Owing to its low-cost, high-yield, and dense integration ability, silicon nanophotonics is a good candidate to tackle the needs of exponentially growing communications in data centers, high-performance computers, and cloud services. Moreover, a number of nanophotonic functions are now available on a single chip, as they take advantages of silicon-foundry process maturity and epitaxial germanium integration. Optical photodetectors are key building blocks in the library of group-IV components and their performances are quite successful nowadays. In particular, silicon-germanium waveguide-integrated photodetectors are fixing new standards for next generation of on-chip interconnects in terms of compactness, speed, power consumption and cost. Indeed, conventional pin photodetectors yield good responsivities (~1 A/W in a 1.5 μm wavelength range), high bandwidths (~50 GHz), and dark currents well below 1 μA. Despite recent advances, their optical power sensitivities remain rather modest and speeds are limited to 25 Gbps only, however. Compensating for the insufficient photodetector sensitivity requires higher transmitter output powers and therefore higher energy consumption. Additional energy savings can be obtained by eliminating receiver electronics. Alternatively, an appealing approach is to exploit device structures with an internal multiplication gain to lower even more the power budget and improve energy efficiency of chip-based optical links. In this work, we report on waveguide-integrated photodetectors with lateral silicon-germanium-silicon heterojunctions. Here, we present avalanche photodetectors fabricated on 200-mm silicon-on-insulator wafers using complementary metal-oxide-semiconductor-compatible processes. Devices operate in the low-gain-regime to facilitate high-speed link operations at 1.55 μm wavelengths. An error-free signal detection was achieved at 28 Gbps, with power sensitivity of -11 dBm for 10-9 bit-error-rate, which is a relevant link rate for emerging chip-scale optical interconnects.
On-chip light detection is universally regarded as a key functionality that enables myriad of applications, including optical communications, sensing, health monitoring or object recognition, to name a few. Silicon is widely used in the micro-electronics industry. However, its electronics bandgap precludes the fabrication of high-performance photodetectors that operate at wavelengths longer that 1.1 μm, a spectral range harnessed by optical communication windows of low fiber attenuation and dispersion. Conversely, Germanium, a group-IV semiconductor as Silicon, with a cut-off wavelength of ~1.8 μm, yields efficient light detection at near-infrared wavelengths. Germanium-based photodetectors are mature building blocks in the library of silicon nanophotonic devices, with a low dark-current, a fast response, a high responsivity and low power consumption with an established fabrication flow. In this work, we report on the design, fabrication and operation of waveguide pin photodetectors that advantageously exploit lateral Silicon/Germanium/Silicon heterojunctions. Devices were fabricated on 200 mm silicon-on-insulator substrates using standard micro-electronics production tools and processes. This photodetector architecture takes advantage of the compatibility with contact process steps of silicon modulators, thereby offering substantially reduced fabrication complexity for transmitters and receivers, while providing improved optical characteristics. More specifically, at a lowbias reverse voltage of -1 V, we experimentally achieved dark-currents lower that 10 nA, a device photo-responsivity up to 1.1 A/W, and large 3-dB opto-electrical bandwidths over 50 GHz. In addition, high-speed data rate transmission measurements via eye diagram inspection have been conducted, with pin photodetector operation at the conventional 10 Gbps up to the future 40 Gbps link speeds.