2024-10-10 カリフォルニア大学サンタバーバラ校(UCSB)
＜関連情報＞
- https://news.ucsb.edu/2024/021634/researchers-create-first-ever-visualization-photoexcited-charges-traveling-across
- https://www.pnas.org/doi/10.1073/pnas.2410428121
超高速電子顕微鏡による半導体ヘテロ接合を横切るホットフォトキャリア移動のイメージング Imaging hot photocarrier transfer across a semiconductor heterojunction with ultrafast electron microscopy
Basamat S. Shaheen, Kenny Huynh, Yujie Quan, +4, and Bolin Liao
Proceedings of the National Academy of Sciences Published:September 26, 2024
DOI:https://doi.org/10.1073/pnas.2410428121
Significance
Semiconductor heterojunctions are crucial for optoelectronic devices. Despite the remarkable performance achieved, a complete understanding of the intricate interplay of the junction electrical potentials and charge transport phenomena across the heterojunction interface is missing. In particular, the “hot” photocarriers immediately after optical excitation play a crucial role in photovoltaic, photocatalytic, and photosensing devices, but their interaction with the heterojunction remains not understood. In this work, we apply scanning ultrafast electron microscopy to provide a holistic view of photoexcited charge dynamics in a Si/Ge heterojunction. We find that the built-in potential and the band offsets drastically modify the diffusion process of hot photocarriers across the heterojunction due to charge trapping, with significant implications for hot-carrier-based applications.
Abstract
Semiconductor heterojunctions have gained significant attention for efficient optoelectronic devices owing to their unique interfaces and synergistic effects. Interaction between charge carriers with the heterojunction plays a crucial role in determining device performance, while its spatial-temporal mapping remains lacking. In this study, we employ scanning ultrafast electron microscopy (SUEM), an emerging technique that combines high spatial-temporal resolution and surface sensitivity, to investigate photocarrier dynamics across a Si/Ge heterojunction. Charge dynamics are selectively examined across the junction and compared to far bulk areas, through which the impact of the built-in potential, band offsets, and surface effects is directly visualized. In particular, we find that the heterojunction drastically modifies the hot photocarrier diffusivities in both Si and Ge regions due to charge trapping. These findings are further elucidated with insights from the band structure and surface potential measured by complementary techniques. This work demonstrates the tremendous effect of heterointerfaces on hot photocarrier dynamics and showcases the potential of SUEM in characterizing realistic optoelectronic devices.
