2572-11 Winter College on Optics: Fundamentals of Photonics - Theory, Devices and Applications 10 - 21 February 2014 Silicon photonics: Waveguide modulators and detectors Laurent Vivien Institut dElectronique Fondamentale CNRS UMR 8622 Université Paris Sud, 91405 Orsay Cedex France Silicon Photonics Silicon-based micro and nanophotonic devices Silicon photonics: Waveguide modulators and detectors Laurent Vivien Institut d’Electronique Fondamentale, CNRS UMR 8622, Université Paris Sud, 91405 Orsay Cedex, France http://silicon-photonics.ief.u-psud.fr/ http://silicon-photonics.ief.u-psud.fr/ 1 Silicon Photonics Silicon-based micro and nanophotonic devices Silicon photonics: Waveguide modulators and detectors L. Vivien, D. Marris-Morini, G. Rasigade, L. Virot, M. Ziebell, D. Perez-Galacho, P. Chaisakul, M-S. Rouifed, P. Crozat, P. Damas, E. Cassan D. Bouville, S. Edmond, X. Le Roux Institut d’Electronique Fondamentale, CNRS UMR 8622, Université Paris Sud, 91405 Orsay Cedex, France http://silicon-photonics.ief.u-psud.fr/ J-M. Fédéli, S, Olivier, Jean Michel Hartmann CEA-LETI, Minatec 17 rue des Martyrs, 38054 Grenoble cedex 9, France G. Isella, D. Chrastina, J. Frigerio L-NESS, Politecnico di Milano, Polo di Como, Via Anzani 42, I-22100 Como, Italy C. Baudot, F. Boeuf STMicroelectronics, Silicon Technology Development, Crolles, France http://silicon-photonics.ief.u-psud.fr/ 2 The Institute for Fundamental Electronics IEF is a joint research unit between CNRS and University of Paris Sud 135 CNRS researchers, professors and lecturers, technical staff +100 PhD students, Post-Doc and visitors ~ 400 students undergoing training within IEF's ground Spintronics and Si-based Nano-electronics Micro-Nano systems and systems Photonics University Technology Center (CTU) MINERVE http://silicon-photonics.ief.u-psud.fr/ 3 Laurent Vivien University Technology Center IEF-MINERVE member of The French Network on “Basic Technological Research” (RTB) University Technology Centre (1000 m²): Photolithography: 2-sided UV lithography with wafer bonding Deep UV lithography (248 nm) 2 e-beams (Raith150 and 100keV nanobeam) Laser Etching: Wet etching (KOH, TMAH, …) Dry etching : fluoride gases RIE (2 systems) ICP Si deep etching IBE 02 plasma etching Chloride gases RIE … http://silicon-photonics.ief.u-psud.fr/ 4 Laurent Vivien Silicon photonics group 4 permanent Researchers 2 engineers, technicians 16 PhD students 2 post-doc 2-4 master students / year Passive devices CEA / LETI Strained Si photonics Grating couplers Pockels effect Waveguides Splitters Optical Distribution Multi-wavelength circuits Ge detectors Photonic crystals Ge-SiGe QW photonics Surface illuminated Optical modulators Slow light Source Integrated All silicon Superprism Modulator NL materials APD NL enhancement detector Ge QW Plasmon CEA / LETI Bottom contact Top contact Ge 3 µm 40 GBit/s Carbon nanotubes for photonics 300 nm http://silicon-photonics.ief.u-psud.fr/ 5 Laurent Vivien Outline Motivation (Pavel’s and Lorenzo’s talks) Photodetectors on silicon Main characteristics Results Optical modulators Figures of Merit Modulation in silicon Results Conclusion http://silicon-photonics.ief.u-psud.fr/ 6 Laurent Vivien FTTH Optical telecommunications Environment Data centers Silicon photonics Chemical/Biological sensors Interconnects Free space communications Military Silicon photonic building blocks Off‐chip III‐V laser On‐chip III‐V laser on Si photodetector RF electrodes Optical coupler Input waveguide Germanium‐based laser 10 µm Emitter Receiver Laser Modulator Detector Modulator http://silicon-photonics.ief.u-psud.fr/ 8 Laurent Vivien Photodetection http://silicon-photonics.ief.u-psud.fr/ 9 Laurent Vivien Basic principle Main characteristic of the material? h e- h+ - h+ e -+ http://silicon-photonics.ief.u-psud.fr/ 10 Laurent Vivien Basic principle The aborption of photons generates electron-hole pairs Photogenerated carriers are then collected thanks to an external field Photocurrent h e- h+ - h+ e -+ http://silicon-photonics.ief.u-psud.fr/ 11 Laurent Vivien Absorption mechanisms (II) Direct gap SC (III-V SC) Indirect gap SC (IV-IV SC) E k Phonon emission h Phonon absorption k absorbed photons generate free electron-hole pairs EG=hc/G G G http://silicon-photonics.ief.u-psud.fr/ 12 Laurent Vivien Material choice Wavelength ranges: 1.3 µm – 1.6 µm 0.85 µm Direct bandgap http://silicon-photonics.ief.u-psud.fr/ 13 Laurent Vivien Material choice Wavelength ranges: 1.3 µm – 1.6 µm 0.85 µm Indirect bandgap http://silicon-photonics.ief.u-psud.fr/ 14 Laurent Vivien Material choice Wavelength ranges: 1.3 µm – 1.6 µm 0.85 µm Two choices: InGaAs or Ge Indirect bandgap Direct gap absorption http://silicon-photonics.ief.u-psud.fr/ 15 Laurent Vivien Material choice InGaAs versus Germanium What is the best material for light detection in near-IR wavelength range ? http://silicon-photonics.ief.u-psud.fr/ 16 Laurent Vivien Material choice versus electronic photonic integration scheme •Use of standard FE CMOS technologies Photonic layer at the 1) Wafer bonding of •High integration density last levels of PIC (high T°C) (AboveIC) metallizations •Multilevel process with back-end 2) BE fab(<400°C) capability fabrication •Specific FE CMOS technology and library Combined •Flip-Chip hybridization of InP components front-end fabrication •Moderate integration density •Efficient connections of EIC and PIC 1) Wafer bonding of •Through substrate Backside PIC (high T°C) fabrication connections •High integration density BE: Back end FE:Front end 2) BE fab(<400°C) http://silicon-photonics.ief.u-psud.fr/ 17 Laurent Vivien Material choice versus integration scheme Ge or Photonic InGaAs layer at the 1) Wafer bonding of last levels of PIC (high T°C) metallizations with back-end 2) BE fab(<400°C) fabrication InGaAs Combined front-end Ge fabrication Ge or 1) Wafer bonding of InGaAs Backside PIC (high T°C) fabrication BE: Back end FE:Front end 2) BE fab(<400°C) InGaAs http://silicon-photonics.ief.u-psud.fr/ 18 Laurent Vivien Are III-V materials integrated in silicon platform? Monolithic integration via epitaxial growth No viable solutions yet Hybrid integration BCB or molecular bonding http://silicon-photonics.ief.u-psud.fr/ 19 Laurent Vivien Exemple of hybrid integration 1. Sample preparation 2. Sample cleaning + removal of cap layer 3. BCB bonding and curing 4. InP substrate removal 5. Removal of sacrificial layers 6. Detector mesa etching III-V materials can be integrated on silicon 7. BCB insulation What about wafer size and technology? 8. Opening of the contact windows 9. Metallization 10. Post-processing http://silicon-photonics.ief.u-psud.fr/ 20 Laurent Vivien Germanium on silicon: Pros and Cons Absorption coefficient of pure Ge: 9000 cm-1 at =1.3µm 95% LABS 3.3µm (!) Low capacitance devices High frequency operation High carrier mobility http://silicon-photonics.ief.u-psud.fr/ 21 Laurent Vivien Crystal lattice structure of Silicon and Germanium Si and Ge have a diamond lattice structure (two interdigitated FCC lattices) Properties Silicon Germanium Lattice parameter: 5.431 5.658 a (Å) Atomic density (cm-3) 5,0.1022 4,42.1022 Atom radius (Å) 0.117 0,122 Lattice structure Diamond Diamond Lattice parameter mismatch: ~4.2 % http://silicon-photonics.ief.u-psud.fr/ 22 Laurent Vivien Germanium on silicon: Pros and Cons Absorption coefficient of pure Ge: Lattice misfit with Si of about 4.2% 9000 cm-1 at =1.3µm specific growth strategies 95% LABS 3.3µm (!) required (wafer-scale and Low capacitance devices localized) High frequency operation Low indirect bandgap: EG=0.66eV High carrier mobility high dark current for MSM devices Can we directly growth Ge on silicon? http://silicon-photonics.ief.u-psud.fr/ 23 Laurent Vivien The lattice mismatch 4.2% of lattice mismatch between germanium and silicon Ge quantum dots QD, QW or Bulk ? Si1-xGex/Si quantum wells Pure Ge on Si SiGe on Si http://silicon-photonics.ief.u-psud.fr/ Laurent Vivien Ge-based structures Ge quantum dots ~20cm-1 (90% absorption length ~ 1.1mm) Si1-xGex/Si quantum wells ~100-200cm-1 (90% absorption length ~ 230-110µm) Pure Ge on Si ~7500cm-1 (90% absorption length ~ 3µm) http://silicon-photonics.ief.u-psud.fr/ Laurent Vivien Ge growth strategies Thick virtual SiGe substrates (10µm) Need for a new integration scheme – difficult to integrate with SOI waveguides. Ge SiGe buffer graded from Si to Ge Si(100) http://silicon-photonics.ief.u-psud.fr/ 26 Laurent Vivien Ge growth strategies Thick virtual SiGe substrates (10µm) Need for a new integration scheme – difficult to integrate with SOI waveguides. Growth on thin SiGe buffers The thickness of the thin SiGe buffer is around 1µm Always too thick for integration with SOI Ge SiGe buffer graded from Si to Ge Si(100) http://silicon-photonics.ief.u-psud.fr/ 27 Laurent Vivien Ge growth strategies Thick virtual SiGe substrates (10µm) Need for a new integration scheme – difficult to integrate with SOI waveguides. Growth on thin SiGe buffers The thickness of the thin SiGe buffer is around 1µm Always too thick for integration with SOI Direct Ge growth on Si Ge Si(100) http://silicon-photonics.ief.u-psud.fr/ 28 Laurent Vivien Germanium growth Two-step growth process: Direct growth of Ge on Si using a low temperature (350°) CVD process thin (a few 10nm) highly-dislocated Ge layer Growth of a thick Ge layer (a few 100nm) at a higher temperature (600°) high quality Ge absorbing layer Thermal annealing to reduce the dislocation density HT Ge (600°C,