Taeil Jung

Photoluminescence study of semipolar {101¯1}InGaN∕GaN multiple quantum wells grown by selective area epitaxy

Semipolar InGaN∕GaN multiple quantum wells (MQWs) were fabricated on the {101¯1} facets of GaN pyramidal structures by selective area epitaxy. Optical properties of the MQWs were investigated by photoluminescence (PL) in comparison with (0001) MQWs. Compared with (0001) MQWs, the internal electric field in the {101¯1} MQWs was remarkably reduced, the PL peak redshifted monotonically with the increasing temperature, and the internal quantum efficiency was estimated to be improved by a factor of 3. These results suggest that the {101¯1} planes are promising for improving the performance of III-nitride light emitters owing to their surface stability and suppression of polarization effects.

Multiple Wavelength Emission From Semipolar InGaN/GaN Quantum Wells Selectively Grown by MOCVD

Multiple wavelength emission is experimentally observed from semipolar InGaN/GaN quantum wells selectively grown by MOCVD. Selective growth rates on different mask opening areas result in a multiple wavelength emission from the same wafer.

ZnO nanorods-graphene hybrid structures for enhanced current spreading and light extraction in GaN-based light emitting diodes

One-dimensional and two-dimensional hybrid structures, composed of vertical ZnO nanorods grown on large-area graphene, are successfully integrated onto the GaN/InGaN light emitting diodes (LEDs). Compared with GaN LED without transparent conducting electrode, current injection and light emission increased almost 2–3 times, respectively, by the introduction of graphene based conducting electrode. Additional ∼66% increase in light emission was achieved by growing the ZnO nanorods on the graphene, which is consistent with the finite difference time domain modeling result. Furthermore, electroluminescence intensity profiles confirm the uniform light emission with high brightness in GaN LED with the ZnO nanorods-graphene hybrid electrode.

Novel Epitaxial Nanostructures for the Improvement of InGaN LEDs Efficiency

We demonstrated that the efficiency of an InGaN LED can be improved by using a novel epitaxial nanostructure, namely, the nanostructured semipolar (NSSP) gallium nitride (GaN). The NSSP GaN template was fabricated on a c-plane GaN surface using a standard GaN metal-organic chemical vapor deposition tool on c-plane sapphire substrates. We showed that the surface of NSSP GaN consisted of two semipolar orientations: (10-11) and (11-22). InGaN/GaN multiple quantum wells (MQWs) fabricated on NSSP GaN exhibited negligible quantum-confined Stark effect (QCSE) and a 30% improvement in internal quantum efficiency as compared to planar c-plane InGaN/GaN MQWs. Using time-resolved photoluminescence (PL), a considerable improvement in radiative recombination lifetime was also observed. We fabricated and characterized semipolar InGaN LEDs on NSSP GaN that emitted at 543 nm and showed negligible QCSE. The NSSP GaN structure can also be applied to improve the photon extraction efficiency of InGaN-based LEDs. The surface texturing was performed in situ together with the LED epitaxy without additional ex situ etching processes. The in situ surface texturing improved the PL intensity by a factor of two. An electrical injection LED structure employing in situ surface texturing was also demonstrated.

Fabrication of site-controlled, highly uniform, and dense InGaN quantum dots

We report fabrication of site-controlled, highly uniform and dense (>=1e10/cm2) InGaN multiple stacks of quantum dots using selective area epitaxy in MOCVD. The dot height and lateral dimension are 3 nm and 30 nm, respectively.

Semi-polar green LEDs on c-plane sapphire substrates

We demonstrated the first semipolar Ill-nitride green LED grown on c-plane sapphire substrates. The emission wavelength under CW current injection was 543 nm and showed negligible quantum confined Stark effect.

Improving quantum efficiency with nanostructured semipolar III-nitride light emitters

We demonstrated nanostructured semipolar III-nitride light emitters on low cost c-plane GaN templates using one-step epitaxy. The total light emission efficiency is improved by a factor of 2.6 compared to polar emitters at room temperature.

Photoluminescence study of InGaN site-controlled nanostructures formed by selective area epitaxy

We studied photoluminescence of InGaN site-controlled nanostructures formed by selective area epitaxy. We developed a theoretical model for the nanoscale growth evolution and used this model for the optimization of optical qualities of InGaN nanostructures.

Improving extraction efficiency of III-nitride LEDs using in situ silane treatment

We demonstrated a novel cost-effective approach to improve extraction efficiency of III-nitride LEDs, Photoluminescence measurement showed a factor of two improvement in extraction efficiency. Electroluminescence under CW injection was also shown.