Abstract
We report on the improvement of light output power of InGaN/GaN blue light-emitting diodes (LEDs) by lateral epitaxial overgrowth (LEO) of GaN using a pyramidal-shaped SiO(2) mask. The light output power was increased by 80% at 20 mA of injection current compared with that of conventional LEDs without LEO structures. This improvement is attributed to an increased internal quantum efficiency by a significant reduction in threading dislocation and by an enhancement of light extraction efficiency by pyramidal-shaped SiO(2) LEO mask.
Highlights
High brightness group III-nitride based light-emitting diodes (LEDs) for visible light emission have many applications in display backlight units, automotive lighting and solid-state lighting
We report on the improvement of light output power of InGaN/GaN blue light-emitting diodes (LEDs) by lateral epitaxial overgrowth (LEO) of GaN using a pyramidal-shaped SiO2 mask
The light output power was increased by 80% at 20 mA of injection current compared with that of conventional LEDs without LEO structures
Summary
High brightness group III-nitride based light-emitting diodes (LEDs) for visible light emission have many applications in display backlight units, automotive lighting and solid-state lighting. The low internal quantum efficiency (ηint) results mostly from the very high density (109-1010 cm−2) of threading dislocations (TDs) that form due to the large mismatch of lattice constants and thermal expansion coefficients between GaN films and sapphire substrates These threading dislocations in GaN act as nonradiative recombination centers and as a leakage path in the LEDs [2]. To reduce the dislocation density, several methods such as lateral epitaxial overgrowth (LEO) [3,4], pendeoepitaxy [5], and in situ SiNx nano-masking [6,7] have been developed Another major reason for the low external quantum efficiency (ηext) is a low light extraction efficiency (ηextraction), which is mainly due to the total internal reflection of light by the difference between the refractive indexes of GaN (n = 2.5) and air (n = 1). The measurement of ηint of LEDs by using temperature-dependent photoluminescence (PL) clearly showed that the ηextraction can be enhanced by changing the LEO mask shape while maintaining the same pattern areas of SiO2 masks
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