Effect of the shape and duration of excitation pulse on the dynamics of excitons and trions in quantum wells

Abstract

We have studied the effect of the shape and duration of a photoexcitation pulse on the temporal evolution of excited electrons when they are both free or bounded in excitons and trions. A quantum well with n-and p-type remotely doped regions is considered to get the necessary excess of free electrons or holes. This configuration allows us to study the evolution of both negative and positively charged excitons simultaneously. Calculations have been done using the matrix density formalism to introduce different pulse types. The temporal behavior of the photoluminescence intensity, which is associated with plasma, exciton, and trion, is obtained by means of the two-dimensional density evolution of the different species.

The role of excitons and trions on electron spin polarization in quantum wells

“…We will show that, although the presence of trions is essential to preserve a reasonable spin polarization, photoexcitation of electrons at trion level is not necessary. We use the matrix density formalism, considering the different generation, recombination and annihilation rates for different types of binding energy and spin polarization 26 . The effect of the interband optical pulse is included through the interband generation function.…”

“…Thus, for τ f = 0 ps we have a square pulse and, for τ f > τ p , the pulse in a gaussian-like one 26 . We simulate a continuous regime excitation by a very long pulse with τ p = 2000 ps and τ f = 10 ps.…”

“…It is important to point out that for such a long pulse, a detuning energy of ∆ = 0.01 meV is enough to reach the maximum of the generation function g(t) (Fig. 2) 26 . Thus, we will use this value in calculations.…”

“…We use the matrix density formalism, considering the different generation, recombination and annihilation rates for different types of binding energy and spin polarization 26 . The effect of the interband optical pulse is included through the interband generation function.…”