pH response of GaN surfaces and its application for pH-sensitive field-effect transistors

Steinhoff, G.; Hermann, M.; Schaff, W. J.; Eastman, L. F.; Stutzmann, M.; Eickhoff, M.
July 2003
Applied Physics Letters;7/7/2003, Vol. 83 Issue 1, p177
Academic Journal
The pH-sensitivity of GaN surfaces in electrolyte solutions has been determined. For this purpose, GaN field-effect transistors and AlGaN/GaN high-electron-mobility transistor (HEMT) structures were used to measure the response of nonmetallized GaN gate regions to changes of the H[SUP+]-concentration in an ambient electrolyte. We found a linear response to changes in the pH between Ph=2 and pH=12 for both as-deposited and thermally oxidized GaN surfaces. Both surfaces showed an almost Nernstian behavior with sensitivities of 57.3 mV/pH for GaN:Si/ GaN:Mg and 56.0 mV/pH for GaN/AlGaN/GaN HEMT structures. This suggests that the native metal oxide on the III-nitride surface is responsible for pH-sensitivity. The investigated devices showed stable operation with a resolution better than 0.05 pH over the entire pH range.


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