Deposition of GaN Films on Glass Substrate and Its Application to UV Electroluminescent Devices
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Deposition of GaN Films on Glass Substrate and Its Application to UV Electroluminescent Devices Tohru HONDA, Kenichi IGA and Hideo KAWANISHI Department of Electronic Engineering, Kohgakuin University, 2665-1 Nakano-machi, Hachiohji, Tokyo 192-0015, JAPAN Takahiro SAKAGUCHI and Fumio KOYAMA P&I Lab., Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, JAPAN Abstract GaN films were deposited on glass substrates using a compound-source molecular beam epitaxy technique. Electroluminescent devices with a double-insulator structure were also fabricated using the deposited films. When the devices were operated using a sine-wave voltage, one of the emission peaks was located in the UV spectral region. Introducing a small ammonia flow increased the deposition rate.
1. Introduction Deposition of GaN at lower substrate temperature than 600 °C is suitable for the application to low-cost and large-area light emitting devices such as flat display panels [1] or photo detectors [2]. Nevertheless synthesis of GaN required higher deposition temperatures than 700 °C [3], we consider that low substrate temperature will be realized using GaN powder as a source material and its sublimation [4]. The sublimation of GaN has already been reported [5]. However, hydrogen atoms remained in the GaN powder act as transport assistance during the sublimation. The quantity of remained hydrogen atoms is decreased during the deposition. Thus the sublimation rate is decreased during the sublimation [6]. It is not suitable for the fabrication of light emitting devices, because the deposition rate and quality of deposited films is changed during the deposition. To obtain the constant deposition rate, GaN source powders were pre-annealed in vacuum before the deposition. Although the deposition using compound source molecular beam epitaxy (CS-MBE) technique and no additional nitrogen source was performed, the layers deposited at room temperature were Ga-rich amorphous GaN. The N/Ga ratio in the film was able to control by changing the substrate temperature [7]. Although the control of substrate temperature is effective to obtain high light intensity of photoluminescence spectra, the deposition rate was decreased as increasing the substrate temperature, because of the re-evaporation of Ga metal in the surface. The low deposition rate of 80 nm/h is not enough to the device fabrication. In this paper, the fabrication of electroluminescent devices (ELDs) using deposited GaN films at the substrate temperature of 450 °C is reported. The introduction of ammonia during the growth is discussed in the view of deposition rate and optical properties.
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2. Deposition of GaN films For the deposition, GaN powder (5N) was used as the source material. This GaN, which was synthesized from Ga metal and ammonia, was kept at 960 °C in a Knudsen cell (K-cell) during the deposition. Because it contained hydrogen, the source was annealed in vacuum at 900°C for more than 10 hours to reduce the hydrogen contamination. The GaN powder was y
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