Photodetectors Research Articles

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.

Fabrication of ZnSnO3 single crystal films on sapphire substrates by pulsed laser deposition for solar-blind photodetectors

ZnSnO3 single crystal films were prepared on c-plane sapphire substrates using pulsed laser deposition and post-annealing methods. For the as-grown sample at 700 °C, post-annealing at 700 °C resulted in a significant improvement in the crystalline quality of the single crystal films, while post-annealing at 800 °C led to decomposition of ZnSnO3. Compared with the amorphous and mixed crystal ZnSnO3-based photodetectors (PDs), the single crystal ZnSnO3-based PD has a better light-to-dark current ratio (1.32 × 106) and higher responsivity (8.71 A/W) at 5 V under 254-nm UV (1.1 mW/cm2) illumination. Such a good performance serves as resounding validation of the remarkable potential of ZnSnO3 epitaxial films in the context of solar-blind PDs.

Silica-Based Hybrid-Integrated Receiver Optical Subassembly for 400 Gbps Ethernet

A silica-based hybrid-integrated receiver optical subassembly (ROSA) for 400 Gbps Ethernet (400GbE) is demonstrated, which consists of an 8-channel silica-based arrayed waveguide grating (AWG), two 4-channel InP-based surface-illuminated photodetector (PD) arrays, two 4-channel transimpedance amplifier (TIA) arrays, and a high-frequency flexible printed circuit (FPC). All lanes of the ROSA exhibit responsivities of over 0.539 A/W, 3-dB bandwidths of greater than 30.86 GHz, and receiver sensitivities of less than −11.7 dBm. The ROSA has achieved a transmission rate of 8 × 50 Gbps for data center interconnect.

Miniaturized computational spectrometer based on two-photon absorption

On-chip spectrometers hold significant promise in the development of laboratory-on-a-chip applications. However, the spectrometers usually require extra on-chip or off-chip photodetectors (PDs) to sense optical signals, resulting in increased footprints and costs. In this paper, we address this issue by proposing a fully on-chip spectrometer based on two-photon absorption (TPA) in a simple micro-ring resonator (MRR) configuration. While TPA is a commonly undesired phenomenon in conventional silicon devices due to its attached absorption losses and nonlinearity, we exploit it as a powerful and efficient tool for encoding spectral information, instead of using additional PDs. The input spectrum can be reconstructed from the sensed TPA current. Our proposed spectrometer achieves a bandwidth of 10 nm with a resolution of 0.4 nm while occupying a small footprint of only 16×16µm2, and the bandwidth can be further improved through several cascaded MRRs. This advancement could enable forward fully integrated and miniaturized spectrometers with low cost, which holds far-reaching applications in in situ biochemical analysis, remote sensing, and intelligent healthcare.

Achieving Low Cost and High Performance Flexible CsPbIBr2 Perovskite Photodetectors Arrays with Imaging System via Dual Interfacial Optimization and Structural Design

AbstractAll‐inorganic metal halide perovskites are competitive candidate as next‐generation flexible photodetectors (PDs) materials due to the remarkable photoelectric properties, enhanced heat stability, and mechanical flexibility. However, constructing low‐cost flexible perovskites PDs with high photodetection performance, good operation stability and mechanical robustness, and manufacturing corresponding flexible PDs array have been a challenge. Herein, the PbCl2 and Zinc(II) Dibenzyldithiocarbamate (Zn(DBDTC)2) are employed to modify bottom and top interface of CsPbIBr2 perovskite layer, respectively, to passivate surface trap state, enhance hydrophobicity and resist phase segregation, and improve interface contact. Consequently, the self‐powered champion PDs with low‐cost Bi2Te3 electrode reach a responsivity of 0.38 A W−1 and a maximum detectivity of 3.44 × 1013 Jones at 570 nm, and maintain the outstanding long‐term and operational stability without additional encapsulation. Meanwhile, the HTL‐free flexible PDs based on low‐temperature CsPbIBr2 perovskite layer exhibit impressive photodetection performance and mechanical robustness in bending test. More importantly, the flexible PDs array (5 × 5 pixels) and corresponding imaging system are fabricated with uniform and clear imaging results under flatting and bending state. This research is of great significance for the application of stable and high‐performance inorganic perovskites PDs and flexible array imaging systems.

Tuning the Optoelectronic Properties of Pulsed Laser Deposited “3D”‐MoS2 Films via the Degree of Vertical Alignment of Their Constituting Layers

AbstractPulsed‐laser‐deposition (PLD) is used to deposit MoS2 thin films at substrate temperatures (Td) ranging from 25 to 700 °C. A Td = 500 °C is identified as the optimal temperature that yields MoS2 films consisting of highly‐crystallized 2H‐MoS2 phase with a strong (002) preferential orientation, a direct optical bandgap (Eg) of ∼1.4 eV and a strong photoresponse of ∼1500%. Raman spectroscopy revealed that the degree of vertical alignment of MoS2 layers in the films also reaches its maximum at Td = 500 °C. High‐resolution‐transmission‐electron‐microscopy has provided a clear‐cut evidence that the PLD‐MoS2 films predominantly consist of vertically aligned MoS2 layers over all the film thickness of ∼90 nm, enabling those “3D” films to behave as a direct‐bandgap “2D‐MoS2” with exceptional optoelectronic properties. Indeed, at Td = 500 °C, the PLD‐MoS2 based photodetectors (PDs) devices are shown to exhibit the highest responsivity (R) and detectivity (D*) values (125 mA W−1 and 9.2 × 109 Jones, respectively) ever reported for large area (≥ 1 cm2) MoS2‐based PDs operating at a voltage as low as 1 V. For the first time, a constant‐plus‐linear relationship between Eg, R, and D* of the PDs and the degree of vertical alignment of the MoS2 layers is established. Such a correlation is fundamental for the controlled growth of PLD‐MoS2 films and the tuning of their properties in view of their integration with standard large‐scale‐integration processing.

Vacuum-ultraviolet (λ < 200 nm) photodetector array

The vacuum-ultraviolet (VUV, 10–200 nm) imaging photodetector (PD) based on the wide bandgap semiconductor (WBGS) can realize a more detailed observation of solar storms than the silicon ones. Here, an 8 × 8 VUV PD array based on the semiconductor AlN with an ultra-wide bandgap is presented, exhibiting the shortest cutoff wavelength (203 nm) reported so far. The PD array with a Pt/AlN/SiC/Ti/Au photovoltaic structure shows an excellent selective response to VUV light, an extremely low dark current density of 2.85 × 10–11 A·cm−2@ -2 V, a responsivity of 0.054 A·W−1@ 0 V and an ultra-short rise time of 13 ns. Also, the clear boundaries and an obvious contrast between light and dark of the VUV image displayed in the imaging measurement indicate the good imaging ability of this PD array, which can be used for the imaging application with high signal-to-noise ratio and high response speed. These results provide rich experience for the development of VUV imaging PDs based on WBGSs both in their fabrication and the practical applications in VUV detection.

Unveiling the contribution of piezoelectric and ferroelectric effect to inorganic halide perovskites photodetectors

Compression and tensile strain based on piezo-phototronic effect represent a valid method for modulating the photocurrent of photodetectors. However, the underlying mechanism responsible for the asymmetric increase/decrease of photocurrent under identical compressive/tensile stresses remains unclear. Herein, a PVDF/CsPbBr3 composite fiber incorporating orthorhombic CsPbBr3 (a piezoelectric phase) is fabricated through room-temperature electrospinning. Subsequently, flexible photodetectors (PDs) based on PVDF/CsPbBr3 are constructed to explore the impact of strain on photocurrent. The results reveal a 103% increase in photocurrent under a strain of −0.09% (compressive strain), significantly exceeding the 38% decrease observed under a strain of 0.09% (tensile strain). Furthermore, the piezoelectric and ferroelectric properties of the orthorhombic CsPbBr3 are computed using density functional theory (DFT), confirming that the asymmetric modulation of photocurrent stems from the nature of the piezoelectric effect and ferroelectric effect. Additionally, the ferroelectric effect exerts a more pronounced influence on the photocurrent, which is 2.2 times greater than the piezoelectric effect. This work provides compelling evidence for the piezoelectric and ferroelectric effects of inorganic halide perovskites, underscoring the substantial potential of these effects in optoelectronic devices.