lecture 23 – examples of thin film...
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Lecture 23 –Examples of Thin Film Deposition
EECS 598-002 Winter 2006Nanophotonics and Nano-scale Fabrication
P.C.Ku
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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!