Growth mechanisms of GaN microrods for 3D core-shell LEDs: The influence of silane flow

The three dimensional growth of GaN structures as a basis for the fabrication of 3D GaN core-shell LEDs has attracted substantial attention in the past years. GaN nanorods or microrods with high aspect ratios can be grown by selective area epitaxy on a GaN buffer through a SiOx mask. It has been found earlier that silane substantially initiates vertical growth, with the exact underlying mechanisms being still unclear. Here, the influence of silane on the 3D GaN column growth was investigated by performing detailed growth experiments in combination with a thorough surface analysis in order to get insight into these mechanisms. The vertical growth rate is significantly enhanced by high silane fluxes, whereas the saturation of growth rate with the time is reduced. Thus, homogenous GaN columns with an aspect ratio of more than 35 could be achieved. A thin Si-rich layer on the non-polar m-plane facets of the columns has been detected using a combination of transmission electron microscopy, energy dispersive X-ray spectroscopy and Auger electron spectroscopy. This layer is suggested to be the reason for the increase in growth rate, modifying the effective collection range of the species along the sidewalls, and preventing the lateral growth.