Investigation of dynamics and controllability of optically injected valley carriers

2023 Fiscal Year Final Research Report

• Project/Area Number: 21K03420
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 13020:Semiconductors, optical properties of condensed matter and atomic physics-related
• Research Institution: Wakayama University
• Principal Investigator: Akimoto Ikuko 和歌山大学, システム工学部, 准教授 (00314055)
• Co-Investigator(Kenkyū-buntansha): 中 暢子 京都大学, 理学研究科, 教授 (10292830)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: バレーキャリア / バレーダイナミクス / IV族半導体 / サイクロトロン共鳴

Outline of Final Research Achievements

In this study, we conducted carrier dynamics research to elucidate inter-valley scattering to control the valley degree of freedom. We performed nanosecond time-resolved cyclotron resonance (CR) of optically injected carriers in a high-purity silicon crystal, and the change in the spectral shape due to an applied DC electric field was measured. We found that within 1 us after photoexcitation, the electric field promotes ionization of excitons and accelerates the electrons of lighter effective mass resulting in much scatter. The resulting hot electrons cannot be observed by the CR technique, but are likely inter-valley scattered by the f-process, inferred from the change in CR spectrum on subsequent delays of the cooled electrons. In contrast, we found that there are also electrons that are not accelerated much even when an electric field is applied, and remain in the band edge region, maintaining the valley polarization for up to several tens of us.

Free Research Field

光物性

Academic Significance and Societal Importance of the Research Achievements

本研究により、今後のバレートロニクスデバイス開発において、バレー分極保持の観点からは、必要最小限の電場印加になるように設計すること、電場によるキャリア加熱を押さえることが必要であること、光キャリアを用いる場合は波長選択が重要であることが分かった。また、今回は励起子の束縛エネルギーが14.7 meVのシリコンでの研究であったが、同じく注目されているダイヤモンドでは励起子の束縛エネルギーが96 meVと大きく、室温でも励起子とキャリアが共存することから、励起子のインパクトイオン化にも注意する必要があること示唆された。