Article pubs.acs.org/Langmuir
Thermal Functionalization of GaN Surfaces with 1‑Alkenes Stefan U. Schwarz,†,‡ Volker Cimalla,‡ Georg Eichapfel,§ Marcel Himmerlich,§ Stefan Krischok,§ and Oliver Ambacher*,†,‡ †
Institute for Microsystems Engineering − IMTEK, University of Freiburg, Georges-Köhler-Allee 106, 79110 Freiburg, Germany Fraunhofer Institute for Applied Solid State Physics IAF, Tullastrasse 72, 79108 Freiburg, Germany § Institute of Physics and Institute of Micro- and Nanotechnologies, Ilmenau University of Technology, Gustav-Kirchhoff-Strasse 7, 98693 Ilmenau, Germany ‡
ABSTRACT: A thermally induced functionalization process for gallium nitride surfaces with 1-alkenes is introduced. The resulting functionalization layers are characterized with atomic force microscopy and X-ray photoelectron spectroscopy and compared to reference samples without and with a photochemically generated functionalization layer. The resulting layers show very promising characteristics as functionalization for GaN based biosensors. On the basis of the experimental results, important characteristics of the functionalization layers are estimated and a possible chemical reaction scheme is proposed.
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were also purchased from Th. Geyer. The 1-alkene TFAAD was provided by the National Institute of Advanced Industrial Science and Technology (AIST, Tsukuba, Japan). The GaN samples were grown by metal−organic chemical vapor deposition (MOCVD) on a Cree 3 in. SiC substrate. To mimic the surface properties of a GaN biosensor,11 comparable high-electron-mobility transistor (HEMT) heterostructures were grown on the substrate (1.8− 1.9 μm GaN bulk layer, 17−22 nm Al0.20−0.29Ga0.71−0.80N barrier, 3.0 nm GaN cap layer). The sample sizes vary from 0.5 × 0.5 cm2 to 1.0 × 1.0 cm2. Methods. Two different cleaning processes were used prior to functionalization. One part of the samples was just rinsed in methanol and DI water with an ultrasonic cleaning system. The other samples were, after the identical rinsing procedure, partially reduced on the surface by a 2 min dip in 2% hydrofluoric acid immediately before the functionalization process (Table 1, line “HF dip”). For the photochemical functionalization process (samples P1−3), 2 μL of the liquid 1-alkene is disposed on the sample surface. The sample is then covered by a polished sapphire slice to obtain a homogeneous film on the sample and stored in the reaction chamber. Besides the sample in its holder, the reaction chamber contains a short-arc mercury/xenon lamp and a Schott UG11 filter to block high energetic UV radiation with wavelengths
