Epitaxial GaN nanostructures are developed, and the influence of the AlN buffer layer (temperature modulation) on material characteristics and optoelectronic device application is assessed. The AlN buffer layer was grown on a Si (111) substrate at varying temperatures (770–830 °C), followed by GaN growth using plasma-assisted molecular beam epitaxy. The investigation revealed that the comparatively lower temperature AlN buffer layer was responsible for stress and lattice strain relaxation and was realized as the GaN nano-obelisk structures. Contrarily, the increased temperature of the AlN growth led to the formation of GaN nanopyramidal and nanowax/wane structures. These grown GaN/AlN/Si heterostructures were utilized to develop photodetectors in a metal–semiconductor–metal geometry format. The performance of these fabricated optoelectronic devices was examined under ultraviolet illumination (UVA), where the GaN nano-obelisks-based device attained the highest responsivity of 118 AW−1. Under UVA (325 nm) illumination, the designed device exhibited a high detectivity of 1 × 1010 Jones, noise equivalent power of 1 × 10−12 WHz−1/2, and external quantum efficiency of 45,000%. The analysis revealed that the quality of the AlN buffer layer significantly improved the optoelectronic performance of the device.

/pdf/stress-relaxed-aln-buffer-oriented-gan-nano-obelisks-based-2ewlky2s.pdf

Stress-Relaxed AlN-Buffer-Oriented GaN-Nano-Obelisks-Based High-Performance UV Photodetector

Inorganic semiconductors like silicon and germanium are the foundation of modern electronic devices. However, they have certain limitations, such as high production costs, limited flexibility, and heavy weight. Additionally, the depletion of natural resources required for inorganic semiconductor production raises concerns about sustainability. Therefore, the exploration and development of organic semiconductors offer a promising solution to overcome these challenges and pave the way for a new era of electronics. New applications for electronic and optoelectronic devices have been made possible by the recent emergence of organic semiconductors. Numerous innovative results on the performance of charge transport have been discovered with the growth of organic electronics. These discoveries have opened up new possibilities for the development of organic electronic devices, such as organic solar cells, organic light-emitting diodes, and organic field-effect transistors. The use of organic materials in these devices has the potential to revolutionise the electronics industry by providing low-cost, flexible, and lightweight alternatives to traditional inorganic materials. The understanding of charge carrier transport in organic semiconductors is crucial for the development of efficient organic electronic devices. This review offers a thorough overview of the charge carrier transport phenomenon in semiconductors with a focus on the underlying physical mechanisms and how it affects device performance. Additionally, the processes of carrier generation and recombination are given special attention. Furthermore, this review provides valuable insights into the fundamental principles that govern the behaviour of charge carriers in these materials, which can inform the design and optimisation of future devices.

Review on Charge Carrier Transport in Inorganic and Organic Semiconductors

In this study, simple-structured wavelength sensors were developed by depositing two back-to-back Au/MAPbI3/Au photodetectors on an MAPbI3 single crystal. This sensor could quantitatively distinguish wavelengths. Further device analysis showed that both photodetectors possess entirely disparate optoelectronic properties. Consequently, the as-developed wavelength sensor could accurately distinguish incident-light wavelengths ranging from 265 to 860 nm with a resolution of less than 1.5 nm based on the relation between the photocurrent ratios of both photodetectors and the incident light wavelengths. Notably, a high resolution and wide detection range are among the optimum reported values for such sensors and enable full-color imaging. Furthermore, technology computer-aided design (TCAD) simulations showed that a mechanism involved in distinguishing wavelengths is attributed to the wavelength-dependent photon generation rate in MAPbI3 single crystals. The high-performance MAPbI3 wavelength sensor can potentially drive the research progress of perovskites in wavelength recognition and full-color imaging.

A Simple-Structured Perovskite Wavelength Sensor for Full-Color Imaging Application.

The integration of graphene with semiconductor materials has been studied for developing advanced electronic and optoelectronic devices. Here, we propose ultrahigh photoresponsivity of β-Ga2O3 photodiodes with a graphene monolayer inserted in a W Schottky contact. After inserting the graphene monolayer, we found a reduction in the leakage current and ideality factor. The Schottky barrier height was also shown to be about 0.53 eV, which is close to an ideal value. This was attributed to a decrease in the interfacial state density and the strong suppression of metal Fermi-level pinning. Based on a W/graphene/β-Ga2O3 structure, the responsivity and external quantum efficiency reached 14.49 A/W and 7044%, respectively. These values were over 100 times greater than those of the W contact alone. The rise and delay times of the W/graphene/β-Ga2O3 Schottky barrier photodiodes significantly decreased to 139 and 200 ms, respectively, compared to those obtained without a graphene interlayer (2000 and 3000 ms). In addition, the W/graphene/β-Ga2O3 Schottky barrier photodiode was highly stable, even at 150 °C.

Ultrahigh Photoresponsivity of W/Graphene/β-Ga2O3 Schottky Barrier Deep Ultraviolet Photodiodes.

Group IV alloys of GeSn have been extensively investigated as a competing material alternative in shortwave-to-mid-infrared photodetectors (PDs). The relatively large defect densities present in GeSn alloys are the major challenge in developing practical devices, owing to the low-temperature growth and lattice mismatch with Si or Ge substrates. In this paper, we comprehensively analyze the impact of defects on the performance of GeSn p-i-n homojunction PDs. We first present our theoretical models to calculate various contributing components of the dark current, including minority carrier diffusion in p- and n-regions, carrier generation-recombination in the active intrinsic region, and the tunneling effect. We then analyze the effect of defect density in the GeSn active region on carrier mobilities, scattering times, and the dark current. A higher defect density increases the dark current, resulting in a reduction in the detectivity of GeSn p-i-n PDs. In addition, at low Sn concentrations, defect-related dark current density is dominant, while the generation dark current becomes dominant at a higher Sn content. These results point to the importance of minimizing defect densities in the GeSn material growth and device processing, particularly for higher Sn compositions necessary to expand the cutoff wavelength to mid- and long-wave infrared regime. Moreover, a comparative study indicates that further improvement of the material quality and optimization of device structure reduces the dark current and thereby increases the detectivity. This study provides more realistic expectations and guidelines for evaluating GeSn p-i-n PDs as a competitor to the III-V- and II-VI-based infrared PDs currently on the commercial market.

Dark Current Analysis on GeSn p-i-n Photodetectors.

This review provides an overview of the basic concepts and operation mechanisms of ultraviolet (UV) photodetectors (PDs), the main research status, and future outlooks of II–VI group compound semiconductor-based UVPDs.

Progress in ultraviolet photodetectors based on II–VI group compound semiconductors

Object detection from remote sensing images is an interesting research topic full of theoretical and application values. Compared with generic images, those of remote sensing contain much less distinguishing representation information due to far-away capturing position and limited camera lens resolution, the perpendicular to ground capturing view, almost unacquirable 3-D object structure and serious roof occlusion, and the inherent unimportance of top roof view. Focusing on this intrinsic disadvantage, in this letter, we propose a general framework of accurate remote sensing object localization constructed with the core idea of maximum image feature exploration. This integrated structure is mainly comprised of cascaded tiny patch correlation (CTPC) based feature digging, averaging local patch regression (ALPR) centered coarse location acquisition, and instance segmentation oriented further refinement (ISOFR). All those components are designed to maximize feature digging and usage. We believe this is the first to implement the idea of maximum feature exploration to each corner of object detection architecture. Extensive experiments on challenging aerial image datasets DOTA and NWPU VHR-10 show state-of-the-art performance.

A Framework of Maximum Feature Exploration Oriented Remote Sensing Object Detection

A sensitive ultraviolet photodetector (UVPD) based on an ultrathin MAPbBr3 nanosheet was developed in this study. A simulation based on technology computer-aided design showed that the optical absorption of MAPbBr3 can be tailored by changing the material thickness, which is reasonable considering the wavelength dependence of the absorption coefficient of MAPbBr3. In addition, an apparent blueshift of the position of the maximum photocurrent is observed upon decreasing the nanosheet thickness. These tunable optoelectronic properties resulted in a device fabricated from medium-bandgap 43-nm-thick MAPbBr3 nanosheets being sensitive to UV light illumination. The device has a maximum photoresponse at 300 nm, a responsivity of 27.2 mA $\cdot \text{W}$ −1, and a response speed of 0.103/0.087 s, respectively, which are comparable to conventional UVPDs based on low-dimensional wide bandgap materials (e.g., ZnO and TiO2). This novel UVPD has application potential to optoelectronic systems.

A Sensitive UV Photodetector Based on Non-Wide Bandgap MAPbBr3 Nanosheet

The objective of pose-guided person image generation is to convert a given person’s pose into the desired pose. Exciting approaches employing the U-net architecture would result in the loss of the majority of fine-grained information, leading to over-smoothed clothing and missing details in the final results. In this paper, we propose a novel semantic-driven dual-attention network to address this issue. The whole framework contains two stages. In the first stage, the spatial misalignment is initially corrected by transferring the semantic parsing map to the target pose. In the second stage, we leverage a novel dual attention mechanism to better incorporate the spatial structure and texture style information into the image generation process. Extensive experiments demonstrate that our proposed method can generate images that are more consistent and photo-realistic than current methods in quantitative and qualitative evaluation.

SDAN: Semantic-Driven Dual Attentional Network for Image Generation

High-precision spectral detection and broadband wavelength sensors have attracted considerable interest for important application in color image sensing. Due to the absorption limitations of silicon, conventional complementary metal–oxide–semiconductors have a relatively limited wavelength region from the ultraviolet to near-infrared spectrum. Here, a simple-structured device is developed by assembling two back-to-back monolayer graphene (MLG)/Si/MLG heterojunctions for high-resolution wavelength sensing applications. The single MLG/Si/MLG photodetector exhibits a responsivity of 0.18 A W−1, a specific detectivity of 1.36 × 109 Jones, and an external quantum efficiency of 28.5%. Thanks to the unique device geometry, the distribution of photo-generation rates in the two photodetectors is completely different, which brings about different photoelectric properties. It is found that the relationship between the photocurrent ratio of both photodetectors and the light wavelength can be fitted by a monotonic function, according to which the wavelength of incident light in the range from 260 to 1050 nm can be accurately estimated. A high resolution of 1 nm is demonstrated across a broadband wavelength from 260 to 1000 nm. This good resolution, along with good repeatability and stability, endow the present device with potential promise in future spectral sensing applications. 

Sensitive and Broadband Wavelength Sensor Based on Two Graphene/Si/Graphene Heterojunctions

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