【作者】 李敏；

【导师】 孙文红；

【作者基本信息】 广西大学 ， 物理学， 2023， 硕士

【摘要】 近年来,AlGaN基紫外发光二极管（UV-LEDs）由于体积小、功耗低、发光波长可调、环境友好等优点而被认为是传统汞灯的理想替代品,因此被广泛应用于紫外固化、杀菌、消毒、光电离、非视距（NLOS）通信等方面。然而,相比于发展成熟的Ga N基可见光LED,AlGaN基UV-LED仍存在发光效率低和可靠性差等问题,这对器件的商业化发展产生了阻碍。因此本文围绕AlGaN UV LED的可靠性方面展开了研究,对不同波长的LED在电流和温度应力下的光功率退化机制进行了详细分析,主要的研究内容和成果如下:（1）采用原位测试的方法,通过光学和电学表征相结合,对234 nm AlGaN远紫外（far-UVC）LED在20 m A恒定电流应力下的退化进行了深入研究,并通过深能级瞬态谱（DLTS）测试建立了器件退化与缺陷变化之间的联系。将DLTS与电容-电压（C-V）测试结合分析,研究表明光功率的显著退化主要与有源区中能级为Ev+（0.201-0.243 e V）的空穴缺陷“h₁”变化为能级为Ev+0.624 e V的缺陷“h₂”有关,该变化被描述为Mg从Mg_Ga中分离产生V_Ga与其他缺陷结合形成V_Ga相关复合物缺陷,这些复合物缺陷作为非辐射复合中心可以降低注入效率,并直接导致光功率的降低。n侧中V_N缺陷“e₂”浓度的上升表明材料晶体质量的进一步恶化。漏电流出现微弱上升,主要与空穴缺陷“h₃”浓度的增加有关。本文中的缺陷研究为制备更高可靠性的AlGaN far-UVC LED提供了一定的参考。（2）对280 nm LED在100-380 K温度范围下的光、电特性参数分别进行了测试,以探究器件在温度应力下光功率发生热下降的机制。研究显示在测试的温度范围中,光功率随温度的升高而呈现下降趋势,其下降程度在小电流注入下更为显著,表明整个温度范围中SRH非辐射复合的存在,有源区中存在的V_N缺陷便可作为非辐射复合中心。除此之外,高温部分（300-380 K）还存在着载流子逃逸,这两部分的增加共同导致了光功率的下降;低温部分（100-300 K）,光功率的热下降主要归因于载流子离域和SRH非辐射复合的作用,虽然该部分随着温度上升,施主和受主掺杂剂的进一步激活会增加器件的注入效率,但光功率升高的作用依然弱于下降的。更多还原

【Abstract】 In recent years,AlGaN-based ultraviolet light-emitting diodes（UV-LEDs）have been regarded as an ideal substitute for traditional mercury lamps due to the small size,low power consumption,adjustable luminescence wavelength and environmentally friendly.Therefore,the LEDs have been widely used in UV curing,sterilization,disinfection,photoionization and non-line-of-sight（NLOS）communication.However,compared with the mature Ga N-based visible LEDs,AlGaN-based UV-LEDs still suffer from low luminescence efficiency and poor reliability,which hinder the commercialization of the devices.Therefore,this paper focuses on the reliability of AlGaN UV LED and conducts a detailed analysis of the optical power degradation mechanism with different wavelengths under current and temperature stress.The main research contents and results are as follows:（1）The degradation of 234 nm AlGaN-based far-UVC light-emitting diodes（LEDs）under constant current stress is studied in-depth by the combination of optical and electrical characterization with an in-situ testing method.In addition,the relationship between the degradation and the variation of defects is established by deep-level transient spectroscopy（DLTS）testing.In combination with the capacitance-voltage characteristics,it is found that the significant degradation of optical power is mainly related to the transition of hole trap"h₁"with the energy level of Ev+（0.201-0.243 e V）to"h₂"with the energy level of Ev+0.624 e V in the active region.The transition is described as the separation of Mg from Mg_Ga to generate the V_Ga,and combined with other defects to form the V_Ga-related complex defects.These complex defects as non-radiative recombination centers could contribute to the reduction of injection efficiency and directly lead to the reduction of optical power.On the n-side,the increased concentration of electron trap"e₂"indicates that the crystal quality of material deteriorates further.The leakage current rises slightly,which is primarily due to the increase in the concentration of hole trap"h₃"with deeper energy levels.This study about the defects behavior of 234nm LED may provide a reference for the fabrication of AlGaN far-UVC LED with higher reliability.（2）The optical and electrical characteristics of 280 nm LED in the temperature range of 100-380 K were tested respectively to explore the mechanism of thermal drop in optical power under temperature stress.The study shows that the optical power decrease with increasing temperature in the tested temperature range,and the decrease is more significant under small injection current,which indicating the existence of SRH non-radiative recombination.The V_N defect in the active region can acted as the non-radiative recombination center.In addition,the carrier escape exists in the high temperature part（300-380 K）.The increase of these two parts together leads to the decrease of optical power.In the low temperature part（100-300 K）,the thermal droop of optical power is mainly attributed to the effect of carrier delocalization and SRH non-radiative recombination.Although in this part,with the increased temperature,the further activation of donor and acceptor dopant will enhance the injection efficiency of the device.But the effect of increasing optical power is still weaker than that of decreasing.更多还原