A model for the temperature dependence of photoluminescence from self-assembled quantum dots

Abstract

Photo-excited carriers, distributed among the localized states of self-assembled quantum dots, often show very anomalous temperature dependent photoluminescence characteristics. The temperature dependence of the peak emission energy may be non-monotonic and the emission linewidth can get narrower with increasing temperature. This paper describes a quasi-thermodynamic model that naturally explains these observations. Specifically, we introduce a temperature dependent function to parameterize the degree of thermalization of carriers. This function allows us to continuously interpolate between the well-defined low and high temperature limits of the carrier distribution function and describe the observed anomalies in the photoluminescence spectra with just two fitting parameters. We show that the description is equivalent to assuming that the partially thermalized carriers continue to be described by equilibrium statistics, but with a higher effective temperature. Our treatment of the problem is computationally simpler than the usually employed rate equations based analyses [e.g. Sanguinetti, et al. Phys. Rev. B 60, 8276 (1999)], which typically also have many more under-determined fitting parameters. The model is extended to quantum dots with a bimodal size distribution.

Optical density of states in ultradilute GaAsN alloy: Coexistence of free excitons and impurity band of localized and delocalized states

“…From the above expression for PL, complete trapping would imply a uniform occupation probability within a band and thus an infinite carrier temperature. 13,27,30 In Fig. 4, carriers from both the free excitonic states ($1.45-1.47 eV) and states between $1.41 and 1.45 eV have nearly the same T e .…”

“…The fact that two T e 's closely follow each other implies that electrons in both the bands are delocalized to a similar degree. 30 while the lower energy cut-off of the PL emission spectrum arises from the density of states, the high energy region (assuming that the band width is very large compared to k B T e ) tail represents the carrier distribution function. 29 The occupation probability can thus be characterized by a single parameter, T e .…”

Interdot carrier transfer in semimagnetic Pb1−xMnxSe nanocrystals embedded in oxide glass

“…Bansal [13] simulated the anomalous temperature dependent behavior of PL spectra from bimodal size distributed dots from an InAs/GaAs self-assembled QDs. Similarly, we believe that temperature induced interdot carrier transfer, from small QDs that correspond to the highest emission energies to larger dots with lower emission energies is responsible for the behavior observed in the PL(T) spectra of Pb 0.95 Mn 0.0.5 Se sample, as shown in Fig.…”

Photoluminescence from localized states in disordered indium nitride

“…As was previously found by Wu, et al [7], the temperature dependence of the PL peak is sample-dependent and does not follow the change in the bandgap (depicted here by the solid line with the Varshni parameters taken from reference [19]). The shift is much smaller, corresponds to local redistribution (partial thermalization [20]) of carriers with increasing temperature, and is largely uncorrelated to the change in the intrinsic bandgap value. Such behavior is often seen in quantum dots [20] and nitride-based semiconductor alloys such as GaInN [21] and dilute nitrides [18].…”

“…The shift is much smaller, corresponds to local redistribution (partial thermalization [20]) of carriers with increasing temperature, and is largely uncorrelated to the change in the intrinsic bandgap value. Such behavior is often seen in quantum dots [20] and nitride-based semiconductor alloys such as GaInN [21] and dilute nitrides [18]. Clearly the same physics is at work here.…”