152 IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 19, NO. 3, FEBRUARY 1, 2007 CMOS-Compatible All-Si High-Speed Waveguide Photodiodes With High Responsivity in Near-Infrared Communication Band M. W. Geis, S. J. Spector, M. E. Grein, R. T. Schulein, J. U. Yoon, D. M. Lennon, S. Deneault, F. Gan, F. X. Kaertner, and T. M. Lyszczarz Abstract—Submicrometer silicon photodiode waveguides, fabri- cated on silicon-on-insulator substrates, have photoresponse from 1270 to 1740 nm (0.8 AW at 1550 nm) and a 3-dB bandwidth of 10 to 20 GHz. The p-i-n photodiode waveguide consists of an in- trinsic waveguide 500 250 nm where the optical mode is confined and two thin, 50-nm-thick, doped Si wings that extend 5 m out from either side of the waveguide. The Si wings, which are doped one p-type and the other n-type, make electric contact to the wave- guide with minimal effect on the optical mode. The edges of the wings are metalized to increase electrical conductivity. Ion implan- tation of Si cm at 190 keV into the waveguide increases the optical absorption from 2–3 dB cm to 200–100 dB cm and causes the generation of a photocurrent when the waveguide is illuminated with subbandgap radiation. The diodes are not dam- aged by annealing to 450 C for 15 s or 300 C for 15 min. The photoresponse and thermal stability is believed due to an oxygen stabilized divacancy complex formed during ion implantation. Index Terms—Integrated optoelectronics, near-infrared, photodetectors, silicon (Si) optoelectronics, silicon (Si) waveguide. I. INTRODUCTION A LTHOUGH the majority of electrical compu- tation is performed using Si complementary metal–oxide–semiconductor (CMOS) circuitry, infrared optical communication components are typically composed of InGaAs (photodetectors and lasers) or LiNbO (modulators), which cannot be integrated with Si. Monolithically integrating these optical components with Si CMOS circuitry would result an electrooptic chip with significant increase in performance and reduction in cost. Here we report on Si waveguide photodetectors formed using the standard CMOS process of ion implantation. These devices have a 10- to 20-GHz bandwidth, internal responsivity, the ratio of the photocurrent to the power in the waveguide, from 1270 to 1740 nm (0.8 AW Manuscript received September 15, 2006; revised November 7, 2006. The Lincoln Laboratory portion of this work was sponsored in part by the EPIC Program of the Defense Advanced Research Projects Agency and in part by the Department of the Air Force under Air Force Contract FA8721-05-C-0002. Opinions, interpretations, conclusions, and recommendations are those of the authors and do not necessarily represent the views of the United States Govern- ment. M. W. Geis, S. J. Spector, M. E. Grein, R. T. Schulein, J. U. Yoon, D. M. Lennon, S. Deneault, and T. M. Lyszczarz are with Lincoln Laboratory, Massachusetts Institute of Technology, Lexington, MA 02420-9108 USA (e-mail: geis@ll.mit.edu). F. Gan and F. X. Kaertner are with Massachusetts Institute of Technology, Cambridge, MA 02139-4327 USA. Color versions of one or more of the figures in this letter are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/LPT.2006.890109 Fig. 1. Waveguide photodiode. (a) Top-view optical micrograph of 0.25-mm waveguide photodiode. (b) Schematic drawing of diode cross section. The wave- guide is the silicon rib in the center of the sketch. All dimensions are in nanome- ters unless otherwise labeled. at 1550 nm), and leakage current of 0.4 A. Because Si is transparent at wavelengths longer than 1100 nm, Si diodes exhibit only a weak response to radiation at these wavelengths, but the response can be extended to longer wavelengths by ion implantation damage [1]. Knights et al. [2] have demonstrated a photoresponse of 0.01 AW at 1550 nm using implantation in Si rib-waveguide photodiodes 3 m wide and 4 m thick. By reducing the dimensions of the waveguide and optimizing the implantation, the performance and stability of the diodes have been dramatically improved. II. FABRICATION A diagram of such a photodiode is shown in Fig. 1. The center of the structure is intrinsic and there are p- and n-doped regions on its opposite sides, forming a lateral p-i-n diode. Damage from ion implantation makes the intrinsic region sensitive to light, which when present in the waveguide causes carrier generation. Away from the waveguide, the doping was cm to give low electrical resistance in the slab. Close to the waveguide and on its edges, the dose was lowered to cm to avoid ex- cessive optical loss. The diodes were fabricated in a silicon-on-insulator (SOI) substrate using standard CMOS processing. Smart-cut [3] SOI wafers were used, and the initial Si thickness of 0.5 m was thinned to 0.22 m through oxidation and SiO removal in buffered HF. A final wet oxidation performed at 900 C for 40 min coated the surface with 90 nm of SiO . The SiO and Si layers were dry etched to form the structure shown in Fig. 1. Doping with P and B ions followed by a 7-s 1000 C anneal 1041-1135/$25.00 © 2007 IEEE