Annealing. Determined by oxygen pressure. N o r t h C a r o l i n a S t a t e U n i v e r s i t y

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1 Annealing Determined by oxygen pressure Controls Carrier Density

2 ITO Conductivity Bixbyite (M3+ 2 O 3 ) is a derivate of the fluorite (M4+ O 2 ) crystal structure with vacancies at 1/4 of the oxygen sites. When Sn 4+ isaddedtoin 2 O 3, the vacancies are filled with O 2- i to compensate for the Sn In+. By processing in reducing atmospheres, the O i 2- can be removed. Atomic Arrangement in ITO (Bixbyite Crystal Structure) O i 2- + O i 2- O 2 (g) + 4e - Gonzalez et al. JAP (2004) Ionic Electronic

3 Annealing Controlled Atmosphere Annealing XRD of ITO Films Before and After Annealing Gas Inlet (N 2 &H) 2 In-situ Transfer Process Parameters Temperature Time Atmosphere Inten nsity ITO After Anneal ITO As Deposited θ ()

4 Annealing Change in Film Conductivity with Annealing Atmosphere Resistivity (Ω*cm) ITO films processed in atmospheres with lower oxygen partial pressures are more conductive ~Oxygen Partial Pressure of Annealing Atmosphere (Torr)

5 Control over plasma frequency In accord with Drude theory SPR frequency can be controlled by adjusting the film conductivity. ω p = 2 ne2 m e ε 0 1/2

6 Film Texture Determined by Ar + pressure Controls Mobility

7 Characterization of ITO Films Analyze crystalline structure by x-ray diffraction (equipped with area detector). Investigate film conductivity by four-point probe. (ρ = ρ sheet t) (σ = 1 / ρ) )

8 Examples Single Crystal or Random Textured Epitaxial Film Polycrystalline Polycrystalline

9 XRD Data Processing Area Detector Data θ-2θ Scan Intensity χ 2θ () 2θ Conventional θ-2θ Scan

10 Texture/Surface Structure Besides crystalline orientation, ti film texturing can affect surface structure/ morphology and roughness. Kamei et al. TSF (1995)

11 Texture Control 10 mtorr Ar / 20 W 7.5 mtorr Ar / 20 W 7.5 mtorr Ar / 30 W No Texture 222-texture 222-texture Counts Counts Counts θ () θ () θ ()

12 Sputter Pressure: AFM 10 mtorr 20 mtorr Grain Size: 100 nm Mobility: 35 cm 2 /Vs Grain Size: < 40 nm Mobility: 7 cm 2 /Vs Reflectanc ce (a.u.) Reflectanc ce (a.u.) Wavenumber (cm -1 ) Wavenumber (cm -1 )

13 Sputter Pressure Hall Carrier Concentration Mobility rrier Conce ntration (cm -3 ) x Change Mobility (cm 2 /V*s) x Change Ca Sputter Pressure (mtorr) Sputter Pressure (mtorr) Although sputter pressure affects the carrier concentration, it has a much larger impact on mobility of the charge carriers

14 EXPERIMENT Decreasing thin film thickness from 160nm to 30nm results in only bulk plasmon being visible 0.6 Electron Volts (ev) Electron Volts (ev) SP PR Reflectance e (a.u.) Electron Volts (ev) Electron Volts (ev) nm 30nm 1.2 Γ = e m e μ Changing the mobility influences the damping constant through mobility,μ, widening the peaks. 0.6 Electron Electron Volts Volts (ev) (ev) Reflectance (a.u.) SPR po mtorr nm Ar mTorr D Wavenumber (cm -1 ) 100 Wavenumber (cm -1 ) Wavenumber (cm -1 ) po 2 1x10-5 mtorr Decreasing carrier concentration,n, lowers the polariton plasmon position. ω p = e 2 n m ε e 0.u.) SPR Reflectance (a nm Wavenumber (cm -1 ) 9000 Increasing thin film thickness from 160nm to 250nm results in a decrease in amplitude of the plasmon polariton Wavenumber (cm -1 (cm ) -1 )

15 a.u.) SPR Reflectance ( THEORY The smaller thickness was inserted into the three layer Fresnel equation to predict the derease in amplitude of the SPP. Electron Volts (ev).u.) Reflectance (a. SPR Electron Volts (ev) nm 160 nm 1.2 The damping Γ in the Drude model was increased from 900 cm -1 to 2500 cm -1 Based on measured decrease in mobility. Electron Volts (ev) po mtorr Ar + 15 mtorr Wavenumber (cm -1 ) 1.0 Wavenumber (cm -1 ) 250 nm The charge carrier 0.8 concentration decreases from The greater thickness was 1.0 to 0.7 x inserted into the three electrons/cm layer Fresnel equation to The predicted frequency shift in ω p was inserted into the Drude model. SP PR Reflectance (a.u.) predict the derease in amplitude of the SPP Wavenumber (cm -1 )

16 Comparison to Metals

17 The Drude conducting model 2 P + Γ P = ne 2 E iωt t 2 t m 0 e e Substitute in the susceptibility P = χ(ω)ε 0 E ε 0 χω ω 2 iωγ E 0 e iωt = ne2 m e E 0 e iωt From the definition χ(ω) =ε(ω) - 1 and the definition of the Drude plasmon resonance frequency 2 2 ω p Γ ω ε ω = 1 p ω 2 + Γ + i 2 ωω 2 + Γ 2 The relaxation constant Γ can be related to the electron mean free path λ and the Fermi velocity v F by Γ = v F /λ 2 2 ω =1 p Γ ω ε = p 1 ω, ε ω 2 + Γ 2 2 ω ωω2 + Γ 2

18 Dielectric function for ITO

19 Dispersion relations from Drude n cz = 2 ε c, n ε c + ε sz = s 2 ε s, n ε s + ε x = c ε c ε s ε s + ε c c s s c s c

20 Predicted Plasmonics (Real) ω p = cm -1 Γ = 500 cm -1 k sp = ω c ε c ω ε s ω ε c ω + ε s ω

21 Predicted Plasmonics

22 Acknowledgements Crissy Rhodes Alina Efremenko Dr. Marta Cerruti Dr. Jaap Folmer Dr. Simon Lappi Dr. Daniel Fischer Dr. Sharadha Sambasivan Stephen Weibel Dr. Jan Genzer Dr. Jon Paul Maria Mark Losego Dr. Gerd Duscher Donovan Leonard Dr. Eric Jiang Forrest Wessner