1. Page 1 Band Edge Electroluminescence from N + -Implanted Bulk ZnO Hung-Ta Wang 1, Fan Ren 1, Byoung S. Kang 1, Jau-Jiun Chen 1, Travis Anderson 1, Soohwan Jang 1, Hyun-Sik Kim 2, Yuanjie Li 2, David Norton 2, and Stephen Pearton 2 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

2. Page 2 Outline Background review Simulation Device fabrication Experimental results Conclusions Acknowledgements

3. 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)

4. 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).

5. Page 5 p-n LED Using MOCVD [W. Z. Xu et al.] Appl. Phys. Lett., 88, 173506 (2006).

6. Page 6 p-n LED Using Sputtering [Jae-Hong Lim et al.] Advance Material, 2006.

7. Page 7 MIS diode Using Ion implantation [Ya. I. Alivov et al.] Solid State Electronics, 48, 2343 (2004). EL CL

8. 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???

9. Page 9 Depth Profile Modeling Simulator: Profile Code (http://www.implantsciences.com/)

10. Page 10 Collision Event Modeling Simulator: SRIM-2003 (Free! http://www.srim.org/) @2000ADensity(cm -3 ) Zn vacancies 6.0×10 21 O vacancies 3.6 × 10 21 total vacancies 9.6 × 10 21 replacement5.2 × 10 20

11. Page 11 Device Fabrication ZnO substrate N + implanted ZnO (300nm) Au (80nm) Ni (20nm) Au (200nm) Ti (20nm) Cermet: (0001) undoped, I grade n 0 =10 17 cm -3 ; μ e =190 cm 2 /V·s Proc. of SPIE, Vol.5941, 59410D-1(2005) Implantation dose 1: 10keV, 2×10 13 cm -2 dose 2: 30keV, 5×10 13 cm -2 dose 3: 65keV, 9×10 13 cm -2 dose 4: 140keV, 2.4×10 14 cm -2 Thermal activation (RTA, furnace; T=600~1000°C) Backside metal: Ti/Au(20/200nm) Front-side metal: Ni/Au(20/80nm)

12. Page 12 I-V of Metal Contacts

13. Page 13 Diode I-V Characteristics Leakage current~10 -4 A @ -6V Ideality factor~11

14. Page 14 Light Intensity Performance Devices 600C RTA 800C RTA 950C RTA P at 100mA (Lumen) 3.57×10 -9 8.5×10 -10 0

15. Page 15 Electroluminescence at Room Temp.

16. Page 16 Electroluminescence at 120K

17. Page 17 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.

18. Page 18 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!

19. Page 19 Properties of GaN and ZnO PropertyGaNZnO Crystal structureWurtziteZinc BlendeWurtzite Lattice constant (nm) a 0 : c 0 : a 0 /c 0 : 0.3189 0.5185 1.6259 0.452 0.45 0.3249 0.5207 1.602 Density (g/cm 3 )6.155.606 Thermal conductivity (W cm -1 °C -1 )>2.10.6, 1-1.2 Linear expansion coefficient (°C -1 ) a 0 : c 0 : 5.59×10 -6 3.17×10 -6 -- -- 6.5×10 -6 3.0×10 -6 Energy bandgap (eV)3.51, direct3.3, direct3.4, direct Exciton binding energy (meV)28-60 Electron effective mass Electron Hall mobility at 300K (cm 2 ⋅ V -1 ⋅ s -1 ) 0.2 ~1000 ~1000 0.24 200 Hole effective mass Hole Hall mobility 0.8 ≤ 200 ≤ 350 0.59 5~50 Electron saturation velocity(10 7 cm ⋅ s -1 ) 2-2.523.2