Efficiency of GaAlAs heterostructure red light-emitting diodes

Electroluminescence efficiency of GaAlAs heterostructure light-emitting diodes (LED’s) fabricated by the temperature difference method is discussed by measuring electroluminescence, carrier lifetime, and absorption coefficient of the active layer. Deep levels, distribution of carriers in the indirect valley and the reabsorption of the emitted light in the active layer contribute to the reduction of the efficiency of the red LED’s. The measured absorption coefficient of Ga0.65Al0.35As active layer is about 103 cm−1 at 6500 Å; therefore the active layer thickness should be designed to be less than about 10 μm, to minimize the reabsorption region of the emitted light. The maximum luminescence efficiency is calculated for GaAlAs double heterostructure LED’s, taking the active layer thickness and the potential barrier height into consideration.