ENERGY AND EFFECTIVE-MASS OF A POLARON IN ASYMMETRIC SEMICONDUCTOR QUANTUM-WELL STRUCTURES

In this paper, the correct electron extended stales wave functions and the density of states in asymmetric single quantum wells (QWs) are gi ven for the first time, we put right mistakes from some previous paper s of some other authors. Within the framework of the second-order pert urbation theory, the ground-state polaron binding energy and effective mass correction in asymmetric single QWs are studied including the fu ll energy specturm, i.e., the discrete energy levels in the well and t he continuum energy spectrum above the barrier, and all possible optic al-phonon modes. The effects of the finite electronic confinement pote ntial and the subband nonparabolicity are considered. The relative imp ortance of the different phonon modes is investigated. Our results sho w that the polaron energy and effective mass are sensitive to the asym metry of the structure and have a close relation to the interface phon on dispersion. When well width and one side barrier height of asymmetr ic QWs are fixed and identical with those of symmetric QW, the polaron binding energy and effective mass in asymmetric QWs are always less t han those in symmetric QW. It is necessary to include the continuum en ergy spectrum as intermediate states in the study of polaron effects i n QWs in order to obtain the correct results. The subband non-paraboli city has little influence on the polaron effects. The polaron energies given in this paper are excellent agreement with our variational resu lts.