Abstract
We investigate the mechanism responding for performance enhancement
of gallium nitride (GaN)-based light-emitting diode (LED) grown on chemical
wet-etching-patterned sapphire substrate (CWE-PSS) with V-Shaped pit features
on the top surface. According to temperature-dependent photoluminescence (PL)
measurement and the measured external quantum efficiency, the structure can
simultaneously enhance both internal quantum efficiency and light extraction
efficiency. Comparing to devices grown on planar sapphire substrate, the threading
dislocation defects of LED grown on CWE-PSS are reduced from 1.28$\,\times {\hbox{10}} ^{9} /{\hbox {cm}}^{2}$ to 3.62$\,\times {\hbox{10}}
^{8} /{\hbox {cm}}^{2}$, leading to a 12.5% enhancement in
internal quantum efficiency. In terms of the theoretical computing of radiation
patterns, the V-Shaped pits roughening surface can be thought of as a strong
diffuser with paraboloidal autocorrelation function, increasing the escape
probability of trapped photons and achieving a 20% enhancement in light extraction
efficiency. Moreover, according to the measurement of optical diffraction
power, CWE-PSS demonstrated superior guided light extraction efficiency than
that of planar sapphire substrate, thus an extra 7.8% enhancement in light
extraction efficiency was obtained. Therefore, comparing to the conventional
LED, an overall 45% enhancement in integrated output power was achieved.
© 2008 IEEE
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