Optical-coupling efficiency of GaP : N green-light-emitting diodes

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Abstract
Optical‐coupling efficiencies of slurry‐diced GaP : N green‐light‐emitting electroluminescent diodes have been measured. Light losses due to absorption in such structures are complicated by the irregular diode geometry, the large refractive index, and the significant energy‐dependent optical absorption present in the green spectral region. We show that the optical‐coupling efficiency can be represented as a product of the red‐emission random‐path optical‐coupling efficiency and a ratio of the integrated external spectrum to the integrated internal spectrum. Optical‐coupling efficiencies of encapsulated green diodes in the range 25 ± 5% have been obtained from the measurements, i.e., three times more light is internally absorbed than is usefully transmitted to the ambient. Unencapsulated diodes have about one‐half of this optical‐coupling efficiency.