Lifetime mapping of photo-excited charge carriers by the transient grating imaging technique for nano-particulate semiconductor films

Makoto Ebihara; Woon Yong Sohn; Kenji Katayama

doi:10.1063/1.5111418

Lifetime mapping of photo-excited charge carriers by the transient grating imaging technique for nano-particulate semiconductor films

Rev Sci Instrum. 2019 Jul;90(7):073905. doi: 10.1063/1.5111418.

Authors

Makoto Ebihara¹, Woon Yong Sohn¹, Kenji Katayama¹

Affiliation

¹ Department of Applied Chemistry, Chuo University, Tokyo 112-8551, Japan.

PMID: 31370435
DOI: 10.1063/1.5111418

Abstract

The transient grating (TG) imaging technique has been developed, where the refractive index change due to the photoexcited charge carriers excited with a stripe patterned light can be visualized. The spatiotemporal imaging of photoexcited charge carriers was demonstrated for a nanoparticulate TiO₂ film. In the analytical procedures to map out the time constant distribution, the averaged response of photoexcited carriers in each image was obtained from the Fourier transform of the TG images since the image has a spatial modulation with a stripe pattern of light. The oscillation response due to the acoustic grating, the decay of the surface trapped electrons (until 1 μs), and thermal diffusion (until 100 µs) were observed. In order to obtain the lifetime imaging of the photoexcited electrons, the target time region (0-1 µs) for the response was selected and fitted with an exponential function, and the time constants were mapped out. We found that the time constants showed a wide range of distribution (68-920 ns), dependent on the sample positions.