Reduction of bright exciton lifetimes by radiation-induced disorder

Quantum-radiative decay is a fundamental process in many optoelectronic systems such as laser diodes and solar cells. The bright exciton lifetime is a critical factor in determining the performance of these systems. Motivated by the ever-increasing need for laser systems in space and nuclear applications, we develop a many-particle approach to predict the radiative lifetime under harsh radiation environments. Using GaAs as a model system, we find that radiation-induced band tailing reduces the bright exciton lifetime. This result shows that the efficiency of radiative recombination, in addition to nonradiative recombination, can be affected by ionization radiation. Our approach enables a detailed understanding of the interplay between correlation, localization, and radiation that affect the performance of gain media.

Figure 1

Schematic representation of band-tailing effect and exciton weight redistribution. This figure shows the difference in the density of states between a pure semiconductor and a damaged one. The color indicates where the majority of the exciton weights are coming from. As radiation-induced damage to the electronic structure instantiates band tails, exciton weight is driven into the localized regions.

Figure 2

Schematic band diagram of laser diode under various bias conditions. In the zero-bias condition, there is one chemical potential. Upon biasing, electrons and holes each have a quasichemical potential. In a multiple quantum-well heterostructure, the band offsets are used to drive electron-hole pairs into a smaller recombination region. In each case, the ability of the gain medium to store energy before converting it to light or heat is proportional to the electron-hole recombination time (bright exciton lifetime).

Figure 3

Electronic structure and lifetime predictions of GaAs. (a) Compares the band structure predicted by DFT [modified Becke-Johnson (mBJ) functional] with the Wannier interpolation. (b) The density of states as a function of disorder strength $W$ (eV). The inset shows a detailed view near the Fermi energy. The disorder strength is exaggerated for clarity. (c) The radiative lifetime ${\tau }_r$ as a function of disorder strength $W$. The points are the average over 100 disorder realizations.

Figure 4

Exciton characteristics as a function of disorder. (a) The ratio for the first and second valence band states normalized by the zero disorder ratio. (b) The overlap metric normalized by the zero disorder value. (c) The exciton energy. The lines are guides to the eye.