Simulation of Time Decay for Photoluminescence Emitted from Silicon Crystals Excited by Short Laser Pulse

Abstract

The time decay for photoluminescence (PL) emitted from silicon crystals excited by a short laser pulse has been simulated for the first time on the basis of two simplified approximations in order to obtain both bulk carrier lifetime (τb) and surface recombination velocity (S). One approximation is that the PL intensity is proportional to the normalized (averaged) excess carrier densities, whereas the other is that it is proportional to the recombination rate. We compared simulated results with experimental ones and obtained better coincidence in the case of the latter rather than the former approximation, which means that the Buczkowski et al.'s algorithm for obtaining both τb and S [J. Appl. Phys. 69 (1991) 6495] cannot be applied to the PL decay method. Therefore, a new algorithm has been developed in this present work.

Surface Recombination in ZnO Nanorods Grown by Aqueous Chemical Methods

“…The fitting parameters ( S and A S /A B ) are 15 ps and 7.5, 20 ps and 3.6, 20 ps and 1.4 for as-grown sample B, Sample B annealed at 500 o C and Sample B annealed at 700 o C, respectively, while the decay time B does not change and remains at about 95 ps for the different annealing conditions. This fact indicates that B B B represents a "bulk" decay time in those ZnO nanorods, as expected from the diffusion equation [6]. The value B =95 ps is similar to the decay time deduced from sample A. Secondly we can see that the value of B S varies between the as-grown sample and the annealed samples.…”

“…There is no observable change of either the crystalline structure of the ZnO nanorods, as deduced from x-ray diffraction curves, or the ZnO nanorods diameter, as concluded from SEM measurements. As earlier demonstrated for Si epilayers [6], the surface recombination can strongly influence the decay time. The near bandgap recombination will exhibit non-exponential or a single exponential decay, depending on whether the surface recombination is the major recombination channel or not.…”

Surface recombination in ZnO nanorods grown by chemical bath deposition

“…The decay curve from the bulk ZnO shows a single exponential time decay, while the ZnO nanorods exhibit a nonexponential decay. As earlier demonstrated for Si epilayer, [28][29][30] the surface recombination can strongly influence the decay time. The excess minority carriers via the near bandgap recombination exhibit a single exponential decay or a nonexponential decay, depending on whether the surface recombination is the major recombination channel or not.…”

“…The surface recombination is characterized by two parameters, i.e., surface recombination velocity S and carrier diffusion length D. tion velocity S on decay time is determined by the diffusion equation with the proper boundary conditions. [28][29][30] In the one-dimensional case, 28 the carriers generated by the laser pulse start out with the following spatial distribution:…”

Annealing effects on optical properties of low temperature grown ZnO nanorod arrays

“…There was no observable change in either the crystalline structure of the ZnO nanorods, as deduced from x-ray diffraction curves, or the ZnO nanorod diameter, as concluded from SEM measurements. As demonstrated earlier for Si epilayers, 52 the surface recombination can strongly influence the decay time. The near band gap recombination will exhibit a nonexponential or a single exponential decay, depending on whether the surface recombination is the major recombination channel or not.…”