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III-nitride semiconductors based light-emitting diodes (LEDs) for solid state lighting represent the most promising next generation lighting technology. Total internal reflection significantly limits the light extraction efficiency in III-nitride LEDs due to the large refractive index of GaN. In this thesis, the light extraction efficiency for III-nitride LEDs was calculated and analyzed using 3D finite difference time domain (FDTD) method. Particularly, detailed studies focused on understanding the mechanisms of enhancing light extraction efficiency in LEDs by using photonic crystals. We found that the effect of photonic crystals does not rely on the photonic band gap effect but is more related to scattering and diffraction. Besides, we also studied the effects of cones and truncated cones on the enhancement of light extraction efficiency in III-nitride LEDs, which can be used as alternatives to PCs. In addition, ZnO represents another type of wide-bandgap material. The wurtzite crystal structure of ZnO possesses strong piezoelectric properties. In the second part of this thesis, we investigated a low cost and scalable approach using PDMS to fabricate a ZnO piezoelectric device based on ZnO nanomaterials grown via chemical vapor deposition (CVD) method. |
