Peak Quantum Efficiency Research Articles

Monolithically integrated dual-wavelength photodetector based on a step-shaped Fabry-Perot filter

A novel long wavelength photodetector with dual-wavelength spectral response is designed and fabricated using a step-shaped Fabry-P′erot (F-P) filter structure. The step-shaped GaAs/AlGaAs distributed Bragg reflectors and the InP PIN photodetector are grown on a GaAs substrate using low pressure metal organic chemical vapor deposition. High quality GaAs/InP heteroepitaxy is realized by employing a thin low temperature buffer layer. The photodetector structure is optimized by theoretical simulation. This device has a dual-peak distance of 19 nm (1 558 and 1 577 nm). The 3-dB bandwidth of 16 GHz is simultaneously obtained with peak quantum efficiencies of 8.5% and 8.6% around 1 558 and 1 577 nm, respectively.

Photocathode aging in MCP PMT

We study aging of alkali-antimonide photocathodes in the microchannel platephotomultiplier tubes (MCP PMT) manufactured in Novosibirsk by ``Ekran FEP'' company.Such PMTs are used in the particle identification systems of KEDR, SND and CMD-3 experiments carried out at e+e− colliders VEPP-4M and VEPP-2000 in the Budker Institute of Nuclear Physics.The quantum efficiency (QE) degradation of a PMT equipped with MCP Chevron has been measured at different photon counting rates from 4⋅107 to 6⋅1010 s−1cm−2. It is found that the QE decrease is proportional to the charge extracted from the MCP nearest to the photocathode rather than to the output charge.The comparison of different types of alkali-antimonide photocathodes has shown that the treatment of photocathode with vapors of cesium and antimony can dramatically reduce the photocathode aging rate.The photocathode lifetime of the best MCP PMT sample has been measured at the photon counting rate of 107 cm−2s−1 and the initial gain of 106.The peak quantum efficiency degraded by 20% after accumulation of 3.3 C/cm2 anode charge.

Atomic layer deposited borosilicate glass microchannel plates for large area event counting detectors

Borosilicate glass micro-capillary array substrates with 20μm and 40μm pores have been deposited with resistive, and secondary electron emissive, layers by atomic layer deposition to produce functional microchannel plates. Device formats of 32.7mm and 20cm square have been fabricated and tested in analog and photon counting modes. The tests show amplification, imaging, background rate, pulse shape and lifetime characteristics that are comparable to standard glass microchannel plates. Large area microchannel plates of this type facilitate the construction of 20cm format sealed tube sensors with strip-line readouts that are being developed for Cherenkov light detection. Complementary work has resulted in Na2KSb bialkali photocathodes with peak quantum efficiency of 25% being made on borosilicate glass. Additionally GaN (Mg) opaque photocathodes have been successfully made on borosilicate microchannel plates.

Long Wavelength Multiple Resonant Cavities RCE Photodetectors on GaAs Substrates

A 1550-nm high-speed, high efficiency, and narrow-linewidth resonant cavity enhanced photodetector with three resonant cavities is demonstrated. The photodetector, operating at a long wavelength, is monolithically integrated by using a heteroepitaxy growth of an InP-based p-i-n structure on the GaAs-based multiple resonant cavities. High-quality heteroepitaxy was realized by employing a thin low-temperature buffer layer. A peak quantum efficiency value of 70%, a spectral response linewidth less than 0.75 nm (full-width at half-maximum), and a 3-dB bandwidth of 36 GHz were simultaneously obtained in the device.

Lifetime-issues of MCP-PMTs

Cherenkov detectors of the DIRC principle will be used at the P̄ANDA experiment at FAIR. Attractive photo sensor candidates for these devices are micro-channel plate (MCP) photomultipliers (PMT). The reasons are their excellent time resolution and their usability inside magnetic fields, although their lifetime is problematic. Various types were investigated. This paper will concentrate on the performance of the Photonis XP85112 and especially its lifetime behavior. For this MCP-PMT a time resolution of 33ps (σ) was measured and it is stable up to photon rates of about 2 MHz/cm2. The peak quantum efficiency (QE) was determined to 24%. Before the actual lifetime measurement several studies were performed, such as scanning the surface of the detector to get the geometrical detector response function. Additionally the gain and time resolution were investigated in a magnetic field up to 2T. Afterwards the lifetime measurements were done up to an integrated charge of 305 mC/cm2, i.e. the collected charge was 1-5 mC/cm2 per day. The gain and QE were determined in irregular intervals of 1-3 days. Also QE scans as a function of the position at the photo cathode were done every 2-3 weeks.

Lead-sulphide quantum-dot sensitization of tin oxide based hybrid solar cells

We have fabricated infrared active hybrid solar cells composed of mesoporous SnO2 sensitized with PbS nanoparticles and infiltrated with organic hole-transporters, 2,2′,7,7′-tetrakis(N,N-di-p-methoxypheny-amine)-9,9′-spirobifluorene(spiro-OMeTAD) or poly(3-hexylthiophene). We observe photo-action to 1100 nm, peak quantum-efficiency over 20%, open-circuit voltages up to 0.5 V and power conversion efficiencies of over 0.5% under simulated sun light. As compared to solar cells composed of mesoporous TiO2 sensitized with the same PbS nanoparticles, the SnO2 based devices generate 4 times the photocurrent density under simulated sun light.

Bulk heterojunction solar cells with thick active layers and high fill factors enabled by a bithiophene-co-thiazolothiazole push-pull copolymer

A push-pull copolymer is presented which can be used in bulk heterojunction (BHJ) solar cells with active layers greater than 200 nm and fill factors above 60%. The efficiencies of most BHJ solar cells are limited by the fact that they have active layers which are between 60 and 110 nm. While this thickness regime enables peak quantum efficiencies (EQE) of 60%–70%, the ability to fabricate thicker devices would increase average EQE values and thus device efficiencies. Discovery of materials which can maintain high performance at large thicknesses will enable higher performance in BHJ hero cells and increase the commercial viability of this technology.

High speed QWIP FPAs on InP substrates

Quantum well infrared photodetector (QWIP) technology has allowed the realization of low cost staring focal plane arrays (FPAs). However, AlGaAs/(In)GaAs QWIP FPAs suffer from low quantum and conversion efficiencies under high frame rate and/or low background conditions. We extensively discuss the effect of sensor gain on the FPA performance under various operating conditions, and highlight the superiority of the InP/InGaAs material system with respect to AlGaAs/GaAs for high speed/low background thermal imaging applications. InP/InGaAs QWIPs, providing a bias adjustable gain in a wide range, offer the flexibility of adapting the FPA to strict operating conditions. We also present an experimental comparison of large format AlGaAs/GaAs and (strained) InP/InGaAs QWIP FPAs under different operating conditions. A 640 × 512 QWIP FPA constructed with the 40-well strained InP/In 0.48Ga 0.52As material system displays a cut-off wavelength of 9.7 μm ( λ p = 8.9 μm) with a BLIP temperature higher than 65 K ( f/2), and a peak quantum efficiency as high as 12% with a broad spectral response (Δ λ/ λ p = 17%). The conversion efficiency of the FPA pixels is as high as 20% under large bias (4 V) where the detectivity is reasonably high (∼3 × 10 10 cm Hz 1/2/W, f/2, 65 K). While providing a considerably higher quantum efficiency than the pixels of a similar AlGaAs/GaAs FPA, the InP/InGaAs QWIP provides similar NETD values with much shorter integration times and, being less sensitive to the read noise, successfully operates with sub-millisecond integration times. The results clearly demonstrate that InP based material systems display high potential for single- and dual-band QWIP FPAs by overcoming the limitations of the standard GaAs based QWIPs under high frame rate and/or low background conditions.

Spectral response and device performance tuning of long-wavelength InAs QDIPs

Long-wavelength InAs QDIPs with different thicknesses of InGaAs cap layer in the confinement-enhanced dots-in-a-well (CE-DWELL) structure were investigated. The sample with 3 nm cap layer shows primarily single band detection at 7 μm that stems from the transition between QD states, but the 5 nm and 7 nm samples reveal voltage-tunable dual band detection in the region of 6–11 μm from transitions to the states in the dots as well as the states in the well. The wavefunction coupling of transition states is effectively modified by the change of cap-layer thickness and the bias polarity, which leads to the observed spectral change and demonstrates the flexibility of the CE-DWELL QDIPs. For higher peak quantum efficiency (QE), thin InGaAs cap layers are used to obtain focused absorption strength. With 3 nm cap layer in the CE-DWELL, a respectable QE of 7.23% is reached for 10-stack QDIPs with 7 μm detection wavelength at 77 K, and a high detectivity of 3.4 × 10 10 Jones is also obtained.

Efficiently Harvesting Excitons from Electronic Type-Controlled Semiconducting Carbon Nanotube Films

We have employed thin films of highly purified semiconducting carbon nanotubes as near-infrared optical absorbers in heterojunction photovoltaic and photodetector devices with the electron acceptor C(60). In comparison with previous implementations of more electrically heterogeneous carbon nanotube/C(60) devices, we have realized a 10× gain in zero-bias quantum efficiency (QE) and even more substantial gains in power conversion efficiency (η(p)). The semiconducting nanotube/C(60) heterojunctions are highly rectifying with a peak external QE, internal QE, and η(p) of 12.9 ± 1.3, 91 ± 22, and 0.6%, respectively, in the near-infrared. We show that the device efficiency is determined by the effective length scale for exciton migration in the nanotube films, confirm the high internal QE via photoluminescence quenching, and demonstrate that the driving force for exciton dissociation at the fullerene-fullerene heterointerface is optimized for diameters <1.0 nm. These results will guide the development of next-generation high-performance carbon nanotube-based solar cells and photosensitive devices.

Pixel Readout Circuit for X-Ray Imagers

This paper describes the per-pixel readout circuit of an X-ray imaging matrix and compares it to other solutions. The per-pixel readout circuit consists of a digital pixel sensor array constituted by a photodiode and a one-bit first-order sigma-delta A/D converter for each pixel. The output of each pixel is a digital bit stream, containing information about the intensity of the light that falls into its photodiode. The sigma-delta A/D converters use only 19 small size MOSFETs and one capacitor. In order to perform the X-ray detection, a scintillator crystal must be placed above each photodiode for converting the X-ray energy into visible light with wavelengths near to the quantum efficiency peak of the photodiodes. Then, the visible light is converted into electronic charges by each photodiode, which is part of digital pixel sensor. The comparison between the solution presented here and other solutions show that the implemented circuit is simpler and its resolution is similar or even superior.

Nanowire superconducting single-photon detectors on GaAs for integrated quantum photonic applications

We demonstrate efficient nanowire superconducting single photon detectors (SSPDs) based on NbN thin films grown on GaAs. NbN films ranging from 3 to 5 nm in thickness have been deposited by dc magnetron sputtering on GaAs substrates at 350 °C. These films show superconducting properties comparable to similar films grown on sapphire and MgO. In order to demonstrate the potential for monolithic integration, SSPDs were fabricated and measured on GaAs/AlAs Bragg mirrors, showing a clear cavity enhancement, with a peak quantum efficiency of 18.3% at λ=1300 nm and T=4.2 K.

Concept and combustion characteristics of the high-luminescence flame for thermophotovoltaic systems

The thermophotovoltaic (TPV) power system mainly consists of a heat source, an emitter and a photovoltaic (PV) cell array. One of the major deficiencies leading to the relatively low overall efficiency of the TPV power system is the spectral mismatch between the emitter radiation and the quantum efficiency peak of the PV cells. Therefore, application of high-luminescent-flame in the visible range is a cost-effective method to enhance the radiant efficiency of a small TPV system. The concept of the high-luminescent-flame combustor is proposed with central-porous liquid fuel-film injection of n-heptane and trace amount of iron pentacarbonyl, and an emitter tube. The metal-porous fuel-film injection is an effective method to increase contact surface and thermal conduction for liquid fuel vaporization and for flame stabilization. Chemiluminescence measurement and Abel deconvolution are further performed to identify the flame structure in two different porous materials, bronze and stainless steel, respectively. Flame structure and stabilization mechanism in the chamber can be related to the tribrachial flame. The radiant intensity of the iron pentacarbonyl flame is significantly enhanced by fivefold, and flame color turns to sliver-white. Inserting an emitter tube in the combustor can further effectively integrate the radiation from the flame luminosity and emitter incandescence, and improve the radiant efficiency of the TPV system.

Thienopyrazine-based low-bandgap polymers for flexible polymer solar cells

The optical gaps of the low-bandgap PPVs (PM-20, PM-19, PM-18) are decreased down to 1.6-1.7 eV compared with that of MDMO-PPV (2.2 eV). The best lateral hole mobility was determined to be 2.1 × 10-3 cm2/V s (PM-18) in field effect transistors and exceeds that of MDMO-PPV (poly-[ 2-methoxy-5-(3'.7'-dimethyloctyloxy)-1.4-phenylenevinylene], 8.5 × 10-4 cm2/V s). This allows to reduce the PCBM ([6.6]-phenyl-C-butanoic acid methyl ester) content in solar cell devices down to 1:2 w/w giving a better than for MDMO-PPV:[60]-PCBM cells (PM-19:[60]-PCBM 2.32% on ITO-PET, 2.86% on ITO glass). The charge transfer to PCBM as acceptor occurs quite normally and shows an effective charge separation using light-induced spin resonance spectroscopy (LESR). The [70]-PCBM signals are shifted to lower field related to those of [60]-PCBM and overlap more with the polaron signal of PM-19. The LESR g-factor components of [70]-PCBM are reported for the first time. The external quantum efficiency peak values achieve up to 42% at ~350–400 nm and 26% at ~640 nm (PM-19:[60]-PCBM).

Low dark current long-wave infrared InAs/GaSb superlattice detectors

Surface leakage reduction has been achieved using BCl3/Cl2/CH4/H2/Ar inductively coupled plasma dry etching for pixel isolation of high performance long-wave infrared superlattice detectors. The leakage has been minimized by effectively increasing the surface resistivity by more than 7.4 times and decreasing the surface state density by more than 3.8 times. Through altering the etch mechanism, the dark current density was reduced by more than two orders of magnitude where a dark current of 1.01×10−5 A/cm2 at 200 mV was achieved at T=77 K for a 10.3 μm detector with a peak quantum efficiency value of 30% (without antireflection coating).

Vertically Coupled Quantum-Dot Infrared Photodetectors

Vertically coupled InAs-GaAs quantum-dot infrared photodetectors (QDIPs) were studied in this letter. With vertically coupled quantum dots (QDs), the QDs in the same column share the same electronic states which remove the QD size variation effect in the growth direction and result in a narrow response band and higher peak quantum efficiency. The coupled states increase the capture probability and also facilitate the carrier flow among QD layers. The frequency response of vertically coupled QDIPs is much faster than that of the conventional ones.

Improvement of peak quantum efficiency and efficiency droop in III-nitride visible light-emitting diodes with an InAlN electron-blocking layer

InAlN electron-blocking layers (EBLs) are shown to improve the emission intensity and to mitigate the efficiency droop problem in III-nitride-based visible light-emitting diodes (LEDs). Using an In0.18Al0.82N EBL in blue LEDs, we have achieved a significant improvement in the electroluminescence emission intensity and a mitigated efficiency droop compared to similar LEDs without an EBL or with an Al0.2Ga0.8N EBL. This indicates that an In0.18Al0.82N EBL is more effective in electron confinement and reduces the efficiency droop possibly caused by carrier spill-over than conventional AlGaN EBLs.

Near infrared photoluminescence of ytterbium(III) complexes from tripodal ligands with different coordination conformations

Fourteen ytterbium(III) complexes of the tripodal ligands triRNTB ( N-substituted tris(benzimidazol-2-ylmethyl)amine) have been prepared and characterized by elemental analysis (EA), infrared spectra (IR), electrospray ionization mass spectrometry (ESI-MS) and single-crystal diffraction analysis. Their coordination conformations can be divided into three different types due to the introduction of secondary ligands or counter anions, i.e. ML 2 , MLL 3 ′ , and MLA 3 types, therefore resulting in different coordination symmetry on the central Yb(III) ions. Accordingly, the near infrared photoluminescence and photophysical properties of the complexes show contrasting results in peak splitting behavior, lifetime, and quantum efficiency, among which the ML 2 type displaying the most complicated splitting, the shortest lifetime and the smallest quantum efficiency.

Reconfigurable multi-channel WDM drop module using a tunable wavelength-selective photodetector array

An integrated reconfigurable four-channel wavelength-division-multiplexed drop module for use in the long-wavelength was demonstrated using a tunable wavelength-selective photodetector array. The array consists of an InP-based p-i-n absorption structure and a GaAs-based multistep Fabry-Pérot filtering cavity. The high quality GaAs/InP heteroepitaxy was realized by employing a thin low temperature buffer layer. The GaAs-based multistep cavity was fabricated by wet etching and regrowth. The dropped central wavelengths were 1538, 1550, 1559, and 1570nm. The tunable range reached 10nm with a tuning power efficiency of 14.2nm/W. A spectral linewidth less than 0.5nm (FWHM), a 3dB bandwidth of 9.2GHz, and the peak quantum efficiencies from 13% to 20% were simultaneously obtained, in agreement with the theoretical simulation.

High Conversion Efficiency InP/InGaAs Strained Quantum Well Infrared Photodetector Focal Plane Array With 9.7 $\mu$m Cut-Off for High-Speed Thermal Imaging

InP/InGaAs material system is an alternative to AlGaAs/GaAs for long wavelength quantum well infrared photodetectors (QWIPs). We demonstrate a large format (640 × 512) QWIP focal plane array (FPA) constructed with the strained InP/InGaAs material system. The strain introduced to the structure through utilization of In0.48Ga0.52As (instead of In0.53Ga0.47As ) as the quantum well material shifts the cut-off wavelength from ˜8.5 to 9.7 μm. The FPA fabricated with the 40-well epilayer structure yields a peak quantum efficiency as high as 12% with a broad spectral response (Δλ/p=17%). The peak responsivity of the FPA pixels is 1.4 A/W corresponding to 20% conversion efficiency in the bias region where the detectivity is reasonably high (2.6 × 1010 cm Hz1/2/W, f/1.5, 65 K). The FPA providing a background limited performance temperature higher than 65 K (f/1.5) satisfies the requirements of most low integration time/low background applications where AlGaAs/GaAs QWIPs suffer from read-out circuit noise limited sensitivity due to lower conversion efficiencies. Noise equivalent temperature differences of the FPA are as low as 19 and 40 mK with integration times as short as 1.8 ms and 430 μs (f/1.5, 65 K).