The Reliability And Thermal Property Of High Brightness Light Emitting Diode

Since LED (Light Emitting Diode, LEDs) was first be developed, it became ahot topic quickly in the semiconductor research field for its good luminescentproperties. In recent years, with the continuous improvement of LED deviceperformance, LED is used in production and all aspects of life more and more widely,and the reliability of device is a critical issue. As LED is electroluminescent devicewhich is converted into light energy from electricity directly, large amounts of heatand light which is produced during lighting is the main reason to cause LED failureand bad light. For high power LED, because of its high power density, the research ofthermal properties and temperature characteristics is very important.This paper was supported by the National High Technology Research andDevelopment Program (863 Program) funded projects (subject code: No2009AA03A1A3, No2008AA03A192), Important national science & technologyspecific projects (2008ZX10001 014), and Innovation Fund for Technology BasedFirms(No: 09C26221100138). This paper carried out by temperature analyzed and thethermal characteristics of the reliability, and mainly researches the impacts of lowtemperature for the application of LED, and the impacts of the GaP current spreadinglayer thickness for the device life. The main contents are organized as the following:1). The thermal resistance and junction temperature characteristics of 1W red,1W white and 1W blue LED have been studied by the forward voltage drop method.When the current is increased from 100mA to 1A, the device junction temperatureand current were in a linear relationship and the resistance changed slightly, whilemeasurement of the current process of change in the main optical parameters of thedevice, and a detailed analysis of the internal mechanism of its trends and impact onthe application.2). The paper is researching on the characteristics at high and low temperature ofthe power LED, the main optical parameters of the LED are measured on line at lowtemperature, and the curves of LED performance parameters are presented. At lowtemperatures, the relative intensity of LED is higher than at room temperature, but thelow temperature led to positive voltage increase, the wavelength blue shift, and thecolor index of the white LED lighting will also drop.3). High brightness AlGaInP red LEDs made by the optoelectronic technologylab were investigate with stress current and temperature speed stress as accelerated factors. At 80℃, 20mA conditions, after 1000 hours aging test, the chip size is 300μm×300μm device degradation flux of about 1.09%, the chip size is 200μm×200μm flux degradation of the device is about 1.28%, and extrapolating the twodevices life time 76602h and 64694h at 25℃, 20mA, where the device's failurecriterion for the flux attenuation over 10%. At last elaborated several LED failuremechanisms.4). High brightness AlGaInP red LEDs made by the optoelectronic technologylab with different GaP current spreading layer thickness have been investigated on lifetime reliability. At 90mA, after 1800 hours aging, GaP layer thickness of 8 m deviceradiated power degradation 9.1% ~ 10.7%, GaP layer thickness of 12 m deviceradiated power degradation 2.12% ~ 3.4%. But the life time of the device reliability isnot with the current expansion and sustained increase in thick layers, when the GaPlayer is too thick, the epitaxial film quality deterioration, higher rates of latticemismatch on the reliability of the device will bring life to negative impacts.