Superlattice as a phonon trap in zincblende quantum wells

In hot carrier photovoltaic devices, photoexcited electrons and holes are spatially separated in "Type II" quantum wells to reduce their recombination rate. But there are well-understood mechanisms by which the optical phonons created in electron-phonon interaction can decay into acoustic phonons and escape the quantum well, cooling down the lattice and carriers. To enhance performance, we have to manage heat transport without compromising the photoelectronic conversion rate. We build a realistic model of a Type II quantum well superlattice and calculate its phonon structure. We use DFT to determine the parameters needed to represent several typical zincblende structures in the form of Tersoff potentials. We then examine how superlattice design can affect phonon transport as desired to improve efficiency. We explore heat management for different designs and seek to engineer the phonon structure to obtain the desired heat dissipation rate. Finding the optimal quantum well design is then a complex interplay between electronic and phononic properties. We use our potentials to go beyond the harmonic approximation and calculate phonon scattering for more realistic predictions. In addition, these potentials will establish a parameter library useful for future device design.