Research Article Study on the Microstructure and ...
8
Research Article Study on the Microstructure and Electrical Properties of Boron and Sulfur Codoped Diamond Films Deposited Using Chemical Vapor Deposition Zhang Jing, 1,2 Li Rongbin, 2 Wang Xianghu, 2 and Wei Xicheng 1 1 School of Materials Science and Engineering, Shanghai University, Shanghai 200072, China 2 School of Mechanical Engineering, Shanghai Dianji University, 1201 Jiang Chuan Road, Shanghai 200245, China Correspondence should be addressed to Li Rongbin; [email protected] Received 23 January 2014; Revised 13 April 2014; Accepted 15 April 2014; Published 21 May 2014 Academic Editor: Jinlong Jiang Copyright © 2014 Zhang Jing et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. e atomic-scale microstructure and electron emission properties of boron and sulfur (denoted as B-S) codoped diamond films grown on high-temperature and high-pressure (HTHP) diamond and Si substrates were investigated using atom force microscopy (AFM), scanning tunneling microscopy (STM), secondary ion mass spectroscopy (SIMS), and current imaging tunneling spectroscopy (CITS) measurement techniques. e films grown on Si consisted of large grains with secondary nucleation, whereas those on HTHP diamond are composed of well-developed polycrystalline facets with an average size of 10–50 nm. SIMS analyses confirmed that sulfur was successfully introduced into diamond films, and a small amount of boron facilitated sulfur incorporation into diamond. Large tunneling currents were observed at some grain boundaries, and the emission character was better at the grain boundaries than that at the center of the crystal. e films grown on HTHP diamond substrates were much more perfect with higher quality than the films deposited on Si substrates. e local I-V characteristics for films deposited on Si or HTHP diamond substrates indicate n-type conduction. 1. Introduction Diamond is a semiconductor material with many excellent physical properties, such as a wide bandgap, a high satu- ration velocity of carriers, and other remarkable electronic properties. ese properties make diamond a promising material for applications in high-power, high-temperature, high-frequency electronics, detectors, and electron emit- ter devices. e ability to produce large-area diamond wafers by chemical vapor deposition (CVD) techniques has aroused intensive interest in the use of the commer- cial material for active electronics. However, progress in this area has been severely hindered by the polycrystalline nature of such films and the difficulty in efficiently incor- porating suitable dopant species [1]. Although homoepi- taxial growth of diamond has been widely demonstrated, substrate cost and dopant incorporation limit commercial applications. Identifying the best donor dopant for diamond is one of the fundamental issues for the development of diamond- based devices. Phosphorus (P) is expected to be a promising n-type dopant candidate for diamond. Katagiri reported that n-type conductivity of homoepitaxial diamond with a Hall mobility of 410 cm 2 V −1 s −1 at room temperature [2]. Sally et al. reported on the n-type conductivity of sulfur-doped polycrystalline samples on silicon [3]. However, the distri- bution of sulfur between grain boundaries and the bulk has still not been reported. Sakaguchi et al. reported an activation energy of 0.38 eV and a Hall mobility of 597 cm 2 V −1 s −1 at room temperature for sulfur-doped n-type diamond grown on (100) substrates [4]. Katayama-Yoshida et al. examined the theoretical aspects of codoping for wide-bandgap semi- conductors [5]. Codoping has been proved as an effective way to incorporate donor dopants. However, up to now, doped films with such high Hall mobility have not been reported. is may be due to the compensation of donors by Hindawi Publishing Corporation Journal of Nanomaterials Volume 2014, Article ID 109869, 7 pages http://dx.doi.org/10.1155/2014/109869
Transcript of Research Article Study on the Microstructure and ...
Research ArticleStudy on the Microstructure and Electrical Properties of Boronand Sulfur Codoped Diamond Films Deposited Using ChemicalVapor Deposition
Zhang Jing,1,2 Li Rongbin,2 Wang Xianghu,2 and Wei Xicheng1
1 School of Materials Science and Engineering, Shanghai University, Shanghai 200072, China2 School of Mechanical Engineering, Shanghai Dianji University, 1201 Jiang Chuan Road, Shanghai 200245, China
Correspondence should be addressed to Li Rongbin; [email protected]
Received 23 January 2014; Revised 13 April 2014; Accepted 15 April 2014; Published 21 May 2014
Academic Editor: Jinlong Jiang
Copyright © 2014 Zhang Jing et al. This is an open access article distributed under the Creative Commons Attribution License,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The atomic-scale microstructure and electron emission properties of boron and sulfur (denoted as B-S) codoped diamondfilms grown on high-temperature and high-pressure (HTHP) diamond and Si substrates were investigated using atom forcemicroscopy (AFM), scanning tunneling microscopy (STM), secondary ion mass spectroscopy (SIMS), and current imagingtunneling spectroscopy (CITS)measurement techniques.The films grown on Si consisted of large grains with secondary nucleation,whereas those on HTHP diamond are composed of well-developed polycrystalline facets with an average size of 10–50 nm. SIMSanalyses confirmed that sulfur was successfully introduced into diamond films, and a small amount of boron facilitated sulfurincorporation into diamond. Large tunneling currents were observed at some grain boundaries, and the emission character wasbetter at the grain boundaries than that at the center of the crystal.The films grown onHTHP diamond substrates were muchmoreperfect with higher quality than the films deposited on Si substrates.The local I-V characteristics for films deposited on Si or HTHPdiamond substrates indicate n-type conduction.
1. Introduction
Diamond is a semiconductor material with many excellentphysical properties, such as a wide bandgap, a high satu-ration velocity of carriers, and other remarkable electronicproperties. These properties make diamond a promisingmaterial for applications in high-power, high-temperature,high-frequency electronics, detectors, and electron emit-ter devices. The ability to produce large-area diamondwafers by chemical vapor deposition (CVD) techniqueshas aroused intensive interest in the use of the commer-cial material for active electronics. However, progress inthis area has been severely hindered by the polycrystallinenature of such films and the difficulty in efficiently incor-porating suitable dopant species [1]. Although homoepi-taxial growth of diamond has been widely demonstrated,substrate cost and dopant incorporation limit commercialapplications.
Identifying the best donor dopant for diamond is oneof the fundamental issues for the development of diamond-based devices. Phosphorus (P) is expected to be a promisingn-type dopant candidate for diamond. Katagiri reported thatn-type conductivity of homoepitaxial diamond with a Hallmobility of 410 cm2 V−1 s−1 at room temperature [2]. Sallyet al. reported on the n-type conductivity of sulfur-dopedpolycrystalline samples on silicon [3]. However, the distri-bution of sulfur between grain boundaries and the bulk hasstill not been reported. Sakaguchi et al. reported an activationenergy of 0.38 eV and a Hall mobility of 597 cm2 V−1 s−1 atroom temperature for sulfur-doped n-type diamond grownon (100) substrates [4]. Katayama-Yoshida et al. examinedthe theoretical aspects of codoping for wide-bandgap semi-conductors [5]. Codoping has been proved as an effectiveway to incorporate donor dopants. However, up to now,doped films with such high Hall mobility have not beenreported. This may be due to the compensation of donors by
Hindawi Publishing CorporationJournal of NanomaterialsVolume 2014, Article ID 109869, 7 pageshttp://dx.doi.org/10.1155/2014/109869
2 Journal of Nanomaterials
00
250
250
500
1.51.0
0.5
500
(nm)
(nm
)
(𝜇m)
(a)
0
250
0 250
500
1.51.0
0.5
500
(nm)
(nm
)
(𝜇m)
(b)
Figure 1: AFM image of the film on an HTHP diamond substrate with B-S codoping.The inset is a three-dimensional image. (a) S/C = 0.001,B/S = 0.01; (b) S/C = 0.005, B/S = 0.02.
00
250
250
500
1.51.0
0.5
500
(nm)
(nm
)
(𝜇m)
(a)
00
250
250
500
1.51.0
0.5(𝜇m)
500
(nm)
(nm
)
(b)
Figure 2: AFM image of the film deposited on a Si substrate with B-S codoping. The inset is a three-dimensional image. (a) S/C = 0.001, B/S= 0.01; (b) S/C = 0.005, B/S = 0.02.
defects or residual acceptor impurities. The improvement inelectrical properties is strongly related to the improvement ofcrystalline perfection, surface microstructure characteristics,and the electron surface states.
2. Methods
In our previous studies, the growth of boron and sulfurcodoped diamond films on p-type (100) silicon substrates(heteroepitaxy) and HTHP diamond substrates (homoepi-taxy) by microwave plasma-assisted chemical vapor depo-sition (MPCVD) is demonstrated. The diamond films were
grown in a microwave reactor using dimethyl disulfide as thesulfur source. Acetone and hydrogen were used as the mainreactant gases. The acetone concentration was 0.5%; the S/Catomic ratio in the gas sources was from 0.001 to 0.005, witha B/S ratio of 0.01-0.02; and the total gas pressure and thesubstrate temperature were 25 Torr and 750∘C, respectively.
In previous research,microstructures and electrical prop-erties of CVD diamond films that were investigated byatomic force microscopy (AFM) and scanning tunnelingmicroscopy (STM) were studied [6, 7]. Current imagingtunneling spectroscopy (CITS) [8] was used to compare thestructures and electrical properties of the doped diamond
Journal of Nanomaterials 3
11.5
11.0
10.5
10.0
9.5
0.0022 0.0024 0.0026 0.0028 0.0030 0.0032 0.0034
DiamondSilicon
Diamond substrate 0.07 eV
Silicon substrate 0.16 eV
1/T (K−1)
ln(𝜌)
Figure 3: The temperature dependence of the resistance of B-S codoped diamond films grown under the different substrates.
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
B
H
C
S
Depth (𝜇m)
20406080100120140
0.0 0.1 0.2 0.3 0.4
B-S codopedS doped
Sin
tens
ity (c
ps)
Seco
ndar
y io
n co
unts
(cps
)
14.0
12.0
10.0
8.0
6.0
4.0
2.0
0.0
×105
Depth (𝜇m)
Figure 4: SIMS depth profile of various elements of doped diamond thin films.The inset showed the concentration of sulfur of B-S codopedand S lone doped films.
films on Si and HTHP diamond substrates. The study ofthe local conductivity characteristics is expected to provideessential information for the development of a controlledprocess and the improvement of crystalline perfection. STMmeasurements were carried out with air-based AFM undera tip bias of 1-2 V with a tip current of 0.1–1 nA. Thesurface of the diamond was connected to ground with silverpaint.
3. Results and Discussion
Figures 1 and 2 show AFM images of films on HTHPdiamond and Si substrates with B-S codoping ((a) S/C =0.001, B/S = 0.01; (b) S/C = 0.005, B/S = 0.02). Figure 1(a)shows well-developed, randomly oriented polycrystallinefacets with an average crystal size of 10–50 nm grown on
HTHPdiamond substrates.Thefilmwas flatwith a roughnessof approximately 1.8 nm. As shown in Figure 1(b), the grainsize of this film was about 5–20 nm, and the roughness ofthis film was approximately 1.6 nm. Figure 2(a) shows thatthe film grown on the Si substrate consisted of large grainswith a high fraction of grain boundaries. The grain sizeof this film was about 100 nm. The roughness of this filmwas approximately 18.5 nm, which was due to the successivesecondary nucleation. Figure 2(b) shows that the film hasrelatively small grains with about 50 nm, and the roughnessof this film was approximately 16 nm. The comparison of (a)in Figures 1 and 2 and (b) in Figures 1 and 2 shows that theaddition of sulfur and boron can decrease the grain size. Theincrease of boron content can improve the crystal quality andthe surface morphology significantly.
Figure 3 showed the temperature dependency of the resis-tivity of B-S codoped diamond films deposited on different
4 Journal of Nanomaterials
1.000(𝜇m)
(a)
1.000(𝜇m)
(b)
(nA
)
5000−500
0.7
0
−0.7
(mV)
(c)
(nA
)
5000−500
0.7
0
−0.7
(mV)
(d)
Figure 5: (a) STM and (b) CITS images for B-S codoped diamond on a Si substrate with S/C = 0.001 and B/S = 0.01. The I-V characteristicswere obtained at low (c) and high (d) emission points.
substratewith a temperature range of 300–650K.As shown inFigure 3, the linear relationship between ln(𝜌) and the inversetemperature indicated that the conductivity of the filmswas thermally activated. For the films deposited on siliconsubstrate, the activated energies of conductivity were deter-mined to be 0.16 eV. But for the films deposited on diamondsubstrate, the activated energies of conductivity decreasedto 0.07 eV. This indicated that conductivity of homoepitaxialfilms is better than that of heteroepitaxial films.
SIMS analyses confirmed that the sulfur was successfullyintroduced into diamond lattice. Figure 4 showed the SIMSspectrum from codoped sample with a B/S ratio of 0.01and the surface of the film consisting of sulfur atoms,boron atoms, and hydrogen atoms. From the inset shown inFigure 4, the sulfur concentration of B-S codoped diamondfilms can increase by almost one order of magnitude of Sdoped diamond films. This indicated that the addition ofboron facilitated sulfur incorporation into diamond.
Figure 5 shows the STM and CITS images for diamondfilms on a silicon substrate with B-S codoping (S/C = 0.001,B/S = 0.01). This image was taken with a sample bias and atunneling current of 1.61 V and 0.10 nA, respectively. Smallsecondary grains or cluster grains with an average sizeless than 10 nm were observed in Figure 5(a). These smallgrains were observed in all crystalline facets and indicatedcontinuous secondary nucleation during CVD processing.Figure 5(b) shows the corresponding CITS image of thesample shown in Figure 5(a). The white regions indicate therelatively high current area, and the black regions indicatelow emission. High electron emission was observed only atsome grain boundaries. These results are in agreement withthe results of Frolov et al. [9]. The local I-V characteristicsat high and low electron emission positions are also shown inFigures 5(c) and 5(d). It can be seen that the tunneling currentat grain boundaries is larger than the current at specific facets.The result shows that the emission efficiency at the grain
Journal of Nanomaterials 5
0 500
(nm)
(a)
0 500
(nm)
(b)
(nA
)
5000−500
1
0
−1
(mV)
(c)
(nA
)
5000−500
1
0
−1
(mV)
(d)
Figure 6: (a) STM and (b) CITS images for B-S codoped diamond on a Si substrate with S/C = 0.005 and B/S = 0.02. The I-V characteristicswere obtained at different points ((c) and (d)).
boundary is higher than the efficiency in the grain facet. Thisis probably due to the heterogeneity in the composition ordefects at the grain boundary. Both results show the typicalnonlinear behavior for the tunneling current. Figure 6 showsthe STM and CITS images for diamond films on a siliconsubstrate with B-S codoping (S/C = 0.005, B/S = 0.02). Smallgrains with an average size less than 5 nm were observed inFigure 6(a). The local I-V characteristics are also shown inFigures 6(c) and 6(d). In these figures, it can be seen that theelectrical conductivity of the diamond film increases with theincrease of the boron-doping concentration. The tunnelingcurrent at a negative voltage applied to the sample is largerthan the current at a positive voltage, which indicates that thediamond film has n-type conductivity [10, 11].
The STM and CITS images of boron-sulfur codopeddiamond deposited on an HTHP diamond substrateare shown in Figure 7. Those images were taken with asample bias and a tunneling current of 2.15 V and 0.11 nA,
respectively. It is noted that the average size of graindeposited on HTHP diamond was approximately 40–70 nm.Figure 7(b) shows the corresponding CITS image of thesample in Figure 7(a). No significant difference in theemission efficiency was observed between the crystallinefacets and the grain boundaries. Therefore, it indicates thatthe growth of homoepitaxial diamond film could improve thecrystal quality and the crystal perfection. The local I-V char-acteristics are also shown in Figures 7(c) and 7(d). In thesefigures, it can be seen that the tunneling current at a negativevoltage is also larger than that at a positive voltage, whichindicates that the diamond film has an n-type electronicconductivity.
4. Conclusions
The structure and the electron field emission properties ofboron-sulfur codoped diamond films on HTHP diamond
6 Journal of Nanomaterials
2.000
(𝜇m)
(a)
2.000
(𝜇m)
(b)
(nA
)
5000−500
1
0
−1
(mV)
(c)
(nA
)
5000−500
1
0
−1
(mV)
(d)
Figure 7: (a) STM and (b) CITS images of B-S codoped diamond film on HTHP diamond substrate under the condition of S/C = 0.001 andB/S = 0.01. The I-V characteristics were obtained at different points ((c) and (d)).
substrates and Si substrates were investigated. It showsthat the crystal grain size and the surface roughness ofhomoepitaxial diamond films were much smaller than thoseof heteroepitaxial diamond films, and films deposited on Sisubstrates had more grain boundaries than those depositedon HTHP diamond substrates. The electronic field emissionefficiency at the grain boundaries is larger than that in thecrystalline facets. The electronic structure was identified asan n-type electronic structure at the surface of films grownwith sulfur and limited amount of boron.
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper.
Acknowledgments
This work was supported by the National Natural ScienceFoundation of China (Grant nos. 51072113 and 10804071)and the Shanghai Outstanding Academic Leaders ProjectFunding (12XD1420700) and the Innovation Program ofShanghai Municipal Education Commission (13ZZ143).
References
[1] F. Brunt, P. Germi, M. Pernet, A. Deneuville, E. Gheeraert, andJ. Mambou, “Effect of boron incorporation on the structure ofpolycrystalline diamondfilms,”Diamond andRelatedMaterials,vol. 6, no. 5–7, pp. 774–777, 1997.
[2] M. S. Katagiri, J. Isoya, S. Koizumi, and H. Kanda, “Lightlyphosphorus-doped homoepitaxial diamond films grown by
Journal of Nanomaterials 7
chemical vapor deposition,” Applied Physics Letters, vol. 85, no.26, pp. 6365–6367, 2004.
[3] C. E. Sally, B. A. Alfred, C. A. John, E. E. Yulia, and V. P.Yuri, “Diamond growth in the presence of boron and sulfur,”Diamond and RelatedMaterials, vol. 12, no. 10-11, pp. 1627–1632,2003.
[4] I. Sakaguchi, M. Nishitani-Gamo, Y. Kukuchi et al., “Sulfur: adonor dopant for n-type diamond semiconductors,” PhysicalReview B, vol. 60, no. 4, pp. R2139–R2141, 1999.
[5] H. Katayama-Yoshida, T. Nishimatsu, T. Yamamoto, and N.Orita, “Codoping method for the fabrication of low-resistivitywide band-gap semiconductors in p-type GaN, p-type AlNand n-type diamond: prediction versus experiment,” Journal ofPhysics Condensed Matter, vol. 13, no. 40, pp. 8901–8914, 2001.
[6] M. Cannaerts,M.Nesladek, Z. Reme, and L.M. Stals, “Scanningtunneling microscopy and spectroscopy of non-doped, hydro-gen terminated CVD diamond,” Physica Status Solidi A, vol. 181,no. 1, pp. 77–81, 2000.
[7] S. Y. Chen, M. Y. Lee, C. S. Chen, and J. T. Lue, “Themechanism of field emission for diamond films studied byscanning tunneling microscopy,” Physics Letters A, vol. 313, no.5, pp. 436–441, 2003.
[8] H.-F. Cheng, Y.-C. Lee, S.-J. Lin, Y.-P. Chou, T. T. Chen, and I.-N. Lin, “Current image tunneling spectroscopy of boron-dopednanodiamonds,” Journal of Applied Physics, vol. 97, no. 4, ArticleID 044312, 2005.
[9] V. D. Frolov, A. V. Karabutov, V. I. Konov, S. M. Pimenov, andA.M. Prokhorov, “Scanning tunnellingmicroscopy: applicationto field electron emission studies,” Journal of Physics D: AppliedPhysics, vol. 32, no. 7, pp. 815–819, 1999.
[10] W. Kaiser, L. Bell, M. Hecht, and F. Grunthaner, “Scanningtunneling microscopy characterization of the geometric andelectronic structure of hydrogen-terminated silicon surfaces,”Journal of Vacuum Science & Technology A, vol. 6, pp. 519–523,1988.
[11] M. Ito, K. Murato, K. Aiso, M. Hori, T. Goto, andM. Hiramatsu,“Scanning tunneling microscopic and spectroscopic character-izationof diamond film prepared by capacitively coupled radiofrequency CH
3OH plasma with OH radical injection,” Applied
Physics Letters, vol. 70, no. 16, pp. 2141–2143, 1997.
Submit your manuscripts athttp://www.hindawi.com
ScientificaHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014
Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014
Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation http://www.hindawi.com Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014
The Scientific World JournalHindawi Publishing Corporation http://www.hindawi.com Volume 2014
Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014
Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014
Nano
materials
Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014
Journal ofNanomaterials
