Synthesis and characterization of Tb-doped AlBNO films for electroluminescence devices
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1195-B13-02
Synthesis and characterization of Tb-doped AlBNO films for electroluminescence devices Keiko Masumoto, Yuta Iwano, Chiharu Kimura, Hidemitsu Aoki and Takashi Sugino Department of Electrical, Electronic and Information Engineering, Graduate School of Engineering, Osaka University, Osaka 5650871, Japan
ABSTRACT Tb-doped AlBNO (AlBNO:Tb) films with various composition ratios are investigated for luminescence layers of inorganic electroluminescence(EL) devices. Luminescence layers with a wide bandgap and a low dielectric constant are required to realize high performance of EL devices. The ultraviolet-visible radiation absorption measurement and capacitance-voltage (C-V) measurement show that the AlBNO:Tb films have wider bandgap and lower dielectric constant than ZnS which is put to practical use as the host material of the luminescence layer. Photoluminescence (PL) measurement indicates that PL intensity increases with increasing B composition ratio in the range of 5 % - 10 %. Moreover, the suppression factor of the PL intensity can be understood through the annealing experiment. The PL intensity of the film with 800 °C annealing is about 10 times larger than that of the film without annealing. X-ray photoelectron spectroscopy (XPS) measurement suggests that Tb4+ ions decrease compared with Tb3+ ions after annealing treatment. O atoms in the AlBNO:Tb film are dissociated from Tb and bonded to B atoms by annealing treatment. This suggests that decrease of Tb4+ ions is related to increase of the PL intensity.
INTRODUCTION Luminescence of rare-earth ions shows the stable and sharp emission band because the luminescence uses the 4f-shell that is shielded from its surroundings by 5s-shell and 5p-shell filled with electrons. Inorganic EL devices which use luminescence of rare-earth ions have attracted attentions because the luminescence layer is allowed to be an amorphous or polycrystalline film. It is expected that inorganic EL devices are cheaper and more suitable to make large area devices than light emitting diodes (LEDs) which need single crystals. However, the operation voltage of inorganic EL devices is higher than that of LEDs. To lower the operation voltage, dielectric constant of the luminescence layer should be low. We have chosen AlBNO films as a host material for the luminescence of rare-earth ions. Moreover, we have used Tb as the rare-earth atom because the luminescence of Tb is green which has high luminous coefficient. Since the dielectric constants of AlN and BN are 9 and 4, respectively, the AlBNO films will have lower dielectric constant than ZnS (εr = 8.3) which has been mainly reported and put to practical use as the host material so far [1]. In addition, the AlBNO films are expected to have wide bandgap which can transmit the visible light because the bandgap of AlN and BN is above 6.0 eV. In this research, AlBNO:Tb films with various composition ratios are grown and characterized. Annealing effect is also investigated.
EXPERIMENT The AlBNO:Tb films were deposited by RF magnetron sputt
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