Molecule-modulated photoconductivity and gain-amplified selective gas sensing in polar GaN nanowires
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(a) The different photocurrent responses of GaN NWs to the 325 nm UV excitation measured in vacuum, air, and pure oxygen. The shadow shows the duration with photoexcitation. (b) The normalized photocurrent rise curves in the vacuum, air, and pure oxygen. Inset: A schematic of the electron-hole spatial separation mechanism induced by SBB in a GaN NW. SDR denotes surface depletion region and NR denotes neutral region. (c) The normalized photocurrent decay curves in the vacuum, air, and pure oxygen.
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(a) The schematics of oxygen and hydrogen molecular effects on the surface of GaN NW. A pristine surface in vacuum with intrinsic SBB induced by the space charges, including trapped surface electrons, and uncompensated donor ions, is also drawn for comparison. The drawing illustrates the oxygen and hydrogen molecules play respectively the donorlike and acceptorlike surface states on the GaN NWs. (b) The in situ measurements of photocurrent and dark current during the repeated alternating exposure in vacuum and air. The and values of air have been subtracted to present the current change of and . The shadow region shows the duration of air exposure. (c) The in situ measurements of during the repeated alternating exposure in the respective oxygen , nitrogen , and hydrogen from the vacuum. The value of vacuum is subtracted to be the zero baseline (the dash line at ).
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