Effect of Doping on Nanowire Morphology during Plasma-assisted Chemical Vapor Deposition
- PDF / 271,208 Bytes
- 7 Pages / 432 x 648 pts Page_size
- 2 Downloads / 169 Views
Effect of Doping on Nanowire Morphology during Plasma-assisted Chemical Vapor Deposition Andrew J. Lohn1,2, Kate J. Norris1,2, Robert D. Cormia3, Elane Coleman4, Gary S. Tompa4 and Nobuhiko P. Kobayashi1,2 1
Baskin School of Engineering, University of California Santa Cruz, Santa Cruz, CA 94040, USA 2 Nanostructured Energy Conversion Technology and Research (NECTAR) of Advanced Studies Laboratories (ASL), University of California Santa Cruz and NASA Ames Research Center, Moffett Field CA, 94035, USA 3 Foothill College, Los Altos Hills CA, 94022, USA 4 Structured Materials Industries Inc, Piscataway NJ, 08854, USA ABSTRACT Morphologies of silicon nanowires grown by plasma-assisted metalorganic chemical vapor deposition were studied in the presence of various dopant precursors. The varied precursors affected the axial and radial growth rates over orders of magnitude where triethylborane showed the strongest enhancements for both axial and radial growth, and triethylarsenic and triethylantimony retarded axial growth. Native oxide thickness is also shown to depend strongly on doping condition resulting in increased oxide thicknesses for increased carrier concentration, using shifts in the measured binding energy of the silicon 2p3/2 state as a proxy for carrier concentration. INTRODUCTION Materials systems based on semiconducting nanowires show exceptional promise in a wide range of potential applications including thermoelectrics1,2, photovoltaics3 and sensors4. This promise derives from a number of materials properties that are altered in a semiconductor with the geometry of a nanowire. Among the altered properties are increased strain relaxation5, increased phonon scattering6, altered density of states7, quantized conductance8, and increased surface to volume ratio9. All of the above properties and the competitive advantages derived from them are inherently related to the morphology and size of the nanowire, control of which during growth is still not entirely understood, particularly in the complex chemical environments during doping. In this study we investigate the effect of varied dopants on geometrical properties of silicon nanowires, particularly diameter, growth rates and native oxide formation when using a remote plasma method, which is technologically important for its potential to increase growth rates while reducing the damage one would expect for growths occurring within the plasma. EXPERIMENT
25
Plasma-assisted metal organic chemical vapor deposition (PA-MOCVD) was used to grow silicon nanowires. Disilane gas was used as the silicon source and various metalorganic precursors were co-supplied as dopant sources. Growth occurred on Si(111) substrates kept outside of the plasma which was ignited upstream of the growth environment. All growths were conducted with temperature at 550 degrees C and pressure at 1.5 Torr. Nanowires grew by the VLS mechanism using gold nanoparticle catalysts formed by melting 2 nm films of evaporated gold. Table 1 summarizes the varied conditions for the 5 samples discussed in
Data Loading...
