Kihyun Keem

Photocurrent in ZnO nanowires grown from Au electrodes

ZnO nanowires were grown between two Au electrodes on an Al2O3-deposited Si wafer. Photoresponse, photoresponse spectrum, and current–voltage (I–V) studies were performed for the investigation into photoconduction mechanism in these nanowires. The photoresponse of the nanowires under the continuous illumination of light with above- or below-gap energies was slow, which indicates that photocurrent in the nanowires is surface-related rather than bulk-related. The photoresponse spectrum represents the above- and below-gap absorption bands for the photocurrents. The I–V characteristics under the illumination of the above-gap light are ohmic, but the characteristics under the illumination of the below-gap light are Schottky. This observation indicates that the above-gap light lowers the potential barrier built in the contact between the ZnO nanowires and electrodes, but that the below-gap light does not lower the potential barrier.

Enhanced Performance of ZnO Nanowire Field Effect Transistors by H2 Annealing

The electrical properties of ZnO nanowires are significantly dependent on their surface states. The surface trap charges degrade the device performance of field effect transistors. These trap charges are reduced by H2 annealing. In this work, a back-gate ZnO nanowire field effect transistor (FET) was fabricated by a photolithographic process, and its electrical properties were characterized. This back-gate FET was subsequently annealed under a flow of H2/Ar gas for 20 min. The back-gate FET annealed for 20 min exhibited remarkably enhanced electrical characteristics, as compared with the as-fabricated back-gate FET; the peak transconductance was increased from 40 to 448 nS, the field effect mobility from 27 to 302 cm2 V-1 s-1, and the Imax/Imin ratio from 1.5 to 105.

Photocurrent of undoped, n- and p-type Si nanowires synthesized by thermal chemical vapor deposition

Photocurrent of undoped, n- and p-type Si nanowires synthesized by thermal chemical vapor deposition is investigated in this study. For an undoped Si nanowire biased at 3 V, photocurrent excited by the 633-nm wavelength light is stronger in intensity than that excited by the 325-nm wavelength light, and photoresponses are rapid when the light is switched on and off. In contrast, for the n- and p-type Si nanowires, photocurrent excited by the 633-nm wavelength light is not measurable, although one excited by 325-nm wavelength light is still detectable. And photoresponses obtained for the doped Si nanowires are slower, compared with the undoped Si nanowire. Photocurrent phenomena observed in the undoped, n- and p-type Si nanowires are discussed in this paper.

Electrical characteristics of ZnO nanowire-based field-effect transistors on flexible plastic substrates

ZnO nanowire field effect transistors were fabricated on flexible substrates of poly(ether sulfone) (PES) by bottom-up and photolithographic processes and their electrical characteristics were investigated. The fabrication of the flexible devices was achieved at a processing temperature of 150 °C. A representative top-gate ZnO nanowire field effect transistor (FET) on a flexible substrate exhibits a peak transconductance of 179 nS, a field effect mobility of 10.7 cm2 V-1 s-1, and an Ion/Ioff ratio of 106. When the PES substrate is bent under a strain of 0.77%, the decrement of the drain current for the FET at VGS=10 V is less than 3%.

Aging effect on the optoelectronic properties of a single ZnO nanowire

The effect of aging on the optoelectronic properties of a single ZnO nanowire is investigated in this study. The photoluminescence (PL), photocurrent spectrum, current–voltage characteristics, and photoresponse were measured for the as-grown ZnO nanowire and for the same nanowire exposed to air for three months. For the aged nanowire, the broad PL band is weaker, the intensity of the photocurrent is stronger, and the photoresponse is slower than those of the as-grown nanowire. One of the possible explanations is that the observed aging effect on the PL is due to the reduction in the number of oxygen vacancies within the nanowire and that the aging effect on the photocurrent and photoresponse originates from the formation of oxygen vacancies near the surface.

Electrical Characteristics of Hybrid Nanoparticle–Nanowire Devices

Gold nanoparticles synthesized by a colloidal method were deposited in an Al2O3 dielectric layer of an omega-gated single ZnO nanowire FET. These gold nanoparticles were utilized as localized trap sites. The adsorption of the gold nanoparticles on an Al2O3-coated ZnO nanowire was confirmed by high-resolution transmission electron microscopy. In this study, a hybrid nanoparticle-nanowire device was fabricated by conventional Si processing. Its electrical characteristics indicated that electrons in the conduction band of the ZnO nanowire can be transported to the localized trap sites by gold nanoparticles for gate voltages greater than 1 V, through the 10-nm-thick Al 2O3 tunneling oxide layer.

Comparison of electrical characteristics of back- and top-gate Si nanowire field-effect transistors

Top-gate(TG) field effect transistors (FETs) with channels composed of Si nanowires were successfully fabricated in this study using photolithographic processes. In the TG FETs fabricated on oxidized Si substrates, the channels composed of Si nanowires with diameters of about 100 nm with natural SiO 2 . The surfaces of the Si nanowires with natural SiO2 were covered with the gate metal to form TG FETs.

Synthesis of Single Crystalline In2O3 Nanowires and Their Photoluminescence Characteristics

Single crystalline In2O3 nanowires have been synthesized by thermal evaporation of ball-milled In2O3 powders without any catalysis. The diameter and length range of the synthesized In2O3 nanowires are about 25 nm and 20–30 µm, respectively. Their X-ray diffraction pattern is indexed to bcc structure with a lattice constant of a=1.0126 nm. High-resolution transmission electron microscopy image shows that the inner part of the In2O3 nanowires is free of dislocations, and that any amorphous layers are not formed on the surface of the nanowires. In their PL spectrum, two peaks are observed in the ultraviolet region centered at 380 nm and in the visible region centered at 550 nm.

Memory characteristics of top-gate ZnO nanowire field-effect transistors with floating gate nodes of Au nanoparticles

In this work, top-gate single ZnO nanowire-based FETs embedded with Au nanoparticles as the charge storage were fabricated and their memory effects were characterized.

Electrical characteristics of hybrid nanoparticlenanowire devices

Gold nanoparticles synthesized by a colloidal method are embedded in dielectric materials of the conventional top-gate ZnO nanowire FET. These gold nanoparticles are utilized as the localized trap sites. The adsorption of gold nanoparticles is confirmed by HRTEM study. In this paper, the hybrid nanoparticle-nanowire device is fabricated by the conventional Si processing, and its electrical characteristics are discussed.