Defect-related degradation of Deep-UV-LEDs

With this paper we describe an extensive analysis of the electro-optical degradation of deep ultraviolet Light-Emitting Diodes emitting at 310 nm, submitted to accelerated stress test. The results obtained within this study indicate that: (i) high current stress can induce a significant decrease in the optical power emitted by the LEDs; (ii) optical power decrease is more prominent at low measuring current levels, indicating that degradation is related to an increase in the concentration of defects, with subsequent decrease in the radiative efficiency of the active layer; (iii) stress can induce a significant increase in the operating voltage of the LEDs, due to the increase in the resistivity of the ohmic contacts or p-type semiconductor; and (iv) after stress, LEDs show a significantly increased green parasitic emission. This result suggest that stress induced an increase in the defectiveness of the active layer. Information on the location of the degraded region is achieved by the analysis of the Apparent Charge Distribution curves obtained by capacitance–voltage measurements.