Defect-Mediated In-Plane Electrical Conduction in Few-Layer sp

Research Article www.acsami.org

Cite This: ACS Appl. Mater. Interfaces 2018, 10, 17287−17294

Defect-Mediated In-Plane Electrical Conduction in Few-Layer sp2‑Hybridized Boron Nitrides Dong Yeong Kim, Hokyeong Jeong, Jaewon Kim, Nam Han, and Jong Kyu Kim* Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang 37673, Republic of Korea S Supporting Information *

ABSTRACT: In-plane electrical conduction in sp2-hybridized boron nitride (sp2-BN) is presented to explore a huge potential of sp2-BN as an active material for electronics and ultraviolet optoelectronics. Systematic investigation on temperature-dependent current−voltage (I−V) characteristics of a few-layer sp2-BN grown by metal−organic vapor-phase epitaxy reveals two types of predominant conduction mechanisms that are Ohmic conduction at the low bias region and space-charge-limited conduction at the high bias region. From the temperature-dependent I−V characteristics, two shallow traps with activation energies of approximately 25 and 185 meV are observed. On the basis of the near-edge X-ray absorption fine-structure spectroscopy, boron−boron (B−B) homoelemental bonding which can be related to grain boundary and nitrogen vacancy (VN) are proposed as the origin of the shallow traps mediating the in-plane conduction in the sp2-BN layer. In addition, a drastic enhancement in the electrical conductivity is observed with the increasing amount of VN that acts as a donor, implying that controlled generation of VN can be an alternative and better approach for the n-type doping of the sp2-BN film rather than ineffective conventional substitutional doping methods. KEYWORDS: boron nitride, space-charge-limited conduction, vacancy, grain boundary, doping, metal−organic chemical vapor deposition

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oxide materials16,17 have been carried out. Space-charge-limited (SCL) transport was observed in monolayer h-BN grown on a Cu(111) foil by the thermal CVD method,18 and weak p-type Ohmic conduction was reported in 1.7 μm thick h-BN grown by metal−organic CVD (MOCVD).19 The origin of the p-type conductivity of h-BN is suggested to be boron vacancy (VB), in analogous to the acceptor-like Ga vacancy in GaN and acceptor-like Al vacancy in AlN.20,21 However, it was not experimentally revealed that what kinds of defects affect the charge transport in sp2-BN because there have been a lack of systematic studies on such defect-mediated electrical conduction properties of sp2-BN. In this study, we present defect-mediated in-plane electrical conduction in wafer-scale few-layer sp2-BN on a 2 in. sapphire substrate grown by MOCVD. Ohmic conduction and SCL conduction (SCLC) are found to be mainly responsible for the electrical conduction at low and high applied biases, respectively. Temperature-dependent current−voltage (I−V) measurement reveals that two shallow traps with activation energies of approximately 25 and 185 meV are involved in the electrical conductions. These traps are suggested to originate

INTRODUCTION 2 sp -Hybridized boron nitride (sp2-BN), especially hexagonal BN (h-BN), has attracted a great attention as passive layers, such as substrates,1−3 dielectrics,4,5 and passivation layers,6,7 for emerging two-dimensional (2D) materials-based electronic devices because of its excellent dielectric properties and chemical, mechanical, and thermal stability. On the other hand, sp2-BN can be potentially used as an excellent active material for high-temperature electronics or deep ultraviolet optoelectronics by taking full advantages of its wide-gap semiconducting nature with strong light−matter interaction.8−12 For exploring such a new and huge potential of active sp2-BN, it is essential to understand its semiconducting properties including electrical conduction and to figure out a way to control conductivity. Nevertheless, many studies have focused on understanding the dielectric properties rather than the semiconducting properties of sp2-BN. Crystalline defects are key features to understand and control the electrical properties of crystals including sp2-BN. The early experimental work showed that the electric conductivity of BN can also be strongly affected by defects by the comparison of two turbostratic BN films grown by sputtering with pure Ar or N2 gases.13 More recently, studies on the transport characteristics of h-BN grown by chemical vapor deposition (CVD) that is widely used for the synthesis of 2D materials14,15 as well as © 2018 American Chemical Society

Received: March 17, 2018 Accepted: April 27, 2018 Published: April 27, 2018 17287

DOI: 10.1021/acsami.8b04389 ACS Appl. Mater. Interfaces 2018, 10, 17287−17294

Research Article

ACS Applied Materials & Interfaces

Figure 1. Structural and optical properties of the MOCVD-grown sp2-BN film. (a) Raman spectrum showing E2g vibration mode of the sp2-BN film at 1370 cm−1. (Inset) E2g in-plane vibration mode of sp2-BN. (b) Optical absorbance spectrum and (inset) corresponding Tauc’s plot. Measured optical band gap energy is about 5.92 eV. (c) Core-level XPS of the sp2-BN film for B 1s and N 1s, whose binding energies are 190.8 and 398.4 eV, respectively. (d) XRR of the sp2-BN film. Film thickness is estimated to be about 2.66 nm.

to the Raman spectroscopy as well as NEXAFS spectroscopy, as shown in Supporting Information S2. Figure 1 shows the structural and the optical properties of the MOCVD-grown BN film. Raman scattering at 1370 cm−1 is observed, which corresponds to the E2g in-plane vibration mode of sp2-BN,24,25 as shown in Figure 1a. Figure 1b is the optical absorption spectrum of the MOCVD-grown sp2-BN film, exhibiting a strong optical absorption at around 202 nm without any long-wavelength tail. This corresponds to the optical band gap energy of 5.92 eV (inset of Figure 1b), which is in the range of reported band gap energy of sp2-BN films.8,24,25 XPS core-level spectra are shown in Figure 1c. The core-level binding energies of B 1s and N 1s states are 190.8 and 398.4 eV, respectively, which are consistent with previous reports on sp2-BN.25,26 The thickness of the grown sp2-BN is estimated to be 2.66 nm by the XRR measurement as shown in Figure 1d, which corresponds to 7−8 atomic layers. The crosssectional transmission electron microscopy (TEM) image clearly shows a layered structure of the grown sp2-BN film with approximately seven atomic layers (see Supporting Information S3). To identify the crystal structure of multilayer sp2-BN, the stacking order should be studied at the atomic level because the sp2-BN film can have AB stacking (hexagonal), ABC stacking (rhombohedral), and random stacking (turbostratic).27,28 Although the crystal structure of BN could not be determined exactly in this work, Figure 1 and X-ray spectroscopies (discussed later) imply that the grown BN film is sp2-hybridized. For the electrical conduction measurement, a series of rectangular Ti/Au (thickness of 20 nm/150 nm) metal electrodes in the form of a transmission line measurement (TLM) type were fabricated on the as-grown sp2-BN film on a sapphire substrate by photolithography, followed by electron beam evaporation of Ti and Au. The deposited metal contact was annealed at 800 °C for 1 min under N2 ambient by using a

from boron−boron (B−B) homoelemental bondings and nitrogen vacancies (VN), respectively, according to the nearedge X-ray absorption fine-structure (NEXAFS) spectroscopy. In addition, a drastic change in the electrical conductivity over 5 orders of magnitude is observed with different amounts of VN in sp2-BN films. This is the first experimental report to demonstrate that VN can act as a donor. On the basis of our experimental findings, we propose the controlled generation of VN as a new and effective n-type doping method for sp2-BN rather than ineffective substitutional doping22 including the Sidoping method.23 These findings can enhance the understanding of the defect-mediated electrical conduction characteristics of sp2-BN as well as the way to control it. Also, these can help to pave the way for the realization of active sp2-BN-based high-temperature electronics and deep ultraviolet optoelectronics by taking advantages of its large band gap energy, strong light−matter interaction, and thermal and chemical stability. sp2-BN films were grown on 2 in. sapphire substrates at the temperature of 1050 °C and the pressure of 30 mbar by a commercial multiwafer MOCVD system. Pulsed injections of 10 sccm triethylborane and 8000 sccm ammonia (NH3) precursors into the MOCVD reactor were used with hydrogen carrier gas to suppress parasitic gas-phase prereactions between the precursors. The details of sp2-BN growth are provided in Supporting Information S1. MOCVD-grown sp2-BN films on sapphire substrates were characterized by Raman spectroscopy, optical absorbance spectroscopy, and X-ray reflectance (XRR). For both X-ray photoemission spectroscopy (XPS) and NEXAFS spectroscopy using a synchrotron X-ray source, the sp2-BN films grown on a sapphire substrate were transferred onto a conductive silicon substrate to prevent the charging effect by the polymethyl methacrylate-assisted method accompanied with diluted hydrofluoric acid treatment, as shown in Supporting Information S2. Transfer process does not seem to have a big influence on the sp2-BN film according 17288


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Figure 2. Temperature-dependent electrical conduction properties of the sp2-BN film. (a) I−V characteristics in a linear scale and schematic structure of the fabricated device and (b) I−V characteristics in a log−log scale for the temperatures of 100, 250, and 500 K. Slopes of the graph gradually increase from 1 to 2 as the voltage increases for all temperatures.

Figure 3. Electrical conduction in sp2-BN under the small applied voltage. (a) Linear I−V characteristics of the sp2-BN film indicating Ohmic conduction and (b) Arrhenius plot of the temperature-dependent conductivity obtained from (a). The temperature-dependent conductivity can fit into two linear lines, indicating the presence of two defects whose activation energies are about 35.6 and 193 meV.

SCLC.29,30 For the low temperature of 100 K, the current is proportional to Vm with m ≈ 2.62 for the voltage from 1.0 to 1.5 V which is due to trap-filled-limited (TFL) conduction.31 Because TFL conduction is only observed at the temperatures of 100 and 150 K (not shown in the graph), there would exist a shallow trap whose trap level is in the order of a few tens of milli electronvolt (meV). For the temperature of 500 K, the slope becomes larger than 2; thus, the current becomes proportional to Vm with m > 2 as the voltage increases. This also indicates that another trap may be involved in the electrical conduction of the sp2-BN film, which can be thermally activated at the high temperature and generate additional free carriers,32−34 which will be discussed later in more detail. Figure 3a shows the temperature-dependent I−V characteristics near zero bias from −0.4 V to 0.4 V. The linear relation means that the dominant conduction mechanism is Ohmic conduction, which is typically observed in dielectric films when a very low bias voltage is applied, while other carrier transport mechanisms do not have a significant contribution.29 Because Ohmic conduction is mainly attributed to the thermally excited carriers from defect states rather than from the valence band in wide band gap semiconductors, the activation energy of the defect can be obtained from the Arrhenius plot of the temperature-dependent conductivity (σ), as shown in Figure 3b. Assuming that the current flows uniformly in the sp2-BN film, the conductivity is simply calculated by σ = l/(R × S), where l is the channel length, S is the channel area, and R is the resistance of the sp2-BN channel obtained from the slope of the I−V curves shown in Figure 3a. According to the Arrhenius-type equation showing the temperature dependence of the conductivity29

rapid thermal annealing system. No measurable current was observed before annealing, as shown in Supporting Information S4. Electrical conduction measurement was carried out in a chamber under the vacuum of ∼10 mTorr at the various temperatures of 100−500 K. The optical image of the fabricated TLM-type sample and schematic of the measurement setup are shown in Supporting Information S5. Figure 2a shows the temperature-dependent I−V characteristics of the sp2-BN film with the channel length of 3 μm and width of 200 μm. It is nonlinear but symmetric for both positive and negative applied voltages, which is like a back-to-back Schottky diode with the same metal contacts. Because the current through the sapphire is in order of few hundreds of fA (see Supporting Information S6), the observed current−voltage characteristic is mainly attributed to the in-plane electrical conduction in the few-layer sp2-BN film. On the other hand, a potential parasitic factor that could affect the electrical conduction by the diffusion of metal atoms from the metal contacts across the sp2-BN film during the annealing at 800 °C is excluded because of the following two reasons: a drastic decrease of conductivity when annealed at temperature higher than the optimum temperature and no noticeable conduction in the same device configuration fabricated on the sapphire substrate (see Supporting Information S7 for a detailed discussion). Figure 2b is the log(I)−log(V) plot of the I−V characteristics measured at the temperatures of 100, 250, and 500 K. For the low-voltage range smaller than 0.5 V [region (i) in the graph], the slopes at all the temperatures are near unity, indicating Ohmic conduction. However, the slopes gradually increase at the region (ii) and become approximately 2 at the voltage range of 15−30 V [region (iii) in the graph] which is related to the 17289


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Figure 4. SCLC in MOCVD-grown sp2-BN films. (a) Linear I−V2 characteristics, indicating SCLC, and (b) Arrhenius-type plot for the temperature dependence of the current at a given applied voltage. Temperature dependence of the current, composed of two linear curves, indicates the presence of two defects at approximately 18 and 178 meV.

Figure 5. NEXAFS spectrum. (a) NEXAFS B K-edge and N K-edge spectrum of the sp2-BN film and (b) NEXAFS B K-edge spectrum showing π* peak with two shoulder peaks. MOCVD-grown sp2-BN includes nitrogen vacancy as well as boron−boron homoelemental bonding, which can be present in the grain boundary.

⎛ E ⎞ σ = σ0 exp⎜ − a ⎟ ⎝ kT ⎠

monolayer h-BN grown on a Cu foil, which is 0.01 cm2/(V· s) when the dielectric constant is assumed to be 3.18 On the other hand, the current becomes proportional to Vm with m > 2 as the temperature and voltage increase (see also Supporting Information S8). This is related to free carrier generation from traps in the sp2-BN film. When assuming the presence of a single-level trap in a film, the SCLC current is given by the following relation considering the ratio of free to trapped carriers, θ

where σ0 is the pre-exponential factor, Ea is an activation energy of the defect, and kT is the thermal energy at a given temperature T, the measured data can be fitted into two linear lines with different slopes, as shown in Figure 3b. This means that two defects are involved in the electrical conduction, whose activation energies are about 35.6 and 193 meV. This observation coincides with the prediction based on the temperature-dependent I−V characteristics of the sp2-BN film plotted in a log-log scale. As discussed, TFL conduction, which was only observed at the temperatures of 100 and 150 K, can predict the presence of the shallow trap at the energy of a few tens of meV. The current proportional to Vm with m > 2 at the temperature of 500 K also implies the presence of another trap. Figure 4a shows the relation between the current and square of the applied voltage. The linear I−V2 relation implies that the dominant conduction mechanism is SCLC following Child’s rule, which is expressed as

I = C·ε0εiμ

I = C·ε0εiμ

V2 W×θ L2

The θ is expressed by θ=

⎛ E ⎞ Nc exp⎜ − t ⎟ ⎝ kT ⎠ Nt

where Nc is the effective density of states in the conduction band, Nt is the concentration of traps, and Et is the energy level of the trap.29,30 Therefore, the temperature dependence of the current at a given bias also shows the trap level involved in the electrical conduction. Figure 4b shows the temperature dependence of the current at six different bias conditions from 5 to 30 V. Similar to the conductivity at the Ohmic conduction regime, the current at a given bias can be explained by two linear lines, indicating two shallow traps at the energies of approximately 18 and 178 meV. The trap levels are slightly smaller than that obtained through the temperature dependence of conductivity because it does not consider the barrier lowering by the electric field, that is, the Poole−Frenkel effect. In any case, the temperaturedependent I−V characteristics of sp2-BN clearly show that

V2 W L2

where C is a parameter which is 0.7 for the rectangular geometry used in this study, ε0 is the vacuum permittivity, εi is the dielectric constant of sp2-BN, μ is the carrier mobility, L is the channel length, and W is the channel width.29,30 Assuming that the dielectric constant of sp2-BN along the in-plane direction is 6.6,35 the carrier mobility of the MOCVD-grown few-layer sp2-BN is estimated to be 0.003 cm2/(V·s). The estimated carrier mobility is comparable to that of the 17290


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Figure 6. Electrical conduction tuning by nitrogen vacancy. (a) NEXAFS B K-edge spectrum for three sp2-BN films. Difference in high-energy shoulder shows that the sp2-BN films have different amounts of nitrogen vacancy, and (b) I−V characteristics of three sp2-BN films measured for the channel length of 6 μm at the temperature of 500 K.

Supporting Information S10), which is much smaller than the channel length. Localized states of the grain boundaries can contribute to space-charge evolution in the channel, which plays an important role in determining the SCLC conduction.43 On the other hand, the high-energy shoulder at around 192.5 eV is attributed to VN.38 The B/N ratio of the sp2-BN film estimated by an XPS/electron spectroscopy for chemical analysis using Al Kα X-ray radiation is over unity, as shown in Supporting Information S11, which also implies the existence of a large amount of VN in the film. Theoretically, VN is predicted to be a shallow-level defect acting as a donor for hBN.44,45 More recent photoluminescence study showed that VN is located at approximately from 100 meV (for multilayer hBN) to 400 meV (for monolayer h-BN) below the conduction band edge depending on the number of atomic layers.46 Taken together with the observations of this study and previous reports, VN is the most likely candidate for the defect corresponding to the trap with the activation energy of approximately 185 meV. Thus, VN can affect the electrical conductivity of sp2-BN because of its small activation energy and controlled generation of VN can be an effective doping method. For verifying the doping effect of VN, the electrical conduction properties of three sp2-BN films grown under different MOCVD growth conditions were compared, as shown in Figure 6. sp2-BN #2 has been grown under the condition introduced earlier in the paper and is the sample that has been discussed so far. The other sp2-BN films were grown under the same conditions with sp2-BN #2 except that the reactor pressure was changed to 400 mbar for sp2-BN #1 and that the carrier gas was changed to nitrogen gas for sp2-BN #3. As the growth pressure increases, VN decreases while the grain boundary in sp2-BN increases because of the enhanced chemical reaction rate and nucleation formation rate.47 Meanwhile, hydrogen carrier gas is necessary to enhance the crystallinity of the MOCVD-grown sp2-BN,27,48 so both VN and grain boundary increase when nitrogen is used as a carrier gas. More detailed information on the growth condition and the structural properties of the sp2-BN films are discussed in Supporting Information S12. Figure 6a shows the NEXAFS B K-edge spectra of the sp2-BN films for the photon energy from 189.5 to 194.5 eV. Looking at the change of high-energy shoulder of the π* peak, sp2-BN #3 has the largest amount of VN, and sp2-BN #1 has the least amount. Figure 6b is the I−V characteristics of the sp2-BN films at the temperature of 500 K with the channel length of 6.0 μm. This shows that SCLC is the dominant conduction mechanism for all of the sp2-BN films (I ∝ Vm, with m ≥ 2), and conduction levels are dramatically

two shallow traps at the energies of approximately 25 and 185 meV affect the electrical conduction in the sp2-BN film. In analyzing the I−V characteristics of sp2-BN films, it is important to distinguish the SCLC in the presence of traps and field-enhanced bulk conduction such as the Poole−Frenkel conduction because they show similar electric field-dependent conductivity at various channel lengths.36 For clarifying that the MOCVD-grown sp2-BN film follows the SCLC, I−V characteristics measured at different channel lengths are compared, as shown in Supporting Information S9. The current should be identical at the same electric field, regardless of the channel length when the Poole−Frenkel conduction is dominant. However, the current not only varies depending on the channel length but also is inversely proportional to the sixth power of the channel length at the same applied bias, which is consistent with the SCLC-type conduction mechanism. However, the current should be inversely proportional to the square of the channel length according to the Childs’s rule assuming a trapfree film. The higher-order dependence is observed when the trap density is exponentially distributed depending on the energy level in the sp2-BN film. To figure out the chemical origin of the defects in the sp2-BN film, NEXAFS spectroscopy, referring the transition from corelevel states to unoccupied states, was performed by using the synchrotron X-ray source at Pohang Accelerator Laboratories. NEXAFS spectroscopy is very sensitive to the local environment of the atoms, so crystalline defects can be reflected in the spectrum.37 Figure 5a shows the NEXAFS B K-edge and N Kedge spectra of the sp2-BN film transferred onto a conductive silicon substrate. In the NEXAFS B K-edge spectrum, the peaks at 192.0 and 199.0 eV correspond to the π* and σ* antibonding states of the sp2-hybridized boron, respectively. Similarly, the peaks at 399.7 and 406.8 eV in the NEXAFS N K-edge spectrum correspond to the π* and σ* antibonding states of the sp2-hybridized nitrogen, respectively.38 One remarkable feature is the shoulder peaks at the vicinity of π* signal in the NEXAFS B K-edge spectrum, which is clearly shown in Figure 5b. The defect forming the trap with the activation energy of approximately 25 meV is presumed to be related to the grain boundaries in the sp2-BN film because the grain boundaries are likely to include B−B homoelemental bondings,39 which is reflected as the low-energy shoulder of the π* signal40,41 of the NEXAFS B K-edge spectrum, as shown in Figure 5b. In addition, the grain boundaries are known to cause in-gap states near the band edge.42 The grain size of the MOCVD-grown sp2-BN is only a few nanometers (see TEM image in 17291


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originating from B−B homoelemental bonding and the nitrogen vacancy according to the NEXAFS spectroscopy. The activation energies of the two shallow defects were estimated to be approximately 25 and 185 meV, respectively. Furthermore, it was also shown that the conductivity of the sp2BN film can be intentionally adjusted by controlling the amount of VN. Because the activation energy of VN (∼185 meV) is much smaller than that of conventional Si dopant (∼1200 meV), controlled generation of VN can be a new and better approach for obtaining n-type sp2-BN than conventional substitutional doping. We believe that understanding the defect-mediated electrical conduction characteristics in sp2BN and a way to control it proposed in our study can pave the way for the realization of active sp2-BN-based high-temperature electronics and deep ultraviolet optoelectronics.

enhanced by increasing VN. Under the same applied voltage, the current through sp2-BN #3 is more than 5 orders higher than that through sp2-BN #1. The I−V characteristics of the sp2-BN film at room temperature show the same trend with those at 500 K, as shown in Supporting Information S13. Therefore, VN can increase the conductivity of the sp2-BN film like a dopant. The carrier type of the MOCVD-grown sp2-BN films with VN is probably an electron; thus, they are n-type semiconductors based on the following three aspects: at first, it has been generally known that VN acts as a donor based on the first-principle calculations.44,45 Second, larger current flows with the Ti/Au contact compared to the Ni/Au contact, as shown in Supporting Information S14. Because Ti has smaller work function (∼4.3 eV) than Ni (∼5.2 eV), it allows larger current for n-type semiconductors. In addition, Ti/Au and Ni/Au contacts are widely used as n-type and p-type Ohmic contacts for III-nitride semiconductors, respectively. The formation of Ti-based Ohmic contact on III-nitride semiconductors is attributed to the formation of Ti-nitrides after thermal annealing that generates VN.49 A similar phenomenon can occur between Ti and sp2-BN. Third, the sp2-BN film shows ntype sensing behavior to the NO2 gas, which means that the current decreases when NO2 is exposed, as shown in Supporting Information S15. Because NO2 is a well-known oxidizing gas capturing electron from the material, n-type sensing behavior infers that the electrical transport depends on the electron density. Therefore, VN can act as a donor providing an electron in the sp2-BN film. In general, substitutional doping is widely employed to control both the amount and the type of conductivity of a semiconductor. However, it was theoretically predicted to be very ineffective for n-type doping for h-BN. The activation energy of silicon substituting boron (SiB) in h-BN is 1.19 eV, which is too high to practiclly employ Si as a donor of h-BN. In addition, other substitutional dopants including SN, CB, GeB, SnB, SeN, and TeN were also found to have very high activation energies (>1 eV) because they induce deep and localized impurity states.22 More recently, the activation energy of the Si dopant was experimentally determined as 1.2 eV, which is consistent with the theoretical prediction.23 Meanwhile, VN, which is revealed to be a donor theoretically and experimentally, shows much smaller activation energy (∼185 meV) compared to the Si dopant. Therefore, VN generation in sp2-BN in a controlled way can be an alternative approach for n-type doping of sp2-BN to replace conventional substitutional doping. VN generation can be controlled in the MOCVD growth of sp2-BN. It was reported that formation of VN is enhanced by decreasing the reactor pressure47 and by using nitrogen carrier gas rather than hydrogen carrier gas.49 Therefore, it is possible to control the generation of VN by regulating the reactor pressure and adjusting the fraction of hydrogen gas and nitrogen gas used as a carrier gas in the MOCVD growth.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.8b04389. MOCVD growth of the BN film; transfer procedure; cross-sectional TEM; metal contact annealing effect; device scheme and measurement setup; electrical conduction of the sapphire substrate; effect of metal diffusion on electrical conduction; SCLC at high temperature; comparison between SCLC and Poole− Frenkel conduction; in-plane TEM; B/N ratio of the sp2BN film; structural properties of various sp2-BN films; I− V characteristics of sp2-BN films at room temperature; contact scheme-dependent I−V characteristics; and sensing behavior of sp2-BN to the NO2 gas (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Dong Yeong Kim: 0000-0003-0365-7668 Nam Han: 0000-0003-1020-4827 Jong Kyu Kim: 0000-0003-1643-384X Author Contributions

The manuscript was written through contributions from all authors. All authors have given approval to the final version of the manuscript. Funding

This work was supported by Samsung Research Funding Center of Samsung Electronics under project number SRFCMA1401-10. Notes

The authors declare no competing financial interest.

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REFERENCES

(1) Dean, C. R.; Young, A. F.; Meric, I.; Lee, C.; Wang, L.; Sorgenfrei, S.; Watanabe, K.; Taniguchi, T.; Kim, P.; Shepard, K. L.; Hone, J. Boron Nitride Substrates for High-Quality Graphene Electronics. Nat. Nanotechnol. 2010, 5, 722−726. (2) Bresnehan, M. S.; Hollander, M. J.; Wetherington, M.; Wang, K.; Miyagi, T.; Pastir, G.; Snyder, D. W.; Gengler, J. J.; Voevodin, A. A.; Mitchel, W. C.; Robinson, J. A. Prospects of Direct Growth Boron Nitride Films as Substrates for Graphene Electronics. J. Mater. Res. 2014, 29, 459−471. (3) Kim, S. M.; Hsu, A.; Park, M. H.; Chae, S. H.; Yun, S. J.; Lee, J. S.; Cho, D.-H.; Fang, W.; Lee, C.; Palacios, T.; Dresselhaus, M.; Kim,

CONCLUSIONS In conclusion, in-plane electrical conduction characteristics of sp2-BN were studied to demonstrate the possibility of sp2-BN as an active material for electronics and deep ultraviolet optoelectronics. In this work, the defect-mediated in-plane electrical conduction property in a few-layer sp2-BN was reported for the first time. The temperature-dependent I−V characteristics revealed that there are two shallow traps 17292


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Defect-Mediated In-Plane Electrical Conduction in Few-Layer sp

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