Initial stage of cubic GaN for heterophase epitaxial growth induced on nanoscale v-grooved Si(001) in metal-organic vapor-phase epitaxy. (9th November 2018) - Lee, S C
Abstract: The initial stages of the nucleation of cubic ( c -) GaN in heterophase epitaxy on a Si v-groove are investigated. Growth of GaN on a nanoscale {111}-faceted v-groove fabricated into a Si(001) substrate proceeds in the hexagonal ( h -) phase that induces a secondary v-groove replicating the substrate topography with two opposing {0001} facets. The secondary v-groove is then orientationally mismatched at the junction of the h -GaN facets ( h –h junction) resulting in structural instability. This instability is relieved either by the formation of voids that reduce the actual junction area or by the transition to c -phase ( h–c transition) suppressing further extension of the h–h junction. The distribution of voids that is locally affected by the island growth mode of h -GaN on Si(111) and the imperfection in the groove geometry impacts the initial stage of heterophase epitaxy. Primarily, The h–c transition is observed as a non-local phenomenon; it occurs homogeneously and simultaneously along the bottom of the entire secondary groove and forms a one-dimensional (1D) seed layer except for some interruptions where the h–h junction is defected by gaps or incomplete voids. Between these interruptions, epitaxy retains a single crystal but results in a series of c -GaN nanodots on the seed layer with large fluctuation in size and spacing. The adatom incorporation observed in this heterophase epitaxy is a 1D analog to the wetting of a substrate followed by the self-assembly in conventional quantum dot epitaxy. The surface morphology of the c -GaN nanodots is governed by the faceting mostly composed of (001)- and (11 n )-orientations and the roughening between these facets that ultimately affect the morphology of the final top surface of the c -III-N. The interruptions interfere with the homogeneity of the h–c transition and can cause antiphase defects and mosaicity. Based on experimental results, a solution to improve these issues is proposed.