Combinatorial Molecular Layer Epitaxy of Hf Based Phosphor Oxides
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COMBINATORIAL MOLECULAR LAYER EPITAXY OF Hf BASED PHOSPHOR OXIDES N. Arai 1, T. W. Kim1, H. Kubota1, Y. Matsumoto 2, H. Koinuma 1,2,3,4 1 Frontier Collaborative Research Center Laboratory, Tokyo Institute of Technology, 4259, Nagatsuta, Midori-ku, Yokohama 226-8503, Japan 2 Materials and Structures Laboratory, Tokyo Institute of Technology, 4259, Nagatsuta, Midori-ku, Yokohama 226-8503, Japan 3 COMET, Tsukuba 305-0044, JAPAN 4 CREST, Tokyo 169-0072, JAPAN ABSTRACT A series of MHfO3: Tm (M =Ca, Sr and Ba) composition spread films and superlattices (SLs) were quickly fabricated on SrTiO3 (001) substrate in the molecular layer-by-layer growth using combinatorial pulsed laser deposition (PLD) under in-situ reflection high-energy electron diffraction (RHEED) monitoring. Crystal structures and luminescence properties of composition-spread and SLs were evaluated by the concurrent X-ray diffractometer and cathode luminescence (CL), respectively. CL properties of the films were found strongly dependent on their composition and stacking sequence. Possible effect of the stress due to the film–substrate interaction on the CL property is discussed. INTRODUCTION Ag and Cl doped ZnS is one of the most efficient blue phosphor materials for cathode-ray tube (CRT) and has an excellent chromaticity with CIE (Commission Internationale de l'Eclairage) driven under a high voltage (25 kV) and low current density (0.5 µA/cm2 ) [1]. Recently, field emission display (FED) having the potential to combine the both advantages of CRT and liquid crystal display has been attracting much interest as a next generation flat panel display. However, the CL efficiency of this CRT’s blue phosphor material tends to saturate at a high current density under the operating conditions of FED. Furthermore, intensive electron excitation induces the decomposition of sulfide-based phosphors to emit S or SO2 gas, which seriously corrodes the cathode of FED. As a result, the lifetime of display decreases. In order to suppress the decomposition of sulfide-based phosphors, coating the phosphors with an oxide thin film is effective, but it seriously decreases the CL efficiency. There has been much interest in oxide-based phosphors due to their excellent chemical stability even under electron beam excitation, as well as to their potential of blue emission with high efficiency under high current density and low voltage [2]. Recently, Tm doped SrHfO3, which has a perovskite structure, was reported to show a blue luminescence of high color purity [3]. For the exploration of new and better Tm based oxide phosphors, we have employed the high-speed material screening using the combinatorial PLD technique under in–situ RHEED monitoring of growth process. This method we developed for parallel fabrication of high quality epitaxial oxide films has proved its capability of high-speed synthesis of magnet resistance [4], UV lasing [5], and transparent magnetic oxides [6]. The growth of epitaxial thin films with high crystallinity is expected to exhibit luminescence properties superi
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