Control of the crystallization process is central to developing novel materials with atomic precision to meet the demands of electronic and quantum technology applications.Semiconductor nanowires grown by the vapor-liquid-solid process are a promising material system in which the ability to form components with structure and composition not achievable in bulk is well-established. Here we use in situ TEM imaging of GaAs nanowire growth to understand the processes by which the growth dynamics are connected to the experimental parameters. We find that two sequential steps in the crystallization processnucleation and layer growthcan occur on similar time scales and can be controlled independently using different growth parameters. Importantly, the layer growth process contributes significantly to the growth time for all conditions, and will play a major role in determining material properties. The results are understood through theoretical simulations correlating the growth dynamics, liquid droplet and experimental parameters.A central challenge in crystal growth is to understand the dynamic and transient processes underlying the nucleation and growth steps. The ability to independently control these two steps would greatly expand the potential to design the structure, morphology and properties of the resulting material. Understanding the steps in crystallization is particularly important in

Growing GaAs nanowires with well-defined crystal structures is a challenging task, but may be required for the fabrication of future devices. In terms of crystal phase selection, the connection between theory and experiment is limited, leaving experimentalists with a trial and error approach to achieve the desired crystal structures. In this work, we present a modeling approach designed to provide the missing connection, combining classical nucleation theory, stochastic simulation, and mass transport through the seed particle. The main input parameters for the model are the flows of the growth species and the temperature of the process, giving the simulations the same flexibility as experimental growth. The output of the model can also be directly compared to experimental observables, such as crystal structure of each bilayer throughout the length of the nanowire and the composition of the seed particle. The model thus enables for observed experimental trends to be directly explored theoretically. Here, we use the model to simulate nanowire growth with varying As flows, and our results match experimental trends with a good agreement. By analyzing the data from our simulation, we find theoretical explanations for these experimental results, providing new insights into how the crystal structure is affected by the experimental parameters available for growth.

The opportunity to engineer III–V nanowires in wurtzite and zinc blende crystal structure allows for exploring properties not conventionally available in the bulk form as well as opening the opportunity for use of additional degrees of freedom in device fabrication. However, the fundamental understanding of the nature of polytypism in III–V nanowire growth is still lacking key ingredients to be able to connect the results of modeling and experiments. Here we show InP nanowires of both pure wurtzite and pure zinc blende grown simultaneously on the same InP [100]-oriented substrate. We find wurtzite nanowires to grow along and zinc blende counterparts along . Further, we discuss the nucleation, growth, and polytypism of our nanowires against the background of existing theory. Our results demonstrate, first, that the crystal growth conditions for wurtzite and zinc blende nanowire growth are not mutually exclusive and, second, that the interface energies predominantly determine the crystal structure of the nanowires.

Ternary III−V nanowires are commonly grown using the Au-seeded vapor−liquid−solid method, wherein the solid nanowires are grown from nanoscale liquid seed particles, which are supplied with growth species from the surrounding vapor phase. A result of the small size of these seed particles is that their composition can vary significantly during the cyclical layer-by-layer growth, despite experiencing a constant pressure of growth species from the surrounding vapor phase. Variations in the seed particle composition can greatly affect the solid nanowire composition, and these cyclical dynamics are poorly understood for ternary nanowire growth. Here, we present a method for simulating nanowire growth which captures the complex cyclical dynamics using a kinetic Monte Carlo framework. In the framework, a nanowire grows through the attachment or detachment of one III−V pair at the time, with rates that are based on the momentary composition of the seed particle. The composition of the seed evolves through the attachment and detachment of III−V pairs to the solid nanowire and through the impingement or evaporation of single atoms to the surrounding vapor. Here, we implement this framework using the As−Au−Ga−In materials system and use it to simulate the growth of Auseeded InGaAs nanowires with an average solid Ga/III ratio around 0.5. The results show that nucleation preferentially occurs via clusters of InAs and that the compositional hierarchy of the liquid seed (X As < X Ga < X In ) determines much of the dynamics of the system. We see that imposing a constraint on the simulation, that only the most recently attached III−V pair can be detached, resulted in a significant narrowing of the compositional profile of the nanowire. In addition, our results suggest that, for ternary systems where the two binaries are heavily mismatched, the dynamics of the seed particle may result in an oscillating compositional profile.

The radius of III–V nanowires is known to have an effect on the resulting crystal structure during particle-assisted growth; however, the causes behind this effect remain under debate. In this work, we use stochastic simulations of nanowire growth to evaluate how the radius (R) affects the growth dynamics and how this in turn affects the crystal structure selection. This is due to the geometry of the growing nanowire: the number of atoms in the seed particle scales with R 3, and the number of III–V pairs per layer scales with R 2. The influx of growth species to the seed can, for instance, scale with the surface area of the seed particle for direct impingement (∝R 2) or the perimeter of the nanowire for sidewall diffusion (∝R 1) or be radius-independent for substrate diffusion in some cases (∝R 0). These differences in radius dependencies cause the particle composition to change more rapidly for thinner nanowires, which in turn leads to nucleation at higher supersaturations and promotion of the wurtzite structure. In addition, the geometry can also make the influx V/III ratio dependent on the nanowire radius, which can influence the selection of crystal structure in different ways depending on the materials system and growth regime.