Fabrication of optoelectronic devices based on vertically aligned one dimensional ZnO nanostructures

Fabrication of optoelectronic devices based on vertically aligned one dimensional ZnO

nanostructures

Thesis submitted to

COCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGY

in partial fulfillment of the requirements for the award of the degree of DOCTOR OF PHILOSOPHY

VIKAS L S

DEPARTMENT OF PHYSICS

COCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGY COCHIN - 682022, KERALA, INDIA

July 2016

Dedicated to my friends and family

Department of Physics,

Cochin University of Science and Technology, Kochi-682022, India

Dr. M. K. Jayaraj 16 ^th July 2016 Professor

Certified that the work presented in this thesis entitled

“Fabrication of optoelectronic devices based on vertically aligned one dimensional ZnO nanostructures” is based on the authentic record of research carried out by Vikas L S under my guidance in the Department of Physics, Cochin University of Science and Technology, Cochin 682 022 and has not been included in any other thesis submitted for the award of any degree. All the relevant corrections and modifications suggested by the audience during the pre-synopsis seminar and recommendations by doctoral committee of the candidate have been incorporated in the thesis.

Dr. M. K. Jayaraj (Supervising Guide)

---

phone: +91 484 2577404 extn. 33 Fax: 91 484 2577595 Email: mkj@cusat.ac.in

Contents

Ele ctr od e Ele ctr od e e

e

e

e

GaN Al

O

Substrate Electrode

1D nanostructure e

e

e

e

0D nanostructure

(a) (b)

29.24%

0.23%

30.23%

39.41%

0.89%

nanobelt nanowire Nanotube nanoribbon Nanorod

14.6%

1.4%

6.55%

8.97%

1.43%

12.2%

1.6%

22.24%

17.88% 4.84%8.3%

SnO2

In2O3

ZnO TiO2

WO3

Fe2O4

Ga2O3

CuO NiO V₂O₅ MoOx

(b)

1990 1995 2000 2005 2010 2015

0 10000 20000 30000 40000 50000 60000

Number of papers per year

Year

(a)

(c)

𝐶 _6𝑣 ⁴

Zn ²⁺ + 4OH ⁻ →Zn(OH) ₄ ²⁻

Zn(OH) ₄ ²⁻ →ZnO + 2H ₂ O

V A

W orkin g Ele ctr ode C ou n ter Electr od e

R ef e re n ce Ele ctr od e

e

e

e

e

Zn O Zn

OH

H

O

Sample

Electron collector Lens

Lens Scan coils

Aperture

Electron gun

Sample

Cantilever AFM tip

XY Z Pie zo scann er

Quadrant photodiode

n m

0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0 1 0 0 1 1 0

0 2 4 6 8 µm

µm 0 1 2 3 4 5

n m

0 1 2 3 4 5 6 7 8

0 2 4 6 8 µm 9

µm 0 1 2 3 4 5 6 7 8 9 AFM tip

Substrate

Surface feature artifact

Fixed platform

Piez oele ctric Sc an n e r

Probe

Curved motion of the probe

a) b)

c)

d)

𝟏 𝒅 _𝒉𝒌𝒍 ^𝟐 = ℎ ² + 𝑘 ² + 𝑙 ²

𝑎 ²

ℎ ² + 𝑘 ² 𝑎 ² + 𝑙 ²

𝑐 ² ℎ ²

𝑎 ² + 𝑘 ² 𝑏 ² + 𝑙 ²

𝑐 ²

4 3

ℎ ² + ℎ𝑘 + 𝑘 ² 𝑎 ² + 𝑙 ²

𝑐 ²

(ℎ ² + 𝑘 ² + 𝑙 ² ) sin ² 𝛼 + 2(ℎ𝑘 + ℎ𝑙 + 𝑘𝑙)(cos ² 𝛼 − cos 𝛼) 𝑎 ² (1 − 3 cos ² 𝛼 + 2 cos ³ 𝛼)

ℎ ²

𝑎 ² sin ² 𝛽 + 𝑘 ²

𝑏 ² + 𝑙 ²

𝑐 ² sin ² 𝛽 − 2ℎ𝑙 cos 𝛽

𝑎𝑐 sin ² 𝛽

ω

2θ φ ψ

Incident beam

Goniometer axis

Detector X-ray source

K ₀ K

Q

θ _o

θ _i

𝑇 _ℎ𝑘𝑙 =

𝐼 _ℎ𝑘𝑙 𝐼 _ℎ𝑘𝑙 ⁰

⁄ 1 𝑁 ∑[ 𝐼 _ℎ𝑘𝑙

𝐼 _ℎ𝑘𝑙 ⁰

⁄ ]

T _hkl I _hkl

I _hkl ⁰

≤ ≤

≤ ≤

𝑄 _𝑥 = ²

𝜆 sin ^2𝜃

2 sin ( ^2𝜃

2 − 𝜔) = ¹

𝜆 {cos 𝜔 − cos(2𝜃 − 𝜔)}

𝑄 _𝑧 = ²

𝜆 sin ^2𝜃

2 cos ( ^2𝜃

2 − 𝜔) = ¹

𝜆 {sin 𝜔 − sin(2𝜃 − 𝜔)}

o θ ω δω

δθ θ θ δθ o δQ

Q

θ

𝐶 _6𝑣 ⁴

𝛤 _𝑜𝑝𝑡 = 1𝐴 ₁ + 2𝐵 ₁ + 1𝐸 ₁ + 2𝐸 ₂

~0.9eV

V _o

VB

~0.22 eV Zn _i

E _g ^{~ 3.06 eV}

V _Zn

O _i

~2.28 eV

CB

𝐼 = 𝐼 ₀ (𝑒 ^{𝑛𝑉𝑇 𝑉𝐷} − 1)

𝑉 _𝑇 = ^𝑘𝑇

𝑞 CB

VB

Type I Type II Type III

𝐼 = 𝐼 ₀ 𝑒 ^{𝑛𝑉𝑇 𝑉𝐷}

ln(𝐼) = ln(𝐼 ₀ ) + ^{𝑉 𝐷}

𝑛𝑉 _𝑇

𝑞 𝑛𝑘𝑇

𝑛 = ¹

𝑠𝑙𝑜𝑝𝑒 X 𝑉 _𝑇

𝑉 = 𝑉 _𝑘 + 𝐼𝑅 _𝑠

∆𝑉 = 𝑉 − 𝑉 _𝑘

V

𝐶 _𝑗 = ^{𝐾 𝑠 𝜀 0 𝐴}

[ ^{2𝐾𝑠𝜀0}

𝑞𝑁𝐷 (𝑉 _𝑏𝑖 −𝑉)]

1 ⁄ 2

1

𝐶 _𝑗 ² = ²

𝑞𝑁 _𝐷 𝐾 _𝑠 𝜀 ₀ 𝐴 ² (𝑉 _𝑏𝑖 − 𝑉)

𝐶 _𝑗 ¹

𝐶 _𝑗 ²

𝑁 _𝐷 = ²

𝑞𝐾 _𝑠 ℰ ₀ 𝐴 ²

|

| ^𝑑(

1 𝐶𝑗 2) 𝑑𝑉 |

|

𝑑( ¹ 𝐶𝑗 2 ) 𝑑𝑉

1

𝐶 _𝑗 ²

𝑅 _𝜆 = ^{𝐼 𝐷}

𝑃

∞

J = J ₀ + A ₁ exp (− ^t

t ₁ )

J = J ₀ + A ₁ exp (− ^t

t ₁ ) + A ₂ exp (− ^t

t ₂ )

0 20 40 60 80 100

TD

Change in photo current (I

-I

) (%)

Time

Normalised sensor current

TR

𝑓 _𝐵𝑊 = ¹

2𝜋𝑅 _𝐿 𝐶 _𝑗

𝑡 _𝑟 = 0.35

𝑓 _𝐵𝑊

𝑍𝑛 ²⁺ + 4𝑂𝐻 ⁻ → 𝑍𝑛(𝑂𝐻) ₄ ²⁻

𝑍𝑛(𝑂𝐻) ₄ ²⁻ → 𝑍𝑛𝑂 + 2𝐻 ₂ 𝑂

𝑇 _{ℎ𝑘𝑖𝑙} =

𝐼 _{ℎ𝑘𝑖𝑙} 𝐼 ₀

⁄ 1

𝑁 ∑ [ 𝐼 _{ℎ𝑘𝑖𝑙} 𝐼 ₀

𝑁 ⁄ ]

𝑛=1

(a) (b)

(c) (d)

20 40 60 80

20 40 60 80

Substrate ED on 30 nm

ED on 20 nm

ED on 10 nm

ED on 5 nm

ED on 0 nm

Counts in log scale (arb. unit)

2 Theta (Degree)

(1120) (0221)(1122) (0004) (0222)

(0220)(0113)

(0112)

(0111)

(0110) (0002) ZnO ICSD

20 40 60 80

20 40 60 80

2 Theta (Degree)

(1120) (0221)(1122) (0004) (0222)

(0220)

(0113)

(0112)

(0111)

(0110) (0002)

Counts (arb. unit)

ED on 30 nm

ED on 20 nm

ED on 10 nm

ED on 5 nm

ED on 0 nm

Substrate ZnO ICSD

20 40 60 80

20 40 60 80

2 Theta (Degree)

Counts (arb. unit)

ED on 30 nm

ED on 20 nm

ED on 10 nm

ED on 5 nm

ED on 0 nm

Substrate

(1120) (0221)(1122) (0004) (0222)

(0220)

(0113)

(0112)

(0111)

(0110) (0002) ZnO ICSD

20 40 60 80

20 40 60 80

2 Theta (Degree)

Counts (arb. unit)

ED on 30 nm

ED on 20 nm

ED on 10 nm

ED on 5 nm

ED on 0 nm

Substrate

ZnO ICSD (1120) (1122) (0221) (0004) (0222)

(0220)

(0113)

(0112)

(0111)

(0110) (0002)

FTO ITO PET AZO 0

2 4 6 8 10

Texture coefficient

Substrates 0 nm 5 nm 10 nm 20 nm 30 nm

0 10 20 30 40 50

Surface roughness

0 5 10 15 20 25 30

0 2 4 6 8 10

Texture coefficient

Seed Layer thickness (nm) (0002)

0 5 10 15 20 25 30

0 1 2 3 4 5 6 7 8

Texture coefficient

Seed layer thickness (nm) (0002)

0 5 10 15 20 25 30

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Texture coefficient

Seed layer thickness (nm) (0002)

0 5 10 15 20 25 30

0 1 2 3 4 5 6

Texture coefficient

Seed layer thickness (nm) (0002)

a) b)

c) d)

e)

a) b)

c) d)

e) f)

a) b)

c) d)

e) f)

a) b)

c) d)

e) f)

a) b)

c) d)

e) f)

0 5 10 15 20 25 30 0.0

0.2 0.4 0.6 0.8 1.0 1.2

Height (m)

Seed layer thickness (nm) FTO ITO PET AZO

0 5 10 15 20 25 30

30 60 90 120 150 180 210

Width (nm)

Seed layer thickness (nm) FTO ITO PET AZO

(a) (b)

n m

0 2 4 6 8 1 0 1 2 1 4 1 6 1 8 2 0 2 2 2 4 2 6 2 8 3 0 3 2 3 4 3 6 3 8 4 0 4 2 4 4 4 6 4 8 5 0 5 2 5 4 5 6 u m

0 0 .0 2 5 0 .0 5 0 .0 7 5 0 .1 0 .1 2 5 0 .1 5 0 .1 7 5 0 .2 0 .2 2 5 0 .2 5 0 .2 7 5 0 .3 0 .3 2 5 0 .3 5 0 .3 7 5 0 .4 0 .4 2 5

a)

b)

μm μm

nm nm

FTO

ITO

μm

n m

0 5 1 0 1 5 2 0 2 5 3 0 3 5 4 0 4 5 5 0 5 5 6 0 6 5 n m

0 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 1 6

c)

d)

nmnm nmnm

PET

AZO

Smooth Substrate

a) b)

Rough Substrate

Nanorods Nanorods

500 750 1000 1250 1500 0

10 20 30 40 50 60 70 80 90 100

Transmission (%)

Wavelength (nm) 0 nm 5 nm 10 nm 20 nm 30 nm

500 750 1000 1250 1500

0 10 20 30 40 50 60 70 80 90 100

Transmission (%)

Wavelength (nm) 0nm

5nm 10nm 20nm 30nm

(a) (b)

(d) (c)

500 750 1000 1250 1500

0 10 20 30 40 50 60 70 80 90 100

Transmission (%)

Wavelength (nm) 0 nm 5 nm 10 nm 20 nm 30 nm

500 750 1000 1250 1500

0 10 20 30 40 50 60 70 80 90 100

Transmission (%)

Wavelength (nm) 0 nm 5 nm 10 nm 20 nm 30 nm

500 750 1000 1250 1500 0

10 20 30 40 50 60 70 80 90 100

Transmission (%)

Wavelength (nm) 0 nm 5 nm 10 nm 20 nm 30 nm

500 750 1000 1250 1500

0 10 20 30 40 50 60 70 80 90 100

Transmission (%)

Wavelength (nm) 0 nm 5 nm 10 nm 20 nm 30 nm

500 750 1000 1250 1500

0 10 20 30 40 50 60 70 80 90 100

Transmisssion (%)

Wavelength (nm) 0 nm

5 nm 10 nm 20 nm 30 nm

(e)

(g)

(f)

300 400 500 600 700 800 0.0

0.2 0.4 0.6 0.8 1.0

Intensity (Normalised)

Wavelength (nm)

FTO ITO AZO PET

300 400 500 600 700 800

0.0 0.2 0.4 0.6 0.8 1.0

Intensity (Normalised)

Wavelength (nm)

FTO ITO AZO

a) b)

100 200 300 400 500 600 0

10 20 30 40 50

E

(L O) E

(Hig h)

E

(T O) A

(T O) E

(L ow )

In te ns ity (a rb. u ni t)

Raman shift (cm

) FTO

ITO AZO

A

(L O)

Glass ZnO:Al ZnO na nor ods

CuO Au

UV light

Bottom Illumination

Glass AZO

(a) ZNA (b)

≈

≈

(c) (d)

(a) (b)

Region 2

Region 3

Region 1 Region 1

Region 2 Region 3

(c)

100 200 300 400 500 600 0

10 20 30 40 50

In tensity (A. U) 439

384

E 2 l ow E 2 h ig h

A 1 TO

Raman shift

cm-1

100 479 A 1 L O

30 35 40 45 50 55 60 65 70 75 80

CuO (a)

Intensity (A. U.)

CuO ICSD 80-1916

ZNA

(1 1 1) (1 1 3) (0 2 2) (2 2 0) (0 0 0 4)

(0 0 0 2)

2 Theta (Degree)

ZnO ICSD 98-000-9341

(a)

(b)

C o u n ts ( ar b . Un it) In tens it y (ar b. U ni t)

CuO JCPDS 80-1916

𝐶 _6𝑣 ⁴

𝐶 _3𝑣

Γ _opt = 1𝐴 ₁ + 2𝐵 ₁ + 1𝐸 ₁ + 2𝐸 ₂

≈

≈

550 600 650 700 750

708nm

642nm

Intensity (A.U)

Wavelength (nm)

568nm

(a) (b)

(c) (d)

300 400 500 600 700 800

0 200 400 600 800

Intensity (A. U.)

Wavelength (nm) Without seed With seed

3.0 3.1 3.2 3.3 3.4 3.5

0 1x10¹⁵ 2x10¹⁵ 3x10¹⁵

Without seed With seed

(h)2 (ev cm-1 )2

h(eV) 3.28

eV

350 400 450 500 550 600 650 700 750 800 0

20 40 60 80 100

Without seed With seed

Transmission %

Wavelength (nm)

-1 0 1 -0.5

0.0 0.5 1.0 1.5 2.0

Current Density (mA/cm2)

Voltage (V) Without seed With seed

(b) (a)

-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 -4

-2 0 2 4

Current (A)

Voltage (V)

AZO/ZNA/AZO Au/CuO/Au

∆E _v = E _g2 − E _g1 + ∆E _c

(a) (b)

-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0

0 1x10¹⁹ 2x10¹⁹ 3x10¹⁹ 4x10¹⁹ 5x10¹⁹ 6x10¹⁹

1/C2 (F-2)

Voltage (V)

100 kHz 1 MHz

Δ

Δ

0.5 0.6 0.7 0.8 0.9 1.0 0.0

0.5 1.0 1.5 2.0

Dark UV from Bottom UV from Top Current Density (mA/cm2)

Voltage (V)

(a) (b)

-1.0 -0.5 0.0 0.5 1.0

-0.5 0.0 0.5 1.0 1.5 2.0

Current Density (mA/cm2)

Voltage (V) Dark

UV from top UV from bottom

≈

J = J ₀ + 𝐴 ₁ exp (− ^𝑡

𝑡 ₁ ) + 𝐴 ₂ exp⁡(− ^𝑡

𝑡 ₂ )

0 2500 5000 7500 10000 12500 15000 17500 19

20 21 22 23

Current Density (mA/cm2)

Time (s)

UV ON

UV OFF

UV ON

UV OFF

(a) (b)

0 1000 2000 3000 4000

19 20 21 22 23

Current Density (mA/cm2)

Time (s) Detector response Decay time fitting Rise time fitting

200 300 400 500 600 700 5

10 15 20 25

Responsivit y (A/W)

Wavelength (nm)

n m

0 2 .5 5 7 .5 1 0 1 2 .5 1 5 1 7 .5 2 0 2 2 .5

0 1 2 3 4 µm

µm 0 0 .5 1 1 .5 2 2 .5 3 3 .5 4 4 .5

n m

0 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 2 0 2 1 2 2 2 3 2 4

n m

0 2 .5 5 7 .5 1 0 1 2 .5 1 5 1 7 .5 2 0

0 1 2 3 4 5 µm

µm 0 0 .5 1 1 .5 2 2 .5 3 3 .5 4 4 .5 5

(a) (b)

(d)

(c)

(a) (b)

(d)

(c)

a) b)

34.0 34.2 34.4 34.6 34.8 35.0

Counts (A.U.)

2Theta (Degree)

GaN (0002)

ZnO (0002)

10 20 30 40 50 60 70 80

(0004)

(0002)

Counts (arb. unit)

2 Theta(Degree)

Counts (arb. unit)

Counts (arb. unit)

34.0 34.2 34.4 34.6 34.8 35.0

GaN (0 0 0 2)

ZnO (0 0 0 2)

Counts (A U)

2 Theta (Degree)

34.0 34.2 34.4 34.6 34.8 35.0

GaN (0 0 0 2)

ZnO (0 0 0 2) Counts (A U)

2 Theta (Degree)

a) b)

c) d)

34.0 34.5 35.0

Counts (A.U.)

2Theta (Degree)

GaN (0002)

ZnO (0002)

34.0 34.2 34.4 34.6 34.8 35.0

Counts (A.U.)

2Theta (Degree)

GaN (0002)

ZnO (0002)

Counts (arb. unit) Counts (arb. unit)Counts (arb. unit)

Counts (arb. unit)

(101̅2)

(101̅2)

< 101̅2 >

(101̅2) (101̅2)

< 0002 >

< 101̅2 >

a)

b)

c)

h

k i

l

(1 0 2) (0 0 0 1)

46.0 46.5 47.0 47.5 48.0 48.5 49.0 49.5 0.0

0.2 0.4 0.6 0.8 1.0

Normalised counts

2 Theta (Degree) ZnO (1 0 1 2) GaN (1 0 1 2)

0 50 100 150 200 250 300 350

0.0 0.2 0.4 0.6 0.8 1.0

Normalised counts

Phi (Degree)

(0002) (0002̅)

(0002)

< 0002 >

(0002) (0002̅)

(0002)

< 101̅2 >

(101̅2) (11̅02) (01̅12) (1̅012) (1̅102) (011̅2)

(1̅012̅) (1̅102̅) (011̅2̅) (101̅2̅) (11̅02̅) (01̅12̅)

{101̅2}

< 101̅2 >

< 0002 >

< 101̅2 >

(1000)

< 0002 >

< 101̅2 >

g) h)

a)

ZnO GaN

ZnO GaN

b)

c)

GaN

GaN

e) d)

GaN

100 200 300 400 500 600 0

200 400 600 800

* E 2 (High)

E 2 (Low) * E 2 (Hig h)

Intensit y (arb.unit )

Raman Shift (cm -1 )

GaN:Mg GZn GZnA

E 2 (Low)

450 500 550 600 650 700 750

642 nm

593 nm

544 nm

Intensity (A.U.)

Wavelength (nm)

GZn DLE 544nm peak 593nm peak 642nm peak Fitted curve

500 550 600 650

593 nm

Intensity (A. U)

Wavelength (nm) GZnA DLE 544nm peak 593nm peak Fitted curve

544 nm

(b)

(c)

(a)

(d)

400 500 600 700

0.0 0.2 0.4 0.6 0.8 1.0

580 nm

440nm

380nm365 nm

GaN:Mg GZn GZnA

Intensity (Normalised)

Wavelength (nm)

~0.9eV V

VB

~0.22 eV Zn

E

~3.06 eV

V

O

~2.28 eV

CB

250 500 750 1000 1250 1500 1750 2000 0

20 40 60 80 100

Transmission (%)

Wavelength (nm) GaN:Mg GZn GZnS

< 0002 >

< 101̅2 >