Study on the stability of the high‐brightness white LED

The high-power white light emitting diode (LED) is packaged by GaN-based blue LED chip with the size of 1 x 1 mm 2 , YAG:Ce yellow fluorescer, epoxy and an effective heat sinking. The wavelength of the LED chip emission blue-shifts from 482 to 475 nm, while that of the fluorescer emission does not change in electroluminescence (EL) spectrum when the injection current increases from 5 to 200 mA. And the correlated color temperature decreases from 5300 to 4800 K. When the injection current increases to 200 mA, the luminous power (P e ) increases to 13.8 mW, which is about 10 times of those of the normal size (0.3 x 0.3 mm 2 ) diodes fabricated with the same wafer and same injection density. P e and forward bias (V f ) at 200 mA are measured for the aging high-power white LED. At the beginning, P e decreases dramatically 20% and V f decreases about 0.2 V in 2 days. And then P e and V f decrease slowly in the remaining 79 days aging. The contact metals electro migration along the channels induced by the threading dislocations may be the dominant aging mechanism.