complex, 3d photonic crystals fabricated by atomic layer ...atomic layer deposition ald is a cvd...

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Complex, 3D Photonic Crystals Fabricated by Atomic Layer Deposition J. S. King, D. Gaillot, T. Yamashita, C. Neff, E. Graugnard, and C. J. Summers School of Materials Science and Engineering Georgia Institute of Technology, Atlanta, GA MRS Fall Meeting December 3, 2004 Boston, Massachusetts

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Page 1: Complex, 3D Photonic Crystals Fabricated by Atomic Layer ...Atomic Layer Deposition ALD is a CVD growth technique utilizing sequential reactant pulses. Zn2+ S2-H+ Cl-ALD Growth of

Complex, 3D Photonic Crystals Fabricated by Atomic Layer Deposition

J. S. King, D. Gaillot, T. Yamashita, C. Neff, E. Graugnard, and C. J. Summers

School of Materials Science and EngineeringGeorgia Institute of Technology, Atlanta, GA

MRS Fall MeetingDecember 3, 2004

Boston, Massachusetts

Page 2: Complex, 3D Photonic Crystals Fabricated by Atomic Layer ...Atomic Layer Deposition ALD is a CVD growth technique utilizing sequential reactant pulses. Zn2+ S2-H+ Cl-ALD Growth of

Outline

• Research Aims• Photonic crystals and challenges• Advanced photonic crystal architectures• Results

• ZnS/TiO2 multi-layered structure• Presinter non-close-packed inverse opal

• Summary

Page 3: Complex, 3D Photonic Crystals Fabricated by Atomic Layer ...Atomic Layer Deposition ALD is a CVD growth technique utilizing sequential reactant pulses. Zn2+ S2-H+ Cl-ALD Growth of

Research Aims

• Development of 3-D photonic crystals through a combination of templating and atomic layer deposition (ALD).

• Advanced architectures: – multi-layered inverse opals– non-close-packed inverse opals

• Increase functionality: luminescent and high index• Enhance properties: wider band gaps, decreased

minimum refractive index requirements

Page 4: Complex, 3D Photonic Crystals Fabricated by Atomic Layer ...Atomic Layer Deposition ALD is a CVD growth technique utilizing sequential reactant pulses. Zn2+ S2-H+ Cl-ALD Growth of

Photonic Crystals

• Photonic Crystal (PC)– Periodic modulation of dielectric constant (refractive index).

• Photonic band gap (PBG) formation• For visible wavelengths, periodicity on order of 200 – 500 nm.• Require high contrast in refractive index (n)• Lattice structure and basis impacts properties.

3D photonic crystal1D photonic crystal 2D photonic crystal

Page 5: Complex, 3D Photonic Crystals Fabricated by Atomic Layer ...Atomic Layer Deposition ALD is a CVD growth technique utilizing sequential reactant pulses. Zn2+ S2-H+ Cl-ALD Growth of

Photonic Crystals: Applications

• Light guiding•Waveguides, resonators, couplers, filters, self-collimation, giant refraction and superprism effects, slow light applications

• Light emission control• Microcavities, photonic crystal phosphors and low threshold lasers

Page 6: Complex, 3D Photonic Crystals Fabricated by Atomic Layer ...Atomic Layer Deposition ALD is a CVD growth technique utilizing sequential reactant pulses. Zn2+ S2-H+ Cl-ALD Growth of

Photonic CrystalsInverse Opals

U

• Reflectance measurements probe photonic band structure: PBG, P-PBG

Silicon Inverse Opal Photonic Band Diagram

n=3.5

PBG

P-PBGs

(111)

Page 7: Complex, 3D Photonic Crystals Fabricated by Atomic Layer ...Atomic Layer Deposition ALD is a CVD growth technique utilizing sequential reactant pulses. Zn2+ S2-H+ Cl-ALD Growth of

Fabrication: Inverse Opal PC

• Provide template using self-assembled silica opal.– 10 µm thick FCC polycrystalline film, (111) oriented.

• Infiltrate interstitial space with high n material.

• Etch SiO2 spheres, forming inverse opal.

Inf. EtchSelf Assembly

Sintered Opal TiO2 Inverse OpalTiO2 Infiltrated OpalKing, et. al. Adv. Mat. (in press)

Page 8: Complex, 3D Photonic Crystals Fabricated by Atomic Layer ...Atomic Layer Deposition ALD is a CVD growth technique utilizing sequential reactant pulses. Zn2+ S2-H+ Cl-ALD Growth of

Inverse Opal Challenges

• High index contrast for complete gap to exist (> 2.8)• For emissive applications: luminescent materials with

low absorption in visible and sufficient index unavailable.

• Two solutions:– Multi-layered inverse opals (luminescent + high n) – Non-close-packed inverse opals* (widen PBG,

decrease index requirements)

* Doosje, et. al. (2000)

Page 9: Complex, 3D Photonic Crystals Fabricated by Atomic Layer ...Atomic Layer Deposition ALD is a CVD growth technique utilizing sequential reactant pulses. Zn2+ S2-H+ Cl-ALD Growth of

Multilayer: Design Considerations

• Combination of two materials offers practical route

• ZnS:Mn (luminescent) + TiO2 (high n) “composite” PC.

• At 400 nm, ZnS/anatase TiO2 PC: full PBG if XZnS < 26%.

350 400 450 500 550 600

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3.0

10% TiO2

Ref

ract

ive

Inde

x

Wavelength

n=2.8

100% TiO2

ZnS + TiO2 refractive index

)()( 2211 λλ nxnxnavg +=

Requires nano-scale control of infiltration amounts; dense,

conformal films

Page 10: Complex, 3D Photonic Crystals Fabricated by Atomic Layer ...Atomic Layer Deposition ALD is a CVD growth technique utilizing sequential reactant pulses. Zn2+ S2-H+ Cl-ALD Growth of

Atomic Layer Deposition

ALD is a CVD growth technique utilizing sequential reactant pulses.

Zn2+ S2- H+ Cl-ALD Growth of ZnS

(a) ZnCl2 Pulse

Nitrogen

(b) N2 Purge

(a) Chemi + physisorption

(b) Physisorbed layer removal

(c) Formation of ZnS

(c) H2S Pulse

Nitrogen

(d) N2 Purge

(d) Removal of H2S and HCl

Surface limited growth: conformal films + monolayer control

Page 11: Complex, 3D Photonic Crystals Fabricated by Atomic Layer ...Atomic Layer Deposition ALD is a CVD growth technique utilizing sequential reactant pulses. Zn2+ S2-H+ Cl-ALD Growth of

Fabrication of ML Inverse Opal

• ZnS:Mn first deposited on bare opal.• TiO2 layer next deposited in remaining interstitial volume.• Inverse opal formed by HF etch.• 3rd step: back-filled inverse opal, yielding 3-layer structure.

• Enabled by ALD’s characteristics: conformal and precise

ZnS:Mn layer

TiO2 layers

TiO2 ALD: TiCl4 + H2O

Page 12: Complex, 3D Photonic Crystals Fabricated by Atomic Layer ...Atomic Layer Deposition ALD is a CVD growth technique utilizing sequential reactant pulses. Zn2+ S2-H+ Cl-ALD Growth of

ML Inverse Opal: SEM Images

ZnS:Mn

TiO2

23 nm TiO2/10 nm ZnS:Mn/20 nm TiO2 Inverse 433 nm OpalKing, et. al. Adv. Mat. (submitted)

Page 13: Complex, 3D Photonic Crystals Fabricated by Atomic Layer ...Atomic Layer Deposition ALD is a CVD growth technique utilizing sequential reactant pulses. Zn2+ S2-H+ Cl-ALD Growth of

ML Inverse Opal: Specular Reflectance

330 nm opal 433 nm opal15° from [111]

400 600 800 1000 1200

(f)

(e)

(d)(c)

(b)

Nor

mal

ized

Ref

lect

ivity

Wavelength (nm)

(a)

Γ-L PBG's

200 400 600 800 1000

(d)

(c)

(b)

Nor

mal

ized

Ref

lect

ivity

Wavelength (nm)

Γ-L 2/3 PPBG

(a)

Γ-L PPBGs8/9 5/6

(a) sintered(b) ZnS:Mn infiltrated(c) ZnS:Mn/TiO2 infiltrated, and (d) ZnS:Mn/TiO2 inverse opal.

(a) ZnS:Mn/TiO2 inverse opaland after backfilling with (b) 20 (c) 40 (d) 60 (e) 80 (f) 100total ALD cycles. (1-5 nm)

Page 14: Complex, 3D Photonic Crystals Fabricated by Atomic Layer ...Atomic Layer Deposition ALD is a CVD growth technique utilizing sequential reactant pulses. Zn2+ S2-H+ Cl-ALD Growth of

PL: ML Inverse Opal

3-layer ZnS:Mn/TiO2 inverse opal (433 nm)

(a) TiO2 (14 nm)/ ZnS:Mn (20 nm)/air inverse opal after backfilling with TiO2 layers of(b) 1 nm(c) 2 nm(d) 3 nm(e) 4 nm(f) 5 nm, thickness

433 nm opal, 337 nm N2 laser excitation

• High-order photonic band PL modulation• 108% increase in relative intensity

400 500 600 700 800

(f)

(c)(e)

(d)

(b)

Relative Intensity

W avelength (nm )

(a)

D=108%

M n2+

Cl-

PL

Reflectivity

Page 15: Complex, 3D Photonic Crystals Fabricated by Atomic Layer ...Atomic Layer Deposition ALD is a CVD growth technique utilizing sequential reactant pulses. Zn2+ S2-H+ Cl-ALD Growth of

Non-Close Packed Inverse Opals

• Increases PBG gap width (up to 100%)*

• Reduces minimum index requirements

* Doosje et al.

Air network in an inverse NCP opal

Dielectric network in an inverse NCP opal

2 parameters define the geometry of the structure instead of one.

• Radius of sphere: R/a

• Radius of connecting cylinder: Rc/a(a is the cubic lattice constant)

Rc was proven to greatly affect gap size compared to R.

Close-packed Structures

Page 16: Complex, 3D Photonic Crystals Fabricated by Atomic Layer ...Atomic Layer Deposition ALD is a CVD growth technique utilizing sequential reactant pulses. Zn2+ S2-H+ Cl-ALD Growth of

Non-Close Packed Inverse Opals

Fabrication Scheme:

• Sinter opal prior to infiltration

• After etching, sphere connectivity is large

• Back-fill inverse opal to create cylinder-like connectivity

Page 17: Complex, 3D Photonic Crystals Fabricated by Atomic Layer ...Atomic Layer Deposition ALD is a CVD growth technique utilizing sequential reactant pulses. Zn2+ S2-H+ Cl-ALD Growth of

NCP Inverse Opals: SEM Results

1050º C 3 hour pre-infiltration heat treatment

TiO2 NCP inverse opal formationClose-packed inverse Opal

PrS inverse opal PrS inverse opal, backfilled 80 ALD

cycles

PrS inverse opal, backfilled 160 ALD

cycles

Page 18: Complex, 3D Photonic Crystals Fabricated by Atomic Layer ...Atomic Layer Deposition ALD is a CVD growth technique utilizing sequential reactant pulses. Zn2+ S2-H+ Cl-ALD Growth of

NCP Inverse Opal: Reflectivity

200 400 600 800 1000

NCPO 8 nm BF

NCPO 4 nm BF

Sintered Opal

Inverse Opal

Infiltrated Opal

Reflectivity

W avelength (nm )

Sintered Opal

2/3 PBG8/9 and 5/6 PBG

15° from [111]433 nm opal

Page 19: Complex, 3D Photonic Crystals Fabricated by Atomic Layer ...Atomic Layer Deposition ALD is a CVD growth technique utilizing sequential reactant pulses. Zn2+ S2-H+ Cl-ALD Growth of

Summary

• Increased PC functionality by formation of

• ZnS:Mn/TiO2 multi-layered inverse opals

• Improved photonic band properties by formation of

• Non-close-packed TiO2 inverse opals

• Demonstrated tuning of luminescent and photonic band properties.

• Established ability to grow complex luminescent PC structures at the nanoscale using ALD.

• Future: Non-close-packed multi-layer PCs.

Page 20: Complex, 3D Photonic Crystals Fabricated by Atomic Layer ...Atomic Layer Deposition ALD is a CVD growth technique utilizing sequential reactant pulses. Zn2+ S2-H+ Cl-ALD Growth of

Acknowledgements

U.S. Army Research Office

• MURI Contract DAAA19-01-1-0603

Georgia Institute of Technology Molecular Design Institute

• Office of Naval Research Contract N00014-95-1-1116