Post on 26-Feb-2016
description
ALD Thin Film Materials
LDRD review 2009NuFact09
ALD of III-V semiconductorsand other structure/materials
What have been done:-GaN-AlN-AlGaN-InNNot too hard for InGaN-TiO2
-ZnO
Other: Pt nanoparticles Ag nanoparticles
Cutoff at 380 nm, up to 50% QE at 310 nm
BiAlkali’s overlayer for e- emission
Absorb at 380nm but surface defect -> re-emits at ~ 540 nm + broad
Fill defect on oxide : very high absorption at 380 nm
very high absorption above 1000 nm
Atomic Layer depositionHome made:
-Transfer: Open in air -> issue-No vacuum inside the ALD chamber-Only Thermal ALD
Commercial: -Load lock + glove bag:Inert gas (N2, Ar…) for sample transfer -In-situ characterization:
EllipsometryMass specQCM and maybe IR spec
-In-situ vacuum post annealing -ALD + Plasma ALD
Mixed Oxide Deposition: Layer by Layer
Mixed Layer Growth• Layer by Layer• note “steps”• atomic layer sequence “digitally” controlled
• Films Have Tunable Resistivity, Refractive Index, Surface Roughness, etc.
[(CH3)3Al // H2O]
100 nm
ZnO
ZnOAl2O3
Al2O3
[(CH3CH2)2Zn// H2O]
• Mixed Layers w/ atomic precision• Low Temperature Growth•Transparent•Uniform•Even particles in pores can be
coated.
LDRD review 2009NuFact09
5
ZnO in Silicon High Aspect Ratio Trench
1 μm
200 nmZnO
Si
ALD is very good at coating non-planar surfaces
Argonne ALD facilities: Plasma ALD (PEALD)
Elemental Metals: Al, Cu, W, Mo…& alloys: NbN, TiN, Pt/Ir etc…
Purer materials-> bulk properties
-Bi Alkalies: CsI3 (g) + H2 (plasma) = CsI + 2HI (g)GeCl4 (g) + 2H2(plasma) = Ge + 4HCl (g).2SnCl5 (g) + 10H2 (plasma) = 2Sn + 10 HCl (g).
ITO, conducting-transparent oxides, or Pt, W, Cu, Mo etc.. With plasma ALD
Light, λ≤400 nm
Work for both Plasma and regular ALD.
e-
Light absorption layer
Need Cs layers for QE~50 to 70%
dMean free path e-hole l < d
MCP
Light, λ≤400 nm
e-
d~50nm,
d’~ 10 nm
ITO for bias ~ few Volts
Metallic wires -> field enhancements:Nanotubes…
d’< l
MCP
Thermal Noise ?
-Nanotubes + free space filled with TiO2
- “AAO” type membrane made out of TiO2 + ALD filled with metals
- AAO membrane filled with both: light absorber and metal
Al2O3
Diamond?
Metallic layer
Shine light laser 325 nm.
λ
e-
e-
AAO
e-
MCP
e-
45 nm Ag nano-particles
Al nano-films
MCP
Metallic electrode
absorption
e-
-Cannot use ALD -> coat inside the tube too
-Plasma ALD -> lower aspect ratios, controlled by plasma exposure time
Light, λ≤400 nm
e-
MCP
Light, λ~600 nm
Surface plasmon:Gold nanoparticules