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

Abstract

On an SiO2-patterned c-plane sapphire substrate, GaN domains were grown with their polarity controlled in accordance with the pattern. While N-polar GaN was grown on hexagonally arranged circular openings, Ga-polar GaN was laterally overgrown on mask regions due to polarity inversion occurring at the boundary of the circular openings. After etching of N-polar GaN on the circular openings by H3PO4, this template was coated with 40-nm Si by sputtering and was slightly etched by KOH. After slight etching, a thin layer of Si left on the circular openings of sapphire,but not on GaN, was oxidized during thermal annealing and served as a dielectric mask during subsequent regrowth. Thus, the subsequent growth of GaN was made only on the existing Ga-polar GaN domains, not on the circular openings of the sapphire substrate. Transmission electron microscopy analysis revealed no sign of threading dislocations in this film. This approach may help fabricating an unholed and merged GaN film physically attached to but epitaxially separated from the SiO2-patterned sapphire.

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).…”

“…Thus, the robust preference of IDBs for the f1120g plane over the f1100g plane in our work suggests that it is necessary to take more than formation energy into consideration to explain this preference. This preferential formation of IDBs on the f1120g plane is in strong contrast with the formation of IDBs on the noncrystallographic circular plane during PILO from N to Ga polarity (Jang et al, 2018). The preferential formation of IDBs on either crystallographic or noncrystallographic planes is assumed to be related to the way in which circular openings are filled up by GaN domains, as explained in the following paragraphs.…”

“…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.…”

“…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).…”

“…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).…”