Radiation Damage Constants of Light-Emitting Diodes by a Low-Current Evaluation Method

An optimum technique has been devised for measuring radiation damage constants of LED's, which avoids "injection annealing" of the damage that can occur during post-irradiation evaluation. It is shown that the low current densities necessary to avoid this annealing may require that measurements be made at constant junction voltage, and may preclude the use of the reverse-charge-recovery technique for direct measurement of carrier lifetime. The correction necessary for the varying voltage drop across the diode series resistance is facilitated by the low measuring currents, and by a novel technique for the accurate measurement of diode series resistance at low currents. Precise measurement techniques permit damage constants to be evaluated by application of only a small radiation dose. Using this method, proton, neutron, and gamma damage constants have been evaluated for commercial (Texas Instruments TIXL-13) GaAs LED's. Agreement between the damage constant describing degradation at these low current densities and the higher levels used in practical applications has been verified.