Toward Unusual-High Hole Mobility of p-Channel Field-Effect-Transistors

Toward High-Performance Self-Powered Near-Ultraviolet Photodetection by Constructing a Unipolar Heterojunction

Constructing a unipolar heterojunction is an effective energy band engineering strategy to improve the performance of photoelectric devices, which could suppress dark current and enhance detectivity by modulating the transfer of carriers. In this work, unipolar heterojunctions of Si/PbI2 and GaSb/PbI2 are constructed successfully for high-performance self-powered near-ultraviolet photodetection. Owing to the unique band offset of unipolar heterojunctions, the transport of holes is blocked, and only photogenerated electrons in PbI2 can flow unimpeded under the driving force of the built-in electric field. Thus, the recombination of photogenerated electron-hole pairs is suppressed, contributing to high-performance near-ultraviolet photodetection. The as-fabricated Si/PbI2 self-powered near-ultraviolet photodetector exhibits a low dark current of 10-13 A, a high Ilight/Idark ratio of 104, and fast response times of 26/24 ms, which are much better than those of the PbI2 metal-semiconductor-metal photodetector. Furthermore, the as-fabricated GaSb/PbI2 unipolar heterojunction photodetector also exhibits impressive self-powered near-ultraviolet photodetection behaviors. Evidently, this work shows the potential of unipolar heterojunctions for next-generation Si-based and GaSb-based high-performance photodetection.

Lattice-mismatch-free construction of III-V/chalcogenide core-shell heterostructure nanowires

Growing high-quality core-shell heterostructure nanowires is still challenging due to the lattice mismatch issue at the radial interface. Herein, a versatile strategy is exploited for the lattice-mismatch-free construction of III-V/chalcogenide core-shell heterostructure nanowires by simply utilizing the surfactant and amorphous natures of chalcogenide semiconductors. Specifically, a variety of III-V/chalcogenide core-shell heterostructure nanowires are successfully constructed with controlled shell thicknesses, compositions, and smooth surfaces. Due to the conformal properties of obtained heterostructure nanowires, the wavelength-dependent bi-directional photoresponse and visible light-assisted infrared photodetection are realized in the type-I GaSb/GeS core-shell heterostructure nanowires. Also, the enhanced infrared photodetection is found in the type-II InGaAs/GeS core-shell heterostructure nanowires compared with the pristine InGaAs nanowires, in which both responsivity and detectivity are improved by more than 2 orders of magnitude. Evidently, this work paves the way for the lattice-mismatch-free construction of core-shell heterostructure nanowires by chemical vapor deposition for next-generation high-performance nanowire optoelectronics.

An Amorphous Native Oxide Shell for High Bias-Stress Stability Nanowire Synaptic Transistor

The inhomogeneous native oxide shells on the surfaces of III-V group semiconductors typically yield inferior and unstable electrical properties metrics, challenging the development of next-generation integrated circuits. Herein, the native GaOx shells are profitably utilized by a simple in-situ thermal annealing process to achieve high-performance GaSb nanowires (NWs) field-effect-transistors (FETs) with excellent bias-stress stability and synaptic behaviors. By an optimal annealing time of 5 min, the as-constructed GaSb NW FET demonstrates excellent stability with a minimal shift of transfer curve (ΔVth ≈ 0.54 V) under a 60 min gate bias, which is far more stable than that of pristine GaSb NW FET (ΔVth ≈ 8.2 V). When the high bias-stress stability NW FET is used as the chargeable-dielectric free synaptic transistor, the typical synaptic behaviors, such as short-term plasticity, long-term plasticity, spike-time-dependent plasticity, and reliable learning stability are demonstrated successfully through the voltage tests. The mobile oxygen ion in the native GaOx shell strongly offsets the trapping states and leads to enhanced bias-stress stability and charge retention capability for synaptic behaviors. This work provides a new way of utilizing the native oxide shell to realize stable FET for chargeable-dielectric free neuromorphic computing systems.

New Approach to Low-Power-Consumption, High-Performance Photodetectors Enabled by Nanowire Source-Gated Transistors

Power consumption makes next-generation large-scale photodetection challenging. In this work, the source-gated transistor (SGT) is adopted first as a photodetector, demonstrating the expected low power consumption and high photodetection performance. The SGT is constructed by the functional sulfur-rich shelled GeS nanowire (NW) and low-function metal, displaying a low saturated voltage of 0.61 V ± 0.29 V and an extremely low power consumption of 7.06 pW. When the as-constructed NW SGT is used as a photodetector, the maximum value of the power consumption is as low as 11.96 nW, which is far below that of the reported phototransistors working in the saturated region. Furthermore, benefiting from the adopted SGT device, the photodetector shows a high photovoltage of 6.6 × 10^-1 V, a responsivity of 7.86 × 10¹² V W^-1, and a detectivity of 5.87 × 10¹³ Jones. Obviously, the low power consumption and excellent responsivity and detectivity enabled by NW SGT promise a new approach to next-generation, high-performance photodetection technology.

Flexible Omnidirectional Self-Powered Photodetectors Enabled by Solution-Processed Two-Dimensional Layered PbI2 Nanoplates

Realizing omnidirectional self-powered photodetectors is central to advancing next-generation portable and smart photodetector systems. However, the traditional omnidirectional photodetector is typically achieved by integrating complex hemispherical microlens on multiple photodetectors, which makes the detection system cumbersome and restricts its application in the portable field. Here, facile and high-performance flexible omnidirectional self-powered photodetectors are achieved by solution-processed two-dimensional (2D) layered PbI₂ nanoplates on transparent conducting substrates. Characterization of PbI₂ nanoplates microstructural/compositional and their photodetection properties have been systematically characterized. Under the irradiation of a 405 nm laser, the photodetectors exhibit an impressively low dark current of 10^-13 A, a high light on/off ratio up to 10⁶, and a fast rise/decay response time of 2/3 ms. Importantly, when light irradiates the photodetector at 5°, it can still maintain high photodetection properties, realizing almost 360° omnidirectional self-powered photodetection. What is more, these self-powered photodetectors exhibit robust omnidirectional photoresponse stability of flexibility even after bending for 1200 cycles. Thus, this work broadens the applicability of 2D layered nanoplates for further extending its applications in advanced optoelectronic devices.

Near-Infrared Polarimetric Image Sensors Based on Ordered Sulfur-Passivation GaSb Nanowire Arrays

The near-infrared polarimetric image sensor has a wide range of applications in the military and civilian fields, thus developing into a research hotspot in recent years. Because of their distinguishing 1D structure features, the ordered GaSb nanowire (NW) arrays possess potential applications for near-infrared polarization photodetection. In this work, single-crystalline GaSb NWs are synthesized through a sulfur-catalyzed chemical vapor deposition process. A sulfur-passivation thin layer is formed on the NW surface, which prevents the GaSb NW core from being oxidized. The photodetector based on sulfur-passivation GaSb (S-GaSb) NWs has a lower dark current and higher responsivity than that built with pure GaSb NWs. The photodetector exhibits a large responsivity of 9.39 × 10² A/W and an ultrahigh detectivity of 1.10 × 10¹¹ Jones for 1.55 μm incident light. Furthermore, the dichroic ratio of the device is measured to reach 2.65 for polarized 1.55 μm light. Through a COMSOL simulation, it is elucidated that the origin of the polarized photoresponse is the attenuation of a light electric field inside the NW when the angle of incident polarization light rotates. Moreover, a flexible polarimetric image sensor with 5 × 5 pixels is successfully constructed on the ordered S-GaSb NW arrays, and it exhibits a good imaging ability for incident near-infrared polarization light. These good photoresponse properties and polarized imaging abilities can empower ordered S-GaSb NW arrays with technological potentials in next-generation large-scale near-infrared polarimetric imaging sensors.

Schottky-Contacted High-Performance GaSb Nanowires Photodetectors Enabled by Lead-Free All-Inorganic Perovskites Decoration

The surface Fermi level pinning effect promotes the formation of metal-independent Ohmic contacts for the high-speed GaSb nanowires (NWs) electronic devices, however, it limits next-generation optoelectronic devices. In this work, lead-free all-inorganic perovskites with broad bandgaps and low work functions are adopted to decorate the surfaces of GaSb NWs, demonstrating the success in the construction of Schottky-contacts by surface engineering. Benefiting from the expected Schottky barrier, the dark current is reduced to 2 pA, the I_light /I_dark ratio is improved to 10³ and the response time is reduced by more than 15 times. Furthermore, a Schottky-contacted parallel array GaSb NWs photodetector is also fabricated by the contact printing technology, showing a higher photocurrent and a low dark current of 15 pA, along with the good infrared photodetection ability for a concealed target. All results guide the construction of Schottky-contacts by surface decorations for next-generation high-performance III-V NWs optoelectronics devices.

Theory of MBE Growth of Nanowires on Adsorbing Substrates: The Role of the Shadowing Effect on the Diffusion Transport

A new model for nanowire growth by molecular beam epitaxy is proposed which extends the earlier approaches treating an isolated nanowire to the case of ensembles of nanowires. I consider an adsorbing substrate on which the arriving growth species (group III adatoms for III-V nanowires) may diffuse to the nanowire base and subsequently to the top without desorption. Analytical solution for the nanowire length evolution at a constant radius shows that the shadowing of the substrate surface is efficient and affects the growth kinetics from the very beginning of growth in dense enough ensembles of nanowires. The model fits quite well the kinetic data on different Au-catalyzed and self-catalyzed III-V nanowires. This approach should work equally well for vapor-liquid-solid and catalyst-free nanowires grown by molecular beam epitaxy and related deposition techniques on unpatterned or masked substrates.

Theory of MBE Growth of Nanowires on Reflecting Substrates

Selective area growth (SAG) of III-V nanowires (NWs) by molecular beam epitaxy (MBE) and related epitaxy techniques offer several advantages over growth on unpatterned substrates. Here, an analytic model for the total flux of group III atoms impinging NWs is presented, which accounts for specular re-emission from the mask surface and the shadowing effect in the absence of surface diffusion from the substrate. An expression is given for the shadowing length of NWs corresponding to the full shadowing of the mask. Axial and radial NW growths are considered in different stages, including the stage of purely axial growth, intermediate stage with radial growth, and asymptotic stage, where the NWs receive the maximum flux determined by the array pitch. The model provides good fits with the data obtained for different vapor-liquid-solid and catalyst-free III-V NWs.