OUTLINE. Preparation of III Nitride thin 6/10/2010

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1 Preparation of III Nitride thin films for LEDs Huaxiang Shen Supervisor: Dr. Adrian Kitai 1 2 Two kinds of EL devices Light emitting diodes Powder EL and thin film EL LED E.PNG 3 4 Advantages High Efficiency Cross section of nitride based LED Mercury Free Small Size Long Lifetime Fast Response Package 5 After Handbook of Nitride Semiconductors and Devices, Volume 3 6 1

2 Color Red Materials AlGaInP Green AlGaInP, InGaN Blue InGaN Evolution of all LED performance with some benchmarks against commonly used lamps After Handbook of Nitride Semiconductors and Devices, Volume 3 7 Ponce, F.A. and D.P. Bour, NItride based semiconductors for blue and green lightemitting devices. Nature, (6623): p Research objective andmethodology Why III nitride? Short wavelength available, cover all visible wavelength range Thermal stability High breakdown field of GaN Difficulty for thin film growth Bulk GaN single crystal is too expensive 9 10 Crystal Symmetry Lattice constant (a; c, nm) Thermal expansion coefficient (a; c) ( 10-6 K -1 ) GaN W (0.3189; ) (5.59; 3.17) Sapphire H (0.4758; 1.299) (7.5; 8.5) 6H-SiC W (0.308; 1.512) (4.2; 4.68) Si C Galina Popovici, H.M., and S. Noor Mohammad, Deposition and properties of group III nitrides by molecular beam epitaxy, in Group III Nitride Semiconductor Compounds, B. Gil, Editor. 1998, Clarendon Press: Oxford. p GaN InN Bandgap 3.4 ev 0.65 ev Melting point 2500 o C 1100 o C Crystal structure Wurtzite Wurtzite Lattice constant a=3.189å, c=5.185å a=3.533å, c=5.693å 12 2

3 (1) (2) (3) (1)Frank van der Merwe (FvdM) or layer by layer two dimensional (2D) growth (2)Volmer Weber (VW) or three dimensional (3D) island growth (3)Stranski Krastanow (SK) or layer by layer plus island growth Wang, K., D. Pavlidis, and J. Singh, Initial stages of GaN/GaAs(100) growth by metalorganic chemical vapor deposition. Journal of Applied Physics, (3): p Mechanism of hexagonal islands coalescence, leading to 2D growth for GaN grown on a buffer layer. Briot, O., MOVPE growth of nitrides, in Group III Nitride Semiconductor Compounds, B. Gil, Editor. 1998, Clarendon Press: Oxford. p Research methodology Comparison Methods Advantages Disadvantages MOCVD MBE Sputtering Mature technology Commercialized Low temperature Excellent thin film quality Simple reaction: Ga+N 2 GaN In+N 2 InN Environmentally friendly High growth rate Low cost High temperature, T>1000 o C Toxic sources: TmGa, TmIn High cost Low growth rate: 500Å/h Quality of thin films Research methodology Sputtering Research methodology Chamber X ray rocking curve from (0002) reflection of GaN prepared by sputtering Park M, et al. X ray and Raman analyses of GaN produced by ultrahigh rate magnetron sputter epitaxy, Appl. Phys. Lett. 81, 1797 (2002); Schematic of reactive sputtering system for the preparation of IIInitride thin film

4 Research methodology Substrate Holder Research methodology Vacuum Mass spectrum of residual gas inside the chamber after pumping Inset: plasma, produced by DC magnetron Research methodology Thin film preparation steps 1. Clean Si wafer, especially by HF 2. Pump the system to Torr as the base pressure 3. Introduce Ar and N 2, Ar:N 2 =1:1, raise the pressure to 12 mtorr 4. Heat the substrate to the required temperature 5. Turn on power supply of sputtering gun to produce plasma 6. Thin film deposition Preliminary Results and Discussion XRD Preliminary Results and Discussion XRD 600 (002) tensity (Counts) Int (100) (101) Theta (Degree) XRD patterns of the GaN films deposited on Si (111) substrate at 700 o C by sputtering XRD patterns of the GaN films deposited on Si (111) substrate at 700 o Cby sputtering

5 Preliminary Results and Discussion SEM Preliminary Results and Discussion EDX N Ga Ga SEM images of GaN thin film deposited on (111) oriented Si at 700 o C by sputtering Left: Surface morphology; Right, Cross section view Summary Reactive sputtering equipment has been set up Preliminary y XRD and SEM results confirmed that GaN thin film can be prepared in this way Future Work Improve thin film quality, highly oriented thin film Prepare p GaN/GaInN quantum well structure Doping, to get p type and n type thin film Acknowledgement Dr. Adrian Kitai (Supervisor) Yingwei Xiang, Bo Li, and Yan Dong (Group members) Thank you!