Short-wave Infrared Detectors Research Articles

Self‐Assembly PbS Quantum Dot‐Conjugated Polymer Hybrid‐Layered Phototransistor Enables SWIR Photodetection with High Detectivity

AbstractLead sulfide colloid quantum dots (PbS QDs) offer great opportunities to revolutionize large‐area short‐wave infrared (SWIR) detection technologies due to high absorption coefficients and spectral selectivity. However, a critical issue for QDs‐based SWIR detectors is high dark current noise due to thermal carriers and the large amounts of surface defect states induced by the ligand exchange process, which hinders the improvement of the room temperature detectivity and linear dynamic range. Herein, it is demonstrated that these dilemmas can be overcome by adopting a novel hybrid‐layered phototransistor device architecture composed of a self‐assembly high‐mobility organic conduction channel and a bulk heterojunction infrared absorber containing PbS QDs as sensitizers. Strong photo absorption in the photoactive layer creates photogenerated charges that are transferred to the conduction channel, where they recirculate many times due to the long trapped‐electron lifetime in the photoactive layer and the high carrier mobility of the channel. Therefore, low dark current noise and high photoconductive gain are achieved by both electrical gating and photodoping for carrier‐density modulation of phototransistors. Finally, an optimized SWIR phototransistor device with a low room‐temperature dark current of 7 pA and a high detectivity of 8 × 1012 Jones under 1650 nm light illumination is demonstrated.

Numerical study on infrared detectors cooling by multi-stage thermoelectric cooler combined with microchannel heat sink

Lightweight, noiseless, and constant low-temperature refrigeration is crucial for cooled infrared (IR) detectors, especially short-wave-infrared (SWIR) detectors. However, some SWIR detectors, such as HgCdTe photovoltaic detectors are working below 210 K. For this application, multi-stage thermoelectric coolers (TEC) are preferable to single-stage thermoelectric coolers because they can generate larger temperature differences. This paper presents a refrigeration design that integrates SWIR and TEC into a vacuum Dewar package and combines them with a microchannel heat sink (MHS) to improve the detection performance and better responsiveness of SWIR. Two different refrigeration models, SWIR + TEC + AHS (air-cooled heat sink) and SWIR + TEC + MHS, were established to evaluate the refrigeration performance of the proposed SWIR + TEC + MHS scheme using the finite element method. The influences of multi-stage TEC leg length and current, inlet water temperature, and water velocity on the refrigeration performance of the TEC are analyzed. The results show that the SWIR + TEC + MHS design scheme has the best comprehensive performance and minimum volume. The influences of all the factors are obvious while the current has the most important effect on the performance. The temperature of SWIR reached 201.69 K at standard working conditions. It shows that the cooling scheme can not only meet the needs of flexible deployment of SWIR but also provide better thermal security. The proposed cooling design has an excellent prospect for short-wave-infrared detectors.

Infrared detectors for first generation extremely large telescope instruments and their characterization program

The detectors for the three first generation extremely large telescope (ELT) instruments MICADO (Multi‐AO Imaging Camera for Deep Observations), HARMONI (A High Angular Resolution Monolithic Optical and Near‐infrared Integral Field Spectrograph), and METIS (A Mid‐infrared ELT Imager and Spectrograph) cover from the optical to longwave infrared wavelengths. MICADO and HARMONI detector focal planes require 17 H4RG (Hawaii‐4RG) near‐infrared whilst the METIS focal planes consist of 5 SWIR (shortwave infrared) detectors and one longwave infrared detector. Procurement of the optical and SWIR detectors has been completed, whilst the H4RGs and long wavelength detectors are still in progress. A custom cryogenic facility for infrared array testing (FIAT) has been designed and developed at European Southern Observatory (ESO) over the last few years in order to characterize the infrared detectors for ELT and future Very Large Telescope instruments. FIAT is currently being commissioned in our labs with an H4RG engineering detector. FIAT will be used to characterize the science H4RG‐15 detectors for MICADO and HARMONI, the two first‐light instruments of the ELT while the existing Mosaic Test Facility (MTF) will be used for characterizing the SWIR detectors for METIS. This paper presents an overview of the detector systems for the three instruments, their engineering challenges, and the requirements for the detectors' performance and their characterization program. The paper will also describe a test setup for H4RG detectors including a new preamplifier design with options to operate the detector in different modes and it will also report on the test results from the engineering H4RG detector, as part of the commissioning of FIAT and discuss detector performance and related detector issues.

Short-wave infrared real-time high dynamic range imaging and display based on correlated double sampling.

A real-time high dynamic range (HDR) imaging and display method based on correlated double sampling is proposed for short-wave infrared (SWIR) cameras in order to effectively improve its range of brightness and contrast, as well as to obtain more image details. The method utilizes the correlated double sampling technique of the SWIR detector to extend the 14-bit raw image into a 16-bit HDR image and achieve 4 times the HDR imaging. Subsequently, a dynamic range compression process, including logarithmic mapping and histogram equalization, is performed for the 16-bit HDR image to be mapped to an 8-bit display. Finally, the experimental results show that the method can enrich the details of SWIR images under the premise of ensuring real-time imaging.

Optical and structural properties of In-rich InxGa1−xAs epitaxial layers on (1 0 0) InP for SWIR detectors

In-rich InxGa1−xAs epitaxial layers were grown on InP (100) substrates by a metalorganic vapor phase epitaxy (MOVPE) technique. The effect of Indium (In) composition on the crystalline quality and optical properties are investigated. High resolution X-ray diffraction (HR-XRD) measurement and Raman scattering spectrum are used to evaluate the crystalline quality, the residual strain and dislocation density property. The number of dislocations in the epitaxial layers is found to increase by increasing the Indium content in order to release the stresses due to the epitaxial clamping. Photoluminescence (PL) measurement is used to characterize the optical properties. At 10 K, PL measurements show that the InGaAs band gap redshifts with the indium content. Moreover, the asymmetry at the low-energy side of the PL peak has been attributed to the presence of localized excitons. In all samples, a blue shift of PL peaks is evidenced by increasing the excitation power density, which is in line with the presence of carrier’s localization and non-idealities in this system. Moreover, the temperature-dependence of the PL peak energy displays an unusual red-blue-red shift (S-shaped) behavior when raising the temperature. These observations can be related to the inhomogeneous distribution of indium which gives rise to the appearance of dislocations and other defects which serve as traps for charge carriers. Interestingly, those highly In-content InxGa1−xAs epitaxial layers show PL emission located between 1637 and 1811 nm (depending on In content) and thus might be suitable for in the design of novel heterostructure devices such as short wave infrared (SWIR) detectors.

InGaAs photo field-effect-transistors (PhotoFETs) on half-inch Si wafer using layer transfer technology

InGaAs photo field-effect transistors (PhotoFETs) integrated on a half-inch Si wafer have been demonstrated by means of layer transfer technology. According to the Raman measurement and scanning transmission electron microscopy, the InGaAs layer was transferred onto the half-inch Si wafer without degradation of crystal quality or introduction of strain. The optical performance of InGaAs photoFETs on Si, operating in shortwave infrared (SWIR) region was also investigated. The photoFETs on Si wafer show a responsivity of ∼3 A W−1 at SWIR of 1550 nm with investigated range of bias. These results demonstrate InGaAs layer transfer technology is suitable for SWIR detectors on CMOS compatible platforms for monolithic integration.

Uncooled Short-Wave Infrared Sensor Based on PbS Quantum Dots Using ZnO NPs.

Shortwave infrared (SWIR) sensors have attracted interest due to their usefulness in applications like military and medical equipment. SWIR sensors based on various materials are currently being studied. However, most SWIR detectors need additional optical filters and cooling systems to detect specific wavelengths. In order to overcome these limitations, we proposed a solution processed SWIR sensor that can operate at room temperature using lead chloride (PbS) QDs as a photoactive layer. Additionally, we adapted zinc oxide (ZnO) nanoparticles (NPs) as an electron transport layer (ETL) to improve the sensitivity of a PbS SWIR sensor. In this study, PbS SWIR sensors with and without a ZnO NPs layer were fabricated and their current–voltage (I–V) characteristics were measured. The on/off ratio of the PbS SWIR sensor with ZnO NPs was 2.87 times higher than that of the PbS SWIR sensor without ZnO NPs at the maximum current difference. The PbS SWIR sensor with ZnO NPs showed more stable current characteristics than that without ZnO NPs because of the ZnO NPs’ high electron mobility and proper lowest unoccupied molecular orbital (LUMO) level.

Simple fabrication of SWIR detectors based on wet deposition of carbon nanotubes and quantum dots

Over the last two decades, carbon based materials and especially carbon nanotubes (CNTs), were the subject of many studies, mainly due to their unique electrical, optical and mechanical properties (Ouyang et al., 2002; Dresselhaus et al., 2003; Dresselhaus et al., 1995). CNTs can combine electrical conductivity with wide absorption spectra, and can be produced in large scale (Danafar et al., 2009) [4]. These properties enable to realize CNTs in simple, low-cost detector. Here we present a proof-of-concept for such a detector operating at the short-wave infrared (SWIR) regime. We use a simple spray technique, which allows creating a large matrix of CNT bundles. Semiconducting quantum dots (QDs) were adsorbed on top of the CNTs, enhancing the sensitivity to the infrared regime. This regime is important for numerous applications in the civil, medical, defense and security fields. Controlled coupling between the QDs and the CNT matrix generates gate-like electro-optical response when light is absorbed. This proof-of-concept for a detector in the SWIR region is presented for large surfaces and substrates, while the responsivity and detectivity of the detector in a range of frequencies and wavelengths was evaluated.

Multi-Channel Optical Receiver for Ground-Based Topographic Hyperspectral Remote Sensing

Receiver design is integral to the development of a new remote sensor. An effective receiver delivers backscattered light to the detector while optimizing the signal-to-noise ratio at the desired wavelengths. Towards the goal of effective receiver design, a multi-channel optical receiver was developed to collect range-resolved, backscattered energy for simultaneous hyperspectral and differential absorption spectrometry (LAS) measurements. The receiver is part of a new, ground-based, multi-mode lidar instrument for remote characterization of soil properties. The instrument, referred to as the soil observation laser absorption spectrometer (SOLAS), was described previously in the literature. A detailed description of the multi-channel receiver of the SOLAS is presented herein. The hyperspectral channel receives light across the visible near-infrared (VNIR) to shortwave infrared (SWIR) spectrum (350–2500 nm), while the LAS channel was optimized for detection in a narrower portion of the near-infrared range (820–850 nm). The range-dependent field of view for each channel is presented and compared with the beam evolution of the SOLAS instrument transmitter. Laboratory-based testing of each of the receiver channels was performed to determine the effectiveness of the receiver. Based on reflectance spectra collected for four soil types, at distances of 20, 35, and 60 m from the receiver, reliable hyperspectral measurements were gathered, independent of the range to the target. Increased levels of noise were observed at the edges of the VNIR and SWIR detector ranges, which were attributed to the lack of sensitivity of the instrument in these regions. The suitability of the receiver design, for the collection of both hyperspectral and LAS measurements at close-ranges, is documented herein. Future development of the instrument will enable the combination of long-range, ground-based hyperspectral measurements with the LAS measurements to correct for absorption, due to atmospheric water vapor. The envisioned application for the instrument includes the rapid characterization of bare or vegetated soils and minerals, such as are present in mine faces and tailings, or unstable slopes.

High-sensitivity short-wave infrared technology for thermal imaging

Thermal imaging technology is widely used in various fields, such as security, defense, medicine and spaceborne applications in the Geo-synchronous Earth Orbit. Most thermal imaging systems operate in the long-wave infrared (LWIR) range or the medium-wave infrared (MWIR) range. However, the longer the wavelength is, the more difficult the imaging system is to provide high resolution due to diffraction limit. Compared to MWIR and LWIR imagers, a short-wave infrared (SWIR) imager achieves higher resolution owing to its higher diffraction limit. However, radiation from an object at 300 k in the SWIR band is weaker than that in the MWIR and LWIR bands. Therefore, the sensitivity is low. With the rapid development of detector technology, the sensitivity of SWIR detector is improved by low dark current and noise. It exhibits good performance in thermal imaging applications. In order to validate SWIR thermal imaging key performance, this study analyzes the thermal imaging capability of an SWIR imager compared to MWIR and LWIR. The noise equivalent temperature differences (NETDs) of SWIR, MWIR, and LWIR imagers for thermal imaging applications are calculated. A compact SWIR imager prototype covering a spectral range of 2.0–2.7 μm is designed and implemented. The facial thermal imaging experiment proves that the high-sensitivity SWIR imager can obtain high-quality thermal images with an NETD of 24 mK at a temperature of 310 K. In addition, in the continuous integration and multiple read-out (IMRO) imaging mode, the dynamic range of the system is extended by 20 dB. The theoretical analysis and experiment show that the SWIR imager can provide high sensitivity with long integration time. In addition, SWIR thermal imaging can provide higher resolution than MWIR and LWIR imagers. Therefore, SWIR imager has considerable potential for high-sensitivity thermal imaging applications in Geo-synchronous Earth Orbit.

Guide star catalog generation for short-wave infrared (SWIR) All-Time star sensor.

As an important part of All-Time star sensor design, the generation of the short-wave infrared (SWIR) guide star catalog is crucial to the system performance. The generation process needs estimation of the instrument magnitude and the guide star selection. Different from the commonly used star sensors, since the SWIR band is far away from the visual band and the detectable magnitude limit of the All-Time star sensor is dynamically changing as the observation conditions vary, the current methods of estimating the instrument magnitude cannot be directly applied and the catalog obtained through the current reduction methods that mainly aimed at improving the distribution uniformity cannot ensure enough stars measured in the field of view under strong sky background radiation. To solve the problems, we propose a method for guide star catalog generation for the All-Time star sensor. First, through the specific analysis of the spectral response curves of the SWIR detector and 2MASS detection bandpasses, the method of estimating instrument magnitudes for the All-Time sensor is determined. Subsequently, dynamic detectable magnitude limits are determined through the signal-to-noise model and the atmospheric background radiation intensity analysis. Based on the dynamic detectable magnitude limits, a reduction method is proposed. The simulation experiment results indicate that the RMS error of the estimation of instrument magnitude is 0.075. Compared to the magnitude filtering method, the guide star catalog obtained through our method can guarantee the completeness, besides, the global distribution uniformity increases by 2.2 times and the local distribution uniformity increases by 10.7 times.

Detector with internal gain for short-wave infrared ranging applications

Highly sensitive photon detectors are regarded as the key enabling elements in many applications. Due to the low photon energy at the short-wave infrared (SWIR), photon detection and imaging at this band are very challenging. As such, many efforts in photon detector research are directed toward improving the performance of the photon detectors operating in this wavelength range. To solve these problems, we have developed an electron-injection (EI) technique. The significance of this detection mechanism is that it can provide both high efficiency and high sensitivity at room temperature, a condition that is very difficult to achieve in conventional SWIR detectors. An EI detector offers an overall system-level sensitivity enhancement due to a feedback stabilized internal avalanche-free gain. Devices exhibit an excess noise of unity, operate in linear mode, require bias voltage of a few volts, and have a cutoff wavelength of 1700 nm. We review the material system, operating principle, and development of EI detectors. The shortcomings of the first-generation devices were addressed in the second-generation detectors. Measurement on second-generation devices showed a high-speed response of ∼6 ns rise time, low jitter of less than 20 ps, high amplification of more than 2000 (at optical power levels larger than a few nW), unity excess noise factor, and low leakage current (amplified dark current ∼10 nA at a bias voltage of −3 V and at room temperature. These characteristics make EI detectors a good candidate for high-resolution flash light detection and ranging (LiDAR) applications with millimeter scale depth resolution at longer ranges compared with conventional p-i-n diodes. Based on our experimentally measured device characteristics, we compare the performance of the EI detector with commercially available linear mode InGaAs avalanche photodiode (APD) as well as a p-i-n diode using a theoretical model. Flash LiDAR images obtained by our model show that the EI detector array achieves better resolution with higher signal-to-noise compared with both the InGaAs APD and the p-i-n array (of 100×100 elements). We have designed a laboratory setup with a receiver optics aperture diameter of 3 mm that allows an EI detector (with 30-μm absorber diameter) to be used for long-range LiDAR imaging with subcentimeter resolution.

Advances on Sensitive Electron-Injection Based Cameras for Low-Flux, Short-Wave Infrared Applications

Short-wave infrared (SWIR) photon detection has become an essential technology in the modern world. Sensitive SWIR detector arrays with high pixel density, low noise levels and high signal-to-noise-ratios are highly desirable for a variety of applications including biophotonics, light detection and ranging, optical tomography, and astronomical imaging. As such many efforts in infrared detector research are directed towards improving the performance of the photon detectors operating in this wavelength range. We review the history, principle of operation, present status and possible future developments of a sensitive SWIR detector technology, which has demonstrated to be one of the most promising paths to high pixel density focal plane arrays for low flux applications. The so-called electron-injection (EI) detector was demonstrated for the first time (in 2007). It offers an overall system-level sensitivity enhancement compared to the p-i-n diode due to a stable internal avalanche-free gain. The amplification method is inherently low noise, and devices exhibit an excess noise of unity. The detector operates in linear-mode and requires only bias voltage of a few volts. The stable detector characteristics, makes formation of high yield large-format, and high pixel density focal plane arrays less challenging compared to other detector technologies such as avalanche photodetectors. Detector is based on the mature InP material system (InP/InAlAs/GaAsSb/InGaAs), and has a cutoff wavelength of 1700 nm. It takes advantage of a unique three-dimensional geometry and combines the efficiency of a large absorbing volume with the sensitivity of a low-dimensional switch (injector) to sense and amplify signals. Current devices provide high-speed response ~ 5 ns rise time, and low jitter ~ 12 ps at room temperature. The internal dark current density is ~ 1 μA/cm2 at room temperature decreasing to 0.1 nA/cm2 at 160 K. EI detectors have been designed, fabricated, and tested during two generations of development and optimization cycles. We review our imager results using the first-generation detectors. In the second-generation devices, the dark current is reduced by two orders of magnitude, and bandwidth is improved by 4 orders of magnitude. The dark current density of the EI detector is shown to outperform the state-of-the-art technology, the

1/f noise in large-area Hg1−xCdxTe photodiodes

The 1/f noise in photovoltaic (PV) molecular-beam epitaxy (MBE)-grown Hg1−xCdxTe double-layer planar heterostructure (DLPH) large-area detectors is a critical noise component with the potential to limit sensitivity of the cross-track infrared sounder (CrIS) instrument. Therefore, an understanding of the origins and mechanisms of noise currents in these PV detectors is of great importance. Excess low-frequency noise has been measured on a number of 1000-µm-diameter active-area detectors of varying “quality” (i.e., having a wide range of I-V characteristics at 78 K). The 1/f noise was measured as a function of cut-off wavelength under illuminated conditions. For short-wave infrared (SWIR) detectors at 98 K, minimal 1/f noise was measured when the total current was dominated by diffusion with white noise spectral density in the mid-10−15A/Hz1/2 range. For SWIR detectors dominated by other than diffusion current, the ratio, α, of the noise current in unit bandwidth in(f = 1 Hz, Vd = −60 mV, and Δf = 1 Hz) to dark current Id(Vd = −60 mV) was αSW-d = in/Id ∼ 1 × 10−3. The SWIR detectors measured at 0 mV under illuminated conditions had median αSW-P = in/Iph ∼ 7 × 10−6. For mid-wave infrared (MWIR) detectors, αMW-d = in/Id ∼ 2 × 10−4, due to tunneling current contributions to the 1/f noise. Measurements on forty-nine 1000-µm-diameter MWIR detectors under illuminated conditions at 98 K and −60 mV bias resulted in αMW-P = in/Iph = 4.16 ± 1.69 × 10−6. A significant point to note is that the photo-induced noise spectra are nearly identical at 0 mV and 100 mV reverse bias, with a noise-current-to-photocurrent ratio, αMW-P, in the mid 10−6 range. For long-wave infrared (LWIR) detectors measured at 78 K, the ratio, αLW-d = in/Id ∼ 6 × 10−6, for the best performers. The majority of the LWIR detectors exhibited αLW-d on the order of 2 × 10−5. The photo-induced 1/f noise had αLW-P = in/Iph ∼ 5 × 10−6. The value of the noise-current-to-dark-current ratio, α appears to increase with increasing bandgap. It is not clear if this is due to different current mechanisms impacting 1/f noise performance. Measurements on detectors of different bandgaps are needed at temperatures where diffusion current is the dominant current. Excess low-frequency noise measurements made as a function of detector reverse bias indicate 1/f noise may result primarily from the dominant current mechanism at each particular bias. The 1/f noise was not a direct function of the applied bias.