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Effects of Ga doping and nitridation on ZnO films prepared by RF Sputtering Takumi Araki1, Jun-ichi Iwata1 and Hiroshi Katsumata1 1 Department of Electronics and Bioinformatics, Meiji University, Kawasaki 214-8571, Japan ABSTRACT GaZnO and GaZnON thin films were deposited on both Si (100) and c-axis oriented sapphire substrates by RF co-sputtering of ZnO target and Ga2O3 tablets in Ar/O2 and Ar/N2, respectively, by changing the number of Ga2O3 tablets (NGa2O3) placed on the ZnO target in the range of 0 to 16. They were subsequently annealed in N2 at 800 °C and then, some of the samples formed by Ar/O2-sputtering were subjected to NH3 treatment at 650 °C for nitridation. XRD measurements revealed that the c-axis lattice parameter calculated from the ZnO (002) peak for GaZnON films on Si (100) was remarkably larger than for GaZnO films on Si (100). Moreover, ZnO (002) was observed up to NGa2O3=16 for GaZnON films formed on sapphire, while no XRD peaks were observed above NGa2O3=8 for GaZnON films on Si (100). Optical band-gap of GaZnO and GaZnON films became wider from 3.34 to 3.67 eV and from 3.21 to 3.40 eV, respectively, with increasing NGa2O3 from 0 to 16. Photoluminescence spectra of GaZnO films showed band-to-band emission at 380 nm, while those of GaZnON films exhibited broad and weak peaks centered at 550 nm and 647 nm. INTRODUCTION ZnO is an interesting wurtzitic semiconducting material with a wide band-gap of 3.3 eV and it has a large exciton binding energy of 60 meV. ZnO-based materials are recently studied as phosphor-free white LED materials[1]. Since the white LED without the phosphor does not have the color conversion loss, high luminous efficiency can be expected. Crystal structure of GaN is the same as that of ZnO, which has hexagonal wurtzitic structure, closely matched lattice constant and nearly the same band-gap of about 3.3 eV. It has been reported that the optical band-gap of Zn1-xGaxO thin films can be engineered from 3.3 to 4.9 eV by varying the Ga content[2]. Moreover, the reduction of the optical band-gap down to 2.4 eV has been observed from (ZnO)x(GaN)1-x solid solution powders with x = 0.81[3]. According to another report, optical band-gap of ZnON decreased from 3.26 to 2.30 eV with increasing the N concentration[4]. In these previous reports, however, (ZnO)x(GaN)1-x has been characterized as only powders, but it has not been characterized as thin films. Furthermore, there have been few observations on their luminescence properties. From these results, we believe that the band-gap of GaZnON materials can be widely controllable from 2.3 to 4.9 eV. The purpose of this study is to produce GaZnON thin films for future phosphor-free white LED materials and to clarify their optical and structural properties. It should be noted that here we present the photoluminescence properties of GaZnO and GaZnON films and the dependence of the type of substrates on their optical and structural properties. EXPERIMENTAL DETAILS

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The substrates used in this study were p-Si (100) or sapphire substrates. Ga