A study on preparation method of room-temperature pure-circular polarization spin LED and its physical mechanims

2020 Fiscal Year Final Research Report

• Project/Area Number: 18H03878
• Research Category: Grant-in-Aid for Scientific Research (A)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Medium-sized Section 29:Applied condensed matter physics and related fields
• Research Institution: Tokyo Institute of Technology
• Principal Investigator: Munekata Hiro 東京工業大学, 科学技術創成研究院, 教授 (60270922)
• Co-Investigator(Kenkyū-buntansha): 西沢 望 東京工業大学, 科学技術創成研究院, 助教 (80511261)
• Project Period (FY): 2018-04-01 – 2021-03-31
• Keywords: スピンフォトニクス / スピントロニクス / 円偏光発光ダイオード / 偏光 / 医療光学 / がん検診

Outline of Final Research Achievements

We have challenged reproduction and physical elucidation of pure circular polarization (CP) electroluminescence (EL) from spin LED reported on 2017. Lithography-free new device process and pulsed current/spin injection approach have made it possible to observe the CP enhancement occurring at 30 to 100 A per square cm or higher region, beyond which dynamic reductions in both EL intensity and junction resistance take place simultaneously. These facts suggest that local heating, presumably around oxide barriers in between metal spin injectors and semiconductor layers, enhances CP values as well as alters electronic/optical characteristics of diodes through abrupt generation of phonons. Namely, pulse-injected hot spins whose spin population are initially weakly polarized are strongly CP polarized via non-elastic scattering with phonons. Re-absorption and -emission also assist this scattering process. Optical spin injection experiments have failed because of the lack of excitation power.

Free Research Field

応用物理学、物性物理学

Academic Significance and Societal Importance of the Research Achievements

新しい素子化工程とは ① 極薄AlAs結晶層の積極的酸化によるスピン注入バリアの形成、ならびに、② メカニカルマスクによる微小スピン注入電極の直接形成を指すが、基礎研究を小回り良く（少量・多種類）進めることに向いた手法である。電流パルスによるスピン注入実験、こちらは半導体レーザ研究開発において局所加熱を回避する手法であるが、円偏光増大に際してフォノンが寄与する可能性が高いことをえぐり取ったという点で、理論提唱された円偏極フォノン [J. Kishineら, PRL 125, 245302 (2020)] とキャリアスピンとの間の散乱の重要性を示唆する結果であり、今後の波及効果が期待される。