|Title:||Recent Advances in High Brightness Blue and White GaN Based LEDs and True Green Laser Diodes|
|Group/Series/Folder:||Record Group 8.15 - Institute for Advanced Study|
Series 3 - Audio-visual Materials
|Location:||8.15:3 box 1.5|
|Notes:||Institute for Advanced Study Distinguished Lectures.|
Abstract: Recently, we have used novel chip designs to increase the efficiency of both c-plane (polar) and non-polar (a-plane, m-plane) LEDs. Current commercially available wurtzite nitrides based visible optoelectronic devices are grown along the c-axis. These devices are characterized by the presence of polarization-induced electric fields in the multi-quantum wells (MQWs). These electric fields, caused by both discontinuities in spontaneous and piezoelectric polarization at heterointerfaces, lead to the Quantum Confined Stark Effect (QCSE) and lowered radiative recombination probability. Additionally, the peak emission wavelength of LEDs grown on c-plane GaN blue-shift with increasing drive current due to screening of the internal fields. Using novel semiconductor fabrication schemes we have achieved blue LEDs with a high external quantum efficiency of 65%, 32.4mW at 20mA, and corresponding white LEDs with luminous efficacies of 152 lm/W at low current densities. Further research is needed to achieve these remarkable efficiencies at the high power levels needed for general lighting. Toward this goal we have also recently developed non-polar LED devices which exhibit efficiencies as high as 31mW at 20mA. The efficiency of non-polar LEDs now approaches that of the best c-plane LEDs with the added benefit of less efficiency roll-off at high current densities. Using Semi-polar GaN crystals we have also recently achieved true direct semiconductor green laser diodes operating at 516nm.
Duration: 55 min.
|Appears in Series:||8.15:3 - Audio-visual Materials|
Videos for Public -- Distinguished Lectures