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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Fast-timing microchannel plate photodetectors: design, fabrication and characterization

We report a detailed design, fabrication, and characterization of 6 x 6 cm(2) fast timing photodetectors based on next-generation microchannel plates (MCPs). The whole assembly is made of low-cost borosilicate glass materials and hermetically sealed with a bialkali photocathode in a vacuum. The flexible photodetector design provides the potential of modifying individual components as well as the entire configuration to fit for different applications. A series of prototype MCP-photodetectors were fabricated following a step-by-step process including functionalization of glass capillary array through atomic layer deposition, MCP baking and scrubbing, photocathode deposition, and hermetic thermo-compression sealing. The prototype MCP-photodetectors exhibit electron gains well beyond 107 level with good relative uniformity. An excellent rise time of 439 ps, timing distribution root-mean-square at a single photoelectron mode of 105 ps, a timing resolution of 20 ps, and magnetic field tolerance up to 1.3 T were achieved for a photodetector with 10 mu m pore size MCPs, comparing to that of 536 ps, 205 ps, 63 ps, and 0.7 T for the one with 20 mu m pore size MCPs. Published under license by AIP Publishing.

fast timing↗
DOE OSTI2015

Design and fabrication of prototype 6×6 cm 2 microchannel plate photodetector with bialkali photocathode for fast timing applications

Planar microchannel plate-based photodetector with bialkali photocathode is capable of fast and accurate time and position resolutions. A new 6 cm x 6 cm photodetector production facility was designed and built at Argonne National Laboratory. Small form-factor MCP-based photodetectors completely constructed of glass were designed and prototypes were successfully fabricated. Knudsen effusion cells were incorporated in the photocathode growth chamber to achieve uniform and high quantum efficiency hotocathodes. The thin film uniformity distribution was simulated and measured for an antimony film deposition, showing uniformity of better than 10%. Several prototype devices with bialkali photocathodes have been fabricated with the described system and their characteristics were evaluated in the large signal (multi-PE) limit. A typical prototype device exhibits time-of-flight resolution of ~ 27 psec and differential time resolution of ~ 9 psec, corresponding to spatial resolution of ~ 0.65 mm.

bialkali photocathode↗
DOE OSTI2014

Efficient Schottky-like junction GaAs nanowire photodetector with 9 GHz modulation bandwidth with large active area

Efficient, low capacitance density GaAs/Indium-Tin-Oxide Schottky-like junction photodetectors with a 50 μm square active are fabricated for operation in the gigahertz range. Modulation bandwidth is experimentally measured up to 10 GHz at various applied reverse biases and optical intensities to explore the effects of photo-generated carrier screening on modulation bandwidth. Last, the bandwidth dependence on applied reverse bias and optical intensity is simulated as a means to quantify average carrier velocities in nanowire material systems.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2022

A visible to near-infrared nanocrystalline organic photodetector with ultrafast photoresponse

Organic photoelectron conversion devices, due to their solution process and wide use in portable devices, have attracted intensive interest. In this work, a newly developed active layer of D18:Y6 is used to fabricate an organic photodetector and the device of ITO/PEDOT:PSS/D18:Y6/Phen-NaDPO/Ag shows a responsivity of 680 mA W –1 and a detectivity of 6.35 × 10 13 Jones (1 Jones = 1 cm Hz 1/2 W –1 ) at a wavelength of 850 nm. Additionally, this device shows a wide linear dynamic range of 120 dB, indicating a potential near-infrared region (NIR) detector system. Owing to the minimal exciton binding energy of 37.6 meV for Y6, a desirable energy offset for efficient electron–hole pair dissociation and an ultrafast charge transfer of ~58 ps at the interface of D18:Y6, the obtained organic photodetector has demonstrated a photoresponse time as fast as 1.8 μs upon laser light excitation without an external driven voltage. More importantly, D18 shows a preferred out-of-plane orientation with strong intensities and Y6 exhibits a preferred orientation along the in-plane direction on lamellar stacking, which facilitates charge transport. This work has demonstrated significant progress in exploring D18:Y6 NIR organic devices with a wide photosensitivity linearity and ultrafast photoresponse.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Visible-enhanced silver-doped PbI{sub 2} nanostructure/Si heterojunction photodetector: effect of doping concentration on photodetector parameters

This paper presents the effect of doping concentration on the properties of PbI{sub 2} nanostructure film and p-PbI{sub 2}:Ag/n-Si photodetector prepared by pulsed laser deposition PLD method. The PbI{sub 2} film was doped with silver at doping concentrations of 1%, 3% and 5%. XRD results show that all deposited PbI{sub 2} films are polycrystalline and well-crystallized along (001) plane with hexagonal structure. The structural studies revealed that the grain size of the film decreases as the doping concentration increase. Energy dispersive X-ray EDX, scanning electron microscope SEM and elemental mapping analysis confirm the presence of Pb, I and Ag elements and the films were near stoichiometric. Raman spectra of PbI{sub 2} film showed the presence of Raman peaks located at 73, 94.3, 108, 165.7, and 208.9 cm{sup −1} corresponding to E{sub 2}{sup 1}, A11, A{sub 1}{sup 2}, 2E{sub 1}{sup 1} and 2A{sub 1}{sup 2} vibration modes, respectively, and a Raman peak at 185 cm{sup −1} was observed for the film doped with 5 wt% which indexed to 2E{sub 1}{sup 1}. The optical energy gap of the film decreased from 2.8 to 2.3 eV after doping with silver. Hall measurement confirms that the deposited PbI{sub 2} films are p-type and the electrical resistivity of the film increases from 1.1 × 10{sup 4} to 1.8 × 10{sup 7} Ω cm as doping concentration increases from 1 to 5%.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Timing Characteristics of Large Area Picosecond Photodetectors

The LAPPD Collaboration was formed to develop ultralast large-area imaging photodetectors based on new methods for fabricating microchannel plates (MCPs). In this paper we characterize the time response using a pulsed, sub picosecond laser. We observe single photoelectron time resolutions of a 20 cm x 20 cm MCP consistently below 70 ps, spatial resolutions of roughly 500 pm, and median gains higher than 10(7). The RMS measured at one particular point on an LAPPD detector is 58 ps, with in of 47 ps. The differential time resolution between the signal reaching the two ends of the delay line anode is measured to be 5.1 ps for large signals, with an asymptotic limit falling below 2 ps as noise-over-signal approaches zero.

LAPPD↗
DOE OSTI2015

An Internal ALD-Based High Voltage Divider and Signal Circuit for MCP-based Photodetectors

We describe a pin-less design for the high voltage (HV) resistive divider of the all-glass LAPPD (TM) 8 in,square thin photodetector module. The divider, which distributes high voltage applied to the photocathode to the two micro-channel plates (MCPs) that constitute the amplification stage, is comprised of the two MCPs and three glass mechanical spacers, each of which is coated with a resistive layer using atomic layer deposition (ALD). The three glass grid spacers and the two MCPs form a continuous resistive path between cathode and anode, with the voltages across the MCPs and the spacers determined by the resistance of each. High voltage is applied on an external tab on the top glass window that connects to the photocathode through the metal seal. The DC ground is supplied by microstrips on the bottom glass plate that form the high-bandwidth anode. The microstrips exit the package through the glass-frit seal of the anode base-plate and the package sidewall. The divider is thus completely internal, with no HV pins penetrating the low-profile flat glass package. Measurements of the performance of the divider are presented for the 8 in.-square MCP and spacer package in a custom test fixture and for an assembled externally pumped LAPPD (TM) prototype with an aluminum photocathode. (C) 2015 Elsevier B.V. All rights reserved.

Adams, Bernhard W.↗
DOE OSTI2013

Large area, low capacitance, GaAs nanowire photodetector with a transparent Schottky collecting junction

We present experimental results on a GaAs/Indium-Tin-Oxide Schottky-like heterojunction photodetector based on a nanowire device geometry. By distributing the active detecting area over an array of nanowires, it is possible to achieve large area detection with low capacitance. Devices with bare GaAs and passivated AlGaAs/GaAs nanowires are fabricated to compare the responsivity with and without surface passivation. We are able to achieve responsivity of >0.5A/W and Signal-Noise-Ratio in excess of 7 dB for 2 V applied reverse bias with passivated nanowire devices. Capacitance-voltage measurement yields <5 nF/cm{sup 2}, which shows a strong possibility for high-speed applications with a broad area device.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Direct minority carrier transport characterization of InAs/InAsSb superlattice nBn photodetectors

We present an extensive characterization of the minority carrier transport properties in an nBn mid-wave infrared detector incorporating a Ga-free InAs/InAsSb type-II superlattice as the absorbing region. Using a modified electron beam induced current technique in conjunction with time-resolved photoluminescence, we were able to determine several important transport parameters of the absorber region in the device, which uses a barrier layer to reduce dark current. For a device at liquid He temperatures we report a minority carrier diffusion length of 750 nm and a minority carrier lifetime of 202 ns, with a vertical diffusivity of 2.78 x 10 –2 cm 2 /s. We also report on the device's optical response characteristics at 78 K.

36 MATERIALS SCIENCE↗