Effect of Hydrogen Treatment on High Efficiency Electroluminescence Device Using Silicon Nanocrystals
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Effect of Hydrogen Treatment on High Efficiency Electroluminescence Device Using Silicon Nanocrystals K. Sato*, T. Izumi*, M. Iwase**, Y. Show***, S. Nozaki*** and H. Morisaki*** * Department of Electronics, Faculty of Engineering, Tokai University, 1117 Kitakaname, Hiratsuka-shi, Kanagawa 259-1292, JAPAN ** Department of Electrical Engineering, Faculty of Engineering, Tokai University, 1117 Kitakaname, Hiratsuka-shi, Kanagawa 259-1292, JAPAN *** Department of Communications and Systems, The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu-shi, Tokyo 182-8585, JAPAN ABSTRACT We have fabricated the electroluminescence (EL) device using silicon (Si) nanocrystals, which were formed on Si substrate by co-sputtering of Si and silicon dioxide (SiO2). By treating with the Si nanocrystals in the hydrofluoric (HF) acid solution, the SiO2 region of the luminous layer reduced, and then, the electrons were efficiently injected in the Si nanocrystals. At the same time, Pb-center (non-radiative recombination center) was decreased by hydrogen termination to the Si-dangling bond in the interface between the Si nanocrystals and the SiO2 layer From these effects of the HF treatment, the high efficiency red light emission with the external quantum efficiency (EQE) of 0.35 % was obtained from the HF treated EL device under the operating voltage of +4.5 V. INTRODUCTION Since strong photoluminescence (PL) from nanometer-sized Si materials, such as porous silicon (PS)[1] and Si nanocrystals in the SiO2 films[2-7], was observed at room temperature, extensive studies have been carried out on nanometer-sized Si structures. Recently, some research groups have focused on EL properties as well as on PL properties, because the EL from the nanometer-sized Si structures is one of candidate materials for the Si based optoelectronic device, such as light emitting diodes (LED) and display devices. The EL devices using the PS and the Si nanocrystals emits visible light at room temperature[8-14]. However, they have been demonstrated a low efficiency light emission below 0.21 %[8,9]. The reason of the low efficiency light emission is due to the existence of the defects, which is the non-radiative recombination center. Moreover, these EL devices require the high operating voltage above 10.0 V, because the surface of the PS and the Si nanocrystals were covered with the oxidized layer (SiO2)[10-14]. From these problems of the EL on the nanometer-sized Si materials, it is necessary to reduce the defects and the SiO2 layer on the surface of the Si nanocrystals to form the high performance EL device. In this paper, we fabricate the EL device using the Si nanocrystals. The Si nanocrystals, F14.30.1
which were deposited by co-sputtering of the Si and the SiO2, in its EL device were reduced the defects and the SiO2 layer on its surface by the various hydrogen (H2) treatments to obtain the high efficiency light emission at the low operating voltage from its EL device. EXPERIMENTAL DETAILS Si nanocrystals in the SiO2 films, which was used as the lu
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