Sixty Thousand Hour Light Output Reliability of AlGaInP Light Emitting Diodes

Both fixed current density and variable current density stress conditions are used to study light output degradation of (Al_xGa_1-x)_0.5In_0.5P light-emitting diodes (LEDs) as functions of LED stress current and LED stress time. Quantification of the resulting data indicates that (Al_xGa_1-x)_0.5In_0.5P LED degradation, D, is a linear function of current density, J, and a logarithmic function of stress time, t, for stress times as long as 60 000 hours in duration. For stress times long enough and current densities high enough to saturate any short-term effects (Al_xGa_1-x)_0.5In_0.5P LED degradation is therefore quantified by the empirical equation D=D₁ +D₂J+(D₃+D₄J)ln(t), where D₁ , D₂, D₃, and D₄ are independent of LED stress current and LED stress time. Within the limits of the data presented here, this equation is shown to accurately describe light output degradation of individual LED lamps, the average degradation behavior of individual LED wafers, and the average degradation behavior of a distribution of multiple LED wafers. The resulting expression may thus provide helpful guidance in quantifying the tradeoff between LED flux and LED degradation, both of which depend linearly on current density