ACS Photonics最新文献

Short-wavelength infrared (SWIR) photodetectors are essential to human activities in military and civilian fields, including night vision, remote sensing, telecommunication, medical applications, safety monitoring, and mineral identification. Recently, the tellurium–selenium (Te_xSe_1–x) alloy has demonstrated considerable potential in infrared photodetection. However, the photodetectors still suffer from poor device performance. Herein, we present an interfacial engineering strategy to enhance carrier transport in the Te_xSe_1–x photodetector by utilizing a self-assembled monolayer (SAM) of [2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid (MeO-2PACz) as an interface layer between the Te_xSe_1–x active layer and the poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine (PTAA) hole transport layer. Density functional theory calculations and in-depth XPS analysis illustrate the occurrence of charge transfer and the formation of P–Se bonds at the Te_xSe_1–x/SAM interface. This interfacial engineering approach leads to a more homogeneous surface potential, an increased built-in voltage, improved energy band alignment, and superior photoelectronic characteristics. The self-powered Te_xSe_1–x photodetector exhibits an external quantum efficiency (EQE) of 46% ± 1% at 980 nm and 19.7% ± 0.5% at 1320 nm. This makes the first demonstration of Te_xSe_1–x photodiode achieving a high responsivity of 0.49 A W^–1, along with a record total noise determined realistic detectivity $\left(D_2^{*}\right)$ of 7.69 × 10¹⁰ Jones (and 5.75 × 10¹¹ Jones when considering only shot noise) at 1319 nm, combined with an ultrafast response time of <547 ns (as measured under femtosecond pulsed laser illumination). Moreover, the photocurrent of this photodetector remains almost unchanged even after 30 days of storage.

Traditional metasurface design approaches largely rely on the prior knowledge of researchers and iterative trial-and-error methods using full-wave simulations, resulting in lengthy and inefficient processes. Deep-learning techniques, such as tandem neural networks (TNNs) and generative networks, show considerable promise in addressing the inverse-design problem. However, TNN faces challenges in creating high-freedom structures and neglects learning one-to-many mappings in inverse problems. The denoising diffusion probabilistic model (DDPM), while superior to other generative networks in generation precision and quality, is hindered by slow structure generation. This paper proposes a novel metasurface design method called the tandem generative network (TGN) to realize accurate and efficient high-degree-of-freedom meta-atom design. TGN constructs an original probabilistic generative model and generates free-form meta-atoms by sampling from the probability space. TGN-generated patterns are validated to produce matching transmittance with an average mean absolute error of 0.0356, achieving decreases of 38% and 86% compared to DDPM and TNN, respectively. Furthermore, the generation speed of TGN is 2990 times faster than that of DDPM. By employing the first probabilistic generative model for metasurface design, TGN paves new avenues in deep learning for inverse design, providing a swift and accurate means to design complex meta-atom structures with desired electromagnetic properties.

The phase-resolved imaging of confined light fields by homodyne detection is a cornerstone of metrology in nano-optics and photonics, but its application in electron microscopy has been limited so far. Here, we report the mapping of optical modes in a waveguide structure by illumination with femtosecond light pulses in a continuous-beam transmission electron microscope. Multiphoton photoemission results in a remanent charging pattern which we image by Lorentz microscopy. The resulting image contrast is linked to the intensity distribution of the standing light wave and is quantitatively described within an analytical model. The robustness of the approach is showcased in a wider parameter range and more complex sample geometries including micro- and nanostructures. We discuss further applications of light-interference-based charging for electron microscopy with in situ optical excitation, laying the foundation for advanced measurement schemes for the phase-resolved imaging of propagating light fields.

This work presents a near-infrared (NIR) phototransistor, the light-triggered feedback field-effect transistor (LT-FBFET), which offers high current gain, low dark current, low static power dissipation, and compatibility with CMOS technology. A 20 nm SiGe alloy in the light-absorbing layer extends the operational wavelength to 1310 nm, enhancing quantum efficiency while maintaining low power consumption. The LT-FBFET operates via NIR absorption in the gate region, eliminating the need for external gate bias. Finite-difference time-domain (FDTD) and technology computer-aided design (TCAD) simulations demonstrate the optimized device’s performance, achieving a quantum efficiency of 48.9 at a drain bias of 0.51 V and a static power dissipation on the order of 10^–6 W/cm². The fabricated device confirms the LT-FBFET’s optical switching behavior under 1310 nm NIR illumination. A metasurface consisting of a periodic array of LT-FBFETs was constructed to enhance performance, significantly increasing light absorption via Mie resonance. In addition, adjusting the size and periodicity of the LT-FBFETs enabled tuning of the operating wavelength to 1200 nm and achieving polarization selectivity, as validated by TCAD and FDTD simulations.

A thorough comprehension of the influence mechanisms associated with van der Waals heterojunctions (vdWHs) is crucial for the advancement of high-performance β-Ga₂O₃ deep-UV photodetectors (DUV PDs). Here, through a multiscale simulation and experiment approach, triple mechanisms (including band alignment, electrode/β-Ga₂O₃ interface modulation, and grain boundary (GB) passivation) of MoS₂/β-Ga₂O₃ vdWHs on the response performance of β-Ga₂O₃ DUV PD were revealed. We find that the effects of the three mechanisms of MoS₂/β-Ga₂O₃ vdWHs with type-I band alignments on the response parameters of β-Ga₂O₃ DUV PD are inconsistent. Because MoS₂/β-Ga₂O₃ vdWH reduces the Schottky barrier of the electrode/β-Ga₂O₃ interface while increasing the carrier concentration at the β-Ga₂O₃ GBs. Meanwhile, the type-I band alignment of MoS₂/β-Ga₂O₃ vdWH optimizes the external quantum efficiency and response speed. However, the straightforward synergy of these three mechanisms is still difficult to improve all response parameters of β-Ga₂O₃ DUV PDs, as the MoS₂/β-Ga₂O₃ vdWHs do not mitigate the dark current. Notably, the hypothetical type-II band alignment of 2D/β-Ga₂O₃ vdWH is effective in reducing carrier recombination and dark current. Consequently, simultaneously introducing type-I and type-II band alignments of vdWHs and combining them with the triple modulation mechanisms can optimize all of the response characteristics at the same time. The responsivity and response time improve almost one and 2 orders of magnitude, respectively. Our works offer in-depth insights into the triple modulation mechanism of 2D/β-Ga₂O₃ vdWH on the β-Ga₂O₃ DUV PD and provide a guideline to design high-performance β-Ga₂O₃ DUV PD.