Dresden 2003 – scientific programme
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HL: Halbleiterphysik
HL 4: GaN: Bauelemente
HL 4.1: Talk
Monday, March 24, 2003, 10:30–10:45, BEY/154
pH response of GaN and AlGaN/GaN field effect transistors — •Georg Steinhoff, Martin Hermann, Stefan Geprägs, Martin Stutzmann, and Martin Eickhoff — Walter Schottky Institut, Technische Universität München, Am Coulombwall 3, 85748 Garching, Germany
Group III-nitrides have a great potential for the realisation of different kinds of chemical sensors. Thus, the performance of Pt:GaN Schottky diodes for detection of hydrogen or hydrocarbons in gases up to 600∘C has been demonstrated. The electronic properties of AlGaN/GaN heterostructures, which form a polarisation induced 2DEG at the heterointerface, are highly sensitive towards changes in surface charge or surface potential and have enabled the realisation of ion detectors and sensors for polar fluid monitoring. Along with their chemical inertness in aqueous solutions, group III-nitrides are a promising material system for biological or chemical sensor applications. In this contribution we present the pH response of GaN and AlGaN/GaN field effect transistors in aqueous solutions with H+ concentrations ranging form 10−1 to 10−13 mol/l. The pH dependence of the surface potential of our devices was approximately 55mV/pH (SiO2: 32mV/pH, Al2O3: 57mV/pH) and did show nearly Nernstian behaviour. Surface analysis of GaN by XPS directly after growth and following exposure to atmosphere showed the formation of a native oxide on the surface. Consequently, the Site-binding Model for oxide/water interfaces is proposed to explain the observed variation of the surface potential with H+ concentration.