Exploiting Strain-relaxed Quantum Wells for Broadband Emission LEDs

Grant Data
Project Title
Exploiting Strain-relaxed Quantum Wells for Broadband Emission LEDs
Principal Investigator
Dr Choi, Hoi Wai   (Principal investigator)
Start Date
Completion Date
Conference Title
Presentation Title
LED, nanotechnology
Engineering (E)
RGC General Research Fund (GRF)
HKU Project Code
HKU 711212E
Grant Type
General Research Fund (GRF)
Funding Year
1) Investigation of strain-relaxation mechanism in InGaN/GaN QW nanostructures: With the aid of high resolution strain mapping using Raman spectroscopy and emission mapping using near-field scanning microscopy (NSOM), the mechanisms for strain relaxation will be studied. The relations between strain/ emission and ion penetration/ damage of nanostructures will be determined, with the target of developing a "core-crust" model to explain the phenomenon. The model will assist with prediction of optical properties of nanostructures, and thus design of devices based on nanostructures; 2) Design of nano-LED for broadband emission: Tapping on the strain relaxation properties of nano-pillars as determined and quantified from objective 1, a nano-LED can be designed containing an array of nano-pillars of different sizes distributed over the entire emission area of an LED chip. Since each pillar emits at a different wavelength according to its diameter, the overall emission spectral characteristics of the device is a combination of individual spectrum, giving rise to broadband emission. The spectral shape can be tailored for different shades of white emission, by controlling the distribution of the differently sized nano-pillars; 3) Realization of a single-chip phosphor-free white-light LED: The key lies with the fabrication of the non-uniformly sized nano-pillars. To ensure practical adaptability of the approach, nanosphere lithography will be employed, the challenge being dispersing nanospheres of various dimensions over a large-area surface in mono-layer fashion, whilst maintaining close-packing between spheres. When this is done, the nano-pillars will be re-connected via a p-type contact layer by epitaxial lateral overgrowth, completing the device structure for electroluminescence.