Reliability Study Of AlGaN-based Deep UV-LED Devices Based On Experiment And Simulation

AlGaN based ultraviolet light emitting diode(UV-LED)has many advantages,including small size,low energy consumption,fast switching,no need for any preheating time,etc.These excellent properties make UV-LED an ideal candidate in many new fields.For example,their fast switching capability enables advanced measurement and detection algorithms and improved baseline calibration to improve system sensitivity.Due to the low working voltage of UVLED,it is very suitable for ordinary battery and solar battery power supply.In addition,due to the variation of Al composition,the resulted UV emission can cover any wavelength spectra of UVC(200-280 nm),UVB(280-320 nm)and UVA(320-400 nm).The UV-LEDs with different wavelengths make them widely used in sewage treatment and food disinfection,phototherapy and plant growth lighting,UV curing and 3D printing.Compared with traditional mercury gas discharge UV light sources,there are still many technical difficulties and less obvious degradation mechanisms in UV-LED devices,which limit the lifetime reliability of UV-LED devices and their ability to quickly penetrate the market.At present,the physical mechanism of UV-LED degradation has not been completely determined.A lot of studies have been conducted on the reliability analysis of UV-LED in recent years.In this paper,the physical mechanisms of UV-LED optical power attenuation based on AlGaN were studied by experiment and numerical simulation methods.The main research contents and results of this paper are as follows:(1)By a group from the same wafer and the standard packaging UVC-LEDs aging,a series of currents stress were applied experimentally.It was discovered that the attenuation of optical power can be divided into two stages,catastrophic degradation and gradual degradation.The optical power attenuation curve was fit numerically,and it was found that attenuation curves are consistent with the same logarithmic function at different stress currents.(2)Through the electroluminescence(EL),optical power-current(L-I),the current-voltage(I-V),capacitance voltage(C-V)and photoluminescence(PL)and so on electro-optical characterization methods,the LED performance was compared before and after the stress.It was found that the current stress does not change the Al composition of the active region.However,it is possible that an increased new impurities within or closed to the active region was introduced through dislocation,leading to the formation of an active area with higher density of non-radiative recombination center and more defect assisted tunneling channel,which will increase the leakage current as a result.From the C-V measurements and the extracted apparent charge distribution(ACD)profiles,it can be analyzed that the decrease of capacitance will lead to the widening of the depletion width on the p side,and the current stress will cause the carrier redistribution in the active region,resulting in the aging of LED devices and the decrease of optical power.(3)By using SiLENSe simulation software,one-dimensional Poisson solver was used to model the device structure and calculate the energy band structure and carrier concentration distribution.The experimental results and simulation results show that the electron blocking layer(EBL)of 265 nm UVC-LED was expanded after the stress.During the current aging,the carrier was redistributed in the multiple quantum well on the n-side and doping on the p side were reduced which lead to the widening of the depletion region.Thus,the spread of the donor impurity concentration in the quantum well and the reduced acceptor impurity concentration of electronic barrier layer changed the p-n junction interface which plays an important role in of the overall LED stress process.