Excimer Laser Crystallized HWCVD Thin Silicon Films: Electron Field Emission
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Excimer Laser Crystallized HWCVD Thin Silicon Films: Electron Field Emission
M. Z. Shaikh, K. A. O’Neill, S. K. Persheyev, M. J. Rose Carnegie Laboratory of Physics, University of Dundee, DD1 4HN, Scotland, United Kingdom
ABSTRACT Thin silicon films deposited using the Hot-Wire Chemical Vapor Deposition (HWCVD) technique are studied here for the effect of XeCl excimer laser crystallization on their structural, optoelectronic, and electron field emission properties. Excimer Laser Annealing (ELA) of the silicon thin films indicated increased dark conductivity and reduced optical gap. Encouraging Field Emission (FE) results were obtained from XeCl excimer laser processed HWCVD films on Cr, V, Mo, and Ti backplanes. Geometric field enhancement factors from surface measurements and Fowler-Nordheim Theory (FNT) were compared. FE thresholds were also found to be particularly influenced by the backplane material.
INTRODUCTION Electron field emission from cold cathodes is the next step for flat panel displays (FPD). Various materials technologies have the potential to become efficient devices for FPDs [1-3]. These technologies are expensive to develop to an industrial capacity. Therefore the ability to develop a FE cold-cathode based on established, low cost, and widely utilized material and techniques, such as amorphous Si and laser processing respectively, is a very attractive concept. The presence of two different phases, namely crystalline and amorphous silicon is confirmed by these experiments. Here we discuss the changes in the optical and electronic properties of the samples after laser crystallization and their application as cold cathodes in electron field emission devices. Preliminary research in this area has been carried out by the Universities of Surrey and Dundee [4,5].
EXPERIMENTAL Thin silicon films were prepared using standard Hot-Wire Chemical Vapor Deposition (HWCVD) [6]. The silicon films (~ 100 nm to 5.5 µm) were deposited on Corning 7059 glass substrates, n-type silicon wafers , and also on Cr, Mo, Ti, and V backplanes – of 100 nm thickness, prepared by sputtering on Corning 7059 glass substrates. However for this study we have concentrated on the 100 nm thin films. Amorphous to microcrystalline phases were grown by increasing the H2/ (SiH4+H2) ratio (from 5 to 97 %). Increasing crystalline fraction with H2 dilution was previously confirmed by Raman spectroscopy [7]. The deposition conditions for the HWCVD films were: H2 dilution 5 to 97 %, deposition pressure 30 to 50 mTorr, gas flow rate 5 to 100 sccm, substrate temperature 20 to 500 °C, deposition time 5 to 30 min, tungsten filament
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temperature 1700°C, and substrate-to-filament distance 50 mm. All the thin films were then irradiated using a pulsed Lambda Physik LPX-200 XeCl excimer laser with wavelength of 248 nm and Guassian beam profile [8]. Surface melt-through fluences ranged from 50 to 200 mJ/cm2 at a sample scan rate of 2 mm/sec. However, laser fluences higher than 100 mJ/cm2 completely ablated the thin films on glass. Ato
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