Dynamics of Photo-excited Hot Carriers in Hydrogenated Amorphous Silicon Imaged by 4D Electron Microscopy

TL;DR

This study uses 4D electron microscopy to directly image and analyze the complex, rapid dynamics of hot carriers in hydrogenated amorphous silicon, revealing unexpected diffusion and charge separation behaviors.

Contribution

It introduces the application of scanning ultrafast electron microscopy to directly visualize hot carrier dynamics in amorphous semiconductors, uncovering new insights into their behavior.

Findings

Fast diffusion immediately after photo-excitation

Spontaneous electron-hole separation observed

Charge trapping induced by atomic disorder

Abstract

The dynamics of charge carriers in amorphous semiconductors fundamentally differ from those in crystalline semiconductors due to the lack of long-range order and the high defect density. Despite intensive technology-driven research interests and the existence of well-established experimental techniques, such as photoconductivity time-of-flight and ultrafast optical measurements, many aspects of the dynamics of photo-excited charge carriers in amorphous semiconductors remain poorly understood. Here we demonstrate direct imaging of carrier dynamics in space and time after photo-excitation in hydrogenated amorphous silicon (a-Si:H) by scanning ultrafast electron microscopy (SUEM). We observe an unexpected regime of fast diffusion immediately after photoexcitation along with spontaneous electron-hole separation and charge trapping induced by the atomic disorder. Our findings demonstrate the rich dynamics of hot carrier transport in amorphous semiconductors that can be revealed by direct imaging based on SUEM.