Fabrication and Characterization of GaN-Based LEDs Grown on Chemical Wet-Etched Patterned Sapphire Substrates

Abstract

Characteristics of GaN-based light-emitting diodes ͑LEDs͒ grown on the chemical wet-etched patterned sapphire substrates ͑CWE-PSS͒ with different crystallography-etched facets were investigated. An improvement of 40% on the overall quantum efficiency was achieved by adopting this CWE-PSS scheme. A Monte Carlo ray-tracing method was employed to derive the optimized condition of sapphire etching time, and the calculated result demonstrated the same trend with real device measurement. Adopting the CWE-PSS in LEDs could not only improve the epitaxial quality but also increase the extraction quantum efficiency due to crystallography-etched facets efficiently scattering the guided light to enter the escape cone on the top of device surfaces. Finally, we observed better aging behaviors of CWE-PSS LEDs, which could be due to the reduction of threading dislocations of the epitaxial layers.

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

“…The unique pyramidal morphological pattern on the sapphire surface might have similar functions with current patterned sapphire substrates, i.e., excellent improvements in the GaN epitaxial quality and the light-extraction efficiency for LED devices. [5][6][7][8][9] So, it is of interesting to grow epitaxial GaN/InGaN LED structure on the n-pss wafer with the pyramidal pattern by MOCVD process. The LED epilayer structure includes a 1.8-lm-thick undoped GaN layer and a 2.5-lm-thick Si-doped n-type GaN cladding layer, an active region of 450-nm emitting wavelength with six periods of InGaN/GaN MQWs, and a 0.3-lm-thick Mg-doped p-type GaN cladding layer.…”

“…3,4 The efficacy enhancement of GaN-based LEDs with the patterned-sapphire substrate technique generally attributes to the improvement in both light extraction efficiency and internal quantum efficiency. [5][6][7][8][9] The regular patterns created on the sapphire substrate counteracts the effect of the total internal reflection at the GaN/sapphire interface. 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][6][7][8][9] The regular patterns created on the sapphire substrate counteracts the effect of the total internal reflection at the GaN/sapphire interface. 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,[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. In this study, a mask-free wet etching process was used to produce a naturepatterned sapphire substrate (n-pss).…”

A precise ray tracing simulation model for GaN based light emitting diodes

“…However till now LEDs still suffer from the insufficient output efficiency due to the low internal quantum efficiency (IQE) caused by large lattice mismatch and low light extraction efficiency (LEE) caused by the large refractive index differences between GaN and surrounding materials. LEDs fabricated on patterned sapphire substrates (LED on PSS) have been reported to have better performance, and it was believed that PSS contributed to the improvement of both LEE and IQE [1][2][3][4][5][6][7]; however, the difficulty in quantifying the separate improvement of LEE hinders better PSS design. On the other hand, temperature-dependent photoluminescence is a common but complicated method for the measurement of IQE [8].…”