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 ͑10 19 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 Ͼ120 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 ͑10 17 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.

Precision, all-optical measurement of external quantum efficiency in semiconductors

“…(12). An earlier investigation 14 as well as a recent theoretical study 25 suggests that nonradiative recombination rate may also depend on the injected carrier density. The fact that we measure the EQE and lifetime at different pump intensities may explain such discrepancies.…”

“…Recent modeling in GaAs/GaInP heterostructures suggests more complex density and temperature dependence as the doping type and level in the core and passivation layers are varied. 25 The temperature dependence of coefficients A, B and C in Eq. (2) predicts higher EQE at lower lattice temperatures.…”

Laser cooling in solids: advances and prospects

“…Laser cooling of semiconductors has been examined theor etically [95,123,[127][128][129][130][131][132][133][134][135] as well as in experimental studies [26,92,93,126,139,136]. A feasibility study by Sheik-Bahae and Epstein outlined the conditions for net cooling based on fundamental material properties and light management [95].…”

Cryogenic optical refrigeration

“…This effect limits the possibility of laser cooling of rare-earth-doped solids at temperatures below about 50 K. In principle this limit does not exist for laser cooling of semiconductors whose electrons and holes are indistinguishable and which thus obey Fermi-Dirac statistics. The feasibility of laser cooling in semiconductors has been extensively investigated both theoretically [17,[51][52][53][54][55][56][57][58][59][60][61] and experimentally [61][62][63][64][65][66][67][68][69]; however, no net temperature reduction has been observed yet. This failure is due to stringent purity requirements, complications associated with inefficient light extraction from the high-refractive-index substrate (η e < 0.2 for nearly index-matched dome [17,66]), and many-body effects such as a carrier-density-dependent quantum efficiency.…”