Optimization of Light emission from Silicon nanocrystals grown by PECVD
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1257-O03-05
Optimization of Light emission from Silicon nanocrystals grown by PECVD Satoshi Ishikawa1, Szu-Lin Cheng2, Yiyang Gong3, Jelena Vuckovic3 and Yoshio Nishi3 Corporate Manufacturing Engineering Center, Toshiba Corporation, Yokohama 235-0017, Japan 2 Department of Materials Science and Engineering, Stanford University, Stanford, CA 94040, U.S.A. 3 Department of Electrical Engineering, Stanford University, Stanford, CA 94040, U.S.A. 1
ABSTRACT Light emission from Si nanocrystals (SiNCs) embedded in Si oxide was studied in this work. SiNCs were fabricated by annealing a Si-rich oxide (SRO) deposited by a plasmaenhanced chemical vapor deposition (PECVD) system, using SiH4 and N2O as precursor gases. The highest photoluminescence (PL) intensity was obtained with a N2O flow rate of 125 sccm, a SiH4 flow rate of 1400 sccm, and annealing temperature of 900 °C. The PL wavelength was controlled by a N2O flow rate and annealing temperature, with blue shifting to the visible wavelengths for increasing N2O flow rate and decreasing annealing temperature. To approach emission at shorter wavelength, a Si oxide with SiNCs / SiO2 multi layer structure (MLS) was fabricated by similar methods. The SiO2 layer was used as a diffusion barrier to excess Si on vertical direction during the annealing process. Such a barrier can effectively reduce the diameter of SiNCs and shift the emission peak to shorter wavelength. A blue shift in PL was clearly observed as the thickness of Si oxide layer with SiNCs in MLS was reduced. Finally, the light emitting diode (LED) which consisted of n-type poly-Si / Si oxide with SiNCs / p-type poly-Si structure was also fabricated to study the electroluminescence (EL) of SiNCs. The current under the forward bias was about 10 times higher than under the reverse bias. The EL was obtained under a forward bias voltage and the EL intensity was proportional to the current.
INTRODUCTION Since photoluminescence (PL) from porous Si at room temperature was observed [1], research on light emission from nanostructured Si have been conducted [2, 3]. Si nanocrystals (SiNCs) have also been expected as one of the potential candidates of the emitting source with the visible and near-infrared wavelengths [4, 5]. Makarova et al. reported that photonic crystal (PC) could enhance the emission from SiNCs embedded in Si nitride in PC cavities [6]. The purpose of this work was to optimize growth conditions and a layer structure to obtain a higher luminescence and a shorter wavelength luminescence from SiNCs, which were fabricated by annealing a Si-rich oxide (SRO) deposited by a plasma-enhanced chemical vapor deposition (PECVD) system. The light emitting diode (LED) with SiNCs was also fabricated by using CMOS processes to study the electroluminescence (EL) of SiNCs.
EXPERIMENTS SRO was deposited on p-type (100) Si substrate by PECVD system under a plasma power of 40 W. Two percent SiH4 (N2 diluted) and N2O were used as precursors. The gas flow ratio was changed by varying a N2O flow rate and fixing a SiH4 flow rate as
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