1/f noise in GaAlAs double hetero junction infrared ray LEDs (IRLEDs) is experimental and theoretical studied over a wide range of bias currents.Experimental results demonstrate that the magnitude of 1/f noise is in proportion to the bias current (IF) in the range below 3 mA,and tends to saturate when the current increases from 3 mA to 5 mA.While,in the current range above 5 mA,the magnitude of 1/f noise increases sharply and is proportional to I2F.Base on the mechanisms of carrier number fluctuations and carrier velocity fluctuations, a model for 1/f noise in GaAlAs IRLEDs is developed.It is discussed from the model that at small currents,1/f noise in GaAlAs IRLEDs comes from trapping and detrapping process between defects in the bulk region of devices (bulk defects) and carriers,which reveals characteristics of bulk defects.While,at large currents,it is due to fluctuations in the surface recombination velocity induced by the surface potential,which is modulated by oxide traps near the space-charge region, at these conditions,1/f noise reveals defects in the active region of devices (actives defects).1/f noise can be used as a sensitive and non-destructive reliability indicator to probe defects in different regions of GaAlAs IRLEDs.