Quantum Cascade Detector Research Articles

A surface plasmonic coupled mid-long-infrared two-color quantum cascade detector

A novel mid-long-infrared two-color photodetector is proposed. It combines quantum cascade detector (QCD) and surface plasmonic coupling structure. The reflection spectrum and electric field are analyzed by algorithm of finite difference time domain method (FDTD). This QCD is sensitive to 4.4μm and 9.0μm infrared light. Mid-infrared and long-infrared pixels are interlaced arranged with specific plasmonic micro-cavity structures integrated. 7.1 and 7 times enhancement in optical absorption are obtained for mid-infrared and long-infrared pixels, respectively. Besides, a polarization-discriminating detection performance has been observed.

Rate equation modelling and investigation of quantum cascade detector characteristics

A simple precise transport model has been proposed using rate equation approach for the characterization of a quantum cascade detector. The resonant tunneling transport is incorporated in the rate equation model through a resonant tunneling current density term. All the major scattering processes are included in the rate equation model. The effect of temperature on the quantum cascade detector characteristics has been examined considering the temperature dependent band parameters and the carrier scattering processes. Incorporation of the resonant tunneling process in the rate equation model improves the detector performance appreciably and reproduces the detector characteristics within experimental accuracy.

Electronic transport in a long wavelength infrared quantum cascade detector under dark condition

We present a joint experimental and theoretical investigation on a long wavelength infrared quantum cascade detector to reveal its dark current paths. The temperature dependence of the dark current is measured. It is shown that there are two different transport mechanisms, namely resonant tunneling at low temperatures and thermal excitation at higher temperature, dominate the carrier flow, respectively. Moreover, the experimental intersubband transition energies obtained by the magneto-transport measurements matches the theoretical predictions well. With the aid of the calculated band structures, we can explain the observed oscillation phenomena of the dark current under the magnetic field very well. The obtained results provide insight into the transport properties of quantum cascade detectors thus providing a useful tool for device optimization.

4.3 μm quantum cascade detector in pixel configuration.

We present the design simulation and characterization of a quantum cascade detector operating at 4.3μm wavelength. Array integration and packaging processes were investigated. The device operates in the 4.3μm CO2 absorption region and consists of 64 pixels. The detector is designed fully compatible to standard processing and material growth methods for scalability to large pixel counts. The detector design is optimized for a high device resistance at elevated temperatures. A QCD simulation model was enhanced for resistance and responsivity optimization. The substrate illuminated pixels utilize a two dimensional Au diffraction grating to couple the light to the active region. A single pixel responsivity of 16mA/W at room temperature with a specific detectivity D* of 5⋅107 cmHz/W was measured.

High-speed, room-temperature quantum cascade detectors at 4.3 μm

We present high-speed, room-temperature operated 4.3 μm quantum cascade detectors. The devices are processed as square mesas with 50 Ω coplanar access line and air-bridge connector. The high frequency features are explored using microwave rectification technique and a RLC circuit model. The -3 dB cutoff frequency is experimentally 9 GHz and 4 GHz for 20×20 μm2 and 50×50 μm2 detectors, respectively. The equivalent circuit analysis shows that a second order filter feature governs the devices. Higher cutoff frequency can be achieved by eliminate the parasitics further.

Two models for the cascade of quantum cascade detector operating in the near infra-red range

Two models for the cascade of quantum cascade detector operating in the near infra-red range

High performance, room temperature, broadband II-VI quantum cascade detector

We report on the experimental demonstration of a room temperature, II-VI, ZnCdSe/ZnCdMgSe, broadband Quantum Cascade detector. The detector consists of 30 periods of 2 interleaved active-absorption regions centered at wavelengths 4.8 μm and 5.8 μm, respectively. A broad and smooth photocurrent spectrum between 3.3 μm and 6 μm spanning a width of 1030 cm–1 measured at 10% above baseline was obtained up to 280 K, corresponding to a ΔE/E of 47%. Calibrated blackbody responsivity measurements show a measured peak responsivity of 40 mA/W at 80 K, corresponding to a detectivity of about 3.1×1010 cmHz/W. Bias dependent photocurrent measurements revealed no significant change in the spectral shape, suggesting an impedance matched structure between the different active regions.

InAs/AlAsSb based quantum cascade detector

In this letter, we introduce the InAs/AlAsSb material system for quantum cascade detectors (QCDs). InAs/AlAsSb can be grown lattice matched to InAs and exhibits a conduction band offset of approximately 2.1 eV, enabling the design of very short wavelength quantum cascade detectors. Another benefit using this material system is the low effective mass of the well material that improves the total absorption of the detector and decreases the intersubband scattering rates, which increases the device resistance and thus enhances the noise behavior. We have designed, grown, and measured a QCD that detects at a wavelength of λ = 4.84 μm and shows a peak specific detectivity of approximately 2.7 × 107 Jones at T = 300 K.

High performance bi-functional quantum cascade laser and detector

An improved bi-functional quantum cascade laser and detector emitting and detecting around 6.8 μm is demonstrated. The design allows a significantly higher laser performance, showing that bi-functional designs can achieve a comparable pulsed performance to conventional quantum cascade lasers. In particular, the device has a threshold current density of 3 kA/cm2, an output power of 0.47 W, and a total wall-plug efficiency of 4.5% in pulsed mode. Optimized electron extraction and the prevention of thermal backfilling allow higher duty cycles, operation up to 10%, with 15 mW average output power at room temperature without optimization of the laser cavity or coatings. At zero bias, the device has a responsivity of around 40 mA/W and a noise equivalent power of 80 pW/Hz at room temperature, which in on-chip configuration outperforms conventional uncooled discrete detectors.

Electron-phonon interaction in three-barrier nanosystems as active elements of quantum cascade detectors

The theory of electron tunneling through an open nanostructure as an active element of a quantum cascade detector is developed, which takes into account the interaction of electrons with confined and interface phonons. Using the method of finite-temperature Green’s functions and the electron-phonon Hamiltonian in the representation of second quantization over all system variables, the temperature shifts and electron-level widths are calculated and the contributions of different electron-phonon-interaction mechanisms to renormalization of the spectral parameters are analyzed depending on the geometrical configuration of the nanosystem. Due to weak electron-phonon coupling in a GaAs/Al0.34Ga0.66As-based resonant tunneling nanostructure, the temperature shift and rf field absorption peak width are not very sensitive to the electron-phonon interaction and result from a decrease in potential barrier heights caused by a difference in the temperature dependences of the well and barrier band gaps.

Quantum cascade detector utilizing the diagonal-transition scheme for high quality cavities.

A diagonal optically active transition in a quantum cascade detector is introduced as optimization parameter to obtain quality factor matching between a photodetector and a cavity. A more diagonal transition yields both higher extraction efficiency and lower noise, while the reduction of the absorption strength is compensated by the resonant cavity. The theoretical limits of such a scheme are obtained, and the impact of losses and cavity processing variations are evaluated. By optimizing the quantum design for a high quality cavity, a specific detectivity of 10(9) Jones can be calculated for λ = 8μm and T = 300K.

Photoresponse of Long-Wavelength AlGaAs/GaAs Quantum Cascade Detectors

We study the photoresponse and photocurrents of long-wavelength infrared quantum cascade detectors (QCDs) based on AlGaAs/GaAs material system. The photocurrent spectra were measured at different temperatures from 20 K to 100 K with a low noise Fourier transforming infrared spectrometer. The main response peak appeared at 8.9 μm while four additional response peaks from 4.5 μm to 10.1 μm were observed as well. We confirmed that the photocurrent comes from phonon assisted tunneling and the multipeak behavior comes from the complicated optical transition in the quantum cascade structure. This work is valuable for the future design and optimization of QCD devices.

Вплив обмежених поляризаційних фононів на електронний спектр трибар’єрної активної зони квантового каскадного детектора

Вплив обмежених поляризаційних фононів на електронний спектр трибар’єрної активної зони квантового каскадного детектора

III-nitride quantum cascade detector grown by metal organic chemical vapor deposition

Quantum cascade (QC) detectors in the GaN/AlxGa1−xN material system grown by metal organic chemical vapor deposition are designed, fabricated, and characterized. Only two material compositions, i.e., GaN as wells and Al0.5Ga0.5N as barriers are used in the active layers. The QC detectors operates around 4 μm, with a peak responsivity of up to ∼100 μA/W and a detectivity of up to 108 Jones at the background limited infrared performance temperature around 140 K.

Plasmonic lens enhanced mid-infrared quantum cascade detector

We demonstrate monolithic integrated quantum cascade detectors enhanced by plasmonic lenses. Surface normal incident mid-infrared radiation is coupled to surface plasmon polaritons guided to and detected by the active region of the detector. The lens extends the optical effective active area of the device up to a 5 times larger area than for standard mesa detectors or pixel devices while the electrical active region stays the same. The extended optical area increases the absorption efficiency of the presented device as well as the room temperature performance while it offers a flexible platform for various detector geometries. A photocurrent response increase at room temperature up to a factor of 6 was observed.

Room temperature quantum cascade detector operating at 4.3 μm

A strain-compensated InP-based InGaAs/InAlAs quantum cascade detector grown by solid source molecular beam epitaxy is demonstrated. The device operates at 4.3 μm up to room temperature (300 K) with a responsivity of 1.27 mA/W and a Johnson noise limited detectivity of 1.02 × 107 cm·Hz1/2/W. At 80 K, the responsivity and detectivity are 14.55 mA/W and 1.26 × 1010 cm·Hz1/2/W, respectively. According to the response range, this detector is much suitable for greenhouse gas detection.

Diagonal-transition quantum cascade detector

We demonstrate the concept of diagonal transitions for quantum cascade detectors (QCD). Different to standard, vertical QCDs, here the active transition takes place between two energy levels in adjacent wells. Such a scheme has versatile advantages. Diagonal transitions generally yield a higher extraction efficiency and a higher resistance than vertical transitions. This leads to an improved overall performance, although the absorption strength of the active transition is smaller. Since the extraction is not based on resonant tunneling, the design is more robust, with respect to deviations from the nominal structure. In a first approach, a peak responsivity of 16.9 mA/W could be achieved, which is an improvement to the highest shown responsivity of a QCD for a wavelength of 8 μm at room-temperature by almost an order of magnitude.

First demonstration of plasmonic GaN quantum cascade detectors with enhanced efficiency at normal incidence.

We have designed, fabricated and measured the first plasmon-assisted normal incidence GaN/AlN quantum cascade detector (QCD) making use of the surface plasmon resonance of a two-dimensional nanohole Au array integrated on top of the detector absorption region. The spectral response of the detector at room temperature is peaked at the plasmon resonance of 1.82 μm. We show that the presence of the nanohole array induces an absolute enhancement of the responsivity by a factor of ~30 over that of the bare device at normal incidence and by a factor of 3 with respect to illumination by the 45° polished side facet. We show that this significant improvement arises from two phenomena, namely, the polarization rotation of the impinging light from tangential to normal induced by the plasmonic structure and from the enhancement of the absorption cross-section per quantum well due to the near-field optical intensity of the plasmonic wave.

High detectivity short-wavelength II-VI quantum cascade detector

We report on the experimental demonstration of a ZnCdSe/ZnCdMgSe-based short-wavelength photovoltaic Quantum Cascade Detector (QCD). The QCD operates in two spectral bands centered around 2.6 μm and 3.6 μm. Calibrated blackbody measurements yield a peak responsivity of 0.1 mA/W or 2400 V/W at 80 K, and a corresponding 300 K background radiation limited infrared performance detectivity (BLIP) of ∼2.5 × 1010 cm √Hz/W. Comparison of background illuminated and dark current-voltage measurements demonstrates a BLIP temperature of 200 K. The device differential resistance-area product, decreases from about 106 Ω cm2 at 80 K to about 8000 Ω cm2 at 300 K, indicative of the ultra-low Johnson noise in the detectors.

Mid-infrared spectroscopy for gases and liquids based on quantum cascade technologies

In this paper we present two compact, quantum cascade laser absorption spectroscopy based, sensors developed for trace substance detection in gases and liquids. The gas sensor, in its most integrated version, represents the first system combining a quantum cascade laser and a quantum cascade detector. Furthermore, it uses a toroidal mirror cell with a volume of only 40 cm(3) for a path length of up to 4 m. The analytical performance is assessed by the measurements of isotope ratios of CO2 at ambient abundance. For the (13)CO2/(12)CO2 isotope ratio, a measurement precision of 0.2‰ is demonstrated after an integration time of 600 s. For the liquid sensor, a microfluidic system is used to extract cocaine from saliva into a solvent (PCE) transparent in the mid-infrared. This system is bonded on top of a Si/Ge waveguide and the concentration of cocaine in PCE is measured through the interaction of the evanescent part of the waveguide optical mode and the solvent flowing on top. A detection limit of <100 μg mL(-1) was achieved with this system and down to 10 μg mL(-1) with a simplified, but improved system.