Two types of excited electron dynamics in zinc oxide

Abstract

We present first-principle evaluations of the electron-phonon coupling strength parameter and associated characteristics of relaxation for the excited electrons in the conduction band of zinc oxide. The evaluations are based on the pseudopotential plane-wave approach to the electronic band structure, the density-functional perturbation theory for the calculations of phonons and electron-phonon interactions, and on the "Fermi golden rule" for evaluations of the electron relaxation time and the energy-loss time. The calculations demonstrate existence of two types of electron dynamics, the picosecond one for electrons near the bottom of the conduction band and the femtosecond for the higher energies. Sensibly good agreement with experimental data confirms the validity of the calculations.

Stochastic model of dispersive multi-step polarization switching in ferroelectrics due to spatial electric field distribution

“…Although the account of these processes is ultimately necessary to describe the electromechanical response of ferroelectrics to an applied electric field, they are not included in common statistical models of polarization response, such as the Kolmogorov-Avrami-Ishibashi (KAI) 7-10 , the nucleation limited switching (NLS) [11][12][13] and the inhomogeneous field mechanism (IFM) [14][15][16] models, dealing with statistically independent parallel 180 • switching processes only. Furthermore, experimental results revealed that both 180 • and non-180 • switching events are required in order to describe the electrical and mechanical response of polycrystalline ceramics to an applied electric field pulse during polarization reversal [17][18][19] .…”

“…Another origin of uncertainty of interpretation of experimental results within the MSM model consists in the simplifying assumption of the uniform electric field all over the system. This assumption does not allow explanation of dispersive polarization and strain responses at later switching stages 23 , which may result from the distribution of local switching times due to the spatially inhomogeneous distribution of the applied field 14,15,25 .…”

“…where the parameter η < 1 quantifies the fraction of the 90 • -switching events, τ i are the unique characteristic switching times for the first and the second 90 • -switching processes (i = 1 and 2, respectively) and the parallel 180 • -processes (i = 3), while α, β and γ are the Avrami indexes of the respective processes related to the dimensionality of the growing reversed polarization domains 8,9 . According to Merz 26 and experimental observations on PZT ceramics [12][13][14][15]19,23 the field dependence of the characteristic switching times is adopted in the form where E…”

Ab initio approach to the rate of radiative electron trapping and electron–hole recombination in B‐, C‐, and N‐doped anatase

“…The details of the calculations are similar to those discussed in the Refs. [26,27]. In order to confirm the acceptability of such simplifications we show in Fig.…”

“…So we can neglect the light attenuation in the bulk and apply the spectral distribution of light in vacuum admitted in the EinsteinPlanck theory. A second support is provided by the firstprinciple calculations of the band structure of anatase, rutile, and zinc oxide and evaluations of the rate of electronphonon relaxation in these species [26,27]. They demonstrate that the electron-phonon relaxation of the excited electrons to the bottom of the CB occurs within the time interval of some tens of femto-seconds, whereas, the electrons near the bottom of the CB reside a time a few orders longer.…”