Browsing by Subject "Detectivity"

Filter results by typing the first few letters
Now showing 1 - 10 of 10
  • Thumbnail Image
    ItemOpen Access
    AlxGa1-xN-based avalanche photodiodes with high reproducible avalanche gain
    (2008) Tut, Turgut; Gökkavas, Mutlu; Özbay, Ekmel
    We report high performance solar-blind photodetectors with reproducible avalanche gain as high as 1570 under ultraviolet illumination. The solar-blind photodetectors have a sharp cut-off around 276 nm. The dark currents of the 40 μm diameter devices are measured to be lower than 8 femto-amperes for bias voltages up to 20 V. The responsivity of the photodetectors is 0.13 A/W at 272 nm under 20 V reverse bias. The thermally limited detectivity is calculated as D* = 1.4 × 1014 cm Hz1/2 W-1 for a 40 μm diameter device. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.
  • Thumbnail Image
    ItemOpen Access
    Analytic thermal modeling for dc to midrange modulation frequency response for thin film high-Tc superconductive edge-transition bolometers
    (OSA Publishing, 2001-03-01) Fardmanesh, M.
    Thin-film superconductive edge-transition bolometers are modeled with a one-dimensional analytic thermal model with joule heating, film and substrate materials, and the physical interface effects taken into consideration. The results from the model agree well with the experimental results of samples made of large-meander-line Yba(2)Cu(3)O(7-x) films on crystalline SrTiO3, LaAlO3, and MgO substrates up to 100 kHz, the limits of the experimental setup. Compared with the results of the SrTiO3 substrate samples, the results from the model of the LaAlO3 and the MgO substrate samples deviate slightly from the measured values at very low modulation frequencies (below similar to 10 Hz). The deviation increases for higher thermal-conductive substrate materials. When the model was used, the substrate absorption and the thermal parameters of the devices could also be investigated. (C) 2001 Optical Society of America
  • Thumbnail Image
    ItemOpen Access
    Atomic layer deposited Al 2O 3 passivation of type II InAs/GaSb superlattice photodetectors
    (AIP, 2012) Salihoğlu, Ömer; Muti, Abdullah; Kutluer, Kutlu; Tansel, T.; Turan, R.; Kocabaş, Coşkun; Aydınlı, Atilla
    Taking advantage of the favorable Gibbs free energies, atomic layer deposited (ALD) aluminum oxide (Al 2O 3) was used as a novel approach for passivation of type II InAs/GaSb superlattice (SL) midwave infrared (MWIR) single pixel photodetectors in a self cleaning process (λ cut-off ∼ 5.1 m). Al 2O 3 passivated and unpassivated diodes were compared for their electrical and optical performances. For passivated diodes, the dark current density was improved by an order of magnitude at 77 K. The zero bias responsivity and detectivity was 1.33 A/W and 1.9 × 10 13 Jones, respectively at 4μm and 77 K. Quantum efficiency (QE) was determined as 41 for these detectors. This conformal passivation technique is promising for focal plane array (FPA) applications. © 2012 American Institute of Physics.
  • Thumbnail Image
    ItemOpen Access
    Design, fabrication and characterization of high-performance solarblind AlGaN photodetectors
    (SPIE, 2005) Özbay, Ekmel
    Design, fabrication, and characterization of high-performance AlxGal-xN-based photodetectors for solar-blind applications are reported. AlxGal-xN heterostructures were designed for Schottky, p-i-n, and metal-semiconductor-metal (MSM) photodiodes. The resulting solar-blind AlGaN detectors exhibited low dark current, high detectivity, and high bandwidth.
  • Thumbnail Image
    ItemOpen Access
    High-performance AlxGA1-xN-Based UV photodetectors for visible/solar-blind applications
    (2004) Bıyıklı, Necmi
    High-performance detection of ultraviolet (UV) radiation is of great importance for a wide range of applications including flame sensing, environmental (ozone layer) monitoring, detection of biological/chemical agents, missile early warning systems, and secure intersatellite communication systems. These applications require high-performance UV photodetectors with low dark current, high responsivity, high detectivity, and fast time response. The widebandgap AlxGa1−xN ternary alloy is well-suited as a photodetector material for operation in the wavelength range of 200 nm to 365 nm. Its outstanding material properties (direct bandgap, tunable cut-off, allows heterostructures, intrinsically solar-blind) make AlxGa1−xN suitable for a variety of harsh environments. If properly constructed, AlxGa1−xN-based photodetectors could offer significant advantages over the older photomultiplier tube (PMT) technology in terms of size, cost, robustness, complexity, dark current, bandwidth, and solar-blind operation. The motivation behind this work is the need for high-performance, solid-state UV photodetectors that can be cost-effectively manufactured into high-density arrays. We have designed, fabricated, and characterized several visible/solar-blind AlxGa1−xN photodiode samples. With solar-blind AlxGa1−xN photodiode samples, we achieved excellent device performance in almost all aspects. Very low dark currents were measured with heterostructure AlxGa1−xN Schottky and p-i-n samples. The extremely low leakage characteristics resulted in record detectivity and noise performance. Detectivity performance comparable to PMT detectivity was achieved. True solar-blind operation (sub-280 nm cut-off) with high visible rejection was demonstrated. In addition, we improved the bandwidth performance of AlxGa1−xN-based solar-blind photodetectors by over an order of magnitude. Solar-blind Schottky, p-i-n, and metal-semiconductor-metal photodiode samples exhibited very fast pulse response with multi-GHz bandwidths.
  • Thumbnail Image
    ItemOpen Access
    High-performance solar-blind AlGaN photodetectors
    (SPIE, 2005) Özbay, Ekmel; Tut, Turgut; Bıyıklı, N.
    Design, fabrication, and characterization of high-performance Al xGa1-xN-based photodetectors for solar-blind applications are reported. AlxGa1-xN heterostructures were designed for Schottky, p-i-n, and metal-semiconductor-metal (MSM) photodiodes. The solar-blind photodiode samples were fabricated using a microwave compatible fabrication process. The resulting devices exhibited extremely low dark currents. Below 3 fA leakage currents at 6 V and 12 V reverse bias were measured on p-i-n and Schottky photodiode samples respectively. The excellent current-voltage (I-V) characteristics led to a detectivity performance of 4.9×1014 cmHz1/2W-1. The MSM devices exhibited photoconductive gain, while Schottky and p-i-n samples displayed 0.15 A/W and 0.11 A/W peak responsivity values at 267 nm and 261 nm respectively. All samples displayed true solar-blind response with cut-off wavelengths smaller than 280 nm. A visible rejection of 4×104 was achieved with Schottky detector samples. High speed measurements at 267 nm resulted in fast pulse responses with >GHz bandwidths. The fastest devices were MSM photodiodes with a maximum 3-dB bandwidth of 5.4 GHz.
  • Thumbnail Image
    ItemOpen Access
    High-performance solar-blind photodetectors based on AlxGa 1_xN heterostructures
    (IEEE, 2004) Özbay, Ekmel; Bıyıklı, Necmi; Kimukin, I.; Kartaloglu, T.; Tut, T.; Aytür, O.
    Design, fabrication, and characterization of high-performance AI xGa1-xN-based photodetectors for solar-blind applications are reported. AlxGa1-xN heterostructures were designed for Schottky. p-i-n, and metal-semicondnctor-metal (MSM) photodiodes. The solar-blind photodiode samples were fabricated using a microwave compatible fabrication process. The resulting devices exhibited extremely low dark currents. Below 3 fA, leakage currents at 6-V reverse bias were measured on p-i-n samples. The excellent current-voltage (I-V) characteristics led to a detectivity performance of 4.9×1014 cmHz1/2W -1. The MSM devices exhibited photoconductive gain, while Schottky and p-i-n samples displayed 0.09 and 0.11 A/W peak responsivity values at 267 and 261 nm, respectively. A visible rejection of 2×104 was achieved with Schottky samples. High-speed measurements at 267 nm resulted in fast pulse responses with greater than gigahertz bandwidths. The fastest devices were MSM photodiodes with a maximum 3-dB bandwidth of 5.4 GHz.
  • Thumbnail Image
    ItemOpen Access
    Investigation of bias current and modulation frequency dependences of detectivity of YBCO TES and the effects of coating of Cu-C composite absorber layer
    (2009) Moftakharzadeh, A.; Kokabi, A.; Bozbey, A.; Ghodselahi, T.; Vesaghi, M.A.; Khorasani, S.; Banzet, M.; Schubert J.; Fardmanesh, M.
    Bolometric response and noise characteristics of YBCO superconductor transition edge IR detectors with relatively sharp transition and its resulting detectivity are investigated both theoretically and experimentally. The magnitude of response of a fabricated device was obtained for different bias currents and modulation frequencies. Using the measured and calculated bolometric response and noise characteristics, we found and analyzed the device detectivity versus frequency for different bias currents. The detectivity versus chopping frequency of the device did not decrease following the response strongly, due to the decrease of the noise at higher frequencies up to 1 kHz, resulting in maximum detectivity around the modulation frequency of 100 Hz. We also improved the responsivity of the device through the increase of the surface absorption by using a novel infrared absorber, which is made of a copper-carbon composite, coated in a low-temperature process. Within the modulation frequency range studied in this paper, comparison of device detectivity before and after coating is also presented. © 2009 IEEE.
  • Thumbnail Image
    ItemOpen Access
    Skin-like self-assembled monolayers on InAs / GaSb superlattice photodetectors
    (IOP Institute of Physics Publishing, 2012) Salihoglu, O.; Muti, A.; Kutluer, K.; Tansel, T.; Turan, R.; Aydınlı, Atilla
    We report on the effects of monolayer (ML) thick skin-like octadecanethiol (ODT, CH 3[CH 2] 17SH) on type-II InAs/GaSb MWIR photodetectors. Circumventing the ageing effects of conventional sulfur compounds, we use ODT, a self-assembling, long molecular chain headed with a sulfur atom. Photodiodes coated with and without the self-assembled monolayer (SAM) ODT were compared for their electrical and optical performances. For ODT-coated diodes, the dark current density was improved by two orders of magnitude at 77K under 100mV bias. The zero bias responsivity and detectivity were 1.04AW 1 and 2.15 × 10 13 Jones, respectively, at 4μm and 77K. The quantum efficiency was determined to be 37% for a cutoff wavelength of 5.1μm.
  • Thumbnail Image
    ItemOpen Access
    Solar-blind AlGaN-based Schottky photodiodes with low noise and high detectivity
    (American Institute of Physics, 2002) Bıyıklı, Necmi; Aytur, O.; Kimukin, I.; Tut, T.; Özbay, Ekmel
    We report on the design, fabrication, and characterization of solar-blind Schottky photodiodes with low noise and high detectivity. The devices were fabricated on n-/n+ AlGaN/GaN heterostructures using a microwave compatible fabrication process. True solar-blind operation with a cutoff wavelength of ∼274nm was achieved with AlxGa1-xN (x=0.38) absorption layer. The solar-blind detectors exhibited <1.8nA/cm2 dark current density in the 0-25 V reverse bias regime, and a maximum quantum efficiency of 42% around 267 nm. The photovoltaic detectivity of the devices were in excess of 2.6×1012cmHz1/2/W, and the detector noise was 1/f limited with a noise power density less than 3×10-29A2/Hz at 10 kHz. © 2002 American Institute of Physics.