Carrier Capture at Defects from Finite-Temperature Lattice Dynamics

Abstract

Defect-assisted carrier capture is commonly described within nonradiative multiphonon (NMP) theory using normal modes of the equilibrium defect structure. This description becomes inadequate when finite-temperature lattice fluctuations explore configurations that cannot be represented by a fixed normal-mode basis. Here, we present a trajectory-based method for calculating carrier capture rate from first principles, which allows lattice relaxation and electron--lattice coupling matrix element to be reconstructed directly from correlation functions of finite-temperature lattice dynamics. For hole capture at C$_\mathrm{N}$ in GaN within harmonic regime, the method reproduces static NMP results including mode mixing and agrees with experiment. For oxygen vacancy in SiO$_2$, by contrast, the thermally sampled potential energy surface is substantially softer than the zero-temperature normal-mode harmonic expansion, strongly modifying the lattice relaxation and electron--lattice coupling, and producing pronounced changes in both the capture coefficient and its temperature dependence. These results establish the finite-temperature configurational ensemble, rather than phonon occupations alone, as an essential ingredient of defect-assisted carrier capture.