Spontaneous Phonon-Enabled Exciton Dissociation in Semiconductors

The role of phonons in the exciton dynamics of semiconductors is a growing area of interest in the first-principles study of materials. One channel of interest, exciton dissociation – whereby an exciton dissociates into a free electron-hole pair – is an important process in optoelectronic devices. Recently, a framework was introduced for computing ab initio phonon-driven exciton dissociation within the Bethe-Salpeter equation via the introduction of a dynamical phonon screening kernel K^phonon (Alvertis et al, PNAS, 2024; Coveney et al, PRB, 2024). This method has been shown to lead to ultrafast dissociation lifetimes in polar indirect gap semiconductors even at 0 K (Gant et al, arXiv, 2025), though a broader examination of exciton dissociation in semiconductors has not been done. Here, we use the ab initio Bethe-Salpeter equation approach with phonon screening to examine a set of representative semiconductors, including a number of indirect gap systems. We compute rates of spontaneous phonon-enabled exciton dissociation (SPEED), and analyze our results in terms of the computed phonon spectra, electron-phonon matrix elements, and exciton wavefunctions. Our work provides new quantitative intuition for the conditions that enhance or suppress this phenomenon in materials.