Self-Powered Lithium Niobate Thin-Film Photodetectors

Schottky barrier reduction on optoelectronic responses in heavy ion irradiated WSe2 memtransistors

Two-dimensional transition metal dichalcogenide-based memtransistors provide simulation, sensing, and storage capabilities for applications in a remotely operated aerospace environment. Swift heavy ion (SHI) irradiation technology is a common method to simulate the influences of radiation ions on electronic devices in space environments. Here, SHI irradiation technology under different conditions was utilized to produce complex defects in WSe2-based memtransistors. Low-resistance state to low-resistance state (LRS-LRS) switching behaviors under light illumination were achieved and photocurrent responses with different spike trains were observed in SHI-irradiated memtransistors, which facilitated the design of devices with enriched analog functions. Reduction of the Schottky barrier height due to the introduced defects at the metal/WSe2 interface was confirmed to be the major factor responsible for the observed behaviors. 1T phase and concentric circle-type vacancies were also created in the SHI-irradiated 2H-WSe2 channel besides the amorphous structure; these complex defects could seriously affect the transport properties of the devices. We believe that this work serves as a foundation for aerospace radiation applications of all-in-one devices. It also opens a new application field of heavy ion irradiation technology for the development of multiterminal memtransistor-based optoelectronic artificial synapses for neuromorphic computing.

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.

High-responsivity and high-speed black phosphorus photodetectors integrated with proton exchanged thin-film lithium niobate waveguides

We present a high-performance broadband (450-1550 nm) black phosphorus photodetector based on a thin-film lithium niobate waveguide. The waveguides are fabricated by the proton exchange method with flat surfaces, which reduces the stress and deformation of two-dimensional materials. At a wavelength of 1550 nm, the photodetector simultaneously achieves a high responsivity and wide bandwidth, with a responsivity as high as 147 A/W (at an optical power of 17 nW), a 3-dB bandwidth of 0.86 GHz, and a detectivity of 3.04 × 1013 Jones. Our photodetector exhibits one of the highest responsivity values among 2D material-integrated waveguide photodetectors.

All-Oxide Transparent Photodetector Array for Ultrafast Response through Self-Powered Excitonic Photovoltage Operation

Can photodetectors be transparent and operate in self-powered mode? Is it possible to achieve invisible electronics, independent of the external power supply system, for on-site applications? Here, a ZnO/NiO heterojunction-based high-functional transparent ultraviolet (UV) photodetector operating in the self-powered photovoltaic mode with outstanding responsivity and detectivity values of 6.9 A W-1 and 8.0 × 1012 Jones, respectively, is reported. The highest IUV /Idark value of 8.9 × 104 is attained at a wavelength of 385 nm, together with a very small dark current value of 9.15 × 10-12 A. A large-scale sputtering method is adopted to deposit the heterostructure of n-ZnO and p-NiO sequentially. This deposition instinctively forms an abrupt junction, resulting in a high-quality heterojunction device. Moreover, developing a ZnO/NiO-heterojunction-based 4 × 5 matrix array with an output photovoltage of 4.5 V is preferred for integrating photodetectors into sensing and imaging systems. This transparent UV photodetector exhibits the fastest photo-response time (83 ns) reported for array configurations, which is achieved using an exciton-induced photovoltage based on a neutral donor-bound exciton. Overall, this study provides a simple method for achieving a high-performance large-scale transparent UV photodetector with a self-powered array configuration.

Broadband, Polarization-Sensitive, and Self-Powered High-Performance Photodetection of Hetero-Integrated MoS2 on Lithium Niobate

High-performance photodetectors hold promising potential in optical communication and imaging systems. However, conventional counterparts are suffering narrow detection range, high power consumption, and poor polarization sensitivity. Characteristics originating from switchable polarization in ferroelectrics can be used to optimize the photo-to-electric procedure and improve the photodetection performance. In this regard, we constructed a configuration by integrating 2-dimensional molybdenum disulfide (MoS₂) with ferroelectric lithium niobate (LiNbO₃), resulting in the MoS₂/LiNbO₃ heterostructured photodetector. Benefiting from the pyroelectric effect of LiNbO₃, the limitation of bandgap on the detection range can be broken, thus broadening the response band of the detector to 365 to 1,064 nm, as well as enabling the self-powered characteristic. Meanwhile, high carrier mobility and decent light absorbance of MoS₂ introduce robust light-matter interactions with the underlying LiNbO₃, leading to ultrafast rise/fall times of ≈150 μs/250 μs and switching ratios of up to ≈190. Moreover, the highest responsivity, specific detectivity, and external quantum efficiency achieved were 17.3 A·W^-1, 4.3 × 10¹¹ Jones, and 4,645.78%, respectively. Furthermore, because of the anisotropy of the spontaneous-polarized LiNbO₃ substrate, the photocurrent of the device achieved a dichroic ratio of 7.42, comparing favorably to most MoS₂-based photodetectors. This work demonstrates the integration potential between ferroelectric LiNbO₃ and 2-dimensional materials for high-performance photodetection.

On-chip ytterbium-doped lithium niobate waveguide amplifiers with high net internal gain

Integrated optical systems based on lithium niobate on insulator (LNOI) have shown great potential in recent years. However, the LNOI platform is facing a shortage of active devices. Considering the significant progress made in rare-earth-doped LNOI lasers and amplifiers, the fabrication of on-chip ytterbium-doped LNOI waveguide amplifiers based on electron-beam lithography and inductively coupled plasma reactive ion etching was investigated. The signal amplification at lower pump power (<1 mW) was achieved by the fabricated waveguide amplifiers. A net internal gain of ∼18 dB/cm in the 1064 nm band was also achieved in the waveguide amplifiers under a pump power of 10 mW at 974 nm. This work proposes a new, to the best of our knowledge, active device for the LNOI integrated optical system. It may become an important basic component for lithium niobate thin-film integrated photonics in the future.

Giant Second Harmonic Generation from Membrane Metasurfaces

Metasurfaces have emerged as a fascinating framework for nonlinear optics, which have advantages of a compact footprint and unprecedented flexibility in manipulating light. But their nonlinear responses are generally limited by the short interaction lengths with light. Therefore, further enhancement is highly desired for building high-efficiency nonlinear devices. Here, we experimentally demonstrate a record high second harmonic generation (SHG) efficiency of 2.0 × 10^-4 using lithium niobate (LN) membrane metasurfaces. Benefiting from the large refractive index contrast in the vertical direction and high fabrication quality, distinct spectral resonances and tight field confinements in the LN layer were achieved. Strong SHG peaks resulting from pump resonances of the metasurfaces were observed. Our nonlinear efficiency is more than 2 orders of magnitude larger than previously reported LN metasurfaces. The results inspire a way to improve the efficiency of nonlinear metasurfaces for ultracompact nonlinear light sources in applications of nonlinear holography, Li-Fi, beam shaping, etc.