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Chemical Doping Effects in Multilayer MoS<sub>2</sub> and Its Application in Complementary Inverter
Yoo, Hocheon,Hong, Seongin,On, Sungmin,Ahn, Hyungju,Lee, Han-Koo,Hong, Young Ki,Kim, Sunkook,Kim, Jae-Joon American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.27
<P>Multilayer MoS<SUB>2</SUB> has been gaining interest as a new semiconducting material for flexible displays, memory devices, chemical/biosensors, and photodetectors. However, conventional multilayer MoS<SUB>2</SUB> devices have exhibited limited performances due to the Schottky barrier and defects. Here, we demonstrate poly(diketopyrrolopyrrole-terthiophene) (PDPP3T) doping effects in multilayer MoS<SUB>2</SUB>, which results in improved electrical characteristics (∼4.6× higher on-current compared to the baseline and a high current on/off ratio of 10<SUP>6</SUP>). Synchrotron-based study using X-ray photoelectron spectroscopy and grazing incidence wide-angle X-ray diffraction provides mechanisms that align the edge-on crystallites (97.5%) of the PDPP3T as well as a larger interaction with MoS<SUB>2</SUB> that leads to dipole and charge transfer effects (at annealing temperature of 300 °C), which support the observed enhancement of the electrical characteristics. Furthermore, we demonstrate a complementary metal-oxide-semiconductor inverter that uses a p-type MoSe<SUB>2</SUB> and a PDPP3T-doped MoS<SUB>2</SUB> as charging and discharging channels, respectively.</P> [FIG OMISSION]</BR>
Air-stable and balanced split-gate organic transistors
Yoo, Hocheon,Nakano, Masahiro,On, Sungmin,Ahn, Hyungju,Lee, Han-Koo,Takimiya, Kazuo,Kim, Jae-Joon Elsevier 2018 Organic electronics Vol.63 No.-
<P><B>Abstract</B></P> <P>Ambipolar organic electronics have been gaining interest as a simple alternative technology for implementing complementary-like circuits. Although practical applications require stable operation in the air, most previous studies on ambipolar organic electronics have reported results measured in high vacuum or N<SUB>2</SUB> atmosphere only. This is because ambipolar properties change to asymmetric p-type dominant or unipolar p-type characteristics when exposed to air. Little effort has been put into the fundamental investigation of the effects of the environmental atmosphere on ambipolar organic semiconductors. In this paper, we demonstrate ambipolar OTFTs with balanced p/n characteristics under ambient air using poly{[<I>N</I>,<I>N</I>′-bis(3-decylpentadecyl)-naphtho[2,3-<I>b</I>:6,7-<I>b</I>′]dithiophene-4,5,9,10-tetracarboxidiimide-2,7-diyl]-<I>alt</I>-5,5′-(2,2′-bithiophene)} (PNDTI-BT-DP). Based on the analysis using XPS, UPS, and electrical characterizations at various atmosphere, we concluded that the PNDTI-BT-DP has 0.45 eV higher than the target value for ambiplar charge injections with respect to Au contact electrode. The energy level of the PNDTI-BT-DP was up-shifted by 0.45 eV when the film was exposed to ambient air, which resulted in a change in the electrical properties. As a proof-of-concept application, we demonstrate the air-stable split-gate OTFTs that operate as either a unipolar p- or n-type device based on electrical control. Finally, we report results showing that the device characteristics for both p- or n-type operations were maintained after ∼120 h of atmospheric exposure.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Comprehensive analysis on air exposure effects by means of XPS, UPS, and electrical characterizations. </LI> <LI> Balanced p/n characteristics including mobility, turn-on voltage, and threshold voltage. </LI> <LI> Demonstration of air-stable split-gate organic transistors. </LI> <LI> Selective p- or n-type operation with on/off current ratio (~10<SUP>4</SUP>) for more than 120 h in ambient air. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>This study suggests a design methodology for air-stable ambipolar materials such that the HOMO/LUMO level of the ambipolar material is 0.3–0.5 eV higher than the target value to compensate for an eventual upward shift that occurs when the device is exposed to ambient air. Based on the methodology, we demonstrate air-stable split-gate OTFTs that show balanced p/n characteristics after ∼120 h of air exposure.</P> <P>[DISPLAY OMISSION]</P>
P-doping Effects of Tungsten Diselenide Transistors by Fluoropolymer Encapsulation
Hyeonji Lee,Seongin Hong,Hocheon Yoo 한국진공학회 2021 한국진공학회 학술발표회초록집 Vol.2021 No.2
We show that the ambipolar charge transport of the WSe<sub>2</sub> transistor can be made into a unipolar p- type through Cytop fluoropolymer and thermal annealing. After doping, the charge transport can be controlled by thermal annealing temperature. The C-F bond is rearranged through thermal annealing, and the well-aligned dipole moment causes the Fermi level to be lowered, enabling the channel transport to be p-doped.
Lee Dong Hyun,Hwang Siwon,Kim Bongjun,Yoo Hocheon 한국물리학회 2023 Current Applied Physics Vol.54 No.-
Inkjet printing technology holds promise as a cost-effective method for fabricating large-area electronics, with high compatibility with various substrates. In this paper, we investigate the electrical doping behaviors of p-type transistors based on single-walled carbon nanotubes (SWCNTs), where semiconducting channels and electrodes are patterned using inkjet printing. We demonstrate improved charge transport properties by encapsulating SWCNTs with phenylphosphonic acid (PPA) without annealing. The PPA-coated SWCNT transistors exhibit significantly enhanced hole mobility, reaching approximately 8.25 cm2 V−1 s−1. The presence of the benzene ring in PPA facilitates hole injection and induces a p-doping effect, resulting in a 4.3-fold increase in the on-current level of the transistors.
P-N junction Photodiode from IGZO/p-Si Heterostructure
Yeri Heo,Gunhoo Woo,Donghyeon Lee,Won Jae Lee,Taesung Kim,Hocheon Yoo 한국진공학회 2021 한국진공학회 학술발표회초록집 Vol.2021 No.2
P-N junction heterostructure photodiodes obtained by combing different energy bandgap structures materials provide promising photo-sensing behaviors. Here, we demonstrated an indium gallium zinc oxide (IGZO)/p-Si heterostructure photodiode which shows clear difference along to light intensity and wavelength without gate. Through this study, we obtained a gateless photo-sensing behavior according to wavelength of light. As a result, we obtained considerably a high on/off current ratio as high as 52.71 A/A.