Polarity and threading dislocation dependence of the surface morphology of c-GaN films exposed to HCl vapor

Abstract

HCl-vapor etching can provide another degree of freedom in polarity-sensitive etching because TD-free N-polar GaN is inert to HCl vapor.

Inversion domain boundary structure of laterally overgrown c-GaN domains including the inversion from Ga to N polarity at a mask pattern boundary

“…Then, further growth would not extend the IDB because the growth front now consists of only one polar domain. This type of circular IDB during PILO was already observed when N-to-Ga polar inversion occurred during ELOG (Jang et al, 2018;Lee et al, 2018). It turns out, however, that the IDBs in PILO from N to Ga polarity can be formed on the energetically favorable f1100g planes in a different geometrical configuration of PILO, presumably because the circular openings of the mask are not uniformly filled up (Kim, 2018a).…”

“…PILO is known to be triggered by a mask pattern boundary. Since the IDBs in PILO were previously reported to be parallel with the AE[0001] direction (Lee et al, 2018), it is quite natural to infer from Figs. 1(a) and 1(b) that polarity inversion may not have occurred at the circular boundary.…”

“…Thus, wet etching in a KOH solution was carried out for polarity identification in this work. Computational simulations were carried out on 800 Â 800 grids to calculate the plan-view shape of a c-GaN domain in PILO by numerically integrating a level set equation; a similar approach has been described elsewhere (Osher & Fedkiw, 2003;Lee et al, 2014Lee et al, , 2018Yoon et al, 2017).…”

“…Adjustment of growth conditions can suppress the spontaneous inversion of N to Ga polarity of c-GaN (Wang et al, 2012;Song et al, 2014). In contrast with the original intention of suppressing the polarity inversion during epitaxial lateral overgrowth (ELOG) (Song et al, 2014), it was shown that the enhanced polarity inversion from N to Ga polarity can be utilized to grow N-polar c-GaN in a controlled manner Lee et al, 2018). Lateral inversion from Ga to N polarity during ELOG was also observed, but the IDBs of the lateral inversion from Ga to N polarity were mainly found on crystallographic planes (Kim, 2018b), while those observed in the lateral inversion from N to Ga polarity were mainly formed on noncrystallographic planes (Jang et al, 2018;.…”

“…Jang et al (2018) proposed a way to fabricate a Gapolar c-GaN film that is physically attached to but epitaxially separated from a sapphire substrate, by utilizing the lateral inversion from N to Ga polarity. Similarly, the lateral inversion from Ga to N polarity can be utilized to fabricate an N-polar c-GaN film that is physically attached to but epitaxially separated from a sapphire substrate, when combined with polarity-inverted lateral overgrowth and selective wet etching and regrowth and Ga-polarity-selective HCl vapor etching of GaN (Jang et al, 2018;Lee et al, 2018;Kim, 2018b).…”