Research Project
GaN has become the prominent material for blue-green light emitting diodes (LEDs). The development of nitride LEDs has had great impact on the lighting industry by enabling the production of full color displays and white light sources. With further improvements nitride LEDs have the potential to replace traditional light sources due to their high efficiency and long life times. The limiting factor to achieving the high efficiencies needed for such applications is the external efficiency due to poor extraction of the emitted light from the device.
In GaN LEDs, photonic crystals (PCs) can be used to increase light extraction and control the emission profile by coupling guided modes in the material to extracted modes in air. Several significant processing challenges are being addressed to optimize the incorporation of PCs into GaN LEDs. To efficiently extract light, 2D triangular lattice PCs with lattice periods in the range of 200nm are patterned into the LED. Electron beam lithography is typically used to pattern these small features; however, new patterning techniques, such as imprint lithography, are being developed and optimized so that PCs can be patterned over large areas more efficiently and inexpensively. Etching of the PCs into the LED is being developed to reliably control PC properties. Furthermore, the challenges presented by the integration of the PCs into LEDs are being addressed. These include etch damage to critical LED material, the effects of the presence of the PC pattern on the electrical contacts and the overall design of the LED to incorporate PCs. GaN PC LED emission is measured by angular resolved luminescence. This technique reveals the emission profile of the LED as well as detailed information about the interaction of the PC with the guided light. GaN/InGaN photonic crystal LEDs have been fabricated, and increases in light extraction in addition to controllable emission profiles have been demonstrated.