K. Teker, O. Moussa, Y.A. Ali, J. Otto
Istanbul Sehir University,
Keywords: InN nanowires, nanowire FETs, electrical characterization, nanophotonics
Summary:The III-nitrides have been intensely studied due to their wide range of applications from high efficiency solid-state lighting and photovoltaics to high-power and high temperature electronics. InN has received great attention due to its unique properties such as large drift velocity at room temperature, small effective electron mass, high mobility at room temperature, and narrow band gap of 0.7–0.9 eV. One dimensional (1D) InN nanowires have attracted interest in growth and potential applications owing to their band gap and electrical charge transport tunability. Various synthesis methods including chemical vapor deposition, molecular beam epitaxy, solvothermal method, and carbon-nitridation reaction have been used for InN nanowires. This paper presents a detailed study of InN nanowire morphology changes originating from the process parameters by chemical vapor deposition using In and NH3 as source materials on SiO2/Si substrates. Various types of catalyst materials, including gold, nickel, silver, cobalt, and iron have been used. The growth experiments have been carried out at temperatures between 800 and 1100oC under H2 as carrier gas. Dramatic shifts in nanowire size and morphology have been observed in accordance with the variations in process parameters. The sources of these variations and the growth mechanisms are discussed in detail. In fact, the InN nanowire diameters range from 10 nm to 250 nm; and lengths up to 50 µm depending on the catalyst type. Figure 1a shows an SEM image of the InN nanowires grown at 1100oC with Ni-film catalyst. Next, InN nanowire field effect transistor (FET) devices have been fabricated to study the electrical and optical properties of them. Figure 1b shows an SEM image of the aligned InN nanowire between electrodes (grown with Ni nanoparticles). Electrodes (10nm Ti/ 90nm Au) were fabricated using standard microfabrication techniques onto SiO2/Si substrate. The average spacing between electrodes is about 3.0 µm. First, nanowires were suspended in isopropyl alcohol. A micropipette was used to apply 2 µL of nanowire solution to the surface of the patterned substrate. Then, AC voltage (Vpp= 5V, f = 10 Hz-100 kHz) was applied via a function generator (HP33120A). In fact, the InN FETs show very high current levels (see Fig. 2 IV curve). Additionally, the InN nanowires have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray diffraction (XRD), and semiconductor parameter analyzer.