Waveguide Photodetector Research Articles

High-responsivity graphene-on-silicon slot waveguide photodetectors

We demonstrated strong optical absorption in a graphene integrated silicon slot waveguide. Due to the increase in light intensity and decrease of optical mode confinement in the silicon slot, the graphene experienced an increased interaction to the in-plane light. A waveguide absorption of 0.935 dB μm(-1) was measured at 1.55 μm wavelengths. Based on the graphene-on-silicon slot waveguide, a compact and high-responsivity photodetector was demonstrated. Benefited from the lack of efficient electron cooling in the suspended graphene and the intensity enhancement effect in the nano slot, a maximum responsivity of 0.273 A W(-1) was achieved in the telecommunication band.

An Array Consisting of 10 High-Speed Side-Illuminated Evanescently Coupled Waveguide Photodetectors Each with a Bandwidth of 20 GHz**Supported by the High-Tech Research and Development Program of China under Grant Nos 2013AA031401, 2015AA016902 and 2015AA016904, the National Natural Science Foundation of China under Grant Nos 61176053, 61274069 and 61435002, and the National Basic Research Program of China under Grant No 2012CB933503.

We design and fabricate a parallel system with 10 high speed side-illuminated evanescently coupled waveguide photodetectors (ECPDs). The 10 ECPDs exhibit a uniform 3 dB bandwidth of 20 GHz and low dark current of about 1 nA at 2 V reverse bias. The 10 ECPDs also exhibit uniform photo-responsivity of about 0.23 A/W with an active region of 5 × 25 μm2. The photodetector array has a total bandwidth of more than 200 GHz and can be integrated with other optoelectronic devices.

An all-solid-state, WDM silicon photonic digital link for chip-to-chip communications.

We describe a multiwavelength hybrid-integrated solid-state link on a 3 µm silicon-on-insulator (SOI) nanophotonic platform. The link spans three chips and employs germanium-silicon electroabsorption waveguide modulators, silicon transport waveguides, echelle gratings for multiplexing and demultiplexing, and pure germanium waveguide photo-detectors. The 8λ WDM Tx and Rx components are interconnected via a routing "bridge" chip using edge-coupled optical proximity communication. The packaged, retimed digital WDM link is demonstrated at 10 Gb/s and 10(-12) BER, with three wavelength channels consuming an on-chip power below 1.5 pJ/bit, excluding the external laser power.

Theoretical investigation of tensile strained GeSn waveguide with Si₃N₄ liner stressor for mid-infrared detector and modulator applications.

We theoretically investigate a tensile strained GeSn waveguide integrated with Si₃N₄ liner stressor for the applications in mid-infrared (MIR) detector and modulator. A substantial tensile strain is induced in a 1 × 1 μm² GeSn waveguide by the expansion of 500 nm Si₃N₄ liner stressor and the contour plots of strain are simulated by the finite element simulation. Under the tensile strain, the direct bandgap E(G,Γ) of GeSn is significantly reduced by lowering the Γ conduction valley in energy and lifting of degeneracy of valence bands. Absorption coefficients of tensile strained GeSn waveguides with different Sn compositions are calculated. As the Si₃N₄ liner stressor expands by 1%, the cut-off wavelengths of tensile strained Ge(0.97)Sn(0.03), Ge(0.95)Sn(0.05), and Ge(0.90)Sn(0.10) waveguide photodetectors are extended to 2.32, 2.69, and 4.06 μm, respectively. Tensile strained Ge(0.90)Sn(0.10) waveguide electro-absorption modulator based on Franz-Keldysh (FK) effect is demonstrated in theory. External electric field dependence of cut-off wavelength and propagation loss of tensile strained Ge(0.90)Sn(0.10) waveguide is observed, due to the FK effect.

High performance silicon waveguide germanium photodetector

High-performance Ge-on-SOI p–i–n waveguide photodetectors with different sizes were fabricated. The performances, in terms of dark-current, photo current responsivity and 3-dB bandwidth, were well studied. A responsivity of 0.842 A/W at 1550 nm and dark current of 70 nA was measured from this detector at -1 V. The detector with a size of 4 μm×10 μm demonstrated an optical band width of 19 GHz at -5 V for 1550 nm. Both the experimental results and the finite-difference time domain simulation show that, when the device size is above a certain threshold, the absorption is not sensitively dependent on such designing parameters as the width and length of the photodetector.

Wavelength-size hybrid Si-VO(2) waveguide electroabsorption optical switches and photodetectors.

Ultra-compact waveguide electroabsorption optical switches and photodetectors with micron- and sub-micron lengths and compatible with silicon (Si) waveguides are demonstrated using the insulator-metal phase transition of vanadium dioxide (VO(2)). A 1 μm long hybrid Si-VO(2) device is shown to achieve a high extinction ratio of 12 dB and a competitive insertion loss of 5 dB over a broad bandwidth of 100 nm near λ = 1550 nm. The device, operated as a photodetector, can measure optical powers less than 1 μW with a responsivity in excess of 10 A/W. With volumes that are about 100 to 1000 times smaller than today's active Si photonic components, the hybrid Si-VO(2) devices show the feasibility of integrating transition metal oxides on Si photonic platforms for nanoscale electro-optic elements.

GeSn p-i-n waveguide photodetectors on silicon substrates

We report an investigation on GeSn p-i-n waveguide photodetectors grown on a Ge-buffered Si wafer. In comparison with a reference Ge detector, the GeSn detector shows an enhanced responsivity in the measured energy range, mainly attributed to the smaller bandgap caused by Sn-alloying. Analysis of the quantum efficiency indicates that increasing the Sn content in the active layers can significantly shorten the required device length to achieve the maximum efficiency. The present investigation demonstrates the planar photodetectors desired for monolithic integration with electronic devices.

High-Responsivity Low-Voltage 28-Gb/s Ge p-i-n Photodetector With Silicon Contacts

We report a high-performance germanium waveguide photodetectors (WPDs) without doping in germanium or direct metal contacts on germanium, grown on and contacted through a silicon p-i-n diode structure. Wafer-scale measurements demonstrate high responsivities larger than 1.0 A/W across the C-band and low dark current of ~3 nA at -1 V and ~8 nA at -2 V. Owing to its small dimensions, the Ge WPD exhibits a high optoelectrical 3-dB bandwidth of 20 and 27 GHz at low-bias voltages of -1 and -2 V, respectively, which are sufficient for operation at 28 Gb/s. The reduced processing complexity at the tungsten contact plug module combined with the high responsivity makes these Ge WPD devices particularly attractive for emerging low-cost CMOS-Si photonics transceivers.

High-Speed InGaAs Photodetectors by Selective-Area MOCVD Toward Optoelectronic Integrated Circuits

We report selective-area growth of high-crystalline-quality InGaAs-based photodetectors with optimized InP/GaAs buffers on patterned (100)-oriented silicon-on-insulator (SOI) substrates by metal-organic chemical vapor deposition. The composite GaAs and InP buffer was grown using a two-temperature method. The island morphology of the low-temperature GaAs nucleation layer inside the growth well of the SOI substrate was optimized. A medium temperature GaAs layer was inserted prior to the typical high-temperature GaAs to further decrease the dislocation densities and antiphase boundaries. Both normal-incidence photodetectors and butt-coupled waveguide photodetectors were fabricated on the same substrate and showed a low dark current and high-speed performance. This result demonstrates a good potential of integrating photonic and electronic devices on the same Si substrate by direct epitaxial growth.

Si⁺-implanted Si-wire waveguide photodetectors for the mid-infrared.

CMOS-compatible Si⁺-implanted Si-waveguide p-i-n photodetectors operating at room temperature and at mid-infrared wavelengths from 2.2 to 2.3 µm are demonstrated. Responsivities of 9.9 ± 2.0 mA/W are measured at a 5 V reverse bias with an estimated internal quantum efficiency of 2.7 - 4.5%. The dark current is found to vary from a few microamps down to less than a nanoamp after a post-implantation annealing of 350°C. The measured photocurrent dependence on input power shows a linear correspondence over more than three decades, and the frequency response of a 250 µm-length p-i-n device is measured to be ~1.7 GHz for a wavelength of λ = 2.2 µm, thus potentially opening up new communication bands for photonic integrated circuits.

30-Gb/s Optical Link Combining Heterogeneously Integrated III–V/Si Photonics With 32-nm CMOS Circuits

We present a silicon photonics optical link utilizing heterogeneously integrated photonic devices driven by low-power advanced 32-nm CMOS integrated circuits. The photonic components include a quantum-confined Stark effect electroabsorption modulator and an edge-coupled waveguide photodetector, both made of III-V material wafer bonded on silicon-on-insulator wafers. The photonic devices are wire bonded to the CMOS chips and mounted on a custom PCB card for testing. We demonstrate an error-free operation at data rates up to 30 Gb/s and transmission over 10 km at 25 Gb/s with no measured sensitivity penalty and a timing margin penalty of 0.2 UI.

Investigation of Random Telegraph Noise in the Dark Current of Germanium Waveguide Photodetector

Dark current variations in the germanium waveguide photodetector were investigated. Contributing to the time dependent dark current variations, random telegraph noise (RTN) was observed and studied for the first time. The RTN at different reverse biases and temperatures were measured. By analyzing the capture and emission time constants, the single trap that was responsible for RTN was estimated to be around 18 nm from the interface between the N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">++</sup> and the intrinsic region. The trap energy levels at different reverse biases were also extracted and the trapping and detrapping dynamics were explained. Through this procedure, the single trap that may lead to device failure can be detected and characterized without destroying the well-fabricated devices.

Silicon Photonic Transceiver Circuits With Microring Resonator Bias-Based Wavelength Stabilization in 65 nm CMOS

Photonic interconnects are a promising technology to meet the bandwidth demands of next-generation high-performance computing systems. This paper presents silicon photonic transceiver circuits for a microring resonator-based optical interconnect architecture in a 1 V standard 65 nm CMOS technology. The transmitter circuits incorporate high-swing ( 2V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> and 4V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> ) drivers with nonlinear pre-emphasis and automatic bias-based tuning for resonance wavelength stabilization. An optical forwarded-clock adaptive inverter-based transimpedance amplifier (TIA) receiver trades off power for varying link budgets by employing an on-die eye monitor and scaling the TIA supply for the required sensitivity. At 5 Gb/s operation, the 4V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> transmitter achieves 12.7 dB extinction ratio with 4.04 mW power consumption, excluding laser power, when driving wire-bonded modulators designed in a 130 nm SOI process, while a 0.28 nm tuning range is obtained at 6.8 μW/GHz efficiency with the bias-based tuning scheme implemented with the 2V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> transmitter. When tested with a wire-bonded 150 fF p-i-n photodetector, the receiver achieves -9 dBm sensitivity at a BER=10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> and consumes 2.2 mW at 8 Gb/s. Testing with an on-die test structure emulating a low-capacitance waveguide photodetector yields 17 μA <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> sensitivity at 10 Gb/s and more than 40% power reduction with higher input current levels.

Reliability characterization of silicon-based germanium waveguide photodetectors

A silicon-based germanium waveguide photodetector was demonstrated and its reliability related items were investigated. For different reverse biases, the slopes of the dark current increment versus stress time curves were first found to be the same, which made the lifetime extrapolation feasible. The lifetime of the photodetector under different bias was predicted by using a simple extrapolation method. In order to maintain the 10-year lifetime of the photodetector, the bias voltage should be kept lower than − 3 V . For the first time, the degradation mechanism under stress biases was analyzed in detail by the reaction-diffusion (RD) model. The experimental results agree well with the theoretical derivation based on RD model.

Monolithically integrated, ultrahigh-frequency cavity nano-optoelectromechanical system with on-chip germanium waveguide photodetector.

We report the first demonstration of a cavity optoelectromechanical system integrated monolithically with a high-efficiency germanium photodetector on a CMOS-compatible platform. Mechanical resonances are recorded from 0.177 to 2.003GHz with quality factor up to 4810. These monolithically integrated devices have paved the way for a new category of on-chip optoelectronic components that take the advantage of the resonant properties of the mechanical element and enables new applications such as ultracompact microwave oscillators, optomechanical sensors, and phase shifters.

Metal-semiconductor-metal ion-implanted Si waveguide photodetectors for C-band operation.

Metal-semiconductor-metal Si waveguide photodetectors are demonstrated with responsivities of greater than 0.5 A/W at a wavelength of 1550 nm for a device length of 1mm. Sub-bandgap absorption in the Si waveguide is achieved by creating divacancy lattice defects via Si(+) ion implantation. The modal absorption coefficient of the ion-implanted Si waveguide is measured to be ≈ 185 dB/cm, resulting in a detector responsivity of ≈ 0.51 A/W at a 50 V bias. The frequency response of a typical 1mm-length detector is measured to be 2.6 GHz, with simulations showing that a frequency response of 9.8 GHz is achievable with an optimized contact configuration and bias voltage of 15 V. Due to the ease with which these devices can be fabricated, and their potential for high performance, these detectors are suitable for various applications in Si-based photonic integrated circuits.

Optimization of spot-size converter for low polarization dependent loss of waveguide photodetector

We present an optimization of spot-size converter (SSC) of waveguide photodetector (PD) for small polarization dependent loss (PDL). Beam-propagation method simulation gives responsivity for each polarization and SSC structure. From the calculated responsivity data, optimum structure of SSC is determined that can be implemented with a sufficient process tolerance. We confirm the optimization by measuring PDL of waveguide PD designed according to the structure obtained through the simulation.

Error-Free Operation of an All-Silicon Waveguide Photodiode at 1.9 $\mu{\rm m}$

Error-free detection at 1 Gb/s is experimentally demonstrated with an all-Si ion-implanted p-i-n waveguide photodetector operating at 1.9 μm, and the receiver sensitivity is measured. The responsivity of the device is compared between operation at 1.9 and 1.55 μm, and a 5 dB drop in responsivity is observed. Simulations show that nearly 25% of this drop is due to the lower confinement of the 1.9 μm wavelength. Theoretical analysis of the waveguide structure optimized for operation at 1.9 μm shows that data rates of 10 Gb/s are possible with a loss in sensitivity of only 3 dB compared with operation at 1.55 μm.

Microdisk enhanced photodetector based on Ge self-assembled quantum dots on silicon-on-insulator

By embedding Ge self-assembled quantum dots (QDs) in microdisk cavity, resonant-cavity-enhanced waveguide photodetector (PD) with ultra-low dark current and high responsivity is experimentally demonstrated around 1.55μm wavelength. Ge QDs are grown on silicon-on-insulator substrate by solid-source molecular beam epitaxy. Microdisk is used to enhance the absorption efficiency of Ge QDs, and a vertical PIN diode is integrated with the microdisk to extract photo-generated current. The dark current density of our PD is as low as 0.97mA/cm2 under −10V bias. At resonant wavelength of 1541.15nm, enhanced peak responsivity of 2.13mA/W is obtained. The wavelength selectivity of the microdisk PD also makes it preferable for wavelength-division multiplexing optical receiver.

Design and fabrication of a high-performance evanescently coupled waveguide photodetector

In this paper, we present the design, fabrication, and measurement of an evanescently coupled waveguide photodetector operating at 1.55 μm, which mainly comprises a diluted waveguide, a single-mode rib waveguide and a p—i—n photodiode with an extended optical matching layer. The optical characteristics of this structure are studied by using a three-dimensional finite-difference time-domain (3D FDTD) method. The photodetector exhibits a high 3-dB bandwidth of more than 35 GHz and a responsivity of 0.291 A/W at 1550 nm directly coupled with a cleaved fiber. Moreover, a linear response of more than 72-mW optical power is achieved, where a photocurrent of more than 21 mA is obtained at a reverse bias voltage of 3 V.