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). L. Cao, J.S. White, J-S Park, J.A. Schuller,Park, J.A. L. Cao, J.S.White, J-S B.M. htcretshows strongenhancements at some Photocurrent

Photocurrent (a.u.)  Spectral photocurrent measurements Spectral photocurrent R=10 nm Spectral Photocurrent Response of Ge nanowires Response of Spectral Photocurrent Wavelength (nm) R=25 nm Clemens, and M.L. Brongersma, Nature Mat. 8, 643-647 (2009). Clemens, and M.L.Brongersma, Nature Mat.8, on Ge nanowires of differentradius R=110 nm  s Q abs = = optical size/physical size σ abs / σ geom σ geom σ abs 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 spectrally splits light of different s into differently-sized beams  Photocurrent from differently-sized beams can be collected separately

 Metafilms offer new ways to perform spectral photon sorting at the nanoscale ! Lateral spectral splitting of light at sub scale

Goal: Demonstrate ability to collect different s into spatially separated regions Absorption spectra small and BIG beams Power flow at short and LONG wavelengths

 = 595nm  = 625nm

Si

Si

 Peak absorbtion (on resonance) in small (blue curve) and BIG (red curve) beams is well over 50%  Total absorption close to unity (black dashed curve)  Spectral splitting without color filters has application in image sensors and biosensors Many 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 ?? !!