Gradient Quantum Well Design To Mitigating Current Crowding By Electron Mobility Enhancement

AlGaN-based deep ultraviolet(DUV)light-emitting diodes(LEDs)with high internal quantum efficiency have been a major alternative of mercury lamps as the new generation of UV light sources.However,there are still many obstacles restricting the further enhancement of output power.The current crowding effect in the traditional n-AlGaN layer is one of them in a common mesa-type LED.In this thesis,we propose a structure with repeated step-shaped potential quantum wells as an option of the traditional n-AlGaN layer with a single component,to reduce resistance by improving the planar electron mobility,while diffusing the current through the horizontal multi-channel.Specifically,the step-shaped potential quantum wells are designed to be a four-layer quantum well with n-Al0.7Ga0.3N as the barriers and Al0.55Ga0.45N/AlxGa1-xN(0.55<x<0.7)as the bi-component well.Then,we estimate the electron mobility by the Lei-Ting equilibrium equation method,in consideration of the built-in electric field induced strong confinement of electron and the scattering from all possible types of optical phonons.The theoretical results show that the electron mobility in such step-shaped quantum well is higher than that in the single-component quantum well over a relatively wide range component 0.57<x<0.68,by avoiding the scattering from interface optical phonons.It is since that electron tends to locate at the interface,while there are no interface optical phonons in this system due to the ternary mixed crystal effect.Therefore,the electron mobility is significantly improving.Combining with the bypassing effect of the multi-channels,the repeated bi-component quantum well design is expected to be useful for mitigating the current crowding in the AlGaN DUV LEDs.