Dislocation- and crystallographic-dependent photoelectrochemical wet etching of gallium nitride

Abstract

Polarity and dislocation dependence study of photoelectrochemical wet etching on GaN was carried out on lateral epitaxial overgrown nonpolar (112̄0)a-GaN/(11̄02)r-plane sapphire substrate. This LEO nonpolar GaN sample has low dislocation density Ga- and N-faces exposed horizontally in opposite directions, which can be exposed to identical etching conditions for both polarity and dislocation dependence study. It is observed that N-face GaN is essentially much chemically active than Ga-face GaN, which shows the hexagonal pyramids with {101̄1̄} facets on the etched N face. No obvious etching was observed on Ga face in the same etch condition. As for dislocation dependence, the “wing” (low dislocation density) region was etched faster than the “window” (high dislocation density) region. Smooth etched surfaces were formed with the (1̄1̄22̄) facet as an etch stop plane both on Ga and N-wing region.

Synthesis of erbium-doped gallium nitride crystals by the ammonothermal route

“…2a and b) while extensive formation of hexagonal pyramidal pits occurred on those labeled as the nitrogen polar surfaces ( Fig. 2c and d) in good agreement with other studies for polarity differentiation [27][28][29][30][31][32][33][34][35][38][39][40].…”

“…2c and d) in both experiments. These results indicate the preferential roughening [35,38,39] of one as-grown polar surface as well as the chemical inertness and flatness of the other in ammonobasic solutions and allude to the former as the nitrogen polar surface and the latter as the gallium polar surface. Further confirmation of these assignments was derived from KOH etching of both surfaces after mechanical polishing which showed microstructure similar to those of Fig.…”

Defect reduction in (112¯) a-plane GaN by two-stage epitaxial lateral overgrowth

“…21 Therefore, we speculate that this phenomenon may be related to differences in chemical stability of Ga-and N-faces since the latter has been shown to be less resistive to wet chemical etching. 22 During the growth of a-GaN, relatively lower amount of ammonia and higher growth temperature in hydrogen atmosphere may make N-face even less stable than the Ga-face, thereby inducing a smaller growth rate for the N-face GaN.…”

Fabrication of dodecagonal pyramid on nitrogen face GaN and its effect on the light extraction

“…Wet etching [5] is another effective and easily realized method for surface roughness especially for N-face surface GaN due to its merit of low cost and simple experimental procedure. Different from Ga-face GaN showing whisker in PEC process [6] and etch pit in hot phosphor acid (H 3 PO 4 ) [7] or molten KOH [8], N-face GaN with PEC process [9] or KOH aqueous solutions [10] shows strongly crystallographic dependent features. As a simple analogy, hot H 3 PO 4 etching should be important for N-face GaN, but to our knowledge, so far there has been no report on wet etching of N-face GaN with hot H 3 PO 4 .…”