Events

PhD Defense: "High-efficiency Light-emitting Devices based on Semipolar III-Nitrides"

Sang Ho Oh

November 4th (Friday), 1:15pm
Elings Hall, Rm 1601


Light-emitting diodes (LEDs) based on III-nitride materials are key elements of the solid-state lighting industry. At present, most commercial blue LEDs are grown utilizing the polar (0001) orientation. These devices have strong polarization-related electric fields in the active region which causes a spatial separation between the electron and hole wavefunctions. This phenomenon, known as the quantum-confined Stark effect (QCSE), reduces radiative recombination due to the poor wavefunction overlap.

Mitigation of the QCSE has been done by utilizing different crystallographic orientations. In many studies, LEDs grown on semipolar III-nitride substrates showed high efficiencies at high current densities: in this presentation, we demonstrate “droop-free” large-chip blue LEDs grown on free-standing (20-2-1) substrates. It exhibits the advantages of semipolar LED again, especially for the standard industrial chip size.

In addition, contact optimization process for (20-2-1) LEDs will be discussed. Series resistance of the (20-2-1) device has been improved through the contact optimization. As a result, the wall-plug efficiency (WPE) of the device was boosted by over 50%, compared to those of the previously reported (20-2-1) LEDs.

Lastly, chip shaping for the semipolar LEDs to enhance the extraction efficiency will be covered in the presentation as well. A new mesa design will be introduced, and the cleaving scheme for semipolar LED wafers will be discussed.

About Sang Ho Oh:

Photo of Sang Ho Sang Ho Oh received his B.S. degree in Electrical Engineering from the Seoul National University in Seoul, Korea in 2010. He received his M.S. degree in Electrical and Computer Engineering (ECE) from the University of California, Santa Barbara in 2012. He is a Ph.D. candidate in the Department of ECE, and his dissertation is being completed under the supervision of Professor Steven DenBaars.

Hosted by: Professor Steven P. DenBaars