High-Dimensional Acousto-optoelectric Correlation Spectroscopy Reveals Coupled Carrier Dynamics in Polytypic Nanowires

The authors combine acousto-optoelectric and multichannel photon correlation spectroscopy to probe spatiotemporal carrier dynamics induced by a piezoelectric surface acoustic wave (SAW). The technique is implemented by combining phase-locked optical microphotoluminescence spectroscopy and simultaneous three-channel time-resolved detection. From the recorded time-correlated single-photon-counting data, the time transients of individual channels and the second- and third-order correlation functions are obtained with subnanosecond resolution. The method is validated by probing the correlations of SAW-driven carrier dynamics between three decay channels of a single polytypic semiconductor nanowire on a conventional ${\mathrm{Li}\mathrm{Nb}\mathrm{O}}_3$ SAW delay line chip. The method can be readily applied to other types of nanosystems and probes SAW-regulated charge-state preparation in quantum dots, charge-transfer processes in van der Waals heterostructures, or other types of hybrid nanoarchitectures.

Figure 1

(a) Schematic of the 3CXC AOES setup. Phase-locked microphotoluminescence spectroscopy probes the nanosystem (here a single NW). Emissions of different recombination channels are spectrally isolated and detected by APDs and recorded by multichannel TCSPC electronics. (b) Schematic of the timing scheme. Local phase of the SAW oscillation (blue) sets absolute time, t, of the experiment. Laser excitation (red bar) is delayed by $T_{\mathrm{SAW}}(\varphi /{360}^{\circ })$ and individual time stamps of subsequent detection events on each channel are registered relative to laser excitation.

Figure 2

Characterization of the studied NW. (a) Photoluminescence spectrum observed at the center of the studied polytypic $\mathrm{Ga}\mathrm{As}\text{−}(\mathrm{Al})\mathrm{Ga}\mathrm{As}$ core-shell NW. (b) Schematic of the band structure along the axis of a NW core and recombination processes corresponding to the three different recombination bands. (c) Spatial PL map along the NW. White dashed line marks transitions for ZB with occasional twins to a mixed WZ-ZB phase, as shown by the schematic. $+k$- and $-k$-propagating SAWs are aligned parallel to the NW.

Figure 3

Single-channel AOES. Stroboscopic PL spectra of the ZB (left panels), indirect ZB-WZ (center panels), and indirect WZ-ZB (right panels) exciton transitions at the center of the NW for (a) $+k$-propagating SAW and (b) $-k$-propagating SAW and phases of $\varphi =[-{360}^{\circ },{360}^{\circ }]$. Electric field orientation at photoexcitation is shown for different phases, $\varphi$, on the right. Recorded transients show SAW-induced oscillations and exhibit clear dependences on the SAW propagation directions (marked by black dashed ellipses and black and red arrows).

Figure 4

Two-channel correlation spectroscopy, $g_{ij}^{(2)}(t_{ij})$, of the indirect ZB-WZ exciton to ZB exciton ($i,j=2,1$, left panels), the indirect WZ-ZB exciton to ZB exciton ($i,j=3,1$, center panels), and the indirect WZ-ZB exciton to ZB-WZ exciton ($i,j=3,2$, right panels) as a function of the phase, $\varphi$, for (a) $+k$- and (b) $-k$-SAW propagation directions. Electric field orientation at photoexcitation is shown on the right. Characteristic correlation features are highlighted by arrows and ellipses.

Figure 5

Three-channel correlation spectroscopy, $g_{1,2,3}^{(3)}(t_{21},t_{31})$, of all three recombination channels for four characteristic values of $\varphi$ for a $+k$-propagating SAW (color scale applies to all panels). Band-edge modulation by the SAW is shown as schematics. Red square marks $T_{\mathrm{SAW}}$ setting the period of the observed oscillations.