Silicon Nanocrystals Fabricated by a Novel Plasma Enhanced Hydrogenation Technique Suitable for Light Emitting Devices
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Silicon Nanocrystals Fabricated by a Novel Plasma Enhanced Hydrogenation Technique Suitable for Light Emitting Devices Mehdi Jamei1, Farshid Karbassian1, Shams Mohajerzadeh1, Yaser Abdi1, Pouya Hashemi1, Michael Robertson2, and Sandra Yuill2 1 School of ECE, University of Tehran, Thin Film and Nanoelectronic Lab., North kargar Ave., Faculty of Engineering, Campus No.2, Tehran, 14395-515, Iran 2 Physics, Acadia University, Acadia University, Wolfville, NS B4P 2R6, Canada ABSTRACT The preparation of nano-crystalline silicon suitable for optoelectronic purposes by plasma-enhanced hydrogenation is reported. The method is compatible with mature ULSI technology because of its low temperature and non-wet processing environment. Visible light emission with peak wavelengths ranging from blue to red has been observed and could be tuned by varying the processing conditions. While the blue light emission may be due to surface defects present in the oxide layer, the green and red light emissions are believed to be due excitonic emission within the nano-crystalline grains as a result of quantum confinement effects. The layers were studied by SEM, TEM, CL and FTIR. A LED was fabricated and electroluminescence demonstrated. INTRODUCTION Porous and nano-crystalline (nc) silicon materials have attracted the attention of many researchers in past 15 years since Canham [1] reported the emission of visible light from porous silicon structures. The motivation for this work was the development of an efficient light emitter based on silicon technology for the fabrication of electronic and optoelectronic devices using a single silicon substrate. Silicon, in its bulk, crystalline form, possesses an indirect band gap and requires a phonon in order for radiative recombination to occur. However, as the nanocrystalline grains become smaller, the electron and hole wavefunctions extend further in momentum space increasing their overlap in the Brillouin zone, and hence the efficiency of light emission can increase significantly. The most mature methods of achieving nano-sized silicon grains which can emit light in the visible regime are anodic (wet) etching of a silicon substrate with a HF/ethanol solution [2, 3] and ion implantation of silicon into an insulator matrix such as SiO2 and Si3N4 [4, 5]. While the former approach is incompatible with existing ULSI manufacturing technologies, the latter does not offer the level of electrical conductance needed for optoelectronic device operation. Another method developed by Tsybeskov et al. [6] involved the formation of nano-crystalline grains in an as-deposited amorphous-silicon (a-Si) layer by high temperature annealing in excess of 1000 oC. This high temperature treatment and the presence of the remaining amorphous layer may limit application of this method in large area electronic technologies. In this paper we report an inexpensive and low-temperature (< 400 oC) technique for the preparation of nano-crystalline porous-silicon films that emit light in the visible regime. This technique in
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