Surface depletion thickness of p-doped silicon nanowires grown using metal-catalysed chemical vapour deposition

An accurate evaluation of the radial dopant profile in a nanowire is crucial for designing future nanoscale devices synthesized using bottom-up techniques. We developed a very slow wet chemical etchant for gradually reducing the diameters of metal-catalysed, boron-doped silicon nanowires with varying diameters and lengths. Particular care has been taken to perform the experiment at room temperature to prevent dopant segregation, which is common in high temperature processes. By ensuring identical surface conditions subsequent to diameter reduction, the resistance of the nanowires was measured and, as anticipated, was found to increase with decreasing diameter. As the diameters were shrunk using wet-chemical etching, nanowires exhibited a non-linear increase of the resistance when the diameter was reduced to similar to 50 nm. This is an indication of near-complete depletion in the nanowires caused by nanowire surface charges. The dopant concentration of the nanowires was found to be 2.1 x 10(18) cm(-3) and the corresponding surface charge density was around 2.6 x 10(12) cm(-2).