Semiconductor Nanowire Nanophotonics and Optoelectronics Speaking: Mark Brongersma @ Stanford University Doing the Work: Linyou Cao, Majid Esfandyarpour, Erik C. Garnett, Soo-Jin Pengyu Fan Soo-Jin Kim, Dianmin Lin, Juhyung Kang, Jung Hyun Park, Isabell Thomann. Funding: AFOSR, DOE EFRC, Samsung Thank you: Mike McGehee group (Stanford) Yi Cui group (Stanford) Pieter Kik (CREOL) Nader Engheta (Upenn) Erez Hasman (Technion) Reflection Absorption/Emission Transmission P << Optoelectronic Devices are Everywhere… Flexible display Image sensors Samsung Solar cells, SunPower Lasers Most Optoelectronic Devices Rely on Planar Device Technologies http://spie.org/Images/Graphics/Newsroom/ CMOS Image sensors (Sony) Imported‐2012/004167/004167_10_fig3.jpg Keisuke Nakayama H.A. Atwater et al., Appl. Phys. Lett. 93, 121904 (2008) www.olympusmicro.com Can metamaterials have an impact on these technologies ??..Lower power, higher speed, thinner.. Enhanced Light-Matter Interaction Comes For Free at the Nanoscale Electronics Optical Properties Semiconductors 1st transistor and IC Semiconductor wafers Current technology Semiconductor nanostructures 30 nm 185 nm Linyou Cao et al., Nano Lett., 2649, 10 (2010) Noble metal and high-index semiconductor nanostructures exhibit strong, tunable optical resonances Development of Metafilms and Metasurfaces from Resonant Nanostructures Assembly nanostructures into metasurfaces and metafilms Absorption/Emission Transmission P << Semiconductor nanostructures 30 nm 185 nm L. Cao, M.L. Brongersma et al., Nano Lett., 2649, 10 (2010) Short History of Resonant High-index Nanostructures 1908 Gustav Mie: Light scattering from a dielectric sphere Gustav Mie, Ann. Phys. 25, 377–445 (1908) 1947 L. Lewin Medium with spheres L. Lewin, Inst. Electr. Eng. III Radio Commun. Eng. 94, 65–68. 1947, 1980 Long, McAllister, and Shen Dielectric Resonator Antennas S. A. Long, M. W. McAllister, and L. C. Shen, "The Resonant Cylindrical Dielectric Cavity Antenna," IEEE Transactions on Antennas and Propagation, 31, 406, 1983. 2000 Kuester & Holloway Artificial dielectrics materials in RF range 2003 – Visible & Near IR: Pendry, Joannopoulos, Kuznetsov, Luk’yanchuk, Evlyukhin, Polman, Novotny, Kivshar, Chang-Hasnein, Brener, Brongersma, Valentine, Zheludev, Rockstuhl, Cui, Seo, etc. – IR: Brener, Brongersma, Hasman, Schuler , Zheludev, etc.. – RF: Cummer, Gopinath, Lippens, Kuester & Holloway, etc. Beneficial Properties of Resonant Semiconductor Nanostructures Engineering optical resonance frequency with size 30 nm 180 nm Diameter D Length Engineering optical resonance frequency with shape Effective light concentration to the deep subwavelength scales E = 550 nm |E|2 d Air d =100nm y Si d g = 10 nm x SiO2 (n = 1.45) Cao, Brongersma et al., Nano Lett., 2649, 10, 2010. Ho-Seok Ee et al., Nano Letters, 15, 1759 (2015). Beneficial Properties of Resonant Semiconductor Nanostructures Wide range of resonances in simple structures Interaction of multiple Mie resonances Person et al., Nano Lett. 13, 1367‐1868 (2013). Y.H. Fu et al., Nature Comm. 4, 1527 (2013). Ohmic loss can be “zero” (h < Egap) or loss can be useful (photocarrier generation!) Light can generate long‐lived carriers and vice versa (detectors, sources,…) Mature processing semiconductor fabrication techniques Doping and band engineering to realize devices (e.g. pn junctions, transistors, Q‐wells..) Electrical doping can be used to tune carrier density and thus the optical properties Mobile carrier densities and thus optical properties are low enough to impact them by gating Quantifying Light Scattering from Nanowires Microscope for performing darkfield light scattering measurements Iscatter scatter (a.u.) I Linyou Cao et al., Nano Lett., 2649–2654, 10, 2010. Quantification of the Color Tuning Scattering spectra show a redshift and multiple peaks emergence for large wires diameter in nm Scattered light intensity (a.u.) Wavelength (nm) Linyou Cao et al., Nano Lett., 2649–2654, 10, 2010. Polarization‐dependence of Light Scattering from SiNWs Observed color under white light illumination can change with illumination conditions scatter (a.u.) I Linyou Cao et al., Nano Lett., 2649–2654, 10, 2010. Optical Properties of Dielectric/Semiconductor Structures Example: Optical properties of high index nanowires Free space photons can couple to Mie or leaky mode resonances Intuitive resonance condition: mλeff = 2πr For top-illumination resonances split in TM and TE modes Nomenclature TMml 2 |H| m: # wavelengths l : # radial maxima Device Applications of Semiconductor Nanowires Example: Optical interconnection schemes require ultrafast, low noise photodetectors Speed typically scales with a linear size of the detector Small detectors are good Power and noise scale typically scale with capacitance/area Example of a fabricated Ge nanowire detector structure Challenge: Wires are small compared to the diffraction limit…… Solution: Light absorption in designed semiconductor nanostructures is naturally enhanced L. Cao, J.S. White, J-S Park, J.A. Schuller, B.M. Clemens, and M.L. Brongersma, Nature Mat. 8, 643-647 (2009). Spectral Photocurrent Response of Ge nanowires Photocurrent shows strong enhancements at some s Spectral photocurrent measurements on Ge nanowires of different radius Qabs = σabs/σgeom = optical size/physical size σabs Photocurrent (a.u.) R=10 nm R=25 nm R=110 nm σgeom Wavelength (nm) L. Cao, J.S. White, J-S Park, J.A. Schuller, B.M. Clemens, and M.L. Brongersma, Nature Mat. 8, 643-647 (2009). Engineering Better NW Photodetectors and Solar Cells Simple optimization procedure 110 nm radius Simulated Experiment 25 nm radius 10 nm radius Can We Build NW Molecules and Materials ? Optical coupling of closely-spaced nanowires 50nm The science of coupling nanowires State of individual nanowires States of coupled nanowires E = ħω Anti-bonding Wire state Bonding state Linyou Cao, Pengyu Fan, and Mark L. Brongersma, Nano Letters 11, 1463-1468, (2011). Dielectric Antennas of more Complex Architecture Dielectric Yagi Uda antenna Electric and Magnetic hotspots A.E. Krasnok et al, Opt. Express 20, 20599 (2012) R.M. Bakker et al., Nano Letters 15, 2137 (2015). Fano Resonance in dielectric oligomers Reflective dielectric metasurfaces A.M. Miroshnichenko, et al., Nano Letters 12, 6459 (2012). S. Liu et al. Optica 1, 320 (2014). Lenses are everywhere Professional Camera Microscope Drone Solar concentrator Optical Communication iPhone’s Protruding Camera 18 Photo credit: google images Optical Antennas + Pancharatnam-Berry phase 100nm Si 3 um “Dielectric Gradient Metasurface Optical Elements,” Dianmin Lin, Science, 298 ‐302, 345 (2014). DGMOE of Axicon and Generated Bessel beam Experiment on DGMOE Axicon based on Si nanobeams λ=550nm Experimentally measured intensity profile of Bessel beam RCP -10 m) 0 μ x ( 10 -50 0 z (μm) 50 100 1.0 y 0.5 I (a.u.) 5 μm 0 x -10 010 x (μm) Semiconductors offer: low optical loss, facile integration with electronics, easy patterning, .. New opportunities to construct low-loss gradient metasurface optical elements Enhancing Light Absorption in a Ge Metafilm on Metal Substrate A 50-nm-thick Ge film is patterned into a metafilm consisting of many subwavelength Ge beams SEM image of fabricated sample Optical reflection image Power flow ( = 800 nm) The continuous film look grey and patterned Ge film look black ! Patterning the Ge film at subwavelength scale enhances the broadband light absorption Optical, Mie-like resonances in the Ge beams are at the origin of the strong light absorption The flow light (Poynting vector) shows an antenna effect that ‘funnels’ light into the beams Soo Jin Kim et al., Nature Communications 6, 7591 (2015). Reflection measurement from Ge nanobeams on Au Example: Array with 60 nm beams illuminated 800 nm, TM polarized light Strong absorption is observed at the nanobeam resonance wavelength Absorptivity ( 1 – Reflectivity) 11 0.9 0.80.8 0.7 0.60.6 beam 0.5 0.40.4 Absorptivity 0.3 0.20.2 Individual 0.1 00 w = 60 nm w 500500 550 600600 650 700700 750 800800 850 900900 Wavelength (nm) Soo Jin Kim et al., Nature Communications 6, 7591 (2015). Tuning of the absorption spectrum by changing the beam width Resonance wavelength is tunable with the beam width Reflection spectra Ge metafilms with constant duty cycle of 1:3 (beam width : period) First-order effective medium theory predicts that optical properties are independent of period For TM polarization: εeff = fGe εGe + (1‐fGe)εair Absorptivity ( 1 – Reflectivity) 11 0.90.9 w = 30 nm 0.80.80.8 w = 45 nm 0.70.7 w = 60 nm 0.60.60.6 0.50.5 0.40.40.4 Absorptivity 0.30.3 0.20.20.2 30 45 60 0.10.1 00 w 500500 550 600600 650650 700700700 750750 800800800 850850 900900900 950 Wavelength (nm) Soo Jin Kim et al., Nature Communications 6, 7591 (2015). Broadband Absorption Can be Achieved with Big and Small Beams Metafilms with wide (120 nm) and narrow (30 nm) beams were created SEM images of the subwavelength nanobeam arrays Just 120 nm beams Just 30 nm beams 120 nm and 30 nm beam 800 nm Reflection measurements show strong absorption at resonance wavelength beams Experiment simulation Sample with wide and narrow beams show strong absorption at short and long Metafilms Offering Lateral Spectral Splitting Capabilities Goal: Demonstrate ability to collect different s into spatially separated regions Schematic showing the concept TEM & SEM images first batch of devices Si Beams of different width resonate and collect light at different wavelengths Device with narrow and wide Si beams