Measurements of the absolute external luminescence quantum efficiency in ZnSe/ZnMgSSe multiple quantum wells as a function of temperature

We report on a novel experimental setup using a miniature integrating sphere fitted into a cryostat to measure spectrally resolved the absolute external photoluminescence quantum efficiency η_lum, in the temperature range from 6 K to beyond room temperature. Direct access to η_lum is achieved by an uncomplicated method to calibrate the spatially integrated emission spectra absolutely. The fraction of light coupled out of the sphere into the detection system is in good approximation independent of the emitted wavelength and the emission characteristics of the investigated samples, due to their smallness compared with the total sphere area. This fact is proved by theoretical calculations for the sphere throughput and the irradiance within the sphere. To demonstrate the capabilities of this setup, we investigate in high quality ZnSe/ZnMgSSe 10X multiple quantum wells, the temperature dependence of the quantum efficiency, simultaneously for the quantum well and the barrier luminescence. Within a thermal activation model, three processes are found to contribute to the thermal quenching of η_lum of the quantum well luminescence.