lecture 23 – examples of thin film...

Lecture 23 –Examples of Thin Film Deposition

EECS 598-002 Winter 2006Nanophotonics and Nano-scale Fabrication

P.C.Ku

2EECS 598-002 Nanophotonics and Nanoscale Fabrication by P.C.Ku

Size dependence (quantum confinement)

g(E) = Density of states

Eg E

g(E)

Eg E

g(E)

Eg E

g(E)

Eg E

g(E)

bulk sheet wire dot

3D 2D 1D 0D

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Self-assembled quantum dots growth

Heteroepitaxial growth:

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Growth modes

Frank-van der Merwe (FvdM) = layer-by-layer growth (2D)Volmer-Weber (VW) = island growth (3D)Stranski-Krastanow (SK) = layer-by-layer + island growth

FvdM VW SK

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Minimization of total energy

Interface energy

Epilayer surfaceenergy

Substrate surfaceenergy+ <>

If “<“ FvdM growth

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Coherent island formation

If interface energy + epilayer surface energy > substrate surface energy coherent islands may form to lower the energy (SK mode).

0VE∆ < Relaxation of elastic energy

0SURFE∆ > Relaxation of elastic energy

0DISE∆ > Energy of the dislocation interface

Q

Γ

DI

CIUF

DIS

SURF

EE∆

Γ =∆

Q = amount of deposited materials

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SK example: InAs on GaAs

Phys. Rev. B 50 (1994) 11687.

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Evolution of growth

Phys. Rev. B 50 (1994) 11687.

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Critical island size

The total energy of the coherent island is:

TOTAL edge SURF VE E E E= + ∆ + ∆

AL2BL 3CL

0TOTALcritical

E L LL

∂= ⇒ =

∂

If L > Lcrit Oswald ripening to reduce the Esurf

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Stacked QD’s

Heinrichsdorff et al., Appl. Phys. Lett. 71 (1997) 22.

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QD’s on patterned substrate

J. Crystal Growth 201/202 (1999) 1209.

MBE grown

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Appl. Phys. Lett. 73 (1998) 2479.

MBE grown

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“Patterned” ?

The simplest version of patterned substrates is substrates coated with oxide or nitride masks.

But it can also be the following:

Strained induced patternEtched substrates

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Selective-area on nonplanar substrates

Appl. Phys. Lett. 72 (1998) 220.

MBE grown

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Strained selective-area growth

Appl. Surf. Sci. 130-132 (1998) 137.

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MOCVD grown

Appl. Phys. Lett. 73 (1998) 2479.

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Single and double QD’s

Appl. Phys. Lett. 76 (2000) 3948.

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Uniformity

Homogeneously broadening linewidth

Phys. Rev. Lett. 87 (2001) 157401.

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Linewidth for QD array

Appl. Phys. Lett. 84 (2004) 2818.

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Quest for uniform QD array

The linewidth from a QD array is > 2000 times more than its intrinsic linewidth!

There is belief that there is no physical limit on why we can not get uniform dots.

But it is a challenge!