Dong Young Jeong

Enhancement-mode silicon nanowire field-effect transistors on plastic substrates.

Semiconductor nanowires (NWs) have unique physical properties due to their 1D structure, which enables the more efficient transport of electrical carriers. Si NW transistors especially have attracted tremendous attention, since their interesting device performance can be utilized for integrated nanoscale electronics. These characteristics are also believed to make them useful nanoscale building blocks for electronic devices on plastic substrates that can be fabricated on a relatively large scale. To realize reliable devices with nanoscale dimensions, an assembly process with controlled orientation and density, control of the doping, and suitable contact properties of the Si NWs is required. Recent studies indicate that conventional approaches to the bottom-up fabrication of Si NWs in nanoelectronics inevitably require complicated assembly procedures including the establishment of the accurate control of the doping level and the formation of reliable metal contacts. For these reasons, most of the previous studies dealing with the bottom-up fabrication of field-effect transistors (FETs) based on Si NWs, which were grown by a deposition technique based on the vapor–liquid–solid (VLS) growth mechanism, mainly focused on homogenously doped NW devices operating mostly in accumulation or depletion mode. In the case of normally on NW FETs, the power consumption of the devices is relatively large and the flow of electric charge does not seem to be accurately modulated by the gate structure. Most recently, an n-type/intrinsic/n-type metal oxide semiconductor

Silicon nanowire-based tunneling field-effect transistors on flexible plastic substrates

A technique to implement silicon nanowire (SiNW)-based tunneling field-effect transistors (TFETs) on flexible plastic substrates is developed for the first time. The p-i-n configured Si NWs are obtained from an Si wafer using a conventional top-down CMOS-compatible technology, and they are then transferred onto the plastic substrate. Based on gate-controlled band-to-band tunneling (BTBT) as their working principle, the SiNW-based TFETs show normal p-channel switching behavior with a threshold voltage of -1.86 V and a subthreshold swing of 827 mV/dec. In addition, ambipolar conduction is observed due to the presence of the BTBT between the heavily doped p+ drain and n+ channel regions, indicating that our TFETs can operate in the n-channel mode as well. Furthermore, the BTBT generation rates for both the p-channel and n-channel operating modes are nearly independent of the bending state (strain = 0.8%) of the plastic substrate.

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.

Nanocrystal-mediated charge screening effects in nanowire field-effect transistors

ZnO nanowire field-effect transistors having an omega-shaped floating gate (OSFG) have been successfully fabricated by directly coating CdTe nanocrystals (∼6±2.5 nm) at room temperature, and compared to simultaneously prepared control devices without nanocrystals. Herein, we demonstrate that channel punchthrough may occur when the depletion from the OSFG takes place due to the trapped charges in the nanocrystals. Electrical measurements on the OSFG nanowire devices showed static-induction transistorlike behavior in the drain output IDS-VDS characteristics and a hysteresis window as large as ∼3.1 V in the gate transfer IDS-VGS characteristics. This behavior is ascribed to the presence of the CdTe nanocrystals, and is indicative of the trapping and emission of electrons in the nanocrystals. The numerical simulations clearly show qualitatively the same characteristics as the experimental data and confirm the effect, showing that the change in the potential distribution across the channel, induced by both the...

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.