Burhan Bayraktaroglu

Mobility Analysis of Highly Conducting Thin Films: Application to ZnO

Hall-effect measurements have been performed on a series of highly conductive thin films of Ga-doped ZnO grown by pulsed laser deposition and annealed in a forming-gas atmosphere (5% H2 in Ar). The mobility as a function of thickness d is analyzed by a simple formula involving only ionized-impurity and boundary scattering and having a single fitting parameter, the acceptor/donor concentration ratio K=NA/ND. For samples with d=3–100u2002nm, Kavg=0.41, giving ND=4.7×1020 and NA=1.9×1020u2002cm−3. Thicker samples require a two-layer formulation due to inhomogeneous annealing.

Highly conductive ZnO grown by pulsed laser deposition in pure Ar

Ga-doped ZnO was deposited by pulsed laser deposition at 200u2009°C on SiO2/Si, Al2O3, or quartz in 10 mTorr of pure Ar. The as-grown, bulk resistivity at 300 K is 1.8×10−4u2002Ωu2009cm, three-times lower than that of films deposited at 200u2009°C in 10 mTorr of O2 followed by an anneal at 400u2009°C in forming gas. Furthermore, depth uniformity of the electrical properties is much improved. Mobility analysis shows that this excellent resistivity is mostly due to an increase in donor concentration, rather than a decrease in acceptor concentration. Optical transmittance is approximately 90% in the visible and near-IR spectral regions.

Biofunctionalized Zinc Oxide Field Effect Transistors for Selective Sensing of Riboflavin with Current Modulation

Zinc oxide field effect transistors (ZnO-FET), covalently functionalized with single stranded DNA aptamers, provide a highly selective platform for label-free small molecule sensing. The nanostructured surface morphology of ZnO provides high sensitivity and room temperature deposition allows for a wide array of substrate types. Herein we demonstrate the selective detection of riboflavin down to the pM level in aqueous solution using the negative electrical current response of the ZnO-FET by covalently attaching a riboflavin binding aptamer to the surface. The response of the biofunctionalized ZnO-FET was tuned by attaching a redox tag (ferrocene) to the 3′ terminus of the aptamer, resulting in positive current modulation upon exposure to riboflavin down to pM levels.