The Fabrication Of New Type Of Electrode LED And Electromigation Of High-voltage LED

Lighting emitting diode(LED)as for its high energy efficiency,long life and low cost,has been widely used in general lighting,agriculture,medical treatment and other fields.The transparent electrode is an essential component of the LED,which expands the current and improve the light extraction efficiency.Indium tin oxide(ITO)is a widely used current expansion layer material,which has problems such as scarce resources and high price.Therefore,it is of great significance to fabricate new transparent electrodes instead of ITO;High-voltage LED(HV-LED)has advantages of high working voltage,low driving current and low power loss of AC/DC conversion,so it has a wide application prospect.However,the study on its reliability is still in lack at home and abroad.In this paper,LEDs with new composite transparent electrodes were designed and fabricated,and photoelectric tests were carried out.In addition,the electromigration reliability of high voltage LED interconnect electrodes was studied by the combination of simulations and experiments.This paper was supported by the National Key R&D Program of China(No : 2017YFB0403100,2017YFB0403102).The main research work and achievements are as follows:(1)Indium tin oxide(ITO)/graphene and silver nanowires(AgNWs)/graphene composite transparent electrodes were designed and fabricated.The test structures were prepared to characterize its specific resistivity,sheet resistance,carrier mobility,carrier concentration and light transmittance.The addition of ITO and AgNWs improved the contact characteristics between graphene and p-GaN.Moreover,the conductivity was improved;Different concentrations of AgNWs composite transparent electrodes were prepared to analyze the relationship between concentration of AgNWs and conductivity and light transmittance.(2)ITO/graphene and AgNWs/graphene composite transparent electrode LEDs were fabricated,the photoelectric properties of the device were tested,and the effects of the insertion layer of ITO and AgNWs on the transparent electrode of graphene were compared and analyzed.The addition of ITO and AgNWs reduced the operating voltage of the device,the effect of ITO was more obvious,and its luminous power and radiant flux were also improved.(3)The three-dimensional finite element model of GaN-based high-voltage LED(100mA,9V)was established to simulate the working state of the device;The electrical-thermal-structural coupling analysis of the simulation model was carried out to obtain the distribution cloud diagram of the current density,temperature,temperature gradients,stress in the interconnect electrode,which provided a reference for the results of the subsequent aging experiments;(4)The accelerated aging tests of GaN-based high-voltage LEDs were carried out,the surface morphology of the interconnected electrodes was observed,and the changes in photoelectric parameters were measured and recorded.The composition of the grown whiskers was analyzed,and the relationship between the electromigration phenomenon of the interconnected electrodes and the aging time and current was studied.The results of the experiments and the simulation were compared to analysis the phenomenon,cause and influence of the electromigration.