| Popis: |
Fabrication of the wide bandgap GaN-based light emitting diodes (LEDs) and physical property are introduced in this section. Traditional planar GaN-based LEDs development is facing performance limit due to the low light-extraction efficiency and strain-induced quantum-confined Stark effect (QCSE) . The lattice mismatch in GaN-based LED epi-structure induces piezoelectric field . The piezoelectric field thus tilts the energy band structure and separates carriers in InGaN/GaN multiple quantum wells (MQWs), resulting in internal quantum efficiency (IQE) droop. To increase surface to volume ratio and strain relaxation, low dimensional structures such as nanorods and nanowires were developed. In Sect. 24.1, bottom-up and top-down approaches will be introduced. By using the Raman scattering measurement, strain in GaN-based epi-structure can be further verified. We show that nanorod structure can mitigate QCSE and improve the electron-hole overlapping ratio. We also indicate that longer nanorod structure has higher optical output, but trade-off has to be made as more defects are picked up during the etching process. |
