Page 1

Band Edge Electroluminescence from

N+-Implanted Bulk ZnO

Hung-Ta Wang1, Fan Ren1, Byoung S. Kang1, Jau-Jiun Chen1, Travis Anderson1, Soohwan Jang1, Hyun-Sik Kim2, Yuanjie Li2, David Norton2, and Stephen Pearton2

1. Department of Chemical Engineering, University of Florida, Gainesville, FL 32611 2. Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611

Pennsylvania State University, University Park, PA

Session DD:P-Type Doping and Electroluminescence in ZnO

June 30, 2006

Page 2

Outline

Background review Simulation Device fabrication Experimental results Conclusions Acknowledgements

Page 3

Advantages of ZnO as Light Emitting Material

Unique properties of ZnO Wurtzite (Hexagonal) structure II-VI compound semiconductor Zn and O at 4f-site Direct wide bandgap = 3.37eV Transparent conducting oxide Binding energy of exciton (300K)= 60 meV

c

a

Oxygen

Zinc

ZnO light emitting diode Higher exciton binding energy Availability of high quality bulk substrate Easier wet etching Simpler growth technology (low cost)

Page 4

p-i-n LED Using Temperature Modulated Epitaxy [A. Tsukazaki et al.]

1. Nature Material, 4, 42 (2005).2. Jpn. J. Appl. Phys., Part 2 21, L643 (2005).

Page 5

p-n LED Using MOCVD [W. Z. Xu et al.]

Appl. Phys. Lett., 88, 173506 (2006).

Page 6

p-n LED Using Sputtering [Jae-Hong Lim et al.]

Advance Material, 2006.

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MIS diode Using Ion implantation [Ya. I. Alivov et al.]

Solid State Electronics, 48, 2343 (2004).

EL

CL

Page 8

ZnO LED by Ion Implantation

Opportunities: Well developed technology High yield rate, low cost technology p-type ZnO film is achievable using ion

implantation Ion implantation to bulk ZnO?

Challenges: How to activate implanted dopant in

damaged ZnO???

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Depth Profile Modeling

0 1000 2000 3000 4000

0.0

5.0x1018

1.0x1019

1.5x1019

2.0x1019

Con

cent

ratio

n(cm

-3)

Depth(A)

140 keV; 2.4e14 cm-2

65 keV; 9e13 cm-2

30 keV; 5e13 cm-2

10 keV; 2e13 cm-2

Sum

Simulator: Profile Code (http://www.implantsciences.com/)

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Collision Event Modeling

Simulator: SRIM-2003 (Free! http://www.srim.org/)

@2000A Density(cm-3)

Zn vacancies 6.0×1021

O vacancies 3.6 × 1021

total vacancies 9.6 × 1021

replacement 5.2 × 1020

0 1000 2000 3000 4000

0.0

5.0x1018

1.0x1019

1.5x1019

2.0x1019

Con

cent

ratio

n(cm

-3)

Depth(A)

140 keV; 2.4e14 cm-2

65 keV; 9e13 cm-2

30 keV; 5e13 cm-2

10 keV; 2e13 cm-2

Sum

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Device Fabrication

ZnO substrate

N+ implanted ZnO (300nm)

Au (80nm)Ni (20nm)

Au (200nm)Ti (20nm)

Cermet: (0001) undoped, I grade n0=1017 cm-3; μe=190 cm2/V·s

Proc. of SPIE, Vol.5941, 59410D-1(2005) Implantation dose 1: 10keV, 2×1013 cm-2

dose 2: 30keV, 5×1013 cm-2

dose 3: 65keV, 9×1013 cm-2

dose 4: 140keV, 2.4×1014 cm-2

Thermal activation (RTA, furnace; T=600~1000°C)Backside metal: Ti/Au(20/200nm)Front-side metal: Ni/Au(20/80nm)

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I-V of Metal Contacts

-0.10 -0.05 0.00 0.05 0.10-0.03

-0.02

-0.01

0.00

0.01

0.02

0.03Ti/Au(20/200nm)

n-n

Cur

rent

(A)

Voltage(V)-10 -5 0 5 10

-0.010

-0.005

0.000

0.005

0.010

Cur

rent

(A)

Voltage(V)

Ni/Au(20/80nm) front-front

Ti/Au(20/200nm) back-back(n-n)

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Diode I-V Characteristics

-15 -10 -5 0 5 10 15-0.04

-0.03

-0.02

-0.01

0.00

0.01

0.02

0.03

0.04N+ implanted ZnO

600C, O2, 2 mins.

800C, O2, 2 mins.

950C, O2, 2 mins.

Cur

rent

(A)

Voltage(V)-10 -8 -6 -4 -2 0 2 4

1x10-10

1x10-8

1x10-6

1x10-4

1x10-2

1x100

800C O2 RTA

-------- linear fit, slope=1.4

Cur

rent

(A)

Voltage(V)

Leakage current~10-4A @ -6V

Ideality factor~11

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Light Intensity Performance

0 5 10 150.00

0.02

0.04

0.06

0.08

0.10

0.12

0.0

5.0x10-8

1.0x10-7

1.5x10-7

2.0x10-7

2.5x10-7

Voltage (V)

Cu

rra

nt (A

)

600C O2 RTA 2mins

current power

Po

we

r(m

W)

Devices600C RTA

800C RTA

950C RTA

P at 100mA (Lumen)

3.57×10-9 8.5×10-10 0

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Electroluminescence at Room Temp.

350 400 450 500 550 6000

50000

100000

150000

200000

250000

300000

350000

400000

450000T= 298 K

Un-implanted ZnO Implanted ZnO

PL

inte

nsity

(ar

b. u

nit)

wavelength (nm)

350 400 450 500 550 600

0

2000

4000

6000

8000

10000

12000

I= 100 mA I= 30 mA I= 10 mA Device off

T= 298 K

EL

inte

nsity

(ar

b. u

nit)

wavelength (nm)

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Electroluminescence at 120K

350 400 450 500 550 600

0

2000

4000

6000

8000

10000

12000

T= 120 K T= 298 K

I= 30 mA

EL

inte

nsity

(ar

b. u

nit)

wavelength (nm)

350 400 450 500 550 6000

50000

100000

150000

200000

250000

300000

350000

400000

450000T= 298 K

Un-implanted ZnO Implanted ZnO

PL

inte

nsity

(ar

b. u

nit)

wavelength (nm)

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Conclusions

MIS diode was achieved by N+_implanted ZnO bulk.Yellow EL was obtained from N+-implanted ZnO at room T.Band-edge EL was obtained at 120K. Future work: 1. p-type conductivity. 2. pn LED.

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Acknowledgements

This work at UF is supported by: DOE Grant No. DE-FC26-04NT42271. DOE Contract No. DE-AC05-00OR22725. USAFOSR under Grant No. F49620-03-1-0370.

Thank you very much!

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Properties of GaN and ZnO

Property GaN ZnOCrystal structure Wurtzite Zinc Blende Wurtzite

Lattice constant (nm)a0:

c0:

a0/c0:

　0.31890.51851.6259

　0.4520.45　

　0.32490.52071.602

Density (g/cm3) 6.15 5.606

Thermal conductivity (W cm-1°C-1) >2.1 0.6, 1-1.2

Linear expansion coefficient (°C-1)a0:

c0:

　5.59×10-6

3.17×10-6

　--

　6.5×10-6

3.0×10-6

Energy bandgap (eV) 3.51, direct 3.3, direct 3.4, direct

Exciton binding energy (meV) 28 - 60

Electron effective massElectron Hall mobility at 300K (cm2 V⋅ -1 s⋅ -1)

0.2~1000

　　~1000

0.24200

Hole effective massHole Hall mobility

0.8≤ 200

　　≤ 350

0.595~50

Electron saturation velocity(107cm s⋅ -1) 2-2.5 2 3.2