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This dissertation, "Phosphor-free Polychromatic Emission InGaN Light-emitting Diode" by Cong, Feng,, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Broadband white light is indispensable for applications involving general illumination and displaying, a task conventionally fulfilled by fluorescent light sources. Light-emitting diodes (LEDs) based on the Group-III nitrides have been taking over that role in recent years, despite the fact that LEDs are inherently monochromatic sources with spectral line-widths in the range of 20 to 50nm. The most adopted industrial solution is to shift part of the light emitted by a blue InGaN chip into longer wavelength, using color converters such as phosphors. To achieve a white light, the Stokes shift is usually above 100nm. The tradeoff is a dramatic energy loss during the color-conversion process. Also, the relatively shorter lifetimes of phosphors compared to that of the LED chips reduces chromatic reliability of such devices. Researches have long been working for a phosphor-free white LED. It is known that c-plane grown InGaN multi-quantum wells (MQWs) experience high strain due to the lattice mismatch between the wells and the barriers. The strain-induced piezoelectric field narrows the effective energy band gap and lead to a red shift of the emission, known as the quantum-confined Stark effect (QCSE). It has been shown that the QCSE can be partially eliminated by releasing the strain via nanoscale structures such as nanopillars. Studies on the strain-relax effect of nanopillars have shown a blue shift of 70-200 meV, depending on the size of the pillars. 200 me