Background Limited Detectivity Research Articles

Suitability of magnetic microbolometers based on paramagnetic temperature sensors for CMB polarization measurements

High resolution maps of polarization anisotropies of the Cosmic Microwave Background (CMB) are in high demand, since the discovery of primordial B-Modes in the polarization patterns would confirm the inflationary phase of the Universe that would have taken place before the last scattering of the CMB at the recombination epoch. Transition Edge Sensors (TES) and Microwave Kinetic Inductance Detectors (MKID) are the predominant detector technologies of cryogenic detector array based CMB instruments that search for primordial B-Modes. In this paper we propose another type of cryogenic detector to be used for CMB survey: A magnetic microbolometer (MMB) that is based on a paramagnetic temperature sensor. It is an adaption of state-of-the-art metallic magnetic calorimeters (MMCs) that are meanwhile a key technology for high resolution $\alpha$, $\beta$, $\gamma$ and X-ray spectroscopy as well as the study of neutrino mass. The effort to adapt MMCs for CMB surveys is triggered by their lack of Johnson noise associated with the detector readout, the possibility of straightforward calibration and higher dynamic range given it possesses a broad and smooth responsivity dependence with temperature and the absence of Joule dissipation which simplifies the thermal design. A brief proof of concept case study is analyzed, taking into account typical constraints in CMB measurements and reliable microfabrication processes. The results show that MMBs provide a promising technology for CMB polarization survey as their sensitivity can be tuned for background limited detection of the sky while simultaneously maintaining a low time response to avoid distortion of the point-source response of the telescope. As the sensor technology and its fabrication techniques are compatible with TES based bolometric detector arrays, a change of detector technology would even come with very low cost.

Long-wavelength infrared photovoltaic heterodyne receivers using patch-antenna quantum cascade detectors

Quantum cascade detectors (QCDs) are unipolar infrared devices where the transport of the photoexcited carriers takes place through confined electronic states, without an applied bias. In this photovoltaic mode, the detector's noise is not dominated by a dark shot noise process, and therefore, performances are less degraded at high temperature with respect to photoconductive detectors. This work describes a 9 μm QCD embedded into a patch-antenna metamaterial, which operates with state-of-the-art performances. The metamaterial gathers photons on a collection area, Acoll, much larger than the geometrical area of the detector, improving the signal to noise ratio up to room temperature. The background-limited detectivity at 83 K is 5.5 × 1010 cm Hz1/2 W−1, while at room temperature, the responsivity is 50 mA/W at 0 V bias. A patch antenna QCD is an ideal receiver for a heterodyne detection setup, where a signal at a frequency of 1.4 GHz and T = 295 K is reported as demonstration of uncooled 9 μm photovoltaic receivers with a GHz electrical bandwidth. These findings guide the research toward uncooled IR quantum limited detection.

Low-Temperature Detectors for CMB Imaging Arrays

We review advances in low temperature detector (LTD) arrays for Cosmic Microwave Background (CMB) polarization experiments, with a particular emphasis on imaging arrays. We briefly motivate the science case, which has spurred a large number of independent experimental efforts. We describe the challenges associated with CMB polarization measurements and how these challenges impact LTD design. Key aspects of an ideal CMB polarization imaging array are developed and compared to the current state-of-the-art. These aspects include dual-polarization-sensitivity, background-limited detection over a 10:1 bandwidth ratio, and frequency independent angular responses. Although existing technology lacks all of this capability, today's CMB imaging arrays achieve many of these ideals and are highly advanced superconducting integrated circuits. Deployed arrays map the sky with pixels that contain elements for beam formation, polarization diplexing, passband definition in multiple frequency channels, and bolometric sensing. Several detector architectures are presented. We comment on the implementation of both transition-edge-sensor bolometers and microwave kinetic inductance detectors for CMB applications. Lastly, we discuss fabrication capability in the context of next-generation instruments that call for $\sim 10^6$ sensors.

Antenna Coupled MKID Performance Verification at 850 GHz for Large Format Astrophysics Arrays

Next generation sub-mm imaging instruments require kilo-pixel focal plane arrays filled with background limited detectors. Microwave kinetic inductance detectors (MKIDs) are a state-of-the-art detector for future instruments due to their inherent multiplexing capabilities. An MKID consists of a superconducting resonator coupled to a feed-line that is used for readout. In the device presented here radiation coupling is achieved by coupling the MKID directly to a planar antenna. The antenna is placed in the focus of an extended hemispherical lens to increase the filling factor and to match efficiently to fore optics. In this paper, we present the design and the optical performance of MKIDs optimized for operation in a 100-GHz band around 850 GHz. We have measured the coupling efficiency, frequency response, and beam patterns and compare those results to simulated performance. We obtain an excellent agreement between the measured and simulated beam pattern, frequency response, and absolute coupling efficiency between a thermal calibration source and the power absorbed in the detector. Additionally, we demonstrate that antenna coupled MKIDs offer background limited radiation detection down to ∼100 aW of power absorbed in the detector.

Recent Progresses in Mid Infrared Nanocrystal Optoelectronics

Over the past few years, colloidal nanoparticles have started to be investigated for their optical properties in the mid-infrared, past 3 μ m. Research on detector application has led to background limited detection and fast video imaging at 5 μ m. With further development, one could imagine that these new materials could vastly reduce the costs of infrared technology and this would lead to a trove of new applications for infrared imaging into our daily lives. This paper reviews the progress regarding the optical, transport, and photodetection properties of thin film based on these materials, and the three different ways by which infrared resonances have been realized with colloidal nanoparticles: interband absorption with small gap semiconductor quantum dots, intraband absorption in lightly doped quantum dots, and plasmonic resonances in heavily doped nanocrystals.

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.

Interband-cascade infrared photodetectors with superlattice absorbers

Interband-cascade infrared photodetectors (ICIPs), composed of discrete superlattice absorbers, are demonstrated at temperatures up to 350 K with a cutoff wavelength near 5 μm at 80 K to beyond 7 μm above room temperature. The peak responsivity exceeds 200 mA/W, higher than the values reported from early interband cascade laser structures, suggesting a significantly enhanced quantum efficiency of the superlattice absorbers. A theoretical model, originally developed for quantum well infrared photodetectors (QWIPs), is applied to ICIPs to analyze their device performance. The Johnson-limited and background-limited detectivities are extracted and indicate that background-limited performance temperatures for two ICIP structures are 126 and 105 K at 5 μm. It is expected that optimized ICIPs will provide improved performance by combining the advantages of conventional photodiodes and the discrete nature of QWIPs and IC lasers.

Mid-wave QWIPs for the [3–4.2 μm] atmospheric window

We report two approaches using Quantum Well Infrared Photodetectors for detection in the [3–4.2 μm] atmospheric window. Taking advantage of the large band gap discontinuity we demonstrated a strained AlInAs/InGaAs heterostructure on InP. The optical coupling in this structure has been experimentally and numerically investigated. The results show that the coupling is mainly due to guided modes. The second approach is based on double barrier strained AlGaAs/AlAs/GaAs/InGaAs active layers on GaAs. The segregation of the elements III in these structures has been investigated using a transmission electron microscope. The results show a strong modification of the conduction band profile. We demonstrate peak wavelengths at 3.9 μm for the InP based detector and 4.0 μm for the GaAs based detector. We report a background limited peak detectivity (2π field of view, 300 K background) at 4.0 μm of about 2 × 10 11 cm Hz 1/2 W −1 at 77 K, and 1.5 × 10 11 cm Hz 1/2 W −1 at 100 K.

Double barrier strained quantum well infrared photodetectors for the 3–5μm atmospheric window

We present a detailed study of double barrier strained Al0.35Ga0.65As/AlAs/GaAs/In0.2Ga0.8As quantum well infrared photodetectors on GaAs substrate. Measurements were made on four different well widths active layers and on several mesa pixels with different optical coupling structures. We obtained responses peaked in the spectral range 3.6–4.6 μm. Based on the experimental results, we show that in the background limited regime, the impact ionization is the restrictive transport process for midwave detectors. We also demonstrate a 4 μm structure with the high background limited detectivity of 2×1011 Jones at 77 K and 9×1010 Jones at 110 K (2π field of view, 300 K background).

Cryogenic technology for CMBPol

Future space telescopes such as CMBPol, SAFIR, DARWIN, SPICA and XEUS will require cooling to very low temperatures. Staged cooling is the most efficient means of achieving low temperature in an observatory or instrument with the least cost and mass. The first stage is usually passive radiators taking advantage of views to deep space. In the past stored cryogen systems provided the next lower stagesof cooling. Mechanical cryocoolers represent a significant enabling technology, especially at the lower temperatures where the passive coolers' effectiveness is limited. These coolers are in general lighter, have more cooling capability, and more operationally flexible than stored cryogens. Sub Kelvin cooling is required for many of the most sensitive detectors. For fundamental reasons, microcalorimeters and bolometers must be cooled to extremely low temperature to achieve their ultimate resolution and, eventually, background-limited detection. The state of the art for these cryogenic cooling technologies are presented along with plans to advance the technology readiness level to enable these future missions.

A high performance quantum-well infrared photodetector detecting below 4.1 µm

We demonstrate a high performance quantum-well infrared photodetector on GaAs(0 0 1) substrate, with a spectral response peaked below the carbon dioxide absorption band. The active layer is based on an AlGaAs/AlAs/InGaAs/AlAs/AlGaAs quantum well and designed to achieve a bound to quasi-bound transition. The external quantum efficiency measured at 130 K and –1 V is as high as 21%, leading to peak absorption higher than 28% when an anti-reflection coating is used. The background limited peak detectivity reaches 7 × 1011 Jones (cm Hz1/2 W−1) at 77 K and f/1.6. The detector operates in the background limited regime up to 100 K. Our measured characteristics are key inputs to estimate the performance of a thermal imager and are directly useable by system designers.

Midinfrared quantum cascade detector with a spectrally broad response

A midinfrared quantum cascade detector with a spectrally broad (ΔE∕E=27.3%) response is designed, fabricated, and tested. This detector consists of 26 differently designed active region stages in order to cover a wavelength region from 4.7to7.4μm. The device could be operated above room temperature and showed peak responsivities of 13mA∕W at 10K and 1.25mA∕W at room temperature. A background limited detectivity of 1.55×1010 Jones was seen up to a temperature TBLIP of 110K.

InP-based quantum cascade detectors in the mid-infrared

We present two InP-based quantum cascade detectors (QCDs) in the mid-infrared wavelength range. Their narrow band detection spectra are centered at 5.3 and 9μm. A vertical intersubband transition followed by a carefully designed extraction cascade, which is adapted to the LO-phonon energy, leads to 10K responsivities R of 3.2 and 9.0mA∕W and background limited detectivities DBLIP* of 2×108 and 3×109 Jones, for the 5.3 and the 9μm devices, respectively. Detection has been observed up to device temperatures of 300K (RT), albeit reasonable performance is restricted to temperatures below 150K (5.3μm) and 70K (9μm). Designed for zero bias operation, QCDs do not produce any dark current and therefore do not suffer from dark current noise and capacitance saturation at long integration times, making them ideal devices for large focal plane arrays.

High-responsivity high-gain In/sub 0.53/Ga/sub 0.47/As-InP quantum-well infrared photodetectors grown using metal-organic vapor phase epitaxy

We report the growth and fabrication of bound-to-bound In/sub 0.53/Ga/sub 0.47/As-InP quantum-well infrared photodetectors using metal-organic vapor phase epitaxy. These detectors have a peak detection wavelength of 8.5 /spl mu/m. The peak responsivities are extremely large with R/sub pk/=6.9 A/W at bias voltage V/sub b/=3.4 V and temperature T=10 K. These large responsivities arise from large detector gain that was found to be g/sub n/=82 at V/sub b/=3.8 V from dark current noise measurements at T=77 K and g/sub p/=18.4 at V/sub b/=3.4 V from photoresponse data at T=10 K. The background-limited temperature with F/1.2 optics is T/sub BLIP/=65 K for 0<V/sub b//spl les/3.4 V. The highest value of peak detectivity is D/sub /spl lambda///sup */=5.4/spl times/10/sup 9/ cm/spl radic/Hz/W at V/sub b/=2.9 V and T=77 K, while for T<T/sub BLIP/=65 K, the background-limited detectivity, which exhibits negligible bias dependence, is D/sub BLIP//sup */=3/spl times/10/sup 10/ cm/spl radic/Hz/W.

Multispectral long-wavelength quantum-well infrared photodetectors

Multispectral detector arrays for application in the 8–11 μm spectral band have been fabricated from GaAs/AlGaAs multiple quantum-well (MQW) materials. For efficient narrow-band coupling of the infrared radiation, three-dimensional diffractive resonant optical cavities are patterned into the MQW material. The peak wavelengths of the multispectral quantum-well infrared photodetectors are tuned by controlling the dimensions of the resonant structure. The full width at half maximum of the spectral response is as narrow as 0.7 μm. As many as 24 different detector designs were implemented on a single array. The spectrally tuned detectors exhibit peak responsivities as high as 2.6 A/W and quantum efficiency as high as 57%. Total conversion efficiency is as high as 35%. The background limited peak detectivity measured at 9.0 μm and 55 K with a 295 K background and f/2.5 is ⩾1×1011 cm Hz0.5/W.

A novel simultaneous unipolar multispectral integrated technology approach for HgCdTe IR detectors and focal plane arrays

In the last few years Rockwell has developed a novel simultaneous unipolar multispectral integrated HgCdTe detector and focal plane array technology that is a natural and relatively straightforward derivative of our baseline double layer planar heterostructure (DLPH) molecular beam epitaxial (MBE) technology. Recently this technology was awarded a U.S. patent. This simultaneous unipolar multispectral integrated technology (SUMIT) shares the high performance characteristics of its DLPH antecedent. Two color focal plane arrays with low-1013 cm−2s−1 background limited detectivity performance (BLIP D*) have been obtained for mid-wave infrared (MWIR, 3–5 m) devices at T>130 K and for long-wave infrared (LWIR, 8–10 m) devices at T∼80 K.

Discrepancies between two formulations of signal-to-noise ratio for background-limited detection

Different investigators have published different relationships for the same problem of predicting the signal-to-noise ratio for incoherent passive detection of infrared radiation. The results of two authors are compared, and a possible basis for the differences is explained.

Performance assessment of quantum well infrared photodetectors

The performance of GaAs/AlGaAs quantum well infrared photodetectors specified in terms of background limited temperature Tb and specific detectivity D* has been calculated based on realistic detector parameters. It is found that for a detector with an external quantum efficiency η of 6.9%, Tb is 76 K for a cutoff wavelength of 10 μm. This value of Tb agrees with the recent experimental result and is significantly higher than the previous estimation given by M. A. Kinch and A. Yariv [Appl. Phys. Lett. 55, 2093 (1989)]. If η is unity, the projected Tb can be as high as 88 K with a D* of 2.2×1011 cm√Hz/W. For a lower temperature operation, D* increases to 7.5×1011 cm√Hz/W at 77 K, comparable to that of a HgCdTe detector.

IR‐device Grade (Hg, Cd)Te Crystals Grown by a Modified Bridgman Method

AbstractElectrical and photoelectrical properties of IR‐devices manufactured on (Hg, Cd)Te‐wafers cut from single crystals grown by modified Bridgman method are reported and compared to those of devices made on THM‐(Hg, Cd)Te.MIS‐structures and photodiodes were used in order to investigate the different materials.The influence of material parameters and device technology respectively is involved in our discussion of device properties. The quality of modified Bridgman‐(Hg, Cd)Te was found to be comparable to that of the THM‐(Hg, Cd)Te.At T = 80 K and FOV = 60° background limited detectivity of photodiodes with a cut‐off wavelength of λco = 10.7 μm was achieved.

Mid-infrared detectors in the 3–5 μm band using bound to continuum state absorption in InGaAs/InAlAs multiquantum well structures

Medium wavelength infrared (MWIR) detectors in the 3–5 μm band are demonstrated using bound to continuum state intersubband absorption in lattice-matched InGaAs/InAlAs multiquantum well (MQW) structures. Photodetectors with responsivity peaked at 4 μm wavelength showed low dark current giving a background-limited detectivity D*BL =2.3×1010 cm(Hz)1/2 /W at temperatures up to 120 K.