The left part of Fig. 5.20b illustrates an electron losing its kinetic energy by emitting a phonon. The electron will be scattered either forward or backward. In the case of backward scattering the electron faces a thick barrier near the source contact and will be reflected with high probability, such that its momentum will again be directed towards the drain contact.
Elastic scattering conserves the energy of carriers, but the current decreases due to elastic backscattering of carriers. Fig. 5.21a shows that for elastic scattering the source and drain current spectra are symmetric. As the electronphonon coupling strength increases, resonances in the current spectrum are washed out and the total current decreases due to elastic backscattering. In the case of inelastic scattering, carriers acquiring enough kinetic energy can emit a phonon and scatter into lower energy states. Therefore, as shown in Fig. 5.21b, the source and drain current spectra are not symmetric.


M. Pourfath: Numerical Study of Quantum Transport in Carbon NanotubeBased Transistors