Direct Dopant Patterning by a Remote Monolayer Doping Enabled by

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Direct Dopant Patterning by Remote Monolayer Doping Enabled by Monolayer Fragmentation Study Ori Hazut, and Roie Yerushalmi Langmuir, Just Accepted Manuscript • Publication Date (Web): 13 May 2017 Downloaded from http://pubs.acs.org on May 21, 2017

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Direct Dopant Patterning by Remote Monolayer Doping Enabled by Monolayer Fragmentation Study Ori Hazut and Roie Yerushalmi* Institute of Chemistry and the Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram Jerusalem, 91904 Israel

KEYWORDS. monolayer doping, silicon, surface chemistry, phosphorous, boron

ABSTRACT

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The development of new doping methods extending beyond the traditional and wellestablished techniques is desired to match the rapid advances made in semiconductor processing methods and nanostructure synthesis in numerous emerging applications, including the doping of 3D architectures. To address this, monolayer doping (MLD) and monolayer contact doping (MLCD) methods were recently introduced. The monolayer doping methods enable separation of the doping process of nanostructures from the synthesis step, hence it is also termed ex-situ doping. Here we present a new ex-situ monolayer doping method termed remote monolayer doping (R-MLD). The non-contact doping method is based on the thermal fragmentation of dopant containing monolayers and evaporation processes taking place during annealing of the un-capped monolayer dopant source positioned in proximity, however, without making physical contact with the target semiconductor surface. We present a two-step anneal procedure that allows the study of the dopant monolayer fragmentation and evaporation stages and quantification of the doping levels obtained during each of the steps. We demonstrate the application of R-MLD for achieving large scale, direct patterning of silicon substrates with sharp doping profiles. The direct dopant patterning is obtained without applying lithographic processing steps to the target substrate. The non-contact doping process, monolayer decomposition and fragment evaporation were studied by thermogravimetric analysis coupled with mass spectrometry (TGA-MS), and sheet resistance measurements. The doped patterns were characterized by scanning electron microscopy (SEM), scanning capacitance microscopy (SCM) and time of flight secondary ion mass spectroscopy (TOF-SIMS).


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The intentional introduction of impurities in semiconductors (SCs), commonly termed doping, is essential for building functional electronic and optical devices. With the increasing demand for processing techniques compatible with nanostructures, and emerging 3D device architectures, the use of common doping methods such as ion implantation become less well-suited because of the induced lattice damage, difficulty to create sharp doping profiles at the nanoscale, and further complications that become of prime concern at the nanoscale.1–3 Some of the doping methods that were developed to address these challenges include spin-on doping (SOD), and more recently the monolayer doping (MLD) and monolayer contact doping (MLCD).4–13 Both MLD and MLCD utilize surface chemistry to form monolayers that are used as the dopant source in the process for achieving a restricted dopant source with well-defined dose and positioning. The monolayer source is then used for generating a sharp and uniform doping profile, typically limited to the semiconductor or nanostructure interface region by a rapid thermal anneal step.8,11 In the context of semiconducting nanostructures, such as nanowires and nanoribbons, the MLD and MLCD methods provides an additional useful feature of separating the doping step from the semiconducting nanostructure synthesis step, therefore these methods are also referred to as exsitu doping methods in contrast to the commonly used in-situ doping methods, such as those implemented in chemical vapor deposition (CVD). MLD requires monolayer formation directly at the SC interface intended for doping. In contrast, for MLCD, the monolayer used as dopant source is formed on a separate substrate, termed the donor substrate, which is then brought to contact with the substrate to be doped, termed target substrate, and both are annealed in contact. During the rapid anneal step the doping precursor monolayer decompose and dopant atoms and fragments diffuse into both the donor and target substrates. Namely, in the MLCD process the surface chemistry treatments required for doping are completely separated from the


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semiconductor intended for doping by applying the surface chemistry required for the monolayer dopant source at a separate substrate and further decoupling the doping procedure from the SC target. MLCD was recently used for demonstrating 3D junction formation at the nano-scale by applying to Si-NWs where the parallel p-i-n junctions across Si-NWs were formed starting from an intrinsic Si-NWs by a one-step process. In this study donor substrates with boron and phosphorous monolayers were applied simultaneously to intrinsic Si-NWs.14 Our results showed that during the MLCD process, although the dopant source is placed in tight contact with the target, fragmented molecular components evaporate and contribute to the overall dopant distribution measured across the NW junction, thereby adding a non-contact component to the process, in addition to the main contact doping processes that dominated the MLCD process.14 However the non-contact doping mechanism and related monolayer fragmentation details were not studied. There is increasing interest in the development of non-lithographic methods for dopant and electrodes patterning, especially for methods compatible with nanostrucutres.13,15–18 Here we present a new method for the doping of silicon using monolayers as dopant source termed remote monolayer doping (R-MLD, Figure 1). R-MLD relies on understanding of the monolayer fragmentation and evaporation details which opens the way for establishing a new monolayer-based doping scheme affording direct dopant patterning using shadow masks. RMLD is performed such that the doping process is carried while placing a separator mask with micron scale gap between the donor and target silicon substrates. The gap between the donor and target substrates created by the mask restricts the mass transfer between the two to the vapor phase exclusively, avoiding the contact mode transfer used in MLCD. The monolayer source undergo fragmentation at the elevated temperature during the rapid thermal anneal generating volatile fragments, including dopant atoms, which are the source for doping of the target


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substrate. We present the application of R-MLD for the direct patterning of silicon substrates with p-type, and n-type regions, without the need for employing processing steps to the target substrates. This method provides a scalable procedure for the direct patterning of dopants in SCs using a monolayer source and therefore extends the available collection of monolayer-based exsitu doping methods.

RESULTS AND DISCUSSION The non-contact doping process details were studied for monolayer sources containing phosphorous and boron atoms using thermogravimetric analysis coupled with mass spectrometry (TGA-MS) for tracking the molecular fragments evaporated from the sample during the anneal process. The doped surfaces were studied using macroscopic 4-point sheet resistance measurements, scanning electron microscopy (SEM), scanning capacitance microscopy (SCM), and time of flight secondary ion mass spectroscopy (TOF-SIMS). The remote monolayer dopinginvolves several processes that are induced by the thermal ramping during the rapid thermal anneal. These processes commence at different temperatures, including breaking of molecular components, evaporation, reaction of the fragments with the oxide surface at the substrate interface, and dopant diffusion through the native oxide layer and the semiconductor below it. A two-step anneal process involving a first non-contact anneal step followed by a second step in contact mode was used for studying the multiple aspects of the RMLD process outlined above (Figure 2a). The details of the two-step experiment were designed as follows: in the first anneal step a donor substrate (A) is annealed without physically contacting the target substrate (B), by placing a 280 µm thick silicon spacer between the two substrates and the anneal is carried out from room temperature to a specified temperature, Tinitial, in the range of


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150-1000°C. Namely, the first step is R-MLD process carried from RT to a specified temperature. Next, substrates A and B that were annealed to the specified temperature in a noncontact mode are used in a second anneal process as donor substrates, this time placed in direct contact with fresh target substrates, C and D, respectively.

Figure 1. Remote monolayer doping (R-MLD) process schematics. A monolayer containing dopant atoms is formed on a donor substrate. A separator mask with desired pattern is placed between the donor substrate and a target substrate and annealed using rapid thermal anneal (RTA). During the anneal process monolayer molecules thermally decompose resulting in evaporation of fragments containing dopant atoms that function as gas-phase dopant source. Further increasing the anneal temperature during the rapid thermal anneal step induce diffusion and activation of the dopants which are incorporated into the semiconductor surface. The second anneal process is performed in contact mode, characteristic of MLCD process,11 at sufficiently high temperature of 1000°C to achieve high activation yield of dopants, if present, for all four substrates (‘A’-‘D’). The two-step process described here separate the fragmentation


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and evaporation of dopants from the thermal activation process. Measuring SR for various Tinitial values for the four substrates obtained by the process described above and studying the molecular details of monolayer fragmentation by TGA-MS result in correlation between the doping processes and molecular fragmentation processes that the monolayer source undergo, as further discussed below. The two-step anneal process was performed for three types of monolayers, diphenyl phosphine oxide (P1), triphenyl phosphine oxide (P2), and diethyl methylenediphosphonate (P3), (Figure 1). The change in SR values with Tinitial values presented in Figure 2b-d can be accounted for by considering the fragmentation, evaporation and diffusion processes taking place for each monolayer type. While both P1 and P3 gave similar results, with significant decrease in SR, depending on the Tinitial values, P2 showed only moderate decrease in SR, indicative of non-efficient doping process, as will be further discussed below. For both P1 and P3 substrates ‘A’ exhibited a decrease in the SR values for all Tinitial temperatures studied compared to the initial SR of untreated intrinsic silicon wafers (untreated wafers gave ~1x106 Ω/□). This result is expected since the dopant containing monolayer is prepared directly on A, being the original donor substrate which is annealed to 1000°C in the second step for all cases functioning as characteristic donor substrate in MLCD process performed up to 1000°C.11 For both P1 and P3 the decrease in SR for substrates ‘B’ evolved with temperature (region I), unlike the almost constant SR values obtained for substrates ‘A’. This result show that the doping levels of substrates ‘B’ which were physically separated from donor substrates ‘A’ by the mask evolved with Tinitial temperature applied in the first anneal step, according to the extent of evaporation of fragments, including of dopant atoms originating from the monolayer source formed on substrate A. Sufficiently high Tinitial temperatures result in full


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fragmentation and evaporation therefore further increase in Tinitial does not result in further significant change in SR values, as shown for regions II-III for P1 and P3 (Figure 2b,d). For both P1 and P3 substrates ‘C’ and ‘D’ showed decrease in SR values for 150 < Tinitial < ~450°C (region I), plateau for ~450 < Tinitial < 750°C (region II), and increase for 750 < Tinitial < 1000°C (region III). This trend can be explained by considering that dopant atoms arrive at both substrates ‘C’ and ‘D’ by a secondary path, from substrates ‘A’ and ‘B’, respectively, functioning as donor substrates in the MLCD process performed in the second anneal step. Therefore, the effectiveness of substrates ‘A’ and ‘B’ to function as dopant donor substrates in the second anneal process, depend on Tinitial applied in the first step; For low Tinitial temperatures (region I) monolayer fragmentation takes place with the fragments containing dopant atoms available at the oxide surface of substrate A, making the substrate an effective source for dopants in the second anneal step. In contrast, because of the relatively low temperatures (region I), evaporation is still limited, leaving substrate ‘B’ void of dopant source. Therefore, in this Tinitial region, substrates ‘C’ are effectively doped by contact doping with ‘A’ at the second anneal step exhibiting low SR values while substrates ‘D’ remains only lightly doped, with high SR values, after annealing in contact with donor substrates ‘B’ which are void of dopant atoms. For intermediate Tinitial temperatures (region II), sufficiently high for fragmentation and evaporation of monolayer fragments originating from donor substrates ‘A’ take place. Therefore the distribution of volatile fragments containing dopants is equalized between substrates ‘A’ and ‘B’ in the gas phase, over the micron scale gap, during the first anneal step. During the second anneal step in contact mode, these fragments diffuse into substrates ‘C’ and ‘D’, hence all four substrates are equally doped and show low sheet resistance values for region II. Finally, in region III, the first anneal process is performed with sufficiently high Tinitial temperatures for inducing


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fragmentation, diffusion and incorporation of dopants onto the bulk of substrates ‘A’ and ‘B’, depleting the surface of these substrates from potential dopants for the second anneal step. Thus, high Tinitial temperatures applied in the first anneal step make dopant transfer non-efficient in the second anneal step, resulting in high SR values for substrates ‘C’ and ‘D’ for region III. Monolayer fragmentation processes for specified anneal temperatures and correlation with the SR values are further studied below using TGA-MS discussed after considering the results obtained for P2.

Figure 2. Two-step anneal process involving a first non-contact remote monolayer doping step and a second contact doping step termed R-MLD and MLCD, respectively. (a) Schematics of the process. Sheet resistance measurements for all four substrates ‘A’-‘D’ using: (b) P1, (c) P2, and


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(d) P3 monolayers formed on ‘A’. Roman letters I-III indicate the temperature ranges used for discussing the results in the text. SR values obtained for P2 in the two-step anneal process resulted in different behavior compared with the results obtained for P1 and P3, showing much lower decrease in SR values for substrates ‘A’-‘D’, indicative of overall lower doping efficiency for this type of monolayer. The traces obtained for P2 (Figure 2c) lack the detailed trends discussed above for both P1 and P3 for each of the substrates ‘A’-‘D’. TGA-MS was used for quantifying the mass loss (evaporation) and for identifying and correlating the molecular fragments evolving for each of the monolayer types studied here for the range of temperatures studied (Figure 3). For both P1 and P3 the atomic masses detected by TGA-MS corresponded to fragments that were associated to molecular components of the original precursors and correlated with the weight-loss dTGA peaks. For P1 (Figure 3a), the peak observed at m/z of 78 is associated with benzene ring, with additional peaks at m/z of 50, 51, and 52 corresponding to the typical fragments of benzene, and possibly HxOP (x=3-5) fragments with the same masses.19 For P3 (Figure 3c), the weight loss peak is accompanied by MS peaks of m/z 31 which correspond to atomic phosphorus and m/z of 108 and 110 which correspond to C2HxO3P fragments where x = 5 and 7, respectively. These fragments are related to the molecular structure of P1 and P3 molecule as highlighted by the dashed circles in Figure 3. For P2 the dTGA mass loss signal is clear while the MS analysis did not yield any signal indicative of fragments (Figure 3b). This result suggests that P2 molecules were desorbed from the oxide surface prior to thermal fragmentation and to thermally induced reactions. It should be noted that the capillary setup used for coupling the TGA to the MS system components has low sensitivity to high atomic masses. Thus evaporated, non-fragmented molecules were not


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detectable in this measurement setup. Previous studies of the incorporation efficiency of phosphorous into SiO2 studied by TGA-XPS provide complementary information since the TGA-XPS analysis quantify the phosphorous retained in the oxide matrix as opposed to the TGA-MS analysis that quantify the evaporated counterpart. The incorporation efficiency based on the TGA-XPS studies were ~70% for P1, ~0% for P2, and ~40% for P3, in agreement with the current TGA-MS and SR results for these precursors.11 Combining the SR measurements and the TGA-MS results obtained for the different molecular precursors studied, point out the roles of molecular fragmentation and type of surface interactions of fragments and whole molecules in the monolayer doping process. Specifically, P2 molecules assemble by physical adsorption at the SiO2 surface, mainly by H-bond interactions without forming covalent interactions with the polar interface, in contrast to P1 and P3 molecules that form covalent binding at the oxide surface.11,20 The non-covalent (H-bond) surface interactions of P2 with the oxide together with the lack of detectable MS signals or fragments while the dTGA data show a clear mass loss signal imply that P2 monolayer heated under vacuum resulting in whole molecule dissociation from the SiO2 surface, namely no dopant atoms or reactive fragments retain on donor substrates ‘A’. We also consider the vapor of the intact molecules present in the gas phase as potential source for doping at elevated temperatures. For evaluating the significance of this source we take into account the mean free path representative of the process, in the order of millimeters for typical process parameters (e.g. T=600°C, chamber pressure=0.1 mbar), making the evacuation time scale of vapors from the gap between the donor and target substrate much shorter than the temperature ramp time, which is in the order of a few seconds. Given the process parameters used here, we conclude that the gas phase concentration of P2 molecules is negligible by the time that the anneal process reach


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sufficient temperatures for fragmentation. Thus, the evaporation of P2 molecules at temperatures close to, or below the decomposition temperatures, without forming fragmented reactive species that can react with the oxide surface for retaining these fragments for the higher process temperatures makes the doping process using P2 molecules non-efficient overall. This result point at the contribution of the covalent binding of P1 and P3 to the oxide surface in assisting in the robustness of the monolayer doping process by allowing processing at sufficiently high temperatures where fragmentation and diffusion process takes place without diminishing the doping source depending on the kinetic process parameters such as ramp rate and molecular decomposition rate. For P2 these considerations becomes cardinal since the reactivity of intact molecules with the oxide surface is not sufficient to allow retention of the dopant source and incorporation in the higher anneal temperatures of the process. In view of these results we suggest that non-covalently bound monolayers may still be applied for monolayer doping methodologies provided that the molecular fragmentation processes initiate at temperatures that are lower than the dissociation temperatures of the molecular precursors in the monolayer assembly. This may be attained by designing molecules with facile bond cleavage mechanisms and non-covalent assemblies that feature stronger H-bond interactions, electrostatic interactions, pi-stacking interactions, or combinations of several types of non-covalent interactions. The R-MLD process was further studied for various process pressures (in the range of 5x10-2 to 300 mbar) and atmospheres, including argon (inert), dry air (oxidizing), and 4% hydrogen in argon (reducing) atmospheres using P3 as monolayer doping source. In addition, the process was studied for different donor-target substrate separations ranging between 0 (contact) and 600 µm gap. Sheet resistance measurements did not show significant dependence of the resulting doping for the R-MLD processes for the range of process pressure, atmosphere types, or gaps studied


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(Figures S1-S2). This result can be explained by considering the mean free path and the gap dimensions between the donor and target substrates. At low pressures the mean free path is in the order of millimeters, as indicted previously, therefore the monolayer fragments transfer rapidly across the gap between the substrates for the range of separator distances studied here (0 to 600 µm, see Figure S2). Nevertheless, it is expected that for macroscopic gap separations, in the range of few millimeters to centimeters, depletion in the doping efficiency would arise. At higher process pressures, where the mean free path is in the order of microns, for the typical process temperatures studied, a few collisions take place on the path between the donor and target substrates. Nevertheless, fragments will eventually deposit at the target substrate due to the large, macroscopic area of the samples relative to the distance between substrates, resulting in deposition similarly to a conventional CVD process. Furthermore, our results suggest that for sufficiently high anneal temperature (1000°C) the specific details of process atmosphere type are secondary in determining the overall SR obtained and thus the doping levels obtained. Further study is in progress for considering the influence of process atmosphere type on the formation of impurity species at the SC-oxide interface as well as the influence of process atmosphere on molecular fragmentation onset temperature which may be an important parameter in the context of monolayer doping processes.


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Figure 3. Degradation of phosphorous containing monolayers on SiO2 nanoparticles (NPs) studied by TGA-MS analysis. Weight change (dTGA) and fragment masses detected by MS during thermal ramping for P1, P2, and P3 (a-c, respectively). Dashed circles highlight the primary fragments detected for P1 with m/z 78 and for P3 with m/z 110. For P2 no MS signals were detected.


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Finally, remote monolayer dopingwas applied for demonstrating large scale, direct patterning of silicon substrates with dopants without the use of lithographic processing steps for the target substrate (Figure 4). The spacer used was 75 µm thick silicon wafer patterned by standard silicon processing methods to form evaporation mask with through-etch openings (Figure 4a). The patterned mask was placed between the donor and target substrates and annealed. The evaporated fragments reach the target substrate in the confined regions defined by the patterned openings in the mask. The resulting doping patterns were characterized using SEM by secondary electrons (SE) imaging (Figure 4b,c). SEM was previously demonstrated as a method capable of generating imaging contrast depending on the surface doping levels.21–23 The pattern uniformity over a large area is shown in the low magnification image (Figure 4b). The doping patterning was also characterized by SCM for mapping the doped regions (Figure 4d).24,25 The patterned features demonstrated here extend over large areas, showing good uniformity, with relatively large feature size of ~ 20 µm, however smaller features can be achieved, if desired, depending on the mask preparation technique used. Both SEM and SCM images show doping that extend beyond the mask pattern which is attributed to gas-phase diffusion between the mask and target substrate that were placed in physical contact without applying additional pressure. This phenomenon may be minimized by a better contact as well as by applying pressure when clamping the target wafer and mask.


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Figure 4. Direct patterning of silicon substrates by remote monolayer doping. (a) Optical microscope image of the mask used, (b) SEM imaging using secondary electrons of a sample doped with P3 showing the dopant pattern at low (b) and high (c) magnification. (d) SCM image of the doped pattern. To demonstrate the generality of the R-MLD process studied here in details for phosphorous containing monolayers, the R-MLD process was employed for the direct patterning of silicon substrates with boron dopants using phenylboronic acid as monolayer forming precursor.14 SEM images show the pattern obtained by the corresponding mask with dopant contrast obtained for


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phosphorus and boron using P3 and phenylboronic acid as monolayer precursors, respectively (Figures 5a,b). The SEM images show higher contrast for boron compared to the phosphorus pattern which may be related to unwanted gas-phase diffusion of dopants between the mask and acceptor substrates, affecting the pattern resolution, as discussed above, as well as to a sharper profile, as further demonstrated by the TOF-SIMS profiles, affecting the pattern contrast (Figure 5c).

Figure 5. Doping profile analysis. False color SEM images of the samples patterned using RMLD and mask with (a) phosphorous, P3, and (b) boron, phenylboronic acid used as monolayer sources. (c) TOF-SIMS phosphorus and boron concentration profiles. CONCLUSIONS In conclusion, we present a new ex-situ doping method termed remote monolayer doping(RMLD). The doping process was demonstrated as a method for direct doping and patterning of silicon wafers using a monolayer source as a dopant source in a one-step process. The process details were thoroughly studied by 4-point probe, TGA-MS, SEM, SCM, and TOF-SIMS. Understanding the molecular details associated with the different types of monolayers studied and the fragmentation processes and their relation to the doping process provided insights that


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will allow the extension of this method for use with other types of dopants and semiconductors in the future.


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MATERIALS AND METHODS Monolayer preparation Formation of monolayers on Si wafers was carried out by cleaning high purity diced Si wafers (Topsil, Res. > 10 kΩ cm) in piranha solution (3:1 H2SO4 : 30% H2O2) for 15 min followed by basic piranha cleaning (5:1:1 H2O : 27% NH4OH : 30% H2O2) for 8 min in a sonication bath at 60 °C, followed by drying at 115°C in oven. The cleaned substrates were immersed in mesitylene precursor solutions of diphenylphosphine oxide (P1, 1.2 mM), triphenylphosphine oxide (P2, 45 mM), or tetraethylmethylene diphosphonate (P3, 40 mM). The reaction was carried out in a sealed vial at 100°C for 2 hrs followed by rinsing in mesitylene (x3), dichloromethane (x3), and drying under N2 flow.

Caution: Piranha solutions are extremely strong and dangerous oxidizing agents and should be used with extreme caution. May explode in contact with organic solvents.

Formation of monolayers on SiO2 nanoparticles (NPs) was performed by reacting 0.1 g NPs in 10 mL of precursor solution for 2 hrs at 100˚C. Then, NPs were removed from the solution by centrifugation and removal of the supernatant phase followed by rinsing in mesitylene (x3) and hexane (x3) and drying in oven at 115°C for 1 hr.

TGA Experiments Thermogravimetric analysis was performed using a Netzsch STA 449 F3 Jupiter TG-DSC coupled with QMS 403 D Aeolos mass spectrometer. Experiments were performed using ~15 mg


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of reacted NPs in alumina crucible, heating from 50°C to 1150°C at a constant ramp rate of 1.5°C/min under Ar flow of 50 mL/min and MS scanning from 1 to 300 amu.

Spacer and mask preparation Si wafers (280 µm thick) were patterned by standard photolithography process using AZ4562 photoresist. The patterned wafers were etched using a Bosch etch process in Oxford instruments Plasmalab 100 ICP-RIE system.

Rapid thermal annealing AnnealSys AS-Micro was used for rapid thermal anneal (RTA) processes. The process chamber was purged in argon (or other gas as noted) and evacuated to 0.05 mbar prior to the anneal process. In experiments performed at higher pressures the chamber was filled with the specified gas after the purge and evacuation cycle. Anneal was carried out by rapid heating to 1000°C in 6 sec and further annealing for 30 sec.

Sheet resistance measurements Four-point probe sheet resistance measurements were performed using Jandel RM3-AR setup. Native oxide was removed from all samples before measurement by dipping in 1% HF solution for 5 min followed by washing in DI water, isopropyl alcohol and drying under N2 flow.

Scanning electron microscopy


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Imaging of dopant patterns by SEM contrast was performed using FEI Magellan 400L scanning electron microscope. The microscope was operated in secondary electrons mode with acceleration voltage of 500 V and beam current of 0.4 nA.

Scanning capacitance microscopy Dopant mapping was performed using Bruker Innova AFM with a scanning capacitance microscopy (SCM) module and PtIr coated AFM tip (Bruker SCSI-COMT). ASSOCIATED CONTENT Supporting Information. Figures S1, S2. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author * Email: [email protected] Notes The authors declare no competing financial interest. ACKNOWLEDGMENT We thank C. Cytermann for assistance in TOF-SIMS measurements. This work was supported in part by the a starting grant from the European Research Council (ERC) under the European Community's Seventh Framework Programme Grant Agreement No. 259312, and the United States-Israel Binational Science Foundation grant 2012088.


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Direct Dopant Patterning by a Remote Monolayer Doping Enabled by

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