Ge Waveguide Photodetectors Research Articles

75 GHz germanium waveguide photodetector with 64 Gbps data rates utilizing an inductive-gain-peaking technique

High-performance germanium (Ge) waveguide photodetectors are designed and fabricated utilizing the inductive-gain-peaking technique. With the appropriate integrated inductors, the 3-dB bandwidth of photodetectors is significantly improved owing to the inductive-gain-peaking effect without any compromises to the dark current and optical responsivity. Measured 3-dB bandwidth up to 75 GHz is realized and clear open eye diagrams at 64 Gbps are observed. In this work, the relationship between the frequency response and large signal transmission characteristics on the integrated inductors of Ge waveguide photodetectors is investigated, which indicates the high-speed performance of photodetectors using the inductive-gain-peaking technique.

Fabrication and characteristics of high performance SOI-based Ge PIN waveguide photodetector

Silicon-based photonics has aroused an increasing interest in the recent year, mainly for optical telecommunications or optical interconnects in microelectronic circuits. The waveguide photodetector is one of the building blocks needed for the implementation of fast silicon photonics integrated circuits. The main considerations for designing such a device are the bandwidth, the power consumption and the responsivity. Germanium is now considered as an ideal candidate for fully integrated receivers based on silicon-on-insulator (SOI) substrates and complementary metal oxide semiconductor (CMOS)-like process because of its large optical absorption coefficient at the wavelength for optical communication. Therefore, the study of high speed and high responsivity Ge waveguide photodetectors is necessary. In this paper, high concentration phosphor doped SOI substrate is achieved by using solid-state source diffusion at first. Secondly, the high quality epitaxial germanium (Ge) is grown on phosphor doped SOI substrate by using low temperature Ge buffer layer technique based on the UHV/CVD system. The surface profile, crystal quality and strain of epitaxial Ge film are characterized by using atomic force microscopy, X-ray diffraction (XRD), and Raman scattering spectrum. The results show that the Ge film has a smooth surface of 1.12 nm roughness and about 0.2% tensile strain, which is verified by XRD characterization result. Thirdly, ptype Ge region is formed by BF2+ implantation, and rapid thermal annealing to repair the implantation damages and activate impurity. Finally, the highperformance Ge PIN waveguide photodetectors with different sizes are fabricated by standard COMS technology. Moreover, the device performances, in terms of dark current versus voltage characteristics, photocurrent responsivity and 3 dB bandwidth, are well studied. The results show that the detector with a size of 4 m20 m demonstrates a dark current density of 75 mA/cm2 at -1 V and a photocurrent responsivity of 0.58 A/W for 1.55 m optical wavelength. In addition, an optical band width of 5.3 GHz at -2 V for 1.55 m is also demonstrated, which is far below theortical value of about 40 GHz. This can mainly be attributed to two aspects. On the one hand, Ge PIN structure contains low temperature Ge buffer layer, which has highdensity dislocation because of large lattice mismatch between Si and Ge. Those dislocations or defects can trap and release the photo-generated carrier, which increases the transit time. On the other hand, the contact characteristics of Al with n+-Si and p+-Ge are not very good, leading to a large contact resistance and RC delay. Through improving the above two aspects, the performance of Ge PIN waveguide photodetector will be further enhanced.

Misalignment-Tolerant Spot-Size Converter for Efficient Coupling Between Single-Mode Fibers and Integrated Optical Receivers

We design a spot-size converter (SSC) on silicon-on-insulator (SOI) platform to interface an integrated optical receiver (IOR) with a single-mode fiber (SMF). Because of the capability of coupling higher order modes by the proposed device, the tolerance of fiber-to-waveguide misalignment is much improved. The concept is suitable for receivers consisting of multimode-compatible components such as the echelle grating demultiplexer and the Ge waveguide photodetector.

(Invited) Performance and Reliability of a 25Gb/s Ge Waveguide Photodetector Integrated in a CMOS Process

This paper describes the monolithically integrated Germanium photo-detectors used by Luxtera in their 4x10Gbps CMOS photonics based transceiver products. When used with optimized receivers, these detectors show exceptional optical sensitivities of ~-24dBm at 10Gbps & 10-12 BER and also support open eyes up to 25Gbps. Aging tests have also demonstrated that these detectors exhibit a very high level of reliability.

Performance and Reliability of a 25Gb/s Ge Waveguide Photodetector Integrated in a CMOS Process

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High‐Speed Near Infrared Optical Receivers Based on Ge Waveguide Photodetectors Integrated in a CMOS Process

We discuss our approach to monolithic intergration of Ge photodectors with CMOS electronics for high‐speed optical transceivers. Receivers based on Ge waveguide photodetectors achieve a sensitivity of −14.2 dBm (10−12 bit error rate (BER)) at 10 Gbps and 1550 nm.

31 GHz Ge n-i-p waveguide photodetectors on Silicon-on-Insulator substrate

We report on evanescently coupled Ge waveguide photodetectors that are grown on top of Si rib waveguides. A Ge waveguide detector with a width of 7.4mum and length of 50 mum demonstrated an optical bandwidth of 31.3 GHz at -2V for 1550nm. In addition, a responsivity of 0.89 A/W at 1550 nm and dark current of 169 nA were measured from this detector at -2V. A higher responsivity of 1.16 A/W was also measured from a longer Ge waveguide detector (4.4 x 100 mum2), with a corresponding bandwidth of 29.4 GHz at -2V. An open eye diagram at 40 Gb/s is also shown.