Deep-level changes associated with the degradation of gallium phosphide red-light-emitting diodes

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Abstract
The degradation of LPE GaP red LED’s in forward‐bias aging is studied by deep‐level capacitance spectroscopy. The decrease of the Zn‐O concentration during aging is found to be a major source of degradation. The Zn‐O concentration decreased to 62±9% of its undergrade value for samples degraded to 50±8% efficiency when measured at 10 mA. Three deep levels consistently appear during degradation with activation energies for emitting carriers to the majority‐carrier band of 0.41±0.04, 0.72±0.07, and 0.97±0.09 eV. Similar deep‐level changes were found for LED’s degraded to 50% efficiency when aged at different temperatures and different currents and for LED’s degraded to 50% efficiency which aged at different rates under the same conditions. In contrast to the red LED, two LPE GaP green LED’s, degraded at 250 °C to 50% efficiency, showed no significant deep‐level changes.