Waveguide-integrated Photodetector Research Articles

Two-dimensional molybdenum ditelluride waveguide-integrated near-infrared photodetector

Low-cost, small-sized, and easy integrated high-performance photodetectors for photonics are still the bottleneck of photonic integrated circuits applications and have attracted increasing attention. The tunable narrow bandgap of two-dimensional (2D) layered molybdenum ditelluride (MoTe2) from ∼0.83 to ∼1.1 eV makes it one of the ideal candidates for near-infrared (NIR) photodetectors. Herein, we demonstrate an excellent waveguide-integrated NIR photodetector by transferring mechanically exfoliated 2D MoTe2 onto a silicon nitride (Si3N4) waveguide. The photoconductive photodetector exhibits excellent responsivity (R), detectivity (D*), and external quantum efficiency at 1550 nm and 50 mV, which are 41.9 A W−1, 16.2 × 1010 Jones, and 3360%, respectively. These optoelectronic performances are 10.2 times higher than those of the free-space device, revealing that the photoresponse of photodetectors can be enhanced due to the presence of waveguide. Moreover, the photodetector also exhibits competitive performances over a broad wavelength range from 800 to 1000 nm with a high R of 15.4 A W−1 and a large D* of 59.6 × 109 Jones. Overall, these results provide an alternative and prospective strategy for high-performance on-chip broadband NIR photodetectors.

On-chip two-dimensional material-based waveguide-integrated photodetectors

In optical systems for communication, sensing, and imaging, integrating optoelectronic and electronic components on-chip to develop optoelectronic applications has become the focus of future research.

Silicon Waveguide-Integrated Carbon Nanotube Photodetector with Low Dark Current and 48 GHz Bandwidth.

Low-dimensional materials with excellent optoelectronic properties and complementary metal-oxide-semiconductor (CMOS) process compatibility have the potential to construct high-performance photodetectors used in a cost-efficient monolithic or hybrid integrated optical communication system. Carbon nanotubes (CNTs) have attracted a lot of attention due to special geometric structure and broad band response, high optical absorption coefficient, ps-level intrinsic light response, high carrier mobility and wafer-scaled production process. Here, we demonstrated a high-performance waveguide-integrated CNT photodetector with asymmetric palladium (Pd) and hafnium (Hf) contact electrodes. The ideal photodetector structure was realized via comparing with simulation and experimental results, where the optimized device achieved a high 3 dB bandwidth ∼48 GHz at 0 V, as well as a responsivity ∼73.62 mA/W and dark current ∼0.157 μA at -2 V bias voltage. This waveguide-integrated CNT photodetector with low dark current and high bandwidth is helpful for next-generation optical communication and high-speed optical interconnects.

A waveguide-integrated self-powered van der Waals heterostructure photodetector with high performance at the telecom wavelength.

Two-dimensional (2D) materials are attractive candidates for high-performance photodetectors due to their wide operating wavelength and potential to integrate with silicon photonics. However, due to their limited atomic thickness and short carrier lifetime, they suffer from high driving source-drain voltages, weak light-matter interactions and low carrier collection efficiency. Here, we present a high-performance van der Waals (vdWs) heterostructure-based photodetector integrated on a silicon nitride photonic platform combining p-type black phosphorus (BP) and n-type molybdenum disulfide (MoS2). Owing to the efficient carrier separation process and dark current suppression at the junction interface of the vdWs heterostructure, high photodetectivity and a fast response speed can be achieved. A fast response time (∼2.08/3.54 μs), high responsivity (11.26 mA W-1), and a high light on/off ratio (104) operating in the near-infrared telecom band are obtained at zero bias. Our research highlights the great potential of the high-efficiency waveguide-integrated vdWs heterojunction photodetector for integrated optoelectronic systems, such as high-data-rate interconnects operated at standardized telecom wavelengths.

Waveguide-integrated mid-IR photodetector and all-optical modulator based on interlayer excitons absorption in a WS2/HfS2 heterostructure

Abstract Novel 2D van der Waals semiconductors facilitate the formation of heterostructures and thus support bandgap engineering for atomically thin modern photonic applications. When these heterostructures form a type II band structure, interlayer excitons (ILEs) are formed as a result of the ultrafast charge transfer between the layers. Here, we present for the first time a waveguide-coupled, mid-IR photodetector and modulator based on the ILE absorption. The device consists of a heterostructure of a single layer of tungsten disulfide (WS2) and a few layers of hafnium disulfide (HfS2) integrated to a silicon waveguide on a sapphire substrate. We measure broadband mid-IR photodetection (3.8–5.5 µm) with responsivity in the order of tens of µA/W and with no significant effect on the waveguide’s transmission. Additionally, we demonstrate waveguide-integrated, mid-IR, all-optical modulation by controlling the ILE population with the interband transition of the individual layers of the heterostructure.

Self-powered waveguide-integrated photodetector based on a defect-engineered WSe2/graphene heterojunction

With integration capability and excellent photoelectronic, two-dimensional materials have attracted increasing interest in photonic circuits as waveguide-integrated photodetectors. Here, we report a waveguide-integrated self-powered photodetector based on a defect-engineered WSe2/graphene (WSe2/G) heterostructure. The WSe2 side of the heterostructure is locally irradiated by the Ga+ ion beam generating S-vacancies (WSe2-0.18/G). The boundary of the irradiated and non-irradiated regions (WSe2/G-WS2-0.18/G) construct a Schottky-metal junction with the photovoltaic property. This WSe2/G-WS2-0.18/G heterostructure exhibits a broad spectral photoresponse from 450 nm to 1550 nm at 0 bias with on/off ratio of 104. As a self-powered photodetector, WSe2/G-WS2-0.18/G heterostructure is integrated with a polymer waveguide. It directly reads optical signal (100 kHz @ 1550 nm) in the waveguide. Our work paves a novel avenue to prepare the self-powered 2D photodetector for integration with photonic circuits.

Waveguide-Integrated PdSe2 Photodetector over a Broad Infrared Wavelength Range.

Hybrid integration of van der Waals materials on a photonic platform enables diverse exploration of novel active functions and significant improvement in device performance for next-generation integrated photonic circuits, but developing waveguide-integrated photodetectors based on conventionally investigated transition metal dichalcogenide materials at the full optical telecommunication bands and mid-infrared range is still a challenge. Here, we integrate PdSe2 with silicon waveguide for on-chip photodetection with a high responsivity from 1260 to 1565 nm, a low noise-equivalent power of 4.0 pW·Hz-0.5, a 3-dB bandwidth of 1.5 GHz, and a measured data rate of 2.5 Gbit·s-1. The achieved PdSe2 photodetectors provide new insights to explore the integration of novel van der Waals materials with integrated photonic platforms and exhibit great potential for diverse applications over a broad infrared range of wavelengths, such as on-chip sensing and spectroscopy.

40 GHz waveguide-integrated two-dimensional palladium diselenide photodetectors

Hybrid integration of two-dimensional (2D) materials with photonic integrated circuits can enable additional functionality in planar waveguides based on excellent optical and electrical properties of 2D materials. 2D layered palladium diselenide (PdSe2) has a narrow energy bandgap and high carrier mobility, and its stability under normal laboratory environment conditions makes it of interest for use as high-performance infrared photodetectors. In this work, we propose and experimentally demonstrate a high-speed waveguide-integrated photodetector which uses chemical vapor deposition grown PdSe2 transferred onto a silicon waveguide. At 1550 nm wavelength, the photodetector can be operated without external bias with a responsivity of 0.57 mA/W and a responsivity of 20 mA/W at 6 V bias voltage. The detector had an impulse response full-width-half-maximum pulse width of about 11 ps, corresponding to a 3-dB bandwidth of 40 GHz.

Wafer-Scale Demonstration of Low-Loss (∼0.43 dB/cm), High-Bandwidth (>38 GHz), Silicon Photonics Platform Operating at the C-Band

The key advantage of silicon photonics comes from its potential for large scale integration, in a low-cost and scalable fashion. This has sustained the growth in the area despite disadvantages such as the lack of a monolithic light source, or the absence of a second order non-linear response (χ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(2)</sup> ). Thus far, the work in the field has focused on reporting individual devices from a single die, with excellent performances. Wafer-level results, an area which has not been addressed sufficiently, is a critical aspect of silicon photonics and will provide the community with information regarding scalability and variation, which will be the key differentiating advantage of silicon photonics over other photonic platforms. In this work, we report the development of a low-loss, high-bandwidth C-band silicon photonic platform on a 200 mm CMOS-compatible process line, demonstrating wafer-level performance in the process. Ultra-low waveguide propagation loss with median values as low as 0.43 dB/cm has been achieved. Silicon Mach-Zehnder and microring modulators with median bandwidth of 38.5 and 43 GHz respectively are presented. Finally, germanium waveguide-integrated photodetectors with median bandwidth of 43 GHz are reported. The results reported in this work are comparable to prior demonstrations concerning individual devices. The baseline designs on this platform presented in this work can be accessed commercially from CompoundTek.

Telecom-Band Waveguide-Integrated MoS2 Photodetector Assisted by Hot Electrons

Telecom-Band Waveguide-Integrated MoS₂ Photodetector Assisted by Hot Electrons

Integrated optoelectronics with two-dimensional materials

<p indent="0mm">As we enter the post-Moore era, heterogeneous optoelectronic integrated circuits (OEICs) are attracting significant attention as an alternative approach to scaling to smaller-sized transistors. Two-dimensional (2D) materials, offering a range of intriguing optoelectronic properties as semiconductors, semimetals, and insulators, provide great potential for developing next-generation heterogeneous OEICs. For instance, Fermi levels of 2D materials can be tuned by applying electrical voltages, while their atomically thin geometries are inherently suited for the fabrication of planar devices without suffering from lattice mismatch. Since the first graphene-on-silicon OEICs were demonstrated in 2011, 2D-material heterogeneous OEICs have significantly progressed. To date, researchers have a better understanding of the importance of interface states on the optical properties of chip-integrated 2D materials. Moreover, there has been impressive progress towards the use of 2D materials for waveguide-integrated lasers, modulators, and photodetectors. In this review, we summarize the history, status, and trend of integrated optoelectronics with 2D materials.

Plasmonic Photovoltaic Double-Graphene Detector Integrated Into TiN Slot Waveguides

Graphene has emerged as an ultrafast photonic material for on-chip photodetection. However, its atomic thickness limits its interaction with guided optical modes, which in turn weakens the photoresponse of waveguide-integrated graphene photodetectors. Nonetheless, it is possible to enhance the interaction of guided light with graphene by nanophotonic means. Herein, we propose a practical design of a plasmon-enhanced photovoltaic double-graphene detector that is integrated into 5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> m long titanium nitride slot waveguides. The use of double-graphene in this configuration yields a high responsivity of 2.18 A/W and more for a 0.5 V bias, across the telecom C-band and beyond. Moreover, the device operates at an ultra-high-speed beyond 100 GHz with an ultra-low noise equivalent power of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$&lt;\!35\,$</tex-math></inline-formula> pW/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sqrt{\text{Hz}}$</tex-math></inline-formula> . The reported features are highly promising and are expected to serve the needs of next-generation optical interconnects.

(Invited) Selective Epitaxy of Submicron Ge Wire Structures for Photodetectors and Optical Modulators in Si Photonics

A selective-area epitaxial growth of Ge on the submicron scale is studied using chemical vapor deposition (CVD) on Si in terms of the fabrication of integrated photonic devices operating at the optical communication wavelengths of around 1.55 μm. A mesa structure of Ge on the micron scale, having a vertical pin junction, is effective for fabricating a waveguide-integrated photodetector in the optical receiver. A 3-dB cutoff frequency is obtained up to approximately 50 GHz. For a higher frequency operation, a narrower structure of submicron-wide Ge wire, having a lateral pin junction, is required. Such a wire structure is also important for the application to an electro-absorption optical intensity modulator in the optical transmitter. Structural and optical properties are investigated for a submicron-wide Ge wire on Si selectively grown by CVD.

On-Chip Ge Photodetector Efficiency Enhancement by Local Laser-Induced Crystallization.

Metal-semiconductor-metal plasmonic nanostructures enable both on-chip efficient manipulation and ultrafast photodetection of strongly confined modes by enhancing local electrostatic and optical fields. The latter is achieved by making use of nanostructured thin-film germanium (Ge) plasmonic-waveguide photodetectors. While their sizes and locations can be accurately controlled during the nanofabrication, the detector efficiencies are significantly reduced due to deposited Ge amorphous nature. We demonstrate that the efficiency of waveguide-integrated Ge plasmonic photodetectors can be increased significantly (more than 2 orders of magnitude) by spatially controlled laser-induced Ge crystallization. We investigate both free-space and waveguide-integrated Ge photodetectors subjected to 800 nm laser treatment, monitoring the degree of crystallization with Raman spectroscopy, and demonstrate the efficiency enhancement by detecting the telecom radiation. The demonstrated local postprocessing technique can be utilized in various nanophotonic devices for efficient and ultrafast on-chip radiation monitoring and detection, offering significantly improved detector characteristics without jeopardizing the performance of other components.

Heterogeneously Integrated Graphene/Silicon/Halide Waveguide Photodetectors toward Chip-Scale Zero-Bias Long-Wave Infrared Spectroscopic Sensing.

Mid-infrared absorption spectroscopy plays an important role in molecule identification and quantification for widespread applications. Integrated photonics provides opportunities to perform spectroscopic sensing on-chip for the minimization of device size, cost, and power consumption. The integration of waveguides and photodetectors is an indispensable step toward the realization of these on-chip sensing systems. It is desired to extend the operating wavelengths of these on-chip sensing systems to the long-wave infrared (LWIR) range to utilize more molecular absorption fingerprints. However, the development of LWIR waveguide-integrated photodetectors faces challenges from both waveguide platforms due to the bottom cladding material absorption and photodetection technologies due to the low LWIR photon energy. Here, we demonstrate LWIR waveguide-integrated photodetectors through heterogeneous integration of graphene photodetectors and Si waveguides on CaF2 substrates. A high-yield transfer printing method is developed for flexibly integrating the waveguide and substrate materials to solve the bottom cladding material absorption issue. The fabricated Si-on-CaF2 waveguides show low losses in the broad LWIR wavelength range of 6.3-7.1 μm. The graphene photodetector achieves a broadband responsivity of ∼8 mA/W in these low-photon-energy LWIR wavelengths under zero-bias operation with the help of waveguide integration and plasmonic enhancement. We further integrate the graphene photodetector with a Si-on-CaF2 folded waveguide and demonstrate on-chip absorption sensing using toluene as an example. These results reveal the potential of our technology for the realization of chip-scale, low-cost, and low-power-consumption LWIR spectroscopic sensing systems.

Silicon-Waveguide-Integrated Carbon Nanotube Optoelectronic System on a Single Chip.

Monolithic optoelectronic integration based on a single material is a major pursuit in the fields of nanophotonics and nanoelectronics in order to meet the requirements of future fiber-optic telecommunication systems and on-chip optical interconnection systems. However, the incompatibility between silicon-based electronics and germanium or compound semiconductor-based photonics makes it very challenging to realize optoelectronic integration based on a single material. Here, the integration between silicon waveguides and a carbon nanotube (CNT) optoelectronic system is demonstrated. Waveguide-integrated photodetectors based on the CNT exhibit 12.5 mA/W photoresponsivity at 1530 nm, which presents an improvement of 97.6 times enhanced absorption efficiency compared to that without the waveguide. Multiplied output signals of cascading photodetectors are used to control the output of CNT-based logic gates, thereby demonstrating that the CNT-based optoelectronic integration system is compatible with silicon photonics. Our work indicates that carbon nanotubes have the potential for future integration between nanophotonics and nanoelectronics on a single chip.

A Transition Metal Dichalcogenide Tunnel FET-Based Waveguide-Integrated Photodetector Using Ge for Near-Infrared Detection

This paper presents a novel approach for the design of a waveguide-integrated photodetector that combines the advantage of atomically thin MoS2 tunnel FET (TFET) with infrared detection capability of Germanium (Ge). The Ge layer acting as a photogate for underlying TFET is optimized to have good optical confinement of guided mode traveling in the SOI rib waveguide. The low-power operation, effective gate control, low OFF-state current, and improved subthreshold characteristics of MoS2 TFET effectively enhance the detector performance for on-chip applications. Due to the high sensitivity of the TFET in the subthreshold region, an addition of the photovoltage to the gate voltage increases the band-to-band tunneling (BTBT) significantly, showing good photoresponse. The analytical and simulation results illustrate that at 1550 nm wavelength with an incident optical power intensity of 3 Wcm−2, a maximum responsivity of 2700 AW−1 and an ON–OFF ratio ( $I_{ON}/I_{OFF}$ ) of 107 is obtained. The device shows good spectral sensitivity with a low dark current.

Plasmonically Enhanced Graphene Photodetector Featuring 100 Gbit/s Data Reception, High Responsivity, and Compact Size

Graphene has shown great potentials for high-speed photodetection. Yet, the responsivities of graphene-based high-speed photodetectors are commonly limited by the weak effective absorption of atomically thin graphene. Here, we propose and experimentally demonstrate a plasmonically enhanced waveguide-integrated graphene photodetector. The device which combines a 6 micron long layer of graphene with field-enhancing nano-sized metallic structures, demonstrates a high external responsivity of 0.5 A/W and a fast photoresponse way beyond 110 GHz. The high efficiency and fast response of the device enables for the first time 100 Gbit/s PAM-2 and 100 Gbit/s PAM-4 data reception with a graphene based device. The results show the potential of graphene as a new technology for highest-speed communication applications.

High-performance flexible waveguide-integrated photodetectors

Mechanically flexible photonic devices are essential building blocks for novel bio-integrated optoelectronic systems, wearable sensors, and flexible consumer electronics. Here we describe the design and experimental demonstration of high-performance flexible semiconductor nanomembrane photodetectors integrated with single-mode chalcogenide glass waveguides. Through a combination of a waveguide-integrated architecture to enhance light–matter interactions and mechanical engineering of multilayer configurations to suppress strains, the detector devices exhibit record optical and mechanical performance. The devices feature a noise equivalent power as low as 0.02 pW·Hz1/2, a linear dynamic range exceeding 70 dB, and a 3-dB bandwidth of 1.4 GHz, all measured at 1530 nm wavelength. The devices withstand 1000 bending cycles at a submillimeter radius without degradation in their optoelectronic responses. These metrics represent significant improvements over state-of-the-art flexible photodetectors.

Chalcogenide glass-on-graphene photonics

Two-dimensional (2-D) materials are of tremendous interest to integrated photonics given their singular optical characteristics spanning light emission, modulation, saturable absorption, and nonlinear optics. To harness their optical properties, these atomically thin materials are usually attached onto prefabricated devices via a transfer process. In this paper, we present a new route for 2-D material integration with planar photonics. Central to this approach is the use of chalcogenide glass, a multifunctional material which can be directly deposited and patterned on a wide variety of 2-D materials and can simultaneously function as the light guiding medium, a gate dielectric, and a passivation layer for 2-D materials. Besides claiming improved fabrication yield and throughput compared to the traditional transfer process, our technique also enables unconventional multilayer device geometries optimally designed for enhancing light-matter interactions in the 2-D layers. Capitalizing on this facile integration method, we demonstrate a series of high-performance glass-on-graphene devices including ultra-broadband on-chip polarizers, energy-efficient thermo-optic switches, as well as graphene-based mid-infrared (mid-IR) waveguide-integrated photodetectors and modulators.