NANO LETTERS
Control of Si Nanowire Growth by Oxygen
2006 Vol. 6, No. 6 1292-1296
Suneel Kodambaka,* James B. Hannon, Rudolf M. Tromp, and Frances M. Ross IBM Research DiVision, T. J. Watson Research Center, Yorktown Heights, New York 10598 Received January 10, 2006; Revised Manuscript Received April 11, 2006
ABSTRACT Semiconductor nanowires formed using the vapor−liquid−solid mechanism are routinely grown in many laboratories, but a comprehensive understanding of the key factors affecting wire growth is still lacking. In this paper we show that, under conditions of low disilane pressure and higher temperature, long, untapered Si wires cannot be grown, using Au catalyst, without the presence of oxygen. Exposure to oxygen, even at low levels, reduces the diffusion of Au away from the catalyst droplets. This allows the droplet volumes to remain constant for longer times and therefore permits the growth of untapered wires. This effect is observed for both gas-phase and surface-bound oxygen, so the source of oxygen is unimportant. The control of oxygen exposure during growth provides a new tool for the fabrication of long, uniformdiameter structures, as required for many applications of nanowires.
Nanowires formed by the vapor-liquid-solid (VLS) growth mechanism1-3 are natural candidates for a range of novel devices having applications in optoelectronics, nanoelectronics, and sensors.4-13 In developing these applications, however, it is important to fabricate long, straight wires with constant diameters. Recipes for growing suitable wires have been developed successfully, allowing the fabrication of nanowire-based devices, but a comprehensive understanding of the key factors affecting wire growth is still lacking. We have therefore investigated the VLS growth mechanism in detail by carrying out all of the stages of wire growth, metal deposition, formation of the eutectic droplets, and semiconductor deposition, under a controlled environment within an in situ electron microscope. Direct observation of each process in situ allows us to quantify growth kinetics while avoiding uncontrolled environmental effects. Furthermore, because measurements of wire diameters are made at the growth front, any subsequent uncatalyzed sidewall growth will not affect the results. We have focused on a commonly used system, the growth of Si nanowires using Au catalyst, carrying out experiments at low pressures (
