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17 February 2009 Universal PIN photodiodes in a 0.35μm BiCMOS mixed-signal ASIC technology
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We present an improvement of monolithically integrated photodiodes in a p-type substrate of a commercial high-speed 0.35μm SiGe heterojunction bipolar transistor (HBT) BiCMOS technology. These photodetectors (PDs) combine low capacitance with high bandwidth and responsivity. Slight process modifications of the standard HBT process have been introduced in order to decrease leakage currents and enhance reach-through stability of the PDs. These modifications have been chosen carefully in order not to alter any other transistor parameters as shown in [1]. To enable low capacitances of the PDs very lightly p-doped epitaxially grown layers of different thicknesses over highly p-doped substrates have been investigated. The improvement becomes manifest, e.g. in a bandwidth of 557MHz and a responsivity of 0.19A/W of a finger photodiode at blue light and a reverse bias voltage of 4V in a 10μm cathode digit-spacing configuration. The capacitance of this finger photodiode is 150fF, overtopping the regular PIN photodiode published in [2] for the same light-sensitive area with a capacitance of 225fF. Results of detectors with interdigitated cathode distances of 5μm, 10μm, 15μm and 30μm are presented over the wide spectrum of technologically significant optical wavelengths from near-infrared to blue and ultraviolet. These detectors fulfil the requirements demanded by photodiode integrated circuits for universal backward compatible optical storage systems.
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Artur Marchlewski, Gerald Meinhardt, Ingrid Jonak-Auer, Verena Vescoli, Ewald Wachmann, Kerstin Schneider-Hornstein, and Horst Zimmermann "Universal PIN photodiodes in a 0.35μm BiCMOS mixed-signal ASIC technology", Proc. SPIE 7220, Silicon Photonics IV, 72200C (17 February 2009);

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