Fig. 5: Schematic representation of the kinetics of hot electrons and hot phonons.
As electrons enter a narrow constriction channel, they are rapidly accelerated by intense electric field E and the effective electron temperature <Te> is elevated, as studied with SNoiM. It causes frequent LO-phonon emission in the Γ-valley (down-pointing wavy arrow in the left column) as well as Γ → X intervalley electron transfer (fat red arrow in the left column). The effective LO-phonon temperature, TLO, is significantly elevated, but X-valley electrons are not efficiently heated by E, so that the LO phonons emitted by Γ-valley electrons are strongly absorbed by X-valley electrons (wavy arrow pointing upward in the left column), suppressing the net energy loss in the channel and causing the “hot-phonon bottleneck effect”. As the electrons exit the channel, Γ-valley electrons are no longer rapidly accelerated by E, but energy is still fed via intervalley back-transfer from X valleys (fat yellow arrow in the right column). TLO drops faster than TX so that X-valley electrons change to emit LO phonons (wavy arrow pointing downward in the right column). The electrons dissipate net energy, causing prominent non-local energy dissipation near the exit. Emitted LO phonons quickly decay into two LA phonons (via Klemens channel), eventually thermalize slowly into heat, and are primarily composed of long wavelength acoustic phonons that are sensed with SThM as the lattice temperature TL.
