Gallium Nitride-Based Liquid Sensor Using FIB Milling Technique

Student thesis: Doctoral Thesis


Gallium Nitride (GaN) is exceedingly apposite for liquid-based sensor applications because of their high internal piezoelectric polarization, chemical and high temperature stability. In this work, the interaction between GaN and H2O has been investigated using a novel methodology. We report the fabrication of single crystal GaN lamella with thickness of few hundreds of nanometer using focused ion-beam (FIB) milling technique, for sensing applications. Results signify that the device resistivity increases with time at room temperature during the GaN-H2O interaction. Such a change in electrical resistivity is explicated via the electron transfer and electrochemical reactions at the GaN surface. Study of the surface chemistry transformation of the tested GaN lamella is conducted using high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM) coupled with electron energy loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDS) techniques. EDS and EELS results signify the presence of a region containing Ga and O at the interface of the H2O/GaN which is a result due to the adsorption of molecular water and its dissociation products implying the occurrence of GaN-water reaction. Furthermore, X-ray photoelectron spectroscopy (XPS) and density-functional theory (DFT) calculations were used to investigate surface oxidation of the dry and wet GaN surface. The results indicate that the water molecules are stably adsorbed on the GaN surface and are favorable to be dissociated into hydrogen atoms and hydroxyl groups on the GaN surface even if the surface is oxidized.
Date of AwardDec 2020
Original languageAmerican English
SupervisorDaniel Choi (Supervisor)


  • Electron energy loss spectroscopy (EELS); Energy dispersive X-ray spectroscopy (EDS); X-ray photoelectron spectroscopy (XPS); Density-functional theory (DFT)
  • GaN-water reaction.

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