Enhanced photothermoelectric conversion in self-rolled tellurium photodetector with geometry-induced energy localization.

Photodetection has attracted significant attention for information transmission. While the implementation relies primarily on the photonic detectors, they are predominantly constrained by the intrinsic bandgap of active materials. On the other hand, photothermoelectric (PTE) detectors have garnered substantial research interest for their promising capabilities in broadband detection, owing to the self-driven photovoltages induced by the temperature differences. To get higher performances, it is crucial to localize light and heat energies for efficient conversion. However, there is limited research on the energy conversion in PTE detectors at micro/nano scale. In this study, we have achieved a two-order-of-magnitude enhancement in photovoltage responsivity in the self-rolled tubular tellurium (Te) photodetector with PTE effect. Under illumination, the tubular device demonstrates a maximum photovoltage responsivity of 252.13 V W-1 and a large detectivity of 1.48 × 1011 Jones. We disclose the mechanism of the PTE conversion in the tubular structure with the assistance of theoretical simulation. In addition, the device exhibits excellent performances in wide-angle and polarization-dependent detection. This work presents an approach to remarkably improve the performance of photodetector by concentrating light and corresponding heat generated, and the proposed self-rolled devices thus hold remarkable promises for next-generation on-chip photodetection.

Multilevel design and construction in nanomembrane rolling for three-dimensional angle-sensitive photodetection.

Releasing pre-strained two-dimensional nanomembranes to assemble on-chip three-dimensional devices is crucial for upcoming advanced electronic and optoelectronic applications. However, the release process is affected by many unclear factors, hindering the transition from laboratory to industrial applications. Here, we propose a quasistatic multilevel finite element modeling to assemble three-dimensional structures from two-dimensional nanomembranes and offer verification results by various bilayer nanomembranes. Take Si/Cr nanomembrane as an example, we confirm that the three-dimensional structural formation is governed by both the minimum energy state and the geometric constraints imposed by the edges of the sacrificial layer. Large-scale, high-yield fabrication of three-dimensional structures is achieved, and two distinct three-dimensional structures are assembled from the same precursor. Six types of three-dimensional Si/Cr photodetectors are then prepared to resolve the incident angle of light with a deep neural network model, opening up possibilities for the design and manufacturing methods of More-than-Moore-era devices.

One-step rolling fabrication of VO2 tubular bolometers with polarization-sensitive and omnidirectional detection.

Uncooled infrared detection based on vanadium dioxide (VO2) radiometer is highly demanded in temperature monitoring and security protection. The key to its breakthrough is to fabricate bolometer arrays with great absorbance and excellent thermal insulation using a straightforward procedure. Here, we show a tubular bolometer by one-step rolling VO2 nanomembranes with enhanced infrared detection. The tubular geometry enhances the thermal insulation, light absorption, and temperature sensitivity of freestanding VO2 nanomembranes. This tubular VO2 bolometer exhibits a detectivity of ~2 × 108 cm Hz1/2 W-1 in the ultrabroad infrared spectrum, a response time of ~2.0 ms, and a calculated noise-equivalent temperature difference of 64.5 mK. Furthermore, our device presents a workable structural paradigm for polarization-sensitive and omnidirectional light coupling bolometers. The demonstrated overall characteristics suggest that tubular bolometers have the potential to narrow performance and cost gap between photon detectors and thermal detectors with low cost and broad applications.

Self-Rolled-Up Ultrathin Single-Crystalline Silicon Nanomembranes for On-Chip Tubular Polarization Photodetectors.

Freestanding single-crystalline nanomembranes and their assembly have broad application potential in photodetectors for integrated chips. However, the release and self-assembly process of single-crystalline semiconductor nanomembranes still remains a great challenge in on-chip processing and functional integration, and photodetectors based on nanomembrane always suffer from limited absorption of nanoscale thickness. Here, a non-destructive releasing and rolling process is employed to prepare tubular photodetectors based on freestanding single-crystalline Si nanomembranes. Spontaneous release and self-assembly are achieved by residual strain introduced by lattice mismatch at the epitaxial interface of Si and Ge, and the intrinsic stress and strain distributions in self-rolled-up Si nanomembranes are analyzed experimentally and computationally. The advantages of light trapping and wide-angle optical coupling are realized by tubular geometry. This Si microtube device achieves reliable Ohmic contact and exhibits a photoresponsivity of over 330 mA W-1 , a response time of 370 µs, and a light incident detection angle range of over 120°. Furthermore, the microtubular structure shows a distinct polarization angle-dependent light absorption, with a dichroic ratio of 1.24 achieved at 940 nm. The proposed Si-based microtubes provide new possibilities for the construction of multifunctional chips for integrated circuit ecosystems in the More than Moore era.

Ferroelectric-tuned van der Waals heterojunction with band alignment evolution.

Van der Waals integration with abundant two-dimensional materials provides a broad basis for assembling functional devices. In a specific van der Waals heterojunction, the band alignment engineering is crucial and feasible to realize high performance and multifunctionality. Here, we design a ferroelectric-tuned van der Waals heterojunction device structure by integrating a GeSe/MoS2 VHJ and poly (vinylidene fluoride-trifluoroethylene)-based ferroelectric polymer. An ultrahigh electric field derived from the ferroelectric polarization can effectively modulate the band alignment of the GeSe/MoS2 heterojunction. Band alignment transition of the heterojunction from type II to type I is demonstrated. The combination of anisotropic GeSe with MoS2 realizes a high-performance polarization-sensitive photodetector exhibiting low dark current of approximately 1.5 pA, quick response of 14 µs, and high detectivity of 4.7 × 1012 Jones. Dichroism ratios are also enhanced by ferroelectric polarization in a broad spectrum from visible to near-infrared. The ferroelectric-tuned GeSe/MoS2 van der Waals heterojunction has great potential for multifunctional detection applications in sophisticated light information sensing. More profoundly, the ferroelectric-tuned van der Waals heterojunction structure provides a valid band-engineering approach to creating versatile devices.

End-Bonded Contacts of Tellurium Transistors.

The development of novel low-dimensional materials makes the metallic contact to nanostructure facing challenges. Compared to side contacts, end-bonded contacts are proposed to be more effective pathways for charge injection and extraction. However, there is a lack of up-to-date understanding regarding end-bonded contacts, especially the recently emerged high-performance field-effect transistors (FETs). Here, the end-bonded contacts in tellurium (Te) transistors are first achieved by inducing metal semiconductor alloy. The formation of Pd-Te alloy structure is confirmed by a high-resolution transmission electron microscope (HRTEM) in Te-nanorod-based FETs. The ultralow specific contact resistance is estimated to be 5.1 × 10-9 Ω cm2 by the transmission line mode. On the basis of this finding, Te FETs are shown to exhibit incredible electronic properties, metal-insulator transition, and photodetection performance. This in-depth investigation of the end-bonded contact between Pd and Te speeds up the potential application of Te nanostructure and provides a feasible method for contact engineering in advanced devices.

A versatile photodetector assisted by photovoltaic and bolometric effects.

The advent of low-dimensional materials with peculiar structure and superb band properties provides a new canonical form for the development of photodetectors. However, the limited exploitation of basic properties makes it difficult for devices to stand out. Here, we demonstrate a hybrid heterostructure with ultrathin vanadium dioxide film and molybdenum ditelluride nanoflake. Vanadium dioxide is a classical semiconductor with a narrow bandgap, a high temperature coefficient of resistance, and phase transformation. Molybdenum ditelluride, a typical two-dimensional material, is often used to construct optoelectronic devices. The heterostructure can realize three different functional modes: (i) the p-n junction exhibits ultrasensitive detection (450 nm-2 µm) with a dark current down to 0.2 pA and a response time of 17 µs, (ii) the Schottky junction works stably under extreme conditions such as a high temperature of 400 K, and (iii) the bolometer shows ultrabroad spectrum detection exceeding 10 µm. The flexible switching between the three modes makes the heterostructure a potential candidate for next-generation photodetectors from visible to longwave infrared radiation (LWIR). This type of photodetector combines versatile detection modes, shedding light on the hybrid application of novel and traditional materials, and is a prototype of advanced optoelectronic devices.

Multifunctional MoS2 Transistors with Electrolyte Gel Gating.

MoS2 , one of the most valued 2D materials beyond graphene, shows potential for future applications in postsilicon digital electronics and optoelectronics. However, achieving hole transport in MoS2 , which is dominated by electron transport, is always a challenge. Here, MoS2 transistors gated by electrolyte gel exhibit the characteristics of hole and electron transport, a high on/off ratio over 105 , and a low subthreshold swing below 50 mV per decade. Due to the electrolyte gel, the density of electrons and holes in the MoS2 channel reaches ≈9 × 1013 and 8.85 × 1013 cm-2 , respectively. The electrolyte gel-assisted MoS2 phototransistor exhibits adjustable positive and negative photoconductive effects. Additionally, the MoS2 p-n homojunction diode affected by electrolyte gel shows high performance and a rectification ratio over 107 . These results demonstrate that modifying the conductance of MoS2 through electrolyte gel has great potential in highly integrated electronics and optoelectronic photodetectors.

MoTe2 p-n Homojunctions Defined by Ferroelectric Polarization.

Doped p-n junctions are fundamental electrical components in modern electronics and optoelectronics. Due to the development of device miniaturization, the emergence of two-dimensional (2D) materials may initiate the next technological leap toward the post-Moore era owing to their unique structures and physical properties. The purpose of fabricating 2D p-n junctions has fueled many carrier-type modulation methods, such as electrostatic doping, surface modification, and element intercalation. Here, by using the nonvolatile ferroelectric field polarized in the opposite direction, efficient carrier modulation in ambipolar molybdenum telluride (MoTe2 ) to form a p-n homojunction at the domain wall is demonstrated. The nonvolatile MoTe2 p-n junction can be converted to n-p, n-n, and p-p configurations by external gate voltage pulses. Both rectifier diodes exhibited excellent rectifying characteristics with a current on/off ratio of 5 × 105 . As a photodetector/photovoltaic, the device presents responsivity of 5 A W-1 , external quantum efficiency of 40%, specific detectivity of 3 × 1012 Jones, fast response time of 30 µs, and power conversion efficiency of 2.5% without any bias or gate voltages. The MoTe2 p-n junction presents an obvious short-wavelength infrared photoresponse at room temperature, complementing the current infrared photodetectors with the inadequacies of complementary metal-oxide-semiconductor incompatibility and cryogenic operation temperature.

Multimode Signal Processor Unit Based on the Ambipolar WSe2-Cr Schottky Junction.

A Schottky barrier is a double-edged sword in electronic and optoelectronic devices, especially devices based on two-dimensional materials. It may restrict the carrier transport in devices, but it can also realize multifunctional devices by architecture design. We designed a simple but novel device structure based on theWSe2-Cr Schottky junction with an asymmetric Schottky contact area of the source and drain. A significant rectification ratio over 105 and multiple rectifying states (e.g., full pass, forward pass, off, and backward pass) were achieved in the single Schottky junction tuned by gate voltage. Furthermore, switching characteristic, rectification characteristic, and amplitude of a sin wave can be effectively modulated by the electrical field or light illumination in a signal process circuit based on the WSe2-Cr Schottky junction. The highly tunable Schottky junction working as a multimode signal processor unit has great potential in future optoelectronic-integrated chips.