Atomic-Scale Phase Transition of Epitaxial GaN on Nanostructured Si(001): Activation and Beyond

Abstract

An atomic-scale phase transition in heterophase epitaxy (HPE) of GaN on a 900 nm-wide v-grooved Si(001) substrate is reported. Two different incorporation mechanisms of adatoms sequentially occur for the hexagonal (h-) to cubic (c-) phase transition: orientation-and phase-dependent incorporation (ODI and PDI). Epitaxy begins with ODI that results in preferential growth of h-GaN individually aligned to opposing Si(111) facets inside a v-groove but incurs a structural instability by crystallographic mismatch at the groove bottom. This instability is relieved by an abrupt transition to c-phase, initiating from single or multiple atomic sites uniquely arranged atop the mismatch along the groove. Epitaxy proceeds with PDI that allows μm-scale c-GaN extended from these sites while suppressing growth of h-GaN. An important condition for HPE and the stability of c-GaN in further growth is derived from equilibrium crystal shape.

Initial stage of cubic GaN for heterophase epitaxial growth induced on nanoscale v-grooved Si(001) in metal-organic vapor-phase epitaxy

“…This implies that SF generation is a partial relief process of the strain within a single domain of c-GaN 7 . Also, the surface undulation of which the period is roughly sub-μm scale observed in previous work could be another strain relief available within a single c-phase domain [11].…”

“…Although the basic growth mechanism for c-III-N has been reported [11], the h-c transition and the associated initial stage of c-GaN growth has yet to be fully elucidated. To complete the phase transition (or nucleation of c-GaN), the local atomic arrangement must go through several steps that impact the crystallinity of the c-phase with sequential correlation.…”

“…The growth was stopped immediately after the h-c transition. The details of the pattern fabrication and growth conditions used in this work have been summarized elsewhere [11]. Figure 2 provides (a) a top-down view SEM image of a single groove and cross sectional (b) TEM and (c) STM images along the center of the groove indicated by two white arrows at both ends in (a).…”

“…In the twodimensional (2D) view at the cross section along the h-h junction, most of the voids including the interruption in the inset of figure 2(b) retain a random shape while some of them such as that in the inset of figure 2(c) are partly enclosed by well-defined facets. Our previous article focused on the inhomogeneous nucleation of c-GaN at the early stage of the h-c transition with the formation of nanodots by irregular agglomeration of Ga adatoms [11]. This work presents more precise observation based on the non-local characteristics of the h-c transition homogeneously providing a c-phase seed layer atop the h-h junction along the groove bottom.…”

Luminescence Characteristics in Hexagonal and Cubic‐Phase GaN on Micropatterned Si(100) Substrate

“…In Figure 3 , XRD measurement on such a structure shows a sharp peak at 40°, which is consistent with the c‐GaN(001) peak, as reported previously in GaN hexagonal‐cubic transition. [ 28 ] As shown in the SEAD pattern in Figure 2f, the yellow ring represents the c‐GaN diffraction spots, which are shown together with the two overlapped hexagonal phase diffraction spots indicated by the blue square. We measured the SEAD pattern of the boundary area in the blue square region in Figure 2e.…”