Cascade Detector Research Articles

Description of transport mechanisms in a very long wave infrared quantum cascade detector under strong magnetic field

Measurements of current have been performed on a very long wave infrared quantum cascade detector under strong magnetic field applied parallel to the growth axis, both under dark and light conditions. The analysis of dark current as a function of temperature highlights three regimes of transport involving the different energy levels of the structure. For photocurrent analysis, we developed a model based on a rate equation approach taking into account all the electronic levels of the structure. This model is in agreement with the oscillatory component of the experimental magnetophotocurrent. It allows to identify the key points controlling the electronic transport such as extraction from the upper level of the optically active quantum well, location of ionized impurities, and scattering mechanisms involved in the structure. This work is valuable for the future conception of high-performance quantum cascade detectors in infrared and far infrared range.

Adult Image Detection Based on AdaBoost

In this paper, a method of detecting adult images based on AdaBoost was proposed. We focused on the detection of the adult images that have naked breasts or naked genitalia. By using basic and rotated Haar-like features extracted from the samples in the training set, we trained a cascade detector. The detector would classify the image whether to be a pornographic one or not. The results showed that this method achieved a high detection rate and a low false alarm rate.

Temperature dependence of electron transport in GaN/AlGaN quantum cascade detectors

In this work we investigate the influence of extractor design and temperature on transport properties of quantum cascade detector. For this purpose we realize numerical calculation of electron lifetimes considering electron–phonon and electron impurities scattering. Electron–phonon interactions are treated using Fermi Golden Rule which allows to calculate lifetime of carriers with temperature and structure design taking into account. Transport characteristics of the quantum cascade detectors have been computed using density matrix theory. As a result, we have obtained the system of ordinary differential equations describing dynamics of electron distribution functions and intersubband correlations. Managing carrier lifetime in quantum wells gives us possibility to make device response faster. Also carrier lifetime is the relevant characteristic, allows us to calculate a lot of parameters such as quantum efficiency and photocurrent.

Two-color GaN/AlGaN quantum cascade detector at short infrared wavelengths of 1 and 1.7 μm

A two-color GaN-based quantum cascade detector is demonstrated. This photodetector operates simultaneously at a peak wavelength of 1.7 and 1 μm at room temperature without any external voltage. These peaks correspond, respectively, to the e1e2 and e1e3 intersubband absorption of the active GaN quantum well. The extractor has been designed to allow for efficient transfer of electrons from both the e2 and e3 states to the next period. The 1 μm detected wavelength is the shortest value reported for an intersubband semiconductor based detector.

A normal incident quantum cascade detector enhanced by surface plasmons

We demonstrate a normal incident quantum cascade detector excited by surface plasmons resonance using an Au two-dimensional hole array integrated on top of the detector absorption region. With normal incidence, the device has a maximal responsivity value of 8.4 mA/W at 160 K and can work up to room temperature with a responsivity of 1.02 mA/W. Compared with the 45° polished edge coupling device, the two-dimensional hole array can lead to quantum efficiency enhancement at most measured temperatures, and at 140 K the quantum efficiency is enhanced most strongly by 69%.

A New Biased Discriminant Analysis Using Composite Vectors for Eye Detection

We propose a new biased discriminant analysis (BDA) using composite vectors for eye detection. A composite vector consists of several pixels inside a window on an image. The covariance of composite vectors is obtained from their inner product and can be considered as a generalization of the covariance of pixels. The proposed composite BDA (C-BDA) method is a BDA using the covariance of composite vectors. We construct a hybrid cascade detector for eye detection, using Haar-like features in the earlier stages and composite features obtained from C-BDA in the later stages. The proposed detector runs in real time; its execution time is 5.5 ms on a typical PC. The experimental results for the CMU PIE database and our own real-world data set show that the proposed detector provides robust performance to several kinds of variations such as facial pose, illumination, eyeglasses, and partial occlusion. On the whole, the detection rate per pair of eyes is 98.0% for the 3604 face images of the CMU PIE database and 95.1% for the 2331 face images of the real-world data set. In particular, it provides a 99.7% detection rate for the 2120 CMU PIE images without glasses. Face recognition performance is also investigated using the eye coordinates from the proposed detector. The recognition results for the real-world data set show that the proposed detector gives similar performance to the method using manually located eye coordinates, showing that the accuracy of the proposed eye detector is comparable with that of the ground-truth data.

Photovoltaic quantum dot quantum cascade infrared photodetector

Design and characterization of a quantum dot quantum cascade detector for photovoltaic midwave infrared photodetection (λpeak = 5.5 μm) is demonstrated. The quantum cascade barrier region provides the internal electric field to transfer photoexcited electrons into quantum dots of the next stack, enabling zero bias operation. Increased carrier relaxation time for intersubband transitions in quantum dots provides a distinct advantage for the carrier transport. Responsivity of 10 mA/W and detectivity of 9 × 109 cm Hz1/2 W−1 at 77 K for f/2 optics has been obtained at zero bias. Dark current density is 6.5 × 10−7A cm−2, at 80 K at zero bias.

Quantum cascade detectors under weak and strong electromagnetic fields

Quantum cascade detectors under weak and strong electromagnetic fields

Predictive circuit model for noise in quantum cascade detectors

Electronic noise in quantum cascade structures is investigated theoretically and experimentally under dark conditions. A model based on a unified and insightful vision of noise generating mechanisms is proposed and describes both thermal and shot noise behaviors. Dark measurements of quantum cascade detectors operating at 8 μm and 15 μm are retrieved with good quantitative agreement. This model is expected to be applicable to other quantum structures and under illumination.

Non-perturbation theory of electronic dynamic conductivity for two-barrier resonance tunnel nano-structure

The non-perturbation theory of electronic dynamic conductivity for open two-barrier resonance tunnel structure is established for the first time within the model of rectangular potentials and different effective masses of electrons in the elements of nano-structure and the wave function linear over the intensity of electromagnetic field. It is proven that the results of the theory of dynamic conductivity, developed earlier in weak signal approximation within the perturbation method, qualitatively and quantitatively correlate with the obtained results. The advantage of non-perturbation theory is that it can be extended to the case of electronic currents interacting with strong electromagnetic fields in open multi-shell resonance tunnel nano-structures, as active elements of quantum cascade lasers and detectors.

Femto-second electron transit time characterization in GaN/AlGaN quantum cascade detector at 1.5 micron

The ultra fast carrier dynamic in GaN/AlGaN quantum cascade detector was investigated using a time-resolved bias-lead monitoring technique. It is demonstrated that the intrinsic speed limitation, governed by the carrier transit time, is smaller than 1 ps, corresponding to a frequency cut off above 200 GHz.

CO2 isotope sensor using a broadband infrared source, a spectrally narrow 4.4 μm quantum cascade detector, and a Fourier spectrometer

We report a prototype CO2 gas sensor based on a simple blackbody infrared source and a spectrally narrow quantum cascade detector (QCD). The detector absorption spectrum is centered at 2260 cm−1 (4.4 μm) and has a full width at half maximum of 200 cm−1 (25 meV). It covers strong absorption bands of two spectrally overlapping CO2 isotopomers, namely the P-branch of 12CO2 and the R-branch of 13CO2. Acquisition of the spectral information and data treatment were performed in a Fourier transform infrared (FTIR) spectrometer. By flushing its sample compartment either with nitrogen, dry fresh air, ambient air, or human breath, we were able to determine CO2 concentrations corresponding to the different gas mixtures. A detection limit of 500 ppb was obtained in these experiments.

Detection of high frequency intensity oscillations at RESEDA using the CASCADE detector

We have explored the technological potential of combining neutron resonance spin echo (NRSE) with the time-of-flight method in quasielastic neutron scattering (QENS) experiments. For these test measurements at the new NRSE instrument RESEDA (FRM II, Munich), we have employed CASCADE, one of the fastest neutron detectors in the world, developed at the University of Heidelberg. Conventionally, scintillation detectors are used, in order to detect neutron intensities with high time resolution. In contrast, we used the new CASCADE detector converting neutrons in thin (10)B layers being capable of resolving neutron intensity modulations up to the megahertz regime. This fast detector allows us to abandon the last resonance flip coil of a standard NRSE setup. The classical spin echo signal is replaced by a time-modulated signal. In this setup, fast intensity modulations are present at the detector position. In order to demonstrate, that NRSE-CASCADE operates well up to detector frequencies of 10 MHz, we performed elastic polarization test measurements on a standard sample. The CASCADE detector is a multidetector accumulating counts in 128 × 128 pixels on a surface of 200 mm × 200 mm. We have analyzed the signal in 600 pixels, providing information about the spin phase reaching the detector and about the resolution function of this new variant tested at RESEDA.

Magnetotransport in quantum cascade detectors: analyzing the current under illumination

Photocurrent measurements have been performed on a quantum cascade detector structure under strong magnetic field applied parallel to the growth axis. The photocurrent shows oscillations as a function of B. In order to describe that behavior, we have developed a rate equation model. The interpretation of the experimental data supports the idea that an elastic scattering contribution plays a central role in the behavior of those structures. We present a calculation of electron lifetime versus magnetic field which suggests that impurities scattering in the active region is the limiting factor. These experiments lead to a better understanding of these complex structures and give key parameters to optimize them further.

Optimization of the configuration of a symmetric three-barrier resonant-tunneling structure as an active element of a quantum cascade detector

On the basis of a model of rectangular potentials and different electron effective masses in wells and barriers of an open resonant-tunneling structure with identical outer barriers, a theory has been developed and the dynamic conductance caused by the interaction of the electromagnetic field with electrons passing through the structure has been calculated. Using the example of the three-barrier resonant-tunneling structure with In0.53Ga0.47As wells and In0.52Al0.48As barriers, it is shown that, independently of the geometrical sizes of potential wells and barriers, there exist three geometrical configurations (positions of the inner barrier with respect to outer ones) at which the nanosystem, as an active element, provides optimum operating conditions of the quantum cascade detector.

Active conductivity of plane two-barrier resonance tunnel structure as operating element of quantum cascade laser or detector

Within the model of rectangular potentials and different effective masses of electrons in different elements of plane two-barrier resonance tunnel structure there is developed a theory of spectral parameters of quasi-stationary states and active conductivity for the case of mono-energetic electronic current interacting with electromagnetic field. It is shown that the two-barrier resonance tunnel structure can be utilized as a separate or active element of quantum cascade laser or detector. For the experimentally studied In$_{0.53}$Ga$_{0.47}$As/In$_{0.52}$Al$_{0.48}$As nano-system it is established that the two-barrier resonance tunnel structure, in detector and laser regimes, optimally operates (with the biggest conductivity at the smallest exciting current) at the quantum transitions between the lowest quasi-stationary states.

GaN-based quantum cascade photodetector with 1.5 µm peak detection wavelength

Demonstrated is a GaN/Al(Ga)N quantum cascade detector operating at room temperature with a peak detection wavelength of 1.5 m, which is the shortest value ever reported for such a device in any material system. The 3 dB detection spectral range spans from 1.37 to 1.57 m wavelength. The calibrated peak responsivity for TM-polarised light is measured to be around 15 V/W at room temperature.

A 10.7 μm InGaAs/InAlAs Quantum Cascade Detector

A 10.7μm quantum cascade detector based on lattice matched InGaAs/InAlAs/InP is demonstrated and characterized in terms of responsivity, resistivity and detectivity. The device operates in the 8–14 μm atmospheric window up to 140K and shows a peak reponsivity of 14.4mA/W at 78K. With a resistance-area product value of 159Ωcm2, the Johnson noise limited detectivity D*J is 2.8 × 109 Jones (cmHz1/2 W−1) at 78K.

Photocurrent analysis of quantum cascade detectors by magnetotransport

Photocurrent measurements have been performed on a quantum cascade detector structure under strong magnetic field $B$ applied parallel to the growth axis. The photocurrent shows oscillations as a function of $B$. In order to describe this behavior, we have developed a rate equation model. The interpretation of the experimental data supports the idea that an elastic scattering contribution plays a central role in the behavior of these structures. We present a calculation of the electron lifetime versus magnetic field which suggests that impurities scattering in the active region is the limiting factor. These experiments lead to a better understanding of these complex structures and identify key parameters to optimize them further.

CASCADE, neutron detectors for highest count rates in combination with ASIC/FPGA based readout electronics

The CASCADE detector system described herein is designed for high intensity neutron applications with high demands on the dynamical range, contrast as well as background. The detector front-end is a hybrid, solid converter gas detector using several gas electron multiplier (GEM) foils as charge transparent substrates to carry solid 10B layers. These coated GEMs are then stacked (“cascaded”) one behind the other to cumulate the detection efficiency of every layer without loosing position information. The use of GEM foils allows high count rates up to 10 7 n/cm 2 s. The well-defined neutron absorption locus inside the thin boron layer provides sub-microsecond absolute time resolution, which opens the door towards new TOF applications. Because 96% isotopically enriched boron is available in large quantities in contrast to 3He, 10B-converter based neutron detector technology is one of the very few technological alternatives to 3He in view of the imminent crisis in world-wide supply of 3He. Using GEM foils, the neutron detection bottleneck shifts to data read-out electronics and its bandwidth. The CASCADE detector uses an ASIC electronic front-end paired with an adaptable integrated FPGA data processing unit to provide high rate capacity and realtime event reconstruction.