Optical phonon modes at GaAs/AlxGa(1-x)As semiconducting interfaces: effects of the concentration of Al

We sludy long-wavelength polar aplical modes al semiconductor interfaces of the GaAs/AlxGa(1_x)As system and take into aceounl the intlucnce of the Al concentratian. We have considered two cases in which the interface is kcpt eithcr al a variable or al a fixed electrostatic potenliaL Thc spectrum of cxcitations then shows existence of localizcd aod resonan! modes dcpending on the conccntration of Al. For the case of a tixco electrostatic potential (rnetallized interface), the appearnnce of a new interface mode hesides the resonant one, is found fm ceflain ranges of the concentration x.