Shortwave Infrared InGaAs Detectors On-Chip Integrated with Subwavelength Polarization Gratings.

Shortwave infrared polarization imaging can increase the contrast of the target to the background to improve the detection system's recognition ability. The division of focal plane polarization indium gallium arsenide (InGaAs) focal plane array (FPA) detector is the ideal choice due to the advantages of compact structure, real-time imaging, and high stability. However, because of the mismatch between nanostructures and photosensitive pixels as well as the crosstalk among the different polarization directions, the currently reported extinction ratio (ER) of superpixel-polarization-integrated detectors cannot meet the needs of high-quality imaging. In this paper, a 1024 × 4 InGaAs FPA detector on-chip integrated with a linear polarization grating (LPG) was realized and tested. The detector displayed good performance throughout the 0.9-1.7 um band, and the ERs at 1064 nm, 1310 nm and 1550 nm reached up to 22:1, 29:1 and 46:1, respectively. For the crosstalk investigation, the optical simulation of the grating-integrated InGaAs pixel was carried out, and the limitation of the ER was calculated. The result showed that the scattering of incident light in the InP substrate led to the crosstalk. Moreover, the deviation of the actual grating morphology from the designed structure caused a further reduction in the ER.

Design and Fabrication of Broadband InGaAs Detectors Integrated with Nanostructures.

A visible-extended shortwave infrared indium gallium arsenide (InGaAs) focal plane array (FPA) detector is the ideal choice for reducing the size, weight and power (SWaP) of infrared imaging systems, especially in low-light night vision and other fields that require simultaneous visible and near-infrared light detection. However, the lower quantum efficiency in the visible band has limited the extensive application of the visible-extended InGaAs FPA. Recently, a novel optical metasurface has been considered a solution for a high-performance semiconductor photoelectric device due to its highly controllable property of electromagnetic wave manipulation. Broadband Mie resonator arrays, such as nanocones and nanopillars designed with FDTD methods, were integrated on a back-illuminated InGaAs FPA as an AR metasurface. The visible-extended InGaAs detector was fabricated using substrate removal technology. The nanostructures integrated into the Vis-SWIR InGaAs detectors could realize a 10-20% enhanced quantum efficiency and an 18.8% higher FPA response throughout the wavelength range of 500-1700 nm. Compared with the traditional AR coating, nanostructure integration has advantages, such as broadband high responsivity and omnidirection antireflection, as a promising route for future Vis-SWIR InGaAs detectors with higher image quality.

Design and fabrication of an InGaAs focal plane array integrated with linear-array polarization grating.

Polarization imaging plays a crucial role in modern photonic applications such as remote sensing, material classification, and reconnaissance. A novel InGaAs focal plane array integrated with linear-array polarization grating is proposed and fabricated to meet the practical needs of near-infrared polarization imaging. In order to accurately evaluate the polarization performance of a fabricated detector, the improved test system is used to measure the transmittance and extinction ratio (ER). The results show that the detectivity reaches ${1}.{06}\; \times \;{{10}^{12}}\;{{\rm cm}\cdot{\rm Hz}^{1/2}}/{\rm W}$1.06×1012cm⋅Hz1/2/W, and the operable pixel factor is more than 99.8%. The transmittance of more than 55% and the ER of greater than 21:1 are realized, which indicates that the fabricated detector has excellent capability for near-infrared polarization imaging.

Research on polarization performance of InGaAs focal plane array integrated with superpixel-structured subwavelength grating.

Polarization imaging has become a widely-applied detection technique, due to the capabilities of enhanced image contrast and object recognition. Here, we demonstrate 320 × 256 InGaAs focal plane array (FPA) integrated with superpixel-structured subwavelength aluminum grating. An extinction ratio of up to 19:1 at 1310 nm is realized, which indicates a good capability of near-infrared polarization detection. Theoretical simulation shows a fairly high extinction ratio for such superpixel structure. This difference between the actual extinction ratio and the theoretical extinction ratio is further discussed by analyzing the effects of the alignment deviation and structural parameter deviations induced during the actual process. Moreover, the imaging results show that the fabricated polarimetric InGaAs FPA presents a more obvious profile for artificial objects, compared to the conventional detector. Such FPAs integrated with superpixel-structured grating are very promising for high performance polarization imaging in the short wavelength infrared band.

Broadband high quantum efficiency InGaAs/InP focal plane arrays via high precision plasma thinning.

We report on the fabrication of a 160×120 visible (Vis)-extended InGaAs/InP focal plane array (FPA) by means of the inductively coupled plasma etching. Compared to the conventional Vis-InGaAs FPAs, higher quantum efficiency in the Vis spectrum has been achieved. High precision thinning of the n-type InP contact layer down to 10 nm has led to quantum efficiencies higher than 60% over a broad wavelength range of 500-1700 nm. Benefiting from the textured surface after plasma etching, 17% lower reflectance over the entire response range was also found. Enhanced Vis/near-infrared (NIR) laboratory imaging capability has also been demonstrated, which has proved the feasibility of such processes for fabrication of future higher definition Vis/NIR InGaAs imagers.

IGA-rule 17 for performance estimation of wavelength-extended InGaAs photodetectors: validity and limitations.

A rule of thumb, denoted as IGA-rule 17, has been developed to describe the temperature and cutoff wavelength-dependent dark currents of wavelength-extended InGaAs photodetectors in a 2-3 µm band. The validity and limitations of the rule are discussed. This rule is intended as an index for device developers to evaluate their technologies in processing, a simple tool for device users to estimate reachable performance at various conditions in their design, and an effective bridge between the two.

Electron-initiated low noise 1064 nm InGaAsP/InAlAs avalanche photodetectors.

We report an electron-initiated 1064 nm InGaAsP avalanche photodetectors (APDs) with an InAlAs multiplier. By utilizing a tailored digital alloy superlattice grading structure, a charge layer and a p type InAlAs multiplier, an unity gain quantum efficiency of 48%, a low room temperature dark current of 470 pA at 90% breakdown voltage, and a low multiplication noise with an effective k ratio of ∼0.2 are achieved. The measured maximum gain factor is 5 at room temperature, which is currently limited by the non-optimized electric field profiles, and can be readily enhanced by modifying the doping and thickness parameters for the multiplier and the charge layer.

Subwavelength Gold Grating as Polarizers Integrated with InP-Based InGaAs Sensors.

There are currently growing needs for polarimetric imaging in infrared wavelengths for broad applications in bioscience, communications and agriculture, etc. Subwavelength metallic gratings are capable of separating transverse magnetic (TM) mode from transverse electric (TE) mode to form polarized light, offering a reliable approach for the detection in polarization way. This work aims to design and fabricate subwavelength gold gratings as polarizers for InP-based InGaAs sensors in 1.0-1.6 µm. The polarization capability of gold gratings on InP substrate with pitches in the range of 200-1200 nm (fixed duty cycle of 0.5) has been systematically studied by both theoretical modeling with a finite-difference time-domain (FDTD) simulator and spectral measurements. Gratings with 200 nm lines/space in 100-nm-thick gold have been fabricated by electron beam lithography (EBL). It was found that subwavelength gold gratings directly integrated on InP cannot be applied as good polarizers, because of the existence of SPP modes in the detection wavelengths. An effective solution has been found by sandwiching the Au/InP bilayer using a 200 nm SiO2 layer, leading to significant improvement in both TM transmission and extinction ratio. At 1.35 µm, the improvement factors are 8 and 10, respectively. Therefore, it is concluded that the Au/SiO2/InP trilayer should be a promising candidate of near-infrared polarizers for the InP-based InGaAs sensors.

Scale effects of low-dimensional relaxor ferroelectric single crystals and their application in novel pyroelectric infrared detectors.

Scaling effects of low-dimensional relaxor ferroelectric single crystals have induced large delocalization of domain switching, leading to a dramatic increase in pyro-electric performances by 2-5.5 times, and promoting the detectivity of fabricated pyroelectric detectors to an international leading level of 2.21 × 10(9) cmHz(1/2) /W at 10 Hz, 4 times higher than that of commercial LiTaO3 -based detectors.

An organic solvent-free microwave-assisted extraction of some priority pollutants of phenols in lake sediments.

Alkaline water was used for the microwave-assisted extraction of some priority pollutants of phenols in sediments, i.e. phenol (Ph), 2-chlorophenol (2CP), 2,4-dichlorophenol (2,4DCP), 4-chlorophenol (4CP), 4-dinitrophenol (4NP) and pentachlorophenol (PCP). This organic solvent-free extraction procedure was optimized by studying the parameters such as pH, volume of the alkaline water, extraction pressure and time. Under the optimized conditions, the recoveries of phenols were in the range of 80% to 110%. The extracts were then cleaned-up and concentrated by microcolumn solid phase extraction (SPE) and determined by gas chromatography-flame ionization detection system. The relative standard deviation of the overall-method for most phenol determinations was about 5.0% (n = 6). The proposed method, which needs little volume (1 mL) of ethanol for SPE, has been applied to determine these phenols in sediment samples, and the analytical results are in good agreement with those achieved by Soxhlet extraction.