Direct measurement of dopant distribution in an individual vapour–liquid–solid nanowire

Abstract

Semiconductor nanowires show promise for many device applications, but controlled doping with electronic and magnetic impurities remains an important challenge. Limitations on dopant incorporation have been identified in nanocrystals, raising concerns about the prospects for doping nanostructures. Progress has been hindered by the lack of a method to quantify the dopant distribution in single nanostructures. Recently, we showed that atom probe tomography can be used to determine the composition of isolated nanowires. Here, we report the first direct measurements of dopant concentrations in arbitrary regions of individual nanowires. We find that differences in precursor decomposition rates between the liquid catalyst and solid nanowire surface give rise to a heavily doped shell surrounding an underdoped core. We also present a thermodynamic model that relates liquid and solid compositions to dopant fluxes.

Surfactant-assisted chemical vapour deposition of high-performance small-diameter GaSb nanowires

“…This is probably owing to the low solubility of sulfur in the Au-Ga catalyst seeds as well as its relatively high vapour pressure. This way, these S atoms cannot be introduced easily into the grown NW core via the VLS mechanism through the catalytic tip and the tip/body interface 40 ; they prefer to accumulate on the NW surface and passivate the active Sb sites, being consistent to the observed XPS results.…”

“…Realistically, during the growth process, it is inevitable that Ga will also be surface-diffused from the NW base and reacted with the surface-terminated Sb, contributing to the unintentional radial (VS) NW growth (red arrow); as a result, the tapering and non-uniform NW diameter (white circle) are obtained (Fig. 5b,c), as commonly found in other III-V NW growth 9,[40][41][42][43][44] . With the aid of sulfur surfactant passivating these surface active Sb sites, the NW sidewall is stabilized (red arrow) and minimal uncontrolled radial growth results (Fig.…”

Contactless monitoring of the diameter-dependent conductivity of GaAs nanowires

“…This also is in accordance with the dramatic effect of surface oxidation on the conductivity, reported in the next section. However, some contribution to the conductivity from inhomogeneous incorporation of impurities, due to changes in the NW growth mode, cannot be completely excluded [10].…”

“…The conductivity of NWs, one of the most important properties exploited in numerous applications, becomes extremely sensitive to the status of the surface with decreasing NW width, and dramatic conductivity changes can be observed when the Debye length becomes comparable to the NW radius [4]. Along with presence of adsorbates and charged surface states [5,6], other factors that may affect the conductivity include the (i) reduced mobility due to enhanced phonon or surface scattering [7,8], (ii) edge effects due to unsaturated bonds of the surface atoms [9], (iii) size-imposed limits to the effective doping concentration [9,10], (iv) size-dependence of depletion width [11], band-gaps [12,13], and recombination barriers [14]. As a result, significant scatter in the conductivity data are observed for individual GaAs NWs purportedly fabricated in the same manner [15].…”

Doping Incorporation in InAs nanowires characterized by capacitance measurements

“…Additionally, it is known from atom probe tomography studies that donor atoms tend to preferentially incorporate at the surface of the nanowire. 7 This affects the capacitance of the structure and hence the determined carrier concentration. It is thus of great importance to measure experimentally and study the capacitance for individual 8,9 as well as arrays of nanowires.…”