Differentiating between constant and concentration-dependent diffusion coefficients via the optical spectroscopy of excitons in quantum wells

Exciton energy calculations, including the binding energy, are presented which show that quantum wells subject to diffusion with constant and concentration-dependent diffusion coefficients can have the same emission/absorption energy. The proposal of I Harrison (1994 Semicond. Sci. Technol. 9 2053), that it is possible to distinguish between these two forms of the diffusion coefficient by fitting emission energies in annealed quantum wells for several different well widths, is validated for a typical II-VI system in which the dominant recombination process is excitonic. An analysis of recent experimental data of exciton energies in CdTe-Cd_1-XMn_xTe quantum wells, before and after a rapid thermal anneal, demonstrates that the diffusion of Mn from the barriers into the wells can be explained in terms of a constant diffusion coefficient.