabricated and then are radiated by an IR laser source at various power levels with a chopper in a frequency range of 1–500 Hz. The responsivity and the noise of the test bolometer are measured and the detectivity is calculated. From the results, the calculated detectivity is 1.1 × 107 cm Hz1/2 W−1. Bolometer detectivity can be increased further if the noise in the device is reduced.

The impact of receiver imperfections on the Performance of optical direct-Detection DPSK

Abstract: The goal of this paper is to analyze the effects of key receiver impairments on the performance of differential phase-shift keying (DPSK), like the responsivity imbalance between the two arms of the receiver balanced photodetector and the detuning of the asymmetric Mach-Zehnder filter. We extend to DPSK a semianalytical technique, based on the Karhunen-Loe/spl grave/ve series expansion, which can be used to obtain reliable performance results in the simulation of IM/DD optical systems. We show that the DPSK receiver imperfections may substantially decrease the sensitivity gain of DPSK over standard IM/DD systems. In particular, the performance turns out to be remarkably insensitive to the responsivity imbalance between the two arms of the receiver balanced photodetector but highly sensitive to the detuning of the asymmetric Mach-Zehnder filter. We also analyze the validity of the application of the Q parameter evaluation, which is extensively used in theory and simulation of intensity-modulation direct-detection (IM/DD) optical systems, to the study of the bit error rate performance of direct-detection DPSK optical systems, showing that its inaccuracy can be very large.

Integration of germanium waveguide photodetectors for intrachip optical interconnects

Abstract: The main characteristics of germanium photodetectors integrated in silicon-on-insulator optical waveguides for intrachip optical interconnects are presented. The epitaxial Ge layers are grown on Si(001) by reduced-pressure chemical vapor deposition. The optical absorption of Ge layers is recorded from 1.2 to 1.7 µm and linked to the layer strain. The responsivity of an interdigitated metal-semiconductor-metal Ge photodetector has been measured. Light coupling from a slightly etched submicron rib silicon-on-insulator waveguide to a Ge photodetector is studied for two configurations: butt coupling and vertical coupling.

AlGaAs emitter/GaAs barrier terahertz detector with a 2.3 THz threshold

Abstract: A heterojunction interfacial work function internal photoemission (HEIWIP) detector with a threshold frequency (f0) of 2.3 THz (λ0=128μm) is demonstrated. The threshold limit of ∼3.3THz (92 μm) due to the Al fraction being limited to ∼0.005, in order to avoid control and transition from alloy to isoelectronic doping behavior, was surpassed using AlGaAs emitters and GaAs barriers. The peak values of responsivity, quantum efficiency, and the specific detectivity at 9.6 THz and 4.8 K for a bias field of 2.0kV∕cm are 7.3A∕W, 29%, 5.3×1011 Jones, respectively. The background-limited infrared photodetector temperature of 20 K with a 60° field of view was observed for a bias field of 0.15kV∕cm. The f0 could be further reduced toward ∼1THz regime (∼300μm) by adjusting the Al fraction to offset the effect of residual doping, and/or lowering the residual doping in the barrier, effectively lowering the band bending.

Novel Standard CMOS Detector using Majority Current for guiding Photo-Generated Electrons towards Detecting Junctions

Abstract: A novel photo-detector is demonstrated using a majority current to drive photogenerated minority carriers from deep within the substrate towards a detecting junction. This improves detector sensitivity and speed and allows obtaining simultaneously a large sensitive area and a small detector capacitance, enhancing output signal to noise ratio and/or speed of attached readout circuits. When the applied current is modulated, a very efficient photonic mixer can be conceived, useful as pixel for Time-Of-Flight 3D image sensing. Measurement results in standard CMOS are presented showing an infrared responsivity of 0.32 A/W and a demodulation efficiency of over 99%.

Compact optical roll-angle sensor with large measurement range and high sensitivity.

Abstract: A simple and effective optical roll-angle sensor based on a magnetic garnet single crystal is demonstrated The measurement is based on the principle that, when linearly polarized light whose polarization varies alternately in two orthogonal directions passes through a polarization analyzer, the transmitted optical intensity varies The output voltage from an optical detector located after the analyzer can be used to determine the roll angle The chief advantages of the sensor are that it is compact, flexible, low cost, and power effective and provides a fast response Most importantly, the sensor is insensitive to various fluctuations such as optical intensity, photodiode responsivity, and temperature and to vibrations This performance is most advantageous in long-distance or long-term measurements Experimental results have shown that the angular resolution is 001 degree in a +/-30 degree range

High detectivity GaN metal–semiconductor–metal UV photodetectors with transparent tungsten electrodes

Abstract: GaN metal–semiconductor–metal (MSM) ultraviolet photodetectors with transparent tungsten (W) electrodes were fabricated and characterized. It was found that the 10 nm thick W film deposited with a 250 W RF power could provide a reasonably high transmittance of 68.3% at 360 nm, a low resistivity of 1.5 × 10−3 Ω cm and an effective Schottky barrier height of 0.777 eV on u-GaN. We also achieved a peak responsivity of 0.15 A W−1 and a quantum efficiency of 51.8% at 360 nm from the GaN MSM UV photodetector with W electrodes. With a 2 V applied bias, it was found that the minimum noise equivalent power (NEP) and the maximum D* of our detector were 1.745 × 10−10 W and 7.245 × 109 cm Hz0.5 W−1, respectively.

Tunable all epitaxial semimetal-semiconductor schottky diode system : ErAs on InAlGaAs

Abstract: We report the growth, fabrication, and electrical properties of a fully epitaxial semimetal-semiconductor Schottky diode materials system: ErAs on InAlGaAs. The coherent, thermodynamically stable, lattice-matched interface eliminates oxide and interfacial third phases, making the Schottky barrier height and associated electrical parameters dependent on the fundamental molecular bonding (e.g., interface dipoles) rather than unintentional extrinsic effects. ErAs:InAlGaAs diodes thus have highly tunable properties; by adjusting composition, doping, and interface type, the Schottky barrier height is tunable from ∼100meVto∼620meV, short circuit responsivity is tunable from 0.5to19A∕W, differential resistance is tunable from 103to1010Ωμm2, and capacitance is tunable from 0.4to2fF∕μm2. Rectification of a rf source has been demonstrated up to 20GHz. ErAs:InAlGaAs is thus a very promising materials system for design of an upper mm-wave, zero-bias, square-law detector with a significantly reduced noise floor.

Fabrication of 40 Gb/s Front-End Optical Receivers Using Spot-Size Converter Integrated Waveguide Photodiodes

Abstract: We fabricated 40 Gb/s front-end optical receivers using spot-size converter integrated waveguide photodiodes (SSC-WGPDs). The fabricated SSC-WGPD chips showed a high responsivity of approximately 0.8 A/W and a 3 dB bandwidth of approximately 40 GHz. A selective wetetching method was first adopted to realize the required width and depth of a tapered waveguide. Two types of electrical pre-amplifier chips were used in our study. One has higher gain and the other has a broader bandwidth. The 3 dB bandwidths of the higher gain and broader bandwidth modules were about 32 and 42 GHz, respectively. Clear 40 Gb/s non-return-to-zero (NRZ) eye diagrams showed good system applicability of these modules.

Response of a SiC photodiode to extreme ultraviolet through visible radiation.

Abstract: The responsivity of a type 6H-SiC photodiode in the 1.5-400 nm wavelength range was measured using synchrotron radiation. The responsivity was 0.20 A/W at 270 nm and was less than 0.10 A/W in the extreme ultraviolet (EUV) region. The responsivity was calculated using a proven optical model that accounted for the reflection and absorption of the incident radiation and the variation of the charge collection efficiency (CCE) with depth into the device. The CCE was determined from the responsivity measured in the 200-400 nm wavelength range. By use of this CCE and the effective pair creation energy (7.2 eV) determined from x-ray absorption measurements, the EUV responsivity was accurately modeled with no free parameters. The measured visible-light sensitivity, although low compared with that of a silicon photodiode, was surprisingly high for this wide bandgap semiconductor.

High bandwidth-efficiency solar-blind AlGaN Schottky photodiodes with low dark current

Abstract: Al 0.38 Ga 0.62 N/GaN heterojunction solar-blind Schottky photodetectors with low dark current, high responsivity, and fast pulse response were demonstrated. A five-step microwave compatible fabrication process was utilized to fabricate the devices. The solar-blind detectors displayed extremely low dark current values: 30 μm diameter devices exhibited leakage current below 3 fA under reverse bias up to 12 V. True solar-blind operation was ensured with a sharp cut-off around 266 nm. Peak responsivity of 147 mA/W was measured at 256 nm under 20 V reverse bias. A visible rejection more than 4 orders of magnitude was achieved. The thermally-limited detectivity of the devices was calculated as 1.8 × 10 13 cm Hz 1/2 W −1 . Temporal pulse response measurements of the solar-blind detectors resulted in fast pulses with high 3-dB bandwidths. The best devices had 53 ps pulse-width and 4.1 GHz bandwidth. A bandwidth-efficiency product of 2.9 GHz was achieved with the AlGaN Schottky photodiodes.