Research Of The Fabrication Progresses For AlGaN-based Ultraviolet Light-Emitting Diodes

With the increasely research of III-group nitride materials,AlGaN-based ultraviolet light-emitting diodes(UV-LEDs)plays an important role.Considering that UV-LEDs are of high efficiency and reliability,they have been widely used in many aspects,such as,lighting,water and air purification,ultraviolet lithography and so on,and have attracted more and more attention.To fully meet some practical needs of high brightness and density,it requires a larger injected current to make LEDs work properly,so it is necessary to fabricate and study in UV-LEDs effectively.Meanwhile,there are some defects in the epitaxial material and structure during the fabrication of LEDs.They will affect the photo-electric characteristics and device reliability,shorten the lifetime,accelerate the aging and lead to the failure due to a serious problem of heat dissipation under large current density.In this thesis,we reviewed the problems in the existing research of AlGaN-based UV-LEDs.Wide investigations for some special problems in the epitaxial growth of materials and the fabrication process of devices were carried out,and some effective improvements were introduced for UV-LEDs,which was summarized as follows:To improve the n-AlGaN layer in UV-LED epitaxial structure,on the one hand,by replacing the uniform-doped(UD)methods with the?-doping and modulation-doping(MD)growth techniques,the UV-LEDs only with a single n-AlGaN layer were fabricated,respectively.On the other hand,by adopting the uniform-doped methods,the UV-LEDs with two kinds of doping concentration in the n-AlGaN layer were fabricated.Especially,there are also different thickness in every low-doped n-AlGaN layer.Then,the influence of electro-static discharge damage on the visible light LED were analyzed and summarized,some targeted solutions to reduce the electrostatic discharge(ESD)damage for UV-LEDs were presented.Moreover,combined the ANSYS thermal simulations with thermal resistance test,to effectively analyze the thermal characteristics of UV-LEDs and device reliability.Through the extensive characterization and analysis of UV-LEDs,and the wafer is encapsulated and measured.It is found that better material quality and photo-electric performance are achieved with the modulation-doping and?-doping methods.It is also found that there is an optimal interval in the thickness of n~--AlGaN layer.When the superior thickness of n~--AlGaN layer is in this range,the output intensity in the photo-electric characteristic is higher.By combining the results of thermal simulation and resistance measurements for packaged LEDs,it is helpful to improve the thermal dissipation performance and enhance the device reliability.Therefore,based on the research and analysis listed above in this thesis,to further meet the increasingly needs,it provide some useful improvements to fabricate the UV-LEDs with better photo-electric output performance,effective heat dissipation property and higher device reliability.