Growth of High Aspect Ratio Wurtzite GaAs Nanowires.

Crystal phase control of III-V semiconductor nanowires grown by the vapor liquid solid mechanism has emerged as a new frontier in nanomaterials in the 2010s. Of particular interest is the ability to grow the metastable wurtzite crystal, which is commercially unavailable in semiconductors such as GaAs and SiGe. The successful growth of wurtzite GaAs nanowires has been demonstrated by precise control of the wetting contact angle of the catalyst particle. However, a recent discovery revealed an inherent limitation, known as the critical length, which restricts the maximum achievable aspect, length-to-diameter, ratio in wurtzite GaAs nanowire below 100. Here, we demonstrate the growth of wurtzite GaAs nanowire above the cirtical length with a stacking fault density of 10 SF/μm and precise crystal phase control down to the monolayer regime using Ga-pulses. The crystal phase control by Ga-pulsing is investigated as a function of pulse duration, frequency and position along the nanowire length. A pulse scheme is developed to stabilize the wurtzite crystal phase for aspect ratios up to nearly 200. This method, involving controlled transitions between wurtzite and zinc blende phases, expands the potential of the GaAs platform to create superlattices in high aspect ratio nanowires.