Jeongmin Kang

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.

Si-based flexible memristive systems constructed using top-down methods.

Si-based memristive systems consisting of Ag, amorphous Si, and heavily doped p-type Si nanowires were successfully constructed on plastic substrates through top-down methods, including the crystallographic wet etching of Si wafers, transfer onto plastic substrates, and thin film patterning. The memristive systems showed excellent memory characteristics and flexibility, such as intrinsic hysteric and rectifying behaviors, on/off resistance ratios of >1 × 10(5), and durability for up to 1000 bending cycles. The correlations between the Ag-filament-related nanostructures formed in amorphous Si and the resistance-switching behaviors were carefully examined with the tunneling current model, transmission electron microscopy, and secondary ion mass spectroscopy to explore the switching mechanism. Our study suggests the promising potential of the Si-based memristive systems for the development of next-generation flexible nonvolatile memory.

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.

Type conversion of n-type silicon nanowires to p-type by diffusion of gold ions

The simple type conversion of n-type silicon nanowires (SiNWs) to p-type by the diffusion of Au ions is demonstrated in this study. An Au thin film with a thickness of 10 nm was thermally deposited on an n-type SiNW and a rapid thermal annealing process was performed subsequently to diffuse the Au ions into the SiNW. The electrical characteristics of a back-gate field-effect transistor with a channel composed of the Au-diffused SiNW show that the Au-diffused SiNW acts as a p-type one. The type conversion phenomenon of the SiNW caused by the diffusion of Au ions is discussed in detail in this paper.

Ultraviolet Electroluminescence Emission from n-Type ZnO/p-Type Si Crossed Nanowire Light-Emitting Diodes

The optical characteristics of an n-type ZnO/p-type Si crossed nanowire (NW) light-emitting diode (LED) were investigated in this study. N-ZnO nanowires (NWs) were synthesized by thermal chemical vapor deposition, and p-Si NWs were fabricated by etching a single crystalline Si wafer. The p–n heterojunction LED formed by the cross of the n-ZnO and p-Si NWs selected from the NWs prepared in this work exhibited the current rectifying behavior with the turn-on voltage of 1.3 V. Our investigation of the photoluminescence spectrum of the as-grown n-ZnO NWs and electroluminescence spectrum of the n-ZnO/p-Si crossed NW LED reveals that both spectra have the same position of peaks at 390 nm. This result indicates that the UV emission from the crossed NW LED is mostly attributed to the band-to-band transition of electrons in the ZnO NW.

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.

Dielectrophoretically Formed Single Wall Carbon Nanotube Network on Polyether Sulfone

AC dielectrophoresis (DEP) is a useful method to fabricate single wall carbon nanotube (SWCNT) network structures on various kinds of substrates. We report on the fabrication of SWCNT networks with varying densities, on transparent and flexible polyether sulfone (PES) substrates by using DEP. From the scanning electron microscope observations and current‐voltage measurements of the fabricated SWCNT network, we obtain the contour map of the density and conductance as functions of Vp‐p and f. Our results show that the maximum density does not necessarily imply the maximum conductance. We find that there exists an optimum density for the maximum conductance.

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.

Synthesis and Optoelectronic Characteristics of Single-crystalline Si Nanowires

Photocurrent of a single-crystalline Si nanowire is investigated in this paper. Single-crystalline Si nanowires with amorphous shells were first synthesized from ball-milled SiO powders by thermal chemical vapor deposition, and then the amorphous shells were etched out from the as-synthesized Si nanowires. For a single-crystalline Si nanowire, photocurrent-voltage curves taken in air at room temperature were non-linear, and rapid photoresponses were observed when the light was switched on and off. The photocurrent was not changed in intensity under the illumination. Photocurrent mechanism in the single-crystalline Si nanowire is discussed in this paper.