nanosilicon Nanophotonics - PDF Free Download

nanosilicon Nanophotonics Lorenzo Pavesi Universita di Trento Italy

Outline Silicon Photonics NanoSilicon photonics Silicon Nanophotonics NanoSilicon Nanophotonics Conclusion

The real truth of semiconductor industry Smaller Cheaper Faster by large scale integration

vs. Silicon Photonics Silicon Photonics LD,PD, microrings,. Silicon CMOS

Silicon photonics Photonic devices produced within standard silicon factory and with standard silicon processing

Silicon pro s and cons Transparent on 1.3-1.5 mm CMOS compatibility Low cost High index contrast, small footprint No electro-optic effect No detection in 1.3-1.5 mm region High index contrast coupling Lacks efficient light emission

The Opportunity of Silicon Photonics Enormous ($ billions) CMOS infrastructure, process learning, and capacity Draft continued investment in Moore s law Potential to integrate multiple optical devices Micromachining could provide smart packaging Potential to converge computing & communications To benefit from this optical wafers must run alongside existing product. CMOS PHOTONICS

Explosion of silicon photonics

Luxtera single-chip 100-Gbps transceiver targets multiple applications The new transceiver chip, which measures 5x6 mm, offers 4x28-Gbps transmission over single mode fiber. The device features waveguide, waveguide structures, modulators, couplers, and photodetectors integrated at the wafer level. The photodetectors are germanium, but applied to the wafer using the same CMOS processes as the other devices. A single CW laser powers all four channels; it attaches to the CMOS wafer via a hybrid integration process. November 8, 2011

Projected integration density Silicon photonic NOC

Outline Silicon Photonics NanoSilicon photonics Silicon Nanophotonics NanoSilicon Nanophotonics Conclusion

NanoSilicon NanoPhotonics: a platform where photon or electron confinement enables new functionalities in silicon photonics

Nanophotonics Confine carriers on nanoscale dimensions Length scale = electron DeBroglie wavelength Confine photons on nanoscale dimensions Length scale = light wavelength

NanoSilicon photonics Confine carriers on nanoscale dimensions Confine photons on nanoscale dimensions 10 μm

NanoSilicon photonics Confine carriers on nanoscale dimensions

Silicon quantum dots 50 nm

Silicon quantum dots E gap Si Egap 2m L 2 2 Increase the emission energy

Silicon quantum dots

Silicon quantum dots Light emission Optical gain Nonlinear optical effects Photoresponse Biocompatibility Interface properties Sensitization action

Bipolar Injection in Nanocrystalline-Si LEDs with Low Turn-on Voltages and High Power Efficiency

Injection into a dielectric The only way is to use the tunneling effect

Tunneling injection Onset voltages > 4.2 V (band offset for electrons) Impact excitation is a dominant mechanism Energy Fowler-Nordheim Tunneling Direct Tunneling Less destructive More efficient <3V >3V Position nc-si Oxide Position

Single vs multilayer

CMOS LED Si-NC LED on a CMOS wafer 28

CMOS LED Si-NC LED on a CMOS wafer 29

Gate current (A) Low onset of EL voltages, < 3.2 V (2 nm SiO 2 / 3 nm SRO) (2 nm SiO 2 / 4 nm SRO) 10-5 10-7 10-9 10-11 10-13 EL data points Forward bias -6-4 -2 0 2 4 6 Gate voltage (V) Reverse bias J. Appl. Phys. 106, 033104 (2009)

Band gap engineering

Graded gap active layer Large nanocrystals: Easy injection Small nanocrystals: high emission

Optical power density (mw / cm 2 ) Power efficiency (%) CMOS LED 1 (2 nm SiO 2 / 3 nm SRO) Graded energy gap (2 nm SiO 2 / 4 nm SRO) 0.1 0.2 0.1 0.01 0.0 10-3 10-2 10-1 1 Current density (ma / cm 2 ) 10-3 10-2 10-1 1 10 1 Current density (ma / cm 2 ) A Anopchenko, et al. Applied Physics Letters 99, 181108 (2011).

Si-NCs:Er LEDs SiO x : LPCVD ~ 50 nm, Si excess: 9-16 at. %; SiO x anneal: 900 C, 1 h; Er implantation: 20 kev, 1x10 15 /cm 2 ; Er post-implantation anneal: 800 C, 6 h n - type silicon Er 3+ 50 nm SiO 2 SRO Si-nc p - type silicon

Si-NCs:Er LEDs - Results External Quantum Efficiency 0.55 % in DC

Outline Silicon Photonics NanoSilicon photonics Silicon Nanophotonics NanoSilicon Nanophotonics Conclusion

Silicon Nanophotonics Confine carriers on nanoscale dimensions Confine photons on nanoscale dimensions 10 μm

Ultra high Q resonator microsphere microtoroid Optical image Quality factor Q 8 10 9 SEM image Q 10 8 Very low scattering losses smooth surface Fabrication process by melting silica microrods by reflowing silica microdisks Unsuitable for photonic circuit integration and mass production K. Vahala, Nature 424, 839 (2003)

Coupling to UHQ resonator Coupling principle: by evanescent field It requires nanometric gaps between the resonator and the fiber Difficult and complex experimental optical setup

Wedge WGM resonator Alternative UHQ WGM resonator CMOS compatible Microdisk with wedge-shaped edge Top Optical image Side SEM image modes are far from the periphery Mode intensity profiles Very low loses Modes are isolated from the surface roughness New Q factor benchmark on a chip Q 9 10 8 using very large resonators >5 mm [millimeter]* Difficult to access to microtoroids Fabrication process By Surface oxidation and wet etch How can we couple with? (*)H. Lee et al, nature photonics (2012)

Conventional lateral coupling Sketch of horizontal coupling scheme Mode profile sketch The coupling principle is by Side evanescent SEM image field The coupling rate decays exponentially with the gap For an accurate gap control a single mask is used

Conventional lateral coupling Coupling becomes inefficient as the wedge mode is retracted In a realistic fabrication, the waveguide retracts forming a wedge shape (quenching the coupling) Side SEM image Finally an off-chip technique is used (with tapered fiber) The same difficult and complex experimental optical setup

Our proposal: Vertical coupling scheme The cavity and the waveguide: Lay in different planes resonator Mode profile sketch waveguide Could be separated by low refractive index solid materials or air Are fabricated independently with different masks This process permits to realize the shallow-angle wedge while the waveguide remains intact Allows to adjust the coupling distance in the horizontal and vertical direction An efficient coupling condition for wedge resonators could be reached

Our proposal: Vertical coupling scheme Additional advantages Vertical coupling vs. Horizontal coupling The 2-mask process allows to use different materials for the waveguide and the resonator A 1-mask process imposes the same material for both the waveguide and the resonator The coupling gap is defined and controlled through deposition, by means of conventional optical Lithography The coupling gap is defined through E-beam or deep-uv Lithography

On-chip wedge WGM resonator Vertically waveguide coupled Wedge resonator Top optical image bird's-eye-view SEM image Calculated Mode intensity profiles 1 st radial family 2 nd radial family SiNx wedge resonator Buried waveguide BPSG Cladding Different shape of the Different borders position of the mode profiles Comparison with conventional disk resonators Top optical image bird's-eye-view SEM image

Transmission spectrum Narrow dips 1 st radial mode family Broad dips 2 nd radial mode family Wedge resonator (radial mode number, the azimutal mode number) It possible to select the radial mode family by means of changing the horizontal position of the waveguide. The first mode family shows less transmission it s coupled more efficiently We have selected the 1 st radial mode family because it shows higher Q s

Q factor analysis Q-factor could be extracted from the lorentzian fit of the transmission spectrum dips Q» l(n, m) FWHM FOR THE WEDGE RESONATOR The mode is split into a doublet because of the scattering-induced coupling between clockwise and counter-clockwise modes FOR THE DISK RESONATOR The coherent sum of lorenzians hides the splitting of the modes wedge resonator shows 5 times larger Q-value due to the reduced scattering losses

Free standing resonator

More complex structures

SEQUENCE OF RING RESONATORS

SCISSOR: theoretical Side-Coupled Integrated Spaced Sequence of Resonators Drop Port Box-like response suitable for coarse WDM and band routing Large extinction

Two resonance mechanisms Ring-like and Bragg-like RB: BB: mλr = neff 2πr λb n = neff 2 L

Through port transmission spectra Ring+Bragg overlapping Bragg Ring

Unexpected resonances... Q: 10 4-10 5 Peaks spacing: 25 GHz

Localized states

Where do they come from? E1 T m 2 n R L R E2 Coupled Resonator Induced Trasparency L CRIT Qs are orders of magnitudes greater than single cavities Qs!! (10 5 vs 10 3 ) π λ

Paired rings as a bulding block R R+ΔR + R R+ΔR + R R+ΔR R+2ΔR R+3ΔR R+4ΔR It is possible to build a tapered SCISSOR that allows to control multiple CRIT

Tapered SCISSOR

experiments

Intensity (db) De-multiplexer: comparison 10 nm 1) R 1 R 2 R 3 R 4 0 2 nm -10 2) -20-30 -40 M. Mancinelli, et al. Optics Express 19, 1222712240 (2011) -50 1542 1543 1544 1545 1546 1547 Wavelenght (nm)

Intensity (db) Structure realized: Mux/Demux, First experimental proof of this design! 7 racetrack based SCISSOR with radius of 3.25 μm Channels bandwidth: 6-7 GHz (Q 20000/30000) Good balance between channels Crosstalk < 10 db Channel losses: 7-8 db 0-5 Experimental data TM simulation 0-5 -10-10 -15-15 -20-20 -25-25 -30 1510 1515 1520 1525 1530 Wavelength (nm) -30 1510 1515 1520 1525 1530 Wavelength (nm)

Outline Silicon Photonics NanoSilicon photonics Silicon Nanophotonics NanoSilicon Nanophotonics Conclusion

Active microdisks Low dimensional Si (Si nanoclusters) Whispering gallery mode microdisk-cavity: 2 22/11/2012 64/35

Introduction active WGM

~200 - upper limit on cavity Q

Outline Silicon Photonics NanoSilicon photonics Silicon Nanophotonics NanoSilicon Nanophotonics Conclusion

Conclusions nanosilicon photonics is a viable platform to improve-enable-widen the scope of silicon photonics A lot of new physics can be found in an already mature research field such as Silicon Photonics

Acknowledgments