Temperature Dependence of Stokes Shifts of Excitons and Biexcitons in Al0.61Ga0.39N Epitaxial Layer

Excitonic optical properties of an Al0.61Ga0.39N epitaxial layer are studied by using photoluminescence (PL) and PL excitation (PLE) spectroscopy. The peak structures due to the biexciton two‐photon and the exciton resonances are clearly observed in the PLE spectra of biexcitons up to 550 K. These observations enable the evaluation of the Stokes shifts of excitons and biexcitons as a function of temperature. The Stokes shifts of both excitons and biexcitons decrease with the increase in temperature up to 300 K, which originates from the gradual delocalization of excitons and biexcitons with the increasing temperature. At temperatures above 300 K, the Stokes shifts of both excitons and biexcitons are independent of the temperature. These observations suggest that the localization mechanism for excitons and biexcitons in AlGaN‐based systems cannot be explained by only the simple alloy disorder model, but there is a particular mechanism of exciton and biexciton localization in addition to the inhomogeneous broadening due to the alloy disorder. The Stokes shifts of excitons and biexcitons in AlGaN layers are evaluated as a function of temperature from 4 to 550 K. The Stokes shifts of both excitons and biexcitons decrease with increasing temperature up to 300 K and are independent of temperature above 300 K. This suggests that the localization mechanism for excitons and biexcitons cannot be explained by only the simple alloy disorder model.