Comprehensive control of optical polarization anisotropy in semiconducting nanowires

Abstract

The demonstration of strong photoluminescence polarization anisotropy in semiconducting nanowires embodies both technological promise and scientific challenge.Here we present progress on both fronts through the study of the photoluminescence polarization anisotropy of randomly oriented nanowire ensembles in materials without/with crystalline anisotropy, small/wide bandgap, and both III-V/II-VI chemistry (InP/ZnO nanowires, respectively). Comprehensive control of the polarization anisotropy is realized by dielectric matching with conformally deposited Ta 2 O 5 (dielectric ratios of 9.6:4.41 and 4.0:4.41 for InP and ZnO, respectively). After dielectric matching, the polarization anisotropy of the nanowire ensembles is reduced by 86% Semiconducting nanowires have attracted significant attention due to the unique electric and optical properties arising from their quasi-1D geometry. 1-3 Among these properties, optical polarization anisotropy is of particular importance for fundamental studies of polarization-sensitive electronic states and potential applications in polarization-sensitive photodetectors. [4][5][6] Detailed control of this polarization anisotropy is critical for progress on both fronts and is the focus of this investigation. The polarization anisotropy for luminescence from a single nanowire is defined as ) /( ) (is the intensity parallel (perpendicular) to the nanowires axis. The most general source of this anisotropy is the variation in dielectric constant between the nanowire (ε) and its environment (ε e ). Specifically, in nanowire ensembles the measured optical polarization anisotropy (which depends on both the absorption anisotropy and luminescence anisotropy) does not disappear, but rather decreases as compared to the single nanowire value due to weighted 3 ensemble averaging. Figure 1a shows a schematic describing how this residual emission polarization can occur in nanowire ensembles. As a result, the ensemble studies presented here can be quantitatively correlated with single nanowire anisotropies. A detailed model for this correlation will be developed below, but first we address the synthesis and measurement of nanowire ensembles. InP and ZnO nanowires are grown using pulsed laser deposition (PLD) 15 that the nanowire has zincblende (ZB) structure with a <111> growth direction for InP nanowires (Fig. 1b, inset) and a wurzite (WZ) structure with a <001> growth direction for ZnO nanowires (Fig. 1c, inset). Previous studies [17][18] . The inset in Fig. 2b shows an 5 SEM image of the nanowires after they have been conformally coated with an average of 670 ± 34nm of Ta 2 O 5. The polarization resolved photoluminescence spectrum (Fig. 2b) reveals that the intensity is nearly identical for perpendicular and parallel configurations leading to  ~ 0.036, a reduction of 86%, consistent with the qualitative expectation that the dielectric matching will suppress the polarization anisotropy.ZnO nanowires, as can be seen in Fig. 2c, range from 30 nm to 50 nm in diameter and exhibit spectrally ...

Polarization memory of photoluminescence related with Si nanoparticles embedded into oxide matrix

“…As shown experimentally in the work [16] by reducing the dielectric contrast between InP and ZnO nanofiber using Ta 2 O 5 deposition, the authors managed to reduce the value of ρ by 84…86%. In the same paper, the model was developed for calculation of the PL intensity dependence on the angle between the directions of exciting light polarization and that of detected one for the structure that contains nanowires (or elongated nanoparticles) randomly oriented in the plane of the sample (similar to our continuous nc-Si−SiO x structures processed in HF).…”

“…6 shows the angular dependence of the normalized PL intensity (points − experimental values, solid line − approximation of the experiment using polynomial) for continuous nc-Si−SiO x sample annealed in vacuum, then processed in HF vapor, the same as presented in Figs 1 and 2. The dotted curve shows the results of simulation that obtained using the expression [16]: (1) (2) PL intensity (arb. units) where ε e and ε are dielectric functions of environment and emitting nanoparticles, accordingly, θ is the angle between excitation and detection.…”

Strong dichroic emission in the pseudo one dimensional material ZrS3

“…4a). Indeed, a similar reduction in ρ has been observed when luminescent nanowires (ZnO, InP) were coated with Ta 2 O 5 , 41 surrounded by a matched dielectric medium, different from that observed under vacuum. From a materials perspective, the reduction of the polarization anisotropy can be explained when one accounts for the interaction between adjacent pseudo-1D chains.…”

Excitonic recombination and absorption in InxGa1−xAs/GaAs heterostructure nanowires

“…The light intensity data are fit well by I = a + b sin 2 (α) (red solid line), with a maximum of the PL intensity when the polarizer axis is perpendicular to the NW axis (α = 90 • ). This polarization is characteristic of an emission from WZ NWs, while it is opposite 5,34 to that of the emission from ZB NWs. In addition, the intensity of the Z and Y 2 recombinations follows the same angular dependence of the X band, thus indicating that all these emissions involve WZ-related electronic levels.…”