In Situ Conformal Coating of Polyaniline on GaN Microwires for Ultrafast, Self-Driven Heterojunction Ultraviolet Photodetectors

Self-Powered UV Photodetector Construction of the P(EDOS-TTh) Copolymer-Modified ZnO Nanoarray

To solve the problem that zinc oxide nanorods (ZnO NRs)-based self-powered ultraviolet (UV) photodetectors cannot obtain both higher responsiveness and shorter response time, P(EDOS-TTh) was prepared using 3,4-ethylenedioxyselenphene (EDOS) and terthiophene (TTh) as copolymers, which modify the ZnO NRs surface, and the ZnO/P(EDOS-TTh) P-N junction self-powered UV device is assembled. The effect of the number of electrochemical polymerization cycles on the UV photodetection performance of ZnO/P(EDOS-TTh) P-N heterojunction was studied by adjusting the number of electrochemical polymerization cycles at the monomer molar ratio of 1:1. Benefiting from the enhanced built-in electric field of the ZnO/P(EDOS-TTh) interface, balancing photogenerated carriers, and charge separation and transport. The results show that the contact between N-type ZnO NRs and P-type P(EDOS-TTh) is best when the number of polymerization cycles is 3, due to the fact that EDOS-TTh and ZnO NRs form excellent P-N heterojunctions with strong internal electric fields, and the devices show good pyroelectric effect and UV photodetection performance. Under 0 V bias and 0.32 mW/cm2 UV irradiation, the responsivity (R) of ZnO/P(EDOS-TTh) reaches 3.31 mA/W, the detectivity (D*) is 7.25 × 1010 Jones, and the response time is significantly shortened. The rise time is 0.086 s, which exhibited excellent photoelectric properties and stability. UV photodetection performance with high sensitivity and fast response time is achieved.

Liquid-Metal-Assisted Synthesis of Patterned GaN Thin Films for High-Performance UV Photodetectors Array

GaN's outstanding physical characteristics allow for a wide range of applications in numerous industries. Although individual GaN-based ultraviolet (UV) photodetectors are the subject of in-depth research in recent decades, the demand for photodetectors array is rising as a result of advances in optoelectronic integration technology. However, as a prerequisite for constructing GaN-based photodetectors array, large-area, patterned synthesis of GaN thin films remains a certain challenge. This work presents a facile technique for pattern growing high-quality GaN thin films for the assembly of an array of high-performance UV photodetectors. This technique uses UV lithography, which is not only very compatible with common semiconductor manufacturing techniques, but also enables precise patterning modification. A typical detector has impressive photo-response performance under 365 nm irradiation, with an extremely low dark current of 40 pA, a high Ilight /Idark ratio over 105 , a high responsivity of 4.23 AW-1 , and a decent specific detectivity of 1.76 × 1012 Jones. Additional optoelectronic studies demonstrate the strong homogeneity and repeatability of the photodetectors array, enabling it to serve as a reliable UV image sensor with enough spatial resolution. These outcomes highlight the proposed patterning technique's enormous potential.

An investigation into the hybrid architecture of Mn-Co nanoferrites incorporated into a polyaniline matrix for photoresponse studies

In this study, an enhanced photoresponse was observed in the Mn-Co Nanoferrites (MCFs)-Polyaniline (PANI) nanohybrid architecture due to the formation of interface between PANI and MCFs, which provided a conduction pathway for the movement of charge carriers, and these interfaces were observed in a high-resolution transmission electron micrograph (HR-TEM). X-ray photoelectron spectroscopy (XPS) suggests that the carbon (C 1s) of the MCF-PANI nanohybrid shows peaks at 287.80 eV for CO, 286.17 eV for C-O, 285.24 eV for C-N, 284.50 eV for the sp3 hybridized carbon (C-C/C-H) and 283.84 eV for the sp2 hybridized carbon (CC). Current-voltage (I-V) curves reveal an ohmic nature of the MCF-PANI nanohybrid photodetector device. The photoresponse measurements were analyzed using the trap depth concept, demonstrating that the conductive polymer increases the photoconduction mechanism efficiency of MCFs. The constructed photodetector device exhibits a high photoresponsivity of 22.69 A W-1, a remarkable detectivity of 1.36 × 1012 cm Hz1/2 W-1 and a fast rise/decay time of 0.7/0.8 s. The excellent performance of the as-fabricated photodetector device could be explained by the intimate interaction between MCFs and PANI at their interface.

Adjusting Microscale to Atomic-Scale Structural Order in PbS Nanocrystal Superlattice for Enhanced Photodetector Performance

An investigation is presented into the effect of the long-range order on the optoelectronic properties of PbS quantum dot (QD) superlattices, which form mesocrystals, for potential use in photodetector applications. By self-assembly of QD nanocrystals on an Si/SiOx substrate, a highly ordered and densely packed PbS QD superlattice with a microscale size is obtained. The results demonstrate that annealing treatment induces mesocrystalline superlattices with preferred growth orientation, achieved by dislodging ligands. The improved orientation and electronic coupling of the mesocrystalline superlattices exhibit superior photodetector performance compared to disordered QD structures and closely packed superlattices. This improved performance is attributed to atomic alignment between QDs, leading to enhanced electronic coupling. The findings suggest that these mesocrystalline superlattices have promising potential for the next generation of QD optoelectronic devices.

Ultrasensitive self-powered heterojunction ultraviolet photodetector of p-GaN nanowires on Si by halide chemical vapour deposition

In this study, we report the fabrication of quasi-aligned p-GaN nanowires (NWs) on n-Si (1 1 1) substrate by halide chemical vapour deposition (HCVD) using MgCl₂precursor and followed by low-energy electron beam irradiation to activate the Mg acceptor doping in GaN NWs. We aimed to attain a comprehensive understanding of p-doping in GaN NWs growth, extensive characterizations and fabrication of UV photodetector (PDs) based on p-GaN NWs/n-Si heterojunction. To realize the efficient UV photodetectors, we measure the current-voltage (I-V) characteristics of heterojunction PDs under dark and illuminated conditions and theI-Vcurve demonstrates good rectifying behaviours with 0.2 V turn-on voltage. At zero bias, the heterojunction PDs show a reverse photocurrent of 1.27 × 10^-6A with a very low dark current of 2.35 × 10^-9A under 325 nm UV illumination. Besides, the significance of the self-powered operation of UV PDs and the charge transfer mechanism are discussed with the aid of the energy band diagram. The substantial photocurrent increment with varying applied potential leads to narrowing the photo potential in the interface. The excitonic bound states present in p-GaN NWs/n-Si heterojunction is further elucidated. As a result, the heterojunction PDs demonstrate the high responsivity, detectivity, and external quantum efficiency of 134 mA W^-1, 3.73 × 10¹³Jones, and 51% respectively, at 0.1 V low applied potential under the reverse bias condition. The proposed work provides an archetype for Mg doping in GaN NWs ensembles, which will help to facilitate the heterojunction with n-Si to unleash the potential of self-powered UV PDs.

Integration of H2V3O8 nanowires and a GaN thin film for self-powered UV photodetectors

H₂V₃O₈/GaN n-n heterojunction ultraviolet photodetectors are fabricated via a facile dip-coating method. The Schottky junction between the GaN and H₂V₃O₈ builds a built-in electric field to achieve the self-powered phenomenon. The photodetector presents a high photocurrent (0.23 μA) and a fast response speed (less than 0.3 s) at 0 V bias and under 365 nm light illumination (24.50 mW cm^-2). Furthermore, the photocurrent increases steadily as the light intensity increases from 0.53 to 24.50 mW cm^-2. The H₂V₃O₈/GaN heterojunction holds great potential to realize high-performance hybrid PDs.

Earth-abundant and environmentally benign Ni-Zn iron oxide intercalated in a polyaniline based nanohybrid as an ultrafast photodetector

Nickel-zinc iron oxide (NZF) was introduced into a polyaniline (PANI) matrix by an in situ chemical oxidation polymerization approach. The surface composition and chemical states were investigated by X-ray photoelectron spectroscopy (XPS), which revealed an Fe 2p spectrum with the two peak positions of Fe 2p_3/2 and Fe 2p_1/2 at 711.00 and 724.48 eV, respectively. Deconvolution of the Fe 2p_3/2 peak revealed two components with binding energies of 713.98 and 718.16 eV, corresponding to the presence of Fe cations in the octahedral and tetrahedral sites. Additionally, the Rietveld refinement of NZF showed a cubic system with the Fd₃m space group. High-resolution transmission electron microscopy (HRTEM) analysis showed that the NZF material strongly interacts with polyaniline, while the selected area electron diffraction (SAED) pattern perfectly matched with the XRD data. Lognormal distribution was used to determine the particle size, which was found to be in the range of 1-100 nm. A flexible photodetector device utilizing the NZF-PANI nanohybrid was fabricated on an environmentally friendly, biodegradable cellulose paper substrate and the device exhibited excellent performance, i.e., a responsivity of 0.069 A W^-1 and detectivity of 7.258 × 10¹⁰ Jones at a very low voltage of 0.1 V. The non-stretched device showed a responsivity of 24.980 A W^-1 at 5 V, whereas at 2 cm^-1 bending curvature, the device showed a responsivity of 20.175 A W^-1, which was much higher than the responsivity of a commercial photodetector (<0.5 A W^-1).

A Spiro-MeOTAD/Ga2O3/Si p-i-n Junction Featuring Enhanced Self-Powered Solar-Blind Sensing via Balancing Absorption of Photons and Separation of Photogenerated Carriers

Solar blind ultraviolet (SBUV) self-powered photodetectors (PDs) have a great number of applications in civil and military exploration. Ga₂O₃ is a prospective candidate for SBUV detection owing to its reasonable bandgap corresponding to the SBUV waveband. Nevertheless, the previously reported Ga₂O₃ photovoltaic devices had low photoresponse performance and were still far from the demands of practical application. Herein, we propose an idea of using spiro-MeOTAD (spiro) as the SBUV transparent conductive layer to construct p-i-n PDs (p-spiro/Ga₂O₃/n-Si). With the aid of double built-in electric fields, the designed p-i-n PDs could operate without any external power source. Furtherly, the influence of spiro thickness on improving the photoelectric performance of devices is investigated in detail and the optimum device is achieved, translating to a peak responsivity of 192 mA/W upon a weak 254 nm light illumination of 2 μW/cm² at zero bias. In addition, the I-t curve of our PD shows binary response characteristics and a four-stage current response behavior under a small forward bias, and also, its underlying working mechanism is analyzed. In sum, this newly developed device presents great potential for booming the high energy-efficient optoelectronic devices in the short run.

Self-Powered MXene/GaN van der Waals Heterojunction Ultraviolet Photodiodes with Superhigh Efficiency and Stable Current Outputs

A self-powered, high-performance Ti₃ C₂ T_x MXene/GaN van der Waals heterojunction (vdWH)-based ultraviolet (UV) photodiode is reported. Such integration creates a Schottky junction depth that is larger than the UV absorption depth to sufficiently separate the photoinduced electron/hole pairs, boosting the peak internal quantum efficiency over the unity and the external quantum efficiency over 99% under weak UV light without bias. The proposed Ti₃ C₂ T_x /GaN vdWH UV photodiode demonstrates pronounced photoelectric performances working in self-powered mode, including a large responsivity (284 mA W^-1 ), a high specific detectivity (7.06 × 10¹³ Jones), and fast response speed (rise/decay time of 7.55 µs/1.67 ms). Furthermore, the remarkable photovoltaic behavior leads to an impressive power conversion efficiency of 7.33% under 355 nm UV light illumination. Additionally, this work presents an easy-processing spray-deposition route for the fabrication of large-area UV photodiode arrays that exhibit highly uniform cell-to-cell performance. The MXene/GaN photodiode arrays with high-efficiency and self-powered ability show high potential for many applications, such as energy-saving communication, imaging, and sensing networks.

Interface Engineering Ti3 C2 MXene/Silicon Self-Powered Photodetectors with High Responsivity and Detectivity for Weak Light Applications

Interfacial engineering and heterostructures designing are two efficient routes to improve photoelectric characteristics of a photodetector. Herein, a Ti₃ C₂ MXene/Si heterojunction photodetector with ultrahigh specific detectivity (2.03 × 10¹³ Jones) and remarkable responsivity (402 mA W^-1 ) at zero external bias without decline as with increasing the light power is reported. This is achieved by chemically regrown interfacial SiO_x layer and the control of Ti₃ C₂ MXene thickness to suppress the dark noise current and improve the photoresponse. The photodetector demonstrates a high light on/off ratio of over 10⁶ , an outstanding peak external quantum efficiency (EQE) of 60.3%, while it maintains an ultralow dark current at 0 V bias. Moreover, the device holds high performance with EQE of over 55% even after encapsulated with silicone, trying to resolve the air stability issue of Ti₃ C₂ MXene. Such a photodetector with high detectivity, high responsivity, and self-powered capability is particularly applicable to detect weak light signal, which presents high potential for imaging, communication and sensing applications.

Ag Nanowire-Plasmonic-Assisted Charge Separation in Hybrid Heterojunctions of Ppy-PEDOT:PSS/GaN Nanorods for Enhanced UV Photodetection

The surface states, poor carrier life, and other native defects in GaN nanorods (NRs) limit their utilization in high-speed and large-gain ultraviolet (UV) photodetection applications. Making a hybrid structure is one of the finest strategies to overcome such impediments. In this work, a polypyrrole (Ppy)-poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/GaN NRs hybrid structure is introduced for self-powered UV photodetection applications. This hybrid structure yields high photodetection performance, while pristine GaN NRs showed negligible photodetection properties. The ability of the photodetector is further boosted by functionalizing the hybrid structure with Ag nanowires (NWs). The Ag NWs-functionalized hybrid structure exhibited a responsivity of 3.1 × 10³ (A/W), detectivity of 3.19 × 10¹⁴ Jones, and external quantum efficiency of 1.0⁶ × 10⁶ (%) under a UV illumination of λ = 382 nm. This high photoresponse is due to the huge photon absorption rising from the localized surface plasmonic effect of a Ag NWs network. Also, the Ag NWs significantly improved the rising and falling times, which were noted to be 0.20 and 0.21 s, respectively. The model band diagram was proposed with the assistance of X-ray photoelectron spectroscopy to explore the origin of the superior performance of the Ag NWs-decorated Ppy-PEDOT:PSS/GaN NRs photodetector. The proposed hybrid structure seems to be a promising candidate for the development of high-performance UV photodetectors.