Abstract
We have investigated the light emission mechanisms of V-shaped, hexagonal-micropit-arranged, InGaN/GaN light-emitting diodes (HMA-LEDs). By near-field scanning optical microscopy and the confocal scanning electroluminescence microscopy, we found that enhanced light output of HMA-LED was significantly contributed by not only improved light-extraction efficiency but also locally improved crystalline quality near the micropit. Etch pit density and cross-sectional transmission electron microscope image indicate that threading dislocation (TD) bending lead to decrease the TD density near the micropit. Furthermore, partially linearly polarized light from the inclined facets of the HMA-LEDs was observed.
Highlights
GaN-based lighting technology is currently driving a lifestyle revolution in modern society because of the strong demands for energy savings and simple packaging requirements [1,2]
We have investigated the light emission mechanisms of Vshaped, hexagonal-micropit-arranged, InGaN/GaN light-emitting diodes (HMA-LEDs)
By near-field scanning optical microscopy and the confocal scanning electroluminescence microscopy, we found that enhanced light output of hexagonal micropit arranged LED (HMA-LED) was significantly contributed by improved light-extraction efficiency and locally improved crystalline quality near the micropit
Summary
GaN-based lighting technology is currently driving a lifestyle revolution in modern society because of the strong demands for energy savings and simple packaging requirements [1,2]. One of the main factors that suppress the light output power is the low light-extraction efficiency, which is caused by photons being trapped inside the chip because of total internal reflection at the LED surface. This photon trapping arises from the large difference between the refractive indices of GaN (n = 2.5) and air (n = 1) [5,6,7]. According to Snell’s law, the critical angle(θcrit = sin−1(nAir/nGaN)) for these structures is approximately 23.6° To surmount this small critical angle, arrangements of V-shaped micropits, which require the use of a regrowth method, can be applied to the top of the LED [8,9,10,11]. We report a reliable physical mechanism for the enhancement of the light output and the phenomenon of quasi-polarized light emission from LEDs with Vshaped micropits by using those methods including the CSEM, the NSOM, the PL/Raman/EL spectroscopy
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