Picosecond imaging of photoexcited carriers in quantum wells: Anomalous lateral confinement at high densities

Abstract

We have measured the in-plane motion of photoexcited carriers in semiconductor quantum wells and have discovered several surprising results. The effective diffusivity of the carriers at densities below n 2x10" cm is found to depend upon the excitation level, possibly indicating defect-limited diffusion or phonon-wind effects. Above this density the spatial profiles exhibit two distinct components with widely differing diffusivities.We postulate that the slowly diffusing component represents carriers which are "thermally confined" to a phonon hot spot.

Probing charge transfer excitons in a MoSe2–WS2 van der Waals heterostructure

“…43 We find that this model can well describe the expansion of the profile after about 20 ps. This diffusion process can be described by the classic diffusion equation, which predicts that the squared width of the profile increases linearly as w 2 (t ) = w 0 2 + 4Dt, where D and w 0 are the exciton diffusion coefficient and the initial width, respectively.…”

Transient Absorption Microscopy of Monolayer and Bulk WSe2

“…56 By a linear fit [the red line in Figure 4b], we obtain an exciton diffusion coefficient of 15 ( 5 cm 2 /s. The measurement is performed with a low-density exciton system.…”

Temperature dependence of ambipolar diffusion in silicon on insulator

“…Therefore, electric detection techniques that are generally used in charge transport studies are inadequate. Several optical techniques including transient grating, 9 pump-probe based on interband absorption, 10 and photoluminescence 11,12 have been used to study ambipolar diffusion in direct-bandgap semiconductors and bulk silicon. However, it is difficult to use these techniques to study carrier dynamics in SOI, due to small thickness and indirect bandstructure of the silicon layer.…”