First-principles theory of nonradiative carrier capture via multiphonon emission

Abstract

We develop a practical first-principles methodology to determine nonradiative carrier capture coefficients at defects in semiconductors. We consider transitions that occur via multiphonon emission. Parameters in the theory, including electron-phonon coupling matrix elements, are computed consistently using state-of-the-art electronic structure techniques based on hybrid density functional theory. These provide a significantly improved description of bulk band structures, as well as defect geometries and wavefunctions. In order to properly describe carrier capture processes at charged centers, we put forward an approach to treat the effect of long-range Coulomb interactions on scattering states in the framework of supercell calculations. We also discuss the choice of initial conditions for a perturbative treatment of carrier capture. As a benchmark, we apply our theory to several hole-capturing centers in GaN and ZnO, materials of high technological importance in which the role of defects is being actively investigated. Calculated hole capture coefficients are in good agreement with experimental data. We discuss the insights gained into the physics of defects in wide-band-gap semiconductors, such as the strength of electron-phonon coupling and the role of different phonon modes.

Determination of the Mott-Hubbard gap inGdTiO3

“…Second, an electron excited to the UHB could recombine with a smallhole-polaron state. A transition at this energy is actually more likely to be nonradiative, 33 and indeed, PL measurements around 0.7 eV do not show any signal in this energy range.…”

Comparative study ofab initiononradiative recombination rate calculations under different formalisms

“…This is expected as discussed in Ref. [17], since only one phonon mode is used, and the phonon mode which induces the electron-phonon coupling is forced to be the same as the phonon modes which involved in the energy conservation. Such restriction can reduce the transition rate.…”

“…In the work of A. Alkauskas et al, a quantum mechanical 1D model is presented [17]. In this 1D model, as discussed above, the atomic movement is along the j i R R R ∆ = -direction, and one phonon degree of freedom along this direction is considered.…”

“…ii)Adiabatic approximation [14], iii) Marcus theory [15], iv) Quantumcharge transfer (CT) theory [16] and v) one-dimensional (1D) formulism [17].…”

“…[10]. Alkauskas et al [17] developed another practical approach to calculate the nonradiative carrier capture coefficients (method v).…”