We report on monolithically integrated PIN photodiodes whose responsivity values could be significantly enhanced over
the whole spectral range by the implementation of a Bottom Antireflective Coating (BARC) process module into
austriamicrosystems 0.35μm CMOS as well as high-speed SiGe BiCMOS technologies. The resulting photodiodes
achieve excellent responsivities together with low capacitances and high bandwidths. We processed finger-photodiodes
with interdigitated n+ cathodes, which are especially sensitive at low wavelengths, and photodiodes with full area n+
cathodes on very lightly p-doped start material. We present a method of depositing an antireflective layer directly upon
the Si surface of the photodiode by changing the standard process flow as little as possible. With just one additional mask
alignment and a well controlled etch procedure we manage to remove the thick intermetal oxide and passivation nitride
stack over the photodiodes completely without damaging the Si surface. The following deposition of a CVD Silicon
Nitride BARC layer not only minimizes the reflected fraction of the optical power but also acts as passivation layer for
the photodiodes. Another benefit of BARC processing is the fact that in-wafer and wafer-to-wafer quantum efficiency
variations can be dramatically reduced. In our experiments we deposited BARC layers of different thicknesses that were
optimised for violet, red and infrared light. Responsivity measurements resulted in values as high as R=0.27A/W at
λ=410nm, R=0.53A/W at λ=670nm and R=0.5A/W at λ=840nm.
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 . 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  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.
In this work we present experimental results of silicon-only bipolar phototransistors fabricated in a 0.35μm commercial
BiCMOS technology without process modifications. The transistors are characterized over a wide optical spectral range
at 410nm, 675nm, 785nm, and 850nm, providing significantly improved -3dB bandwidths up to 390MHz @ 410nm
light and responsivities of 1.76A/W @ 675nm corresponding to quantum efficiencies of 359% normalized in terms of
the quantum efficiency of a silicon photodiode.
Herein we present optical receivers with external large-area photodiode. It is intended as POF receiver for 1.25Gb/s optical fiber-line access networks. Further an overview on high-speed optical receivers with integrated and external detector in CMOS and BiCMOS, as well as in technologies of III-V compounds is provided. This work's receiver circuits are realized in 0.35μm SiGe BiCMOS technology. The first amplifier stage is a two-transistor transimpedance amplifier using a common-emitter and an emitter-follower configuration. The light-sensitive areas of the two receivers presented are 0.25mm2 (squared PIN diode) and 0.5mm2 (circular APD), with a rise time of 0.4ns and 0.7ns, respectively, at 850nm light. A high sensitivity is also required, where the receiver with external PIN diode reaches a sensitivity of -25.9dBm at the optical input using low-cost silicon-based material only.