Theoretical And Experimental Investigation Of White Light Emitting Diode

White light emitting diode (LED) is considered to be the next generation lighting instead of the incandescence lighting because of high efficiency, no pollution, long life, small volume etc. But the white LED is still not bright enough for general lighting because of bad crystal quality, low extraction efficiency etc. The development of novel phosphor free white LED is blocked by the growth difficulty of long wavelength emission InGaN/GaN quantum well.Supported by the National Natural Science Foundation of China and the project of IEF institute, the enhancement of the LED output and the realization of phosphor free white LED were studied in both theory and experiment. The novel achievements are list as following:(1) A multi-layer embedded photonic crystal LED, which could highly increased the LED output based on the three dimensional FDTD simulation, was proposed. The calculation results show that light output of multi-layer embedded photonic crystal LED is three times as that of the conventional LED. It also shows that light output of photonic crystal LED with both surface and embedded photonic crystals is five times as that of the conventional LED.(2) A novel white LED with a strain buffer layer was demonstrated through experimental study. It is consist of a strain buffer, a short wavelength emission active region and a long wavelength emission active region. The strain buffer layer which is under the long emission wavelength active region could lengthen the emitting wavelength. The InGaN/GaN quantum well was designed in theory based on KP method. Also, the growth parameters of InGaN/GaN quantum well were optimized in experiments.(3) A novel AlGaN/GaN Diffraction Bragg Reflector (DBR) white LED was demonstrated through experimental study. DBR, with the peak reflection in the long emission wavelength, was grown under the active region. Under the help of the DBR, the power of the long emission wavelength was increased thus improved the performance of the white LED. AlGaN/GaN DBR was designed in theory in this thesis. Also, the grow parameters of AlGaN/GaN DBR were studied. (4) Two novel kinds of crystal photonic slab with large complete band gap were designed in theory. Conventional photonic crystal slabs only have a bandgap for TE or TM mode. The application of the complete band gap photonic crystal in LED could improve the extraction efficiency in LED. Firstly, the shape of the photonic crystal in plane was designed based on two dimensional simulations. A large gap/midgap ratio could be obtained. Then we modified the structure and confirmed the band gap with a more accurate simulation method, three dimensional finite-difference time-domain method. Also, some experiments have been made and a process to realize the structure was proposed.