Nanometallic Concentration for Enhanced Photodetection

David A. B. Miller Ginzton Laboratory, Center for Nanoscale Science and Engineering, Stanford University,

348 Via Pueblo Mall, Stanford, CA 94305-4088 dabm@ee.stanford.edu

Abstract— Concentrating light into deeply subwavelength photodetectors offers higher speed and lower capacitance, both important for applications such as optical interconnects. Nanometallic and plasmonic antennas and waveguides offer many attractive opportunities for such concentration.

Keywords- plasmonics; nanometallics; optical antennas

Optical interconnections offer many potential benefits to information processing systems. The high densities and low energies potentially possible with optics could allow continued scaling of the performance in future technology generations [1-4]. The necessary optoelectronic technology is, however, challenging. One particularly important parameter is low capacitance in the photodetector elements. Reducing that capacitance can lead to proportionate reductions in optical energy requirements [5].

Decreasing the size of photodetectors below the usual diffraction limits of light could permit particularly low capacitance, possibly into the deeply sub-femtofarad range [6] that would be comparable to the input capacitance of future transistors [4]. In our work, we find that nanometallic structures may allow the concentration of light into such small structures [6-15]. In general, metallic structures may be the only viable approach for the deeply sub-wavelength miniaturization of functional optical components [16].

One particularly important feature of the use of nanometallic or plasmonic structures to concentrate light into photodetector elements is that there can be significant overall system benefits even in the presence of substantial losses in the metals. The reduction of capacitance offers such a benefit to the system performance that it can more than make up for some optical power loss from the nanometallic concentration.

Various approaches are possible for concentrating light into deeply subwavelength volumes for photodetection, including, in our own work, C-apertures [6, 7], nanoantennas [8], and nanometallic waveguides [9-15]. Our work here has featured ~ 100 nm scale concentration into semiconductor elements, both theoretically [9] and experimentally [6-8, 10]. Recently, also, we have been able to combine photodetection and novel non-periodic plasmonic wavelength demultiplexing into one device structure.

The talk will discuss the progress and prospects for nanometallics for concentration into photodetectors.

[1] D. A. B. Miller, "Optics for low-energy communication inside digital processors: quantum detectors, sources, and modulators as efficient impedance converters,” Optics Letters, 14, 146-148, (1989).

[2] D. A. B. Miller, “Physical Reasons for Optical Interconnection,” Int. J. Optoelectronics 11, 155-168 (1997).

[3] D. A. B. Miller, “Rationale and Challenges for Optical Interconnects to Electronic Chips,” Proc. IEEE 88, 728-749 (2000).

[4] D. A. B. Miller, “Device Requirements for Optical Interconnects to Silicon Chips,” Proc. IEEE 97, 1166 - 1185 (2009)

[5] S. Latif, S. E. Kocabas, L. Tang, C. Debaes & D. A. B. Miller, “Low capacitance CMOS silicon photodetectors for optical clock injection”, Appl. Phys. A – Materials Science and Processing 95, 1129-1135 (2009)

[6] L. Tang, D. A. B. Miller, A. K. Okyay, J. A. Matteo, Y. Yuen, K. C. Saraswat, and L. Hesselink, "C-shaped nanoaperture-enhanced germanium photodetector," Opt. Lett. 31, 1519-1521 (2006)

[7] L. Tang, S. Latif, and D. A. B. Miller, “Plasmonic device in silicon CMOS,” Electronics Lett. 45, 706 – 708 (2009)

[8] L. Tang, S. E. Kocabas, S. Latif, A. K. Okyay, D.-S. Ly-Gagnon, K. C. Saraswat and D. A. B. Miller, “Nanometre-Scale Germanium Photodetector Enhanced by a Near-Infrared Dipole Antenna,” Nature Photonics 2, 226 – 229 (2008)

[9] D.-S. Ly-Gagnon, S. E. Kocabas, and D. A. B. Miller, “Characteristic Impedance Model for Plasmonic Metal Slot Waveguides,” IEEE J. Sel. Top. Quantum Electron., 14, 1473 – 1478 (2008)

[10] D.-S. Ly-Gagnon, K. C. Balram, J. S. White, P. Wahl, M. L. Brongersma, and D. A. B. Miller, “On-Chip Optical Propagation and Photodetection in Nanometer-Scale Two-Conductor Plasmonic Waveguides,” 3rd International Topical Meeting on Nanophotonics and Metamaterials, Seefeld, Austria, January 2011, Paper TUE4f.64

[11] S. E. Kocabas, G. Veronis, D. A. B. Miller, and S. H. Fan, "Transmission Line and Equivalent Circuit Models for Plasmonic Waveguide Components," IEEE J. Sel. Top. Quantum Electron.14 (6), 1462-1472 (Dec 2008).

[12] S. E. Kocabas, G. Veronis, D. A. B. Miller, and S. H. Fan, “Modal Analysis and Coupling in Metal-Insulator-Metal Waveguides,” Phys. Rev. B 79, 035120 (2009)

[13] G. Veronis, Z. F. Yu, S. E. Kocabas, D. A. B. Miller, M. L. Brongersma, and S. H. Fan, “Metal-dielectric-metal plasmonic waveguide devices for manipulating light at the nanoscale,” Chinese Opt. Lett.7, 302–308 (2009)

[14] G. Veronis, S. E. Kocabas, D. A. B. Miller, and S. H. Fan, “Modeling of Plasmonic Waveguide Components and Networks,” J. Computational and Theoretical Nanoscience 6, 1808 – 1826 (2009)

[15] S. E. Kocabas, G. Veronis, D. A. B. Miller, and S. H. Fan, “Modal Analysis and Coupling in Metal-Insulator-Metal Waveguides,” Phys. Rev. B 79, 035120 (2009)

[16] D. A. B. Miller, "Fundamental limit for optical components," J. Opt. Soc. Am. B 24, A1-A18 (2007)

[17] T. Tanemura, K. C. Balram, D. S. Ly-Gagnon, P. Wahl, J. S. White, M. L. Brongersma, and D. A. B. Miller, "Multiple-wavelength focusing of surface plasmons with a nonperiodic nanoslit coupler," Nano Letters, to be published.

664

ThA1 (Invited)8:30 AM – 9:00 AM

978-1-4244-8939-8/11/$26.00 ©2011 IEEE