Time-Periodic Markers Revealing the Growth Mechanism of GaN Nanowires by Si-Assisted MOVPE

Among the different methods used for the fabrication of GaN nanowires, the growth by metalorganic vapor-phase epitaxy (MOVPE) using the Si-assisted process efficiently produces much longer nanowires (ranging from 10 to 500 μm high) than other catalyst-free epitaxial methods. Although the silicon effect is well established to promote vertical growth, the lack of in situ methods to observe MOVPE nanowires during growth is an obstacle to the precise understanding of the vertical growth mechanism. In this work, the authors exploit time-periodic markers within the nanowires, induced by the periodic variation of the trimethylgallium (TMGa) partial pressure during growth, to have a calibrated insight into the growth process. These markers witness the evolution of the nanowire dimensions during the whole growth (i.e., on their time-dependent growth rate), as well as their exact form, and provide key information on the overall mechanism resulting in vertical growth. Based on this quantitative information, a complete model of Si-assisted GaN nanowire growth by MOVPE is constructed from the initial nucleation to the final steady growth state. This model is then used to establish a mathematical description of the process, which accurately reproduces the actual nanowire growth and thereby establishes the foundations for engineering and predicting the growth of GaN nanowires in an MOVPE environment depending on the growth conditions.