Research On Photoelectric Performance Of AlGaN Based Deep UV-LED Based On N Electrode Structure Optimization

AlGaN-based deep ultraviolet light-emitting diodes(DUV-LED)covering the UVC band are environmentally friendly,energy-saving,and safe.They can replace traditional mercury light sources and have a wide range application prospects of civilian fields such as air sterilization,water sterilization and purification,food preservation,and medical sterilization.After the outbreak of the new coronavirus pneumonia at the end of 2019,researchers found that deep ultraviolet in the UVC band can also effectively kill the new coronavirus,and the deep ultraviolet sterilization market quickly became hot.At present,although AlGaN-based DUV-LEDs have been commercially produced,the external quantum efficiency level of AlGaN-based DUV-LEDs is still very low,and the typical value does not exceed 7%.There have been research reports to improve the efficiency of DUVLED by optimizing the epitaxial structure,chip layout,reflective structure,photonic crystal and other means.This paper uses a novel reflective N-contact electrode,which can effectively improve the light extraction efficiency of AlGaN-based DUV-LED chips compared to traditional Ncontact electrodes.This paper studied the effects of changes in the reflective N electrode structure on the contact characteristics,surface morphology,and the photoelectric performance of AlGaN-based DUV-LEDs and device reliability.The specific contents of this thesis are as follows:(1)The effect of annealing temperature and thickness parameters of Cr/Al/Ti/Au reflective electrode on its electrical properties was studied.The increase of the annealing temperature can not only repair the surface damage caused by ICP etching,but also form a highly doped area and reduce the contact barrier.However,an excessively high temperature will cause the metal of the upper covering and protection layer to diffuse into the AlGaN layer,destroying the alloy interface of the gold semi-contact.With the help of a focused ion beam/electron beam double-beam electron microscope(FIB-SEM),the influence of the thickness of the metal Al layer in the electrode on the surface morphology of the annealed Cr/Al/Ti/Au reflective electrode was studied.The increase in the thickness of the metal Al contributes to the formation of ohmic contacts and reduces the contact resistance.However,the thickness of Al will make the metal spheroidization more serious and affect the flatness of the contact electrode.(2)Study the photoelectric performance and device reliability of AlGaN-based DUVLEDs with N reflective electrodes with different morphologies.In view of the abnormal leakage of the lamp beads in the life aging test,the infrared hot spot microscope system,focused ion beam/electron beam double beam electron microscope,energy spectrum analysis(EDAX)and other analytical methods are used to find the leakage channel and clarify the morphology of the N electrode to the device the mechanism of the formation of the leakage channel.The photoelectric characteristics of the AlGaN-based DUV-LED with a flat morphology and optimized structure of the N reflective electrode are verified to be similar to the performance of commercial products,and the reliability is good.After 1000 h life aging,the optical output power maintenance rate is still over 85%.