Aspect ratio engineering of microlens arrays in thin-film flip-chip light-emitting diodes

Applied Optics
Peifen ZhuNelson Tansu

Abstract

Light extraction efficiency of thin-film flip-chip InGaN-based light-emitting diodes (LEDs) with a TiO2 microlens arrays was calculated by employing the finite-difference time-domain method. The microlens arrays, formed by embedding hexagonal close-packed TiO2 sphere arrays in a polystyrene (PS) layer, were placed on top of the InGaN LED to serve as an intermediate medium for light extraction. By tuning the thickness of the PS layer, in-coupling and out-coupling efficiencies were optimized to achieve maximum light extraction efficiency. A thicker PS layer resulted in higher in-coupling efficiency, while a thinner PS layer led to higher out-coupling efficiency. Thus, the maximum light extraction efficiency becomes a trade-off between in-coupling and out-coupling efficiency. In addition, the cavity formed by the PS layer also affects light extraction from the LED. Our study reveals that a maximum light extraction efficiency of 86% was achievable by tuning PS thickness to 75 nm with maximized in-coupling and out-coupling efficiency accompanied by the optimized resonant cavity condition.

References

Jun 7, 2008·Langmuir : the ACS Journal of Surfaces and Colloids·Pisist KumnorkaewJames F Gilchrist
Jan 20, 2015·Nature Nanotechnology·Chee-Keong Tan, Nelson Tansu
Apr 23, 2015·Nature Materials·Philipp PustWolfgang Schnick

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