Electrical Characteristics and Temperature Effects of Electroluminescing Silicon Nanocrystals
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E.W Forsvthe*, E. A. Whittaker*, D. Morton', B.A. Khan", B.S. Syweý, Y.Lut, S. Liangt, C. Gorlal, and G.S. Tompart * Stevens Institute of Technology; Physics and Eng. Physics Dept., Hoboken NJ, 07030 t Army Research Laboratories, Ft. Monmouth, NJ 07703 t Philips Electronics North American, Inc., Briarcliff Manor, NY, 10510 The Rutgers University, Piscataway, NJ, 08855-0909 • Structured Materials Industries, Inc; Piscataway, NJ, 08854 ABSTRACT The white electroluminescence (EL) demonstrated from Si nanocrystals in a wider bandgap amorphous oxide matrix based structure has exciting opportunities in electroptic applications as well as novel LEDs. In this report, we review the electroluminescent properties of the devices for rapid thermally annealed samples at anneal temperatures ranging from 875TC to 1025C. Depending upon the anneal conditions the EL spectra has shown two distinct spectral features; a strong emission peak at 380nm with a width of 50nm, and a broader features centered above 800nm,. Further, the I-V characteristics and corresponding EL spectra have been measured for sample temperatures ranging from 317K to 240K. In addition, Raman scattering estimated the mean particle sizes of the Si nanocrystals of 6.5nm and 8nm as well as provide insight to the nature of the amorphous matrix. The novel light emission from our devices demonstrates an exciting opportunity for Si nanocrystal (and nanocrystals in general) technology in a wide variety of applications. INTRODUCTION The recent work in light emission from Si nanocrystals has demonstrated the feasibility of electroluminescing Si based devices [1-8]. Electroluminescence (EL) has been observed in Si nanocrystals in a wider bandgap amorphous matrix. [1,2,6-8]. Photoluminescence (PL) from these materials has a spectra with emission in the visible [3-5]. However, the origin of the light emission of these nanocrystalline materials is complicated. The models for the light emission properties of these materials have included contributions from the nanoscale Si regions [1-3,9-11], chemical species [12-15], and interfacial states [16]. In the following work, we shall report the effects of annealing the Si nanocrystalline based films on the EL and PL with a nanostructure probed by Raman scattering. Next, the temperature dependent EL and corresponding DC I-V curves were measured for one device. Both studies demonstrated the correlation between the current density and the EL light emission achievable from Si nanocrystalline based devices. EXPERIMENTAL DETAILS A low pressure chemical vapor deposition process with Sill4 and N20 gas precursors formed the I pim semi-insulating Si-rich SiO 2 film on an n-doped Si substrate [6]. Next, the asgrown films were annealed at 850 0 C, 950TC and 1025TC in an N 2 atmosphere by rapid thermal annealing for 30secs. After the N 2 annealing, a 3mm diameter indium tin oxide (ITO) dot was deposited on the top of the film by rf-sputtering. Thus, the EL device was a vertical structure with the ITO providing the top contact and the l
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