Fabrication of Pyramidal Patterned Sapphire Substrates for High-Efficiency InGaN-Based Light Emitting Diodes

Abstract

In this study, a wet-etched pyramidal patterned sapphire substrate (PSS) was used to fabricate the near-ultraviolet InGaN-based light-emitting diodes (LEDs). The pyramidal PSS was etched using a 3normalH2SnormalO4:1normalH3PnormalO4 mixture solution and the activation energy of this reaction is determined to be 28.2kcal∕mol . Three symmetric sidewall facets of the etched pyramidal hole were {112false¯kfalse¯} on the (0001) sapphire. It was found that the GaN epi layer grew laterally from the top of the pyramid pit and overhung the cavity. An evident reduction in dislocation density of the GaN-on-PSS sample can be confirmed by the etch-pit-density, double-crystal X-ray, and micro photoluminescence measurement results. Under a 20mA forward injection current, the output power of the conventional and pyramidal PSS LEDs (in epoxy lamp form, λnormalD=400nm ) were 7.45 and 9.35mW , respectively. A 25% enhancement in output power was achieved in the pyramidal PSS LED as compared with that of the conventional LED sample. The enhanced output power is not only due to the improvement of the internal quantum efficiency upon decreasing the dislocation density, but also due to the enhancement of the extraction efficiency using a pyramidal PSS. From light-tracing calculation, the pyramidal reflector arrays can offer more probability of escaping photons from the GaN/sapphire interface, resulting in an increase in light extracting efficiency.

Characterization study of GaN-based epitaxial layer and light-emitting diode on nature-patterned sapphire substrate

“…5 And, the enhancement in the internal quantum efficiency benefits from the reduction of threading dislocations by possible lateral growth of GaN epilayer on the patternedsapphire substrate. 5,[10][11][12][13] Numerous patterning features produced on the patternedsapphire substrate by either dry etching or wet etching processes, which includes circle cavities, square cavities, hemispheric bumps, and trenched stripes, have been studied. 5,[14][15][16] Yet, no matter what etching process is used to create the patterns, a hard mask lithographic process is required on the flat c-plane sapphire wafer.…”

Formation of Patterned Sapphire Substrate using UV Imprint Processes

“…To increase their external quantum efficiency, improvements in the internal quantum and light extraction efficiencies are expected. The epitaxial lateral overgrowth (ELO) method [1][2][3][4] and the lateral epitaxy with the patterned sapphire substrate (PSS) [5][6][7][8][9][10][11][12][13] can improve the internal quantum efficiency to reduce the threading dislocation density (TD) in GaN epilayers. To improve the light extraction efficiency, the PSS, rough surface that has random uneven structures, and photonic crystal (PC) structures are useful [14][15][16].…”

Fabrication of InGaN-Based Vertical Light Emitting Diodes Using Electroplating

“…Although the ELOG and PE process can dramatically decrease dislocation density, the related growth process is complicated and time consuming. Recently, it has been reported that one can not only reduce the threading dislocation density in GaN films, but also enhance the light extraction efficiency by using patterned sapphire substrate (PSS) (Yamada, et al 2002;Tadatomo, et al 2001;Wuu, et al 2006). The PSS technique has attracted much attention for its high production yield due to the single growth process without any interruption.…”