Optoelectronic detectors and receivers: speed and sensitivity limits

This invited paper first reviews the recent advances in the area of photodetectors and optoelectronic integrated circuit (OEIC) receivers for the preferred 1.55 μm light-wave fiber-optic communication links. The m-s-m (metal-semiconductor-metal) and the p-i-n photodetectors are based on lattice-matched InGaAs photoabsorption layers on semi-insulating InP substrates, and the receiver integrates one of these photodetectors with a low-pass high bandwidth amplifier based on either compatible heterostructure bipolar or field-effect transistors (HBTs or HFETs) and passive resistors. The primary focus of this paper is on: (a) the theoretical and experimental results identifying the high-frequency limits of different types of photodetectors, (b) an optimized design approach to p⁺(n^-)p⁺/HBT and n⁺ (p^-)n⁺/HFET OEIC transimpedance receivers with flat frequency response, and (c) their speed and sensitivity limits in the presence of the background device and circuit noise, and the inter-symbol interference (ISI). The transit-time limited frequency response of the photodetectors is found to be directly proportional to the slower hole carrier effective velocity, and inversely proportional to the effective separation of the detector´s electrodes. For m-s-m photodetectors with metallization width and separation of 0.25 μm, and for vertical p-i-n photodiodes with 0.2 μm electrode separation the 3-dB bandwidth limits of both devices are found to be approximately 80 GHz. Similar frequency limits can be obtained from IC compatible p ⁺(n^-)p⁺ or n⁺(p^-)n⁺ surface-oriented lateral photodetectors. When these detectors are integrated together with compatible transistors having comparable current gain cut-off frequency (f_c), either in p⁺(n^-)p⁺/HBT or n⁺(p^-)n⁺/HFET OEIC receivers with optimized transimpedance (≅1.5 kΩ), the expected bit-rate and sensitivity limits are shown to exceed 31 Gb/s and -22 dBm, respectively