Metodi di fabbricazione PhC

Transcription

1 Metodi di fabbricazione PhC

2 PhC in 1D a n 1 n 2 z Deposizione multilayer (MBE,MOCVD,PVD,CVD) Silicio poroso Litografia

3 Crescita per deposizione Physical deposition Chemical deposition InP by MOCVD

4 Deposizione controllata MBE

5 Heterointerfaces AlAs AlAs

6 Per la fotonica bastano precisioni inferiori Thermal evaporation Sputtering, PVD CVD

7 Silicio poroso Etching elettrochimico controllato

8 Disordered porous silicon n eff = n Si V V Si Si + n + V Air Air V Air

9 Multilayers

10 Litografia

11 Litografia La geometria delle strutture può essere disegnata a piacere

12 PhC in 2D a n 1 n 2 y x Silicio poroso Litografia

13 2 configurazioni fori colonne

14 Silicio macroporoso ordinato

15 Litografia

16 PhC in 3D a n 1 n 2 Self assembly Litography Direct laser writing Micromanipulation Olographic litography

17 (evaporate) Self assembly of Colloids silica (SiO 2 ) microspheres (diameter < 1µm) sediment by gravity into close-packed fcc lattice! silica (SiO 2 ) CdS/ZnO

18 In Order To Form a More Perfect Crystal [ figs courtesy D. Norris, UMN ] 65C meniscus silica 1 micron 250nm silica spheres in ethanol evaporate solvent 80C Convective Assembly [ Nagayama, Velev, et al., Nature (1993) Colvin et al., Chem. Mater. (1999) ] Heat Source Capillary forces during drying cause assembly in the meniscus Extremely flat, large-area opals of controllable thickness

19 Massive PhC

20 Inverse Opals [ figs courtesy D. Norris, UMN ] fcc solid spheres do not have a gap sub-micron colloidal spheres but fcc spherical holes in Si do have a gap 3D Template (synthetic opal) Infiltration complete band gap Remove Template Inverted Opal ~ 10% gap between 8th & 9th bands small gap, upper bands: sensitive to disorder

21 Inverse-Opal Photonic Crystal [ fig courtesy D. Norris, UMN ] [ Y. A. Vlasov et al., Nature 414, 289 (2001). ]

22 Layer-by-Layer Lithography Fabrication of 2d patterns in Si or GaAs is very advanced (think: Pentium IV, 50 million transistors) inter-layer alignment techniques are only slightly more exotic So, make 3d structure one layer at a time Need a 3d crystal with constant cross-section layers

23 A Layered Structure We ve Seen Already (diamond-like: rods ~ bonds ) C rod layer A B hole layer [ S. G. Johnson et al., Appl. Phys. Lett. 77, 3490 (2000) ] Up to ~ 27% gap for Si/air

24 Making Rods & Holes Simultaneously side view substrate Si top view

25 Making Rods & Holes Simultaneously expose/etch holes substrate A A A A A A A A A

26 Making Rods & Holes Simultaneously backfill with silica (SiO 2 ) & polish substrate A A A A A A A A A

27 Making Rods & Holes Simultaneously deposit another Si layer layer 1 substrate A A A A A A A A A

28 Making Rods & Holes Simultaneously dig more holes offset & overlapping layer 1 B B B B substrate B B B B B B B A A A B B B B B B B A A A B B B B B B B A A A

29 Making Rods & Holes Simultaneously backfill layer 1 B B B B substrate B B B B B B B A A A B B B B B B B A A A B B B B B B B A A A

30 Making Rods & Holes Simultaneously etcetera (dissolve silica when done) layer 1 layer 2 substrate layer 3 C C C C B B B B one period C B C B C B C B C A B C A B C A B C C B C B C B C B C A B C A B C A B C C A B C A B C A B C A B C B C B C B C A A A

31 Making Rods & Holes Simultaneously etcetera layer 2 layer 3 C C C C one period layer 1 B B B B hole layers substrate C B C B C B C B C A B C A B C A B C C B C B C B C B C A B C A B C A B C C A B C A B C A B C A B C B C B C B C A A A

32 Making Rods & Holes Simultaneously etcetera layer 2 layer 3 C C C C one period layer 1 B B B B rod layers substrate C B C B C B C B C A B C A B C A B C C B C B C B C B C A B C A B C A B C C A B C A B C A B C A B C B C B C B C A A A

33 A More Realistic Schematic [ M. Qi, H. Smith, MIT ]

34 e-beam Fabrication: Top View 5 µm [ M. Qi, H. Smith, MIT ]

35 Stacking by Micromanipulation [ K. Aoki et al., Appl. Phys. Lett. 81 (17), 3122 (2002) ] microsphere into hole break off suspended layer lift up and move to substrate tap down holes onto spheres spheres enforce alignment goto a;

36 Stacking by Micromanipulation [ K. Aoki et al., Appl. Phys. Lett. 81 (17), 3122 (2002) ] 20 layers 50nm accuracy: 1µm

37 Stacking by Micromanipulation an earlier design: (& currently more popular) The Woodpile Crystal [ K. Ho et al., Solid State Comm. 89, 413 (1994) ] [ H. S. Sözüer et al., J. Mod. Opt. 41, 231 (1994) ] (diamond-like, bonds ) Up to ~ 17% gap for Si/air [ Figures from S. Y. Lin et al., Nature 394, 251 (1998) ]

38 Woodpile by Wafer Fusion 2nd substrate + logs, rotated 90 and flipped substrate + first log layer [ S. Noda et al., Science 289, 604 (2000) ]

39 Woodpile by Wafer Fusion fuse wafers together substrate + first log layer [ S. Noda et al., Science 289, 604 (2000) ]

40 Woodpile by Wafer Fusion dissolve upper substrate substrate + first log layer [ S. Noda et al., Science 289, 604 (2000) ]

41 Woodpile by Wafer Fusion double, double, toil and trouble [ S. Noda et al., Science 289, 604 (2000) ]

42 1.25 Periods of Woodpile (4 log layers = 1 period) [ S. Y. Lin et al., Nature 394, 251 (1998) ] Si gap UV Stepper: e-beam mask at ~4x size + UV through mask, focused on substrate Good: high resolution, mass production Bad: expensive ($20 million)

43 Direct laser writing (two photon) ANCHE AL LENS 2 2-photon probability ~ (light intensity) 2 hν = E e E 0 hν hν N-photon probability ~ (light intensity) N photon photon 3d Lithography Atom lens dissolve unchanged stuff (or vice versa) some chemistry (polymerization)

44 2µm

45 A Two-Photon Woodpile Crystal [ B. H. Cumpston et al., Nature 398, 51 (1999) ] (much work on materials with lower power 2-photon process) Arbitrary lattice No mask Fast/cheap prototyping Difficult topologies [ fig. courtesy J. W. Perry, U. Arizona ]

46 One-Photon Holographic Lithography [ D. N. Sharp et al., Opt. Quant. Elec. 34, 3 (2002) ] Four beams make 3d-periodic interference pattern k-vector differences give reciprocal lattice vectors (i.e. periodicity) absorptive material (1.4µm) beam polarizations + amplitudes (8 parameters) give unit cell

47 One-Photon Holographic Lithography [ D. N. Sharp et al., Opt. Quant. Elec. 34, 3 (2002) ] 10µm huge volumes, long-range periodic, fcc lattice backfill for high contrast

48 One-Photon Holographic Lithography [ D. N. Sharp et al., Opt. Quant. Elec. 34, 3 (2002) ] [111] cleavages simulated structure 5µm [111] closeup 1µm 1µm titania inverse structure

49 PhC in 2.5D a a,d λ d n 1 n 2 y x Litografia + selective etching

50 GaAs AlGaAs

51 Individual sphere Altri design per confinamento quasi 3D Whispering gallery modes