Published online by Cambridge University Press: 01 February 2011
Silicon nanowires with high aspect ratios have been grown at high density using a variation of Plasma Enhanced Chemical Deposition (PECVD) known as Pulsed PECVD (PPECVD). Growth rate and morphology were investigated for a range of catalysts: gold, silver, aluminum, copper, indium and tin. The thickness of the catalyst layer was 100nm. Deposition was carried out in a parallel plate PECVD chamber at substrate temperatures up to 350°C, from undiluted semiconductor grade Silane. A 1 kHz square wave was used to modulate the 13.56 MHz RF power. Samples were analyzed using either a Phillips XL20 SEM or a ZEISS 1555 VP FESEM. The average diameter for nanowires grown using a gold catalyst layer was 150nm and the average length was 4μm although some nanowires were observed with lengths up to 20μm. Back-scattered-electron images clearly show gold present at the tips of the silicon nanowires grown using gold as a catalyst, confirming their growth by the vapor liquid solid (VLS) mechanism. Sporadic growth of nanowires was detected when using copper as a catalyst. Although gold performed best as catalyst for nanowire growth it was, however, closely followed by tin. The other catalysts produced nanowires with properties between these extremes.
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