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Abstract
Nanopatterned aluminum nitride (NP-AlN) templates were used to enhance the light extraction efficiency of the light-emitting diodes (LEDs). Here, the NP-AlN interlayer between the sapphire substrate and GaN-based LED was used as an effective light outcoupling layer at the direction of bottom side and as a buffer layer for growth of GaN LEDs. The cross-sectional transmission electron microscopy (TEM) analysis showed that the formation of stacking faults and voids could help reduce the threading dislocations. Micro Raman spectra also revealed that the GaN-based epilayer grown on the NP-AlN template had smaller residual stress than that grown on a planar sapphire substrate. The normalized electroluminescence (EL) spectra at the top and bottom sides of device revealed that the enhancement of the bottom side emission of the LED with the NP-AlN interlayer was more notable than a planar sapphire substrate due to the graded-refractive-index (GRIN) effect of the NP-AlN.
Highlights
Light-emitting diodes (LEDs) are in high demand due to their application in the areas of signals, displays, and illumination devices [1,2]
The Nanopatterned aluminum nitride (NP-aluminum nitride (AlN)) interlayer between the sapphire substrate and GaN-based light-emitting diodes (LEDs) was used as an effective light outcoupling layer at the direction of bottom side and as a buffer layer for growth of GaN LEDs
The cross-sectional transmission electron microscopy (TEM) analysis showed that the formation of stacking faults and voids could help reduce the threading dislocations
Summary
Light-emitting diodes (LEDs) are in high demand due to their application in the areas of signals, displays, and illumination devices [1,2]. Enhancement of the light extraction efficiency was achieved by reducing the total internal reflection (TIR) [4]. For TIR reduction, several approaches have been proposed: surface roughening [5], GaN epilayer growth on a patterned sapphire substrate [6,7], and integration of two dimensional (2-D) photonic crystal (PC) structures [8]. Incorporating geometric structures inside an LED [9] and graded-refractive-index (GRIN) pillars on the emitting surface [10] have been reported. Among the III-nitride semiconductors, AlN exhibits the largest direct band gap (6.2 eV), high thermal conductivity, and a refractive index of ~2.15, which is roughly the median point between GaN (n = 2.40) and a sapphire substrate (n = 1.78).
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