Absolute external luminescence quantum efficiency of GaAs/Al0.3Ga0.7As multiple quantum wells

We use a spatially integrating sphere to measure the absolute external luminescence quantum efficiency of GaAs/Al0.3Ga0.7As multiple quantum well (MQW) structures with and without GaAs substrate. The substrate reduces the external quantum efficiency by a huge amount depending on structure design and absorption coefficients, thus making it impossible to obtain information about the internal efficiency of the structures with substrate. From the temperature dependence of the efficiency we calculate with a thermal activation model the ratios between radiative and nonradiative lifetimes and extract the activation energies. The individual efficiencies of the various emission bands (i.e. hh, lh and defects) are extracted separately. Furthermore we present a simple model for the efficiency gain after the removal of the substrate. With this model we estimate the internal efficiencies of the samples.