The role of composition and diameter in the crystal purity of InAsxP1−x nanowires

Ternary InAsxP1−x nanowires are widely considered promising building blocks for fundamental studies and applications in nano- and opto-electronics. However, it is admittedly challenging to maintain the necessary control over the crystal purity of nanowires. Furthermore, the crystal phase trends in ternary III–V nanowires remain generally unknown. In this work, we present wurtzite InAsxP1−x nanowires with different compositions x, ranging from 0 to 0.54, grown via chemical beam epitaxy on InP(111)B substrates using Au colloidal catalysts of different diameters. Transmission electron microscopy studies reveal that a pure wurtzite phase of the nanowires requires larger InAs fractions x for larger diameters of Au colloids (in particular, x = 0.36 for 20 nm diameter and x = 0.54 for 30 nm diameter Au colloids). We developed a model for the critical composition of thin vapor–liquid–solid III–V ternary nanowires xc corresponding to the transition from a polytypic structure at x < xc to a pure wurtzite structure at x > xc. For the InAsxP1−x material, the critical composition increases with the nanowire diameter, which explains our experimental findings. These results shed more light on the composition- and diameter-dependent polytypism, offering valuable insights for the design and crystal phase control of InAsxP1−x and other III–V ternary nanowires.