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

ZnO

Al2O3

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