On Power Enhancement and Polarized Light GaN-based Light Emitting Diodes Encompassed with Nanorods
Date Issued
2009
Date
2009
Author(s)
Pan, Kun-Mao
Abstract
Since p-type GaN is well developed in 1990’s, GaN has been widely used in light emitting diodes. There are several advantages such as short response time, good reliability, long life time, and low power consumption for GaN light emitting diodes. In recent year, the demands of light emitting diodes such as backlight module increased dramatically. Since the refraction index is different between GaN and air, total reflection which decreases low external quantum efficiency causes at the interface. On the other hand, the commercial method to get polarized light is place polarizer between the backlight and liquid crystal. This method will leads light intensity decay at least 50% when light passes through the polarizer. Therefore, there are interesting topics of LEDs such as getting a polarized light source and improving the light extraction efficiency. In my thesis, by spin-coating a monolayer of self-aligned SiO2 nanosphere as the etching mask, nanorods array which encompassed with square shape light emitting mesa are fabricated. Since no additional lithography-mask needs by using the nanoparticle natural lithography, it has well potential to fabricate the low-cost nanostructure. We demonstrate a method of utilizing self-assembled nanorods array to collect the laterally propagating guided modes from a light emitting diode (LED). We measure a light intensity enhancement factor of 40% from GaN-based LEDs encompassed with 20μm thick nanorods array which filling factor is 0.21. Such power enhancement is found to be omni-directional due to a broken symmetry from a randomized distribution of the nanorods array placed along the periphery of the LED’s mesa. These observations indicate that the use of nanorods array can efficiently redirect the propagation of the laterally guided modes to the surface normal direction. Continuing from the previous experiment, we provide a noval and low-cost method by using nanorods to get polarized light source and enhance the output power of light emitting diodes－finger shape p-mase encompassed with self-aligned nanorods array by using natural lithography. Since the bragg diffraction of laterally propagated p-polarized mode by nanorods is more efficient than the s-polarized light, the p/s ratio of the device with nanorods is higher than that without rods. The polarization behavior of the light emitting diodes with and without nanorods surrounding the p-mesa is investigated. In my research, the p/s ratio of the LED with nanorods is 1.96 at 90˚, and is 1.52 when the integrating intensity between 0˚ and 90˚ is considered.
Subjects
GaN
nanorods array
natural lithography
p/s ratio
extraction efficiency
Type
thesis
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