Design, fabrication and characterization of aluminum gallium nitride (AlGaN) based solar-blind UV photodetectors.

摘要

The unique properties of direct band-gap semiconductors such as GaN and its alloys for example AlGaN, AlInGaN and AlInN are of utmost interest in the field of opto-electronic devices, particularly blue light emitting diodes (LED) and ultra-violet (UV) sensors.; This PhD dissertation topic focuses on the design, fabrication, and characterization of a novel solar-blind Schottky barrier photo detector using AlGaN compound semiconductors with high Al content (≥40%) as the device active epilayer. These photodetectors have the unique ability to be sensitive to UV (ultra-violet) adiation with wavelengths shorter than 280 nm. These solar-blind photodetectors find important applications in the field of missile detection, heat and flame sensing etc. The major achievement of this dissertation research is the design, fabrication and characterization of ultra-violet (UV) solar-blind Schottky barrier AlGaN photodetectors with record high parameters of 0.07 A/W responsivity, 3 orders of magnitude UV-visible rejection ratio, and 6 nA dark current.; In the course of this work, the research also investigated and developed solutions to the problems related to the fabrication of a Schottky barrier photo detector using Al_xGa_1−xN with aluminum mole fraction x% in excess of 40%.; A novel co-doping approach using silicon and indium is investigated and applied to achieve the requisite doping levels for Schottky barrier photodetectors.; New metallization schemes for ohmic and Schottky contacts to very high aluminum content epilayers are developed and optimized. A new low ohmic contact resistivity value of 3 × 10−4 Ω-cm 2 to 40% AlGaN epilayer is achieved using a new Ti/Al ratio. Ohmic contacts to n-SiC and p-GaN are also investigated, in order to provide different device modifications and future development.; Epitaxial materials for UV blind photodetectors were characterized using X-ray diffraction, photoluminescence, atomic force microscope and scanning electron microscope analysis.; Electrical and optical parameters of photodetectors were tested using Current-Voltage, Capacitance-Voltage, CW and pulse optical measurement of responsivity and speed of response.