Colossal injection of catalyst atoms into silicon nanowires

Abstract

The incorporation of impurities during the growth of nanowires from the vapour phase alters their basic properties substantially, and this process is critical in an extended range of emerging nanometre-scale technologies. In particular, achieving precise control of the behaviour of group III and group V dopants has been a crucial step in the development of silicon (Si) nanowire-based devices. Recently it has been demonstrated that the use of aluminium (Al) as a growth catalyst, instead of the usual gold, also yields an effective p-type doping, thereby enabling a novel and efficient route to functionalizing Si nanowires. Besides the technological implications, this self-doping implies the detachment of Al from the catalyst and its injection into the growing nanowire, involving atomic-scale processes that are crucial for the fundamental understanding of the catalytic assembly of nanowires. Here we present an atomic-level, quantitative study of this phenomenon of catalyst dissolution by three-dimensional atom-by-atom mapping of individual Al-catalysed Si nanowires using highly focused ultraviolet-laser-assisted atom-probe tomography. Although the observed incorporation of the catalyst atoms into nanowires exceeds by orders of magnitude the equilibrium solid solubility and solid-solution concentrations in known non-equilibrium processes, the Al impurities are found to be homogeneously distributed in the nanowire and do not form precipitates or clusters. As well as the anticipated effect on the electrical properties, this kinetics-driven colossal injection also has direct implications for nanowire morphology. We discuss the observed strong deviation from equilibrium using a model of solute trapping at step edges, and identify the key growth parameters behind this phenomenon on the basis of a kinetic model of step-flow growth of nanowires. The control of this phenomenon provides opportunities to create a new class of nanoscale devices by precisely tailoring the shape and composition of metal-catalysed nanowires.

Evolution of morphology and microstructure of GaAs/GaSb nanowire heterostructures

“…For most NWs, EDS cannot detect any obvious Au signal, but for some NWs, a much smaller Au particle is found to reside on the middle region of them. This suggests that the Au catalyst particle may diffuse away from the NW top and mainly diffuse into the bulk NW during our GaSb growth; similar results have also been reported in silicon NWs by previous literatures [33][34][35]. The diffusion behavior of Au atoms has exerted an important influence on the GaSb growth mode.…”

Rapid, Low-Temperature Synthesis of Germanium Nanowires from Oligosilylgermane Precursors

“…30,31 The rapid formation of steps and also the high step velocity enhances the impurity, or the solute trapping, and its incorporation into the matrix. 32,33 Rapid formation of Ge nanowires with oligosilylgermane precursors provides a high step velocity during the synthesis of the nanowires which enhances the probability of In adatoms being trapped at the catalyst-nanowire interface with the fast deposition of successive layers during nanowire growth. The fact that nanowires with faster growth kinetics, synthesized with precursor 1 over 5 min reaction time, exhibited higher In incorporation (1.8 at%) compared to nanowires with slower growth rates synthesized with precursor 2 over a 10 min reaction time (0.9 at%), is evidence that kinetic-dependent solute trapping of In incorporation in the Ge nanowire lattice is happening.…”

Three-dimensional nanoscale study of Al segregation and quantum dot formation in GaAs/AlGaAs core-shell nanowires

“…[4][5][6][7][8][9][10] Quantum dots can be inserted in semiconductor nanowires either deterministically, with specific shape and composition, [11][12][13][14] or as self-assembled structures. [15][16][17][18] Nanowires, furthermore, represent a model system for atom probe analysis, [19][20][21][22][23][24] as they closely approximate the shape of a field-emission tip. Nevertheless, and despite the interest of nanowire-based QDs for quantum information [25][26][27][28][29] and for their integration in nanoscale optoelectronic devices, [30][31][32][33] no studies of nanowire QDs by APT have been reported yet.…”