Electrostatic Control of InsulatorâMetal Transition in La-doped SrSnO3

Subscriber access provided by UNIV OF NEW ENGLAND ARMIDALE

Letter 3

Electrostatic Control of Insulator-Metal Transition in La-doped SrSnO Films Laxman Raju Thoutam, Jin Yue, Abhinav Prakash, Tianqi Wang, Kavinraaj Elangovan, and Bharat Jalan ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b22034 • Publication Date (Web): 14 Feb 2019 Downloaded from http://pubs.acs.org on February 17, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Electrostatic Control of Insulator-Metal Transition in La-doped SrSnO3 Films

Laxman Raju Thoutam*, Jin Yue, Abhinav Prakash, Tianqi Wang, Kavinraaj Ella Elangovan and Bharat Jalan*

Department of Chemical Engineering and Materials Science University of Minnesota - Twin Cities, Minneapolis, Minnesota 55455, USA

*

Corresponding authors: [email protected] and [email protected]

ACS Paragon Plus Environment

1

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 17

Abstract We investigate the ion-gel gating of wide bandgap oxide, La-doped SrSnO3 films grown using radical-based molecular beam epitaxy. An applied positive bias resulted in a reversible electrostatic control of sheet resistance over three orders of magnitude at low temperature driving sample from Mott variable range hopping to a weakly localized transport. Analysis of low temperature transport behavior revealed electron-electron interaction and weak localization effects to be the dominant scattering mechanisms. A large voltage window (- 4V ≤ Vg ≤ + 4V) was obtained for reversible electrostatic doping of SrSnO3 films showing robustness of stannate with regards to redox chemistry with electrolyte gating irrespective of the bias type.

Keywords: Reversibility; Electrostatic gating; Ion-gel; Insulator-metal transition; Electronelectron interaction; wide bandgap semiconductor; Hybrid molecular beam epitaxy.


2

Page 3 of 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Wide bandgap oxides with high conductivity at room-temperature (RT) have been of significant interest for transparent conducting applications. These materials have also gained much attention as high critical field strength material for power electronics. Recently, a new class of wide bandgap oxides based on perovskite structure, BaSnO3 (BSO) and SrSnO3 (SSO) has emerged.1-4 Most of the works have focused on BSO, owing to the recent discovery of high RT electron mobility as high as 320 cm2V-1s-1 in bulk2 and 20-180 cm2V−1s−1 in La-doped thin films.5-11 The SSO, on the other hand, has remained relatively unexplored, largely due to its complex structural phase transition and difficulty in obtaining phase pure films.12 SSO has smaller lattice constant,12-13 and a wider bandgap, 4 – 4.5 eV than BSO.14 SSO possesses similar electron effective mass as that of BSO, 0.3 me - 0.4 me owing to Sn 5s-derived conduction band.12, 15 The smaller lattice constant of SSO has allowed for strain-engineered heterostructures with commercially available substrates as compared to BSO.12 Introducing chemical dopants like La16 or Sb17 or Nd17 in SSO has resulted in transparent conducting properties. RT ferromagnetism has also been realized in Fe-doped18 and more recently, in oxygen vacancydoped SSO films.19 Critical progress has recently been made with thin film growth of strainstabilized structures of SSO using molecular beam epitaxy (MBE) leading to RT electron mobility exceeding 55 cm2V−1s−1 at remarkably high carrier density, 6 × 1019 cm-3, when doped n-type with La.12, 20 Metal-semiconductor field effect transistors (MESFETs) using SSO channel is also demonstrated.21 The fundamental understanding of SSO is however largely unknown including the critical knowledge of the importance of ionized and neutral impurity scattering mechanisms, dislocation scattering, and the choice of dopant atoms and doping sites on electronic transport. Basic knowledge pertaining to the insulator-metal transition as a function of doping


3


Page 4 of 17

concentration is also unknown. Electrolyte gating using ionic-liquid or ion-gel in electric doublelayer transistors (EDLTs) configuration provides an exceptional route to control carrier density without introducing disorder caused with chemical doping.22-24 EDLT consists of semiconductor, electrolyte, and metal electrodes.22-25 Under an applied bias, an EDL can form at the semiconductor/ion-gel interface comprising of electrolyte cations (anions) and induced surface electrons (holes). The surface charge density can exceed 1014 cm-2 owing to the large electric field (~ 10 MV/cm) in the EDL.22-24 It is this aspect of EDLTs that has led to many fruitful studies concerning investigations of transport behavior in extreme doping regime, which are not achievable in conventional field effect using traditional dielectrics.22-24 However, large electric field can also lead to electrical breakdown of semiconductor or can become a source of irreversible redox chemistry at electrolyte/semiconductor interface.23-25 In this letter, we show reversible and purely electrostatic control of an insulator-to-metal transition (IMT) in a lightly-doped, insulating SSO film using ion-gel gating. With increasing positive bias, temperature dependent transport reveals an IMT near 1.5 × 1013 cm-2, marked by crossing of quantum resistance (h/e2 = 25.7 kΩ), the onset of weakly temperature-dependent resistance accompanied by negative magnetoresistance (MR) at low temperatures, and a dramatic increase in electron mobility. Using a metallic La-doped SSO film, we further demonstrate reversibility and electrostatic nature of gating with an exceptionally wide voltage window (- 4 V ≤ Vg ≤ + 4 V). Epitaxial La-doped SSO films were grown on GdScO3 (GSO) (110) substrates using an oxide MBE system with a base pressure of 10-10 Torr. Details of our MBE approach are discussed elsewhere.12, 20 A brief description will be provided here. SSO films were grown using the radical-based hybrid MBE approach. Sr and La were evaporated using effusion cells, and


4

Page 5 of 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


oxygen was supplied using an RF plasma source. For Sn, a metal-organic chemical precursor, hexamethylditin (HMDT) was used.26 The oxygen pressure and substrate temperature were fixed at 5×10-6 Torr and 900 °C (thermocouple temperature) respectively. For electrical measurements, a Hall bar [1 mm (channel length) × 0.5 mm (width)] was defined using a hard mask and ion milling. Metal contacts (20 nm Ti capped with 180 nm Au) were deposited using a second mask to define source, drain, and co-planar gate electrodes. For gating operation, an ion-gel (consisting of

poly

vinylidene

fluoride-co-hexafluoropropylene

(PVDF-HFP)

polymer,

1-ethyl-3-

methylimidazaolium bis-trifluoromethylsulfonyl imide (EMI : TFSI) ionic liquid, and acetone as the solvent in the ratio 1:4:7)27 was placed on the channel area and on the gate electrodes as illustrated in figure 1a (see supplemental material for additional details about the ion-gel). Sample was then transferred into the low vacuum environment inside the physical property measurement system (Quantum Design Dynacool) to avoid potential exposure and degradation of ion-gel in air. Gate voltage (Vg) was applied at 280 K to create EDL at SSO/ion-gel interface as shown in figure 1a. A waiting time of 20 min at 280 K was allowed to ensure sufficient ion movement in ion-gel prior to cooling down to 2 K. Transport measurements were then taken during heating. As shown in figure S1, the gate leakage becomes significant above T > 200 K due to the glass transition in the ion-gel. For this reason, we only report data that were taken below 200 K. Figure 1b shows an optical micrograph of the patterned Hall bar consisting of 12 nm Ladoped SSO/12 nm undoped SSO/GSO (110) prior to placing the ion-gel. Phase-purity, and surface morphology were confirmed using high-resolution x-ray diffraction, atomic force microscopy, and reflection high-energy electron diffraction (figure S2). For La doping, effusion cell temperature was kept at 1170 °C. Figure 1d shows temperature-dependent sheet resistance,


5


Page 6 of 17

Rs as a function Vg, and an inset highlighting a minimum in Rs, along with linear fits to the Rs vs. log10T at low temperatures. The black arrows mark the temperature at which Rs appears to change slope with decreasing temperature. Additionally, the inset reveals that the temperature at which upturn in Rs (i.e.

!!! !"

< 0) occurs, decreases with increasing Vg. As-patterned sample

without ion-gel (n2D = 4 × 1012 cm-2, µ = 6 cm2V−1s−1 at 150 K) showed an insulating behavior and sheet resistance exceeding the quantum resistance of h/e2 at all temperatures. Figure 1c shows ln [Rs] vs. T-1/4 of this film revealing the governing transport mechanism in the insulating regime is Mott 3D variable range hopping.20 With increasing Vg , Rs decreases by over three orders of magnitude accompanied by transition from strongly localized to a weakly localized transport at low temperatures. At Vg = 1 V, sample first showed a weak insulating behavior with decreasing temperature and then, an exponential dependence exceeding h/e2 value at lower temperatures (T < 20 K). At higher applied biases (Vg > 1 V), sample showed metallic behavior followed by an insulating-like behavior with a linear dependence on Rs vs. log10 T plot (see inset of figure 1d). The linear behavior can be attributed to the quantum corrections due to twodimensional (2D) weak localization (WL) and/or electron-electron (e-e) interaction effects. Theoretically, 2D WL and e-e effects produce similar logarithmic temperature dependence to the Rs in zero-magnetic field, but significantly different Hall-effect behavior.28-31 For WL, the Hall coefficient (RH) doesn’t depend on temperature whereas RH exhibits logarithmic temperature dependence for e-e interaction.29,

31

Specifically, the e-e interaction theory predicts the

normalized Hall coefficient change as a function of temperature, sheet resistance change,

∆!! !!

for e-e interaction effect,29-31 i.e., if

∆!! !!

∆!! !!

to be twice the normalized

=𝛾

∆!! !!

; 𝛾 = 2 indicates e-e

interaction, and 𝛾 = 0 indicates WL. The intermediate values between 0 and 2 suggest the


6

Page 7 of 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


presence of both WL and e-e interaction.28, 31-32 For normalization, Rs corresponds to the sheet resistance at the onset of quantum correction. Figure 2a shows -1/eRH vs. T plot, and an inset revealing a linear relationship between ∆!!

!!

[= (!"# !)

!! ! !!! !" ! !! !"#!

] vs. !

!

∆!!

[= (!"# !)

!! ! !!! !" ! !! !"#!

] with a slope (𝛾) of ~1. Note that for

the fitting in the inset, we chose RH (T) and Rs (T) only below ~15 K as RH (T) is logarithmically dependent in this temperature range. We note that Hall voltage was completely linear between magnetic field, – 9 T and + 9 T (figure S3). Figure 2b shows µ as a function of induced surface charge density, nHall. With increasing Vg, both -1/eRH and µ increase from 4×1012 cm-2, and 6 cm2V-1s-1 respectively at Vg = 0 V, T = 150 K (not shown), to 1.5×1013 cm-2 and 27 cm2V-1s-1 at Vg =1 V reaching up to 3.5 × 1013 cm-2 and 38 cm2V-1s-1 at Vg = 4 V. It is noted that a similar gating effect but at higher applied bias was previously obtained in undoped BSO films using ionic-liquid gating.33 Irrespective of an applied bias, -1/eRH remains nominally unchanged for 15 K < T < 150 K and decreases logarithmically for T < 15 K. This temperature is nominally similar to the temperature marked by the black arrows in the inset of figure 1d suggesting e-e may dominate over the 2D WL at T below ~15 K. A similar effect of drop in carrier density (or 1/eRH) at low temperatures has also recently reported in δ-doped Si near insulator-metal transition with doping densities in the range (0.2- 2) x 1014 cm-2 revealing the influence of e-e interaction effects.34 However, one may still argue that the drop in -1/eRH due to carrier freezeout or from the charge trapping at the SSO/ion-gel interface.35 We rule these possibilities out by growing heavily doped, metallic SSO films. Figure S4 shows temperature dependent -1/eRH of pristine samples with different doping densities revealing an identical drop in -1/eRH at low temperature even without ion-gel. The results also show that, regardless of doping density, the


7


Page 8 of 17

drop in -1/eRH persisted at nearly same temperature providing good evidence against carrier freeze-out. Applying magnetic field can eliminate WL effects.36 In principle, a maximum of h/e2 in longitudinal sheet resistance change (∆Rs) can be expected with increasing applied magnetic field, B (T), if quantum correction to the resistance is entirely due to the WL effect. To this end, we measured ∆RS as a function of B (T) for different applied biases. Figure 2c shows magnetic field dependent ∆RS in terms of h/e2 for different bias at 10 K revealing negative magnetoresistance, which is consistent with the presence of WL effect.36 This result is again in agreement with the smaller value of 𝛾 (< 2) as discussed above. We note that the presence of e-e interaction has previously been discussed in La-doped BSO in the context of bandgap normalization.37 Additional measurements and quantitative analyses are needed to separate the effect of WL and e-e interaction to Rs, and to reveal the microscopic origin of e-e interaction. This will be a subject of future study. We now turn to the discussion of electronic vs. electrochemical effects as well as reversibility of gating using ion-gel. We examined this using a metallic La-doped SSO film and by subjecting it to varying magnitudes of both positive and negative applied biases. Figure 3a shows temperature dependent Rs of a 30 nm La-doped SSO/12 nm undoped SSO/ GSO (110) for - 4 V ≤ Vg ≤ + 4 V. Note the RT mobility and n2D of this sample prior to the ion-gel gating was of 51 cm2V-1s-1 and 1 × 1014 cm-2 respectively. As expected, Rs decreases with a positive bias (electron accumulation) and increases with a negative bias (electron depletion). The inset to the figure 3a shows temperature dependent Rs of the film with no ion-gel (pristine sample), with iongel at 0 V, and after removing the ion-gel revealing no obvious difference between them. It is worth noting that before the ion-gel was removed, film was subjected to multiple sequences of Rs


8

Page 9 of 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


vs. T at both positive and negative gate biases between – 4 V and + 4 V. These results thus reveal highly reversible gating effect in La-doped SSO film regardless of the sign of applied bias up to Vg = ± 4 V. This result also suggests electrostatic nature of ion-gel gating. The key distinguisher between electrostatic control vs. redox chemistry or electrochemical control where ions penetrates in and out of the semiconductor can be the rate of change.24, 38 The later is typically slower and can also be irreversible.24, 38 To this end, we performed continuous measurements of resistance of this sample under different applied bias where each bias was held fixed for 20 minutes at 280 K. The bias cycle is illustrated in figure 3b. The corresponding changes in resistance, [∆Rs = R (Vg) - R (0 V)] as a function of time is shown in figure 3c. Note that for each Vg, two cycles of measurements (0 à Vg à 0 à Vg à 0) were performed to check the robustness of the measurement. It should be noted that these resistances are measured at 280 K where gate leakage was non-negligible (figure S5). However, these measurements provide a good sense of response time during gating process. The fact that application and removal of bias results in drastic change followed by a small transient (< 2 minute) in resistance is consistent with the electrostatic nature. It should also be noted in figure 3c, the base line for zero applied bias shifts systematically downwards with increasing negative bias and then upward for increasing positive bias. We attribute this behavior to a systematic change in the gate leakage current over time (figure S5) and not to the irreversible nature of gating. Clearly, irreversibility is negligible when resistance is measured below 150 K as illustrated in the inset to figure 3a. To be more quantitative, we show in figure 3d the gate effect and irreversibility at 280 K as defined by !!" !! !!! ! ! !! ! !

× !""

, and

[!!"" !! !!! ! ! ]× !"" !! ! !

respectively. Here, 𝑅! 0 𝑉 , 𝑅!" 𝑉!

and

𝑅!"" 𝑉! are measured resistance at 0 V, Vg and off-state, i.e. Vg → 0 V respectively as indicated in the inset to figure 3d. Nearly negligible irreversibility in - 4 V ≤ Vg ≤ + 4 V is again apparent.


9


Page 10 of 17

A small negative irreversibility (~ - 2%) for Vg < - 1 V and a positive irreversibility, ~ 3% at Vg = + 4 V are apparent in figure 3d. We note this is due to the uncertainly in the measurements of Rs in the presence of high gate leakage (figure S5). It is also worth noting that the gate effect is relatively small and asymmetric, which we attribute to the contribution from the bulk conduction as the EDL influences only the near surface charge density. Future work should focus on separating quantitatively the EDL vs. bulk contribution to the resistance in doped SSO, and to investigate different mobility-limiting scattering mechanisms in the EDL. In summary, we have demonstrated an insulator-to-metal transition in SSO film using ion-gel-gated Hall bar structure. Analysis of the low temperature transport in insulating regime revealed the Mott variable range hopping as governing transport mechanism whereas in the metallic regime (Rs < h/e2), transport was governed by 2D WL and e-e interaction effects. It was found that ion-gel gating is highly reversible and electrostatic in nature in an exceptionally wide voltage window, - 4 V ≤ Vg ≤ + 4 V regardless of the sign of applied bias. This study establishes the ion-gel gating as an effective and reversible method to electrostatically tune electronic phase transition in stannate perovskite thin films and heterostructures.

Acknowledgement: The authors thank David Goldhaber Gordon and A. Kamenev for helpful discussion, and Helin Wang for the help with ion-gel preparation. This work was primarily supported by UMN MRSEC program under Award Number DMR-1420013. The part of this work was supported through the Young Investigator Program of the Air Force Office of Scientific Research (AFOSR) through Grant FA9550-16-1-0205 and through DMR-1741801. Portions of this work were conducted in the Minnesota Nano Center, which is supported by the National Science


10

Page 11 of 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Foundation through the National Nano Coordinated Infrastructure Network (NNCI) under Award Number ECCS-1542202. Sample structural characterizations were carried out at the University of Minnesota Characterization Facility, which receives partial support from NSF through the MRSEC program.

References 1. Luo, X.; Oh, Y. S.; Sirenko, A.; Gao, P.; Tyson, T. A.; Char, K.; Cheong, S. W., High Carrier Mobility in Transparent Ba1−xLaxSnO3 Crystals with a Wide Band Gap. Appl. Phys. Lett. 2012, 100 (17), 172112. 2. Kim, H. J.; Kim, U.; Kim, T. H.; Kim, J.; Kim, H. M.; Jeon, B.-G.; Lee, W.-J.; Mun, H. S.; Hong, K. T.; Yu, J.; Char, K.; Kim, K. H., Physical Properties of Transparent Perovskite Oxides (Ba,La)SnO3 with High Electrical Mobility at Room Temperature. Phys. Rev. B 2012, 86 (16), 165205. 3. Kim, H. J.; Kim, U.; Kim, H. M.; Kim, T. H.; Mun, H. S.; Jeon, B.-G.; Hong, K. T.; Lee, W.J.; Chanjong, J.; Kim, K. H.; Char, K., High Mobility in a Stable Transparent Perovskite Oxide. Appl. Phys. Express 2012, 5 (6), 061102. 4. Ismail-Beigi, S.; Walker, F. J.; Cheong, S.-W.; Rabe, K. M.; Ahn, C. H., Alkaline Earth Stannates: The Next Silicon? APL Mater. 2015, 3 (6), 062510. 5. Paik, H.; Chen, Z.; Lochocki, E.; H., A. S.; Verma, A.; Tanen, N.; Park, J.; Uchida, M.; Shang, S.; Zhou, B.-C.; Brützam, M.; Uecker, R.; Liu, Z.-K.; Jena, D.; Shen, K. M.; Muller, D. A.; Schlom, D. G., Adsorption-Controlled Growth of La-doped BaSnO3 by molecularBeam Epitaxy. APL Mater. 2017, 5 (11), 116107. 6. Raghavan, S.; Schumann, T.; Kim, H.; Zhang, J. Y.; Cain, T. A.; Stemmer, S., High-Mobility BaSnO3 Grown by Oxide Molecular Beam Epitaxy. APL Mater. 2016, 4 (1), 016106. 7. Prakash, A.; Xu, P.; Faghaninia, A.; Shukla, S.; Ager Iii, J. W.; Lo, C. S.; Jalan, B., Wide bandgap BaSnO3 films with Room Temperature Conductivity Exceeding 104 Scm−1. Nat. Commun. 2017, 8, 15167. 8. Prakash, A.; Xu, P.; Wu, X.; Haugstad, G.; Wang, X.; Jalan, B., Adsorption-Controlled Growth and the Influence of Stoichiometry on Electronic Transport in Hybrid Molecular Beam Epitaxy-Grown BaSnO3 films. J. Mater. Chem. C 2017, 5 (23), 5730. 9. Ganguly, K.; Prakash, A.; Jalan, B.; Leighton, C., Mobility-Electron Density Relation Probed via Controlled Oxygen Vacancy Doping in Epitaxial BaSnO3. APL Mater. 2017, 5 (5), 056102. 10. Yu, S.; Yoon, D.; Son, J., Enhancing Electron Mobility in La-doped BaSnO3 Thin films by Thermal Strain to Annihilate Extended Defects. Appl. Phys. Lett. 2016, 108, 262101. 11. U. S. Alaan; Shafer, P.; N'Diaye, A. T.; Arenholz, E.; Suzuki, Y., Gd-doped BaSnO3: A Transparent Conducting Oxide with Localized Magnetic Moments. Appl. Phys. Lett. 2016, 108, 042106. 12. T. Wang, A. P., Y. Dong, T. Truttmann, A. Bucsek, R. James, D. D. Fong, J.-W. Kim, P. J. Ryan, H. Zhou, T. Birol, and B. Jalan, Engineering SrSnO3 Phases and Electron Mobility at


11


Page 12 of 17

Room Temperature using Epitaxial Strain. ACS Appl. Phys. and Mater. Article ASAP 2018, DOI: 10.1021/acsami.8b16592. 13. Glerup, M.; Knight, K. S.; Poulsen, F. W., High Temperature Structural Phase Transitions in SrSnO3 Perovskite. Mater. Res. Bull. 2005, 40 (3), 507. 14. Schumann, T.; Raghavan, S.; Ahadi, K.; Kim, H.; Stemmer, S., Structure and Optical Band Gaps of (Ba,Sr)SnO3 Films Grown by Molecular Beam Epitaxy. J. Vac. Sci. Technol. A 2016, 34 (5), 050601. 15. Ong, K. P.; Fan, X.; Subedi, A.; Sullivan, M. B.; Singh, D. J., Transparent Conducting Properties of SrSnO3 and ZnSnO3. APL Mater. 2015, 3, 062505. 16. Baba, E.; Kan, D.; Yamada, Y.; Haruta, M.; Kurata, H.; Kanemitsu, Y.; Shimakawa, Y., Optical and Transport Properties of Transparent Conducting La-doped SrSnO3 Thin Films. J. of Phy. D: Appl.Phys. 2015, 48, 455106. 17. Liu, Q.; Dai, J.; Zhang, X.; Zhu, G.; Liu, Z.; Ding, G., Perovskite-Type Transparent and Conductive Oxide Films: Sb- and Nd-doped SrSnO3. Thin Solid Films 2011, 519 (18), 60596063. 18. Prathiba, G.; Venkatesh, S.; Kumar, N. H., Structural, Magnetic and Semiconducting Properties of Fe Doped SrSnO3. Solid Stat. Comm. 2010, 150, 1436. 19. Gao, Q.; Chen, H.; Li, K.; Liu, Q., Band Gap Engineering and Room-Temperature Ferromagnetism by Oxygen Vacancies in SrSnO3 Epitaxial Films. ACS Appl. Phys. and Mater. 2018, 10, 27503. 20. T. Wang, L. R. T., A. Prakash, W. Nunn, G. Haugstad, and B. Jalan, Defect-Driven Localization Crossovers in MBE-Grown La-doped SrSnO3 Films. Phys. Rev. Mater. (R) 2017, 1, 061601. 21. Chaganti, V. R. S. K.; Prakash, A.; Yue, J.; Jalan, B.; Koester, S. J., Demonstration of a Depletion-Mode SrSnO3 n-Channel MESFET. IEEE Elec. Dev. Lett. 2018, 39, 1381. 22. A. M. Goldman, A. M., Electrostatic Gating of Ultrathin Films. Annu. Rev. Mater. Res. 2014, 44 (1), 45-63. 23. S. Z. Bisri; Shimizu, S.; Nakano, M.; Iwasa, Y., Endeavor of Iontronics: from Fundamentals to Applications of Ion-Controlled Electronics. Adv. Mater. 2017, 29, 1607054. 24. Leighton, C., Electrolyte-Based Ionic Control of Functional Oxides. Nat. Mater. 2018, 18, 13. 25. Kim, S. H.; Hong, K.; Xie, W.; K. H. Lee, S. Z.; Lodge, T. P.; Frisbie, C. D., Electrolyte‐ Gated Transistors for Organic and Printed Electronics. Adv. Mater. 2013, 25, 1822. 26. Prakash, A.; Dewey, J.; Yun, H.; Jeong, J. S.; Mkhoyan, K. A.; Jalan, B., Hybrid Molecular Beam Epitaxy for the Growth of Stoichiometric BaSnO3. J. Vac. Sci. Technol. A 2015, 33, 060608. 27. Keun, H. L.; Moon, S. K.; Zhang, S.; Gu, Y.; Lodge, T. P.; Frisbie, C. D., “Cut and Stick” Rubbery Ion Gels as High Capacitance Gate Dielectrics. Adv. Mater. 2012, 24, 4457. 28. Lee, A. P.; Ramakrishnan, T. V., Disordered Electronic Systems. Rev. Mod. Phys. 1985, 57 (2), 287-337. 29. Altshuler, A. L.; Khmelnitzkii, D.; Larkin, A. I.; Lee, P. A., Magnetoresistance and Hall effect in a Disordered Two-Dimensional Electron Gas. Phys. Rev. B 1980, 22, 5142. 30. Altshuler, B. L.; Aronov, A. G.; Lee, P. A., Interaction Effects in Disordered Fermi Systems in Two Dimensions. Phys. Rev. Lett. 1980, 44, 1288. 31. Altshuler, B. L.; Aronov, A. G., Electron-Electron Interactions in Disorder Systems. NorthHolland: Amsterdam, 1985.


12

Page 13 of 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


32. Koon, D. W.; Castner, T. G., Hall Effect Near the Metal-Insulator Transition. Phs. Rev. B. 1990, 41 (17), 12054-12070. 33. Fujiwara, K.; Nishihara, K.; Shiogai, J.; Tsukazaki, A., Enhanced Electron Mobility at the Two-Dimensional Metallic Surface of BaSnO3 Electric-Double-Layer Transistor at Low Temperatures. App. Phy. Lett. 2017, 110 (20), 203503. 34. Goh, K. E. J.; M. Y, S.; Hamilton, A. R., Use of Low-Temperature Hall Effect to Measure Dopant Activation: Role of Electron-Electron Interactions. Phs. Rev. B. 2007, 76 (19), 193305. 35. Xia, Y.; Xie, W.; Ruden, P. P.; Frisbie, C. D., Carrier Localization on Surfaces of Organic Semiconductors Gated with Electrolytes. Phs. Rev. Lett. 2010, 105 (3), 036802. 36. Bergmann, G., Weak localization in Thin Films: A Time-of-Flight Experiment with Conduction Electrons. Phys. Rep. 1984, 107, 1. 37. Z. L. Higgins; Scanlon, D. O.; Paik, H.; Sallis, S.; Nie, Y.; Uchida, M.; Quackenbush, N. F.; Wahila, M. J.; Sterbinsky, G. E.; Arena, D. A.; Woicik, J. C.; Schlom, D. G.; Piper, L. F. J., Direct Observation of Electrostatically Driven Band Gap Renormalization in a Degenerate Perovskite Transparent Conducting Oxide. Phys. Rev. Lett 2016, 116, 027602. 38. Leng, X.; Bollinger, A. T.; Božović, I., Purely Electronic Mechanism of Electrolyte Gating of Indium Tin Oxide Thin Films. Sci. Rep. 2016, 6, 31239.


13


Page 14 of 17

Figures (color online):

Figure 1: (a) Schematic of an ion-gel-gated Hall bar structure illustrating the formation of EDL at the SSO film/ion-gel interface, (b) optical micrograph of the patterned Hall bar, (c) logarithmic sheet resistance versus T-1/4 plot for the pristine 12 nm La-doped SSO/12 nm undoped SSO/GSO (110) film, (d) temperature-dependent Rs of the same sample as a function of applied gate bias. Inset shows the Rs vs. ln T plots for Vg ≥ 2V. Dotted lines are fit to the data. Arrows indicate the temperature at which slope of the linear fits appears to deviate.


14

Page 15 of 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2: (a) Temperature dependent -1/eRH of 12 nm La-doped SSO/12 nm undoped SSO/GSO (110) at different applied bias. The inset shows normalized Hall coefficient change as a function of temperature, !

∆!! !

(!"# !)

as a function of the normalized sheet resistance change, !

!

∆!! (!"# !)

revealing a linear relationship, (b) the Hall mobility measured at 150 K as a function of induced surface charge density, nhall, (c) normalized MR at 10 K at different gate biases. Note the background charge density of 4 × 1012 cm-2 at 0 V is neglected in the determination of nhall owing to their low mobility.


15


Page 16 of 17

Figure 3: (a) Temperature dependent Rs of 30 nm La-doped SSO/12 nm undoped SSO/ GSO (110) as a function of Vg. The inset shows the excellent overlap of the measured temperature dependent Rs before and after the ion-gel gating processes, (b) Vg cycle as a function of time, (c) the corresponding change in Rs at T = 280 K as a function of time due to the voltage cycle illustrated in part b. (d) Gate effect (red solid symbols) and irreversibility (blue solid symbols) at T = 280 K at different Vg. Inset shows a representative cycle of resistance change with time after application and removal of Vg. 𝑅! 0 𝑉 , 𝑅!" 𝑉! and 𝑅!"" 𝑉! are measured sheet resistance at 0 V, Vg and 0 V respectively as indicated in the inset.


16

Page 17 of 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TOC 76x44mm (300 x 300 DPI)


Electrostatic Control of InsulatorâMetal Transition in La-doped SrSnO3

Recommend Documents

Electrostatic Control of InsulatorâMetal Transition in La-doped SrSnO3