The Simulation And Analysis Of Polarization Effect On Nearly Ultra Violet LED

Light-emitting diodes(LEDs) have been unmitigatedly developed since they can be applied in the market of solid-state lighting. To the present, the conventional white LEDs are composed by the In Ga N LEDs with blue emission and the YAG phosphors that are pumped by the blue light to generate amber emission. However, the white LEDs that can also be fabricated by using the near-ultraviolet(N UV) LEDs coupling with red, green, and blue phosphors have attracted much attention due to the advantages of excellent color rendering and color stability. Therefore, the NUV LEDs still have great potentials in the application of solid-state lighting.The polarization effect is an essential characteristic for NUV LEDs. The existence of the strong electrostatic fields, which are generated by the spontaneous and piezoelectric polarizations, has a significant influence on the band profile, especially in quantum well region. Consequently the large polarization field existed in Ga N material system tilts the energy band, which in turn results in the poor overlap of electron-hole wave functions and the decrease in radiative recombination. And internal quantum efficiency and optical performance of the light- emitting diodes are limited. In this thesis, the effect of polarization on the N UV LEDs has been numerically investigated. In addition, the appropriate design of the structure is proposed to enhance the optical characteristics of the light-emitting diodes.In this paper, indium gallium nitride early violet In Ga N light-emitting diode is studied by the simulation software APSYS. The effects of total polarization, spontaneous polarization and piezoelectric polarization are investigated, including the luminescence properties, band structure, polarization electric field, carrier distribution,radiation recombination rate and other characteristics. The results show that the piezoelectric effect severely affects the performance of the device due to the presence of interface charges. The interface charge accumulation result in the exist of the internal e lectric field, which cause serious band tilt so electrons and holes apart on both sides of the quantum well, which led to poor overlap between electron and hole wave functions, so that the light-emitting power of the device is greatly reduced. At the same time, the polarization electric field blocks the carrier transport, resulting in uneven distribution of the carriers. That is, to improve the luminescence properties of the device, necessary to suppress the piezoelectric polarization effects.In addition, this paper designed the structure of near-violet LEDs to improve piezoelectric polarization effect, using polarization- matched In Ga N/Al Ga In N multiple quantum well combined with wide bandgap materials as electronic blocking layer. Simulation results show that the use of polarization matching In Ga N/Al Ga In N quantum well as an active area, which can reduce the electron overflow, own better overlap rate of electron and hole wave functions, and obtain uniform carrier distribution and lower Auger recombination rate and so on. In this situation the efficiency droop epiphenomenon of the device is not obvious. Especially with the larger bandgap material is used as an electron blocking layer EBL, the devices can further limit the carriers in the quantum wells, and optimize the luminescence properties of LEDs...