PHONON-ASSISTED INTERSUBBAND TRANSITIONS IN STEP QUANTUM-WELL STRUCTURES

We evaluate effects of heterointerfaces on optical phonon modes and ph onon assisted electron intersubband transition rates in step quantum w ell structures for intersubband lasers. Various phonon modes and elect ron-phonon interaction Hamiltonians, including the interface modes, co nfined longitudinal-optical modes, and half space modes in the quantum well structures are calculated based on the macroscopic dielectric co ntinuum model and microscopic analysis. The transfer matrix method is used to calculate the interface modes. The intersubband transition rat es due to electron-phonon scattering by these phonon modes are evaluat ed using Fermi's golden rule, with the electron wave functions obtaine d by solving the Schrodinger equation for the heterostructures under i nvestigation. Our results show that, compared with the transition rate s in the same structures calculated using the bulk phonon modes and th e bulk Frohlich interaction Hamiltonian, the electron interface-phonon interactions give significantly larger transition rates up to an orde r of magnitude. Therefore, the effects of localized phonon modes, espe cially the interface modes, must be taken into consideration for optim al device design. (C) 1998 American Institute of Physics. [S0021-8979( 98)03915-2].