Ex situ doping of silicon nanowires with boron

An ex situ proximity technique is demonstrated for the electrical doping of silicon nanowires with spin on dopant (SOD) used as the boron source. The technique is based on solid-state diffusion and is comprised of two stages: predeposition and drive in. During predeposition, a predetermined amount of boron is introduced into the near surface region of the nanowires by holding the SOD source in close proximity to the nanowires. The boron concentration in the nanowires is controlled by the appropriate selection of predeposition temperature and time, with 800 and 950 °C and 5-10 min used in the present studies. The boron is then diffused further into the nanowires during the drive-in stage. The doped nanowires were characterized using scanning electron microscopy, secondary ion mass spectrometry, transmission electron microscopy, and four-probe electrical transport measurements. The high temperatures employed in this doping process do not result in any observable damage to these 120-180 nm diameter nanowires and good control over the dopant concentration in the range from 10¹⁸ to 10²⁰ cm^-3 is obtained. This ex situ doping technique provides a useful alternative to the methods currently available for electrical doping of nanowires, which are predominantly in situ techniques.