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[Chia‐Hung Wu](https://orcid.org/0000-0003-4489-3050), Chi‐Wen Chen, Hung‐Jung Shen, Hsiang‐Yu Chuang, [Hark Hoe Tan](https://orcid.org/0000-0002-7816-537X), [Chennupati Jagadish](https://orcid.org/0000-0003-1528-9479), [Tien‐Chang Lu](https://orcid.org/0000-0003-4192-9919), [Satoshi Ishii](https://orcid.org/0000-0003-0731-8428), [Kuo‐Ping Chen](https://orcid.org/0000-0001-6256-9145)

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[Reversible Carrier Modulation in InP Nanolasers by Ionic Liquid Gating with Low Energy Consumption](https://mdr.nims.go.jp/datasets/324eb143-1e7e-4151-a15b-5bd567707cbc)

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Reversible Carrier Modulation in InP Nanolasers by Ionic Liquid Gating with Low Energy ConsumptionRESEARCH ARTICLEwww.advancedscience.comReversible Carrier Modulation in InP Nanolasers by IonicLiquid Gating with Low Energy ConsumptionChia-Hung Wu, Chi-Wen Chen, Hung-Jung Shen, Hsiang-Yu Chuang, Hark Hoe Tan,Chennupati Jagadish, Tien-Chang Lu, Satoshi Ishii, and Kuo-Ping Chen*Nanoscale light sources are demanded vigorously due to rapid developmentin photonic integrated circuits (PICs). III-V semiconductor nanowire (NW)lasers have manifested themselves as indispensable components in this field,associated with their extremely compact footprint and ultra-high optical gainwithin the 1D cavity. In this study, the carrier concentrations of indiumphosphide (InP) NWs are actively controlled to modify their emissiveproperties at room temperature. The InP NW lasers can achieve repetitiveswitching between photoluminescence (PL) and lasing with an extinction ratioof 22-fold by applying a gate voltage of 3 V using ionic liquid (IL) as a dielectriclayer. IL brings forth ultra-high capacitance due to the nanometer-wide electricdouble layer (EDL) between interfaces, mapping out gating efficiency of≈100-fold compared to the conventional bottom gate configurations. ThisIL-embedded nanolaser device can be a promising platform for the advancedintegrated nanophotonic system.1. IntroductionIII-V semiconductor nanowires (NWs) have been studied to agreat extent due to their extremely small footprint and capabil-ity of enabling strong light-matter interaction. Thus, promotingthemselves to become an indispensable piece in photoelectronicapplications, such as memory device,[1] photovoltaics, and quan-tum computing.[2–8] Semiconductor with its high refractive indexand in the geometry of a subwavelength wire, offers light to beC.-H. Wu, K.-P. ChenCollege of PhotonicsNational Yang Ming Chiao Tung University301 Gaofa 3rd Road, Tainan 71150, TaiwanE-mail: kpchen@ee.nthu.edu.twC.-H. Wu, S. IshiiInternational Center for Materials Nanoarchitectonics (MANA)National Institute for Materials Science (NIMS)1-1 Namiki, Tsukuba, Ibaraki 305-0044, JapanThe ORCID identification number(s) for the author(s) of this articlecan be found under https://doi.org/10.1002/advs.202412340© 2024 The Author(s). Advanced Science published by Wiley-VCHGmbH. This is an open access article under the terms of the CreativeCommons Attribution License, which permits use, distribution andreproduction in any medium, provided the original work is properly cited.DOI: 10.1002/advs.202412340confined in a 2D guided mode along thewire axis. The end facets of the nanowireprovide large optical gain and form theFabrey-Perot laser cavity, introducing ananoscale coherent light source.To meet the demand for high-speed datatransmission with low energy consump-tion, two types of approaches have beentaken; one is the down-scaling of inte-grated circuits to break Moore’s Law[9] andthe other is alternative signal transmissionparadigms like quantum communicationand photoelectronic chips.[10,11] However,past studies on photoelectronic integratedcircuits rely on external light sources whichare typically fiber-coupled lasers resultingin size incompatibility with chips becomingeven smaller.Nanowire laser with its extremely smallfootprint, furnishes nano/micro-scalewaveguiding,[12–15] supports multimoderesonance, and provides a coherent light source in thenanoscale.[16–21] Additionally, carrier dynamics in NWs is a cru-cial topic as it directly influences the optical and electronic prop-erties of the material. Modulations of NW lasers have beenexplored by techniques such as chemical doping during thegrowth process,[22] 2D material integrated heterostructures,[23]and electro-doping with gating.[24] However, the first two tech-niques are irreversible after sample fabrication. The gatingC.-W. ChenInstitute of Photonic SystemCollege of PhotonicsNational Yang Ming Chiao Tung University301 Gaofa 3rd Road, Tainan 71150, TaiwanH.-J. Shen, H.-Y. Chuang, K.-P. ChenInstitute of Photonics TechnologiesNational Tsing Hua UniversityHsinchu 300, TaiwanH. H. Tan, C. JagadishARC Centre of Excellence for Transformative Meta-Optical SystemsDepartment of Electronic Materials EngineeringResearch School of PhysicsThe Australian National UniversityCanberra, ACT 2600, AustraliaT.-C. LuDepartment of PhotonicsCollege of Electrical and Computer EngineeringNational Yang Ming Chiao Tung UniversityHsinchu 30010, TaiwanAdv. Sci. 2025, 12, 2412340 2412340 (1 of 8) © 2024 The Author(s). Advanced Science published by Wiley-VCH GmbHhttp://www.advancedscience.commailto:kpchen@ee.nthu.edu.twhttps://doi.org/10.1002/advs.202412340http://creativecommons.org/licenses/by/4.0/http://creativecommons.org/licenses/by/4.0/http://crossmark.crossref.org/dialog/?doi=10.1002%2Fadvs.202412340&domain=pdf&date_stamp=2024-12-16www.advancedsciencenews.com www.advancedscience.commethod like back and top-gating requires high power consump-tion (i.e., high gate voltage (VGS)) and complex designs to fabri-cate the insulating layer for NWs modulation. Commonly knownoxides for the insulating layer applied in field effect transistors(FETs) such as SiO2, Al2O3, and HfO2 typically require high-temperature fabrication, hindering broad applications such asflexible devices based on plastic substrates. Another solid-stategating design is the wrap-gate,[25,26] where a thin insulating layeris wrapped around the nanowire using atomic layer deposition(ALD) to prevent leakage. Metal is then wrapped around thenanowire to increase the contact area, significantly enhancinggating efficiency. This configuration is particularly effective foruniaxial nanowire systems, providing a sixfold improvement overplain back-gate setups for hexagonal nanowires. Solid-state gat-ing delivers stable and fast electrical switching. However, thehigh cost of fabrication, the required transparent electrodes likegraphene and ITO for optical applications, and the low yield ratehighlight the need for alternative approaches.Ionic liquids (ILs) can manipulate the electrical properties ofdevices by the organization and accumulation of ions. With ILs,a more energy-efficient and simplified approach to device modu-lation can be achieved. A key element steering the functionalitiesof these devices is through the electric double layer (EDL) formedat the liquid-solid (target material) interface.[27] Previously, Wanget al. have proposed that EDL formation is a two-step process.[28]In the first step, for the liquid-solid case, molecules in the solu-tion approach collide with the solid surface due to liquid pres-sure. This forms a strong electron cloud overlap between the so-lution and the originally neutral solid surface, leading to electrontransfer and ion bonding. In the second step, the charged surfaceof the solid may attract ions of opposite polarity in the solutiondue to electrostatic force, forming the EDL. To employ this phe-nomenon in semiconductor devices, an external electric field isapplied to emphasize the migration of the ions, actively trans-ferring the designated charges to the target material. For exam-ple, when positive bias is applied to the gate electrode, anionsin the IL migrate and accumulate at the gate terminal. In con-trast, the cations repel from the gate and accumulate around thesource terminal, forming EDLs at each interface, and inducingn-type doping of the semiconductor. This induces an ultra-highcapacitance of up to several μF•cm−2 across a few nanometer-thick EDLs. Thus, it is possible to modify the semiconductor’selectrical properties with minimal energy consumption.In this work, a simple three-step fabrication method wasdemonstrated to actively modulate carrier concentration at a lowvoltage in indium phosphide (InP) NW lasers, using IL as thegate dielectric. The modulation was investigated and interpretedthrough the threshold and wavelength shifts of InP NW lasers’stimulated emission. Two devices were fabricated and studied inthis manuscript; one is a silicon-based substrate with InP NW ona graphene channel, and the other is a glass substrate with twogold electrodes and InP NW on one of them. Graphene, char-acterized by its semi-metallic, flexibility, atomic thickness, andtransparent properties, has been verified as an exceptional can-didate for the development of wearable or transparent devices.Additionally, the resistivity of graphene is known to be sensitiveto carrier concentration change throughout the channel. Leverag-ing the abovementioned characteristics, graphene has been em-ployed as both a transparent electrode and a monitoring tool todetect variations in ion distribution surrounding the channel inthe proposed device. As previously mentioned, doping was in-duced under gate bias as the IL forms an EDL around the InPNWs at the source terminal. The n-type doping of InP NW causesa donor band (ED) to form in the vicinity of the conduction band(EC). At room temperature (≈300 K), these excess electrons in theED received ≈25.85 meV propelling potential to a higher energystate, eventually filling up the conduction band (CB). A fractionof the excess electrons and carriers excited from the valence band(VB) due to radiation above the bandgap may enter a miniband,inducing population inversion at a lower pumping power leadingto a threshold decrease for stimulated emission. As these carri-ers recombine from a higher energy level state, the radiation lossduring recombination exhibited higher photon energy, leading toa blue shift in the lasing peak. The collective occurrence of thesephenomena is known as the Moss-Burstein effect.[23,29] Overall,utilizing ILs as gate dielectrics yielded advantages in propertiessuch as high capacitance, low energy consumption, transparency,and compatibility with flexible devices. The proposed concept ofintegrating IL gating with NW lasers facilitates straightforwardmodulation and simple fabrication, positioning itself as advanta-geous for the optoelectronic industry.2. Results and Discussion2.1. Device Fabrication and NW Emissive PropertiesA schematic diagram of the proposed devices is shown in Figure1a,b. The silicon photonics-compatible device is marked as De-vice A (Figure 1a) and the semi-transparent device is markedas Device B (Figure 1b) throughout this manuscript. In deviceA, 300 nm of SiO2 was deposited on a silicon substrate. Thegraphene channel was formed by oxygen plasma etching for 40s after the chemical vapor deposition (CVD) grown graphenesheet was transferred to the target position,[30] which is detailedin Methods. Graphene in the device monitored the gating of theIL and may be seen as an extension of the source electrode, thussimplifying the transfer steps of the InP nanowires. Becauseof its mechanical stability and interfacial van der Waals forceintroducing strong adhesion to the substrate, graphene couldwithstand the polydimethylsiloxane (PDMS) stamping transfermethod of InP NWs. The drain, source, and gate electrodes were100 nm gold deposited by thermal deposition with a shadowmask as depicted in Figure 1a. InP NWs were transferred ontothe designated location of the graphene channel by a home-built transfer system (See Figure S2, Supporting Information).Finally, to form an IL layer, 1 μL of 1-Ethyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide (EMIM-TFSI) was drop castonto the sample and encapsulated the liquid with a cover glass toavoid droplet formation. IL is in contact with the gate and source(graphene) electrodes as shown in Figure 1a. The NW located onthe graphene channel was pointed out with an arrow in Figure 1c.Device B was proposed to show the tunable NW laser could beuniversally applied with just a simple fabrication. As shown inFigure 1b, the gate and source electrodes were 100 nm gold madeby a shadow mask and thermal deposition. Because the depositedgold can be ruined during the PDMS stamping process, the InPNWs were transferred to a region adjacent to the source terminal,and then carefully pushed onto the electrode (Figure 1c) with aAdv. Sci. 2025, 12, 2412340 2412340 (2 of 8) © 2024 The Author(s). Advanced Science published by Wiley-VCH GmbH 21983844, 2025, 8, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/advs.202412340 by National Institute For, Wiley Online Library on [01/05/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.advancedscience.comwww.advancedsciencenews.com www.advancedscience.comFigure 1. Schematic and emission profile of the device. a,b) Schematic of the IL gate NW setups. Sub-panel (a) shows a NW on a graphene with asilicon platform (Device A). Sub-panel (b) shows a universally applicable form of IL-gated InP NW laser based on a glass substrate (Device B). c) Opticalmicroscope image of NWs on the graphene channel in Device A. The characterized NW was indicated with a yellow arrow. d) Optical microscope imageof an InP NW on the source electrode of Device B. e) Stimulated emission spectrum of NW in Device A. Inset: Far-field emission polarization of the NW.micro-manipulator that is typically used for TEM sample pick-ups. (See Figure S3, Supporting Information for NW locationmanipulating.) The IL layer was encapsulated with a cover glassto form a gating system. The laser spectral profile of the NW isshown in Figure 1d. According to Figure 1d inset, the emission ispolarized normally to the NWs, indicating the excitation of pho-tonic modes.[16,31]2.2. Characterization and Modal Analysis of InP NWsThe crystal structures of IP NWs are known to be sensitive togrowth conditions;[32,33] they can be either Zinc Blende (ZB) orWurtzite (WZ). Emission properties of different crystal forma-tions InP NWs show significant disparity.[34–36] Thus, it is essen-tial to study the characteristics of the NWs before consideringtheir applications. The SEM image of the NW on graphene isshown in Figure 2a. From the SEM images, the selected NWsfor Devices A and B have a length (lNW) and diameter of ≈13 μmand ≈600 nm, respectively. The modal analysis provides a betterunderstanding of the system supporting rational design. Experi-mental group index ng of the IL-gated NW system was extractedfrom the lasing wavelength. 𝜆lasing, mode spacing Δ𝜆 and cavitylength lNW where ng =𝜆lasing22⋅Δ𝜆⋅lNW. In Device A, the InP nanowire(NW) is immersed in ionic liquid, the lasing wavelength 𝜆lasingis found to be 881 nm, and the mode spacing Δ𝜆 is measuredat 5.7 nm, as provided in Figure S6b (Supporting Information).From these data, a group index ng of 5.23 is calculated. Finite Dif-ference Eigenmode Solver (FDE) mode analysis was conducted,with the simulation background refractive index set to 1.42 asthe NW is immersed in IL. The computed field profile, as illus-trated in Figure 2b, shows that the NW operates in the photonicmode, with substantial field confinement near the InP NW edge.This fits our system design as the electric double-layer inducedcarriers are pronounced and limited to the subsurface depth ofthe NW. For crystallographic analysis, TEM images of the NWsare shown in Figure 2c,d. To prepare TEM samples, platinumwas coated on the InP NW for protection and thinned down to≈50 nm in the axial direction with a focused ion beam (FIB). Theselected-area electron diffraction (SAED) pattern and TEM anal-ysis confirm that the NW was a single crystal, and the structurewas WZ as shown in Figure 2d inset. The lattice constant wasmeasured to be ≈6.7 Å, which was in good agreement with theprevious studies on WZ InP.[37,38]2.3. Comparison Between IL and Backside Gated ConfigurationsIn Figure 3, we compare the gating efficiency difference betweenbackside gating and IL gating methods via graphene. It is wellknown that graphene exhibits the highest channel resistancewhen the doping level is at the Dirac point.[39,40] As a semi-metal,once the graphene Fermi level is displaced into the conductionor the VB, more free electrical carriers may contribute to the cur-rent flow when applied to an external electric field, introducing alowering of channel resistance. In Figure 3a,c insets show the ILand backside gating method schematics respectively. The IL gat-ing active region was formed by the electric double layer (EDL)introduced by the IL, whereas the active layer in the backside gat-ing configuration is in the deposited SiO2. According to the mea-sured results in Figure 3a,c, it is clear that the IL gating setup re-quires much less gate voltage to modify the graphene Fermi levelinto the n and p-type regions. This large contrast in energy con-sumption originated from the ultra-high capacitance provided bythe IL compared to SiO2.[41] The remarkable capacitance was dueto the formation of EDL in IL that had a thickness of only a cou-ple of nanometers, whereas in the backside gating configuration,the SiO2 was 300 nm. Figure 3b,d shows the graphene channelIV curve with respect to different gating voltage levels of IL andbackside gating configuration. Additionally, to study the electri-Adv. Sci. 2025, 12, 2412340 2412340 (3 of 8) © 2024 The Author(s). Advanced Science published by Wiley-VCH GmbH 21983844, 2025, 8, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/advs.202412340 by National Institute For, Wiley Online Library on [01/05/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.advancedscience.comwww.advancedsciencenews.com www.advancedscience.comFigure 2. Characterization of the IP NW crystal and mode properties. a) Scanning electron microscope image of the NW on graphene; the scale bar is5μm. b) Modal analysis of InP NW immersed in IL; the scale bar is 200 nm. c) TEM image of the InP sample; the scale bar is 1 μm. The inset shows athree-layer structure, silicon, InP, and Pt from bottom to top. d) High-resolution TEM image of the InP within the red box region of (b), which shows thelattice constant to be ≈6.7 Å; the scale bar is 2 nm. Inset: Selected-area electron diffraction image of the grown InP; the scale bar is 2 nm−1.Figure 3. Comparison between IL-gated and backside-gated graphene. a,c) Measured IDS–VGS curve under VDS = 0.1 V of IL-gated and backside-gatedsetups respectively. b) The IDS–VDS curves of the IL-gated setup under VGS = 0 to −1.4 V. d) The IDS–VDS curves of the backside gated setup under VGS= 0 to −30 V. e) Raman spectroscopy of the as-grown and transferred graphene used in Device A. The 2D / G ratio maintained a value ≈2 indicatinggood quality graphene after the transfer.Adv. Sci. 2025, 12, 2412340 2412340 (4 of 8) © 2024 The Author(s). Advanced Science published by Wiley-VCH GmbH 21983844, 2025, 8, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/advs.202412340 by National Institute For, Wiley Online Library on [01/05/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.advancedscience.comwww.advancedsciencenews.com www.advancedscience.comFigure 4. Threshold modulation of Device B under various doping levels. a) The spectrum of NW on Device B under VGS = 0, 0.8, and 1.6 V. b) Light-inversus light-out curves of the IL gated NW laser under VGS = −1, 0 and 2V. c) Schematic of carrier dynamics in the system when positive and negativegate biases are applied. At positive (negative) VGS, electrons (holes) would accumulate inside the NW cavity, introducing n (p) – type doping. d) Cyclicmeasurement of NWs under VGS = 0 and 3 V at 78.5 μW pumping energy, showing electrical on and off switching of stimulated emission.cal properties of gated graphene, it is inappropriate to ignore thewrinkles and folds that come along with the wet transfer method.The CVD-grown graphene and its quality were characterized withRaman spectroscopy as shown in Figure 3e. The 2D / G peak ra-tios before and after transferring graphene both show values ex-ceeding 2, indicating high quality.2.4. Working Principle and Device PerformanceAs reported in the literature, the lasing threshold and electri-cal properties of semiconductor NWs can be tuned accordingto the doping levels.[24,42] However, previous studies regardingthreshold modulation in NWs have been mostly focused on fieldconfinement due to nanostructure coupling,[21,43] or impuritydoping.[44,45] Both are not tunable after the fabrication, causinga lack of freedom in tunings. Hereby, the tunability of NWs im-mersed in IL has been tested by applying different gate voltagesto introduce different doping levels. Figure 4a shows an increasein emission power under the same excitation laser power of 78.5μW. The black line shows the amplified spontaneous emission(ASE) of the NW under 0 V gate voltage, with VG increasing from0.8 to 1.6 V (orange and purple lines respectively), the stimulatedemission (lasing) was clearly observed on the NW, indicating thethreshold decrease in the NW lasers. Next, we measured the ex-citation power-dependent emission intensity of the NW laser un-der VGS = −1, 0, and +2 V represented in blue, black, and redcolors in Figure 4b, respectively. The mechanism of the observedphenomenon is illustrated in Figure 4c. By applying positive gatevoltage, anions (TFSI-) in the IL aggregate around the gate elec-trode, while cations (EMIM+) were attracted to the source elec-trode forming electric double layers (EDLs) at each liquid / solidinterface. The NW on the source electrode then be bathed incations generating an accumulation of negative charges through-out the NW, realizing n-type doping. The n-type doping intro-duced a donor band (ED) located in the vicinity of the conduc-tion band (EC). At room temperatures (around 300 K), part of thedonors contributed as free electrons in the CB. When the abovebandgap illumination is introduced, electrons from the VB anddonor band are excited to the CB and then eventually fall backdown into the VB where carriers recombine, resulting in spon-taneous emission. However, some electrons may get trapped inthe miniband during the process and as the pumping energy in-creases, electron accumulation in the miniband forms popula-tion inversion, which causes stimulated emission. Note that then-type doping from IL decreased the lasing threshold as it intro-duced excess electrons to the system. This correlates with ourexperimental results; once the wires are n-doped (more donors),the threshold of the stimulated emissions drops drastically. Onthe contrary, if the NW were accumulated by positive charges (p-type doping), the acceptor band near the VB hinders electrons’transition from VB to CB resulting in an increase in the lasingthreshold. To accumulate positive charges in the NW, a nega-tive gate voltage was applied as depicted in the bottom panel ofFigure 4c. The robustness of emission functionality of the pro-posed NW laser concept was tested through a repeated on-and-offcycle. Figure 4d shows 5 cycles of VGS = +3 and 0 V, the emissionof the NW shows the capability of switching the laser on/off withAdv. Sci. 2025, 12, 2412340 2412340 (5 of 8) © 2024 The Author(s). Advanced Science published by Wiley-VCH GmbH 21983844, 2025, 8, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/advs.202412340 by National Institute For, Wiley Online Library on [01/05/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.advancedscience.comwww.advancedsciencenews.com www.advancedscience.comFigure 5. Emissive properties of Device A under various doping levels. Relation between 881 nm stimulated emission intensity and channel resistanceof graphene under a) positive and b) negative gate bias. Variations in graphene resistance point out the carrier concentration change throughout thechannel. Different color boxes are added for better visibility, referring to different VGS levels. c) Extracted lasing wavelength shift under gate voltagevariation, showing a minor blue shift as the NW is gradually n-doped. The red (blue) data points refer to negative (positive) gate bias assigning p (n) –type doping in the NW. d) PL spectrum of NW on Device A at VGS = −2 to 2 V.no obvious degradation. This experiment was tested on differentNW lasers with more cycles, and all showed similar trends exceptfor the slight deviations on the VGS for the on-state. The reasonis due to variations in NWs geometry and their intrinsic chargedstate.One way to reveal the evidence of NW carrier modulation is toperform Kelvin probe microscopy (KPFM) as it records changesin surface potential. However, it is impossible for surface analy-sis in this setup because the NWs were immersed in IL and en-capsulated under a cover glass. To study charge accumulation,the graphene channel resistance and the lasing intensity at 874nm of the NW were measured. As shown in Figure 3a, it is clearthat the resistance of graphene varies under different dopinglevels. Figure 5a,b shows the relation between the lasing emis-sion and doping level. As VGS increases (Figure 5a), the Fermilevel of graphene moves further into the n-type regime, causinga decrease in resistance from gate-induced electrons throughoutthe channel. The NWs lasing intensity shows a 300% enhance-ment at VGS = + 3.5 V compared to VGS = 0 V with the exci-tation power set to 130 μW. Though the enhancement in emis-sion is obvious and shows no trend of saturation, the IL limitsthe applied gate voltage to ≈4 V due to the electrochemical in-stability. Note that the pristine graphene used throughout thismanuscript is slightly p-type. We can see in Figure 5a that afterVGS = 3.5 V was turned off, the resistance of graphene increaseddrastically and then dropped gradually indicating the relaxationof gate-induced carriers throughout the channel (n-type to neu-tral to p-type pristine state). As depicted in Figure 5b, the VGSwas given negative voltage introducing anion gathering aroundthe NW, resulting in hole accumulation in the cavity. Opposite toFigure 5a, the NW lasing emission was suppressed and gradu-ally turned off. As the pristine graphene was positively charged,the more negative gate voltage was applied, the smaller chan-nel resistance it exhibited. The lasing peak wavelength (𝜆Lasing)was extracted and shown in Figure 5c. The peak wavelength ofNW-stimulated emission shifts when the charge concentrationchanges inside the NW cavity. By varying the gate voltage fromVGS = −1.6 V to +3.5 V, 𝜆Lasing showed a blueshift of ∆𝜆 = 1.4nm. Gate-induced N-type doping increases the carrier concentra-tion throughout the nanowire cavity, reducing the cavity refrac-tive index as predicted by the Drude model. Whereas P-type dop-ing decreases the carrier concentration due to the opposite po-larity of majority carriers in the as-prepared intrinsic N-type InPnanowire. Resulting in the highest refractive index under nega-tive biased conditions and leads to a red shift in emission wave-length. From our observations, the small shift in emission wave-length could also be explained by the Moss-Burstein effect.[29,46,47]When the semiconductor nanowires are subjected to N-type dop-ing, a high concentration of electrons fills up the energy lev-els near the bottom of the conduction band (CB). Thus, photo-excited carriers have to occupy states with a higher energy, re-sulting in higher photoenergy emission (blue shift) when theexcited carriers recombine. In the proposed device, photolumi-nescence intensity under below-threshold excitation also varieswith different gate voltages, as shown in Figure 5d. The band-filling model applies to both stimulated and spontaneous emis-sion, as both types are driven by carrier recombination, resultingin similar optical trends, as previously discussed. These opticaltrends mirror those observed in the lasing and PL experiments,supporting the conclusion that threshold modulation is primarilyAdv. Sci. 2025, 12, 2412340 2412340 (6 of 8) © 2024 The Author(s). Advanced Science published by Wiley-VCH GmbH 21983844, 2025, 8, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/advs.202412340 by National Institute For, Wiley Online Library on [01/05/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.advancedscience.comwww.advancedsciencenews.com www.advancedscience.comdue to electrical doping induced by the EDL formed by the ionicliquid.3. ConclusionIn summary, this study showcases the concept of dynamicallymodulating charges in III-V semiconductor NWs at room tem-perature by employing ILs as the dielectric gating layer throughconcise fabrication. Utilization of IL as the dielectric layer en-hances the gating efficiency up to 100-fold compared to the back-side gating configuration. This setup only requires a pair of elec-trodes and is compatible with all insulating platforms, even flexi-ble ones. By applying bias at the gate terminal, anions and cationsin the IL aggregated and lined up in a manner with respect tothe polarity of the bias, forming EDLs at each solid/liquid inter-face. The EDL formed around the NW that was placed on thesource electrode dopes the NW with electrons/holes, causing thethreshold and the lasing peak wavelength to decrease/increaseand blueshift/redshift, respectively. The total wavelength shiftmeasured in this manuscript is 1.4 nm, under the gate voltageshift from −1.4 to 3.5 V. In the context of n-doped InP NWs, adonor band is formed in the vicinity of CB which causes electronsto fill up the lower energy states in the CB. This led to the thresh-old lowering and blueshift in emission spectrums when opticallypumped, as the system contained surplus excited electrons fromhigher energy states. On the contrary, p-doped InP NWs exhib-ited opposite behaviors as the electrons in the system were de-pleted to a certain level. The proposed setup demonstrated activecarrier modulations of III-V semiconductor NWs, highlightingsubstantial potential to accommodate the vast applications in theoptoelectronic industry.4. Experimental SectionGrowth of InP Nanowires: InP nanowires were grown on a 2 in. (100)InP substrate by using the metal–organic chemical vapor deposition(MOCVD). Temperature and pressure for growth were set to 500 °C and100 Torr respectively, with a V/III ratio of 80. The grown InP NWs havelengths and diameters ranging from 10 to 20 μm and from 100 to 500 nm,respectively.Device Fabrication: Device A was fabricated starting from a 300 nm sil-icon dioxide deposition by an electron beam evaporation system (ULVACVT1-10CE) on a silicon wafer. After the deposition, a graphene sheet wastransferred onto the substrate followed by oxygen plasma etching (OMNI-RIE) for 40 s to form a channel. Gate and source/drain electrodes werethermally deposited 100-nm thick gold films with a shadow mask. The InPNWs were precisely transferred onto the graphene channel using a PDMSstamp clamped to a probe station as shown in Figure S3 (Supporting In-formation). Finally, 1 μL of EMIM-TFSI was drop cast on the graphenechannel and encapsulated with a cover glass to avoid the formation ofdroplets. Device B was fabricated using a glass substrate where the pro-cess was compatible with flexible substrates such as PET and PDMS. Goldelectrodes of the gate and source were deposited on the substrate. The InPNWs were stamped on the substrate in the vicinity of electrode pads as thePDMS stamp may damage the deposited gold. InP nanowires were pushedcarefully onto the source electrode with a micro-manipulator as depictedin Figure S3b (Supporting Information). Finally, IL was drop cast onto theelectrode and encapsulated with a cover glass.Graphene Wet Transfer: A chemical vapor deposition (CVD) grownmonolayer graphene sheet on copper foil was transferred to the target sub-strate using the wet transfer method. Prior to the removal of copper foil,graphene was protected by spin coating a thin layer of photoresist (PMMA-A4) to avoid mechanical damage from fluid tensions during the etchingprocess. The copper foil was etched by floating the stack on Fe(NO3)3 so-lution (33 wt%) at room temperature (≈300 K) for ≈12 h. After the etch-ing process, the stack was left with graphene and photoresist. To removethe etchant residue, the stack was cleaned for 1 h using deionized water.The substrate was treated with UV–ozone before the transfer to enhancesurface energy, providing a position-adjustable transfer process withoutdamaging the graphene. The sample was left in a dry cabinet overnightto complete dehydration. After the sample was completely dry, the pho-toresist was removed by acetone and subsequently washed in isopropanol(IPA).Optical Measurements: The InP NW of interest was identified with avisible charge-coupled device (CCD), then pumped from an incident angleof ≈45 degrees using a 532 nm pulsed laser with a repetition rate of 4 kHzand pulse width of 1 ns. The beam spot was focused with a 5 cm focallength convex lens which resulted in an elliptic shape with short and longaxes to be 40 and 130 μm, respectively. The emission from the InP NWswas collected at normal incidence by a 50x objective lens (SLMPLN50X,Olympus) with a numerical aperture of 0.35 and a working distance of18 mm. The signal was then directed into a spectrometer (Kymera 193i,Andor). To determine the emission polarization as in Figure 1e inset, arotatable polarizer was placed in front of the spectrometer. Schematic ofthe above is shown in Figure S4 (Supporting Information).Supporting InformationSupporting Information is available from the Wiley Online Library or fromthe author.AcknowledgementsThis work was supported by the National Science and Technology Coun-cil (NSTC 111-2923-E-007-008-MY3; 111-2628-E-007-021; 112-2223-E-007-007 -MY3; 112-2923-E-007 -004 -MY2; 112-2119-M-A49-008; 113-2628-E-007-024; 113-2218-E-A49-029). The support from the International Coop-erative Graduate Program (ICGP), NIMS, and Taiwan Semiconductor Re-search Center (TSRI) are highly appreciated.Conflict of InterestThe authors declare no conflict of interest.Author ContributionsC.-H.W. performed sample fabrication and characterization. C.-H.W., T.-C.L., S.I., and K.-P.C. analyzed the experimental data. C.-H. W. and K.-P.C.wrote the manuscript. All authors discussed the results and commentedon the manuscript.Data Availability StatementThe data that support the findings of this study are available from the cor-responding author upon reasonable request.Keywordscarrier modulation, flexible substrate, InP nanolasers, ionic liquidReceived: October 4, 2024Revised: November 13, 2024Published online: December 16, 2024Adv. Sci. 2025, 12, 2412340 2412340 (7 of 8) © 2024 The Author(s). Advanced Science published by Wiley-VCH GmbH 21983844, 2025, 8, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/advs.202412340 by National Institute For, Wiley Online Library on [01/05/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.advancedscience.comwww.advancedsciencenews.com www.advancedscience.com[1] M. S. Ram, K.-M. Persson, A. 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Saxena, S. Mokkapati, Z. Li, C. R. Hall, J. A. Davis,Y. Wang, L. M. Smith, L. Fu, P. Caroff, Nat. Commun. 2016, 7,11927.[46] M. Muñoz, F. H. Pollak, M. Kahn, D. Ritter, L. Kronik, G. M. Cohen,Phys. Rev. B 2001, 63, 233302.[47] Y. Kim, M. Takenaka, T. Osada, M. Hata, S. Takagi, Sci. Rep. 2014, 4,4683.Adv. Sci. 2025, 12, 2412340 2412340 (8 of 8) © 2024 The Author(s). Advanced Science published by Wiley-VCH GmbH 21983844, 2025, 8, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/advs.202412340 by National Institute For, Wiley Online Library on [01/05/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.advancedscience.com Reversible Carrier Modulation in InP Nanolasers by Ionic Liquid Gating with Low Energy Consumption 1. Introduction 2. Results and Discussion 2.1. Device Fabrication and NW Emissive Properties 2.2. Characterization and Modal Analysis of InP NWs 2.3. Comparison Between IL and Backside Gated Configurations 2.4. Working Principle and Device Performance 3. Conclusion 4. Experimental Section Supporting Information Acknowledgements Conflict of Interest Author Contributions Data Availability Statement Keywords