BIEXCITONS IN GaN AND AlGaN EPITAXIAL LAYERS

摘要

Optical characterization of biexcitons in GaN and AlGaN epitaxial layers is reviewed on the basis of experimental observations. Nonlinear optical properties of biexcitons in GaN are studied by means of time-resolved nonlinear luminescence spectroscopy, which is based on an excitation correlation technique. A superlinear signal of nonlinear biexciton luminescence, which indicates an enhancement of luminescence efficiency, is observed. The enhancement originates from higher-order nonlinearity with respect to the density of biexcitons, and is attributed to the stimulation of biexciton luminescence. The effect of localization due to alloy disorder on biexcitons in Ga-rich AlGaN ternary alloys is also studied by means of photoluminescence excitation spectroscopy. A Stokes shift of biexcitons as well as a binding energy of biexcitons is determined as a function of aluminum composition on the basis of two-photon absorption of biexcitons. The biexciton localization results in a strong enhancement of the biexciton binding energy.