Enhance Light Emitting Diode Light Extraction Efficiency by an Optimized Spherical Cap-Shaped Patterned Sapphire Substrate

Abstract

This work has proposed a new way to optimize the spherical cap-shaped patterned sapphire substrate (PSS) for highly efficient GaN-based light emitting diodes (LEDs), which has been compared with the hemisphere patterned one. This pattern is achieved by changing the height of hemispherical units on the basis of hemispherical PSS. The height, the distance and the radius of the spherical cap-shaped unit are subsequently optimised by optical simulation. It is revealed that this optimised spherical cap-shaped PSS can enhance light extraction yield of LEDs by over 10% compared with LEDs grown on the optimal hemispherical PSS. The effectiveness of this spherical cap-shaped PSS has been demonstrated by subsequent crystal growth and characterization of LED wafers, and therefore sheds light on a further improvement on LED efficacy by the design of novel patterns for the application of PSS technology.

Highly-efficient GaN-based light-emitting diode wafers on La0.3Sr1.7AlTaO6 substrates

“…The skew dislocation density, and pure edge and mixed dislocation densities in as-grown GaN epi-layer are estimated to be 7.9 × 10 7 , and 8.8 × 10 7  cm −2 , respectively2728. This crystalline quality of GaN-based LEDs grown on LSAT substrates is much better than traditional GaN-based LEDs prepared on sapphire and nanopatterned sapphire substrates2930313233.…”

“…Actually, there is a ~1.5 nm blue shift in PL peak conducted at LT when compared with that at RT. This is attributed to the fact that there are high-energy carriers existing at low temperature, which lead to the low wavelength during the radiative recombination293031323345. It is widely accepted that the IQE can be estimated as the ratio of the peak PL intensities I RT at RT and I LT at LT, where the LT IQE is assumed to be 100%46.…”

Application of patterned sapphire substrate for III-nitride light-emitting diodes

“…Wang et al proposed spherical cap-shaped PSS based on the hemispherical PSS. 154 They confirmed that spherical cap-shaped PSS with specific intercepted ratio and edge spacing could improve the LEE of LED more effectively, as compared to hemispherical PSS (Fig. 13a-c).…”

Heteroepitaxy, an Amazing Contribution of Crystal Growth to the World of Optics and Electronics

“…In all this, the idea of using patterned substrates was also not neglected. Thus enhanced light emitting diodes (LED) with relatively high output power were fabricated from InGaN [27] and GaN [28] on sapphire patterned substrates. However, real progress in LED technology was achieved after discoveries of techniques such as Epitaxial Lateral Overgrowth (ELO) [29,30] and PENDEO (from Latin: to hang or to be suspended) epitaxy [30,31].…”