1 Department of Photonics Engineering, Technical University of Denmark2 Diode Lasers and LED Systems, Department of Photonics Engineering, Technical University of Denmark
This thesis focuses on the optical properties analysis of Donor-Acceptor-Pair (DAP) co-doped Fluorescent Silicon Carbide (f-SiC) as a wavelengthconversion material in white Light-Emitting Diodes (LEDs). Different methods of fabricating surface Antireflective Structures (ARS) on f-SiC to enhance its light extraction efficiency are presented. White LEDs are the most promising techniques to replace the conventional lighting sources. A typical white LED consists of a Gallium Nitride (GaN) blue or Ultraviolet (UV) LED stack and a wavelengthconversion material. Silicon Carbide (SiC) has a wide optical bandgap and could be tailored to emit light at different wavelength by introducing different dopants. Combined emitting spectra of two types of DAP co-doped f-SiC could cover the whole visible spectral range and make f-SiC as a good candidate of wavelength-conversion material. It has a better color rendering performance and a much longer material lifetime compared with the commonly used wavelength-conversion material like Phosphors. In this thesis, f-SiC with different doping concentrations are analyzed and optimized in order to enhance the quantum efficiency. On the other hand, semiconductor materials usually suffer from the low light extraction efficiency due to the large refractive index difference between air and semiconductor interface. To ease this limitation, ARS have been widely applied on the semiconductor surface in LED and solar cell applications. This thesis has theoretically investigated the impact of surface ARS on colorimetry and light extraction efficiency of f-SiC based white LED. Furthermore, various approaches of fabricating periodic and pseudoperiodic ARS are demonstrated. By introducing ARS, a significant surface reflection suppression and a considerable omnidirectional luminescence enhancement have been observed.