Excitons and biexcitons bound to a positive ion in a bismuth-doped inorganic-organic layered lead iodide semiconductor

Abstract

We have studied optical properties of an inorganic-organic layered lead iodide semiconductor doped with bismuth ions $({\mathrm{Bi}}^{3+})$. A new absorption band was observed at $2.15\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ that is by $0.21\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ lower than two-dimensional $1s$ excitons $(2.36\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ and is assigned to excitons bound to the bismuth ions. In the photoluminescence spectra with high excitation density $(\ensuremath{\sim}0.4\phantom{\rule{0.3em}{0ex}}\mathrm{MW}∕{\mathrm{cm}}^{2})$, a novel emission band was observed at the energy of $2.51\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ that is by $0.15\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ higher than the exciton resonance, and is attributed to biexcitons bound to the bismuth ions. On the basis of the experimental results, the binding energies of the bismuth-bound exciton and biexciton were estimated approximately as 210 and $10\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$, respectively. It is found that the binding energy of the positive-ion $({\mathrm{Bi}}^{3+})$ bound biexciton is by far smaller than that of the corresponding bound exciton. The much lower stability of the positive-ion bound biexciton is discussed.