  The physicochemical processes at the surfaces of semiconductor nanostructures
involved in electrochemical and sensing devices are strongly influenced by the
presence of intrinsic or extrinsic defects. To reveal the surface controlled
sensing mechanism, intentional lattice oxygen defects are created on the
surfaces of GaN nanowires for the elucidation of charge transfer process in
methane (CH4) sensing. Experimental and simulation results of electron energy
loss spectroscopy (EELS) studies on oxygen rich GaN nanowires confirmed the
possible presence of 2(ON) and VGa-3ON defect complexes. A global resistive
response for sensor devices of ensemble nanowires and a localized charge
transfer process in single GaN nanowires are studied in situ scanning by Kelvin
probe microscopy (SKPM). A localized charge transfer process, involving the
VGa-3ON defect complex on nanowire surface is attributed in controlling the
global gas sensing behavior of the oxygen rich ensemble GaN nanowires.
