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Integration of graphene and quantum dots (QD) is a promising route to improved material and device functionalities. Underlying the improved properties are alterations in carrier dynamics within the graphene/QD heterostructure. In this study, it is shown that graphene functions as a carrier redistribution and supply channel when integrated with InAs QDs. Photoluminescence (PL) spectroscopy provides evidence that graphene modifies the redistribution, escape, and recombination dynamics of carriers in the InAs QD ensemble, which ultimately leads to enhanced radiative recombinations at all temperatures and excitation densities probed. It is also shown that the PL enhancement from the graphene/InAs QD heterostructure is greatest with a thin GaAs cap and at higher temperatures where devices operate. This study advances the understanding of graphene/QD heterostructures and can aid the design of mixed-dimensional optoelectronic devices., (© 2024 2024 The Author(s). Small published by Wiley‐VCH GmbH.)

Monolithic integration of III-V quantum dot (QD) lasers onto a Si substrate is a scalable and reliable approach for obtaining highly efficient light sources for Si photonics. Recently, a combination of optimized GaAs buffers and QD gain materials resulted in monolithically integrated butt-coupled lasers on Si. However, the use of thick GaAs buffers up to 3 μm not only hinders accurate vertical alignment to the Si optical waveguide but also imposes considerable growth costs and time constraints. Here, for the first time, we demonstrate InAs QD lasers epitaxially grown on a 700 nm thick GaAs/Si template, which is approximately four times thinner than the conventional III-V buffers on Si. The optimized 700 nm GaAs buffer yields a remarkably smooth surface and low threading dislocation density of 4 × 10 8 cm -2 , which is sufficient for QD laser growth. The InAs QD lasers fabricated on these ultrathin templates still lase at room temperature with a threshold current density of 661 A/cm 2 and a characteristic temperature of 50 K. We believe that these results are important for the monolithically integrated III-V QD lasers for Si photonics applications.

2 µm photonics and optoelectronics is promising for potential applications such as optical communications, LiDAR, and chemical sensing. While the research on 2 µm detectors is on the rise, the development of InP-based 2 µm gain materials with 0D nanostructures is rather stalled. Here, we demonstrate low-threshold, continuous wave lasing at 2 µm wavelength from InAs quantum dash/InP lasers enabled by punctuated growth of the quantum structure. We demonstrate low threshold current densities from the 7.1 µm width ridge-waveguide lasers, with values of 657, 1183, and 1944 A/cm 2 under short pulse wave (SPW), quasi-continuous wave (QCW), and continuous wave operation. The lasers also exhibited good thermal stability, with a characteristic temperature T0 of 43 K under SPW mode. The lasing spectra is centered at 1.97 µm, coinciding with the ground-state emission observed from photoluminescence studies. We believe that the InAs quantum dash/InP lasers emitting near 2 µm will be a key enabling technology for 2 µm communication and sensing.

Monolithic integration of GaSb-based optoelectronic devices on Si is a promising approach for achieving a low-cost, compact, and scalable infrared photonics platform. While tremendous efforts have been put into reducing dislocation densities by using various defect filter layers, exploring other types of extended crystal defects that can exist on GaSb/Si buffers has largely been neglected. Here, we show that GaSb growth on Si generates a high density of micro-twin (MT) defects as well as threading dislocations (TDs) to accommodate the extremely large misfit between GaSb and Si. We found that a 250 nm AlSb single insertion layer is more effective than AlSb/GaSb strained superlattices in reducing both types of defects, resulting in a 4× and 13× reduction in TD density and MT density, respectively, compared with a reference sample with no defect filter layer. InGaSb quantum well light-emitting diodes were grown on the GaSb/Si templates, and the effect of TD density and MT density on their performance was studied. This work shows the importance of using appropriate defect filter layers for high performance GaSb-based optoelectronic devices on standard on-axis (001) Si via direct epitaxial growth.

Fabrication of high quantum efficiency nanoscale device is challenging due to increased carrier loss at surface. Low dimensional materials such 0D quantum dots and 2D materials have been widely studied to mitigate the loss. Here, we demonstrate a strong photoluminescence enhancement from graphene/III-V quantum dot mixed-dimensional heterostructures. The distance between graphene and quantum dots in the 2D/0D hybrid structure determines the degree of radiative carrier recombination enhancement from 80% to 800% compared to the quantum dot only structure. Time-resolved photoluminescence decay also shows increased carrier lifetimes when the distance decreases from 50 to 10 nm. We propose that the optical enhancement is due to energy band bending and hole carrier transfer, which repair the imbalance of electron and hole carrier densities in quantum dots. This 2D graphene/0D quantum dot heterostructure shows promise for high performance nanoscale optoelectronic devices.

InAs quantum dashes (Qdash) engineered to emit near 2 μm are envisioned to be promising quantum emitters for next-generation technologies in sensing and communications. In this study, we explore the effect of punctuated growth (PG) on the structure and optical properties of InP-based InAs Qdashes emitting near the 2-μm wavelength. Morphological analysis revealed that PG led to an improvement in in-plane size uniformity and increases in average height and height distribution. A 2 × boost in photoluminescence intensity was observed, which we attribute to improved lateral dimensions and structural stabilization. PG encouraged formation of taller Qdashes while photoluminescence measurements revealed a blue-shift in the peak wavelength. We proposed that the blue-shift originates from the thinner quantum well cap and decreased distance between the Qdash and InAlGaAs barrier. This study on the punctuated growth of large InAs Qdashes is a step toward realizing bright, tunable, and broadband sources for 2-μm communications, spectroscopy, and sensing., (© 2023. The Author(s).)

We report on the photoluminescence enhancement of 1.3 μm InAs quantum dots (QDs) epitaxially grown on an ultrathin 250 nm GaAs buffer on a Si substrate. Decreasing the GaAs buffer thickness from 1000 to 250 nm was found to not only increase the coalesced QD density from 6.5 × 10 8 to 1.9 × 10 9 cm -2 but also decrease the QD photoluminescence emission intensity dramatically. Inserting an Al 0.4 Ga 0.6 As potential barrier layer maintained strong photoluminescence from the QDs by effectively suppressing carrier leakage to the GaAs/Si interfacial region even when the GaAs buffer was thinned to 250 nm. We then fabricated a light-emitting diode using the ultrathin 250 nm GaAs buffer on Si and confirmed strong electroluminescence peaking at 1.28 μm without interfacial defect emission at room temperature. We believe that this work is promising for monolithically integrated evanescent Si lasers using InAs/GaAs QDs.

Current infrared thermal image sensors are mainly based on planar firm substrates, but the rigid form factor appears to restrain the versatility of their applications. For wearable health monitoring and implanted biomedical sensing, transfer of active device layers onto a flexible substrate is required while controlling the high-quality crystalline interface. Here, we demonstrate high-detectivity flexible InAs thin-film mid-infrared photodetector arrays through high-yield wafer bonding and a heteroepitaxial lift-off process. An abruptly graded In x Al 1- x As (0.5 < x < 1) buffer was found to drastically improve the lift-off interface morphology and reduce the threading dislocation density twice, compared to the conventional linear grading method. Also, our flexible InAs photodetectors showed excellent optical performance with high mechanical robustness, a peak room-temperature specific detectivity of 1.21 × 10 9 cm-Hz 1/2 /W at 3.4 μm, and excellent device reliability. This flexible InAs photodetector enabled by the heteroepitaxial lift-off method shows promise for next-generation thermal image sensors.

Texture characterization from the metrological point of view is addressed in order to establish a physically relevant and directly interpretable feature. In this regard, a generic formulation is proposed to simultaneously capture the spectral and spatial complexity in hyperspectral images. The feature, named relative spectral difference occurrence matrix (RSDOM) is thus constructed in a multireference, multidirectional, and multiscale context. As validation, its performance is assessed in three versatile tasks. In texture classification on HyTexiLa, content-based image retrieval (CBIR) on ICONES-HSI, and land cover classification on Salinas, RSDOM registers 98.5% accuracy, 80.3% precision (for the top 10 retrieved images), and 96.0% accuracy (after post-processing) respectively, outcompeting GLCM, Gabor filter, LBP, SVM, CCF, CNN, and GCN. Analysis shows the advantage of RSDOM in terms of feature size (a mere 126, 30, and 20 scalars using GMM in order of the three tasks) as well as metrological validity in texture representation regardless of the spectral range, resolution, and number of bands.

We demonstrate flexible GaAs photodetector arrays that were hetero-epitaxially grown on a Si wafer for a new cost-effective and reliable wearable optoelectronics platform. A high crystalline quality GaAs layer was transferred onto a flexible foreign substrate and excellent retention of device performance was demonstrated by measuring the optical responsivities and dark currents. Optical simulation proves that the metal stacks used for wafer bonding serve as a back-reflector and enhance GaAs photodetector responsivity via a resonant-cavity effect. Device durability was also tested by bending 1000 times and no performance degradation was observed. This work paves a way for a cost-effective and flexible III-V optoelectronics technology with high durability.

Aims: Matrine (MAT), a quinolizidine alkaloid derived from the herb Radix Sophorae flavescens, has been recently found to be beneficial in experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis, mainly through its anti-inflammatory effect. In the present study, we tested the effect of MAT on ongoing EAE and defined possible mechanisms underlying its effects on myelination and oligodendrocytes., Main Methods: EAE was induced in C57BL/6 mice and MAT treatment was started at disease onset. Clinical scores were monitored daily; spinal cords and the corpus callosum brain region of mice were harvested on day 23 p.i. for inflammatory infiltration and demyelination of the central nervous system. Myelin content and the development of oligodendrocytes and their precursors were determined by immunostaining, and expression of p-Akt, p-mTOR, p-PI3K, and p-P70S6 was determined by Western blot., Key Findings: MAT effectively suppressed EAE severity and increased the expression of proteolipid protein, a myelin protein that is a marker of CNS myelin. MAT treatment largely increased the number of mature oligodendrocytes, and significantly activated the PI3K/Akt/mTOR signaling pathway, which is required for oligodendrocyte survival and axon myelination., Significance: These findings demonstrate a beneficial effect of MAT on oligodendrocyte differentiation and myelination during EAE, most likely through activating the PI3K/Akt/mTOR signaling pathway., (Copyright © 2017 Elsevier Inc. All rights reserved.)

11 kinds of HBV, HCV and HDV serum markers were investigated in 46 patients with HCC, 48 patients with LC, and 52 controls without liver disease. The prevalence of one out of HBV or HCV or HDV markers (M) in HCC and LC was 91.3% and 95.8% respectively, significantly higher than that in controls (17.3%). Positivity of HBV-M in HCC and LC was remarkably higher than those of HCV-M and HDV-M (P < 0.05). Prevalence of HCV-M in HBV-M negative HCC and LC was 66.7% and 75.0% respectively, significantly higher than that in HBV-M positive cases (P < 0.05). Frequency of viral replication in HCC and LC was significantly higher than that in controls (P < 0.01). The co-occurrence of two or three kinds of viral markers in HCC was more prevalent than that in LC (38% vs 14%, P < 0.05). Patients with coinfection from both HBV and HDV had a significantly younger age than those infected by HBV alone or infected by HCV (more than 10 years earlier). Among HCC and LC, 36% of HBV seronegative cases had HBV DNA detectable in their serum. Our data suggest that HCC and LC have a close association with the infection of HBV HCV and HDV especially HBV. Active viral replication and coinfection of several kinds of virus play on important role in the determination of HCC or LC development, and HDV appears to provide an additional risk for HCC and LC. In HBV-M negative cases, HCV infection may be more important for HCC and LC development than HBV.