Selective growth of GaN on sapphire substrates treated with focused femtosecond laser pulses

Lateral Polarity Control in GaN Based on Selective Growth Procedure Using Carbon Mask Layers

“…Based on previous scanning electron microscope (SEM) and atomic force microscope (AFM) measurements, we confirm that GaN growth has been suppressed over the laser-irradiated area. 11) In contrast, with increasing laser-pulse energy up to 0.95 J (the top feature), the center of the laser-irradiated area was covered with a GaN layer again. Since this GaN domain frequently coalesced to the adjacent Ga-face (þc) layer, the growth is epitaxial with respect to the underlying substrate, suggesting re-exposure of the substrate surface after laserirradiation.…”

“…Specifically, for patterning process, we employed carbon mask layers to avoid the etching process. 11,12) We have found that this carbon mask layer can be formed onto a sapphire substrate via modification of an organic polymer layer with focused laser irradiation, 11) as well as electron beam exposure. 12) After performing selective growth, this carbon mask layer was removed by thermal treatments, and the re-exposed sapphire surface was nitrided, so that the polarity of GaN was locally inverted during MOCVD growth.…”

“…1(c)]. 11) The laser pulses were generated using a regeneratively amplified Ti:sapphire laser ($100 fs, 800 nm, 1 kHz). The laser beam was magnified, collimated, and then focused onto the substrate using a microscope objective with an effective numerical aperture (NA) of 0.32.…”

“…1(e)]. 11) After selective growth was carried out, next, the carbon mask layers were removed by thermal treatments, leading to exposure of substrate again only for the laser-irradiated area [Fig. 1(f)], followed by nitridation of the re-exposed substrate [Fig.…”

“…We describe below a selective growth procedure using carbon mask layers [Figs. 1(a)-1(d)], 11) which would be employed later to control the polarity of GaN. To reveal the laser-induced formation of carbon species, XPS measurements were performed.…”