Enhancement of Device Performances in GaN-Based Light-Emitting Diodes Using Nano-Sized Surface Pit.

We report the improvement in optical and electrical properties of GaN-based green light-emitting diodes (LEDs) with nano-sized etch pits formed by the surface chemical etching. In order to control the density and sizes of etch pits formed on top surface of green LEDs, H3PO4 solution is used as a etchant with different etching time. When the etching time was increased from 0 min to 20 min, both the etch pit size and density were gradually increased. The improvement of extraction efficiency of LEDs using surface etching method can be attributed to the enlarged escape angle of generated photon by roughened p-GaN surface. The finite-difference time-domain (FDTD) simulation results well agreed with experimentally observed results. Moreover, the LED with etched p-GaN surface for 5 min shows the lowest leakage current value and the further increase of etching time resulting in increase of densities of the large-sized etch pit makes the degradation of electrical properties of LEDs.

Enhancement of photoluminescence intensity of GaN-based light-emitting diodes with coated polystyrene/silica core-shell nanostructures.

We report the enhancement of the photoluminescence (PL) intensity of GaN-based light-emitting diode (LED) structures by using of a surface coating of polystyrene (PS)/silica (SiO2) core-shell nanospheres. PS/SiO2 core-shell nanosphere-coated LEDs show the highest PL intensity among various type LEDs. The relative PL intensity of PS/SiO2 core-shell nanosphere-coated LEDs increased by 10% and 14% compared with that of LEDs coated with only SiO2 nanospheres and conventional LEDs without any nanostructures, respectively. Moreover, the theoretically investigated results using finite-difference time-domain (FDTD) simulations show the 1.33 times improvement of total intensity integrated over the measured sample coated by PS/SiO2 core-shell nanospheres than that of a conventional LED without the coating of nanospheres, which corresponds to the experimentally observed results. The enhancement in PL intensity using PS/SiO2 core-shell nanostructures can be attributed to the improvement in light extraction efficiency by both increasing the probability of light escape by reducing Fresnel reflection and by multiple scattering within the core-shell nanospheres.