Imaging hot photocarrier transfer across a semiconductor heterojunction with ultrafast electron microscopy

• 成果类型: Article
• 署名作者: Shaheen, Basamat S.; Huynh, Kenny; Quan, Yujie; Choudhry, Usama; Gnabasik, Ryan; Xiang, Zeyu; Goorsky, Mark; Liao, Bolin
• 署名单位: University of California System; University of California Santa Barbara; University of California System; University of California Los Angeles
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-8578
• DOI: 10.1073/pnas.2410428121
• 发表日期: 2024-10-01
• 关键词: carrier dynamics; precise determination; solar-cells; Visualization; SURFACES

摘要

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.