Doped Silicon Nanoparticles Synthesized by Nonthermal Plasma
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1031-H14-04
Doped Silicon Nanoparticles Synthesized by Nonthermal Plasma Xiaodong Pi1, Rebecca Anthony1, Stephen Campbell2, and Uwe Kortshagen1 1 Department of Mechanical Engineering, University of Minnesota, 111 Church Street SE, Minneapolis, MN, 55455 2 Department of Electrical Engineering and Computer Science, University of Minnesota, 200 Union Street, Minneapolis, MN, 55455 ABSTRACT Silicon nanoparticles (Si-NPs) < 6 nm have been doped with B and P in nonthermal plasma. The doping efficiency of B is smaller than that of P, consistent with the theoretically predicted larger formation energy of B than P. The effect of doping on the oxidation-induced changes in light emission from Si-NPs is different between B and P. It is suggested that P is at or near the surface of Si-NPs, and that B is well incorporated inside Si-NPs. Inks based on doped Si-NPs are produced by attaching alkyl ligands to the surface of Si-NPs and dispersing them in organic solvents.
INTRODUCTION Accurately doping bulk Si to tune its properties is one of the most important achievements that have led to the success of the microelectronic industry. This has stimulated similar efforts to dope Si nanoparticles (Si-NPs). Fujii et al. [1–5] doped Si-NPs embedded in silicon oxide with B or P. They showed that the photoluminescence (PL) of Si-NPs is attenuated by B doping or highconcentration P doping. The decrease in PL efficiency resulted from the Auger effect, which involves a photogenerated exciton (electron-hole pair) and a dopant-induced free carrier (electron or hole). When P was doped at a low concentration, the PL of Si-NPs was usually enhanced. This implied that P passivated defects such as dangling bonds at the Si-NP/oxide interface. Švrček et al. [6] and Tchebotareva et al. [7] studied the effect of P doping on the PL of Si-NPs, which were also embedded in silicon oxide. Their results were similar to Fujii et al.’s. For applications such as photovoltaics which employ the modified electrical properties of doped Si-NPs, embedded Si-NPs in a dielectric such as silicon oxide are likely not a good choice, as the matrix prohibits efficient charge transport among Si-NPs. This problem can be solved by doping free-standing Si-NPs and then making films of them. Baldwin et al. [8] have doped free-standing Si-NPs synthesized in a liquid phase with P. A P concentration of 6% in SiNPs was achieved. Impurities resulting from their chemical reaction, however, prevented detailed characterization of the P-doped Si-NPs. In this paper we present an investigation of the doping of B or P in plasma-synthesized free-standing Si-NPs that are free of impurities except for partial coverage of H at the surface [9]. Doped Si-NP colloids (inks) have also been prepared for the formation of Si-NP films. .
EXPERIMENT The nonthermal plasma system used to synthesize intrinsic or doped Si-NPs was essentially similar to those described in previous papers [10–12]. SiH4/Ar plasma was employed to synthesize intrinsic Si-NPs. B2H6/H2 (10%/90% in volume) and PH3/H2 (15%/85% in vo
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