Enhancing Broadband Light Absorption And Emission By Photonic Crystal Hybird Structure

Efficient broadband optical absorbers have wide range of applications in solar cells, photodetectors, military stealth,and so on. In 1982, Yablonovitch proposed light absorption limit in a uniform thin film semiconductor. However, Yablonovitch limit applies only to geometric optics, for subwavelength structures, by designing of the structure legitimately, the absorption efficiency will far exceed the Yablonovitch limit. Currently, scientists have proposed a lot of micro-nano optical coupling periodic structures with precious metals to achieve enhanced absorption of sunlight. But periodic structures can only be achieved high absorption in the narrow-band resonant mode.White LED, as an important element of light-emitting, its applications penetrate into many fields, such as lighting, display, and so on. Owing to by a single crystal type LED to produce white LED, that is a monochrome LED with the corresponding phosphors, the drive circuit designing will be easier, less expensive compared by polymorph LED to produce white LED. Using UV LED to excite RGB three-wavelength phosphors to achieve white light, its luminous efficiency is better than using blue LED to excite. Now, with the increasing business needs, the luminous efficiency of white LED is needed to be further improved. In optical communications, lighting, other aspects of geological survey, improving the near-infrared LED luminous efficiency is also important.To overcome these narrow bandwidth and low absorption LED luminous efficiency problem, researchers proposed photonic crystal composite structure, to achieve:（1） Broadband, efficient and wide-angle solar absorption is enhanced covering from near-ultraviolet to the infrared band, and exceeds Yablonovitch limit in the infrared.（2） Achieving a high reflectance in violet, blue, green,red bands, and near-infrared band,and improving the luminous efficiency of LED eventually. Using rigorous coupled wave analysis（RCWA） and finite difference time-domain（FDTD）, to study transmittance, reflection, absorption, intensity distribution and the effect of varying incidence angle. The main contents and results are as follows:1. Combining Si thin film surface with one-dimensional photonic crystal structure and random metal triangle reflector, obtaining: for the TM mode, the absorption efficiency is higher than the average of 60% within 0.3⁹.9 um broadband high absorption, and the absorption efficiency is not sensitive to the incidence angle changing.2. Expanding the above constructions, combining Si thin film surface with two-dimensional photonic crystal structure and two-dimensional random metal triangle reflector, achieving : for both s-polarization and p-polarization, broadband high absorption is achieved within 0.3 9.9 um, and the absorption efficiency is not sensitive to changes in the angle of incidence.3. Designing the structure of（SiO₂/TiO₂）N, achieving a high absorption in narrow ultraviolet band, and broadband high absorption in blue, green and red bands. Therefore, enhancing the purple LED excitation and blue, green and red phosphors emission, and enhancing the white LED luminous ultimately. And when the angle of incidence within 0 ° 25 ° and the TiO₂ thickness within 40 nm 54 nm, highly reflective band is essentially the same, therefore reducing the manufacturing difficulty.4. Designing the structure of（SiO₂/Si）N, achieving a high absorption in near infrared, therefore enhancing the infrared LED’s luminous efficiency.