Improving the light output power of GaN-based light-emitting diodes through the use of SiO2 cones

We introduced a simple wet-etching process to form SiO2 cones and investigated the effect of the size and coverage of the SiO2 cones on the output power of GaN-based light-emitting diodes (LEDs). The diameter of the cones varies from 2.8 to 17.1 μm and the height from 0.6 to 2.0 μm. It is shown that regardless of the sizes of the cones, all of the LEDs exhibit a same forward-bias voltage of 3.31 V at an injection current of 20 mA. As the size of the cones increases, the light output increases, reaches maximum at cone #3 (12.4 μm in diameter and 2.0 μm in height), and then decrease slightly. For example, the LEDs fabricated with different SiO2 cones exhibit 11.4–35.9% higher light output power (at 20 mA) than do the LEDs without the cones. The electroluminescence (EL) intensity (at 20 mA) also exhibits cone size dependence similar to that of light output power. For example, the LEDs fabricated with different cones exhibit 7.7–36.3% higher EL intensity than the LEDs without the cones.