Optical bleaching phenomenon in indirect semiconductors

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K05368
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 30020:Optical engineering and photon science-related
• Research Institution: Waseda University
• Principal Investigator: JIA Junjun 早稲田大学, 理工学術院, 准教授 (80646737)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: 光ブリーチング / 間接遷移 / 直接遷移 / フェルミーディラック分布関数 / ホットキャリア / 時間分解測定 / 過渡透過率 / 過渡反射率

Outline of Final Research Achievements

The optical bleaching due to the intensive laser irradiation was investigated in the direct and indirect bandgap semiconductors in this study. After massive excitation, the photoexcited electrons are firstly thermalized in the conduction band. Our experimental results show that the occupation probability of thermalized electrons in the conduction band can be explained by a hot Fermi-Dirac distribution. Such electron occupation also causes the increase of transient transmission, namely optical bleaching. The epitaxial Ge film with indirect band gap has a longer optical bleaching time than the epitaxial InN film with direct band gap. Likewise, the Drude-like response due to the collective motion of thermalized carriers causes the increase in transient reflectivity. Out results open a new way for designing ultrafast optical switching devices in communication applications.

Free Research Field

光工学、応用物理

Academic Significance and Societal Importance of the Research Achievements

半導体材料における光ブリーチング現象を利用して、光通信分野における超高速光スイッチング制御への研究例はない。この研究の学術的意義として、直接遷移型や間接遷移型半導体における光誘起ブリーチング現象を実験的に調べたうえで、光誘起ブリーチングの物性モデルを提案した。本研究によって、光誘起ブリーチング材料の創出に関する基礎的な知見が得られたものと思われる。有望な半導体材料を見出せれば、光通信波長帯に超高速光制御ができ、ひいては光ダイオードなど新規光デバイスの発展が期待できる。