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

Abstract

Wet etching has been widely used in defect evaluation for Ga-face GaN and surface roughness for N-face GaN dodecagonal pyramids has been fabricated on laser-lift-off N-face GaN by hot phosphor acid etching. The dodecagonal pyramid shows twelve facets including six {20-2-3} and six {22-4-5} planes. From cross-sectional TEM image, it is shown that the pyramid corresponds to the top of the edge dislocation. Compared with hexagonal pyramid-surface light emitting diodes (LEDs) etched by commonly used photoelectrochemical (PEC) process in KOH aqueous, the dodecagonal pyramid-surface LEDs show improved light extraction efficiency because of more facets, which effectively reduces the total internal reflection. GaN, N face, wet etching, H 3 PO 4 , dodecagonal pyramid, light extraction Citation:Qi S L, Chen Z Z, Sun Y J, et al. Fabrication of dodecagonal pyramid on nitrogen face GaN and its effect on the light extraction.

N-polar GaN etching and approaches to quasi-perfect micro-scale pyramid vertical light-emitting diodes array

“…However, according to Eqs. (6) and (7) and the activation energy in KOH, we obtained above (0.73 eV), c ER between etching KOH and H 3 PO 4 (353 K) is calculated enormous high to $5.32 Â 10 12 . It quite contradicts with the experiment results from which c ER (353 K) is calculated to be in the range of (10,200).…”

“…6,7 It is attributed to the facet-selective etching due to the competition between facets that have different surface energy and etching rates. However, we found that it was the dislocation serving as the preferential spatial site for pyramids evolvement initiated the etching process and accelerated the dissociation.…”

“…By comparing the different etching characteristics of Ga-polar and N-polar GaN, Li et al 4,5 has concluded that it was only due to the different states of surface bonding. Zhang 6,7 has found that the N-polar GaN exhibits dodecagonal pyramid feature after etching in H 3 PO 4 instead of conventional hexagonal pyramid feature after etching in KOH. However, there are few researches that deep into the specific etching process of N-polar GaN, for example, the pyramid's shape taking, evolved process and distribution rules, role of dislocation in etching.…”

Changing oblique angles of pyramid facets fabricated by wet etching of N polar GaN

“…For hexagonal facets of {10-1-1}, the direction of the edge projection is ,11-20.. As a result, we set the directions of O9A, O9C as [2-1-10] and [11][12][13][14][15][16][17][18][19][20], O9B as . In the triangle AO9B, a 1 9 and a 2 9 correspond to the angles Y and w, respectively.…”

“…11 In our previous work, we observed dodecagonal pyramids on N-polar GaN and concluded that thermodynamics and kinetics related factors led to the formation of the pyramids. 3,12 Hot H 3 PO 4 etching is more kinetic-limited than KOH etching. The crystallographic planes of the pyramids are not stable, and the oblique angles between the etched facets and the base plane are varied from 44u-52u.…”