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Department of Electrical and Computer Engineering Ph.D. Public Defense


Mid-infrared InAs-based Photodetectors: Effects of Processing and Structures on Dark Currents

Xiaoyu Du

Supervised by Professor Gary Wicks

Wednesday, August 15, 2018
3:00 p.m.
Computer Studies Building, Room 426

Mid-Wave Infrared (MWIR) photodetectors based on III-V semiconductors have drawn special attention during the past decade, attributed to their lower cost and easier manufacturability. Many challenges still remain for accomplishing their full capacity, including the optimization of material quality, detector structure, and processing technology. MWIR detectors are subject to high dark currents at room temperature due to the nature of these small bandgap materials, thus they are generally operated with a cooling system. Demands for a less bulky and less power hungry cooling system are a driving force for exploring detectors with lower dark currents. Dark current can be separated into two components: bulk and surface. It is important to understand these dark current generation mechanisms in order to be able to suppress them. Advanced detector structures, processing schemes, and processing techniques can be used to suppress these dark currents. Studying all these dark current mechanisms will contribute to the further optimization of MWIR photodetectors.

InAs has a cutoff wavelength around 3.5 µm in the MWIR range and is an important absorber material for MWIR photodetectors. Conventional pn junction based InAs photodiodes are subject to many diff t dark current mechanisms, including bulk and surface mechanisms, which often limit the detector performance. In contrast, InAs-based nBn photodetectors have improved dark current performance over the pn junction photodiodes due to the ability to suppress various dark current mechanisms. However, structures and processing schemes still have to be further optimized for nBn photodetectors in order to obtain peak performance.

In this thesis work, dark current mechanisms associated with the InAs-based pn junction photodiodes have been studied.  InAs-based nBn photodetectors have been shown to have improved dark current performance over  the  pn  junction photodiodes. Structural effects on the characteristics of InAs-based nBn photodetectors have been studied for  further  optimization  of  the  nBn  structure. The processing scheme associated lateral diff has been studied. Additional structures and processing schemes have been proposed to address this problem. Advantages and shortcomings are discussed. Dark current mechanisms and device physics associated with these structures and processing schemes are further studied.