KrF Laser-Induced Nanometer Si Crystallites Formation and Tem Observation
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ABSTRACT We report the preparation of the nanometer Si crystallites constrained between aSiN,:H barrier layers by means of KrF excimer laser induced crystallization, X-ray diffraction (XRD) and Raman scattering spectra demonstrate that ultra thin a-Si:H well layers have been crystallized. The average grain size of Si crystallites is on the order of magnitude of a nanometer. Small-angle XRD spectrum indicates multilayer structures have not undergone laser damage. The results of TEM are presented to show smooth and abrupt interfaces of layered structures and nanometer Si crystallites arrayed one-by-one in the Si layer. The thermodynamics of KrF laser-induced crystallization of ultra-thin Si layer has been discussed.
INTRODUCTION Nanosized crystallites of various semiconductor materials with their promising properties of visible room temperature light emission for future opto-electronic applications have attracted the attention of many researchers. The recent discovery of visible room temperature photo-luminescence (PL) in porous silicon (PS) [1] prepared by electrochemical etching stimulated intensive research of "Si quantum dots". In order to fabricate such nanosized Si quantum dots materials, a variety of techniques, including compact chemical vapor deposition (CVD) [2], microwave plasma decomposition of Si4I- [3] and solution-phase synthetic methods [4] have been reported. However, the microscopic origin and mechanism of visible light emission from nanosized Si are still not clear. In this paper we report nanometer Si crystallites formation in KrF excimer laser crystallized a-Si:H/a-SiNx:H multi-quantum well (MQW) films and visible light emission from nano-Si crystallites at room temperature. Visible PL in similar structures by using Ar ion laser induced crystallization method was discovered before [5][6]. Ultra-violet (UV) excimer laser crystallization of a-Si:H thin films has been widely employed in large area electronics with the aim to prepare high mobility thin film transistors (TFTs) for liquid crystal displays (LCD) [7]. We introduce this technique to crystallize ultra-thin a-Si:H sublayers within MQWs for fabricating Si nano-crystallites. We expect to improve the surface morphology and microstructures of laser crystallized MQWs films, and to investigate the interaction mechanism between the pulse laser beam and ultra-thin Si layer within the multilayer structures. The results show that this method would be a new approach to fabricating luminescent Si with low-temperature and dry processes. 375 Mat. Res. Soc. Symp. Proc. Vol. 397 0 1996 Materials Research Society
EXPERIMENT The a-Si:H/a-SiN,:H MQW films were deposited on Corning 7059 glass or fused quartz substrates by a computer-controlled plasma enhanced chemical vapor deposition (PECVD) technique. The sublayer thickness was 4 nm for a-Si:H and 12 nm for a-SiNx:H, respectively. The deposition rate was 0. 11 nm/s under a total reaction pressure of 36 Pa at a substrate temperature of 250 "C . The details of the sample preparation were reported previously
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