An Instantaneous Recombination Rate Method for the Analysis of Interband Recombination Processes in ZnO Crystals

Abstract

Time-resolved photoluminescence (TRPL) analysis is often performed to assess the qualitative features of semiconductor crystals using predetermined functions (e.g., double- or multi-exponentials) to fit the decays of PL intensity. However, in many cases—including the notable case of interband PL in direct gap semiconductors—this approach just provides phenomenological parameters and not fundamental physical quantities. In the present work, we highlight that within a properly chosen range of laser excitation, the TRPL of zinc oxide (ZnO) bulk crystals can be described with excellent precision with second-order kinetics for the total recombination rate. We show that this allows us to define an original method for data analysis, based on evaluating the “instantaneous” recombination rate that drives the initial slope of the decay curves, acquired as a function of the excitation laser fluence. The method is used to fit experimental data, determining useful information on fundamental quantities that appear in the second-order recombination rate, namely the PL (unimolecular) lifetime, the bimolecular recombination coefficient, the non-radiative lifetime and the equilibrium free-carrier concentration. Results reasonably close to those typically obtained in direct gap semiconductors are extracted. The method may represent a useful tool for gaining insight into the recombination processes of a charge carrier in ZnO, and for obtaining quantitative information on ZnO excitonic dynamics.

ALD-Deposited NiO Approaches the Performance of Platinum as a Hydrogen Evolution Cocatalyst on Carbon Nitride

“…As expected from an α ≈ 1, the fluorescence intensity of all samples also follows a second-order kinetic decay, which suggests that bimolecular charge recombination dominates the decay kinetics (Figure S8). − Despite the differences we observed in the slope of the second-order kinetics, we determined that the rate constants are similar for all samples. This is attributed to the fact that we monitor the PL intensity, not the concentration of charge carriers, which is affected by the different optical properties of the films (see the trPL second-order reaction kinetics section in the Supporting Information for further discussion).…”

Optical properties of ytterbium-doped and undoped Cs2AgInCl6 thin films deposited by co-evaporation of chloride salts

“…Multiple time constants may indicate the heterogeneity of the trap emission or result from nonlinear recombination kinetics. 39,40 Indeed, we could fit these curves equally well with a combination of first and second-order charge carrier recombination. We use this classical multiexponential analysis only to parametrize the changes in the decay curves and, following Péan et al 's 40 advice, do not interpret or ascribe any meaning to them.…”

“…These time constants varied weakly with Yb concentration (Fig.9b), annealing temperature, and duration (Fig.S10 †). Multiple time constants may indicate the heterogeneity of the trap emission or result from nonlinear recombination kinetics 39,40. Indeed, we could t these curves equally well with a combination of rst and second-order charge carrier recombination.…”