Highly Sensitive and Tunable Self-Powered UV Photodetectors Driven Jointly by p-n Junction and Ferroelectric Polarization

Ultrahigh Bipolar Photoresponse in a Self-Powered Ultraviolet Photodetector Based on GaN and In/Sn-Doped Ga2O3 Nanowires pn junction

Self-powered ultraviolet photodetectors with bipolar photoresponse have great potential in the fields of ultraviolet optical communication, all-optical controlled artificial synapses, high-resolution ultraviolet imaging equipment, and multiband photoelectric detection. However, the current low optoelectronic performance limits the development of such polar switching devices. Here, we construct a self-powered ultraviolet photodetector based on GaN and In/Sn-doped Ga2O3 (IGTO) nanowires (NWs) pn junction structure. This unique nanowire/thin film structure allows GaN and IGTO to dominate the absorption of light at different wavelengths, resulting in a highly bipolar photoresponse. The device has a responsivity of 2.04 A/W and a normalized detectivity of 7.18 × 1013 Jones at 254 nm and a responsivity of -2.09 A/W and a normalized detectivity of -7 × 1013 Jones at 365 nm, both at zero bias. In addition, it has an extremely high Ilight/Idark ratio of 1.05 × 105 and ultrafast response times of 2.4/1.9 ms (at 254 nm) and 5.7/5.2 ms (at 365 nm). These excellent properties are attributed to the high specific surface area of the one-dimensional nanowire structure and the abundant voids generated by the nanowire network to enhance the absorption of light, and the p-n junction structure enables the rapid separation and transfer of photogenerated electron-hole pairs. Our findings provide a feasible strategy for high-performance wavelength-controlled polarity switching devices.

Quantum enhanced efficiency and spectral performance of paper-based flexible photodetectors functionalized with two dimensional materials

Flexible photodetectors (PDs) have exotic significance in recent years due to their enchanting potential in future optoelectronics. Moreover, paper-based fabricated PDs with outstanding flexibility unlock new avenues for future wearable electronics. Such PD has captured scientific interest for its efficient photoresponse properties due to the extraordinary assets like significant absorptive efficiency, surface morphology, material composition, affordability, bendability, and biodegradability. Quantum-confined materials harness the unique quantum-enhanced properties and hold immense promise for advancing both fundamental scientific understanding and practical implication. Two-dimensional (2D) materials as quantum materials have been one of the most extensively researched materials owing to their significant light absorption efficiency, increased carrier mobility, and tunable band gaps. In addition, 2D heterostructures can trap charge carriers at their interfaces, leading increase in photocurrent and photoconductivity. This review represents comprehensive discussion on recent developments in such PDs functionalized by 2D materials, highlighting charge transfer mechanism at their interface. This review thoroughly explains the mechanism behind the enhanced performance of quantum materials across a spectrum of figure of merits including external quantum efficiency, detectivity, spectral responsivity, optical gain, response time, and noise equivalent power. The present review studies the intricate mechanisms that reinforce these improvements, shedding light on the intricacies of quantum materials and their significant capabilities. Moreover, a detailed analysis of the technical applicability of paper-based PDs has been discussed with challenges and future trends, providing comprehensive insights into their practical usage in the field of future wearable and portable electronic technologies.

Nonvolatile and reconfigurable two-terminal electro-optic duplex memristor based on III-nitride semiconductors

With the fast development of artificial intelligence (AI), Internet of things (IOT), etc, there is an urgent need for the technology that can efficiently recognize, store and process a staggering amount of information. The AlScN material has unique advantages including immense remnant polarization, superior temperature stability and good lattice-match to other III-nitrides, making it easy to integrate with the existing advanced III-nitrides material and device technologies. However, due to the large band-gap, strong coercive field, and low photo-generated carrier generation and separation efficiency, it is difficult for AlScN itself to accumulate enough photo-generated carriers at the surface/interface to induce polarization inversion, limiting its application in in-memory sensing and computing. In this work, an electro-optic duplex memristor on a GaN/AlScN hetero-structure based Schottky diode has been realized. This two-terminal memristor shows good electrical and opto-electrical nonvolatility and reconfigurability. For both electrical and opto-electrical modes, the current on/off ratio can reach the magnitude of 104, and the resistance states can be effectively reset, written and long-termly stored. Based on this device, the "IMP" truth table and the logic "False" can be successfully reproduced, indicating the huge potential of the device in the field of in-memory sensing and computing.

Negative Photoconductivity in 2D α-MoO3/Ir Self-Powered Photodetector: Impact of Post-Annealing

Surface plasmon technology is regarded as having significant potential for the enhancement of the performance of 2D oxide semiconductors, especially in terms of improving the light absorption of 2D MoO3 photodetectors. An ultrathin MoO3/Ir/SiO2/Si heterojunction Schottky self-powered photodetector is introduced here to showcase positive photoconductivity. In wafer-scale production, the initial un-annealed Mo/2 nm Ir/SiO2/Si sample displays a sheet carrier concentration of 5.76 × 1011/cm², which subsequently increases to 6.74 × 1012/cm² after annealing treatment, showing a negative photoconductivity behavior at a 0 V bias voltage. This suggests that annealing enhances the diffusion of Ir into the MoO3 layer, resulting in an increased phonon scattering probability and, consequently, an extension of the negative photoconductivity behavior. This underscores the significance of negative photoconductive devices in the realm of optoelectronic applications.

High-Performance Self-Driven Solar-Blind Ultraviolet Photodetectors Based on HfZrO2/β-Ga2O3 Heterojunctions

Ga₂O₃ is a wide-bandgap semiconductor that has shown great potential for application in solar-blind ultraviolet (UV) photodetectors. However, the responsivity and detectivity of Ga₂O₃-based self-driven solar-blind UV photodetectors are insufficient for practical applications at present because of the limited separation of photogenerated carriers in the devices. In this work, Hf_0.5Zr_0.5O₂/β-Ga₂O₃ heterojunction-based self-driven solar-blind UV photodetectors are constructed by combining ferroelectric Hf_0.5Zr_0.5O₂ (HfZrO₂) material with Ga₂O₃, taking advantage of the ultrawide bandgap of HfZrO₂ and the favorable II-type energy band configuration between both. Upon optimization, a HfZrO₂/β-Ga₂O₃ heterojunction-based UV photodetector with a HfZrO₂ layer thickness of 10 nm is shown to provide remarkable responsivity (R = (14.64 ± 0.3) mA/W) and detectivity (D* = (1.58 ± 0.03) × 10¹² Jones), which are much superior to those of a single Ga₂O₃-based device toward 240 nm light illumination. Further, the device performance is adjustable with varying poling states of HfZrO₂ and shows substantial enhancement in the upward poling state, benefiting from the constructive coupling of the ferroelectric depolarization electric field in HfZrO₂ and the built-in electric field at the HfZrO₂/β-Ga₂O₃ interface. Under illumination of weak light of 0.19 μW/cm², the upward poled device shows significantly enhanced R (52.6 mA/W) and D* (5.7 × 10¹² Jones) values. The performance of our device surpasses those of most previously reported Ga₂O₃-based self-driven photodetectors, indicating its great potential in practical applications for sensitive solar-blind UV detection.

Self-Powered Bipolar Photodetector Based on a Ce-BaTiO3 PTCR Semiconductor for Logic Gates

Ferroelectric materials bring new opportunities for self-powdered photodetectors, taking advantage of their anomalous bulk photovoltaic effect. However, ferroelectric-based photodetectors suffer from relatively poor responsivity and detectivity due to obstacles of low electrical conductivity and low photoelectric conversion ability. The present work proposes a strategy based on heterovalent ion Ce-doping into BaTiO₃ (Ce-BTO) that gives rise to a good room temperature conductivity combined with a significant PTCR (positive temperature coefficient of resistivity) effect. By utilizing a Ce-BTO PTCR semiconductor, a high-performance self-powered photodetector ITO/Ce-BTO/Ag is fabricated, demonstrating a polarity-switchable photoresponse with the change of wavelength due to the competition between hot electrons induced by the Ag plasmonic effect and electron-hole pairs separated by a Schottky barrier. Moreover, benefiting from the reduced bandgap and the introduced impurity states, good responsivity (9.85 × 10^-5 A/W) and detectivity (1.25 × 10¹⁰ Jones) as well as fast response/recovery time (83/47 ms) is achieved under 450 nm illumination. Finally, four representative logic gates ("OR", "AND", "NOR", and "NAND") are demonstrated with one photodetector via the bipolar photoresponse. This work opens an avenue to promote the application of PTCR semiconductors in optoelectronics, offering a conceivable means toward high-performance self-powered photodetectors.

Recent Advances in Ferroelectric-Enhanced Low-Dimensional Optoelectronic Devices

Ferroelectric (FE) materials, including BiFeO₃ , P(VDF-TrFE), and CuInP₂ S₆ , are a type of dielectric material with a unique, spontaneous electric polarization that can be reversed by applying an external electric field. The combination of FE and low-dimensional materials produces synergies, sparking significant research interest in solar cells, photodetectors (PDs), nonvolatile memory, and so on. The fundamental aspects of FE materials, including the origin of FE polarization, extrinsic FE materials, and FE polarization quantification are first discussed. Next, the state-of-the-art of FE-based optoelectronic devices is focused. How FE materials affect the energy band of channel materials and how device structures influence PD performance are also summarized. Finally, the future directions of this rapidly growing field are discussed.

Extended linear detection range of a Bi0.5Na0.5TiO3 thin film-based self-powered UV photodetector via current and voltage dual indicators

Ferroelectric materials are widely recognized for their ability to generate photovoltaic voltages larger than their bandgap, making them ideal candidates for photodetector applications. Here, we report a self-powered UV photodetector based on a Bi_0.5Na_0.5TiO₃ (BNT) thin film prepared by the sol-gel method. Compared with conventional photodetectors based on a single detection indicator, the demonstrated photodetector realizes UV light intensity detection over a wide linear range using a current and voltage dual indicator detection method. When the UV light intensity is lower than 1.8 mW cm^-2, the voltage can be used to detect the light signal. Conversely, the current can be utilized to detect the signal. This method not only broadens the linear detection range of UV light intensity, making it possible to detect weak UV light of 45.2 nW cm^-2, but also allows the detector to maintain relatively high sensitivity within the detectable range. To investigate the distribution of spatial UV light intensity, a self-powered photodetector array system has been utilized to record the output voltage signals as a map.

Self-powered p-CuI/n-GaN heterojunction UV photodetector based on thermal evaporated high quality CuI thin film

With vacuum thermal evaporation, the CuI film was deposited on quartz and n-GaN substrates, and the morphology, crystalline structure and optical properties of the CuI films were investigated. According to the XRD results, the CuI film preferentially grew along [111] crystal orientation on the GaN epilayer. With Au and Ni/Au ohmic contact electrodes fabricated on CuI and n-GaN, a prototype p-CuI/n-GaN heterojunction UV photodetector strong UV spectral selectivity was created. At 0 V and 360 nm front illumination (0.32 mW/cm²), the heterojunction photodetector displayed outstanding self-powered detection performance with the responsivity (R), specific detectivity (D*), and on/off ratio up to 75.5 mA/W, 1.27×10¹² Jones, and ∼2320, respectively. Meanwhile, the p-CuI/n-GaN heterojunction photodetector had excellent atmosphere stability.

Self-powered UV photodetectors and imaging arrays based on NiO/IGZO heterojunctions fabricated at room temperature

Self-powered UV photodetectors and imaging arrays based on p-type NiO/n-type InGaZnO (IGZO) heterojunctions are fabricated at room temperature by using ratio-frequency magnetron sputtering. The p-n heterojunction exhibits typical rectifying characteristics with a rectification ratio of 7.4×10⁴ at a ±4 V applied bias. A high photo-responsivity of 28.8 mA/W is observed under zero bias at a wavelength of 365 nm. The photodetector possesses a fast response time of 15 ms which is among the best in reported oxide-based p-n junction-based UV photodetectors. Finally, recognition of an "H" pattern is demonstrated by a 10×10 photodetector array at zero bias. The results indicate that the NiO/IGZO based photodetectors may have a great potential in constructing large-scale self-powered UV imaging systems.

Ferro-Pyro-Phototronic Effect in Monocrystalline 2D Ferroelectric Perovskite for High-Sensitive, Self-Powered, and Stable Ultraviolet Photodetector

2D hybrid perovskite ferroelectrics have drawn great attention in the field of photodetection, because the spontaneous polarization-induced built-in electric field can separate electron-hole pairs, and makes self-powered photodetection possible. However, most of the 2D hybrid perovskite-based photodetectors focused on the detection of visible light, and only a few reports realized the self-powered and sensitive ultraviolet (UV) detection using wide bandgap hybrid perovskites. Here, 2D ferroelectric PMA₂PbCl₄ monocrystalline microbelt (MMB)-based PDs are demonstrated. By using the ferro-pyro-phototronic effect, the self-powered Ag/Bi/2D PMA₂PbCl₄ MMB/Bi/Ag PDs show a high photoresponsivity up to 9 A/W under 320 nm laser illumination, which is much higher than those of previously reported self-powered UV PDs. Compared with responsivity induced by the photovoltaic effect, the responsivity induced by the ferro-pyro-phototronic effect is 128 times larger. The self-powered PD also shows fast response and recovery speed, with the rise time and fall time of 162 and 226 μs, respectively. More importantly, the 2D PMA₂PbCl₄ MMB-based PDs with Bi/Ag electrode exhibit significant stability when subjected to high humidity, continuous laser illumination, and thermal conditions. Our findings would shed light on the ferro-pyro-phototronic-effect-based devices, and provide a good method for high-performance UV detection.

Enabling Distributed Intelligence with Ferroelectric Multifunctionalities

Distributed intelligence involving a large number of smart sensors and edge computing are highly demanded under the backdrop of increasing cyber-physical interactive applications including internet of things. Here, the progresses on ferroelectric materials and their enabled devices promising energy autonomous sensors and smart systems are reviewed, starting with an analysis on the basic characteristics of ferroelectrics, including high dielectric permittivity, switchable spontaneous polarization, piezoelectric, pyroelectric, and bulk photovoltaic effects. As sensors, ferroelectrics can directly convert the stimuli to signals without requiring external power supply in principle. As energy transducers, ferroelectrics can harvest multiple forms of energy with high reliability and durability. As capacitors, ferroelectrics can directly store electrical charges with high power and ability of pulse-mode signal generation. Nonvolatile memories derived from ferroelectrics are able to realize digital processors and systems with ultralow power consumption, sustainable operation with intermittent power supply, and neuromorphic computing. An emphasis is made on the utilization of the multiple extraordinary functionalities of ferroelectrics to enable material-critical device innovations. The ferroelectric characteristics and synergistic functionality combinations are invaluable for realizing distributed sensors and smart systems with energy autonomy.

Reversible Rectification of Microscale Ferroelectric Junctions Employing Liquid Metal Electrodes

Both ferroelectric crystals and liquid metal electrodes have attracted extensive attention for potential applications in next-generation devices and circuits. However, the interface information between ferroelectric crystals and liquid metal electrodes has so far been lacking. To better understand the optoelectronic properties of microscale ferroelectric crystals (potassium tantalate niobate, KTN) and its potential integration with liquid metal electrodes (a "printing ink" for flexible electric circuit production), microscale KTN crystals sandwiched by eutectic gallium indium (EGaIn, a liquid metal) with varied contact geometries were studied. Unlike the bulk KTN crystal junctions, the microscale KTN junctions show electrical rectifying characteristics upon light illumination, and the directionality of the rectification can be reversed by increasing the ambient temperature to a few degrees. Furthermore, a strong suppression of the current upon increasing voltage, that is, the quasi-negative differential resistance, is observed when the microscale KTN is half-enclosed by the EGaIn electrode. Our results show that trapping/detrapping of carriers affected by the crystal size and the ambient temperature is the dominant physical mechanism for these observations. These results not only facilitate a better understanding of charge transport through the microscale ferroelectric crystals but also advance the design of miniaturized hybrid devices.