Achieving Ultra‐High Background‐Limited Detectivity by a Brillouin Zone Folding Induced Quasi‐Bound State in the Continuum

• Published in: Advanced optical materials 2024-12, Vol.12 (35), p.n/a
• Main Authors: Zhu, Tianyun, Jing, Wenji, Deng, Jie, Wang, Bo, Wang, Ruowen, Ye, Tao, Shi, Mengdie, Ye, Jiexian, Cui, Tianyuan, Shen, Jinyong, Li, Fangzhe, Ning, Jun, Zhou, Jing, Chen, Xiaoshuang
• Format: Article
• Language: English
• Subjects: Background noise; Background radiation; breaking the background noise limitation; Brillouin zone folding induced quasi‐bound state in the continuum; Brillouin zones; Coupling; dimerized grating; Folding; Infrared detectors; long‐wavelength infrared; Narrowband; Noise generation; Q factors; Quantum well infrared photodetectors; Radiation; Target detection; Thermal radiation
• ISSN: 2195-1071; 2195-1071
• DOI: 10.1002/adom.202401857

During infrared detection, the thermal radiation from the background generates substantial photon noise and thus severely limit the capability of an infrared detector to identify a target. Going beyond this limitation has been a long‐standing challenge in the development of infrared detectors. This paper proposes to break this limitation by creating a narrow photoresponse band with a high peak responsivity to reject the background radiation and enhance the responsivity to the target with characteristic emission lines. This scheme is numerically demonstrated in a dimerized grating integrated quantum well infrared photodetector, based on critical coupling with a Brillouin zone folding induced quasi‐bound state in the continuum (BIC). The asymmetric deformation of the grating structure folds the photonic band and generates a quasi‐BIC with a tunable high radiation Q factor (QR) at the Γ point. By reducing the doping concentration of the quantum wells for a high absorption Q factor (QA) and tuning the QR to make QR = QA for critical coupling, a narrowband photoresponse with a high peak responsivity is achieved and the background‐limited specific detectivity of 4.55 × 1012 cm Hz1/2 W−1 is obtained for a 2π field of view, surpassing the ideal‐photoconductor limit by 92 times. The table of contents graphic illustrates the structure of a QWIP integrated with a dimerized grating. Based on this design, by exciting the quasi‐BIC mode and controlling the critical coupling, the QWIP achieves a narrowband absorption, high peak absorptance, and suppresses dark current. Consequently, the background‐limited detectivity of this device reaches 92 times that of an ideal photoconductive detector.