Effects of Fluorine Doping on the Electrical Performance of ZnON Thin

Subscriber access provided by UNIV OF NEWCASTLE

Article

The effects of fluorine doping on the electrical performance of ZnON thin-film transistors Hyoung-Do Kim, Jong Heon Kim, Kyung Park, Jung Hyun Kim, Jozeph Park, Yong Joo Kim, and Hyun-Suk Kim ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b03385 • Publication Date (Web): 03 Jul 2017 Downloaded from http://pubs.acs.org on July 4, 2017

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 free 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 accessible to all readers and 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.

ACS Applied Materials & Interfaces 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 26

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

The effects of fluorine doping on the electrical performance of ZnON thin-film transistors Hyoung-Do Kim1, Jong Heon Kim1, Kyung Park2, Jung Hyun Kim3, Jozeph park4*, Yong Joo Kim5*, and Hyun-Suk Kim1* 1

Department of Materials Science and Engineering, Chungnam National University, Daejeon 34134, Republic of Korea

2

School of Integrated Technology, Yonsei University, Incheon 21983, Republic of Korea

3

Department of Advanced Materials Science and Engineering, Hanbat National University, Daejeon

34158, Republic of Korea 4

Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon 34141, Republic of Korea

5

Biosystems Machinery Engineering, Chungnam National University, Daejeon 34134, Republic of Korea

Abstract In this work the effects of fluorine incorporation in high mobility zinc oxynitride (ZnON) semiconductor are studied by both theoretical calculations and experimental evaluation of thin film transistors (TFTs). From density functional theory (DFT) calculations, fluorine acts as a carrier suppressor in the ZnON matrix when it substitutes a nitrogen vacant site (VN). Thin films of ZnON and ZnON:F were grown by reactively co-sputtering Zn metal and ZnF2 targets, and their electrical, physical and chemical characteristics were studied. Xray photoelectron spectroscopy (XPS) analyses of the nitrogen 1s peaks in ZnON and ZnON:F suggest that as the fluorine incorporation increases, the relative fraction of Zn-N bonds from stoichiometric Zn3N2 increases. On the other hand, the Zn-N bond characteristics arising from non-stoichiometric ZnxNy and N-N bonds decrease, implying that indeed fluorine anions have an effect of passivating the N-related defects. The corresponding TFTs exhibit optimum transfer characteristics and switching ability when approximately 3.5 atomic percent of fluorine is present in the 40 nm-thick ZnON:F active layer.

Keywords: zinc oxynitride (ZnON), fluorine doping, thin film transistors (TFTs), negative bias illumination stress (NBIS), fluorine doped zinc oxynitride (ZnON:F), reactive RF co1

ACS Paragon Plus Environment


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

sputtering, density functional theory (DFT), first-principles calculations

Introduction Increasing demands for cost effective switching or driving transistors in the flat panel display industry have led to the development of metal oxide semiconductors such as In-GaZn-O (IGZO)1-3. Thin-film transistors (TFT) that incorporate such materials exhibit field effect mobility exceeding 10 cm2/Vs, and are suitable for the fabrication of large size liquid crystal display (LCD) panels with ultra-high definition (4000 × 2000 pixels). However, further advances in display technology aim at producing organic light-emitting diodes (OLEDs) that require relatively high driving currents. In this regard, devices with even higher field effect mobility (> 30 cm2/Vs) must be integrated in the backplane array4. Recent studies of a relatively new type of semiconductor, zinc oxynitride (ZnON)5-8, have shown that high mobility semiconductor films can be obtained by reactively sputtering a Zn metal target5,6, which involves a simple and inexpensive process. The optimization of the associated TFT properties usually consists of controlling the nitrogen to oxygen anion ratio9,10 or thermally annealing the ZnON layer11-13, so as to obtain sufficiently low leakage current levels while preserving sufficiently high field effect mobility. It is usually reported that the nitrogen vacant sites (VNs) act as the major source of free electrons and carrier traps6,14-16 that may degrade the device properties over prolonged bias stress. In order to passivate such defects, fluorine plasma treatment or fluorine doping were attempted in nitride semiconductors17-21. The present work is a study on the effect of directly incorporating fluorine anions during the thin film growth, by co-sputtering a ZnF2 target alongside the Zn metal target. First-principles calculations indicate that fluorine may act as a carrier suppressor in the ZnON matrix by filling in the VN sites, which is an energetically favorable reaction. The properties of F-doped ZnON (ZnON:F) are investigated through various characterization methods, and the performance of the TFT devices incorporating ZnON:F active layers are studied next.

Experimental Section First principles density functional theory (DFT) calculations were performed using 2


Page 2 of 26

Page 3 of 26

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


the Vienna Ab initio Simulations Package (VASP) code22, employing a plane-wave basis set with an energy cutoff of 400 eV, within the projector augmented-wave (PAW) approach23. A conventional cell of Zn3N2 crystal with 48 Zn and 32 N atoms was selected as the reference structure. The Brillouin zone was sampled with 2×2×2 k-points sampling. The Zn3N2 was calculated using the generalized gradient approximation (GGA)22 and the HSE06 hybridfunctional25 with 32% of the HF exchange energy modified to fit the experimental bandgap of Zn3N226. In the calculations, an 80-atom Zn48N32 supercell was adopted to simulate the pure Zn3N2 and then the defect formation energies, band structures and formation enthalpies were studied. 40 nm-thick ZnON and ZnON:F layers were grown on highly doped p-type Si substrates with a thermally grown 100 nm-thick SiOx dielectric, by co-sputtering Zn and ZnF2 targets. The power exerted on the Zn metal target was fixed at 40 W, and the power on the ZnF2 target was varied. The reactive gas flow rate ratio was Ar:O2:N2 = 50:1:200. The crystal structures of separate ZnON films annealed at different temperatures were examined by grazing incidence angle X-ray diffraction (GIAXRD) using a Cu Kα radiation (Rigaku, D/MAX-2500). Also, X-ray photoelectron spectroscopy (XPS, K-Alpha model, Thermo Fisher Scientific) with a pass energy of 50 eV was performed in order to study the chemical bonding states of nitrogen and oxygen anions, using a monochromatic AlKα X-ray source. Before performing the XPS analyses, the surface of each film was sputtered with a low energy Ar+ ion beam (200 eV) for 30 s in order to minimize any possible contamination. A relatively small amount of carbon was intentionally left so that the peak position could be calibrated with respect to the C 1s peak, of which the standard binding energy is about 284.5 eV. This amount of carbon does not affect the XPS analysis of the elements of interest. An electron flood gun was used to neutralize the positive charge from the Ar+ ions. TFT devices were fabricated with 40 nm-thick ZnON and ZnON:F active layers, which were patterned using shadow masks. After thermal annealing at 250 °C in vacuum, 100 nmthick indium tin oxide (ITO) source/drain electrodes were deposited (Ar gas flow rate: 18 sccm, RF power : 50 W, deposition rate : 10 nm/min) and patterned also using shadow masks. The initial transfer characteristics of the devices with width / length = 800 µm / 200 µm were evaluated using a HP 4145B semiconductor parameter analyzer in a dark room under ambient conditions. The threshold voltage (VTH), subthreshold swing (S.S.), and field effect mobility (µFE) were extracted in compliance with the gradual channel approximation27. 3


The field


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 4 of 26

effect mobility values were extracted in the linear regime with the drain voltage (Vd) fixed at 0.1 V.. The devices were then subjected to NBIS, with VG = -20 V and VD = 0.1 V. A light source with a luminance of 1500 lux was used to illuminate the devices from the top. Each stress experiment was conducted at room temperature for a total time of 1 hour.

Results and discussion The ZnON host considered for the first principles calculations consists of a nitrogenrich matrix, therefore DFT calculations were carried out based on a crystalline Zn3N2 cubic supercell. Two types of N vacancies were introduced by removing N atoms at two different sites (N1 and N2)28. Zn vacancies were also examined by removing one Zn atom from the Zn48N32 supercell. The calculated formation energies Eform for different types of defects are calculated by equation (1) below.

Eform = E(defect) – E(pure) ± ∑

(1)

Here E(defect) is the total energy derived from supercell calculations with one native defect in the cell, where defect represents N or Zn vacancies or interstitials, E(pure) denotes the total energy of the pure Zn48N32. The number of atoms of species i that are added to or removed from the supercell when forming the defects is described by ni, and µi is the chemical potential of the corresponding species. The calculated formation energies of different defects are listed in table 1, which shows the Eform of N and Zn vacancies and interstitials obtained by GGA and HSE06. Both methods result in similar trends, where the formation energies of N vacancies are lower than those of the other defects. This implies that the formation of N vacancies is energetically favorable. Table 2 shows formation energies when a fluorine atom is substituting the N1 and N2 sites (FN1 and FN2 respectively), or when it is present as an interstitial defect in an octahedral or tetrahedral site. The results suggest that fluorine is highly likely to occupy a substitutional anion site in N-rich ZnON. By comparing the formation energies of VN and FN defects, the latter exhibit more negative values, and at this point it may be expected that when fluorine is incorporated in ZnON, it will readily fill in the VN sites. The band structures of the Zn3N2 supercells in the pure form, with N vacancies and 4


Page 5 of 26

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


with substitutional F atoms are shown in figure 1. The band structures with VN defects exhibit flat conduction bands compared with that of pure Zn3N2. On the other hand, the band structures with FN defects are similar to that of pure Zn3N2, which may imply that the fluorine incorporation has rendered the VN defects inactive. The electrical properties of ZnON and ZnON:F films were evaluated by Hall measurements and 4-probe meter with respect to the power of ZnF2 target. Figure 2 shows the (a) Hall mobility, (b) sheet resistance and (c) carrier concentrations as a function of ZnF2 power. The Hall mobility and carrier concentration values decrease with increasing ZnF2 power, and as a result the sheet resistance increases. ZnF2 is well known to be electrically insulating29, so the decrease in electrical conductivity is reasonable. For further analyses, the ZnON:F film grown with a ZnF2 target power of 6 W (ZnON:F 6 W) was selected as the optimum condition before drastic increase in sheet resistance occurs, and the film deposited with a ZnF2 power of 10 W (ZnON:F 10 W) was chosen for comparison. The optical transmittance was measured for pure ZnON and ZnON:F 6, 10 W films as shown in figure 3 (a). The optical band gap values were extracted using the Tauc method30, as shown in figure 3 (b). As the fluorine incorporation increases, the optical transmittance of the corresponding film increases in the visible region (400-800 nm) increases, along with the optical band gap. The extracted optical band gap values of ZnON and ZnON:F 6, 10 W are 1.17, 1.27 and 1.35 eV, respectively. To examine the microstructure of ZnON and ZnON:F films, grazing incidence angle X-ray diffraction (GIAXRD) and atomic force microscopy (AFM) were performed. The XRD patterns of ZnON and ZnON:F thin film are shown in figure 4. All films exhibit amorphous structures, irrespective of the ZnF2 target power. The surface AFM topography images of the ZnON and ZnON:F 6, 10 W layers are shown in figure 5. Only small changes in roughness are observed with fluorine incorporation, where a decrease by 0.1 nm occurs when the ZnF2 target power is as high as 10 W. In order to examine how the chemical bond properties are influenced by the presence of fluorine, X-ray photoelectron spectroscopy (XPS) analyses were carried out next. The relative element ratio of ZnON and ZnON:F 6, 10 W layers obtained by XPS depth profiling are listed in table 3. The results indicate that as the ZnF2 target power increases to 6 and 10 W, the ratio of fluorine content increases up to 3.47 and 9.22 at. %, respectively. The amount of nitrogen on the other hand decreases down to 20.5 and 19.2 at. %, respectively. Note that the 5



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 6 of 26

oxygen content remains relatively constant. Figures 6 (a)-(c) consist of the XPS O 1s peak spectra of the pure ZnON and ZnON:F 6, 10 W films. The O 1s peak was resolved into two into two sub-peaks labelled O1 and O2, which are generally known to occur from oxygen forming metal-oxygen bonds and oxygen near oxygen vacant sites (OV) in oxide semiconductors, respectively31. No apparent variation in the relative area ratios of sub-peaks O1 and O2 is observed, which implies that the incorporated fluorine does not affect the oxygen-related bonding states. Figures 6 (d)-(f) consist of XPS N 1s peak spectra of pure ZnON and the ZnON:F 6, 10 W layers. The N 1s peaks were resolved into three different sub-peaks. The lowest energy sub-peak originates from nitrogen atoms in non-stoichiometric ZnxNy (including nitrogen vacancies), while the middle sub-peak arises from the nitrogen atoms in stoichiometric Zn3N2. The highest energy sub-peak represents mostly N-N bonds10,32-34. The relative peak area ratios of the three sub-peaks within a single N 1s peak are represented in figure 6 (h), and listed in table 4. Note that as the amount of incorporated fluorine increases, the relative fraction of nitrogen from stoichiometric Zn3N2 peak increases. Accordingly, the peak intensities from non-stoichiometric ZnxNy and N-N bonds diminish. The above results may be interpreted to occur from the fluorine anions passivating the vacant N sites that contribute to the sub-peak originating non-stoichiometric ZnxNy, so that the relative fraction of the latter appears to decrease with increasing F content, and consequently the sub-peak from stoichiometric Zn3N2 increases. To understand the decrease in N-N bond peak intensity, additional DFT calculations were carried out to estimate the formation enthalpies of zinc nitride and F-doped zinc nitride by the following equations:

48 Zn + 16 N2 → Zn48N32

(2)

48 Zn + 31/2 N2 + 1/2 F2 → Zn48N31F

(3)

From equations 2 and 3, the calculated formation enthalpy is 8.20 eV for Zn48N32 and 6.47 eV for Zn48N31F. The incorporation of fluorine not only has an effect of passivating nitrogen vacancies but also promotes the formation of more stable compound, with fewer nitrogen anions. The probability of finding N-N bonds therefore decreases, which is observed 6


Page 7 of 26

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


in the XPS analyses. Figure 6 (g) shows the XPS F 1s peak intensities in the ZnON:F 6 and 10 W films. The F 1s peak intensity of the ZnON:F 10 W layer is obviously stronger than that in ZnON:F 6 W sample, which confirms that the fluorine content increases with increasing ZnF2 target power. The structure of a TFT device incorporating ZnON or ZnON:F active layers is schematically illustrated in figure 7. The transfer characteristics of the devices based on ZnON and ZnON:F are shown in figure 8. Because N-rich ZnON was synthesized as the host material, a relatively large number of nitrogen vacancies is formed so as to convey a high free carrier density10. The pure ZnON device exhibits high off-state current, which diminishes as the fluorine content in the semiconductor increases. The representative transfer parameters are listed in table 5. The threshold voltages shift towards positive values with increasing F content. A field effect mobility of 151 cm2/Vs is obtained using ZnON:F 6 W as the semiconductor, with sufficiently low off-state current and threshold voltage near zero, so that the device may be used as a switching element in electronic applications. Representative device parameters from previous studies available in the literature are compared in Table 6, in order to emphasize the high on/off ratio achieved in the present work while preserving field effect mobility values higher than 100 cm2/Vs. To evaluate the effect of fluorine incorporation on the device stability, negative bias stress (NBS) and negative bias illumination stress (NBIS) tests were performed as shown in figure 9. As the stress time increases, both ZnON and ZnON:F 6 W TFTs undergo negative shifts in threshold voltage (∆VTH) without significant degradation in device performance. The ∆VTH values under NBS are similar, but the ∆VTH under NBIS of the ZnON TFT is larger than that of the ZnON:F TFT. The negative shift in VTH generally occurs either by the trapping of net positive charge near the gate dielectric/semiconductor interface35-37, or the generation of excess free electrons in the semiconductor. However during NBS, because ZnON is n-type and there is no light present to generate hole carriers, it is highly likely that metastable nitrogen vacant sites have released free electrons under negative bias stress. In the case of NBIS tests, photon radiation is likely to have induced the ionization of VN that releases excess free carriers. The passivation of such defects by fluorine incorporation is suggested to have improved the NBIS stability of the device based on ZnON:F 6 W, as compared with that incorporating pure ZnON. The gate leakage current was measured for all 7



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

samples as shown in figure 10. Note that because the entire silicon wafer was used as the gate electrode, the gate leakage in this study does not reflect the exact gate insulator properties.

Conclusion In this work, the effect of fluorine incorporation in high mobility ZnON semiconductor was studied by first principles calculations and thin film analyses. ZnON and ZnON:F films were grown by co-sputtering Zn metal and ZnF2 targets, and the film properties were examined along with the associated TFT characteristics. DFT calculations suggest that fluorine is likely to suppress the formation of free carriers in ZnON by passivating the nitrogen vacant sites. Reduction in electrical conductivity was verified by the incorporation of fluorine, which was confirmed by the electrical characterization of the ZnON and ZnON:F layers as well as the corresponding TFT devices. XPS studies on the nitrogen 1s peak of ZnON and ZnON:F thin films also suggest that fluorine anions may substitute the VN sites, and promote the contribution of photoelectrons arising from nitrogen in stoichiometric Zn3N2-like environments. The TFT field-effect mobility and switching characteristics could be optimized by properly adjusting the RF power applied on the ZnF2 target (6 W), and the NBS/NBIS stability was improved in comparison with devices based on pure ZnON active layers. The latter effect is again attributed to the passivation of VN defects by fluorine anions. The incorporation of fluorine in a high mobility ZnON host thus allows the fabrication of high mobility and high stability TFTs.

AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected] (Jozeph Park) *E-mail: [email protected] (Yong Joo Kim) *E-mail: [email protected] (Hyun-Suk Kim) Author Contributions H.-D.K. and J.H.K. contributed equally to this work. The manuscript was written through contributions of all authors. All authors have given approved to the final version of the manuscript. 8


Page 8 of 26

Page 9 of 26

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


Notes The authors declare no competing financial interest

ACKNOWLEDGEMENTS This work was mainly supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (Grant No: 2014R1A1A2055138) and partially by the MOTIE (Ministry of Trade, Industry & Energy (Grant No: 10051403)) and KDRC (Korea Display Research Corporation) support program for the development of future devices technology for display industry. Also, this work was supported by Nano·Material Technology Development Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (2009-0082580) and by the National Institute of Supercomputing and Network/Korea Institute of Science and Technology Information with supercomputing resources including technical support (Grant No: KSC-2016-C3-0001).

References (1) Nomura, K.; Otha, H.; Takagi, A.; Kamiya, T.; Hirano. M.; Hosono. H. Roomtemperature Fabrication of Transparent Flexible Thin-film Transistors using Amorphous Oxide Semiconductors Nature 2004, 432, 488–492. (2) Park, J. S.; Maeng, W.-J.; Kim, H.-S. & Park, J.-S. Review of Recent Developments in Amorphous Oxide Semiconductor Thin-film Transistor Devices Thin Solid Films 2012, 520, 1679–1693. (3) Park, J.-S.; Kim, H. & Kim, I.-D. Overview of Electroceramic Materials for Oxide Semiconductor Thin Film Transistors J. Electroceram 2014, 32, 117–140. (4) Kamiya, T.; Nomura, K.; Hosono, H.; Present Status of Amorphous In-Ga-Zn-O Thinfilm Transistors Sci. Technol. Adv. Mater 2010, 11, 044305. (5) Ye, Y.; Lim, R.; White, J. M.; High Mobility Amorphous Zinc Oxynitride Semiconductor Material for Thin Film Transistors J. Appl. Phys 2009, 106, 074512. (6) Kim, H.-S.; Jeon, S. H.; Park, J. S.; Kim, T. S.; Son, K. S.; Seon, J.-B.; Seo, S.-J.; Kim, S.-J.; Lee, E.; Chung, J. G.; Lee, H.; Han, S.; Ryu, M.; Lee, S. Y.; Kim, K. Anion Control as a Strategy to Achieve High-mobility and High-stability Oxide Thin-film Transistors Sci. Rep 9



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

2013, 3, 1459. (7) Lee, E.; Benayad, A.; Shin, T.; Lee, H.; Ko, D.-S.; Kim, T. S.; Son, K. S.; Ryu, M.; Jeon, S.; Park, G.-S. Nanocrystalline ZnON; High mobility and Low Band Gap Semiconductor Material for High Performance Switch Transistor and Image Sensor Application Sci. Rep 2014, 4, 4948. (8) Gao, H.; Zhang, X.; Zhao, Y.; Yan, B. The Correlation of Material Properties and Deposition Condition of ZnON Thin Films AIP Adv 2017, 7, 025111 (9) Kim, D,-H.; Jeong, H,-S.; Jeong, C,-Y.; Song, S,-H.; Kwon, H,-I. Effects of Oxygen Flow Rate on the Electrical Stability of Zinc Oxynitride Thin-film Transistors Jpn. J. Appl. Phys 2017, 56, 020301 (10) Park, J.; Kim, Y. S.; Ok, K.-C.; Park, Y. C.; Kim, H. Y.; Park, J.-S. & Kim, H.-S. A Study on the Electron Transport Properties of ZnON Semiconductors with respect to the Relative Anion Content Sci. Rep 2016, 6, 24787 (11) Park, J.; Kim, Y. S.; Kim, J. H.; Park, K.; Park, Y. C.; Kim, H.-S. The Effects of Active Layer Thickness and Annealing Conditions on the Electrical Performance of ZnON Thin-film Transistors J. Alloys Compd 2016, 688, 666-671 (12) Jeong, H.; Jeong, H.-S.; Kim, D.-H.; Jeong, C.-Y.; Kwon, H.-I. Effects of PostDeposition Thermal Annealing Temperature on Electrical Properties of ZnON Thin-Film Transistors IEEE Electron Device Lett 2016, 37, 747-750. (13) Ok, K.-C.; Jeong, H.-J.; Kim, H.-S.; Park, J.-S. Highly Stable ZnON Thin-Film Transistors with High Field-Effect Mobility Exceeding 50 cm2/Vs IEEE Electron Device Lett 2015, 36, 38-40. (14) Long, R., Dai, Y., Yu, L., Huang, B. & Han, S. Atomic Geometry and Electronic Structure of Defects in Zn3N2 Thin Solid Films 2008, 516, 1297–1301. (15) Lee, S.; Nathan, A.; Ye, Y.; Guo, Y. & Robertson, J. Localized Tail States and Electron Mobility in Amorphous ZnON Thin Film Transistors Sci. Rep 2015, 5, 13467. (16) Kim, H.-S.; Park, J. S.; Kim, T. S.; Son, K. S.; Seon, J.-B.; Seo, S.-J.; Kim, S.-J.; Lee, S.; Kim, E. S.; Ryu, M.; Han, S.; Cho, S.-H.; Park, Y. Defect Control in Zinc Oxynitride Semiconductor for High-performance and High-stability Thin-film Transistors Solid-State Phenom 2013 205-206, 446–450. (17) Chen, K.; Zhou, C. Enhancement-mode AlGaN/GaN HEMT and MIS-HEMT Technology Phys. Status Solidi 2011 208, 434–438. 10


Page 10 of 26

Page 11 of 26

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


(18) Sun, X.; Zhang, Y.; Chang-Liao, K. S.; Palacios, T.; Ma, T. P. Impacts of Fluorinetreatment on E-mode AlGaN/GaN MOS-HEMTs IEEE Int. Electron Devices Meet 2014, 17, 438-441. (19) Cai, Y.; Zhou, Y.; Lau, K. M.; Chen, K. Control of Threshold Voltage of AlGaN/GaN HEMTs by Fluoride-Based Plasma Treatment: From Depletion Mode to Enhancement Mode IEEE Trans. Electron Devices 2006, 53, 2207-2215 (20) Gao, Z.; Hou, B.; Liu, Y.; Ma, X. Impact of Fluorine Plasma Treatment on AlGaN/GaN High Electronic Mobility Transistors by Simulated and Experimental Results Microelectron. Eng 2016, 154, 22–25 (21) Roberts, J. W.; Chalker, P. R.; Lee, K. B.; Houston, P. A.; Cho, S. J.; Thayne, I. G.; Guiney, I.; Wallis, D.; Humphreys, C. J. Control of Threshold Voltage in E-mode and Dmode GaN-on-Si metal-insulator-semiconductor Heterostructure Field Effect Transistors by in-situ Fluorine Doping of Atomic Layer Deposition Al2O3 Gate Dielectrics Appl. Phys. Lett 2016, 108, 072901. (22) Kresse, G.; Furthmuller, J. Efficient Iterative Schemes for ab initio Total-energy Calculations using a Plane-wave Basis Set Phys. Rev. B 1996, 54, 11169. (23) Blochl, P. E. Projector Augmented-wave Method Phys. Rev. B 1994, 50, 17953-17979. (24) J. P. Perdew,; K. Burke.; M. Ernzerhof, Generalized Gradient Approximation Made Simple Phys. Rev. Lett 1996, 77, 3865 (25) Krukau, A. V.; Vydrov, O. A.; Izmaylov, A. F.; Scuseria, G. E. Influence of the Exchange Screening Parameter on the Performance of Screened Hybrid Functionals J. Chem. Phys 2006, 125, 224106 (26) Suda, T.; Kakishita, K. Band-gap Energy and Electron Effective Mass of Polycrystalline Zn3N2 Appl. Phys. Lett 2006, 99, 076101 (27). Sze, S. M. & Ng. K. K. Physics of Semiconductor Devices Wiley 2007. (28) Yoo, S.-H.; Walsh, A.; Scanlon, D. O.; Soon, A. Electronic Structure and Band Alignment of Zinc Nitride, Zn3N2 RSC Adv 2014, 4, 3306-3311 (29) Suzuki, I., Omata, T., Shiratsuchi, Y., Nakatani, R., Kitimura, N., Otsuka-Yao Matsuo, S. Fabrication of ZnF2 Thin Films and Their Vacuum Ultraviolet Transparency Thin Solid Films 2013, 534, 508–514 (30) Tauc, J., Grihorovici, R. & Vancu, A. Optical Properties and Electronic Structure of Amorphous Germanium Phys Status Solidi 1966, 15, 627–637. 11



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

(31) Ok, K.C.; Jeong, H.J.; Lee, H.M.; Park J.; Park, J.S. Comparative Studies on the Physical and Electronic Properties of Reactively Sputtered ZnO and ZnON Semiconductors Ceram. Int 41 2015, 13281-13284. (32) Tabet, N.; Faiza, M.; Al-Oteibib, A. XPS Study of Nitrogen-implanted ZnO Thin Films Obtained by DC-magnetron Reactive Plasma J. Mater. Res 2008, 163, 15-18. (33) Petravic, M.; Deenapanray, P.; Coleman, V.; Jagadish, C.; Kim, K.J.; Kim, B.; Koike, K.; Sasa, S.; Inoue, M.; Yano, M. Chemical States of Nitrogen in ZnO Studied by Near Edge Xray Absorption Fine Structure and Core-level Photoemission Spectroscopies Surf. Sci 2006, 600, 81-85. (34) Li, X. H.; Xu, H. Y.; Zhang, X. T.; Liu, Y. C.; Sun, J. W.; Lu, Y. M. Local Chemical States and Thermal Stabilities of Nitrogen Dopants in ZnO Film Studied by Temperaturedependent X-ray Photoelectron Spectroscopy Appl. Phys. Lett 2009, 95, 191903. (35) Lee, K. H.; Jung, J. S.; Son, K. S.; Park, J. S.; Kim, T. S.; Choi, R.; Jeong, J. K.; Kwon, J. Y.; Koo, B.; Lee, S. The Effect of Moisture on the Photon-enhanced Negative Bias Thermal Instability in Ga-In-Zn-O Thin Film Transistors Appl. Phys. Lett 2009, 95, 232106. (36) Shin, J. H.; Lee, J. S.; Hwang, C. S.; Park, S. H. K.; Cheong, W. S.; Ryu, M.; Byun, C.W.; Lee, J. I.; Chu, H. Y. Light Effects on the Bias Stability of Transparent ZnO Thin Film Transistors ETRI J 2009, 31, 62-64. (37) Jeon, J. H.; Kim, J. H.; Ryu, M. K. Instability of an Amorphous Indium Gallium Zinc Oxide TFT under Bias and Light Illumination J. Korean Phys. Soc 2011, 58, 158-162.

Figure Captions Figure 1.

The calculated band structures of (a) pure Zn3N2, (b) Zn3N2 containing VN1, (c)

Zn3N2 containing VN2, (d) Zn3N2 containing FN1 and (e) Zn3N2 containing FN2. Figure 2. (a) Hall mobility, (b) sheet resistance, (c) carrier concentration of ZnON & ZnON:F films grown with various RF power applied on the ZnF2 target. Figure 3. (a) Optical transmittance of ZnON & ZnON:F films measured with a UV-Vis spectrophotometer, (b) optical band gap values of ZnON & ZnON:F thin films extracted 12


Page 12 of 26

Page 13 of 26

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


using the Tauc plot method.

Figure 4. Grazing incidence angle X-ray diffraction (GIAXRD) patterns of ZnON and ZnON:F films grown with various RF power applied on the ZnF2 target. Figure 5. Atomic force microscope images of (a) ZnON, (b) ZnON:F 6 W, and (c) ZnON:F 10 W layers.

Figure 6. XPS O 1s spectra of (a) ZnON, (b) ZnON:F 6 W, (c) ZnON:F 10 W, XPS N 1s spectra of (d) ZnON, (e) ZnON:F 6 W, (f) ZnON:F 10 W and (g) XPS F 1s spectra of ZnON:F 6, 10 W. (h) Sub-peak areal ratio of N 1s spectra as a function of the ZnF2 target power.

Figure 7.

Schematic diagram of ZnON and ZnON:F TFTs fabricated on highly-doped p-

type silicon wafers.

Figure 8. Transfer characteristics of the ZnON and ZnON:F TFTs.

Figure 9. Time evolution of the transfer curves under NBS and NBIS tests. (a) NBS and (b) NBIS of ZnON TFTs. (c) NBS and (d) NBIS of ZnON:F 6 W TFTs.

Figure 10. Gate leakage current measurements in ZnON, ZnON:F 6W, and ZnON:F 10W TFTs.

Table Captions Table 1. Formation energies (eV) of neutral point defects in Zn3N2 based on GGA and Hybrid calculations.

Table 2. Computed formation energies (eV) of single atom F defects as substitutional or 13



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 14 of 26

interstitial defects in Zn3N2. Table 3. Relative atomic fraction of elements in the ZnON and ZnON:F 6, 10 W films obtained by XPS depth profile analyses.

Table 4. Areal ratio of the N-rich ZnxNy, stoichiometric Zn3N2, and N-N sub-peaks in the XPS N 1s peaks of the ZnON and ZnON:F 6, 10 W layers.

Table 5.

Representative transfer parameters of the ZnON and ZnON:F 6 W TFTs.

Table 6. Representative transfer parameters of ZnON TFTs in former studies available in the literature.

Table 1. Defect

VN1

VN2

Ni(Te)

Ni(Oct)

VZn

Zni(Oct)

Zni(Te)

GGA Ef (eV)

+1.228 +1.168 +5.686

+5.849

+2.197

+3.789

+3.789

Hybrid Ef (eV)

+2.064 +2.090 +3.038

+7.351

+4.066

+6.703

+3.380

Table 2. Dopant

FN1

FN2

Fi (Oct)

Fi (Te)

GGA Ef (eV)

-1.993

-1.778

-0.027

-0.389

Hybrid Ef (eV)

-1.743

-1.326

+0.072

+0.138

Table 3.

ZnON

Zn

O

N

F

70.33 %

7.43 %

22.24 %

0%

14


Page 15 of 26

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


ZnON:F 6 W

68.16 %

7.84 %

20.53 %

3.47 %

ZnON:F 10 W

64.45 %

7.10 %

19.23 %

9.22 %

Table 4.

ZnON

N-rich ZnxNy 47.0 %

Zn3N2 27.4 %

N-N 25.6 %

ZnON:F 6 W

43.7 %

27.9 %

28.4 %

ZnON:F 10 W

42.9 %

40.2 %

16.9 %

Table 5. µFE (cm2/Vs)

S.S. (V/dec)

Ion/Ioff

VTH (V)

ZnON

318

4.03

105

-6.41

ZnON:F 6 W

151

0.89

107

3.76

ZnON:F 10 W

23

1.01

106

1.86

Table 6. µFE (cm2/Vs)

Ion/Ioff ratio

VTH (V)

This works

151

107

3.76

Ref. 9.

40

107

-2.82

Ref. 11.

116

106

-8.18

Ref. 12.

40.1

107

1.9

15



8

(a) pure Zn3N2

4

8

(b) VN1

0

-4

-8

0

-4

-8 Γ

P

8

0

-4

-8 N

Γ

P

N

8

(d) FN1

4

Energy (eV)

N

(c) VN2

4

Energy (eV)

Energy (eV)

4

Γ

P

Γ

P

(e) FN2

4

Energy (eV)

8

Energy (eV)

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 16 of 26

0

-4

-8

0

-4

-8 N

Γ

P

Figure 1.

16


N

Page 17 of 26

100

2

Hall mobility (cm /Vs)

(a) 98 93 90

83 80

71

70 60

55

50 40

46 0

2

4

6

8

10

ZnF2 target power (W)

Sheet resistance (KΩ/sq)

(b)

350 300

320

250

230

200 150 100 50

40

23

11

81

0 0

2

4

6

8

10


(c)

18

17

-3

Carrier concentration (10 cm )

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


16.1

16 14 12

9.2

10 8

6.9

6

4.6 3.4

4

2.2

2 0

2

4

6

8

10


Figure 2. 17



100

80

2

2

(αhυ) (X10 eV /cm )

3

2

10

60

1 ZnON ZnON:F 6 W ZnON:F 10 W

2

40

0 0.00

0.75

1.50

2.25

3.00

Photon Energy (eV)

20

0

ZnON ZnON:F 6 W ZnON:F 10 W 500

1000

1500

2000

Wavelength (nm) (b) 1.5

1.27

Optical Band Gap (eV)

(a)

Transmittance (%)

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 18 of 26

1.35

1.17 1.0

0.5

0.0

ZnON

ZnON:F 6 W ZnON:F 10 W

FilmType Figure 3. 18


2500

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


Normalized Intensity (a.u.)

Page 19 of 26

ZnON:F 10 W ZnON:F 8 W ZnON:F 6 W ZnON:F 4 W ZnON:F 2 W ZnON

20

30

40

50

60 o

2θ ( )

Figure 4.

19


70

80


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 5.

20


Page 20 of 26

Page 21 of 26

(b) O1s Peak

ZnON Raw Fit O1: M-O O2: Vo

ZnON:F 6 W Raw Fit O1: M-O O2: Vo

O1 80.1%

O2 19.9%

530

Raw Fit O1: M-O O2: Vo

O1 79.2%

(e)

N1s Peak

ZnON

530

540

Binding Energy (eV) N1s Peak

ZnON:F 6 W

530

Binding Energy (eV)

(f)

Raw Fit ZnxNy

Raw Fit ZnxNy

Zn3N2

Zn3N2

Zn3N2

N-N

N-N

N-N

400

396

400


N1s Peak

ZnON:F 10 W

Raw Fit ZnxNy

Binding Energy (eV) (g)

O1 83.1%

O2 16.9%

540

Binding Energy (eV)

O1s Peak

ZnON:F 10 W

O2 20.8%

540

(d)

(c) O1s Peak

396

400

Binding Energy (eV) (h)

396

Binding Energy (eV)

100

ZnON:F 6 W ZnON:F 10 W

690

F1s Peak

Binding energy (eV)

Peak Ratio (%)


(a)


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


Zn3N2 N-N

60 40 20 0

680

ZnxNy

80

0

2

4

6

ZnF2 Power

Figure 6.

21


8

10


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 7.

22


Page 22 of 26

Page 23 of 26

-4

10

VD = 0.1 V -5

10

-6

Drain Current (A)

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


10

-7

10

-8

10

-9

10

-10

10

ZnON ZnON:F 6 W ZnON:F 10 W

-11

10

-12

10

-30

-20

-10

0

10

Gate Voltage (V)

Figure 8.

23


20

30


(a) -4 10

(b) -4 10

ΔVTH= -2.09 V

ΔVTH= -0.55 V -5

10

-5

-6

10

-6

10

-7

10

-8

10

0s 600 s 1200 s 1800 s 2400 s 3000 s 3600 s

-9

10

-10

10

-11

10

Drain Current (A)

Drain Current (A)

10

-7

10

-8

10

-30

(c) -4 10

10

-10

10

-11

10

-12

-20

-10

0

10

20

10

30

Gate Voltage (V)

-30

-10

0

10

20

30

ΔVTH= -1.91 V

ΔVTH= -0.47 V -5

10

-5

-6

10

-6

Drain Current (A)

10

-7

10

-8

10

0s 600 s 1200 s 1800 s 2400 s 3000 s 3600 s

-9

10

-10

10

-11

10

-7

10

-8

10

0s 600 s 1200 s 1800 s 2400 s 3000 s 3600 s

-9

10

-10

10

-11

10

-12

-30

-20

Gate Voltage (V)

(d) -4 10

10

10

0s 600 s 1200 s 1800 s 2400 s 3000 s 3600 s

-9

-12

10

Drain Current (A)

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 24 of 26

-12

-20

-10

0

10

20

10

30

-30

Gate Voltage (V)

-20

-10

0

10

Gate Voltage (V)

Figure 9.

24


20

30

Page 25 of 26

-4

10

ZnON ZnON:F 6 W ZnON:F 10 W

-5

10

Leakage Current (A)

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


-6

10

-7

10

-8

10

-9

10

-10

10

-11

10

-12

10

-30

-20

-10

0

10

20

Gate Voltage (V)

Figure 10.

25


30


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

Table of Contents (TOC)

26


Page 26 of 26

Effects of Fluorine Doping on the Electrical Performance of ZnON Thin

Recommend Documents