Waveguide Photodetector Research Articles

Graphene-on-plasmonic slot waveguide photodetector

Integrated silicon-based plasmonic photodetectors have attracted more and more attention recently, due to their potential applications in THz bandwidth. In this paper, by utilizing a simplified two-step lithography process, the photoconductive detector is fabricated with the core structure of plasmonic slot waveguide in two symmetric metallic slabs as microwave electrodes to integrate with mechanically exfoliated graphene. The 3-dB bandwidth of the graphene-on-plasmonic slot waveguide photodetector is exceeded 120 GHz under the theoretical calculation, and the measured bandwidth is still beyond 70 GHz due to the lack of larger-bandwidth equipment. High-speed data reception is demonstrated for 72 Gbit/s NRZ and 64 Gbit/s PAM-4 signals with a BER below 15% soft-decision FEC threshold. Based on the enhanced interactions of light and graphene induced by the subwavelength confinement from the plasmonic structure, the responsivity of 0.13 A/W is achieved under the condition of the 7-μm long detection zone and the 0.4-V bias voltage. With the advantages of ultra-compact, high-speed, large-bandwidth and compatible with the CMOS process, our photodetector has the potential to be used in high-speed optical interconnection, terahertz transmission and terahertz communication.

Design of Ge1-xSnx-on-Si waveguide photodetectors featuring high-speed high-sensitivity photodetection in the C- to U-bands.

We present the design of Ge1-xSnx-on-Si waveguide photodetectors for the applications in the C- to U-bands. The GeSn photodetectors have been studied in respect to responsivity, dark current, and bandwidth, with light butt- or evanescent-coupled from an Si waveguide. With the introduction of 4.5% Sn into Ge, the GeSn waveguide PD with evanescent-coupling exhibits high responsivity of 1.25 A/W and 3 dB bandwidth of 123.1 GHz at 1.675 µm. Further increasing the Sn composition cannot improve the absorption in the U-band significantly but does lead to poorer thermal stability and higher dark current. This work suggests a promising avenue for future high-speed high-responsivity photodetection in the C- to U-bands.

High‐Responsivity Mid‐Infrared Black Phosphorus Slow Light Waveguide Photodetector

AbstractBlack phosphorus (BP) offers unique opportunities for mid‐infrared (MIR) waveguide photodetectors due to its narrow direct bandgap and layered lattice structure. Further miniaturization of the photodetector will improve operation speed, signal‐to‐noise ratio, and internal quantum efficiency. However, it is challenging to maintain high responsivities in miniaturized BP waveguide photodetectors because of reduced light–matter interaction lengths. To address this issue, a method utilizing the slow light effect in photonic crystal waveguides (PhCWGs) is proposed and experimentally demonstrated. A shared‐BP photonic system is proposed and utilized to fairly and precisely characterize the slow light enhancement. Close to the band edge around 3.8 µm, the responsivity is enhanced by more than tenfold in the BP photodetector on a 10 µm long PhCWG as compared with the counterpart on a subwavelength grating waveguide. At a 0.5 V bias, the BP PhCWG photodetector achieves a 11.31 A W−1 responsivity and a 0.012 nW Hz−1/2 noise equivalent power. The trap‐induced photoconductive gain is validated as both the dominant photoresponse mechanism and the major limiting factor of the response speed. The BP slow light waveguide photodetector is envisioned to realize miniaturized high‐performance on‐chip MIR systems for widespread applications including environmental monitoring, industrial process control, and medical diagnostics.

Hybrid ultrathin-silicon/graphene waveguide photodetector with a loop mirror reflector.

Graphene has emerged as a promising solution for on-chip ultrafast photodetection for its advantages of easy integration, high mobility, adjustable chemical potential, and wide operation wavelength range. In order to realize high-performance photodetectors, it is very important to achieve efficient light absorption in the active region. In this work, a compact and high-speed hybrid silicon/graphene photodetector is proposed and demonstrated by utilizing an ultra-thin silicon photonic waveguide integrated with a loop mirror. With this design, the graphene absorption rate for the fundamental mode of TE polarization is improved by ∼5 times compared to that in the conventional hybrid silicon/graphene waveguide with hco=220 nm. One can achieve 80% light absorption ratio within the active-region length of only 20 µm for the present silicon/graphene waveguide photodetector at 1550 nm. For the fabricated device, the responsivity is about 25 mA/W under 0.3V bias voltage and the 3-dB bandwidth is about 17 GHz. It is expected to achieve very high bandwidth by introducing high-quality Al2O3 insulator layers and reducing the graphene channel length in the future.

High-Performance Germanium Waveguide Photodetectors on Silicon**Supported by the National Key Research and Development Program of China (Grant No. 2017YFA0206404), the National Natural Science Foundation of China (Grant Nos. 61435013, 61534005, 61534004, 61604146, and 61774143), the Key Research Program of Frontier Sciences, CAS (Grant No. QYZDY-SSW-JSC022), and the Beijing Education Commission Project (Grant No. SQKM201610005008).

Germanium waveguide photodetectors with 4 μm widths and various lengths are fabricated on silicon-on-insulator substrates by selective epitaxial growth. The dependence of the germanium layer length on the responsivity and bandwidth of the photodetectors is studied. The optimal length of the germanium layer to achieve high bandwidth is found to be approximately 8 μm. For the 4 × 8 μm2 photodetector, the dark current density is as low as 5 mA/cm2 at −1 V. At a bias of −1 V, the 1550 nm optical responsivity is as high as 0.82 A/W. Bandwidth as high as 29 GHz is obtained at −4 V. Clear opened eye diagrams at 50 Gbits/s are demonstrated at 1550 nm.

High-performance silicon\u2212graphene hybrid plasmonic waveguide photodetectors beyond 1.55\u2009\u03bcm

Graphene has attracted much attention for the realization of high-speed photodetection for silicon photonics over a wide wavelength range. However, the reported fast graphene photodetectors mainly operate in the 1.55 μm wavelength band. In this work, we propose and realize high-performance waveguide photodetectors based on bolometric/photoconductive effects by introducing an ultrathin wide silicon−graphene hybrid plasmonic waveguide, which enables efficient light absorption in graphene at 1.55 μm and beyond. When operating at 2 μm, the present photodetector has a responsivity of ~70 mA/W and a setup-limited 3 dB bandwidth of >20 GHz. When operating at 1.55 μm, the present photodetector also works very well with a broad 3 dB bandwidth of >40 GHz (setup-limited) and a high responsivity of ~0.4 A/W even with a low bias voltage of −0.3 V. This work paves the way for achieving high-responsivity and high-speed silicon–graphene waveguide photodetection in the near/mid-infrared ranges, which has applications in optical communications, nonlinear photonics, and on-chip sensing.

JFET Integration Using a Foundry SOI Photonics Platform

We explore the monolithic integration of conventional electronics with SOI photonics using the commercial silicon photonics foundry technology offered by A*STAR’s Institute of Microelectronics (IME). This process offers optical waveguide modulators and photodetectors, but was not intended to support transistors. We present the implementation of junction field effect transistors (JFETs) integrated with optical waveguides and photodetectors. A simple SPICE model is developed for the JFETs based on the available ion implant parameters, and the geometry feature size allowed by the technology’s layout rules. We have demonstrated the monolithic integration of photonics and electronics circuits. This work could be useful for application in waveguide sensors and optical telecommunications.

Foundry-Enabled High-Power Photodetectors for Microwave Photonics

We report on arrayed germanium-on-silicon waveguide photodetectors for high-power analog applications utilizing the AIM Photonics silicon foundry. Photodetector arrays with two, four, and eight elements reach output powers of -0.4 dBm, 10 dBm, and 14.3 dBm at 18 GHz, 12 GHz, and 5 GHz, respectively. The 4-photodiode array has an output third order intercept point (OIP3) above 20 dBm up to 12 GHz and shows a 5-dB improvement over a single photodiode. An integrated 20 GHz receiver based on a pair of balanced photodiodes and a Mach-Zehnder delay line interferometer is successfully demonstrated in an optical phase-modulated link.

Implementation of lateral Ge–on–Si heterojunction photodetectors via rapid melt growth and self-aligned microbonding for Si photonics

Heterogeneous integration of Ge on a Si lateral p–i–n junction by rapid melt-growth method and self-aligned microbonding is presented. A very thin Ge (100 nm) strip butt-coupled to a Si waveguide for implementing a waveguide photodetector is reported with a low dark current of 1 nA at −3 V bias. The measured 3 dB cut off frequency for the photodetectors is 30 GHz. The internal device responsivity is estimated to be 0.72 A W−1 at the reverse bias of 3 V.

Detecting ultra-fast and near-infrared pulses based on two-photon absorption in multiple quantum wells

A theoretical framework and the computational infrastructure for optical characterization of a waveguide (WG) photodetector (PD) are presented based on multiples quantum well (MQW) with a rib structure that is able to resolve a light pulse with a temporal width of 10[Formula: see text]fs. Such pulses are limited to the C-band of optical telecommunications. This pulse width is shorter than the temporal resolution limit of a commercial PD, due to the nonlinear phenomenon known as nondegenerate two-photon absorption (ND2PA). The results show the importance of the operating characteristics that affect carrier generation rate (CGR).

High‐Speed and High‐Responsivity Hybrid Silicon/Black‐Phosphorus Waveguide Photodetectors at 2 µm

AbstractSilicon photonics is being extended from the near‐infrared window of 1.3–1.5 µm for optical fiber communications to the mid‐infrared (mid‐IR) wavelength‐band of 2 µm or longer for satisfying the increasing demands in many applications. Mid‐IR waveguide photodetectors on silicon have attracted intensive attention as one of the indispensable elements for various photonic systems. However, when combining traditional semiconductor materials with silicon, there are some challenges due to lattice mismatch and thermal expansion mismatch. As an alternative, two‐dimensional (2D) materials provide a new and promising option for enabling active photonic devices on silicon. Here black‐phosphorus (BP) thin films with optimized medium thicknesses (≈40 nm) are introduced as the active material for light absorption and silicon/BP hybrid ridge waveguide photodetectors at 2 µm are demonstrated with a high responsivity of 306.7 mA W−1 at a low bias voltage of 0.4 V. The 3 dB‐bandwidth is up to 1.33 GHz and an experiment of a 4.0 Gbit s−1 data receiving is also demonstrated.

Defect Characterization of InAs/InGaAs Quantum Dot p-i-n Photodetector Grown on GaAs-on-V-Grooved-Si Substrate

The performance of semiconductor devices on silicon can be severely degraded by the presence of dislocations incurred during heteroepitaxial growth. Here, the physics of the defect mechanisms, characterization of epitaxial structures, and device properties of waveguide photodetectors (PDs) epitaxially grown on (001) Si are presented. A special GaAs-on-V-grooved-Si template was prepared by combining the aspect ratio trapping effects, superlattice cyclic, and strain-balancing layer stacks. A high quality of buffer structure was characterized by atomic force microscopy (AFM) and electron channeling contrast imaging (ECCI) results. An ultralow dark current density of 3.5 × 10–7A/cm2 at 300 K was measured under −1 V. That is 40× smaller than the best reported value of epitaxially grown InAs/GaAs quantum dot photodetector structure on GaP/Si substrate. Low frequency noise spectroscopy was used to characterize the generation and recombination related deep levels. A trap with an activation energy of 0.4 eV was id...

25 Gbps low-voltage hetero-structured silicon-germanium waveguide pin photodetectors for monolithic on-chip nanophotonic architectures

Near-infrared germanium (Ge) photodetectors monolithically integrated on top of silicon-on-insulator substrates are universally regarded as key enablers towards chip-scale nanophotonics, with applications ranging from sensing and health monitoring to object recognition and optical communications. In this work, we report on the high-data-rate performance pin waveguide photodetectors made of a lateral hetero-structured silicon-Ge-silicon (Si-Ge-Si) junction operating under low reverse bias at 1.55 μm. The pin photodetector integration scheme considerably eases device manufacturing and is fully compatible with complementary metal-oxide-semiconductor technology. In particular, the hetero-structured Si-Ge-Si photodetectors show efficiency-bandwidth products of ∼9 GHz at −1 V and ∼30 GHz at −3 V, with a leakage dark current as low as ∼150 nA, allowing superior signal detection of high-speed data traffic. A bit-error rate of 10−9 is achieved for conventional 10 Gbps, 20 Gbps, and 25 Gbps data rates, yielding optical power sensitivities of −13.85 dBm, −12.70 dBm, and −11.25 dBm, respectively. This demonstration opens up new horizons towards cost-effective Ge pin waveguide photodetectors that combine fast device operation at low voltages with standard semiconductor fabrication processes, as desired for reliable on-chip architectures in next-generation nanophotonics integrated circuits.

High-Speed Photodetectors for Microwave Photonics

This paper reviews high-power photodiodes, waveguide photodetectors, and integrated photodiode-antenna emitters with bandwidths up to 150 GHz. Results from heterogeneous III-V photodiodes on silicon and Ge-on-Si photodiode arrays for analog applications are presented.

Monolithic Waveguide-Based Linear Photodetector Array for Use as Ultracompact Spectrometer

We propose a monolithic spectral waveguide photodetector (SWGPD) concept based on a waveguide with a chemical gradient of the semiconductor alloy forming the absorbing medium that allows for spectrally resolved detection. The chemical gradient correlates the absorption of different wavelengths with the position on the waveguide. The generated charge carriers are collected by a linear array of photodetectors along the waveguide. As model system and proof of concept (Mg,Zn)O alloys in the wurtzite phase (Zn-rich) are considered that allow photon detection in the near ultraviolet spectral region. Our concept allows for high overall detection of (in principle) all photons coupled into the waveguide. The spectral range and resolution are determined by the chemical gradient, the spectral broadening of the absorption edges, and the optical confinement factor. At the same time, the photodetectors can provide high-time resolution, limited by the photodetector geometry.

Cost-effective 400-Gbps micro-intradyne coherent receiver using optical butt-coupling and FPCB wirings.

We present a cost-effective and bandwidth-enhanced 64-Gbaud micro-intradyne coherent receiver based on hybrid integration of InP waveguide-photodetector (WG-PD) and silica planar lightwave circuit (PLC). InP waveguide-photodetector (WG-PD) arrays are simply chip-to-chip bonded and optically butt-coupled to a silica-based dual-polarization optical hybrid chip. Multiple flexible printed circuit boards are adapted for electrical RF and DC wirings, which provide low-cost integration and good RF performance of the receiver. A 3-dB bandwidth of the fabricated coherent receiver is extended to ~36 GHz by optimization of bondwire inductance between the WG-PD array and the transimpedance amplifier (TIA), even when commercial TIAs with a typical bandwidth of ~29 GHz are used. Through optimization of the silica hybrid integrated coherent receiver, 64-Gbaud DP-16QAM signal transmission over 1050-km standard single-mode fiber is successfully demonstrated below a bit error rate of 2 × 10-3. This is the threshold for a soft decision-based forward error correction, at the optical signal to noise ratio of 23.8 dB.

GaSb MSM Photodetectors on Si Waveguides by Rapid Melt Growth Method

Metal-semiconductor-metal (MSM) photodetectors made of gallium antimonide (GaSb) on silicon waveguides by the rapid melt growth method are investigated. By controlling the thermodynamics of crystal regrowth and optimizing the process condition, single-crystal GaSb stripes are monolithically integrated on the silicon substrate. The MSM GaSb waveguide photodetector shows a responsivity of 0.57 A/W at 1550 nm.

Segmented waveguide photodetector with 90% quantum efficiency.

We demonstrate a novel InGaAsP/InP segmented waveguide photodetector based on directional couplers. By matching the imaginary parts of the propagation constants of the even and odd modes, we designed a photodetector with 6 elements, each with an absorber volume of only 19 μm3 and a bandwidth of 15 GHz, that has an internal quantum efficiency (QE) of 90% at 1550 nm wavelength corresponding to 1.13 A/W.

Forward-biased nanophotonic detector for ultralow-energy dissipation receiver

Generally, reverse-biased photodetectors (PDs) are used for high-speed optical receivers. The forward voltage region is only utilized in solar-cells, and this photovoltaic operation would not be concurrently obtained with high efficiency and high speed operation. Here we report that photonic-crystal waveguide PDs enable forward-biased high-speed operation at 40 Gbit/s with keeping high responsivity (0.88 A/W). Within our knowledge, this is the first demonstration of the forward-biased PDs with high responsivity. This achievement is attributed to the ultracompactness of our PD and the strong light confinement within the absorber and depleted regions, thereby enabling efficient photo-carrier generation and fast extraction. This result indicates that it is possible to construct a high-speed and ultracompact photo-receiver without an electrical amplifier nor an external bias circuit. Since there is no electrical energy required, our estimation shows that the consumption energy is just the optical energy of the injected signal pulse which is about 1 fJ/bit. Hence, it will lead to an ultimately efficient and highly integrable optical-to-electrical converter in a chip, which will be a key ingredient for dense nanophotonic communication and processors.

Fast MoTe2 Waveguide Photodetector with High Sensitivity at Telecommunication Wavelengths

Two-dimensional (2D) materials integrated with planar photonic elements enable a new class of electro-optical components and hold much promise for a novel 2D material integrated circuit technology. Here, we present a few-layer MoTe2 waveguide photodetector that is operable across the entire O-band of the near-infrared optical telecommunication spectral range. The device is realized in a two-terminal in-plane electrode configuration without applying external gating. It features a competitive photoresponsivity of 23 mA/W as well as a low dark current, both of which lead to a highly sensitive photodetection with a large dynamic range. Moreover, the design of the photodetector exhibits a fast photoresponse with a bandwidth approaching 1 GHz, outperforming prior TMDC-based photodetectors. Optical data experiments proved the operation of our device at data rates of 1 Gbit/s, revealing the applicability of integrating 2D materials for practical optical data communication applications.