Photonic structure enhancement on photodetection

• Main Author: Suo, Fei
• Other Authors: Zhang Dao Hua
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Engineering::Electrical and electronic engineering::Optics, optoelectronics, photonics; Engineering::Electrical and electronic engineering::Semiconductors
• Online Access: https://hdl.handle.net/10356/153305
• Institution: Nanyang Technological University

Infrared photodetectors have been extensively used in military and civilian applications. Currently, antimony (Sb) based III–V semiconductors are considered as viable alternatives to Mercury-Cadmium Telluride material which takes the dominant position in middle infrared range. Among them, InAs1-xSbx has gained much interest owing to their various benefits for realizing high-performance middle infrared photodetectors. However, it still faces the challenge in realizing high-temperature operational photodetection. This PhD program will primarily deal with the optimization of InAsSb-based heterojunction photodiode and enhancement of photodetection performance by integrating with different two-dimensional photonic structures. In this thesis, InAsSb-based photodiodes with heterojunction architectures are proposed to achieve middle infrared photodetection with low dark current. The photodiode includes wide bandgap and thin quaternary layers to reduce the bulk dark current. Photodiodes with square mesas from 500 μm to 20 μm were fabricated and their dark currents are characterized at temperatures from 77 K to room temperature (293 K). The results indicate that the methods we adopted for reducing dark current are effective. The dark current densities achieved are lower than or comparable with that of the state-of-the-art middle infrared photodetectors. To further improve the detection performance, various photonic structures are investigated for manipulating photoresponse capability. As the raised light-matter interaction in active region can facilitate light absorption without sacrificing the response speed, the quantum efficiency of the device can be significantly improved without involving a very thick absorption layer. Detailed simulations have been done to demonstrate the broadband absorption enhancement. The internal resonance phenomenon is also studied to figure out the physical mechanisms. Different plasmonic structures were selected for integration with the heterojunction photodiode to enhance quantum efficiency. It is because the metallic nanostructures at sub-wavelength scale own the capability to concentrate light and produce strong electric field in the extremely small volume, thus facilitating the significant absorption of electromagnetic waves. Using this strategy, a maximum one order of magnitude of enhancement in middle infrared room-temperature detectivity (to about 2.0×1010 Jones) is achieved under zero bias without sacrificing the response speed. Another enhancement technique we applied is to fabricate a photon-trapping hole-array structure in the heterojunction photodiode. With the help of the photon-trapping structure, the combined effects of the formed lateral propagating modes and reduced effective refractive index can lead to polarization-independently enhanced absorption. Broadband photoresponse improvements of 26% to 170% are demonstrated in 2-5 µm range under zero bias at temperatures from 293 K to 78 K. Furthermore, the photon-trapping hole-array structure is also fabricated in the InAsSb-GaSb heterostructure for the dual-band photoresponse enhancement in near- and mid-infrared regions. The responsivity enhancement factors under zero bias are 12% and 33% for the near- and mid-infrared, respectively, at room temperature, and they are increased to 71% and 79% at 220 K.