Simulation Investigation Of Device Structure In AlGaN-based Deep Ultraviolet Light-emitting Diodes

Recently, with the blue light-emitting diodes(LEDs) reaching its maturity, the shorter wavelength ultraviolet light-emitting diodes(UV LEDs) based on high Al content Al Ga N materials have attracted researchers' attention. UV LEDs have great applied value in many fields, such as disinfection, screen printing, polymer curing, environmental protection, white light illumination, military detection, and so on. But it is still difficult to fabricate high Al content Al Ga N-based deep UV LEDs at present, and its emission efficiency is still low. Moreover, the efficiency decreases monotonously as the injection current increases, which limits its applications. Therefore, it is very important to further improve the performance of Al Ga N-based deep ultraviolet light-emitting diodes.This dissertation first briefly describes the research background and development of Al Ga N-based deep UV LED, the working principles of LED devices and related physical properties as well as the semiconductor device simulation software APSYS. Then, we detailly introduced the designs and simulation of quantum well structure and p-type electron blocking layer in Al Ga N-based deep UV LED by utilizing Crosslight APSYS. Two kinds of new device structures are proposed and their effects on the device properties have been detailedly investigated by simulation respectively:(1) We have theoretically investigated the effects of two layers and three layers staggered Al Ga N quantum well on the performance of Al Ga N based deep UV LEDs separately. Detailed analysis has been carried out on the light output power, energy band, carrier distribution, radiative recombination rate, and so on. The simulation results reveal that the deep UV LEDs with staggered quantum wells can not only increase the overlap of the electron and hole wavefunctions, but also improve the density of electron and hole in quantum wells. These two effects can enhance the radiative recombination rate, and improve efficiency droop, which together improve the emission efficiencies in a wide range of injection currents. The device performance of the three-layereds staggered quantum well structure is better than the two-layereds one.(2) We have investigated the effects of different triangle electron blocking layers(Al content graded type, inverted V type and V type) on the properties of Al Ga N-based deep UV LED. By analyzing different physical mechanisms of the three triangular EBL structures in improving the emission efficiency we can draw a conclusion that the former two kinds of Al content graded type and inverted V type structures can improve the lattice matching between last barrier and EBL interface and reduce polarization electric field. While the last kind of V type structures can stretch the energy band by forming potential well in EBL and decrease the band-bending between the last barrier and EBL, which increases the electron effective barrier height and simultaneously reduces the hole effective barrier height. At the same time, holes gather in the EBL due to the well. These two mechanisms can significantly enhance the electron confinement and hole injection efficiency, and thus improve the emission efficiency and reduce efficiency droop.