Exploiting Strain-relaxed Quantum Wells for Broadband Emission LEDs
Dr Choi, Hoi Wai (Principal investigator)
RGC General Research Fund (GRF)
HKU Project Code
General Research Fund (GRF)
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.