AZO Thesis_Mohammad Shakil Khan

Characterization of Al-doped Conductive Layer of ZnO for Thin

Film Solar Cell

Presenting by:

Mohammad Shakil Khan3rd BatchExam Roll: 409, Reg. No: HA-297

OVERVIEW OF THIS PRESENTATION

Objective of the Thesis ZnO Layer Conductive Layer: AZO Methodology: Literature Review AZO Preparation: Sol-gel Method AZO Preparation Steps

i


Experimental Layer PreparationGlass Substrate Sample Slide Cleaning AZO Solution Preparation Magnetic Stirring of the Solution Deposition & Spin Coating of the Sample

Slides Ageing using OvenDrying in Ambient TemperatureAnnealing for DensificationPreparation Completion ii


AZO Characterization Thickness Measurement• Testing Preparation - Wet Etching Process• HNO3 Solution• Etching the Substrates• Testing• Result• Observation

Surface Morphology Test• Testing• Result• Observation iii


Hall Effect Measurement• Testing• Result• I-V Curve• Observation

Future Work Scope

iv

OBJECTIVE OF THIS THESIS

Observe technology for improving conductivity by Al doping on ZnO layer

Observe the layer thickness and relative characteristical change in the substrate

Identify dopant material requirement for optimization of layer resistivity

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OBJECTIVE OF THIS THESIS

Impact of deposition on a fixed range of substrates

Observing affect of

surface roughness produced at fixed temperatures

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ZnO LAYER

II-VI compound semiconductors

Wurtzite Crystal

Structure

Large band gap (Eg=3.37ev)

Large excitation energy of 60 meV

Source: https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwizu6PsuNTKAhVTj44KHcm6D7wQjhwIBQ&url=http%3A%2F%2Fpubs.rsc.org%2Fen%2Fcontent%2Farticlehtml%2F2013%2Fdt%2Fc3dt51578h&psig=AFQjCNFtdQPZyTVEjOzaTVhKcXUeifhc9Q&ust=1454343198573957

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ZnO LAYER

High optical transmittance in the visible region

Blocks 95% of all UV radiation

Impurity doped ZnO has Good transparent conducting oxide (TCO) characteristics

Good electrical conductivity and low optical loss Source: https://www.google.com/url?

sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwizu6PsuNTKAhVTj44KHcm6D7wQjhwIBQ&url=http%3A%2F%2Fpubs.rsc.org%2Fen%2Fcontent%2Farticlehtml%2F2013%2Fdt%2Fc3dt51578h&psig=AFQjCNFtdQPZyTVEjOzaTVhKcXUeifhc9Q&ust=1454343198573957

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CONDUCTIVE LAYER: AZO

Doped binary compounds, Composed of Al and Zn, common and inexpensive materials

Deposited by sputtering from targets composed of 2-4% Al metal incorporated in ZnO

Electrical conductance, measured as bulk resistivity or as sheet resistance, related to deposition properties and thickness

5Source: http://materion.com/ResourceCenter/ProductData/InorganicChemicals/Oxides/AZOTransparentConductiveCoating.aspx


Full range of sheet resistance, from < 50 Ω/sq to M Ω/sq, can be obtained with AZO by varying deposition thickness and parameters

No substrate heat is required. Patterning of films by etching is easier than with ITO films. Weak acids of <1% concentration (0.2% HNO3 for 2 minutes at 18° C) can be used

The refractive indices for reactive magnetron sputtered AZO at 600 nm wavelength range from 1.90 ± 0.02. Pulsed DC magnetron sputter deposition of AZO produces an index ~2.00

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Property of high transmission in the visible region and useable transmission to IR wavelengths as long as ~12 μm.

In contrast, the more commonly known TCO,

ITO, reflects IR at wavelengths longer than ~2 μm.

Transmittance loss for a 120 nm thick coating on Ge is <10% out to ~12 μm.

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METHODOLOGY: LITERATURE REVIEW

Preparation and characterization of ZnO thin films deposited by sol-gel spin coating method

Thickness changes inversely with increasing or decreasing chuck rotation

Effect of Sol Concentration on Structural and Optical Behavior of ZnO Thin Films Prepared by Sol-Gel Spin Coating

Grain size increases with increase in molar concentration of the deposited thin films 8

METHODOLOGY:LITERATURE REVIEW

Al-doped ZnO via Sol-Gel Spin-coating as a Transparent Conducting Thin Film

Crystallite size increases but Electrical resistivity decreases with increasing Al concentration

Structural and optical properties of ZnO: Al films prepared by the sol–gel method

Increasing Al concentration leads to an amorphous stage of the film appears higher than 2 wt.% of concentration

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METHODOLOGY:LITERATURE REVIEW

Damp heat stability of AZO transparent electrode and influence of thin metal film for enhancing the stability

Mobility decreased with increasing Al concentration

Low Temperature Sol-Gel Technique For Processing Al-Doped Zinc Oxide Films

Each annealing concentration of oxygen increased and concentration of carbon decreased in the films

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AZO PREPARATION: SOL-GEL METHOD

Method for producing solid materials from small molecules

Conversion of monomers:

A colloidal solution (sol) that acts as the precursor for an integrated network Gel of either discrete particles or network polymers

Sol (or solution) evolves gradually towards the formation of a gel-like network containing both a liquid phase and a solid phase

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Sol-gel Method steps:

HydrolysisCondensationGelationAgeingDryingDensification

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AZO PREPARATION STEPS

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EXPERIMENTAL LAYER PREPARATION

Glass Substrate: 1’’×1’’Sample Slide Cleaning: Ultrasonic Bath

(USB) process Cleaned by brush with de-ionized water and

washed by methanol as mechanical scrubbing- Methanol for 10mins- Acetone for 10mins- Methanol for 10mins-De-ionized Water for 10mins

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AZO Solution Preparation

Magnetic Stirring of the Solution: - 2hour at 60 degree Celsius - Solution was allowed to aged for 24 hr in room temperature

Elements Role

Amount

Zinc acetate dehydrate [Zn(CH3COO)2. 2H2O]

Starting Materia

l5.39g

2-methoxy ethanol (CH3OCH2CH2OH) Solvent 46.93g

Mono-ethanol-amine [(HOCH2CH2)NH2]Stabiliz

er 1.5ml

Aluminum nitrate nonahydrate [Al2(NO3)3.9H2O]

Doping Materia

l0.11g

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Deposition & Spin Coating of the Sample Slides

-Solution: 0.5 ml

- RPM: 3000

- Spin Time: 30 seconds

- Rotation/Sec2: 500

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Ageing using Oven

- At 300 degree Celsius - Cycle was done for 5, 10 & 15 times

- Kept in Oven for 10mins

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Drying in Ambient Temperature

- Pre-heating stability gain

- At room temperature - for 10mins for all

substrates Annealing for

Densification

- Both Air & Vacuum annealing

- Nitrogen purging for Air annealingat 500 Degree Celsius

- Vacuum annealing for 1 hour

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Preparation Completion

- Kept for 24 hours for making samples stable

- AZO substrates are ready for experiment

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AZO CHARACTERIZATION

Thickness Measurement

- layer thickness influence the efficiency- Being too thin affect efficiency and durability, being too

thick can increase cost- Profilometer is used to measure the surface thickness

Surface Morphology Test

- Analytical Imaging test- Test is performed for detecting surface defect and

roughness- Surface Imaging Information: Surface structures & defects

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AZO CHARACTERIZATION

Hall Effect Measurement

- Production of a voltage across an electrical conductor, transverse to an electric current in the conductor and a magnetic field perpendicular to the current

- Determining resistivity & conductivity

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THICKNESSMEASUREMENT

Testing Preparation Wet Etching Process- Using masking tap in one side- Weak solution of HNO3

HNO3 Solution Preparation

- 125ml of De-Ionized (DI) water in beaker - 0.32ml of HNO3 poured in it - De-Ionized water upto 500ml

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Etching the Substrates

- Kept substrates drenched 10mins in solution- Taken up and rinsed by De-Ionized

water, then dried 10mins- Removed mask and got side etch

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Testing

- Stylus Surface Profilometer, Model: Detak-150 was used

- Layer: 1, 10 & 20 timesAZO solution deposited

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Result

- For 1-layer: 504nm - For 10-layer: 5851.9nm - For 20-layer: 10311.8nm

Observation

- Huge improvement in layer thickness with each deposition- Each deposition obtained significant improvement

in layer thickness hence increase performance

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Observation

1-layer 10-layer 20-layer0

2000

4000

6000

8000

10000

12000

Layer Thickness

Layer

Thic

knes

s (µ

m)

Improvement trend of layer thickness with deposition

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SURFACE MORPHOLOGYTEST

Testing

- Used Stylus Surface Profilometer, Model: Detak-150- Observe the surface roughness of the

substrates in particular its adhesion, microstructure and final topography

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Result

The layer roughness are:

For 1-layer, Ra: 45.3nmFor 10-layer, Ra: 11545.1nmFor 20-layer, Ra: 1885.1nm

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Observation

Roughness of surface increased by the number of layer

1-deposition the roughness is futile; doesn’t affect the surface (grain size) at all

From 1-times to 10-times roughness increases highly

From 10-times to 20-times not significantly Increasing of doping concentration doesn’t

increase the smoothness after certain layer deposition

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HALL EFFECTMEASUREMENT

Testing

10 times deposited layer Instrument: ECOPIA HMS-3000

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Result

Bulk Concentration: -9.675×1010 /cm3 Mobility: 1.564×103 cm3/VS Resistivity: 4.126×104 Ω-cm Magneto-Resistance: 2.698×108 Ω Sheet Concentration: -6.627×106/cm2 Conductivity: 2.423×10-5/ Ω-cm Average Hall Coefficient: -6.452×107cm3/C

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I-V Curve

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Observation

Hall Coefficient value was measured as -6.452×107cm3/C

Negative sign of the Hall coefficient indicates Al-doped ZnO are n-type

Conductivity is 2.423×10-5/ Ω-cm means the substrates has optimized conductivity

After Vacuum Annealing the resistivity is 4.126×104 Ω-cm

Indicates post-heat-treatment in a reducing environment efficiently reduced the electrical resistivity, affected mainly the oxygen vacancy concentration

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Increasing efficiency of Al doped ZnO will increase efficiency of Thin film

Need to endeavor:

- Impact of layer deposition on roughness - Impact of conductivity increase at annealing

temperature variation - Optimize high efficient grain size doping (i. e.)

material and chemical composition

FUTURE WORK SCOPE

35

Thank You

Q/A

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AZO Thesis_Mohammad Shakil Khan