GaN-based Chemical Sensors and Their On-chip Integration Using Nanowire Networks

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This project investigates key technologies for realization of GaN-based high-sensitivity chemical sensors and their on-chip integration using nanowires. The main conclusions are as follows: (1) Interface models on Schottky barrier formation are surveyed, and key issues related to AlGaN/GaN Schottky barriers including Fermi level pinning, Schottky barrier height (SBH) and reverse leakage currents are discussed. The current transport is explained by the thin surface barrier (TSB) model. Leakage currents can be reduced by the oxygen gettering process. (2) Pd Schottky barrier hydrogen sensors fabricated on AlGaN/GaN HEMT wafers exhibit unprecedented high sensitivities by applying the oxygen gettering process. (3) Its sensing mechanism is SBH reduction by interface dipole formed by atomic hydrogen which is produced at the Pd surface and diffuses to the Schottky interface. The rate limiting process for transient responses is surface reaction. Mathematical formulas for description of steady-s … More tate and transient response are given. (4) Sensitivity of AlGaN/GaN hydrogen sensors increases at higher temperatures, and they perform better than those by other major III-V semiconductors. (5) Slow transients are observed in hydrogen sensor diodes, and they can be explained by the dispersive transport due to time-continual hopping of electrons through surface states. This has led to a new model of current collapse in AlGaN/GaN HEMTs. (6)pH sensing HEMTs fabricated using an electrolyte/AlGaN gate structure, show nearly ideal Nernstian responses. Issues related to realization of bio-sensors using this structure are discussed. (7) For on-chip integration of sensors, implementation of a BDD (binary decision diagram) information processing architecture on hexagonal nanowire networks has been proposed. The proposal includes key elements such as basic integration unit, a sensor bridge, a sensor array structure, a selective MBE method for nanowire network formation and a wireless communication circuit integrated with an on-chip antenna. Their feasibilities have been proved. Less