Showing papers on "Responsivity published in 2012"

Hybrid graphene-quantum dot phototransistors with ultrahigh gain

Abstract: A phototransistor in which electric charges are absorbed by colloidal quantum dots and circulated in graphene exhibits high values for gain, responsivity and specific detectivity.

Microcavity-Integrated Graphene Photodetector

Abstract: There is an increasing interest in using graphene(1, 2) for optoelectronic applications.(3-19) However, because graphene is an inherently weak optical absorber (only ≈2.3% absorption), novel concepts need to be developed to increase the absorption and take full advantage of its unique optical properties. We demonstrate that by monolithically integrating graphene with a Fabry-Perot microcavity, the optical absorption is 26-fold enhanced, reaching values >60%. We present a graphene-based microcavity photodetector with responsivity of 21 mA/W. Our approach can be applied to a variety of other graphene devices, such as electro-absorption modulators, variable optical attenuators, or light emitters, and provides a new route to graphene photonics with the potential for applications in communications, security, sensing and spectroscopy.

Infrared Photodetectors Based on CVD-Grown Graphene and PbS Quantum Dots with Ultrahigh Responsivity

Abstract: 12 ] Therefore, graphene-based IR detectors have much lower responsivities than photoconductors based on QDs. It is reasonable to consider that the responsivity of a graphene-based IR detector can be improved substantially by modifying the graphene fi lm with QDs, which can absorb IR light more effi ciently. On the other hand, if the carriers gener-ated by IR light can transfer to the graphene fi lm, their mobility will be much higher and thus the responsivity will be dramati-cally improved for a QD-based IR detector. Moreover, an array of graphene devices can be easily patterned by state-of-the-art techniques and this could possibly lead to elimination of the crosstalk between neighboring pixels that occur in silicon devices.

Zero-bias 40Gbit/s germanium waveguide photodetector on silicon.

Abstract: We report on lateral pin germanium photodetectors selectively grown at the end of silicon waveguides. A very high optical bandwidth, estimated up to 120GHz, was evidenced in 10 µm long Ge photodetectors using three kinds of experimental set-ups. In addition, a responsivity of 0.8 A/W at 1550 nm was measured. An open eye diagrams at 40Gb/s were demonstrated under zero-bias at a wavelength of 1.55 µm.

A 1 k-Pixel Video Camera for 0.7–1.1 Terahertz Imaging Applications in 65-nm CMOS

Abstract: A 1 k-pixel camera chip for active terahertz video recording at room-temperature has been fully integrated in a 65-nm CMOS bulk process technology. The 32 × 32 pixel array consists of 1024 differential on-chip ring antennas coupled to NMOS direct detectors operated well-beyond their cutoff frequency based on the principle of distributed resistive self-mixing. It includes row and column select and integrate-and-dump circuitry capable of capturing terahertz videos up to 500 fps. The camera chip has been packaged together with a 41.7-dBi silicon lens (measured at 856 GHz) in a 5 × 5 × 3 cm3 camera module. It is designed for continuous-wave illumination (no lock-in technique required). In this video-mode the camera operates up to 500 fps. At 856 GHz it achieves a responsivity Rv of about 115 kV/W (incl. a 5-dB VGA gain) and a total noise equivalent power (NEPtotal) of about 12 nW integrated over its 500-kHz video bandwidth. At a 5-kHz chopping frequency (non-video mode) a single pixel can provide a maximum responsivity Rv of 140 kV/W (incl. a 5-dB VGA gain) and a minimum noise equivalent power ( NEP) of 100 pW/√Hz at 856 GHz. The wide-band antenna and pixel design achieves a 3-dB bandwidth of at least 790-960 GHz.

Realization of a high-performance GaN UV detector by nanoplasmonic enhancement

Abstract: Realization of highly responsivity UV detectors is a critical challenge for accelerating the application of UV detectors. Exploiting nanoplasmonic enhancement, Ag nanoparticles have been formed on the GaN surface and the responsivity of the GaN UV detector has been enhanced about 30 times compared with that without Ag nanoparticles.

CMOS Integrated Antenna-Coupled Field-Effect Transistors for the Detection of Radiation From 0.2 to 4.3 THz

Abstract: This paper reports on field-effect-transistor-based terahertz detectors for the operation at discrete frequencies spanning from 0.2 to 4.3 THz. They are implemented using a 150-nm CMOS process technology, employ self-mixing in the n-channels of the transistors and operate well above the transistors' cutoff frequency. The theoretical description of device operation by Dyakonov and Shur is extended in order to describe the device impedance, responsivity, and noise-equivalent power for a novel detection concept, which couples the signal to the drain. This approach enables quasi-static (QS) detection and calibration of the detectors. The different transport regimes (i.e., QS, distributed resistive, and plasmonic mixing) and their transitions are theoretically discussed and experimentally accessed. Responsivity values of 350 V/W at 595 GHz, 30 V/W at 2.9 THz, and 5 V/W at 4.1 THz are reported. At 0.595 THz, we determine the optical noise equivalent power (NEP) to be 42 pW/√Hz ; at 2.9 THz, the value is 487 pW/√Hz. All values are reported for optimum gate bias with respect to NEP at 295 K. For 0.595 THz, theory predicts a NEP value at threshold as low as 2 pW/√Hz for ideal coupling of the radiation.

GeSn/Ge heterostructure short-wave infrared photodetectors on silicon

Abstract: A surface-illuminated photoconductive detector based on Ge0.91Sn0.09 quantum wells with Ge barriers grown on a silicon substrate is demonstrated. Photodetection up to 2.2µm is achieved with a responsivity of 0.1 A/W for 5V bias. The spectral absorption characteristics are analyzed as a function of the GeSn/Ge heterostructure parameters. This work demonstrates that GeSn/Ge heterostructures can be used to developed SOI waveguide integrated photodetectors for short-wave infrared applications.

Waveguide based compact silicon Schottky photodetector with enhanced responsivity in the telecom spectral band

Abstract: We experimentally demonstrate an on-chip compact and simple to fabricate silicon Schottky photodetector for telecom wavelengths operating on the basis of internal photoemission process. The device is realized using CMOS compatible approach of local-oxidation of silicon, which enables the realization of the photodetector and low-loss bus photonic waveguide at the same fabrication step. The photodetector demonstrates enhanced internal responsivity of 12.5mA/W for operation wavelength of 1.55µm corresponding to an internal quantum efficiency of 1%, about two orders of magnitude higher than our previously demonstrated results [22]. We attribute this improved detection efficiency to the presence of surface roughness at the boundary between the materials forming the Schottky contact. The combination of enhanced quantum efficiency together with a simple fabrication process provides a promising platform for the realization of all silicon photodetectors and their integration with other nanophotonic and nanoplasmonic structures towards the construction of monolithic silicon opto-electronic circuitry on-chip.

GeSn p-i-n detectors integrated on Si with up to 4% Sn

Abstract: GeSn heterojunction photodetectors on Si substrates were grown with Sn concentration up to 4%, fabricated for vertical light incidence, and characterized. The complete layer structure was grown by means of ultra low temperature (100 °C) molecular beam epitaxy. The Sn content shifts the responsivity into the infrared, about 310 nm for the 4% Sn sample. An increase of the optical responsivity for wavelengths higher than 1550 nm can be observed with increasing Sn content. At 1600 nm, the optical responsivity is increased by more than a factor of 10 for the GeSn diode with 4% Sn in comparison to the Ge reference diode.

Room-temperature photodetection dynamics of single GaN nanowires.

Abstract: We report on the photocurrent behavior of single GaN n–i–n nanowires (NWs) grown by plasma-assisted molecular-beam epitaxy on Si(111). These structures present a photoconductive gain in the range of 105–108 and an ultraviolet (350 nm) to visible (450 nm) responsivity ratio larger than 6 orders of magnitude. Polarized light couples with the NW geometry with a maximum photoresponse for polarization along the NW axis. The photocurrent scales sublinearly with optical power, following a I ∼ Pβ law (β < 1) in the measured range with β increasing with the measuring frequency. The photocurrent time response remains in the millisecond range, which is in contrast to the persistent (hours) photoconductivity effects observed in two-dimensional photoconductors. The photocurrent is independent of the measuring atmosphere, either in the air or in vacuum. Results are interpreted taking into account the effect of surface states and the total depletion of the NW intrinsic region.

Long-wave infrared nBn photodetectors based on InAs/InAsSb type-II superlattices

Abstract: Long-wave infrared InAs/InAsSb type-II superlattice nBn photodetectors are demonstrated on GaSb substrates. The typical device consists of a 2.2 μm thick absorber layer and has a 50% cutoff wavelength of 13.2 μm, a measured dark current density of 5 × 10−4 A/cm2 at 77 K under a bias of −0.3 V, a peak responsivity of 0.24 A/W at 12 μm, and a maximum resistance-area product of 300 Ω cm2 at 77 K. The calculated generation-recombination noise limited specific detectivity (D*) and experimentally measured D* at 12 μm and 77 K are 1 × 1010 cm Hz1/2/W and 1 × 108 cm Hz1/2/W, respectively.

Wavelength selective uncooled infrared sensor by plasmonics

Abstract: A wavelength selective uncooled infrared (IR) sensor using two-dimensional plasmonic crystals (2D PLCs) has been developed. The numerical investigation of 2D PLCs demonstrates that the wavelength of absorption can be mainly controlled by the period of the surface structure. A microelectromechanical systems-based uncooled IR sensor with 2D PLCs as the IR absorber was fabricated through a complementary metal oxide semiconductor and a micromachining technique. The selective enhancement of responsivity was observed at the wavelength that coincided with the period of the 2D-PLC absorber.

High responsivity ZnO nanowires based UV detector fabricated by the dielectrophoresis method

Abstract: ZnO nanowires UV photodetectors with different interdigital electrode distances were fabricated by using a dielectrophoresis method in this work. The multiple horizontal nanowires array integrated that photodetectors were composed by lots of paralleled ZnO nanowires. Experimental results showed the responsivity of the detector with the electrode distance of 6.5 mu m could reach 40 A/W at 10V bias. It was also observed that the rising and decaying stages of the time-resolve photocurrent were both two processes, which was possibly attributed to the relaxation processes of the surface states and the deep level traps. (C) 2011 Elsevier B.V. All rights reserved.

High Efficiency Si/CdS Radial Nanowire Heterojunction Photodetectors Using Etched Si Nanowire Templates

Abstract: p-Si/n-CdS radial heterojunction nanowires have been grown by pulse laser deposition of CdS on vertically aligned Si nanowires fabricated using a room temperature wafer-scale etching of p-type Si. Temperature-dependent photoluminescence characteristics have been studied in detail in the blue–green–red regions from these p-Si/n-CdS core–shell nanowires. The photocurrent spectra of the nanowire heterojunctions have been investigated at room temperature to study the spectral responsivity and detectivity of the core–shell nanowire diodes. The peak responsivity (1.37 A/W) and detectivity (4.39 × 1011 cm Hz1/2/W) at −1 V show the potential of the nanoscaled devices for the high efficiency photodetectors in the visible–near-infrared spectrum.

Double graphene-layer plasma resonances terahertz detector

Abstract: We propose a detector of terahertz radiation based on a double graphene-layer heterostructure utilizing the tunnelling between graphene layers and the resonant excitation of plasma oscillations (standing plasma waves). Using the developed device model, we substantiate the detector operation and calculate the spectral characteristics. It is shown that the detector responsivity exhibits the resonant peaks when the frequency of incoming terahertz radiation approaches the resonant plasma frequencies. These frequencies are tuned by the bias voltage. The height of the responsivity resonant peaks in sufficiently perfect double graphene-layer heterostructures can markedly exceed those in the resonant plasma–wave detectors based on the standard heterostructures and utilizing the plasma hydrodynamic nonlinearity.

Carbon nanotube arrays based high-performance infrared photodetector [Invited]

Abstract: The carbon nanotubes (CNTs) are an ideal material for infrared applications due to its excellent electronic and optoelectronic properties, suitable bandgap, mechanical and chemical stabilities. In this paper, we demonstrate a photovoltaic infrared detector which is based on aligned single-walled CNT (SWCNT) arrays. The device is fabricated by asymmetrically contacting the two ends of the SWCNT arrays with Pd and Sc of different work functions, which are known to form ohmic contacts with the valence and conduction bands of semiconducting SWCNTs respectively. The device is characterized at room temperature, exhibiting excellent diode characteristics, high responsivity of 9.87 × 10−5 A/W and infrared spectral detectivity of 1.09 × 107 cmHz1/2/W. The demonstration of the SWCNT arrays based infrared detector which is fabricated using a doping-free process paves the way to applications of CNT in such field as high-performance infrared sensors.

Tuning the Photoresponse in Organic Field-Effect Transistors

Abstract: We report on the fabrication of solution-processed organic phototransistors (OPTs) based on perylenebis(dicarboximide)s (PDIs). We found that the responsivity to the photoillumination depends on the transistor’s channel length and that it can be tuned by varying the device geometry. The analysis of different morphologies of the active semiconducting layer revealed that single PDI fibers exhibit the higher photoresponse when compared to more poorly organized films. The highest responsivity value of 4.08 ± 1.65 × 105 A/W was achieved on a multifiber-based OPT. These findings represent a step forward toward the use of organic based phototransistors as photosensors.

High-responsivity, low-noise, room-temperature, self-mixing terahertz detector realized using floating antennas on a GaN-based field-effect transistor

Abstract: Using only optical lithography, we have fabricated a GaN/AlGaN high-electron mobility transistor with distinctive source and drain antennas electrically isolated from the electron channel. Working at room temperature, it efficiently detects terahertz radiation via self-mixing, with a responsivity (3.6 kV/W) exceptionally high for a III-V device and with a noise (40 pW / ) just above the thermal limit. Performance improves at 77 K. While the device itself is micrometer-sized, our modeling indicates the asymmetric antennas induce a rather localized (<200 nm) region of strong self-mixing. Thus, a nanometer-scale active region is achieved by design and without recourse to electron-beam lithography

Continuous Wave Terahertz Generation From Ultra-Fast InP-Based Photodiodes

Abstract: We present theoretical analysis and experimental results for an optimized Traveling Wave Uni-Traveling Carrier Photodiode for continuous wave millimeter-wave and Terahertz generation. The devices employed a mode-converting waveguide for efficient coupling from a lensed fiber. A DC responsivity of 0.53 A/W at a wavelength of 1.55 μm and 3-dB electrical bandwidth of 108 GHz were obtained from temperature-controlled coplanar waveguide-integrated devices together with record levels of power from a photomixer in the millimeter-wave range with 1 mW at 200 GHz. High levels of Terahertz output power from broadband, heat sink-mounted antenna-integrated devices were measured with 5 μW at 1.02 THz.

In-doped Ga2O3 nanobelt based photodetector with high sensitivity and wide-range photoresponse

Abstract: Doping is an efficient way to tune the electrical and photoelectrical performances of one-dimensional semiconductors which have potential application as active materials in high performance nanoscale devices. Ga2O3 is one the most promising 1D semiconducting systems. However, controlled doping of Ga2O3 toward higher photoelectrical performances in Ga2O3-based photodetectors remains problematic. Herein high-quality In-doped Ga2O3 nanobelts are fabricated through a facile and effective thermal evaporation process. Their morphology and structure are systematically characterized. Indium has successfully been doped into the Ga2O3 nanobelts based on the data obtained. The In-doped Ga2O3 nanobelt-based photodetector has shown a higher sensitivity (9.99 × 104%), responsivity (5.47 × 102 A W−1), quantum efficiency (2.72 × 105%) and less rise/decay time (1/0.6 s), i.e. much better figures compared with not only the undoped Ga2O3 nanobelt/film but also other reported doped photodetectors. In addition, the above photodetector has a wider range photoresponse. In doping has led to significant improvements in the values of key parameters of the Ga2O3-based photodetector, beneficial for the fabrication of high-performance photodetectors.

An improved model for non-resonant terahertz detection in field-effect transistors

Abstract: Transistors operating well above the frequencies at which they have gain can still rectify terahertz currents and voltages, and have attracted interest as room-temperature terahertz detectors. We show that such rectifying field-effect transistors may still be treated as a lumped element device in the limit where plasma resonances of the electron gas do not occur. We derive analytic formulas for important transistor parameters, such as effective rectification length and device impedance using a transmission-line model. We draw conclusions for plasma-resonant detection where possible. We derive the THz response of a field-effect transistor with a two-dimensional electron-gas channel by a Taylor expansion of the drain–source bias. We connect circuit theory to the existing theories that describe the bias in the gated region by differential equations. Parasitic effects, such as the access resistance, are included. With the approach presented in this paper, we derive the responsivity for a novel field detector ...

310 GHz gain-bandwidth product Ge/Si avalanche photodetector for 1550 nm light detection.

Abstract: We report a normal incidence Ge/Si avalanche photodiode with separate-absorption-charge-multiplication (SACM) structure by selective epitaxial growth. By proper design of charge and multiplication layers and by optimizing the electric field distribution in the depletion region to eliminate germanium impact-ionization at high gain, a high responsivity of 12 A/W and a large gain-bandwidth product of 310 GHz have been achieved at 1550 nm.

280GHz and 860GHz image sensors using Schottky-barrier diodes in 0.13μm digital CMOS

Abstract: Millimeter and sub-millimeter-wave imaging using solid-state circuits is gaining attention for security and medical applications. To lower cost and increase integration, MOSFETs in CMOS are being investigated for implementing broadband detectors [1–3]. However, neither measured noise-equivalent power (NEP) nor noise floor of the imager was given in [1]. Although NEP of 17pW/Hz1/2 was achieved at 650GHz in [2], an external lens was attached to the 65nm SOI CMOS chip. In [3], an NEP of 66pW/Hz1/2 was measured at 1.05THz using 65nm CMOS without a lens attached to the chip. Additionally, although the efforts reported in [1–3] realized an array, none demonstrated the image-array function. As an alternative, polysilicon-gate-separation (PGS) Schottky-barrier diodes (SBD) with cut-off frequency of ∼2THz were fabricated in CMOS without process modifications [4] and were used to demonstrate a 280GHz detector with NEP of 30pW/Hz1/2 [5,6]. To significantly enhance the scanning speed, a 16-pixel 280GHz SBD imager is fabricated and its array function is reported in this paper. The imager including baseband amplifiers achieves responsivity of 5.1kV/W and NEP of 29pW/Hz1/2. More importantly, its operation was demonstrated in a setup that requires no mirror or lens that is bulky and costly. Next, an 860GHz SBD detector is demonstrated with a measured non-amplified responsivity of 355V/W and NEP of 32pW/Hz1/2. This NEP is ∼2X lower than the best reported work in CMOS [3]. Both chips are fabricated in a 0.13μm logic CMOS. The results suggest a path for high performance, compact and affordable sub-millimeter-wave and terahertz CMOS imagers using SBDs.

Microelectromechanical systems bimaterial terahertz sensor with integrated metamaterial absorber

Abstract: This Letter describes the fabrication of a microelectromechanical systems (MEMS) bimaterial terahertz (THz) sensor operating at 3.8 THz. The incident THz radiation is absorbed by a metamaterial structure integrated with the bimaterial. The absorber was designed with a resonant frequency matching the quantum cascade laser illumination source while simultaneously providing structural support, desired thermomechanical properties and optical readout access. Measurement showed that the fabricated absorber has nearly 90% absorption at 3.8 THz. A responsivity of 0.1°/μW and a time constant of 14 ms were observed. The use of metamaterial absorbers allows for tuning the sensor response to the desired frequency to achieve high sensitivity for potential THz imaging applications.

$D$ -Band Total Power Radiometer Performance Optimization in an SiGe HBT Technology

Abstract: A D-band SiGe HBT total power radiometer is reported with a peak responsivity of 28 MV/W, a noise equivalent power (NEP) of 14-18 fW/Hz1/2, and a temperature resolution better than 0.35 K for an integration time of 3.125 ms. The 1/f noise corner of the radiometer is lower than 200 Hz. Fabricated in a developmental technology with 270-GHz fT and 330-GHz/max, it includes a five-stage low-noise amplifier (LNA) with 4-7-GHz bandwidth and over 35 dB of gain centered at 165 GHz, along with a square-law detector with an NEP below 6 pW/Hz1/2 up to 170 GHz. An average system noise temperature of 1645 K is obtained using the Y-factor method and a noise bandwidth of 10 GHz calculated from the measured S21(f) characteristics of the radiometer. The reduced 1/f noise corner frequency in the presence of the amplifier, compared to that of the detector, appears to indicate that, unlike in III-V radiometers, LNA gain fluctuations are not a problem in SiGe HBT radiometers. The circuit consumes 95 mW and occupies 765 × 490 μm2. Wafer mapping of the radiometer sensitivity and of the amplifier gain was performed across different process splits. The mapping results demonstrate that the radiometer can be employed as a relatively simple and area-efficient transistor noise-measure monitor, useful in SiGe HBT vertical profile optimization.

10-Gb/s 850-nm CMOS OEIC Receiver With a Silicon Avalanche Photodetector

Abstract: We present a 10-Gb/s optoelectronic integrated circuit (OEIC) receiver fabricated with standard 0.13-μm complementary metal-oxide-semiconductor (CMOS) technology for 850-nm optical interconnect applications. The OEIC receiver consists of a CMOS-compatible avalanche photodetector (CMOS-APD), a transimpedance amplifier (TIA), an offset cancellation network, a variable equalizer (EQ), a limiting amplifier (LA), and an output buffer. The CMOS-APD provides high responsivity as well as large photodetection bandwidth. The TIA is composed of two-stage differential amplifiers with high feedback resistance of 4 kΩ. The EQ compensates high-frequency loss by controlling the boosting gain with a capacitor array. The LA consists of five-stage gain cells with active feedback and negative capacitance to achieve broadband performance. With the OEIC receiver, we successfully demonstrate transmission of 10-Gb/s optical data at 850 nm with a bit error rate of 10-12 at the incident optical power of -4 dBm. The OEIC receiver has the core chip area of about 0.26 mm2 and consumes about 66.8 mW.

Ultrahigh sensitive plasmonic terahertz detector based on an asymmetric dual-grating gate HEMT structure

Abstract: We report on ultrahigh sensitive, broadband terahertz (THz) detectors based on asymmetric dual-grating-gate (A-DGG) high electron mobility transistors, demonstrating a record responsivity of 2.2 kV/W at 1 THz with a superior low noise equivalent power of 15 pW/√Hz using InGaAs/InAlAs/InP material systems. When THz radiation is absorbed strong THz photocurrent is first generated by the nonlinearity of the plasmon modes resonantly excited in undepleted portions of the 2D electron channel under the high-biased sub-grating of the A-DGG (as a quadratic nature of the product of local carrier density and velocity perturbations), then the THz photovoltaic response is read out at high-impedance parts of 2D channel under the other sub-grating biased at the level close to the threshold. Extraordinary enhancement by more than two orders of magnitude of the responsivity is verified with respect to that for a symmetric DGG structure.

High responsivity of amorphous indium gallium zinc oxide phototransistor with Ta2O5 gate dielectric

Abstract: This study investigates the electrical performance of amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) with a Ta2O5 gate dielectric under monochromatic illumination. The relationship between the phototransistor performance and oxygen partial pressure is determined. The oxygen content of the a-IGZO channel significantly affects the electrical and optical characteristics of a-IGZO TFTs. At applied gate biases of 0, 0, and 0.25 V, oxygen partial pressures of 0%, 0.1%, and 0.2% yielded measured device responsivities of 0.23, 0.44, and 4.75 A/W, respectively. Oxygen content can be used to control the mobility of TFTs, which can amplify photocurrent and enhance the responsivity of a-IGZO TFTs with a Ta2O5 gate dielectric.

Far-infrared intersubband photodetectors based on double-step III-nitride quantum wells

Abstract: Far-infrared photoconductive detectors based on intersubband transitions in III-nitride semiconductor quantum wells are demonstrated. The device active material is based on a double-step quantum-well design, where two different (Al)GaN compositions are used both in the wells and in the barriers. With this approach, one can create a virtually flat multiple-quantum-well potential energy profile, where the deleterious effects of the intrinsic spontaneous and piezoelectric fields of nitride heterostructures are almost completely eliminated. Photocurrent spectra centered at a wavelength of 23 μm (13 THz frequency) are resolved up to 50 K, with responsivity of approximately 7 mA/W.