Spontaneous inversion of in-plane polarity ofa-oriented GaN domains laterally overgrown on patternedr-plane sapphire substrates

Abstract

Spontaneously regulated in‐plane polarity inversion of a‐oriented GaN domains has been demonstrated for the first time. Crystallographic analysis revealed that each domain grown on circular‐hole‐patterned r‐plane sapphire substrates has basal faces with oppositely oriented in‐plane polarity. The inverted orientation of in‐plane polarity on the opposite basal faces is not due to merging between in‐plane polarity‐inverted domains nucleated on the patterned r‐plane sapphire substrate, but it was found to be due to spontaneous formation of an inversion domain boundary on the growth fronts of existing domains. This result provides new insights into controlling the in‐plane polarity of a‐oriented GaN, because the nucleation of in‐plane polarity‐inverted domains of a‐oriented GaN on r‐plane sapphire is symmetrically not allowed.

Polarity-inverted lateral overgrowth and selective wet-etching and regrowth (PILOSWER) of GaN

“…Due to different chemical reactivity, it is well known that Ga- and N-polar surfaces have very different surface morphologies upon KOH or H 3 PO 4 wet etching. Upon wet chemical etching, a Ga-polar surface remains to be flat, but a N-polar surface is filled with pyramidal hillocks 16 , 17 , 27 , 28 . In this work, wet chemical etching was used for polarity identification of GaN.…”

Transferable Thru-Hole Epitaxy of GaN and ZnO, Respectively, Over Graphene and MoS2 as a 2D Space Layer

“…It is known that the quasi-equilibrium shape of isolated GaN domains can be significantly changed by growth conditions and is well described by the kinetic Wulff plot. 13,14 In this work, a gable-roof-shape (instead of a flat-top-shape) was chosen as the quasi-equilibrium shape of a-GaN domains as previously observed in similar growth conditions, 15 since they are readily recognizable for the crystallographic alignment with one another. Figure 1a,b shows scanning electron microscopy (SEM) images of GaN domains grown on multilayer graphene transferred four and six times onto r-sapphire substrates, respectively.…”

Faceted growth of ({\bf {\overline 1}103})-oriented GaN domains on an SiO2-patterned m-plane sapphire substrate using polarity inversion

“…An additional measurement to check the polarity of the polar facet is necessary to confirm that this GaN sample is really (1103) oriented. Upon wet chemical KOH etching, it is well known that Àc and +c facets reveal distinct characteristic surface morphologies of their own: severely etched and covered by hexagonal-shaped pyramids versus barely etched (Shin et al, 2013;Lee et al, 2010;Zhuang & Edgar, 2005). Thus, this sample was chemically wet etched in 2.5 M KOH solution at room temperature, and an SEI of the chemically wet etched sample is shown in Fig.…”

“…The simulated domains are composed of a polarity-inverted part (in red) and a noninverted part (in blue), each of which was set to be nucleated at the edge of the SiO 2 mask. On the basis of the reports of identical growth rates of side-by-side domains with opposite polarities when grown with N 2 as carrier gas using hydride vapour-phase epitaxy (Shin et al, 2013) or by using metalorganic chemical vapour deposition (Collazo et al, 2006;Aleksov et al, 2006), the growth rates of +c and Àc facets in each domain (marked in red and blue, respectively) were set to be the same in this simulation. As the time evolution of GaN domains reveals, the boundary between the polarityinverted part (in red) and the non-inverted part (in blue) is a good match with the boundary between the domains with and without planar defects parallel with c facets in the TEM image.…”

“…As discussed above, the clear difference in the effectiveness of suppressing the QCSE between the (1103) and the (1103) orientation is one good example of the importance of polarity control in III nitrides. Although many papers on the polaritycontrolled or polarity-regulated growth of c-oriented (Lee et al, 2010;Collazo et al, 2006;Sumiya & Fuke, 2005) and nonpolar (Shin et al, 2013;Lee et al, 2014) GaN have been published, not so much attention has been paid to the polaritycontrolled growth of semipolar GaN. The polarity-controlled growth of (1103)-oriented semipolar GaN can be of great significance in effectively suppressing the QCSE, not only because it is much more inexpensive in comparison with homoepitaxial growth of (1103)-oriented GaN on a GaN substrate but also because it is relatively easier to grow a semipolar GaN film than a nonpolar GaN film.…”