Silicon Photonics University of Pune Physics Short Course

Transcription

1 Silicon Photonics University of Pune Physics Short Course August 11-13, 16, 17, 2010 India-U.S. Professorship Award Lectures S.Saini (Queens College), J. Michel (MIT) 2010 Sub-Micron Planar Platform - E-P Convergence - Materials Integration Device Physics - Materials Science Sajan Saini Queens College City University of New York Sponsored by: The Indo-U.S. Science & Technology Forum and The American Physical Society

2 Lecture 1: Introduction to Si Photonics Lecture 2: Waveguides & Mode-Engineered Devices Lecture 3: Resonators & Photodetectors Lecture 4: Modulators & Lasers Lecture 5: Photonics in 3 rd Gen. Photovoltaics Electronic-Photonic Integration Confinement Physics Scatering mechanisms, Si-compatible waveguides Turns, splitters, rotators, couplers WDM & standing/traveling wave cavities Si vs. Ge detectors Plasma dispersion & electroabsorption modulators III integrated lasers, ultra-high Q, Ge laser The case for a solar economy 3rd Gen. PV materials & devices 62

3 Passive Photonics: Wavelength Division Multiplexing Dense WDM function Si-compatible, compact footprint T. Barwicz et al., Optics Express v.12(7), (2004). Microrings, racetracks, slot rings Higher-order filters, embedded rings Polarization effects GHz-precision trimming

4 1st-Order Ring & Racetrack Microring Filters Drop 6 μm Si Silicon Si 3 N 4 In Drop Port Power (Arb Units) 6 μm Lithography: 248nm Q ~ 2000, FSR~16 nm 5 μm ring FSR=18nm Q= μm Ring FSR=21nm; Q= Wavelength (nm) 2μm Ring FSR=48.6nm; Q=1050 Thru-port m n = 2r m = 1,2,... Q~500 D. R. Lim, B. E. Little, K. K. Lee, M. Morse, H. H. Fujimoto, H. A. Haus, and L. C. Kimerling, Micron-sized channel dropping filters using silicon waveguide devices, Proc. SPIE, 3847, pp (1999). eff Power -- same scale (au) Thru-port 1x4 WDM (silicon nitride Rings) Wavelength (nm) Port1 Port2 Port3 Port4 Thru 64

5 >2nd Order Rings Resonance Frequency Central ring: different coupling coefficient different resonant frequency Compensated ring design (wider waveguide) ensures common resonance frequency flatband response B.E. Little et al., IEEE Photon. Technol. Lett. 16, 2263 (Oct 2004) e-beam lithography M.A. Popovi, T. Barwicz, M.R. Watts, P.T. Rakich, L. Socci, E.P. Ippen, F.X. Kärtner and H.I. Smith, Multistage high-order microring-resonator add-drop filters, Opt. Lett., vol. 31, no. 17, pp , September M.A. Popovi, M.R. Watts, T. Barwicz, P.T. Rakich, L. Socci, E.P. Ippen, F.X. Kärtner and H.I. Smith, Highindex-contrast, wide-fsr microring-resonator filter design and realization with frequency-shift compensation, in Optical Fiber Communication Conference (OFC/NFOEC) Technical Digest (Optical Society of America, Washington, DC, March 6-11, 2005), paper OFK1, vol. 5, pp

6 >2nd Order Rings Mode Conversion Loss Insertion loss from bus to racetrack resonator for high-n waveguides Key clue: gap < 100 nm to ensure coupling for single mode wavegudie Formation of extended slot waveguide mode: reflection mismatch Incident power reflects in bus Standing wave forms within bus, along length of racetrack Loss (db/cm) Gap (nm) 35±4 117±5 50±5 103±5 68±7 87±5 151±20 0 F. Xia, L. Sekaric, Y.A. Vlasov, Mode conversion losses in silicon-on-insulator photonic wire based racetrack resonators, Opt. Exp. v.14(9), p.3872 (2006). 66

7 Polarization Independent Add-Drop Filter Performance ~ 2.5 db drop-loss ~ 50 GHz bandwidth > 35 db in-band extinction < 1 db polarization-dependent loss (PDL) Excellent spectral alignment of the 6 stages T. Barwicz, M.R. Wat, <.A. Popovic, P.T. Rakich, L. Socci, F.X. Kartner, E.P. Ippen and H.I. Smith, Polarization-transparent microphotonic devices in the strong confinement limit, Nature Phot., v.1, pp (2007). 67

8 GHz-Trimming of a Ring Resonator SiO 2 Undercladding Single Mode Si 3 N 4 Waveguides Polysilane Top Cladding Drop Port P~1 μw within ~(100 nm) 2 waveguide -section: ~10 kw/cm 2 negligible increase in T Waveguide integrated onto IC chip: T~100 C Thermal expansion (dv/dt) ~ 0.05% (negligible) Thermo-optic shift in refrac. index (dn/dt): n eff /n eff ~5% Input 100 μm Through Port Lithography -section error/variation (~25 nm): n eff /n eff ~5% n/n ~ 5% variation: GHz-shift in WDM add/drop Need novel cladding for athermal Si waveguides Require option for post-process GHz-tuning: trimming Top Cladding Removed for Illustration Silicon 4 x10-4 K-1 SiO 2, SiON, Si 3 N 4 ~ 10-5 K -1 Polymers Polysilane cladding Thermo-optic Coeff. -1x10-4 to -4x10-4 K -1 n/n ~ 4% change in refractive index with photo-oxidation UV: sensitive to < 300 nm Loss (db) FSR UV Exposure 300 s UV Exposure 420 s Wavelength (nm) 25 Absolute Resonance Shift (nm) TE experimental data TM experimental data UV Flux (μj/cm 2 ) D.K. Sparacin, C.Y. Hong, L.C. Kimerling, J. Michel, J.P. Lock and K. Gleason, Trimming of microring resonators by photo-oxidation of a plasma-polymerized Organosilane cladding material, Opt. Lett., v.30(17), pp (2005). 68

9 Active Photonics: Photodetectors G. Dehlinger et al., IEEE Phot. Tech. Lett.,v.16(11), (2004). Broadband, highly efficiency IR detector Low voltage operation Si processing, integrated into CMOS process flow Integration with ICs Graded buffer Ge-on-Si GeOI, Ge-Directly-on-Si Waveguide-detector integration Si detectors

10 Photodetector Basics (μm) From: Sze, Physics of Semiconductor Devices 70

11 Ge Graded Buffer Detector Low dislocation density (~10 6 cm -1 ) Low voltage operation Low dark current Responsivity of 0.13A/W Samavedam, et al. S.B. Samavedam, M.T. Currie, T.A. Langdo, E.A. Fitzgerald, Applied Physics Letters, v 73, p 2125 (1998) 71

12 Ge-directly-on-Si Photodetector 2-step UHV-CVD + cyclic thermal annealing C cyclic anneal 10 TDD: cm cm -2 increases hole mobility H.C. Luan, D.R. Lim, K.K. Lee, K.M. Chen, J.G. Sandland, K. Wada and L.C. Kimerling, APL, v.75(19), pp (1999). L. Colace, G. Masini, G. Assanto, H.C. Luan, K. Wada and L.C. Kimerling, APL, v.76(10), pp (2000). G. Masini, L. Colace, G. Assanto, H.C. Luan and L.C. Kimerling, IEEE Trans. Electron Devices, v.48(6), pp (2001). J. Liu, J. Michel, W. Giziewicz, D. Pan, K. Wada, D. D. Cannon, S. Jongthammanurak, D. T. Danielson, L. C. Kimerling, J. Chen, F. O. Ilday, F. X. Kartner, and J. Yasaitis, Appl. Phys. Lett. 87, (2005). 72

13 GeOI Photodetector Ge Narrow bandgap: strong IR absorption = db/cm (=850 nm); 70 Si = db/cm (=1330 nm) 3 faster electron/hole mobility than Si Ge-on-bulk Si limits bandwidth carrier absorption in Si 400 nm Ge absorp. layer on thinned (15nm) SOI μm p-i-n diodes Area=1010μm 2, finger spacing=0.4 μm 3-dB bandwidth: 29 V bias =-1 V =0.34 Narrow bandgap dislocations on Si I dark =0.02 V bias =-1 V G. Dehlinger, S.J. Koester, J.D. Schaub, J.O. Chu, Q.C. Ouyang and A. Grill, High-Speed Germanium-on-SOI Lateral PIN Photodiodes, IEEE Phot. Tech. Lett., v.16(11), pp (2004). 73

14 Waveguide - Photodetector Integration Performance Gain (Bandwidth) x (Quantum efficiency) (GHz) μm20μm Q.E: 90% Transit time limit d=0.5μm Waveguide-integrated Photodetector RC time limit Detector Size (μm 2 ) Discrete, free-space Photodetectors d=2.0μm D. Ahn, J.F. Liu, MIT 74

15 Ge-directly-on-Si Photodetector Waveguide Integration vertical coupler butt coupler Si Ge n+ region oxide Poly-Si Ge in SiGe p+ region out Si (P+) 7.3GHz bandwidth at -0.5V bias Dark current: 60nA at 0.1V D. Ahn, C.-Y. Hong, J. Liu, W. Giziewicz, M. Beals, L. C. Kimerling, J. Michel, J. Chen, and F. X. Kärtner, Optics Express 15, 3916 (2007) 1 A/W responsivity >4 GHz bandwidth Dark current: 0.13nA at 0.1V J. F. Liu, et al., 2006 OVC International Symposium on Optoelectronics (IEEE Cat. No. 06EX1626), 2006, p

16 Ge-directly-on-Si Photodetector Waveguide Integration Parameter Speed (GHz) Dark Current Typical value > 20 Gb/s 2 μa 31 GHz bandwidth at -2.0V bias T. Yin, R. Cohen, M. M. Morse, G. Sarid, Y. Chetrit, D. Rubin, and M. J. Paniccia; Opt. Express 15, (2007) Responsivity Device Size 0.85 A/W 20 μm 2 G. Masini, G. Capellini, J. Witzens, C. Gunn, th IEEE International Conference on Group IV Photonics, Sept

17 Si Photodetectors at =850 nm Si: poor absorption at =850 nm resonant design low spectral range: poor WDM design lateral deep trench design high speed & high responsivity low capacitance lower I dark, lower V bias to reach max. 3-dB bandwidth Performance 1.5 GHz 6-dB bandwidth 2.5 V bias =-3.3 V J.D. Schaub, S.J. Koester, G. Dehlinger, Q.C. Ouyang, D. Guckenberger, M. Yang, D. Rogers, J. Chu and A. Grill, High-speed, lateral PIN photodiodes in silicon technologies, Semiconductor Photodetectors, Proc. SPIE v.5353, pp.1-11 (2004). M. Yang, K. Rim, D.L. Rogers, J.D. Schaub, J.J. Welser, D. M. Kuchta, D.C. Boyd, F. Rodier, P.A. Rabidoux, J.T. Marsh, A.D. Ticknor, Q. Yang, A. Upham and S.C. Ramac, A High-Speed, High-Sensitivity Silicon Lateral Trench Photodetector, IEEE Electron Device Lett., v.23(7), pp (2002). 77

18 Si Detector for near IR Si waveguide (SOI) Si implantation created stable defects Absorption coefficient in near IR increased 100x High bias voltage required 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, CMOS-compatible, all-si, high-speed, waveguide photodiodes with high responsivity in near-infrared communication band, IEEE Photonics Technology Letters, 19, Feb. 2007, p