PHOTOLUMINESCENCE QUANTUM YIELD IN GAAS ALAS SUPERLATTICES/

Accurate measurement of the internal quantum yield of photoluminescenc e is difficult since only a small fraction of the emitted light is col lected in a luminescence experiment. We propose a novel and alternativ e method to measure the photoluminescence quantum yield. This method i s suitable for any material grown on top of another material with a lo wer band gap. We use a GaAs/AlAs superlattice on a GaAs layer. The int ensity of luminescence emitted by the GaAs layer when it is directly e xcited (excitation energy above GaAs band gap, but below the SL band g ap) is compared to the intensity of luminescence emitted when it is in directly excited by luminescence light from the superlattice. In the f irst approximation the internal quantum yield of the superlattice phot oluminescence is obtained from the ratio of the two luminescence inten sities. This simple method leads to a slight underestimation of the qu antum yield, whereas usual and more complicated methods using the exte rnal quantum efficiency may lead to a large overestimation in the case of high quantum efficiency and photon recycling effects.