Yonghan Roh

n- and p-Type Doping Phenomenon by Artificial DNA and M-DNA on Two-Dimensional Transition Metal Dichalcogenides

Deoxyribonucleic acid (DNA) and two-dimensional (2D) transition metal dichalcogenide (TMD) nanotechnology holds great potential for the development of extremely small devices with increasingly complex functionality. However, most current research related to DNA is limited to crystal growth and synthesis. In addition, since controllable doping methods like ion implantation can cause fatal crystal damage to 2D TMD materials, it is very hard to achieve a low-level doping concentration (nondegenerate regime) on TMD in the present state of technology. Here, we report a nondegenerate doping phenomenon for TMD materials (MoS2 and WSe2, which represent n- and p-channel materials, respectively) using DNA and slightly modified DNA by metal ions (Zn(2+), Ni(2+), Co(2+), and Cu(2+)), named as M-DNA. This study is an example of interdisciplinary convergence research between DNA nanotechnology and TMD-based 2D device technology. The phosphate backbone (PO4(-)) in DNA attracts and holds hole carriers in the TMD region, n-doping the TMD films. Conversely, M-DNA nanostructures, which are functionalized by intercalating metal ions, have positive dipole moments and consequently reduce the electron carrier density of TMD materials, resulting in p-doping phenomenon. N-doping by DNA occurs at ∼6.4 × 10(10) cm(-2) on MoS2 and ∼7.3 × 10(9) cm(-2) on WSe2, which is uniform across the TMD area. p-Doping which is uniformly achieved by M-DNA occurs between 2.3 × 10(10) and 5.5 × 10(10) cm(-2) on MoS2 and between 2.4 × 10(10) and 5.0 × 10(10) cm(-2) on WSe2. These doping levels are in the nondegenerate regime, allowing for the proper design of performance parameters of TMD-based electronic and optoelectronic devices (VTH, on-/off-currents, field-effect mobility, photoresponsivity, and detectivity). In addition, by controlling the metal ions used, the p-doping level of TMD materials, which also influences their performance parameters, can be controlled. This interdisciplinary convergence research will allow for the successful integration of future layered semiconductor devices requiring extremely small and very complicated structures.

Coverage Control of DNA Crystals Grown by Silica Assistance

The impetus behind the current interest in combining DNA materials with conventional nanotechnologies, such as nanoelectronics, biosensors, and nanophotonics, emanates from an ambition to exploit its remarkable properties. One of these properties is self-assembly that is driven by the thermodynamics of sticky end hybridization and makes structural DNA nanotechnology a prime candidate for bottom-up fabrication schemes in these fields. However, unless self-assembled DNA nanostructures can be fabricated on solid surfaces to at least the degree of accuracy of existing top-down methods, it will be unfeasible to replace it with existing technologies. An intermediate step toward this goal has been to merge the two approaches such that DNA nanostructures are self-assembled onto lithographically patterned substrates. Previous works have been successful at depositing self-assembled DNA nanostructures on patterned substrates and controlling the spatial orientations of tailored DNA origami motifs at specifically designated sites. All these approaches have used random depositions (or similar methods) of preformed DNA structures onto lithographically patterned substrates. What has been lacking in literature is a method of precisely controlling the coverage of DNA structures on various substrates, that is, the percentage of the surface covered by crystals, especially on silica (SiO2), which is crucial if DNA is to be universally employed in electronics. We provide a solution to this problem by introducing a new surface-assisted fabrication method, termed the silica-assisted growth (SAG) method, to selfassemble DNA nanostructures on SiO2 surfaces. The novel fabrication technique presented herein bears two important distinctions from previous studies. Firstly, direct annealing on the substrates allows for very accurate control of the amount of DNA structures that self-assemble on the substrate, that is, the coverage. Secondly, because of electrostatic interactions with the silica surface, structures grown by this method show drastic topological changes that lead to previously unreported novel structures. The pretreatment process of SiO2 substrates and the various DNA structures grown on them are shown in Figure 1. Silanol groups on the SiO2 surface become deprotonated once the substrates are treated in a 10 TAE/Mg buffer (see the Experimental section for details) since the pH of this buffer exceeds the isoelectric point of SiO2. [13] This approach allows Mg ions to bind to the substrate surface, which in turn binds the negatively charged DNA backbones (Figure 1a). To demonstrate the SAG method, four different types of DNA nanostructures were prepared. 8 helix tubes (8 HT) and 5 helix ribbons (5 HR) were constructed from single-stranded tiles (SST), while double-crossover (DX) crystals and DX crystals with biotin modifications were fabricated from DX tiles (see Figure S1–S3 in the Supporting Information). The schematic diagrams of the various DNA structures are illustrated in Figure 1b–f and their corresponding AFM images on SiO2 substrates are shown in Figure 1g–p (Figure 1g–k show structures made from the free solution annealing method deposited onto SiO2 for imaging and Figure 1 l–p show structures made using the SAG method where the structures are annealed directly on the substrate, see Figure S4 in the Supporting Information). For the 8 HT, there is a dramatic difference between the structure formations of the free solution annealing method and the SAG method. Caused by a local minimum in the free energy landscape, monodisperse 8 HT structures on SiO2 fabricated from the free solution annealing method are stable, which can be clearly seen in Figure 1g. In this case, the structures have already been formed in solution before they are deposited onto the substrate. Meanwhile, in the case of SAG, the charges of the Mg ions bound on the substrate surface interact with the DNA strands to prevent the formation of tubes. Through these interactions, an acute topological change of the structures occurs, allowing SSTs to bind edgewise and to remain in a single-layer state (Figure 1 l) with some of the tiles overlapping along their boundaries (Figure 1 l, bright regions). To the best of our knowledge, this is the first observation of 2D crystals arising from SST motifs. Another type of 1D structure, the 5 helix ribbon, was also successfully fabricated using both the free solution annealing and SAG methods as can be seen in Figure 1h and m, respectively. The substrate acts as a catalyst to reduce the amount of energy needed for DNA structures to form, resulting in large-scale structure formations on the substrates. In the case of DX crystals, two-tile units of DXmonomers were used as building blocks to fabricate periodic arrays. One [*] J. Lee, J. Kim, Prof. S. H. Park Sungkyunkwan Advanced Institute of Nanotechnology (SAINT) and Department of Physics, Sungkyunkwan University Suwon 440-746 (Korea) E-mail: sunghapark@skku.edu S. Kim, Prof. Y. Roh School of Information and Communication Engineering, Sungkyunkwan University Suwon 440-746 (Korea) E-mail: yhroh@skku.edu

Size‐Controllable DNA Rings with Copper‐Ion Modification

by simple molecular modi-fication, it makes DNA nanostructures one of the most viable biomaterials for use with current techniques. Although many developments took advantage of these characteristics, what has been lacking in DNA nanotechnology is sufficient investi-gation into specific interactions between DNA nanostructures and metal ions. Due to DNA’s poor conductivity,

Ultra-low Doping on Two-Dimensional Transition Metal Dichalcogenides using DNA Nanostructure Doped by a Combination of Lanthanide and Metal Ions.

Here, we propose a novel DNA-based doping method on MoS2 and WSe2 films, which enables ultra-low n- and p-doping control and allows for proper adjustments in device performance. This is achieved by selecting and/or combining different types of divalent metal and trivalent lanthanide (Ln) ions on DNA nanostructures, using the newly proposed concept of Co-DNA (DNA functionalized by both divalent metal and trivalent Ln ions). The available n-doping range on the MoS2 by Ln-DNA is between 6 × 109 and 2.6 × 1010 cm−2. The p-doping change on WSe2 by Ln-DNA is adjusted between −1.0 × 1010 and −2.4 × 1010 cm−2. In Eu3+ or Gd3+-Co-DNA doping, a light p-doping is observed on MoS2 and WSe2 (~1010 cm−2). However, in the devices doped by Tb3+ or Er3+-Co-DNA, a light n-doping (~1010 cm−2) occurs. A significant increase in on-current is also observed on the MoS2 and WSe2 devices, which are, respectively, doped by Tb3+- and Gd3+-Co-DNA, due to the reduction of effective barrier heights by the doping. In terms of optoelectronic device performance, the Tb3+ or Er3+-Co-DNA (n-doping) and the Eu3+ or Gd3+-Co-DNA (p-doping) improve the MoS2 and WSe2 photodetectors, respectively. We also show an excellent absorbing property by Tb3+ ions on the TMD photodetectors.

Effect of Charge Trapping on the Asymmetrical Shift of Memory Window in MFIS Devices

We investigated the effects of charge trapping on the asymmetrical increase of the memory window in metal-ferroelectric-insulator-semiconductor (MFIS) devices. We suggest that defect centers located at the SBN-Y 2 O 3 interface play important roles for generating the asymmetrical increase of the memory window: For example, electron trapping at the SBN-Y 2 O 3 interface via Fowler-Nordheim tunneling (FNT) injection from the Si substrate results in the preferential domain switching, causing the asymmetrical increase of the memory window. We also suggest that FNT injection in the Pt/SBN/Si MIS capacitors causes the symmetrical increase of the memory window because the SBN-Y 2 O 3 interface does not exist. However, charge trapping in the SBN layer reduces the memory window with time after FNT injection had stopped, while no significant degradation of the memory window was observed in the Pt/SBN-Y 2 O 3 /Si capacitors.

Characteristics of Ultrashallow Hetero Indium–Gallium–Zinc–Oxide/Germanium Junction

In this letter, we demonstrate an n-indium-gallium-zinc-oxide (IGZO)/i-germanium (Ge) heterojunction diode with an ultrashallow junction depth of ~ 37 nm. X-ray diffraction, atomic force microscopy, and secondary ion mass spectrometry analyses are performed to precisely investigate the n-IGZO and n-IGZO/i-Ge junctions. When the junction diodes are annealed at between 400 °C and 600 °C, a very high on-current density (180-320 A/cm2), which is comparable to that of a Ti/i-Ge reference junction, is obtained. In particular, after the 600 °C anneal, a fairly high on/ off-current ratio (7×102) is also observed.

Assembling CdSe/ZnS core–shell quantum dots on localized DNA nanostructures

We have demonstrated the assembly of CdSe/ZnS core–shell quantum dots (Qdots) on DNA templates that could potentially be used in practical devices and sensors. Qdots were aligned on one and two dimensional DNA nanostructures through electrostatic interaction between Qdots and DNA nanostructures. About 2 to 3 times larger adsorption ratios of Qdots on DNA templates were observed on both positively and negatively charged substrates. Moreover, assembled Qdots on DNA templates exhibit significant improvement in electric characteristics with a distinct semiconductor-like plateau. The results obtained in this research show the specific complementary relationship between Qdots and DNA nanostructures: the DNA nanostructures guide precise control of Qdot assembly on desired places and assembled Qdots help to increase the functionality of complexes. These approaches open up opportunities to control accurate positioning of specific nano and biomaterials with full functionality and efficiency in a given system.

Analysis of asymmetrical hysteresis phenomena observed in TMD-based field effect transistors

To realize field effect transistors with multi-layered MoS2 and WSe2 (hereafter denoted as MoS2 FET and WSe2 FET), many device instability problems should be surmounted, such as the hysteresis generation of the devices. In order to clarify the mechanism of the asymmetrical hysteresis phenomena observed in the transfer characteristics of the MoS2 and WSe2 FET, the temperature dependencies of their characteristics are analyzed. Based on these analyses, it can be concluded that donor-like traps present in both the SiO2/MoS2 interface and the MoS2 bulk in multi-layered MoS2 FETs, and that acceptor-like traps present in both the SiO2/WSe2 interface, and the WSe2 bulk in multi-layered WSe2 FETs. Furthermore, based on the chemical analyses and the arguments presented in previous studies, we propose that the sulfur vacancy (SV) is the origin of donor-like traps present in MoS2, and the tungsten vacancy (TV) is the origin of acceptor-like traps present in WSe2. This work may provide a potential clue to overcome many practical problems for realization of the transition metal dichalcogenides (TMDs) based FETs.To realize field effect transistors with multi-layered MoS2 and WSe2 (hereafter denoted as MoS2 FET and WSe2 FET), many device instability problems should be surmounted, such as the hysteresis generation of the devices. In order to clarify the mechanism of the asymmetrical hysteresis phenomena observed in the transfer characteristics of the MoS2 and WSe2 FET, the temperature dependencies of their characteristics are analyzed. Based on these analyses, it can be concluded that donor-like traps present in both the SiO2/MoS2 interface and the MoS2 bulk in multi-layered MoS2 FETs, and that acceptor-like traps present in both the SiO2/WSe2 interface, and the WSe2 bulk in multi-layered WSe2 FETs. Furthermore, based on the chemical analyses and the arguments presented in previous studies, we propose that the sulfur vacancy (SV) is the origin of donor-like traps present in MoS2, and the tungsten vacancy (TV) is the origin of acceptor-like traps present in WSe2. This work may provide a potential clue to overcome ma...

Study on electrical characteristics of HfO 2 treated by Nf 3 plasma

Summary form only given. Plasma process was used widely to manufacture semiconductor device due to low temperature and good performance. In particular, capacitively coupled plasma (CCP) and inductively coupled plasma (ICP) system were commonly used for dry etch, deposition and plasma treatment process in semiconductor device. In this paper, the fluorine plasma treatment process on high-k dielectric HfO2 was studied for improvement of dielectric performance. Fluorine can recover the trap due to passivation into oxygen vacancy of HfO2 dielectric. Plasma treatment is one of promising candidates to inject the ionized fluorine atom into oxygen vacancy of HfO2 effectively. Both CCP system with low density plasma (LDP, ~0.01%) and ICP system with high density plasma (HDP, ~1%) with NF3 gas were used for fluorine ionization. Composition and structure of the fluorinated-HfO2 treated by plasma were analyzed with TEM, XPS and Tof-SIMS. Electrical characteristics of I-V and C-V were measured with semiconductor device analyzer. Interfacial layer (IL) thickness of the fluorinated-HfO2 increasingly increased under the condition of ICP system, which led to the decrease of capacitance and degradation of dielectric. Also, crystallization and agglomeration of HfO2 was observed at TEM image. These result from fluorine ion bombardment and high temperature induced by plasma with high energy. Fluorine ionized by ICP system collides with HfO2. Bombardment of ionized fluorine can convert from HfO bond to Hf-F bond partially due to thermal energy and ion bombardment. Dissociated oxygen diffuses out surface or into silicon substrate, and then oxygen piled up on silicon substrate is combined with silicon. This results in the increase of IL thickness. Also, High thermal energy (>;550°C) generated from ion bombardment by ICP system can crystallize and agglomerate HfO2 dielectric sufficiently. Based on this model, we suggest that the fluorine treatment with low temperature and low density plasma can incorporate fluorine into oxygen vacancy of HfO2 without the damage of HfO2 and the increase of IL thickness on substrate silicon. We improved electrical characteristics of fluorinated-HfO2 without degradation of dielectric at the condition of low temperature (>;250°C) and low power with HFRF in CCP system. VBD (breakdown voltage) and IG (gate leakage current) of fluorinated-HfO2 were sharply improved about 10% and 50% compared to that of conventional HfO2. Stress induced leakage current (SILC) of fluorinated-HfO2 was improved in terms of dielectric reliability.