Frontier technology of infrared photodetector $ Materials and devices for multi-mode infrared detection
2021, 50(1): 20211006.
doi: 10.3788/IRLA20211006
The long wavelength infrared polarimetric detector can greatly improve the recognition ability of thermal imaging. Owing to the physical limitation of the diffraction limit, the polarization extinction ratio of the current micro-grid polarizer-type long wavelength infrared polarimetric detectors can basically only be as high as about 10∶1. In this paper, a metal/dielectric/metal plasmonic microcavity structure has been fabricated, with the infrared detection active layer of the quantum wells being embedded inside the microcavity. Due to the near-field coupling between the upper grating and bottom reflector metals, a lateral Fabry-Perot resonance was established in the double-metal region, forming the plasmonic microcavity. Benefited from the mode selection characteristics of the microcavity and its resonant coupling with the quantum well intersubband transition, the normal incident light, which cannot be directly absorbed by the intersubband transition of the quantum wells, was coupled into the plasmonic microcavity, transforming its propagation direction into lateral and being absorbed by the quantum wells. The mechanism was confirmed by finite element simulation and the microcavity key parameters such as the grating width and the thicknesses were designed and optimized. Such a structure was applied to the detecting pixels sized at 27 × 27 μm, which was suitable for focal plane arrays. Resulting from the capture and confinement of the incident photons, the detectivity of the detecting pixels could be promoted by about one order of magnitude comparing to the un-structured 45o edge facet coupled detector fabricated from the same epitaxy wafer. The polarization extinction ratio greater than 100∶1 at about 13.5 μm of detecting peak wavelength in the long wavelength infrared waveband was achieved, while the peak intensity dependence on the polarizer azimuth angle fitted Malus law very well. Such a work provides a novel physical foundation and technical route for the development of high extinction ratio long wavelength infrared polarimetric imaging focal planes.
2021, 50(1): 20211007.
doi: 10.3788/IRLA20211007
Recently, the anomalous carrier transport in the quantum wells with the PN junction structures has been found experimentally, and the corresponding physical mechanism and the carrier transport model have been proposed. It is observed that the open circuit voltage or short-circuit current can be measured in the resonant excitation mode. Comparing the photoluminescence (PL) spectra of the two kinds of external circuits, it is found that the PL intensity decreased significantly under the short circuit condition. This suggests that the photogenerated carriers under the short circuit condition are not confined in the quantum well, but escaping from the junction region. However, this phenomenon of photocarriers escaping from the quantum wells is not found in the NN-type quantum well structure. Therefore, the effect of thermal excitation or tunneling is excluded to drive the carrier escaping from the quantum well. Based on this, the corresponding physical mechanism and carrier transport model are proposed. It is concluded that photogenerated carriers can escape from the quantum well directly under the built-in electric field of PN junction, and the radiative recombination luminescence occurs after the carrier escape process.
2021, 50(1): 20211008.
doi: 10.3788/IRLA20211008
In order to meet the needs of accurately detecting and recognizing many kinds of high-value targets (such as stealth), the continuous development of detection technology, and realizing high probability true or false target recognition and high precision target detection, location and tracking in complex battlefield environment, it is of great significance to research stealth and weak feature target detection and anti-jamming detection in complex battlefield environment, the high integration of polarization focal plane infrared detector technology is one of the important direction. Focusing on the development of an integrated MW 256×256 HgCdTe polarization focal plane infrared detector, the research progress from the integration of polarization detectors to design and preparation of polarization structures were introduced, as well as the performance testing of polarization detector. A subwavelength metal grating array was designed and fabricated, the polarization detector was integrated by flip chip, and the infrared polarization performance was tested and evaluated on MW256×256 HgCdTe focal plane device.
2021, 50(1): 20211013.
doi: 10.3788/IRLA20211013
Uncooled infrared detectors are widely used in the infrared field due to their low cost, small size, and low power consumption because they do not need the cooling device and can work at room temperature. In military application field, the uncooled detector has gradually entered the application domain of previous refrigerated detector, and has been widely used in some low-cost weapon systems, even replaced the original uncooled detectors in some application fields. In the civil field, it has shown its advantages in price and ease of use, and has aroused widespread interest and attention in civil in-vehicle night vision, security monitoring and other application field. The working theory of several typical uncooled infrared detectors such as Bolometer, pyroelectric, thermopile, etc. were introduced, and the status of the main products that have been commercialized at home and abroad was enumerated, the development of pixel pitch, array specifications, performance and packaging of mainstream bolometer devices was focused, which were currently the most widely used. In addition to the bolometer, pyroelectric, SOI diode and other products that had been commercialized, some new uncooled detection technologies or new detectors were introduced in detail: such as the application of metasurfaces in enhancing absorption in certain wavebands, the research progress of new materials bolometer, new bi-material uncooled devices, graphene, quantum dots, nanowires and other photoelectric detection technologies. Finally, the future development trend of uncooled infrared detectors were predicted in the end of the review.
2021, 50(1): 20211009.
doi: 10.3788/IRLA20211009
Quantum well infrared photodetectors (QWIPs) has been considered as another excellent candidate in long-wavelength and very-long-wavelength infrared detection. It shows more distinctive advantages than the traditional HgCdTe technology in long-wave infrared detection, multi-color detection and focal plane technology area. Keep research on QWIPs will greatly promote the development of our country's infrared detector technology. The outstanding advantages of QWIPs are its good maturity of III–V compound growth and processing techniques. However, due to the low quantum efficiency and the forbiddance of directly normal incident radiation absorption for n-type QW, it is necessary to design and prepare various gratings or microcavity structures for optical coupling and local electromagnetic field enhancement for different detection wavelengths. How to more effectively improve the optical coupling efficiency of QWIPs, reduce dark current, and increase the operating temperature of the device are still the hotspots of current research. The new type of QWIPs with local electromagnetic field enhancement in the past 5 years was emphatically introduced and summarizesd, focusing on the optical coupling, dark current and working temperature. Finally, the development of QWIPs with local electromagnetic field enhancement were given for future work.
Metal-2D material-metal photodetectors is the most common type of 2D material photodetectors. Due to the simple structure and the ease of integration with other systems, metal-2D material-metal photodetectors have received the widest range of attentions and research interest. The self-driven mode of this type of photodetectors has very low dark current, and then it is regarded as a promising new route for high performance infrared detection. However, there are two bottleneck problems for self-driven metal-2D material-metal photodetectors: (1) photoresponse cancellation caused by antisymmetric 2D material-contact junctions, (2) low responsivity due to limited light absorption of 2D materials. The recent progress on the study of metal-2D material-metal photodetectors with asymmetrically integrated plasmonic nanostructures was introduced, where asymmetrical light coupling was utilized to break the anti-symmetry between the photocurrents at the two contact-2D material junctions for self-driven net photoresponse, and the induced strong local field was utilized to enhance the absorptance and the responsivity of the 2D material. In the hybrid device of graphene and plasmonic nanocavities, the contrast between photoresponses at the two contacts is more than 100 times, which breaks through the problem of photoresponse cancellation caused by symmetric optical coupling. Due to the superior capability to couple the incident light into a localized mode, the plasmonic nanocavity can enhance the responsivity of graphene over one order of magnitude higher than a subwavelength metal grating.
2021, 50(1): 20211012.
doi: 10.3788/IRLA20211012
Terahertz radiation refers to electromagnetic waves with a wavelength range of 30 μm-1 mm, characterized by strong penetration, high safety, strong specificity and good orientation. Therefore, terahertz technology has broad application prospects in the fields of astronomical observation, safety monitoring, substance identification and biomedicine. Blocking-impurity-band detector has the advantages of high sensitivity, large array size and wide detection spectrum, which is an excellent choice for terahertz radiation detection. At present, the blocking-impurity-band detector is mainly based on three material systems, namely Si, Ge and GaAs. Si, Ge and GaAs-based blocking-impurity-band detectors can be used for ultra-wide band detection from 3 μm to 500 μm. Superstructure is an artificial composite structure composed of subwavelength structural units. By introducing superstructure into the photoelectric detector, the electromagnetic field energy will be strongly localized at the interface between the metal and the detector through plasmon resonance and dipole resonance modes. So, the combination of superstructure and blocking-impurity-band detector can effectively regulate the detection peak, reduce the full width at half maximum (FWHM) of detection peak and enhance the spectral resolution ability. So it is expected to be widely used in multiband fusion detection of 3-500 μm. At the same time, the combination of the two technologies can further improve the response rate of the device, reduce the size of the device and reduce the process difficulty. This paper briefly described the working mechanism of the blocking-impurity-band detector. And the research history and status of blocking-impurity-band detector at home and abroad are also introduced. Finally, the superstructure/blocking-impurity-band detector was described in detail in terms of band regulation, spectral resolution and absorption enhance. Combining with the bottleneck problem of this technology, the future research prospect was proposed in the aspects such as high purity material growth and the mechanism of local effect of light field.
