Ballistic Electron Surface-Emitting Cold Cathode by Porous Polycrystalline Silicon Film Formed on Glass Substrate
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Ballistic Electron Surface-Emitting Cold Cathode by Porous Polycrystalline Silicon Film Formed on Glass Substrate Takuya Komoda, Tsutomu Ichihara, Yoshiaki Honda, Koichi Aizawa, and Nobuyoshi Koshida1 Advanced Technology Research Laboratory, Matsushita Electric Works, Ltd., Osaka, 571-8686, Japan 1 Faculty of Technology, Tokyo University of Agriculture and Technology, Tokyo, 184-8588, Japan ABSTRACT It is demonstrated that a porous polycrystalline silicon (PPS) film is useful as a ballistic electron emitter for excitation source of a flat panel display. A 1.5 m polysilicon layer is deposited on a silicon substrate by Low Pressure Chemical Vapour Deposition (LPCVD) technique and subsequently anodised in an ethanoic HF solution and oxidised in a Rapid Thermal Oxidation (RTO) furnace. A thin Au film is deposited onto the RTO-treated PPS layer and used as a top electrode. The electron emission current Ie and the diode current Ips are measured as a function of the bias voltage Vps. Electron emission of which onset voltage is about 8 V rapidly increases with increasing Vps. The Ie value reaches about 2 mA/cm2 for Vps= 20 V at which the emission efficiency defined as Ie/Ips is about 1 %. The emission mechanism has also been investigated in terms of the correlation between the emitted electron energy and the structure of PPS layer. The observed energy distribution curve of output electrons suggests that the PPS layer acts as a ballistic transport medium and the emission occurs based on multiple tunnelling through silicon nanocrystallites. The PPS layer is also formed on the polysilicon layer deposited on a glass substrate by Plasma Enhanced Chemical Vapour Deposition (PCVD) technique. In this case, the film is treated by an electrochemical oxidation (ECO) in an H2SO4 solution. Similar emission characteristics are observed, although the emission current is lower than that formed on silicon substrate. We also demonstrate the 2.6 inches diagonal 53x40 pixels multicolour flat panel display. We name it ballistic electron surface-emitting display device (BSD). BSD shows the possible application to the future flat panel display. INTRODUCTION The dramatic discovery of room temperature visible photoluminescence (PL) of chemically etched porous silicon (PS) [1] and electroluminescence (EL) of the PS diode [2] was an important milestone along the route to the eventual realisation of a silicon-based optoelectronics technology. Subsequent research revealed that the EL efficiency can be improved up close to a practical level [3] and intensive research and development to achieve high efficient, high intensity, tuneable visible light emitting devices based on other related materials [4,5]. On the course of investigating the electrical excitation process in PS in order to clarify the mechanism of electroluminescence, electron emission from a PS diode with a structure of Au/PS/Si substrate was discovered by one of the authors in 1995 [6]. It triggered another possibility of an application of porous silicon to a novel cold cathode [7]. Until
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