Electron scattering and capture rates in quantum wells by emission of hybrid optical phonons

Abstract

Intra and intersubband scattering rates and electron capture rates are considered when mediated by hybrid optical phonons in an AlAs/GaAs/AlAs double heterostructure confined between two outer metallic barriers. In evaluating scattering rates we concentrate first on an infinite quantum well for the electrons and show that the presence of the outer metal barriers results in reductions of the intra and intersubband scattering rates due to the suppression of the interface-like modes. For a quantum well (QW) with a finite depth we find that the outer barriers are responsible for the existence of a discrete energy spectrum above the well. The electron capture process under these circumstances is defined as the electron transition from the first electron subband above the well to all possible subbands inside the well by the emission of hybrid phonons. Explicit calculations reveal that the capture rates are characterized by sharp peaks, referred to as electron resonances which arise when a new electron state is generated on increasing the quantum well width. Other sharp peaks are identified as phonon resonances and arise when the energy of the initial state differs by a phonon energy from an electron state at the bottom of a quantum well subband.