Effect of n-p-n heterostructures on interface recombination and semiconductor laser cooling

Abstract

The design of doped n-p-n semiconductor heterostructures has a significant influence on the structures’ nonradiative decay and can also affect their photoluminescence characteristics. Such structures have recently been explored in the context of semiconductor laser cooling. We present a theoretical analysis of optically excited n-p-n structures, focusing mainly on the influence of the layer thicknesses and doping concentrations on nonradiative interface recombination. We find that high levels of n-doping (1019 cm−3) can reduce the minority-carrier density at the interface and increase the nonradiative lifetime. We calculate time-dependent luminescence decay and find them to be in good agreement with experiment for temperatures >120 K, which is the temperature range in which our model assumptions are expected to be valid. A theoretical analysis of the cooling characteristics of n-p-n structures elucidates the interplay of nonradiative, radiative, and Auger recombination processes. We show that at high optical excitation densities, which are necessary for cooling, the undesired nonradiative interface recombination rates for moderate (1017 cm−3) n-doping concentrations are drastically increased, which may be a major hindrance in the observation of laser cooling of semiconductors. On the other hand, high n-doping concentrations are found to alleviate the problem of increased nonradiative rates at high excitation densities, and for the model parameters used in the calculation we find positive cooling efficiencies over a wide range of excitation densities.