Photosensitivity of bulk and monolayer MoS2-based two-terminal devices

Cho Sangeun,Park Wooyoung,Im Hyunsik,김형상 한국물리학회 2023 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.83 No.5

Transition metal dichalcogenides (TMDCs), such as MoS2, MoSe2, WS2, and WSe2, have attracted enormous attention owing to their unique electrical and optical properties. A type of material known as TMDC has the MX2 formula with a direct bandgap in ultra-thin layers and indirect bandgap properties in the bulk. TMDCs have attracted significant research interest due to their use in nano-devices, opto-electronics, and next-generation electronics. In the study, two different MoS2 devices, Au–bulk MoS2–Au and Au–monolayer MoS2–Au, were fabricated, and their photon-induced current–voltage characteristics at different wavelengths (red ≈ 650 nm, green ≈ 532 nm and blue ≈ 450 nm) and values were compared. Additionally, the time-dependent photoresponses of these devices under red light irradiation (wavelength, λex = 650 nm) were analyzed. The Au–monolayer MoS2–Au device had a higher current response compared with the Au–bulk MoS2–Au device. These results suggest that single-layer MoS2 devices could be more efficient and responsive than bulk MoS2 devices for a variety of applications.

Modulating Electronic Properties of Monolayer MoS₂ <i>via</i> Electron-Withdrawing Functional Groups of Graphene Oxide

Oh, Hye Min,Jeong, Hyun,Han, Gang Hee,Kim, Hyun,Kim, Jung Ho,Lee, Si Young,Jeong, Seung Yol,Jeong, Sooyeon,Park, Doo Jae,Kim, Ki Kang,Lee, Young Hee,Jeong, Mun Seok American Chemical Society 2016 ACS NANO Vol.10 No.11

<P>Modulation of the carrier concentration and electronic type of monolayer (1L) MoS2 is highly important for applications in logic circuits, solar cells, and light-emitting diodes. Here, we demonstrate the tuning of the electronic properties of large-area IL-MoS2 using graphene oxide (GO). GO sheets are wellknown as hole injection layers since they contain electron-withdrawing groups such as carboxyl, hydroxyl, and epoxy. The optical and electronic properties of GO-treated 1L-MoS2 are dramatically changed. The photoluminescence intensity of GO-treated 1L-MoS2 is increases by more than 470% compared to the pristine sample because of the increase in neutral exciton contribution. In addition, the Aig peak in Raman spectra shifts considerably, revealing that GO treatment led to the formation of p-type doped 1L-MoS2. Moreover, the current vs voltage (I-V) curves of GO-coated 1L-MoS2 field effect transistors show that the electron concentration of 1L-MoS2 is significantly lower in comparison with pristine 1L-MoS2. Current rectification is also observed from the I-V curve of the lateral diode structure with 1L-MoS2 and 1L-MoS2/GO, indicating that the electronic structure of MoS2 is significantly modulated by the electron-withdrawing functional group of GO.</P>

Large-scale chemical vapor deposition growth of highly crystalline MoS₂ thin films on various substrates and their optoelectronic properties

Nguyen, Van Tu,Ha, Seongju,Yeom, Dong-Il,Ahn, Yeong Hwan,Lee, Soonil,Park, Ji-Yong Elsevier 2019 Current Applied Physics Vol.19 No.10

<P><B>Abstract</B></P> <P>Large-scale growth of mostly monolayer molybdenum disulfide (MoS<SUB>2</SUB>) on quartz, sapphire, SiO<SUB>2</SUB>/Si, and waveguide substrates is demonstrated by chemical vapor deposition with the same growth parameters. Centimeter-scale areas with large flakes and films of MoS<SUB>2</SUB> on all the growth substrates are observed. The atomic force microscopy and Raman measurements indicate the synthesized MoS<SUB>2</SUB> is monolayer with high quality and uniformity. The MoS<SUB>2</SUB> field effect transistors based on the as-grown MoS<SUB>2</SUB> exhibit carrier mobility of 1–2 cm<SUP>2</SUP>V<SUP>−1</SUP>s<SUP>−1</SUP> and On/Off ratio of ~10<SUP>4</SUP> while showing large photoresponse. Our results provide a simple approach to realize MoS<SUB>2</SUB> on various substrates for electronics and optoelectronics applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Mostly monolayer MoS<SUB>2</SUB> can be grown in the same CVD setup with the same procedure on various substrates such as quartz, sapphire, SiO<SUB>2</SUB>/Si, and waveguide substrates. </LI> <LI> The growth region extends almost cm-scale, which shows that scale-up production can be possible with CVD. </LI> <LI> Devices based on as-grown MoS2 show large albeit slow photoresponse under visible light illuminations. </LI> </UL> </P>

Temperature dependence of the dielectric function of monolayer MoS₂

Le, V.L.,Kim, T.J.,Park, H.G.,Nguyen, H.T.,Nguyen, X.A.,Kim, Y.D. ELSEVIER 2019 Current Applied Physics Vol.19 No.2

<P><B>Abstract</B></P> <P>An analytic expression of the dielectric function of monolayer molybdenum disulfide (MoS<SUB>2</SUB>) <I>ε</I> = <I>ε</I> <SUB>1</SUB> + <I>iε</I> <SUB>2</SUB> is presented for energies from 1.4 to 6.0 eV and temperatures from 35 to 350 K. The dielectric function parametric model is used to express <I>ε</I> as a sum of polynomials, which naturally includes asymmetry of critical-point lineshapes. The temperature dependence is achieved by fitting model parameters. In this way, the dielectric function of MoS<SUB>2</SUB> for arbitrary temperature can be calculated. We observed the fundamental absorption peak, which occurs at the <I>K</I> point of the Brillouin zone. These results are expected to be useful in designing and understanding applied-device technologies based on monolayer MoS<SUB>2</SUB>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We successfully reconstructed the dielectric function of monolayer MoS<SUB>2</SUB> using parametric model. </LI> <LI> We observe the fundamental absorption peak, which occurs at the <I>K</I> point of the Brillouin zone. </LI> <LI> We obtain the temperature dependence of the dielectric function of monolayer MoS<SUB>2</SUB> from 35 to 350 K. </LI> <LI> We use a cubic polynomial to interpolate the dielectric function of monolayer MoS<SUB>2</SUB> at arbitrary temperatures. </LI> <LI> These results enable the development of potentially important devices based on monolayer MoS<SUB>2</SUB>. </LI> </UL> </P>

MoS₂@VS₂ Nanocomposite as a Superior Hybrid Anode Material

Samad, Abdus,Shin, Young-Han American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.35

<P>Using density functional theory, MoS2@VS2 nanocomposite is reported as a hybrid anode with upgraded electronic conductivity and Li/Na storage capacity. The chemically active monolayer VS2 can be stabilized in energy and phonon vibrations by using the monolayer MoS2 as a substrate. The stability of the chemically active monolayer VS2 is attributed to the interfacial charge accumulation between the monolayer MoS2 and VS2. The maximum specific capacity of the nanocomposite has been enhanced to 584 mAh/g both for Li and for Na storage. We attribute the high enhancement in the Li/Na storage capacity of MoS2@VS2 nanocomposite to the charge redistribution in the formation of the nanocomposite. The lithiation/sodiation open-circuit voltage range of the nanocomposite is quite feasible to be used as anode. Diffusion barriers of Li/Na ions on the surfaces of the nanocomposite are comparable to the barriers on corresponding monolayers, while at the interface the barriers are lower than that for bulk MoS2. This study utilizes different aspects of the two different materials in a hybrid anode with highly enhanced electrochemical performance.</P>

Impurity-Free, Direct Transferable Large-Area MoS2 Monolayer and Studies on Its Li-Storage Properties

VELUSAMYSENTHILKUMAR,김용수 한국물리학회 2018 New Physics: Sae Mulli Vol.68 No.2

MoS2 monolayer with a large-area grain boundary was prepared over a SiO2/Si substrate by using conventional chemical vapor deposition. The structural and the optical properties of MoS2 were investigated by using a range of analytical techniques. These studies clearly revealed the formation of a monolayer with a single-crystalline nature. The prepared monolayer MoS2 was transferred directly to a copper electrode by using hydrofluoric acid under a impurity-free condition. The electrochemical performance of the MoS2 monolayer was evaluated in a half-cell assembly with metallic Li. The maximum reversible capacity of Li/MoS2 was ∼26 μAhcm–2 at 1 μAcm–2. Furthermore, the test cell also exhibited excellent cycling stability and capacity retention characteristics. A cyclic voltammetry study was performed to understand the Li-storage mechanism for this MoS2 monolayer.

Nonvolatile Ferroelectric Memory Based on PbTiO3 Gated Single-Layer MoS2 Field-Effect Transistor

Hyun Wook Shin,Jong Yeog Son 대한금속·재료학회 2018 ELECTRONIC MATERIALS LETTERS Vol.14 No.1

We fabricated ferroelectric non-volatile random access memory (FeRAM) based on a fieldeffect transistor (FET) consisting of a monolayer MoS2 channel and a ferroelectric PbTiO3(PTO) thin film of gate insulator. An epitaxial PTO thin film was deposited on a Nb-dopedSrTiO3 (Nb:STO) substrate via pulsed laser deposition. A monolayer MoS2 sheet wasexfoliated from a bulk crystal and transferred to the surface of the PTO/Nb:STO. Structuraland surface properties of the PTO thin film were characterized by X-ray diffraction and atomicforce microscopy, respectively. Raman spectroscopy analysis was performed to identify thesingle-layer MoS2 sheet on the PTO/Nb:STO. We obtained mobility value (327 cm2/V·s) ofthe MoS2 channel at room temperature. The MoS2-PTO FeRAM FET showed a wide memorywindow with 17 kΩ of resistance variation which was attributed to high remnant polarizationof the epitaxially grown PTO thin film. According to the fatigue resistance test for the FeRAMFET, however, the resistance states gradually varied during the switching cycles of 109.

Enhanced Triboelectric Nanogenerators Based on MoS₂ Monolayer Nanocomposites Acting as Electron-Acceptor Layers

Wu, Chaoxing,Kim, Tae Whan,Park, Jae Hyeon,An, Haoqun,Shao, Jiajia,Chen, Xiangyu,Wang, Zhong Lin American Chemical Society 2017 ACS NANO Vol.11 No.8

<P>As one of their major goals, researchers attempting to harvest mechanical energy efficiently have continuously sought ways to integrate mature technologies with cutting-edge designs to enhance the performances of triboelectric nanogenerators (TENGs). In this research, we introduced monolayer molybdenum-disulfide (MoS2) into the friction layer of a TENG as the triboelectric electron-acceptor layer in an attempt to dramatically enhance its output performance. As a proof of the concept, we fabricated a vertical contact-separation mode TENG containing monolayer MoS2 as an electron-acceptor layer and found that the TENG exhibited a peak power density as large as 25.7 W/m(2), which is 120 times larger than that of the device without monolayer MoS2. The mechanisms behind the performance enhancement, which are related to the highly efficient capture of triboelectric electrons in monolayer MoS2, are discussed in detail. This study indicates that monolayer MoS2 can be used as a functional material for efficient energy harvesting.</P>

Large-scale chemical vapor deposition growth of highly crystalline MoS2 thin films on various substrates and their optoelectronic properties

Van Tu Nguyen,하성주,염동일,안영환,이순일,박지용 한국물리학회 2019 Current Applied Physics Vol.19 No.10

Large-scale growth of mostly monolayer molybdenum disulfide (MoS2) on quartz, sapphire, SiO2/Si, and waveguide substrates is demonstrated by chemical vapor deposition with the same growth parameters. Centimeterscale areas with large flakes and films of MoS2 on all the growth substrates are observed. The atomic force microscopy and Raman measurements indicate the synthesized MoS2 is monolayer with high quality and uniformity. The MoS2 field effect transistors based on the as-grown MoS2 exhibit carrier mobility of 1–2 cm2V−1s−1 and On/Off ratio of ~104 while showing large photoresponse. Our results provide a simple approach to realize MoS2 on various substrates for electronics and optoelectronics applications.

Wafer-Scale Substitutional Doping of Monolayer MoS₂ Films for High-Performance Optoelectronic Devices

Kim, Youngchan,Bark, Hunyoung,Kang, Byunggil,Lee, Changgu American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.13

<P>The substitutional doping method is ideally suited to generating doped two-dimensional (2D) materials for practical device applications as it does not damage or destabilize such materials. However, recently reported substitutional doping techniques for 2D materials have given rise to discontinuities and low uniformities, which hamper the extension of such techniques to large-scale production. In the current work, we demonstrated uniform substitutional doping of monolayer MoS<SUB>2</SUB> in a 2 in. wafer of area >13 cm<SUP>2</SUP>. The devices based on doped MoS<SUB>2</SUB> showed extremely high uniformity and stability in electrical properties in ambient conditions for 30 days. The photodetectors based on the doped MoS<SUB>2</SUB> samples showed an ultrahigh photoresponsivity of 5 × 10<SUP>5</SUP> A/W, a detectivity of 5 × 10<SUP>12</SUP> Jones, and a fast response rate of 5 ms than did those based on undoped MoS<SUB>2</SUB>. This work showed the feasibility of real-life applications based on functionalized 2D semiconductors for next-generation electronic and optoelectronic devices.</P> [FIG OMISSION]</BR>