# Fileset

[2025-ACSomega-Nakajima-structural-and-electric-characterization-of-sputtered-pt-wse2-contacts-toward-high-performance-2d-p-fets.pdf](https://mdr.nims.go.jp/filesets/d672e834-a4d4-4c70-8091-e9979a3fc064/download)

## Creator

Ryuichi Nakajima, [Tomonori Nishimura](https://orcid.org/0000-0002-8000-5164), [Kaito Kanahashi](https://orcid.org/0000-0003-2571-3384), [Shogo Hatayama](https://orcid.org/0000-0002-2914-1072), [Wen Hsin Chang](https://orcid.org/0000-0002-8501-6276), [Yuta Saito](https://orcid.org/0000-0002-9576-1560), Toshifumi Irisawa, Keiji Ueno, [Yasumitsu Miyata](https://orcid.org/0000-0002-9733-5119), [Takashi Taniguchi](https://orcid.org/0000-0002-1467-3105), [Kenji Watanabe](https://orcid.org/0000-0003-3701-8119), [Kosuke Nagashio](https://orcid.org/0000-0003-1181-8644)

## Rights

[Creative Commons BY-NC-ND Attribution-NonCommercial-NoDerivs 4.0 International](https://creativecommons.org/licenses/by-nc-nd/4.0/)

## Other metadata

[Structural and Electric Characterization of Sputtered Pt/WSe<sub>2</sub> Contacts toward High-Performance 2D p-FETs](https://mdr.nims.go.jp/datasets/d76d31a6-d038-448e-b0fc-b15a929f6d20)

## Fulltext

Structural and Electric Characterization of Sputtered Pt/WSe2 Contacts toward High-Performance 2D p-FETsStructural and Electric Characterization of Sputtered Pt/WSe2Contacts toward High-Performance 2D p‑FETsRyuichi Nakajima, Tomonori Nishimura, Kaito Kanahashi, Shogo Hatayama, Wen Hsin Chang,Yuta Saito, Toshifumi Irisawa, Keiji Ueno, Yasumitsu Miyata, Takashi Taniguchi, Kenji Watanabe,and Kosuke Nagashio*Cite This: ACS Omega 2025, 10, 42973−42979 Read OnlineACCESS Metrics & More Article Recommendations *sı Supporting InformationABSTRACT: For high-performance p-type field-effect transistors(FETs) based on two-dimensional (2D) materials, the use of Pt asthe contact metal, with its high work function, is advantageous foreffective hole injection into the 2D channel. However, the high-energy sputtering process required to deposit Pt, due to its highmelting point, often induces significant damage to the 2Dmaterials. Recently, the achievement of nearly ideal van derWaals contacts in Sb2Te3/MoS2 via sputtering has motivated us toinvestigate WSe2 p-FETs with sputtered Pt electrodes. Notably,reasonable p-FET performance was observed even in monolayerWSe2. However, various characterizations revealed that the crystalstructure of WSe2 was no longer preserved, suggesting theformation of a quasi-edge contact between Pt-sputtered WSe2and the WSe2 channel. Moreover, from the perspective of sputtering applicability, the relationship between deposition methods,deposited materials, and the resulting extent of damage was systematically examined.■ INTRODUCTIONTwo dimensional (2D) layered materials, particularly tran-sition metal dichalcogenides (TMDCs) such as MoS2, WS2,and WSe2, hold significant potential for next-generation field-effect transistors (FETs)1 because the atomic thickness of theirchannels is tolerant against short channel effects and the highon-state current can be retained even in the monolayer (1L)limit.2 To realize complementary metal oxide semiconductor(CMOS) circuits composed entirely of 2D FETs, both high-performance 2D n-type and p-type FETs are necessary. Whilehigh-performance 2D n-FETs have been achieved,3,4 suchsuperior characteristics of 2D p-FETs remain limited.5 Itshould be noted that the operation mechanism of 2D FETs isbased on a Schottky barrier (SB) transistor, whose operationmode and performance are primarily influenced by the currentinjection through the SB at the metal/2D channel interface,6,7as opposed to a metal oxide semiconductor FET (MOSFET).This introduces a key challenge for high-performance 2D p-FETs: reducing the Schottky barrier height (SBH) between theFermi level of metal electrodes with a high work function(WF) and the valence band of the 2D channel for efficient holeinjection. A well-known issue in this regard is Fermi levelpinning (FLP) at the metal/2D channel interface, where theFermi level of metal electrodes is forcefully pinned close to theconduction band edge of 2D materials regardless of metal WFs,especially in MoS2 cases.8−10 However, prior studies on WSe2FETs indicate that their operation mode could be controlledby metal WF without significant treatment of the metaldeposition method, suggesting that the strength of FLP inWSe2 is relatively mild compared to the case of MoS2.11 Sincethe FLP is generally attributed to both the intrinsic mechanismand extrinsic defects in semiconductors, it is essential toexplore deposition methods for metal electrodes with high WF.Platinum (Pt) with the highest work function (∼5.7 eV)among stable single-element metals12 is considered as apromising candidate for FET electrodes to demonstrate high-performance p-FETs. However, due to its high melting point(∼1768 °C) and low vapor pressure, only electron beam (EB)evaporation or sputtering can be employed for physicaldeposition, as illustrated in Figure 1a. These depositionmethods typically lead to significant defect formation on 2Dmaterials,13−17 potentially causing severe FLP at the metal/2Dchannel interface or degradation of the transport properties ofthe 2D channels. Consequently, when Pt was utilized aselectrodes for 2D channels, relatively thick multilayerReceived: June 17, 2025Revised: August 26, 2025Accepted: September 5, 2025Published: September 15, 2025Articlehttp://pubs.acs.org/journal/acsodf© 2025 The Authors. Published byAmerican Chemical Society42973https://doi.org/10.1021/acsomega.5c05764ACS Omega 2025, 10, 42973−42979This article is licensed under CC-BY-NC-ND 4.0Downloaded via NATL INST FOR MATLS SCIENCE (NIMS) on December 8, 2025 at 02:43:04 (UTC).See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Ryuichi+Nakajima"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Tomonori+Nishimura"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Kaito+Kanahashi"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Shogo+Hatayama"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Wen+Hsin+Chang"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Yuta+Saito"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Yuta+Saito"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Toshifumi+Irisawa"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Keiji+Ueno"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Yasumitsu+Miyata"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Takashi+Taniguchi"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Kenji+Watanabe"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Kosuke+Nagashio"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Kosuke+Nagashio"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/showCitFormats?doi=10.1021/acsomega.5c05764&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsomega.5c05764?ref=pdfhttps://pubs.acs.org/doi/10.1021/acsomega.5c05764?goto=articleMetrics&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsomega.5c05764?goto=recommendations&?ref=pdfhttps://pubs.acs.org/doi/10.1021/acsomega.5c05764?goto=supporting-info&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsomega.5c05764?fig=abs1&ref=pdfhttps://pubs.acs.org/toc/acsodf/10/37?ref=pdfhttps://pubs.acs.org/toc/acsodf/10/37?ref=pdfhttps://pubs.acs.org/toc/acsodf/10/37?ref=pdfhttps://pubs.acs.org/toc/acsodf/10/37?ref=pdfhttp://pubs.acs.org/journal/acsodf?ref=pdfhttps://pubs.acs.org?ref=pdfhttps://pubs.acs.org?ref=pdfhttps://doi.org/10.1021/acsomega.5c05764?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://http://pubs.acs.org/journal/acsodf?ref=pdfhttps://http://pubs.acs.org/journal/acsodf?ref=pdfhttps://acsopenscience.org/researchers/open-access/https://creativecommons.org/licenses/by-nc-nd/4.0/https://creativecommons.org/licenses/by-nc-nd/4.0/https://creativecommons.org/licenses/by-nc-nd/4.0/https://creativecommons.org/licenses/by-nc-nd/4.0/https://creativecommons.org/licenses/by-nc-nd/4.0/films,8,18−24 transferred electrodes,10,25 and prepreparedbottom electrodes26,27 were employed to mitigate these issues.Nevertheless, p-FET operation in 1L-WSe2 has beendemonstrated with Pt electrodes deposited via rapid EBevaporation with long pauses to maintain the substratetemperature at room temperature (RT).28 Furthermore, nearlyideal van der Waals (vdW) contacts have been reported forSb2Te3/MoS2 and Bi2Te3/WSe2 by applying a conventionalsputtering method.29,30 In this research, therefore, weinvestigated the FET performance of 1L and bilayer (2L)WSe2 FETs with sputtered Pt electrodes and the impact of Ptsputtering-induced damage on WSe2.■ RESULTS AND DISCUSSIONFirst, the impact of deposition methods on FET performance iscompared. 1L-WSe2 was prepared on a 90 nm SiO2/n+-Sisubstrate by mechanically exfoliating bulk WSe2 flakes using apoly(dimethylsiloxane) (PDMS) film. The layer numbers wereconfirmed based on the contrast of optical images on the SiO2/n+-Si substrate,31 assisted by Raman spectroscopy. Followingthe resist pattering for source/drain electrodes performed via amaskless aligner, a low-concentration UV-ozone treatment of∼5 ppm was applied for 5 min at RT to minimize resist residuein the contact area. Subsequently, Pt source/drain electrodeswere deposited via either EB evaporation (AEV-HR1, AVCCorp.) or sputtering (QAM-4-ST, ULVAC Corp.). In the EBevaporation process, a 10 nm Pt film was initially deposited viaEB evaporation, followed by a 20 nm Au film via thermalevaporation to increase the thickness of electrodes. During EBevaporation, on the other hand, the sample was maintained atRT through external cooling to reduce damage induced byradiation heating. The detailed device fabrication conditionsare summarized in Figure S1. All electrical measurements wereperformed at RT by using a semiconductor parameter analyzer(Keysight, B1500A) in a vacuum prober.Figure 1b shows the transfer characteristics of 1L-WSe2Schottky FETs with Pt electrodes, deposited via either EBevaporation or sputtering, as a function of the back gate voltage(Vbg). It should be noted that the device with sputtered Ptelectrodes was annealed at 200 °C in an Ar/H2 atmosphere for10 min to reduce strain induced in Pt electrodes during thesputtering. This process proved to be effective in enhancing thetransfer characteristics by stabilizing sputtered Pt electrodes, asshown in Figure S2. However, such an improvement was notobserved in EB-evaporated Pt electrodes after annealing. It wasanticipated that the 1L-WSe2 FETs with Pt electrodes wouldexhibit p-type behavior due to the ideal band alignment with anegligible SBH for the valence band edge of WSe2 and a largeSBH exceeding 1 eV for the conduction band edge.12,32However, both WSe2 FETs exhibited an ambipolar behavior.Additionally, a critical difference is the variation in thethreshold voltage difference (ΔVth) between the n- and p-branch in the FET operations, as shown in Figure 1b. Thisdifference largely depends on the Pt deposition methods. Thenarrower ΔVth in the FET with EB-evaporated electrodesimplies a reduction in the effective SBHs for the conductionband edge of WSe2, likely due to the formation of numerousdefect states in WSe2 during Pt deposition. Although the WSe2channel was maintained at RT through external cooling duringEB evaporation to mitigate damages induced by radiationheating,28 secondary or backscattered electrons might stillcontribute to the degradation of the WSe2 channel. In contrast,the 1L-WSe2 FET with sputtered Pt electrodes exhibited awider ΔVth, which could enhance the p-type operation of theWSe2 FET by ensuring a stable off-state across a wider gatevoltage range. The detail of the relationship between ΔVth andthe effective SBH is described in Figure S3. The wider ΔVthimplies that the defect states density at the metal/WSe2interface generated by sputtering is lower than that producedby EB evaporation, contrary to our intuition.Based solely on these implications, the expected bandalignments at the Pt/WSe2 interfaces are schematicallysummarized in Figure 1c under the assumption that the defectstates associated with EB-evaporated Pt electrodes aresymmetrically distributed within the band gap of WSe2.However, this interpretation appears to contradict the widelyaccepted understanding that sputtering processes induce moredamage to the underlying material than EB evaporation.17Indeed, through subsequent investigations, we show that thisinitial assumption regarding the band alignment wasfundamentally incorrect.Next, the impact of Pt deposition on the structural andelectronic properties of WSe2 is examined using X-rayphotoelectron spectroscopy (XPS), Raman spectroscopy, andFigure 1. (a) Schematic illustration of the relationship between the melting points of the deposited materials and the various deposition techniques.(b) Id−Vbg characteristic of 1L-WSe2 FETs with Pt electrodes deposited by EB evaporation or sputtering, measured at a constant drain bias voltage(Vd) of 1 V at RT. (c) Schematic representation of the band alignment at the Pt/WSe2 interfaces, derived from Id−Vbg curves, for both EBevaporation and sputtering techniques.ACS Omega http://pubs.acs.org/journal/acsodf Articlehttps://doi.org/10.1021/acsomega.5c05764ACS Omega 2025, 10, 42973−4297942974https://pubs.acs.org/doi/suppl/10.1021/acsomega.5c05764/suppl_file/ao5c05764_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acsomega.5c05764/suppl_file/ao5c05764_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acsomega.5c05764/suppl_file/ao5c05764_si_001.pdfhttps://pubs.acs.org/doi/10.1021/acsomega.5c05764?fig=fig1&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsomega.5c05764?fig=fig1&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsomega.5c05764?fig=fig1&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsomega.5c05764?fig=fig1&ref=pdfhttp://pubs.acs.org/journal/acsodf?ref=pdfhttps://doi.org/10.1021/acsomega.5c05764?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-asphotoluminescence (PL) spectroscopy to elucidate the differ-ences in FET characteristics and deposition-induced damageassociated with various deposition methods. For the XPSanalysis, 1L-WSe2 grown on a sapphire substrate via chemicalvapor deposition (CVD) was employed instead of exfoliatedflakes since a large surface area is required for XPSmeasurements. A 1 nm Pt film was deposited via either EBevaporation or sputtering onto the entire 1 × 1 cm2 1L-WSe2/sapphire substrate. The core-level spectra of W 4f and Se 3dare shown in Figure 2a and b, respectively. The sample withthe EB-evaporated Pt film exhibited minimal changes in thecore-level peaks of W and Se, while the sample with thesputtered Pt film exhibited new peaks at 37.6, 35.4, and 59.4eV on the higher binding energy side of the initial peaks. Thesenew peaks are likely attributable to the formation of WOx andSeOx,33,34 and their emergence would be ascribed to residualoxygen within the sputtering chamber or exposure to air priorto the XPS measurement. This indicates that WSe2 undergoesdegradation during the Pt sputtering process. Furthermore,another peak appeared at around 51.3 eV on the lower bindingenergy side of the initial Se 3d peak, which likely suggests theformation of PtSex compounds as a result of the Pt sputteringprocess, given the electronegativities of Pt (2.28) and Se(2.05).Raman spectroscopy using a 488 nm semiconductor laserwas performed at RT on 1L-WSe2 exfoliated on a 90 nm SiO2/n+-Si substrate, both before and after Pt deposition. For a faircomparison, all spectra were normalized to the intensity of theSi substrate peak around 520 cm−1, as shown in Figure 2c. Thetwo main peaks of 1L-WSe2, observed around 250 cm−1 andcorresponding to E12g and A1g modes,35 were clearly presenteven after EB evaporation of Pt, suggesting that the crystalstructure of 1L-WSe2 was preserved after EB evaporation of Pt.However, these peaks were absent in 1L-WSe2 after Ptsputtering, indicating the disruption of the crystal structure ofWSe2. The significant diminution of these peaks even in 2L-WSe2 after Pt sputtering exhibited adverse effects on theunderlying layer of WSe2, as well as on the top layer. Moreover,PL measurements were also performed at 4 K to investigate theelectronic structure of 1L-WSe2, as shown in Figure 2d. Thesamples used for PL measurements were identical to thoseused for Raman measurements. Each spectrum was normalizedto the maximum peak intensity except for that of Pt-sputtered1L-WSe2. The PL peaks corresponding to the exciton (1.71eV) and trion (1.68 eV)36,37 were absent in 1L-WSe2 after Ptsputtering, suggesting that the Pt sputtering process enhancesnonradiative recombination or induces significant degradationin the band structure of 1L-WSe2.Although the 1L-WSe2 device with sputtered Pt electrodesshowed FET operation, XPS, Raman spectroscopy, and PLanalyses indicated that the crystal integrity was not preserved.Here, let us consider the interface structure of EB-evaporatedFigure 2. XPS spectra of (a) W and (b) Se obtained from CVD-grown 1L-WSe2 measured before and after Pt deposition. (c) Raman spectra ofexfoliated 1L-WSe2 measured before and after Pt deposition. (d) PL spectra of 1L-WSe2 measured before and after Pt deposition. (e) Schematicillustration of the expected Pt/WSe2 interfaces for EB evaporation and sputtering.ACS Omega http://pubs.acs.org/journal/acsodf Articlehttps://doi.org/10.1021/acsomega.5c05764ACS Omega 2025, 10, 42973−4297942975https://pubs.acs.org/doi/10.1021/acsomega.5c05764?fig=fig2&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsomega.5c05764?fig=fig2&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsomega.5c05764?fig=fig2&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsomega.5c05764?fig=fig2&ref=pdfhttp://pubs.acs.org/journal/acsodf?ref=pdfhttps://doi.org/10.1021/acsomega.5c05764?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-asand sputtered Pt/WSe2 devices. In the case of EB evaporation,evaporated Pt is unlikely to chemically react with WSe2, asevidenced by the minimal qualitative changes observed in XPS,Raman, and PL spectra. A Schottky junction is thereforeexpected to form at the Pt/WSe2 interface as a conventionaltop contact in the out-of-plane direction, as schematicallyillustrated in Figure 2e. Despite the minimal reaction, theeffective SB lowering expected from the narrower ΔVth inFigure 1b suggests that defects are generated in 1L-WSe2 underthe EB-evaporated Pt electrode. In contrast, the Pt-sputtered1L-WSe2 did not preserve an ideal Pt/WSe2 interface butinstead will form a reacted layer comprising other compounds,such as oxides or selenides as identified through XPS analysis(additional characterization is shown in Figure S4). Never-theless, the FET operation with a wider ΔVth was observed.The high power of Pt sputtering could lead to different contactgeometries as well as high-density defect formation. That is,this FET operation could be interpreted within a model wherethe Schottky junction is likely formed not between Pt and thereacted layer but rather between the reacted layer and WSe2,functioning as a quasi-edge contact in the in-plane direction. Inthis model, almost no potential barrier would exist at theinterface between sputtered Pt and the reacted layer, meaningthe reacted layer would act as a metallic layer. 200 °Cannealing after Pt sputtering would enhance the metallizationof the reacted layer. The wider ΔVth in Figure 1b suggests arelatively lower defect state density at the interface between thereacted layer and WSe2. Small Id values could also be explainedby the small contact area of the quasi-edge contact. Comparedwith the conventional edge contact fabrication process,38 thepresent study will provide alternative process for edge contactformation without channel etching and precise control ofposition alignment.From several characterizations, a quasi-edge contact betweensputtered Pt electrodes and WSe2 was suggested. Since thiscurrent injection mechanism differs from that of the conven-tional top contact formed via EB evaporation, the performanceand contact resistance of p-FETs after contact doping might beimproved. Therefore, it would be worth exploring thefeasibility of sputtered Pt contacts on WSe2 by evaluatingthem.39 Although molecular doping40 is commonly employedin the research of 2D semiconductors, it is incompatible withthe practical FET fabrication process that involves thermalannealing. In this work, charge transfer from WOx formed byself-limiting layer-by layer oxidation was selected due to itsstable and reliable doping mechanism.41−43 Since the Fermilevel in WO3 is located below the conduction band composedof empty d states, WO3 can possess a high work function of∼6.5 eV.44 Figure 3a illustrates the schematic of contactdoping via ozone oxidation. The depletion layer of WSe2 at themetal/WSe2 contact becomes thinner due to hole doping fromWOx, resulting in a more efficient hole injection. Compared toour previous studies on p-WSe2 operation using thermallyevaporated Au electrodes and hole transfer from WOx,39 theuse of sputtered Pt source/drain electrodes may alsocontribute to enhance hole injection by lowering the Fermilevel. To surely maintain the continuous WSe2 channel layereven after oxidation of the top WSe2 layer, 2L-WSe2 wasselected. The details are described in Figure S5. For thefabrication of the 2L-WSe2 FET, the WSe2 channel transferredonto a SiO2/n+-Si substrate was first patterned by CF4 plasmaetching. Hexagonal boron nitride (h-BN) was then transferredas a top gate insulator using a PDMS film, with the thickness ofthe h-BN layer measured at 10.2 nm via atomic forcemicroscopy (AFM) measurement. Subsequently, Pt source/drain electrodes were sputtered, and the Au top gate electrodewas thermally evaporated. The device was subsequentlyannealed to stabilize the sputtered Pt electrodes. Finally, holedoping into WSe2 was introduced by UV-ozone oxidation at aconcentration of ∼650 ppm and 60 °C. Electrical measure-ments were performed before and after ozone oxidation.Notably, this concentration for layer-by-layer oxidation ismuch higher than the concentration of ∼5 ppm to minimizeresist residue in the contact area.Figure 3b shows the transfer characteristics of the 2L-WSe2FET before and after hole doping via ozone oxidation as afunction of top gate voltage (Vtg). It is important to note thatthe operation mechanism of this top-gate WSe2 FET adheresto the principles of the MOSFET. The inset of Figure 3bpresents an optical image of the device after ozone oxidation.The on-current in p-FET operation increased from 10−7 A to10−5 A after a 10 min ozone oxidation process. Furthermore,an additional 20 min of ozone oxidation further enhanced theon-current and induced a positive Vth shift, indicating furtherhole doping and a notable reduction in contact resistance withprolonged oxidation. However, the optical contrast on theuncovered area of the WSe2 channel did not change even afterthe additional ozone oxidation, as shown in Figure S6a,suggesting that only a very small area of WSe2 was converted toWOx. This observation aligns with the previous TEMobservation.39 The subthreshold swing (SS), field-effectmobility (μFE), and contact resistance (Rc) were extractedfrom the transfer characteristics obtained after the additionalozone oxidation, as detailed in Figure S6b−e. The SS and μFEwere estimated to be ∼110 mV dec−1 and ∼37 cm2 V−1 s−1,respectively. Since Rc can be assumed as a constant valueindependent of Vtg for the top gate structure, the Y-functionmethod,45−47 which is applicable to individual two-terminaldevices with constant Rc, was employed to evaluate Rc. Usingthe Y function (Y = Id/√gm, where gm is the trans-conductance), Rc was calculated to be ∼3.7 × 102 kΩ μm.This value, while higher than initially anticipated, is notablycomparable to those obtained in our previous studies on the h-BN top-gate WSe2 FET with Au source/drain electrodes andFigure 3. (a) Schematic illustration showing the cross-sectional deviceview in the vicinity of the contact area after ozone oxidation, alongwith the corresponding electronic band diagram of 2L-WSe2 FET. (b)Id−Vtg characteristics of the 2L-WSe2 FET with sputtered Ptelectrodes, measured before and after ozone oxidation at a constantVd of 1 V at RT. The inset shows an optical image of the device afterthe second ozone oxidation.ACS Omega http://pubs.acs.org/journal/acsodf Articlehttps://doi.org/10.1021/acsomega.5c05764ACS Omega 2025, 10, 42973−4297942976https://pubs.acs.org/doi/suppl/10.1021/acsomega.5c05764/suppl_file/ao5c05764_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acsomega.5c05764/suppl_file/ao5c05764_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acsomega.5c05764/suppl_file/ao5c05764_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acsomega.5c05764/suppl_file/ao5c05764_si_001.pdfhttps://pubs.acs.org/doi/10.1021/acsomega.5c05764?fig=fig3&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsomega.5c05764?fig=fig3&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsomega.5c05764?fig=fig3&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsomega.5c05764?fig=fig3&ref=pdfhttp://pubs.acs.org/journal/acsodf?ref=pdfhttps://doi.org/10.1021/acsomega.5c05764?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashole transfer from WOx.39 Figure S7 compares the transfercharacteristics, optical images, and the extracted values of bothdevices. The comparable Rc values for Pt and Au electrodesstrongly suggest that the p-FET performance of WSe2 FETswith ozone oxidation is primarily governed by charge transferfrom WOx rather than the SBH at the metal/WSe2 interface.Interfacial density states density (Dit) distribution within theband gap of WSe2, particularly near the valence band, can beextracted from the curve fitting of the transfer characteristics.The detailed method and the result of Dit extraction aredescribed in Figure S8.In contrast, vdW contacts such as Sb2Te3/MoS2 and Bi2Te3/WSe2 have been successfully achieved through sputteringmethods.29,30 Therefore, the relation between depositiontechniques, deposited materials, and defect density generatedin 2D materials is further explored. For a more generalizeddiscussion, mechanically exfoliated 1L-MoS2 on a 90 nm SiO2/n+-Si substrate was utilized as a model 2D material, where thedefect density has been quantitatively correlated with theintensity of Raman LA(M) around 230 cm−1.48 Figure 4apresents the Raman spectra of 1L-MoS2 measured after thedeposition of various materials with a few nanometerthickness.29 All spectra are normalized to the intensity of theA1g peak except for that of the sputtered Pt sample. Regardingthe full width at half-maximum (fwhm) of the A1g peak, nosignificant differences were observed between the pristine,thermally evaporated Au, EB-evaporated Ni, and EB-evaporated Pt samples. However, the fwhms in the sputteredSb2Te3 and HfO2 samples exhibited noticeable increases, andthe peak disappeared in the Pt-sputtered sample, exhibitingbehavior similar to that observed in WSe2. To quantitativelyevaluate the defect density in 1L-MoS2,48 the relative intensityof the LA(M) peak to the A1g peak was analyzed, as shown inFigure 4b. Although the excitation wavelength (532 nm) in theoriginal study differs from that used in this study (488 nm), itis assumed that this difference does not greatly affect theresults. It should be noted that in the case of Sb2Te3 sputtering,MoS2 already contained defect states of ∼1 × 1013 cm−2 beforesputtering because it was grown by CVD, with no significantincrease in defect density after the sputtering process. Incontrast, the defect density for HfO2 sputtering was found tobe ∼2 × 1013 cm−2, nearly double that for Sb2Te3 sputtering.This discrepancy could be caused by a difference in sputteringpower. Conversely, despite the same power being used forboth HfO2 and Pt sputtering, the degree of crystal structuredegradation was significantly different. This variation may beascribed to the differing chemical reactivities of the materialsinvolved. The Gibbs free energies of formation at 300 K forvarious compounds are summarized in Figure S9.49 Nospontaneous reaction is expected between MoS2 (or WSe2)and the materials (Pt, Au, HfO2, and so on) employed in thisresearch. However, when Pt is deposited on MoS2 in thepresence of O2, the reaction MoS2 + 1/2 Pt + 2O2 (g) →MoO2 + SO2 (g) + 1/2 PtS2 is expected to occurspontaneously due to the negative Gibbs free energy change.A similar spontaneous reaction is also expected for WSe2.Given the detection of WOx and SeOx by XPS, as shown inFigure 2a,b, this reaction likely occurred, driven by the highenergy gain during sputtering. This emphasizes that residualoxygen during the sputtering of metal electrodes onto TMDCsmust be carefully controlled.■ CONCLUSIONIn this study, p-FET performance was demonstrated even inthe 1L-WSe2 FET with sputtered Pt electrodes. Variouscharacterization techniques, including XPS, PL, and Ramanspectroscopy, elucidated that the crystal structure of WSe2 wasno longer preserved, suggesting the formation of a quasi-edgecontact at the Pt/WSe2 channel. From the perspective ofsputtering applicability, the selection of deposited materials,the sputtering powers required for their deposition, and thecontrol of residual O2 are critical factors that must be carefullyconsidered.■ ASSOCIATED CONTENT*sı Supporting InformationThe Supporting Information is available free of charge athttps://pubs.acs.org/doi/10.1021/acsomega.5c05764.The deposition condition of Pt, the effect of annealingafter Pt deposition, the relationship between ΔVth andeffective SBH, the structural analysis of the reacted layerunder sputtered Pt, the reason for 2L-WSe2 selection forcontact doping by layer-by layer oxidation, analysis ofWSe2 p-FET with sputtered Pt contact after additionalFigure 4. (a) Raman spectra of 1L-MoS2 measured before and after the deposition of various materials. The spectrum for SB2Te3-sputtered MoS2 iscited from ref 29. The applied sputtering power and melting points of Pt, HfO2, and Sb2Te3 are denoted alongside. (b) Defect densities in 1L-MoS2estimated from the relative intensity of the LA(M) peak to the A1g peak. (a) Adapted from W. H. Chang et al., Adv. Electron. Mater. 2023, 9,2201091. Published under a Creative Commons Attribution License (CC BY 4.0).ACS Omega http://pubs.acs.org/journal/acsodf Articlehttps://doi.org/10.1021/acsomega.5c05764ACS Omega 2025, 10, 42973−4297942977https://pubs.acs.org/doi/suppl/10.1021/acsomega.5c05764/suppl_file/ao5c05764_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acsomega.5c05764/suppl_file/ao5c05764_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acsomega.5c05764/suppl_file/ao5c05764_si_001.pdfhttps://pubs.acs.org/doi/10.1021/acsomega.5c05764?goto=supporting-infohttps://pubs.acs.org/doi/10.1021/acsomega.5c05764?fig=fig4&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsomega.5c05764?fig=fig4&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsomega.5c05764?fig=fig4&ref=pdfhttps://pubs.acs.org/doi/10.1021/acsomega.5c05764?fig=fig4&ref=pdfhttp://pubs.acs.org/journal/acsodf?ref=pdfhttps://doi.org/10.1021/acsomega.5c05764?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-asozone oxidation, comparison to our previous researchusing evaporated Au contact, Dit extraction from curvefitting, and thermodynamics calculation betweenTMDCs and deposited materials (PDF)■ AUTHOR INFORMATIONCorresponding AuthorKosuke Nagashio − Department of Materials Engineering,The University of Tokyo, Tokyo 113-8656, Japan;orcid.org/0000-0003-1181-8644; Email: nagashio@material.t.u-tokyo.ac.jpAuthorsRyuichi Nakajima − Department of Materials Engineering,The University of Tokyo, Tokyo 113-8656, JapanTomonori Nishimura − Department of Materials Engineering,The University of Tokyo, Tokyo 113-8656, Japan;orcid.org/0000-0002-8000-5164Kaito Kanahashi − Department of Materials Engineering, TheUniversity of Tokyo, Tokyo 113-8656, Japan; orcid.org/0000-0003-2571-3384Shogo Hatayama − Semiconductor Frontier Research Center,National Institute of Advanced Industrial Science andTechnology (AIST), Ibaraki 305-8569, Japan; orcid.org/0000-0002-2914-1072Wen Hsin Chang − Semiconductor Frontier Research Center,National Institute of Advanced Industrial Science andTechnology (AIST), Ibaraki 305-8569, Japan; orcid.org/0000-0002-8501-6276Yuta Saito − Device Technology Research Institute, NationalInstitute of Advanced Industrial Science and Technology(AIST), Ibaraki 305-8569, Japan; Research Center for GreenX-tech and Department of Materials Science, TohokuUniversity, Sendai, Miyagi 980-8579, Japan; orcid.org/0000-0002-9576-1560Toshifumi Irisawa − Device Technology Research Institute,National Institute of Advanced Industrial Science andTechnology (AIST), Ibaraki 305-8569, JapanKeiji Ueno − Department of Chemistry, Saitama University,Saitama 338-8570, JapanYasumitsu Miyata − Department of Physics, TokyoMetropolitan University, Tokyo 192-0397, Japan; ResearchCenter for Materials Nanoarchitectonics, National Institutefor Materials Science, Ibaraki 305-0044, Japan;orcid.org/0000-0002-9733-5119Takashi Taniguchi − Research Center for MaterialsNanoarchitectonics, National Institute for Materials Science,Ibaraki 305-0044, Japan; orcid.org/0000-0002-1467-3105Kenji Watanabe − Research Center for Electronic and OpticalMaterials, National Institute for Materials Science, Ibaraki305-0044, Japan; orcid.org/0000-0003-3701-8119Complete contact information is available at:https://pubs.acs.org/10.1021/acsomega.5c05764NotesThe authors declare no competing financial interest.■ ACKNOWLEDGMENTSThis research was supported by the JSPS KAKENHI (GrantNumbers: JP21H05237, JP21H05236, JP21H05232,JP21H05233, JP21K04826, JP22H04957, JP22K04212,JP22H05445, JP23K23243, JP23K02052, JP23K26745, andJP24K08195), the NICT (Grant Number: 05901), the JST-Mirai Program (Grant Number: JPMJMI22708192), the JSTCREST (Grant Number: JPMJCR23A4, JPMJCR24A3, andJPMJCR24A5), the JST FOREST Program (Grant NumberJPMJFR213X), and the World Premier International ResearchCenter Initiative (WPI), MEXT, Japan.■ REFERENCES(1) Ago, H.; Okada, S.; Miyata, Y.; Matsuda, K.; Koshino, M.; Ueno,K.; Nagashio, K. Science of 2.5 Dimensional Materials: Paradigm Shiftof Materials Science toward Future Social Innovation. Sci. Technol.Adv. Mater. 2022, 23 (1), 275−299.(2) Akinwande, D.; Huyghebaert, C.; Wang, C.-H.; Serna, M. I.;Goossens, S.; Li, L.-J.; Wong, H.-S. P.; Koppens, F. H. L. Grapheneand Two-Dimensional Materials for Silicon Technology. Nature 2019,573 (7775), 507−518.(3) Desai, S. B.; Madhvapathy, S. R.; Sachid, A. B.; Llinas, J. P.;Wang, Q.; Ahn, G. H.; Pitner, G.; Kim, M. J.; Bokor, J.; Hu, C.; Wong,H.-S. P.; Javey, A. MoS2 Transistors with 1-Nanometer Gate Lengths.Science 2016, 354 (6308), 99−102.(4) Uchiyama, H.; Maruyama, K.; Chen, E.; Nishimura, T.;Nagashio, K. A Monolayer MoS2 FET with an EOT of 1.1 NmAchieved by the Direct Formation of a High-κ Er2O3 InsulatorThrough Thermal Evaporation. Small 2023, 19 (15), 2207394.(5) Li, W.; Zhou, J.; Cai, S.; Yu, Z.; Zhang, J.; Fang, N.; Li, T.; Wu,Y.; Chen, T.; Xie, X.; Ma, H.; Yan, K.; Dai, N.; Wu, X.; Zhao, H.;Wang, Z.; He, D.; Pan, L.; Shi, Y.; Wang, P.; Chen, W.; Nagashio, K.;Duan, X.; Wang, X. Uniform and Ultrathin High-κ Gate Dielectricsfor Two-Dimensional Electronic Devices. Nat. Electron. 2019, 2 (12),563−571.(6) Houssa, M.; Dimoulas, A.; Molle, A.. In 2D Materials forNanoelectronics; Houssa, M., Dimoulas, A., Molle, A., Eds.; CRCPress, 2016.(7) Fang, N.; Nagashio, K. Accumulation-Mode Two-DimensionalField-Effect Transistor: Operation Mechanism and Thickness ScalingRule. ACS Appl. Mater. Interfaces 2018, 10 (38), 32355−32364.(8) Das, S.; Chen, H.-Y.; Penumatcha, A. V.; Appenzeller, J. HighPerformance Multilayer MoS2 Transistors with Scandium Contacts.Nano Lett. 2013, 13 (1), 100−105.(9) Kim, C.; Moon, I.; Lee, D.; Choi, M. S.; Ahmed, F.; Nam, S.;Cho, Y.; Shin, H.-J.; Park, S.; Yoo, W. J. Fermi Level Pinning atElectrical Metal Contacts of Monolayer Molybdenum Dichalcoge-nides. ACS Nano 2017, 11 (2), 1588−1596.(10) Liu, Y.; Guo, J.; Zhu, E.; Liao, L.; Lee, S.-J.; Ding, M.; Shakir, I.;Gambin, V.; Huang, Y.; Duan, X. Approaching the Schottky−MottLimit in van Der Waals Metal−Semiconductor Junctions. Nature2018, 557 (7707), 696−700.(11) Sotthewes, K.; van Bremen, R.; Dollekamp, E.; Boulogne, T.;Nowakowski, K.; Kas, D.; Zandvliet, H. J. W.; Bampoulis, P. UniversalFermi-Level Pinning in Transition-Metal Dichalcogenides. J. Phys.Chem. C 2019, 123 (9), 5411−5420.(12) Michaelson, H. B. The Work Function of the Elements and ItsPeriodicity. J. Appl. Phys. 1977, 48 (11), 4729−4733.(13) Ni, Z. H.; Wang, H. M.; Ma, Y.; Kasim, J.; Wu, Y. H.; Shen, Z.X. Tunable Stress and Controlled Thickness Modification inGraphene by Annealing. ACS Nano 2008, 2 (5), 1033−1039.(14) Qiu, X. P.; Shin, Y. J.; Niu, J.; Kulothungasagaran, N.; Kalon,G.; Qiu, C.; Yu, T.; Yang, H. Disorder-Free Sputtering Method onGraphene. AIP Adv. 2012, 2 (3), 032121.(15) Shi, W.; Lin, M.-L.; Tan, Q.-H.; Qiao, X.-F.; Zhang, J.; Tan, P.-H. Raman and Photoluminescence Spectra of Two-DimensionalNanocrystallites of Monolayer WS2 and WSe2. 2d Mater. 2016, 3 (2),025016.(16) Wu, Z.; Zhao, W.; Jiang, J.; Zheng, T.; You, Y.; Lu, J.; Ni, Z.Defect Activated Photoluminescence in WSe2 Monolayer. J. Phys.Chem. C 2017, 121 (22), 12294−12299.ACS Omega http://pubs.acs.org/journal/acsodf Articlehttps://doi.org/10.1021/acsomega.5c05764ACS Omega 2025, 10, 42973−4297942978https://pubs.acs.org/doi/suppl/10.1021/acsomega.5c05764/suppl_file/ao5c05764_si_001.pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Kosuke+Nagashio"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://orcid.org/0000-0003-1181-8644https://orcid.org/0000-0003-1181-8644mailto:nagashio@material.t.u-tokyo.ac.jpmailto:nagashio@material.t.u-tokyo.ac.jphttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Ryuichi+Nakajima"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Tomonori+Nishimura"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://orcid.org/0000-0002-8000-5164https://orcid.org/0000-0002-8000-5164https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Kaito+Kanahashi"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://orcid.org/0000-0003-2571-3384https://orcid.org/0000-0003-2571-3384https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Shogo+Hatayama"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://orcid.org/0000-0002-2914-1072https://orcid.org/0000-0002-2914-1072https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Wen+Hsin+Chang"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://orcid.org/0000-0002-8501-6276https://orcid.org/0000-0002-8501-6276https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Yuta+Saito"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://orcid.org/0000-0002-9576-1560https://orcid.org/0000-0002-9576-1560https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Toshifumi+Irisawa"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Keiji+Ueno"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Yasumitsu+Miyata"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://orcid.org/0000-0002-9733-5119https://orcid.org/0000-0002-9733-5119https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Takashi+Taniguchi"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://orcid.org/0000-0002-1467-3105https://orcid.org/0000-0002-1467-3105https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Kenji+Watanabe"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://orcid.org/0000-0003-3701-8119https://pubs.acs.org/doi/10.1021/acsomega.5c05764?ref=pdfhttps://doi.org/10.1080/14686996.2022.2062576https://doi.org/10.1080/14686996.2022.2062576https://doi.org/10.1038/s41586-019-1573-9https://doi.org/10.1038/s41586-019-1573-9https://doi.org/10.1126/science.aah4698https://doi.org/10.1002/smll.202207394https://doi.org/10.1002/smll.202207394https://doi.org/10.1002/smll.202207394https://doi.org/10.1038/s41928-019-0334-yhttps://doi.org/10.1038/s41928-019-0334-yhttps://doi.org/10.1021/acsami.8b10687?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acsami.8b10687?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acsami.8b10687?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/nl303583v?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/nl303583v?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acsnano.6b07159?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acsnano.6b07159?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acsnano.6b07159?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1038/s41586-018-0129-8https://doi.org/10.1038/s41586-018-0129-8https://doi.org/10.1021/acs.jpcc.8b10971?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acs.jpcc.8b10971?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1063/1.323539https://doi.org/10.1063/1.323539https://doi.org/10.1021/nn800031m?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/nn800031m?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1063/1.4739783https://doi.org/10.1063/1.4739783https://doi.org/10.1088/2053-1583/3/2/025016https://doi.org/10.1088/2053-1583/3/2/025016https://doi.org/10.1021/acs.jpcc.7b03585?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttp://pubs.acs.org/journal/acsodf?ref=pdfhttps://doi.org/10.1021/acsomega.5c05764?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as(17) Telkhozhayeva, M.; Girshevitz, O. Roadmap toward ControlledIon Beam-Induced Defects in 2D Materials. Adv. Funct. Mater. 2024,34 (45), 2404615.(18) Tosun, M.; Chuang, S.; Fang, H.; Sachid, A. B.; Hettick, M.;Lin, Y.; Zeng, Y.; Javey, A. High-Gain Inverters Based on WSe2Complementary Field-Effect Transistors. ACS Nano 2014, 8 (5),4948−4953.(19) Lee, I.; Rathi, S.; Li, L.; Lim, D.; Atif Khan, M.; Kannan, E. S.;Kim, G.-H. Non-Degenerate n-Type Doping by Hydrazine Treatmentin Metal Work Function Engineered WSe2 Field-Effect Transistor.Nanotechnology 2015, 26 (45), 455203.(20) Yu, L.; Zubair, A.; Santos, E. J. G.; Zhang, X.; Lin, Y.; Zhang,Y.; Palacios, T. High-Performance WSe2 Complementary Metal OxideSemiconductor Technology and Integrated Circuits. Nano Lett. 2015,15 (8), 4928−4934.(21) Jo, S.; Kang, D.; Shim, J.; Jeon, J.; Jeon, M. H.; Yoo, G.; Kim, J.;Lee, J.; Yeom, G. Y.; Lee, S.; Yu, H.; Choi, C.; Park, J. A High-Performance WSe2/h-BN Photodetector Using a Triphenylphosphine(PPh3)-Based N-Doping Technique. Adv. Mater. 2016, 28 (24),4824−4831.(22) Ma, Z.; Zhang, L.; Zhou, C.; Chan, M. High Current Nb-Doped P-Channel MoS2 Field-Effect Transistor Using Pt Contact.IEEE Electron Device Lett. 2021, 42 (3), 343−346.(23) Li, S.; Wu, Q.; Ding, H.; Wu, S.; Cai, X.; Wang, R.; Xiong, J.;Lin, G.; Huang, W.; Chen, S.; Li, C. High Gain, Broadband p-WSe2/n-Ge van Der Waals Heterojunction Phototransistor with a SchottkyBarrier Collector. Nano Res. 2023, 16 (4), 5796−5802.(24) Patoary, N. H.; Xie, J.; Zhou, G.; Al Mamun, F.; Sayyad, M.;Tongay, S.; Esqueda, I. S. Improvements in 2D P-Type WSe2Transistors towards Ultimate CMOS Scaling. Sci. Rep. 2023, 13(1), 3304.(25) Takeyama, K.; Moriya, R.; Watanabe, K.; Masubuchi, S.;Taniguchi, T.; Machida, T. Low-Temperature p-Type Ohmic Contactto WSe2 Using p+-MoS2/WSe2 van Der Waals Interface. Appl. Phys.Lett. 2020, 117 (15), 153101.(26) Movva, H. C. P.; Rai, A.; Kang, S.; Kim, K.; Fallahazad, B.;Taniguchi, T.; Watanabe, K.; Tutuc, E.; Banerjee, S. K. High-MobilityHoles in Dual-Gated WSe2 Field-Effect Transistors. ACS Nano 2015,9 (10), 10402−10410.(27) Nazir, G.; Kim, H.; Kim, J.; Kim, K. S.; Shin, D. H.; Khan, M.F.; Lee, D. S.; Hwang, J. Y.; Hwang, C.; Suh, J.; Eom, J.; Jung, S.Ultimate Limit in Size and Performance of WSe2 Vertical Diodes. Nat.Commun. 2018, 9 (1), 5371.(28) Wang, Y.; Kim, J. C.; Li, Y.; Ma, K. Y.; Hong, S.; Kim, M.; Shin,H. S.; Jeong, H. Y.; Chhowalla, M. P-Type Electrical Contacts for 2DTransition-Metal Dichalcogenides. Nature 2022, 610 (7930), 61−66.(29) Chang, W. H.; Hatayama, S.; Saito, Y.; Okada, N.; Endo, T.;Miyata, Y.; Irisawa, T. Sb2Te3/MoS2 Van Der Waals Junctions withHigh Thermal Stability and Low Contact Resistance. Adv. ElectronMater. 2023, 9 (4), 2201091.(30) Chang, W. H.; Hatayama, S.; Saito, Y.; Okada, N.; Endo, T.;Miyata, Y.; Irisawa, T. Thermally Stable Bi2Te3/WSe2 Van Der WaalsContacts for PMOSFETs Application. Sci. Rep. 2024, 14 (1), 28572.(31) Hsu, C.; Frisenda, R.; Schmidt, R.; Arora, A.; de Vasconcellos,S. M.; Bratschitsch, R.; van der Zant, H. S. J.; Castellanos-Gomez, A.Thickness-Dependent Refractive Index of 1L, 2L, and 3L MoS2,MoSe2, WS2, and WSe2. Adv. Opt. Mater. 2019, 7 (13), 1900239.(32) Guo, Y.; Robertson, J. Band Engineering in Transition MetalDichalcogenides: Stacked versus Lateral Heterostructures. Appl. Phys.Lett. 2016, 108 (23), 233104.(33) Jaegermann, W.; Schmeisser, D. Reactivity of Layer TypeTransition Metal Chalcogenides towards Oxidation. Surf. Sci. 1986,165 (1), 143−160.(34) Smyth, C. M.; Addou, R.; McDonnell, S.; Hinkle, C. L.;Wallace, R. M. WSe2-Contact Metal Interface Chemistry and BandAlignment under High Vacuum and Ultra High Vacuum DepositionConditions. 2d Mater. 2017, 4 (2), 025084.(35) Luo, X.; Zhao, Y.; Zhang, J.; Toh, M.; Kloc, C.; Xiong, Q.;Quek, S. Y. Effects of Lower Symmetry and Dimensionality on RamanSpectra in Two-Dimensional WSe2. Phys. Rev. B 2013, 88 (19),195313.(36) Wang, G.; Bouet, L.; Lagarde, D.; Vidal, M.; Balocchi, A.;Amand, T.; Marie, X.; Urbaszek, B. Valley Dynamics Probed throughCharged and Neutral Exciton Emission in Monolayer WSe2. Phys. Rev.B 2014, 90 (7), 075413.(37) Jones, A. M.; Yu, H.; Ross, J. S.; Klement, P.; Ghimire, N. J.;Yan, J.; Mandrus, D. G.; Yao, W.; Xu, X. Spin-Layer Locking Effects inOptical Orientation of Exciton Spin in Bilayer WSe2. Nat. Phys. 2014,10 (2), 130−134.(38) Ngo, T. D.; Choi, M. S.; Lee, M.; Ali, F.; Yoo, W. J.Anomalously Persistent P-Type Behavior of WSe2 Field-EffectTransistors by Oxidized Edge-Induced Fermi-Level Pinning. J.Mater. Chem. C Mater. 2022, 10 (3), 846−853.(39) Kato, R.; Uchiyama, H.; Nishimura, T.; Ueno, K.; Taniguchi,T.; Watanabe, K.; Chen, E.; Nagashio, K. P-Type Conversion of WS2and WSe2 by Position-Selective Oxidation Doping and Its Applicationin Top Gate Transistors. ACS Appl. Mater. Interfaces 2023, 15 (22),26977−26984.(40) Ji, H. G.; Solís-Fernández, P.; Yoshimura, D.; Maruyama, M.;Endo, T.; Miyata, Y.; Okada, S.; Ago, H. Chemically Tuned P-and N-Type WSe2 Monolayers with High Carrier Mobility for AdvancedElectronics. Adv. Mater. 2019, 31 (42), 1903613.(41) Yamamoto, M.; Dutta, S.; Aikawa, S.; Nakaharai, S.;Wakabayashi, K.; Fuhrer, M. S.; Ueno, K.; Tsukagoshi, K. Self-Limiting Layer-by-Layer Oxidation of Atomically Thin WSe2. NanoLett. 2015, 15 (3), 2067−2073.(42) Yamamoto, M.; Nakaharai, S.; Ueno, K.; Tsukagoshi, K. Self-Limiting Oxides on WSe2 as Controlled Surface Acceptors and Low-Resistance Hole Contacts. Nano Lett. 2016, 16 (4), 2720−2727.(43) He, J.; Fang, N.; Nakamura, K.; Ueno, K.; Taniguchi, T.;Watanabe, K.; Nagashio, K. 2D Tunnel Field Effect Transistors(FETs) with a Stable Charge-Transfer-Type p+-WSe2 Source. Adv.Electron Mater. 2018, 4 (7), 1800207.(44) Greiner, M. T.; Lu, Z.-H. Thin-Film Metal Oxides in OrganicSemiconductor Devices: Their Electronic Structures, Work Functionsand Interfaces. NPG Asia Mater. 2013, 5 (7), No. e55.(45) Ghibaudo, G. New Method for the Extraction of MOSFETParameters. Electron. Lett. 1988, 24 (9), 543−545.(46) Chang, H.-Y.; Zhu, W.; Akinwande, D. On the Mobility andContact Resistance Evaluation for Transistors Based on MoS2 orTwo-Dimensional Semiconducting Atomic Crystals. Appl. Phys. Lett.2014, 104 (11), 113504.(47) Liu, C.; Xu, Y.; Noh, Y.-Y. Contact Engineering in OrganicField-Effect Transistors. Mater. Today 2015, 18 (2), 79−96.(48) Mignuzzi, S.; Pollard, A. J.; Bonini, N.; Brennan, B.; Gilmore, I.S.; Pimenta, M. A.; Richards, D.; Roy, D. Effect of Disorder on RamanScattering of Single-Layer MoS2. Phys. Rev. B 2015, 91 (19), 195411.(49) Chang, Y.-R.; Nishimura, T.; Nagashio, K. ThermodynamicPerspective on the Oxidation of Layered Materials and Surface OxideAmelioration in 2D Devices. ACS Appl. Mater. Interfaces 2021, 13(36), 43282−43289.ACS Omega http://pubs.acs.org/journal/acsodf Articlehttps://doi.org/10.1021/acsomega.5c05764ACS Omega 2025, 10, 42973−4297942979https://doi.org/10.1002/adfm.202404615https://doi.org/10.1002/adfm.202404615https://doi.org/10.1021/nn5009929?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/nn5009929?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1088/0957-4484/26/45/455203https://doi.org/10.1088/0957-4484/26/45/455203https://doi.org/10.1021/acs.nanolett.5b00668?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acs.nanolett.5b00668?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1002/adma.201600032https://doi.org/10.1002/adma.201600032https://doi.org/10.1002/adma.201600032https://doi.org/10.1109/LED.2021.3056178https://doi.org/10.1109/LED.2021.3056178https://doi.org/10.1007/s12274-022-5081-0https://doi.org/10.1007/s12274-022-5081-0https://doi.org/10.1007/s12274-022-5081-0https://doi.org/10.1038/s41598-023-30317-4https://doi.org/10.1038/s41598-023-30317-4https://doi.org/10.1063/5.0016468https://doi.org/10.1063/5.0016468https://doi.org/10.1021/acsnano.5b04611?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acsnano.5b04611?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1038/s41467-018-07820-8https://doi.org/10.1038/s41586-022-05134-whttps://doi.org/10.1038/s41586-022-05134-whttps://doi.org/10.1002/aelm.202201091https://doi.org/10.1002/aelm.202201091https://doi.org/10.1038/s41598-024-79750-zhttps://doi.org/10.1038/s41598-024-79750-zhttps://doi.org/10.1002/adom.201900239https://doi.org/10.1002/adom.201900239https://doi.org/10.1063/1.4953169https://doi.org/10.1063/1.4953169https://doi.org/10.1016/0039-6028(86)90666-7https://doi.org/10.1016/0039-6028(86)90666-7https://doi.org/10.1088/2053-1583/aa6beahttps://doi.org/10.1088/2053-1583/aa6beahttps://doi.org/10.1088/2053-1583/aa6beahttps://doi.org/10.1103/PhysRevB.88.195313https://doi.org/10.1103/PhysRevB.88.195313https://doi.org/10.1103/PhysRevB.90.075413https://doi.org/10.1103/PhysRevB.90.075413https://doi.org/10.1038/nphys2848https://doi.org/10.1038/nphys2848https://doi.org/10.1039/D1TC04148Ghttps://doi.org/10.1039/D1TC04148Ghttps://doi.org/10.1021/acsami.3c04052?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acsami.3c04052?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acsami.3c04052?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1002/adma.201903613https://doi.org/10.1002/adma.201903613https://doi.org/10.1002/adma.201903613https://doi.org/10.1021/nl5049753?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/nl5049753?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acs.nanolett.6b00390?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acs.nanolett.6b00390?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acs.nanolett.6b00390?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1002/aelm.201800207https://doi.org/10.1002/aelm.201800207https://doi.org/10.1038/am.2013.29https://doi.org/10.1038/am.2013.29https://doi.org/10.1038/am.2013.29https://doi.org/10.1049/el:19880369https://doi.org/10.1049/el:19880369https://doi.org/10.1063/1.4868536https://doi.org/10.1063/1.4868536https://doi.org/10.1063/1.4868536https://doi.org/10.1016/j.mattod.2014.08.037https://doi.org/10.1016/j.mattod.2014.08.037https://doi.org/10.1103/PhysRevB.91.195411https://doi.org/10.1103/PhysRevB.91.195411https://doi.org/10.1021/acsami.1c13279?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acsami.1c13279?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://doi.org/10.1021/acsami.1c13279?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttp://pubs.acs.org/journal/acsodf?ref=pdfhttps://doi.org/10.1021/acsomega.5c05764?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as