Quantum Cascade Detector Research Articles

Spectrum of localized three-level quasiparticle resonantly interacting with polarization phonons at cryogenic temperature

The new method of calculation of a mass operator of Fourier image of Green’s function, based on the generalized method of Feynman–Pines diagram technique for the multi-level systems, is proposed for the three-level localized quasiparticle interacting with phonons at Т = 0 К. The main classes of multiplicative diagrams separated in the proposed approach made it possible to renormalize the mass operator and present it as a sum of continuous branch chain fractions with typical links. It is shown that the renormalized spectrum of the system contains the complexes of bound-to-phonon satellite states of quasiparticle. In resonant structures, like extractors in quantum cascade detectors, such complexes create an infinite number of dense groups of equidistant energy levels.

Grating-Coupled Silicon-on-Sapphire Polarization Rotator Operating at Mid-Infrared Wavelengths

We provide an experimental demonstration of mid-infrared polarization rotators built on a silicon-on-sapphire platform at the mid-infrared wavelength of $4.55~\mu \text{m}$ to enable integration of quantum cascade lasers (QCLs) and detectors with slotted photonic crystal waveguide (PCW) gas sensors for on-chip optical spectroscopy applications. The polarization rotators are essential to convert the preferentially transverse magnetic (TM) polarized light from a QCL to transverse electric (TE) polarization to interface with the preferential TE-guiding slotted PCW sensors. The polarization rotator consists of an adiabatic-tapered mode converter followed by a phase shifter and a multimode interferometer that effectively transfers energy from an input fundamental TM00 polarization to a first-order TE10 polarization that is then converted to the fundamental TE00 mode. Polarization-selective sub-wavelength grating couplers are designed and fabricated to effectively couple TE or TM polarizations at the designed wavelengths into and out of the polarization rotator device for efficient device characterization. TM00–TE10 conversion efficiency of 100% is simulated. Fabrication tolerances in the phase shifter result in an experimental 80:20 splitting ratio of the measured output TE00-polarized light between two output arms.

Mid-Infrared GaN/AlGaN Quantum Cascade Detector Grown on Silicon

We demonstrate the first implementation of a GaN-based infrared photodetector epitaxially grown on silicon. The device is a GaN/AlGaN quantum cascade detector that consists of layered quantum well structure grown by plasma-assisted molecular beam epitaxy on a 4-in Si (111) substrate. The design, simulations, growth process, optical measurements and device performance are presented and discussed. The photosignal, centered at a wavelength of 4.4 μm, is resolved up to 150 K. The zero bias responsivity is 44 μA/W at 19 K and the detectivity is 2 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> Jones.

Short infrared wavelength quantum cascade detectors based on m-plane ZnO/ZnMgO quantum wells

This paper reports on the demonstration of quantum cascade detectors (QCDs) based on ZnO/ZnMgO quantum wells (QWs) grown by molecular beam epitaxy on an m-plane ZnO substrate. The TM-polarized intersubband absorption is peaked at a 3 μm wavelength. The sample has been processed in the form of square mesas with sizes ranging from 10 × 10 μm2 up to 100 × 100 μm2. The I-V characteristics reveal that 86% of the 260 devices are operational and that the surface leakage current is negligible at room temperature, which is not the case at 77 K. The photocurrent spectroscopy of 100 × 100 μm2 QCDs reveals a photocurrent resonance at a 2.8 μm wavelength, i.e., slightly blue-shifted with respect to the intersubband absorption peak. The photocurrent persists up to room temperature. The calibrated peak responsivity amounts to 0.15 mA/W under irradiation at Brewster's angle of incidence. This value allows us to estimate the transfer efficiency (1.15%) of the photoexcited electrons into the active QW of the next period.

Analytical method for calculation of the potential profiles of nitride-based resonance tunneling structures

Using the effective mass model for an electron and the dielectric continuum model, analytical solutions of the self-consistent Schr\"odinger-Poisson system of equations are obtained. Quantum mechanical theory of electronic stationary states, the oscillator strengths of quantum transitions and a method of potential profile calculation is developed for the experimentally constructed three-well resonance-tunneling structure --- a separate cascade of quantum cascade detector. For the proposed method, a comparison with the results of other methods and with the results of the experiment was carried out. A good agreement between the calculated value of the detected energy and its experimental value has been obtained, the difference being no more than $2.5\%$.

Repeatable Room Temperature Negative Differential Resistance in AlN/GaN Resonant Tunneling Diodes Grown on Sapphire

AbstractResonant tunneling diodes (RTDs) are candidates for high power terahertz oscillators, and form the basis for understanding the quantum confinement and vertical transport in quantum structures such as quantum cascade lasers and quantum cascade detectors. In this work, repeatable negative differential resistance (NDR) is achieved in AlN/GaN RTDs grown on sapphire substrate by plasma‐assisted molecular‐beam epitaxy. Two reproducible NDR regions sequentially following two preresonance replicas are demonstrated at room temperature. A current region exhibiting negative correlation with temperature and oscillation‐like features is first identified under reverse bias, which is interpreted as a combined contribution of weak resonant tunneling channels through different bound states in the well. The revealed peak‐to‐valley current ratio ranges from 1.1 to 1.8, and peak current density ranges from 5 to 164 kA cm−2. Using an analytic model, resonant tunneling transports in both bias directions are quantitatively characterized and show good agreements with experiment results, demonstrating the capability of accurate quantum transport control using III‐nitride grown on sapphire substrate. The findings will promote the implementation of low cost III‐nitride monolithic microwave circuits and resonant tunneling structures based on sapphire, SiC, and even silicon substrates.

High-frequency very long wave infrared quantum cascade detectors

High speed quantum cascade detectors (QCDs) in a very long wave infrared range have been fabricated and characterized. Based on the resonant longitudinal optical-phonon scattering extraction relaxation mechanism, the QCD material behaves at an intrinsically high speed. In order to achieve high speed operation, we integrated microwave technology into the device process to reduce the parasitic parameters and ensure a low time constant of the effective resistance, iInductance, capacitance (RLC) circuit. The peak response is located at 14.2 μm at 77 K. The electrical response characteristics of these QCDs was tested using a microwave rectification technique. The −3 dB cutoff frequency of a 100 × 100 μm2 QCD is 3.2 GHz. The cutoff behavior of our devices were modeled with a second order filter RLC circuit model and showed good agreement with the experimental data.

Influence of Quantum Dots on Response of Quantum Cascade Detector

Influence of Quantum Dots on Response of Quantum Cascade Detector

Long wavelength infrared quantum cascade detector with a broadband response

A novel structure to achieve long wavelength infrared broadband detection ranging from 7.6–10.4 µm is proposed via quantum cascade detector. With a pair of identical coupled quantum wells separated by a thin barrier, acting as absorption regions, the relative linewidth (ΔE/E) of response can be dramatically broadened to 30.7%. Moreover, this structure introduces about 30% enhancement in blackbody responsivity. It is shown that the spectral shape can be tuned by the bias voltage effectively, while it is insensitive to the working temperature. The device can work at liquid nitrogen temperature with Johnson noise limited blackbody detectivity of 5.4 × 108 Jones.

Normal-incidence quantum cascade detector coupled by nanopore structure

A normal-incidence quantum cascade detector coupled by a nanopore array structure (NPS) is demonstrated. The NPS is fabricated on top of an In0.53Ga0.47As contact layer by inductively coupled plasma etching using anodic aluminum oxide as a mask. Because of the nonuniform volume fraction at different areas of the device mesa, the NPS acts as subwavelength random gratings. Normal-incidence light can be scattered into random oblique directions for inter-sub-band transition absorption. With normal incidence, the responsivities of the device reach 24 mA/W at 77 K and 15.7 mA/W at 300 K, which are enhanced 2.23 and 1.96 times, respectively, compared with that of the 45°-edge device.

Self-Consistent Calculation of Potential Profile of GaN/AlN Resonace Tunnelling Structures

For resonant tunneling structure with GaN – potential wells and AlN – potential barriers, calculation of internal fields caused by piezoelectric and spontaneous polarization was carried. In the model the effective mass of an electron and a dielectric continuum model using finite difference method self-consistent solutions of the Schrödinger and Poisson system of equations taking into account the contribution of piezoelectric and spontaneous polarizations was found.Based on the found solutions of the Schrödinger and Poisson system of equations for resonance tunneling structure, which functioned as a cascade experimentally realized a quantum cascade detector, calculation of the potential profile and the electron energy spectrum was carried. It was found, that calculated value of detected energy is different from the experimentally obtained not more than 3 %.

The limit of quantum cascade detectors: A single period device

In this work, we demonstrate a 4.1 μm quantum cascade photodetector with external quantum efficiencies of 40% at 80 K and 25% at 300 K. Such high efficiencies have been made possible by using a single period active region embedded in a facet coupled low-loss dielectric ridge waveguide. This emphasizes the relevance of enhancing the optical interaction for this type of detector in a different manner from increasing the number of periods. Low noise operation was achieved by using photovoltaic operation at zero bias and an elaborate band structure design to prevent undesired scattering paths. A noise equivalent power of 10 pW/Hz and a corresponding specific detectivity of 7×107 cmHz/W at room-temperature, as well as background limited operation below 124 K with a detectivity close to an ideal photodetector, are demonstrated.

Effect of polarization on the performance of ZnO/MgZnO quantum cascade detector

The impact of polarization effect on the performance of ZnO/MgZnO quantum cascade detector (QCD) is investigated with different scattering mechanisms taken into account. The energy band structure and wave functions are achieved by self-consistent calculation of Schrodinger-Poisson equations considering the spontaneous and piezoelectric polarization effects. The polarization field in the well or barrier of the QCD is obtained by assuming continuity of the displacement vector and the electronic transport is determined by piezoelectric polarization induced piezoelectric scattering, LO-phonon scattering and some other scattering mechanisms. The results show that the polarization charges at the interface make a significant contribution to the confining potential, which reduces the dark current, and increases the detectivity. The peak responsivity drops only 6.37% from 57 to 400 K without apparent redshift and the detectivity can be significantly improved by increasing doping concentration. This work is beneficial for the ZnO/MgZnO QCD design.

Erratum: “High photoresponse in room temperature quantum cascade detector based on coupled quantum well design” [Appl. Phys. Lett. 109, 261107 (2016)

First Page

Role of interface roughness scattering, temperature, and structural parameters on the performance characteristics of III-nitride quantum cascade detectors

A III-nitride quantum cascade detector (QCD) for the fiber optic communication wavelength (∼1.5 μm) has been designed, and the effect of intersubband scattering processes such as longitudinal-optical phonon scattering, ionized impurity scattering, and more importantly interface roughness scattering on responsivity performance has been analyzed. Carrier transport in the detector is modeled using a simplified rate equation approach. It is observed that inclusion of interface roughness scattering in the carrier transport model significantly enhances the responsivity performance of the detector. The effects of roughness conditions for instance mean roughness height and correlation length on responsivity have been examined. The responsivity of the designed detector drops by 2.16 mA/W at 400 K compared to its low temperature value at 50 K and the detection wavelength change with temperature is insignificant, which are very helpful for the stable detection of the radiation for a wide range of operating temperatures and show the thermal stability of III-nitride QCDs. The effects of active well widths, extractor barrier widths, and extractor well widths have been further investigated. A higher responsivity performance is observed for narrower barrier widths. It is noticed that change in the active well width significantly modifies the responsivity of the detector and the wavelength gets red shifted for larger active well widths.

Quantum dot quantum cascade photodetector using a laser structure

We report on a quantum dot quantum cascade detector (QD-QCD), whose structure is derived from a QD cascade laser. In this structure, more ordered InAs QD layers formed in the Stranski–Krastanow growth mode on a thin GaAs buffer layer are incorporated into the active region. This QD-QCD can operate up to room temperature with a peak detection wavelength of 5.8 μm. A responsivity of 3.1 mA/W at 160 K and a detectivity of 3.6 × 108 Jones at 77 K are obtained. The initial performance of the detector is promising, and, by further optimizing the growth of InAs QDs, integrated QD-quantum cascade laser/QCD applications are expected.

High photoresponse in room temperature quantum cascade detector based on coupled quantum well design

We report high photoresponse measured in a room temperature quantum cascade detector (QCD) based on a coupled quantum well design that operates with a peak response wavelength of 5.4 μm. The coupled quantum well design is expected to produce higher photocurrents when compared with device active regions that use a combination of simple quantum wells. The coupled quantum well QCD demonstrated high responsivity of 22 mA/W at room temperature with a commonly used 45° wedge-based light coupling configuration. Application of a waveguide configuration to the proposed QCD yielded an elevated responsivity of ∼130 mA/W and a specific detectivity (D*) of 1.1 × 108 cm W−1 Hz1/2 at room temperature.

Study on temperature effect on properties of ZnO/MgZnO based quantum cascade detector in mid-infrared region

The effect of temperature on a ZnO/Mg0.3Zn0.7O quantum cascade detector (QCD) in the mid-infrared region is investigated with consideration of bound-to-bound electronic-transport processes in the dark and under illumination. The temperature-dependent band structures of the QCD system, which comprises four quantum wells and five barriers in one period, are numerically calculated. The electronic transition is obtained with a standard electron-optical phonon Hamiltonian, and the photon absorption is described by the two-dimensional absorption coefficient. The responsivity of the ZnO/Mg0.3Zn0.7O QCD shows a good temperature stability without an obvious redshift, and the peak responsivity decreases by only 14% when the temperature increases from 50 to 300 K.

A Polarization-Dependent Normal Incident Quantum Cascade Detector Enhanced Via Metamaterial Resonators.

The design, fabrication, and characterization of a polarization-dependent normal incident quantum cascade detector coupled via complementary split-ring metamaterial resonators in the infrared regime are presented. The metamaterial structure is designed through three-dimensional finite-difference time-domain method and fabricated on the top metal contact, which forms a double-metal waveguide together with the metallic ground plane. With normal incidence, significant enhancements of photocurrent response are obtained at the metamaterial resonances compared with the 45° polished edge coupling device. The photocurrent response enhancements exhibit clearly polarization dependence, and the largest response enhancement factor of 165% is gained for the incident light polarized parallel to the split-ring gap.

Wavelength independent normal incident quantum cascade detectors.

We demonstrate a novel technique for normal-incident absorption in intersubband infrared detectors by taking advantage of light scattering from the side-walls of a wet-etched mesa. We fabricate 'spiral' and 'hairpin' shaped quantum cascade detector at a peak wavelength of 6.6 μm, and compare their performance with a standard rectangular mesa. We achieve a peak responsivity of 6 mA/W for the spiral and 12 mA/W for the hairpin detectors at normal incidence, comparable to the 8.8 mA/W obtained for the mesa at 45 degree incidence. We obtain a background limited detectivity of about 3×1010 cmHz/W for the spiral and hairpin detectors at 80 K, compared to 3×108 cmHz/W for the standard mesa. This method to achieve normal incidence absorption is wavelength independent, and does not involve complicated fabrication procedures, paving the way for widespread use of intersubband detectors in sensor applications.