Heterobarrier for converting hot-phonon energy to electric potential

Abstract

We show that hot phonons emitted in energy conversion or resistive processes can be converted to electric potential in heterobarrier structures. Using phonon and electron interaction kinetics and self-consistent ensemble Monte Carlo, we find the favorable conditions for unassisted absorption of hot phonons and design graded heterobarriers for their direct conversion into electric energy. Tandem barriers with nearly optical-phonon height allow for substantial potential gain without current loss. We find that 19% of hot phonons can be harvested with an optimized GaAs/Al x Ga 1−x As barrier structure over a range of current and electron densities, thus enhancing the overall energy conversion efficiency and reducing waste heat.

Toward reversing Joule heating with a phonon-absorbing heterobarrier

“…The electron current channel with the phonon-recycling heterobarrier-grading is simulated using the self-consistent MC method (incorporating barrier-caused electron nonequilibrium occupancy), and improving over our previous simpler analysis (with the nonconserving lateral momentum neglecting the Al-alloying effects on the transport and scattering) [5]. In the self-consistent MC method applied here, the dynamics of sampled electrons is calculated by Eq.…”

“…The conservations of the LO and acoustic (A) modes are followed in each bin. The phonon energy transfer between A and LO modes is based on the three-phonon (p-p) interactions (up-and downconversion) with the associated material and phonon properties [5,8,32,33]. Using the energy conservation, the change in phonon energy (per unit area) for mode i (LO or A) in the j-th bin (z j = z o +j∆z, bin size ∆z = 5 nm) over a time step (∆t, t ∼ t + ∆t) is The q p,i,R (or q p,i,L ) is determined from T p,i and k p,i (k p,A = 54 W/K-m and k p,LO = 1…”

“…However, in electron scattering by the barrier, the lateral momentum can change during the barrier transition, depending on the interface condition. Fully-nonconserving lateral momentum (over the entire electron wavelength spectrum) has been applied to rough barrier interfaces [5,12] and represents one of the limits. The other limit is the fullyconserving lateral momentum (ideally smooth interface), which is the most restrictive and is used here to assess the phonon recycling under such condition.…”

“…The potential distribution is created by the band discontinuity controlled by the x Al variation, and this structure induces the local phonon absorption/emission favorable regions. Since the interaction with the optical phonons has the highest probability, the optical-phonon population varies with that interaction kinetics, but the up and downconversion by the three-phonon interaction processes quickly recovers from the nonequilibrium created between the optical and acoustic-phonon temperatures (T p,O and T p,A ) [5]. The absorption and emission rates are made relative to the uniform joule heating, and with larger absorption compared to emission there is electron potential gain (∆ϕ e,g ).…”

“…1(a) to (d) [5,6] aimed at returning the emitted phonons to electric potential. The doping density is uniform and moderate (< 10 23 m −3 , assuming nondegenerated electrons), so the equilibrium electron density is also uniform and the ep interactions dominate.…”