An atomic force microscopy study of a temperature dependent morphology transition of GaN grownj on sappire by MOCVD

摘要

The dependence of the surface morphology of GaN epilayers grown by metal-organic chemical vapour deposition on the growth temperature at tow different pressures has been studied using atomic force microscopy. First, the {0 0 0 2}, {1 1 0 1} and the {1 1 0 0} faces. Experimental results show that on Ga terminted GaN films both the (0 0 0 1) and the {1 1 0 1} faces are present for a considerable temperature range. At low deposition temperatures the {1 1 0 1} faces dominate, whereas at higher growth temperatures the morphology is determined by growth in the [0 0 0 1] direction. It is shown that a growth rate parameter, α_GaN, proportional to the relative growth rates of the (0 0 0 1) and the {1 1 0 1} faces, can be used to describe the morphology of the film. The (0 0 0 1) surfaces show growth spirals emerging from screw dislocations. used to describe the morphology of the films. The (0 0 0 1) surfaces show growth spirals emerging from screw dislocations. The single or double spirals are composed of monatomic steps. The double steps tend to split at the spiral centers, which can be explained by entropy repulsion and a high surface diffusion. Most spiral centers are accompanied by hollow cores, the size of which is larger than prided using Frank's theory. A possible explanation for the large diameter of the hollow cores is given by the precipitation of vacancies along the dislocations.