A silicon-based integrated NMOS-p-i-n photoreceiver

For large-volume optoelectronics applications, the low cost, manufacturability and reliability of silicon MOSFET technology are advantageous. In addition, silicon photodetectors operate quite efficiently at the 850 nm wavelength of economical AlGaAs light sources. In this paper, we report on a silicon-based monolithic optical receiver. The fabrication of the integrated lightwave receiver was carried out on a nominally undoped p-type Si substrate. The p-i-n photodetector was fabricated directly on the high-resistivity substrate so that the thickness of the detector depletion layer was approximately equal to the optical absorption length of 850 nm light in silicon. A more heavily-doped p-well was formed for the NMOSFET fabrication. The silicon photodiodes had a dark current of 20 nA at 5 V, a breakdown voltage greater than 60 V, and a zero-bias capacitance of 40 fF. The external quantum efficiency of the photodiode at 870 nm was approximately 67% at 5 V without an AR coating, and the bandwidth of the device was approximately 1.3 GHz. Frequency response evaluation of the receiver indicated a circuit-design-limited bandwidth of 30 MHz with open eye diagrams demonstrated at 40 MB/s.