Photodetectors Research Articles

Experimental demonstration of an integrated continuously adjustable true time delay chip

A continuously adjustable delay scheme based on Mach-Zehnder interferometer (MZI) switch, compatible with the reconfigurable binary true time delay lines (RBTTDL), has been theoretically analyzed and experimentally validated. It is designed to compensate for the limitation of RBTTDL, which can only provide discrete delay steps. The continuously adjustable delay is achieved by employing different interference between the two paths of the MZI switch with the assistance of monitoring photodetectors (PD). The structure parameters related to the continuous delay performance, the broadband characteristic and the amplitude flatness are deeply discussed. The experimental results show good agreements with the theoretical calculations. Therefore, without adding extra components in the RBTTDL structure, this scheme can provide the continuously adjustable delay within the minimum step increment delay of RBTTDL, while the larger delay values are provided by RBTTDL itself, which presents potential in the OTTD technology.

Photo-controlled programmable logic gate via self-powered Cu2O/BiFeO3/TiO2 ferroelectric heterojunction photodetectors

The increased demands for high integration, fast computation, and a wide range of data processing in digital logic circuits have triggered an interest in programmable logic gates that can run different logic operations. Photodetectors (PDs) based on ferroelectric materials can obtain different ferroelectric polarization states utilizing pre-biased voltage regulation to achieve programmable logic functions, but low photoelectric conversion efficiency and slow photoresponse speed are still key problems to be addressed for programmable logic gate devices. Herein, the Cu2O/BiFeO3(BFO)/TiO2 ferroelectric heterojunction PDs were constructed by introducing a p-type hole transport layer Cu2O on the BFO/TiO2 ferroelectric heterojunction films, which not only broadens the photoresponse spectra range to the red light, but also forms a stepped energy band structure at the heterojunction interface, and the interfacial electric field promotes the separation and transport of photogenerated carriers, improving the self-powered photodetection performance of the devices. The Cu2O/BFO/TiO2 PDs demonstrate a responsivity of 3.0 mA/W and a photoresponse rise time/decay time of 2.3/23.9 ms at 420 nm light illumination. The Cu2O/BFO/TiO2 PD can be polarized in different states by pre-biased voltage and outputs different electrical signal values under the ultraviolet (365 nm) and visible (420 nm) monochromatic light or the mixed light irradiation, thus the device can realize the "AND" gate output in the positive bias polarization state and the "OR" gate output in the negative bias polarization state, which shows that the ferroelectric heterojunction PDs has a great potential application in the field of photo-controlled programmable logic gate circuits.

Boosting the Performance of Flexible Perovskite Photodetectors Using Hierarchical Plasmonic Nanostructures

Plasmonic nanostructures can enhance the performance of photodetectors (PDs) owing to their amplification effect in light absorption, leading to overcoming the inherent properties of the photoactive layer. Herein, hierarchical plasmonic nanopatterns have been prepared and used for high‐performance flexible perovskite PDs. The developed hierarchical nanostructures, featuring nanoposts on cross‐nanograting patterns, exhibit a notably enhanced light trapping effect compared to hierarchical nanostructures based on a unidirectional simple nanograting structure. Moreover, hierarchical pattern‐based perovskite PDs show a photoresponsivity of 580 mA W−1 and a specific detectivity of 3.2 × 1012 Jones, which are 420% and 990% higher than those of perovskite PDs without plasmonic nanostructures, respectively. Furthermore, a flexible 10 × 10 PD array has been developed, which enables the accurate mapping of light signals with exceptional operational and mechanical stabilities, under a bending radius as small as 8 mm and after undergoing more than 1000 bending cycles. Comprehensive analyses using finite‐difference time‐domain calculations and photoluminescence mapping reveal the effective light trapping effect of hierarchical plasmonic patterns in the perovskite layers. This work provides an efficient approach to achieve high‐performance perovskite optoelectronic devices.

Spacer Conformation Induced Multiple Hydrogen Bonds in 2D Perovskite toward Highly Efficient Optoelectronic Devices.

Two-dimensional (2D) Dion-Jacobson (DJ) perovskites typically outperform Ruddlesden-Popper (RP) analogs in terms of photodetection (PD). However, the mechanism behind this enhanced performance remains elusive. Theoretical calculations for elucidating interlayer spacer conformation-induced multiple hydrogen bonds in 2D perovskite are presented, along with the synthesis of DPAPbBr4 (DPB) single crystals (SCs) and their PD properties under X-ray/ultraviolet (UV) excitation. The high-quality DPB SC enhances PD with exceptional photoresponse attributes, including a high on/off ratio (4.89×104), high responsivity (2.44 AW⁻1), along with large dynamic linear range (154 dB) and low detection limit (7.1 nWcm⁻2), which are currently the best results among 2D perovskite SC detectors, respectively. Importantly, high-resolution images are obtained under UV illumination with weak light levels. The SC X-ray detector exhibits a high sensitivity of 663 µC Gyair⁻1 cm-2 at 10 V and a detection limit of 1.44 µGyair s⁻1. This study explores 2D DJ perovskites for efficient and innovative optoelectronic applications.

Pyro-phototronic effect enhanced the performance of TiO2 NRs/BiOCl//PEDOS heterojunction for a UV photodetector

This study presents the construction of an organic–inorganic heterojunction ultraviolet (UV) photodetector (PD) through face-to-face assembly. The synergistic effects of bismuth oxychloride (BiOCl) and titanium dioxide nanorods (TiO2 NRs) improve carrier transport efficiency and enhance the performance of the UV photodetector. The combination of BiOCl with TiO2 NRs generates a pyro-phototronic effect and increases the surface oxygen vacancies of TiO2 NRs, resulting in enhanced carrier transport efficiency, increased transient photocurrent, and reduced dark current in TiO2-based UV photodetectors. The enhanced photosensitivity of chloride (Cl) ions bound to selenium (Se) ions promotes easy electron injection from poly (3,4-ethylene dioxyselenophene) (PEDOS) into BiOCl, leading to accelerated electron transfer and a shortened response time. Compared to TiO2 NRs/BiOCl//TiO2 NRs/BiOCl, the TiO2 NRs/BiOCl//PEDOS heterojunction exhibits a fast photoresponse with a rise time of 0.0802 s and a fall time of 79.8 ms. The responsivity is significantly improved from 11.0 mA/W to 108.8 mA/W (a 10-fold enhancement), and the detectivity is increased from 0.67 × 1011 Jones to 1.25 × 1011 Jones at 365 nanomaterials (0 V). These findings provide valuable insights into the mechanism by which BiOCl nanosheets enhance the photodetection performance of devices, contributing to the advancement of UV photodetector technology.

Flexible 2 × 2 multiple access visible light communication system based on an integrated parallel GaN/InGaN micro-photodetector array module

In recent studies, visible light communication (VLC) has been predicted to be a prospective technique in the future 6G communication systems. To suit the trend of exponentially growing connectivity, researchers have intensively studied techniques that enable multiple access (MA) in VLC systems, such as the MIMO system based on LED devices to support potential applications in the Internet of Things (IoT) or edge computing in the next-generation access network. However, their transmission rate is limited due to the intrinsic bandwidth of LED. Unfortunately, the majority of visible light laser communication (VLLC) research with beyond 10 Gb/s data rates concentrates on point-to-point links, or using discrete photodetector (PD) devices instead of an integrated array PD. In this paper, we demonstrated an integrated PD array device fabricated with a Si-substrated GaN/InGaN multiple-quantum-well (MQW) structure, which has a 4×4 array of 50 μm×50 μm micro-PD units with a common cathode and anode. This single-integrated array successfully provides access for two different transmitters simultaneously in the experiment, implementing a 2×2 MIMO-VLLC link at 405 nm. The highest data rate achieved is 13.2 Gb/s, and the corresponding net data rate (NDR) achieved is 12.27 Gb/s after deducing the FEC overhead, using 2.2 GHz bandwidth and superposed PAM signals. Furthermore, we assess the Huffman-coded coding scheme, which brings a fine-grain adjustment in access capacity and enhances the overall data throughput when the user signal power varies drastically due to distance, weather, or other challenges in the channel condition. As far as we know, this is the first demonstration of multiple visible light laser source access based on a single integrated GaN/InGaN receiver module.

Dynamic switching from coherent perfect absorption to parametric amplification in a nonlinear spoof plasmonic waveguide

Coherent perfect absorption (CPA) and amplification of electromagnetic waves are converse phenomena, where incoming radiations are coherently dissipated or amplified by structured incidences. Realizing such two phenomena simultaneously in a single device may benefit various applications such as biological sensing, photo detection, radar stealth, solar-thermal energy sharing, and wireless communications. However, previous experimental realizations of CPA and amplification generally require precise controls to the loss and gain of a system, making dynamic switching between the absorption and amplification states a challenge. To this end, we propose a nonlinear approach to realize CPA and parametric amplification (PA) simultaneously at the same frequency and demonstrate experimentally dynamic switch from the CPA to PA states in a judiciously designed nonlinear spoof plasmonic waveguide. The measured output signal gain can be continuously tuned from −33 dB to 22 dB in a propagation length of 9.2 wavelengths. Compared to the traditional linear CPA, our approach relaxes the stringent requirements on device dimensions and material losses, opening a new route to actively modulate the electromagnetic waves with giant amplification-to-absorption contrast in a compact platform. The proposed nonlinear plasmonic platform has potential applications in on-chip systems and wireless communications.

High-speed GeSn resonance cavity enhanced photodetectors for a 50 Gbps Si-based 2 μm band communication system

Expanding the optical communication band is one of the most effective methods of overcoming the nonlinear Shannon capacity limit of single fiber. In this study, GeSn resonance cavity enhanced (RCE) photodetectors (PDs) with an active layer Sn component of 9%–10.8% were designed and fabricated on an SOI substrate. The GeSn RCE PDs present a responsivity of 0.49 A/W at 2 μm and a 3-dB bandwidth of approximately 40 GHz at 2 μm. Consequently, Si-based 2 μm band optical communication with a transmission rate of 50 Gbps was demonstrated by using a GeSn RCE detector. This work demonstrates the considerable potential of the Si-based 2 μm band photonics in future high-speed and high-capacity optical communication.

P(VDF-TrFE) interlayer enables high performance of Sb2Se3 photodetectors

Antimony selenide (Sb2Se3) has been extensively studied in photodetectors (PDs) for its extraordinary photoelectric properties. In this study, we report a new attempt to apply ferroelectric material P(VDF-TrFE)) in Sb2Se3 PDs. The P(VDF-TrFE) thin films were coated on Sb2Se3, which effectively improved the interface quality between the Sb2Se3 thin films and the C electrode, leading to a smaller leakage current. Moreover, due to the ferroelectric effect of P(VDF-TrFE), the remanent polarization enhances the separation and transmission of photogenerated carriers, which significantly improves the photoelectric performance of Sb2Se3 PDs. Experimental results show that the insertion of P(VDF-TrFE) enables the device to have a low dark current (from 2.0 × 10−3 to 1.6 × 10−4 μA) and ultra-high On/Off ratio (from 5.06 × 102 to 1.26 × 104). In addition, the resulting device exhibits weak light detection ability with a photo-responsive at a weak light of 5 × 10−6 W cm−2.

Flexible UV photodetector based on copper tetraiodogallate (CuGaI4) film

AbstractThe Cu‐based halide semiconductor CuGaI4 was prepared by a high‐temperature melting method. Optoelectronic characterization and density functional theory calculations of CuGaI4 reveal a direct bandgap of 2.9 eV. The corresponding UV photodetector (PD) based on CuGaI4 demonstrates excellent UV response and rapid response time. In addition, a flexible PD based on CuGaI4 is prepared, which also displays excellent photoresponse characteristics and mechanical stability. This work provides a systematic study of this novel Cu‐based halide semiconductor and demonstrates the great potential of CuGaI4 for future UV optoelectronic devices.

Positioning algorithm based on space constraint of the PD array in VLP system

Due to factors such as indoor multipath effects and noise, the positioning signal becomes unstable, posing a challenge for visible light positioning systems relying on a single photodetector (PD) to achieve accurate position estimation. To enhance localization precision and ranging accuracy, a positioning algorithm based on spatial constraints of the PD array is introduced in this paper. By leveraging spatial information from the PD array and the channel state information (CSI) from multiple PDs, cross-matching among multiple PDs is performed to alleviate the limitation of unstable positioning information of a single PD during the positioning process. Moreover, the distances obtained through cross-matching are fused with those based on CSI, and the measured distance is iteratively updated to reduce the interference of reflection paths on ranging. This algorithm utilizes the spatial arrangement of the PD array to constrain positioning information received by multiple PDs, rather than relying on a single PD for positioning. This method can achieve joint optimization of positioning accuracy and ranging accuracy without requiring additional equipment or modifying the transceiver structure. Simulation results within a 4 m × 4 m × 3 m indoor space showcase the proposed method's effectiveness. The average positioning error has been reduced to 1.28 cm, and the root mean square error has been reduced to 1.51 cm. In comparison to the least squares (LS) algorithm based on CSI and the nonlinear LS algorithm based on CSI, the new approach reduces average localization errors by approximately 50.4% and 41.3%, respectively. Additionally, the algorithm attains a ranging accuracy of 3.86 cm, outperforming CSI-based distance estimation accuracy by 41.9%.

Performance boosting of Sb2Se3 photodetectors by a sol–gel auto-combustion ZnO overlayer

Antimony selenide (Sb2Se3) is a promising material for low-cost, high-performance optoelectronic devices. In this study, a sol–gel auto-combustion ZnO overlayer was introduced into the Sb2Se3 photodetector (PD) for the first time. The sol–gel auto-combustion method is simple, efficient and low-cost, and when the solution ratio of the ZnO overlayer (Zn(CH3COO)2·2H2O: Zn(NO3)2·6H2O) is optimized to 6:4, the constructed heterojunction improves the electron transport efficiency and shows the best performance. The results showed that the ameliorated PD exhibits higher on/off ratio (6054), responsivity (R) (23.5 mA W−1) and detectivity (D*) (2.1 × 1011 Jones) than the original device, which are improved by 22 times, 6 times and 10 times @ 660 nm, respectively. This work can enlighten the synthesis and application of low temperature ZnO thin film that can be applied for high performance Sb2Se3 PDs and other optoelectronic devices with heat-labile materials.

Space‐Time Projection Enabled Ultrafast All‐Optical Diffractive Neural Network

AbstractAll‐optical neural networks have advantages in higher throughput, higher speed as well as lower energy consumption compared to electrical neural networks. Optical neural networks have already shown great potential in various applications; however, the operation speed of the network is limited by the 2D detector as most optical neural networks rely on space to space projection. Here, a space to time projection approach to build diffractive deep neural network (D2NN) is proposed, which can project spatial intensity distribution into time‐domain intensity variation, thus bypassing the detection speed limit of 2D imaging device. Based on this scheme, high‐speed all‐optical logic gates are theoretically analyzed and experimentally realized. In this case, the network's operation speed is only limited by the photodetector (PD), which can reach GHz levels. Moreover, the method will show great advantage when it comes to wavelengths where 2D detectors are not achievable easily such as infrared, terahertz or microwaves.

Coherent perfect absorption of light by undoped graphene monolayer

We show theoretically that coherent perfect absorption (CPA) of light is possible by a graphene monolayer without doping. To achieve the CPA, undoped graphene is embedded inside a multilayer structure called mirror structure, which increases the effective impedance of the surrounding medium. The increased effective impedance allows the destructive interference of light outside the structure that induces an increased Joule heat generating perfect absorption of light by graphene. We find that the CPA is possible for any wavelength as long as the thickness of each layer of the structure is a quarter of the corresponding wavelength. By changing the incident wavelength, but keeping the thickness of each layer, we show that the optical absorption is sensitive to the change of the incident wavelength. Therefore, we can design a photo detector for a specific wavelength.

MXene/AlGaN van der Waals heterojunction self-powered photodetectors for deep ultraviolet communication

Self-powered deep ultraviolet (DUV) photodetectors (PDs) have attracted considerable attention in environmental, industrial, and military fields because of their power-independent and environmentally sensitive photodetection. However, DUV PDs based on traditional thin film structures are limited by the low intrinsic mobility of aluminum-gallium nitride (AlGaN) and the large barrier width of the heterogeneous structure, which makes it difficult to achieve efficient spontaneous separation, resulting in lower responsiveness and a slow response speed. Herein, a 2D/3D DUV PD based on the MXene, niobium carbide (Nb2CTx)/AlGaN van der Waals heterojunctions (vdWHs) has been proposed. The as-prepared DUV PDs revealed self-powered properties with a high responsivity of 101.85 mA W−1, as well as a fast response (rise/decay time of 21/22 ms) under 254 nm DUV illumination, thanks to the excellent electrical conductivity and tunable work function of the MXene. It also showed a large linear dynamic range of 70 dB under −2 V bias because of the strong DUV absorption of MXene/AlGaN vdWH, and the enhanced carrier mobility under high illumination density. This study presents an easy processing route to fabricate high-performance self-powered DUV PDs based on MXene/AlGaN vdWHs for DUV communication.

Quasi van der Waals Epitaxy of Single Crystalline GaN on Amorphous SiO2/Si(100) for Monolithic Optoelectronic Integration.

The realization of high quality (0001) GaN on Si(100) is paramount importance for the monolithic integration of Si-based integrated circuits and GaN-enabled optoelectronic devices. Nevertheless, thorny issues including large thermal mismatch and distinct crystal symmetries typically bring about uncontrollable polycrystalline GaN formation with considerable surface roughness on standard Si(100). Here a breakthrough of high-quality single-crystalline GaN film on polycrystalline SiO2/Si(100) is presented by quasi van der Waals epitaxy and fabricate the monolithically integrated photonic chips. The in-plane orientation of epilayer is aligned throughout a slip and rotation of high density AlN nuclei due to weak interfacial forces, while the out-of-plane orientation of GaN can be guided by multi-step growth on transfer-free graphene. For the first time, the monolithic integration of light-emitting diode (LED) and photodetector (PD) devices are accomplished on CMOS-compatible SiO2/Si(100). Remarkably, the self-powered PD affords a rapid response below 250µs under adjacent LED radiation, demonstrating the responsivity and detectivity of 2.01×105 A/W and 4.64×1013Jones, respectively. This work breaks a bottleneck of synthesizing large area single-crystal GaN on Si(100), which is anticipated to motivate the disruptive developments in Si-integrated optoelectronic devices.

Eigen-function division multiplexed coherent optical transmission in time domain by using higher-order Hermite-Gaussian pulses.

We describe a new multiplexing technique and its application to demultiplexing in the time domain by using higher-order Hermite-Gaussian (HG) pulses, which are solutions of the Schrödinger equation. We call this technique eigen-function division multiplexing (EDM). This method enables us to further increase the total transmission capacity by superimposing many different HG pulses in the same time slot. This technique is different from a conventional optical time domain multiplexing (OTDM) technique using interleaving, where one pulse exists only in one time slot. The transmitted EDM HG pulses can be demultiplexed by adopting the time-domain orthogonality of the HG pulses (eigen-function orthogonality). The information carried by the mth-order HG pulse (HGm pulse) can be coherently detected by a photo detector, where photo-mixing with a phase-locked HGm pulse generated by a local oscillator can realize demultiplexing. The overlap integral with a different HG pulse becomes zero due to the time domain orthogonality. First, we show numerically that such a new EDM transmission scheme in the time domain is possible. We then show experimentally that we could successfully carry out an EDM HG coherent pulse transmission with four different HG pulses (HG0, HG1, HG2, and HG3), where we report a 400∼480 Gbit/s (10 Gbaud x 4 eigen-functions x 2 pol-mux.) 32∼64 QAM EDM transmission over 300∼450 km.

Surface Passivation to Enhance the Interfacial Pyro-Phototronic Effect for Self-Powered Photodetection Based on Perovskite Single Crystals.

The interfacial pyro-phototronic effect (IPPE) presents a novel approach for improving the performance of self-powered photodetectors (PDs) based on metal halide perovskites (MHPs). The interfacial contact conditions within the Schottky junctions are crucial in facilitating the IPPE phenomenon. However, the fabrication of an ideal Schottky junction utilizing MHPs is a challenging endeavor. In this study, we present a surface passivation method aimed at enhancing the performance of self-powered photodetectors based on inverted planar perovskite structures in micro- and nanoscale metal-halide perovskite SCs. Our findings demonstrate that the incorporation of a lead halide salt with a benzene ring moiety for surface passivation leads to a substantial improvement in photoresponses by means of the IPPE. Conversely, the inclusion of an alkane chain in the salt impedes the IPPE. The underlying mechanism can be elucidated through an examination of the band structure, particularly the work function (WF) modulated by surface passivation. Consequently, this alteration affects the band bending and the built-in field (VBi) at the interface. This strategy presents a feasible and effective method for producing interfacial pyroelectricity in MHPs, thus facilitating its potential application in practical contexts such as energy conversion and infrared sensors.

Resonant-cavity-enhanced 4H-SiC thin film MSM UV photodetectors on SiO2/Si substrates

Heterogeneous integration of 4H-SiC film with Si substrate can produce ultraviolet (UV) photodetectors (PD) with higher performance and easier integration with silicon CMOS circuits than homogenous epitaxy of 4H-SiC on SiC substrates. In this study, 1.2 µm thick high-quality single crystalline 4H-SiC thin films were successfully bonded with SiO2/Si (100) substrates using the Smart-Cut technique, achieving bubble-free bonding interfaces and 6.03 MPa bonding strength. UV PDs of metal–semiconductor–metal type with a resonant cavity structure were fabricated for the first time using the heterogenous film sample. The device exhibits a low dark current of 1.6 × 10−13 A in reverse bias of 20 V and a maximum specific detectivity of about 5.2 × 1012 Jones at 280 nm, which is significant for a device with a resonance-enhanced structure. These results demonstrate a promising approach for the fabrication of 4H-SiC devices with silicon CMOS circuits.

Electrically Tunable Multiple-Effects Synergistic and Boosted Photoelectric Performance in Te/WSe2 Mixed-Dimensional Heterojunction Phototransistors.

Mix-dimensional heterojunctions (MDHJs) photodetectors (PDs) built from bulk and 2D materials are the research focus to develop hetero-integrated and multifunctional optoelectronic sensor systems. However, it is still an open issue for achieving multiple effects synergistic characteristics to boost sensitivity and enrich the prospect in artificial bionic systems. Herein, electrically tunable Te/WSe2 MDHJs phototransistors are constructed, and an ultralow dark current below 0.1pA and a large on/off rectification ratio of 106 is achieved. Photoconductive, photovoltaic, and photo-thermoelectric conversions are simultaneously demonstrated by tuning the gate and bias. By these synergistic effects, responsivity and detectivity respectively reach 13.9 AW-1 and 1.37×1012 Jones with 400 times increment. The Te/WSe2 MDHJs PDs can function as artificial bionic visual systems due to the comparable response time to those of the human visual system and the presence of transient positive and negative response signals. This work offers an available strategy for intelligent optoelectronic devices with hetero-integration and multifunctions.