The recently proposed method of our research group named as directional Lyapunov exponents (DLEs) is presented.Then,DLEs are used to analyze the eigenstructure of the output phase space around the equilibrium points.Finally,the impacts of the superlattice parameter changes on the characteristics of the output chaotic signal are analyzed.The experimental results show that parameter changes of the superlattice will affect the eigenstructure around the equilibrium points in the output phase space,and DLEs are sensitive to these changes.