Effect of Excimer Laser Annealing on Optical Properties of GaN Films Deposited by R.F. Magnetron Sputtering
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Effect of Excimer Laser Annealing on Optical Properties of GaN Films Deposited by R.F. Magnetron Sputtering Man Young Sung, Woong-Je Sung, Yong-Il Lee, Chun-Il Park, Woo-Beom Choi, Sangsig Kim Department of Electrical Engineering, Korea University, 1,5-Ka Anam-dong, Sungbuk-ku, Seoul 136-701, South Korea. ABSTRACT GaN thin films on sapphire were grown by RF magnetron sputtering with ZnO buffer layer. The tremendous mismatch between the lattices of GaN and sapphire can be partly overcome by the use of thin buffer layer of ZnO. The dependence of GaN film quality on ZnO buffer layer was investigated by X-ray diffraction(XRD). The properties of the sputtered GaN are strongly dependent on ZnO buffer layer thickness. The optimum thickness of ZnO buffer layer is around 30nm. Using XRD analysis, we have found the optimal substrate temperature which can grow high quality GaN thin film. In addition, the effect of excimer laser annealing(ELA) on structural and electrical properties of GaN thin films was investigated. The surface roughness and images according to the laser energy density were investigated by atomic force microscopy(AFM) and it was confirmed that the crystallization was improved by increasing laser energy density.
INTRODUCTION GaN-based wide band-gap semiconductors have been very attractive in recent years because of their unique properties and applications in optoelectronics and electronics devices working in the ultra-violet(UV) to blue wavelength range[1-5]. To grow a large area single crystal of GaN, one needs a suitable seed or a suitable substrate[6-9]. The most widely used substrate for the growth of GaN has been Sapphire(Al2O3). But there are large differences in the lattice parameter and thermal expansion coefficients between GaN and sapphire. Such a large mismatches induce stresses in the first few layers of GaN grown on sapphire. As the crystal grows, these stresses are reduced by forming stacking faults and dislocations[10]. Therefore, to obtain high quality GaN film, we need buffer layer which decreases lattice and thermal expansion mismatch rates. Also to recrystallize of GaN thin film, it needs proper annealing procedure. In this study, we report optimal deposition condition of ZnO and GaN thin films which were deposited by RF magnetron sputtering. Furthermore in order to make clear what effect the excimer laser annealing has on the crystallization of GaN films, we report results on changes with various the laser energy densities.
EXPERIMENTAL DETAILS Thin films growth and annealing ZnO and GaN thin films were deposited on (0001) sapphire substrate by RF magnetron sputtering. In this work, sintered 4 inch ZnO and GaN targets with 99.99% purity were used as the source materials. The substrates were first degreased and cleaned using standard cleaning I3.5.1
procedure. Firstly ZnO thin films were deposited with RF power 70W, substrate temperature 240 , Ar:O2 gas ratio 1:2. To investigate the effect of ZnO buffer layer thickness on it's quality, we varied the ZnO deposition time with 5 minutes int
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