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Effect of subsurface boron on photoluminescence from silicon nanocrystals
Surface Science 605 (2011) 799–801
Contents lists available at ScienceDirect
Surface Science j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / s u s c
Effect of subsurface boron on photoluminescence from silicon nanocrystals Navneethakrishnan Salivati a,1, Nimrod Shuall b, Joseph M. McCrate a, John G. Ekerdt a,⁎ a b
Department of Chemical Engineering, University of Texas at Austin, Austin, TX 78712, USA D.C. Sirica Ltd., Nesher, 36680, Israel
a r t i c l e
i n f o
Article history: Received 29 April 2010 Accepted 18 January 2011 Available online 26 January 2011 Keywords: Silicon nanocrystals Temperature programmed desorption Passivation Photoluminescence Boron
a b s t r a c t Silicon (Si) nanocrystals (NCs) less than 5 nm in diameter are grown on SiO2 surfaces using hot wire chemical vapor deposition in an ultrahigh vacuum chamber and the dangling bonds are passivated using atomic deuterium. The passivated NCs are subsequently exposed to BDx radicals formed by dissociating deuterated diborane (B2D6) over a hot tungsten filament and photoluminescence quenching is observed. Temperature programmed desorption spectra reveal the presence of additional D2 desorption peaks beyond those found for surfaces that have only been passivated by atomic deuterium. The additional peaks appear at lower temperatures and this can be attributed to deuterium desorption from surface Si atoms bonded to subsurface boron atoms. The subsurface boron likely enhances nonradiative Auger recombination leading to photoluminescence quenching. © 2011 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
Silicon (Si) nanocrystals (NCs) are promising candidates for light emitting devices because they exhibit size-dependent light emission [1–5]. However, in order to exploit the potential of such materials, the role of surface passivation and doping needs to be fully understood [6–10]. Photoluminescence (PL) intensity from Si NCs increases as the concentration of mono-, di- and trideuteride species on the NC surface increases and as the surface deuteride species lead to unreconstructed Si-dimer bonds and passivated (occupied) dangling bonds [6,7]. The insertion of dopants into Si NCs has been shown to quench PL and this has been attributed to an increase in nonradiative Auger recombination [8–10]. In a previous manuscript, the influence of deuteride and NDx surface chemistry on the PL emitted from ammonia (ND3)-passivated Si NCs was examined [7]. Although the NC surface was covered by mono-, di- and trideuteride species and nitrogen containing species, such as Si-ND2 and Si2ND, intense PL was observed from ND3 passivated Si NCs. In this paper we use a combination of temperature programmed desorption (TPD) and PL measurements to show that the presence of subsurface B atoms has a significant negative impact on the opto-electronic properties of Si nanocrystals and quenches the PL signal of a deuterium-passivated NC.
The experimental apparatus consists of a load lock, growth chamber, a PL chamber, and an analytical chamber, all connected to each other via an intermediate transfer chamber under a base pressure of 5×10− 9 Torr. More details of the system are available elsewhere [11,12] and the hot wire chemical vapor deposition (HWCVD) experimental procedure has been described earlier [6,7]. Si(100) wafers with 10 nm of thermal oxide were cut into squares of 1.6 cm× 1.6 cm and inserted into the growth chamber and heated to the growth temperature of 875 K. A hot tungsten filament situated 3 cm away from the substrate is used in HWCVD; a constant filament current of 4 A was used that led to an estimated filament temperature of 1775 K [6,7]. Disilane (Voltaix; 4% in He) partial pressure during HWCVD was 1.6 × 10− 7 Torr and the particle size was controlled by varying the HWCVD time. After growth, the samples were cooled to 375 K under vacuum, and subsequently the hot filament was turned on (4 A filament current) and the samples were subjected to various doses of deuterium (D2) (Voltaix; 99.99%) followed by doses of diborane (B2D6) (Voltaix; 1% in He) under a D2 or B2D6 partial pressure of 5 × 10−6 Torr. The samples were then transferred in situ to the PL chamber where PL was measured at a substrate temperature of 310 K. A 405 nm continuous wave diode laser with an output power of 20 mW was used for excitation and a QE65000 Ocean optics spectrometer (wavelength range 300 nm to 1050 nm) was used for detection. A 450 nm long pass filter was used to cut off the scattered laser illumination. The sample was next transferred to the analytical chamber, where X-ray photoelectron spectroscopy (XPS) and TPD spectra were collected
⁎ Corresponding author at: The University of Texas at Austin, Department of Chemical Engineering C0400, Austin, TX 78712 USA. Tel.: +1 512 471 4689; fax: +1 512 471 7060. E-mail address: [email protected] (J.G. Ekerdt). 1 Current address: Intel Corporation, Hillsboro, OR 97124. 0039-6028/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.susc.2011.01.022
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N. Salivati et al. / Surface Science 605 (2011) 799–801
in that order. A differentially pumped Thermo Electron Smart IQ+ mass spectrometer covered by a nose cone with a 0.5 cm opening was used to collect TPD measurements. The TPD ramp rate was 3 K/s. The analytical chamber is also equipped for XPS using a VG Microtech 8025 XPS system with a CLAM2 cylindrical analyzer employing Al Kα radiation and a pass energy of 100 eV. A fresh sample was grown and used for each PL-TPD run. 3. Results and discussion We use the same nomenclature for the deuteride states on the surface of the NC as described earlier [6,7]. The mono- and dideuteride are denoted by β1 and β2, which desorb around 780 K and 680 K, respectively; the trideuteride, denoted by β3 appears as a broad low temperature feature before the dideuteride feature. D2 and B2D6 exposures are reported in Langmuir (1 L = 10−6 Torr s). Scanning electron microscopy (SEM) images of the nanocrystals grown using HWCVD can be found in Ref. [6]. The particle number density is estimated to be in the range of 8 × 1011 cm− 2. Initially, Si NCs grown using 15 min of HWCVD (~4 nm in diameter) were subjected to various hot wire doses of B2D6 at 375 K without first passivating the surfaces with deuterium and were moved to the transfer chamber where PL was measured at 310 K. No PL was observed from diborone-only passivated Si NCs. In order to understand the reason for the lack of PL, Si NCs were first subjected to a 3600 L hot wire dose of D2, which results in a deuterium passivated surface [6], and these NCs were subsequently subjected to various hot wire doses of B2D6. The PL results displayed in Fig. 1 show that PL intensity decreases as the B2D6 dose is increased and is completely quenched with a 600 L dose. It was difficult to see a measurable B signal in XPS at these hot wire doses; however, at higher doses (3000 L B2D6) a weak B signal (not shown) was observed at 188 eV. D+ 2 TPD spectra are shown in Fig. 2. The dotted line is from a control experiment in which the Mo ring used to mount the sample was subjected to a 600 L hot wire dose of B2D6. The mono-, di- and trideuteride features for a surface that was only exposed to atomic deuterium are labeled β1, β2 and β3, respectively, in Fig. 2 [6,13]. Additional low temperature features are observed in the D+ 2 TPD from NCs exposed to the same hot wire D2 dose and then to hot wire doses of B2D6. As the B2D6 dose is increased, the β1 and β2 features broaden, and the lower temperature peaks labeled β1⁎ and β2⁎ develop at a 300 L B2D6 dose. STM studies by Wang et al. have shown that B on Si(100) prefers to go subsurface [14]. In the TPD spectra, Kim et al. have observed similar low temperature desorption features, they labeled as β1⁎ and β2⁎, in addition to the conventional β1 and β2 features for B-treated Si(100) surfaces [15,16]. These low temperature features arise due to a B-induced decrease in the Si⁎–D bond strength, where Si⁎ represents surface Si atoms bonded to second-layer B atoms. The decreased Si⁎–D
Fig. 1. PL intensity from Si NCs grown using 15 min of HWCVD and exposed to a 3600 L hot wire dose of D2. This was followed by various hot wire doses of B2D6.
Fig. 2. Comparison of D+ 2 TPD from Si NCs exposed to hot wire doses (3600 L) of D2 followed by hot wire doses of B2D6. The dotted line corresponds to the signal recorded after a 600 L hot wire dose of B2D6 on the Mo sample transfer ring.
bond strength has been associated with increased Si⁎ dimer strain as the Si–B bond length (2.0–2.1 Å), is considerably shorter than the Si–Si bond length (2.35 Å) and also to the Si⁎–B backbond charge transfer, which takes place because of the higher electronegativity of B [15,17]. The lower temperature β1⁎ and β2⁎ desorption features over Si NCs in Fig. 2 are likely associated with the same phenomena that result with surface Si(100) atoms bonded to subsurface B atoms. In addition to the β1⁎ and β2⁎ desorption features that appear following BDx exposure, three desorption peaks appear below 600 K as the B2D6 dose is increased (Fig. 2); the new features, as a set, are labeled β3⁎. Comparable β3⁎ features were not reported on Si(100) [15,16]. We have previously reported that, unlike Si(100), the monodeuteride (β1), dideuteride (β2) and trideuteride (β3) do not fill sequentially on Si NCs [6,13]. The β3⁎ features may also form on Si(100) under the appropriate atomic D exposure conditions. The β3⁎ features are tentatively attributed to D2 desorption from boron-weakened trideuteride species. The reason for multiple β3⁎ features was not revealed in this study; it is possible that back-bonded B atoms may have affected the trideuteride stability differently at the various NC edge and surface sites. Based on the TPD results and drawing analogies to Si(100), it can be concluded that BDx radicals formed by the dissociation of B2D6 at the hot filament lead to subsurface B, with the surface Si atoms back-bonded to these B atoms. These subsurface B atoms can act as a p-type dopant and enhance the nonradiative Auger recombination of excitons, which quenches the PL intensity [8–10]. Si NCs grown using 11 min (~3 nm in diameter) and 10 min of HWCVD (particle size is below resolution of the SEM) were deuterium
Fig. 3. PL from Si NCs of different sizes after deuterium passivation and then followed by exposure to hot wire doses of B2D6. The PL was quenched for each NC size; 300 L B2D6 quenched the 11 min and 10 min HWCVD samples, and 600 L B2D6 quenched the 15 min HWCVD sample.
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bonds and deuterium desorption is observed at lower temperatures. The presence of subsurface B is detrimental for PL.
Acknowledgements The authors thank the Welch Foundation (Grant No. F-1502) and Sirica Corporation for funding.
References
Fig. 4. D+ 2 TPD from Si NCs exposed to hot wire doses of D2 followed by hot wire doses of B2D6.
passivated and then exposed to hot wire doses of B2D6. As the particle size is reduced, PL shifts to a lower wavelength (Fig. 3) as reported previously [6]. Complete PL quenching is observed at a B2D6 dose of 300 L for the 3 nm size NC. Less deuterium exposure is needed to fully passivate the smaller Si NCs [6] and less BDx exposure is also needed for complete PL quenching. D+ 2 TPD spectra (Fig. 4) indicate the presence of the β1⁎, β2⁎ and β3⁎ desorption features that signify the presence of subsurface B for the smaller Si NCs as well. The PL quenching observed with diborane is in sharp contrast with an earlier work with ammonia [7]. Boron prefers to go subsurface while nitrogen stays at the surface. The quenching of PL from Si NCs is observed even at low doses of B2D6, indicating that the presence of subsurface B atoms is extremely detrimental for PL. 4. Conclusion TPD experiments reveal that surface Si atoms are back-bonded to the subsurface B atoms. The back-bonded B atoms weaken the surface Si⁎–D
[1] Z.H. Lu, D.J. Lockwood, J.M. Baribeau, Nature 378 (1995) 258. [2] J.D. Holmes, K.J. Ziegler, R.C. Doty, L.E. Pell, K.P. Johnston, B.A. Korgel, J. Am. Chem. Soc. 123 (2001) 3743. [3] L.Y. Chen, W.H. Chen, F.C.N. Hong, Appl. Phys. Lett. 86 (2005) 193506. [4] A. Anopchenko, A. Marconi, E. Moser, S. Prezioso, M. Wang, L. Pavesi, G. Pucker, P. Bellutti, J. Appl. Phys. 106 (2009) 033104. [5] A. Marconi, A. Anopchenko, M. Wang, G. Pucker, P. Bellutti, L. Pavesi, Appl. Phys. Lett. 94 (2009) 221110. [6] N. Salivati, N. Shuall, E. Baskin, V. Garber, J.M. McCrate, J.G. Ekerdt, J. Appl. Phys. 106 (2009) 063121. [7] N. Salivati, N. Shuall, J.M. McCrate, J.G. Ekerdt, J. Phys. Chem. C. 114 (2010) 16924. [8] A. Mimura, M. Fujii, S. Hayashi, K. Yamamoto, Solid State Commun. 109 (1999) 561. [9] X.J. Hao, E.C. Cho, C. Flynn, Y.S. Shen, G. Conibeer, M.A. Green, Nanotechnology 19 (2008) 424019. [10] M. Fujii, S. Hayashi, K. Yamamoto, J. Appl. Phys. 83 (1998) 7953. [11] W.T. Leach, J.H. Zhu, J.G. Ekerdt, J. Cryst. Growth 240 (2002) 415. [12] W.T. Leach, J.H. Zhu, J.G. Ekerdt, J. Cryst. Growth 243 (2002) 30. [13] N. Salivati, J.G. Ekerdt, Surf. Sci. 603 (2009) 1121. [14] a Y. Wang, R.J. Hamers, Appl. Phys. Lett. 66 (1995) 2057; b Y. Wang, R.J. Hamers, J. Vac. Sci. Technol. A 13 (1995) 1431; c Y. Wang, R.J. Hamers, E. Kaxiras, Phys. Rev. Lett. 74 (1995) 403. [15] H. Kim, G. Glass, S.Y. Park, T. Spila, N. Taylor, J.R. Abelson, J.E. Greene, Appl. Phys. Lett. 69 (1996) 3869. [16] H. Kim, G. Glass, T. Spila, N. Taylor, S.Y. Park, J.R. Abelson, J.E. Greene, J. Appl. Phys. 82 (1997) 2288. [17] B.E. Weir, R.L. Headrick, Q. Shen, L.C. Feldman, M.S. Hybertson, M. Needels, M. Schluter, T.R. Hart, Phys. Rev. B 46 (1992) 12861.
Contents lists available at ScienceDirect
Surface Science j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / s u s c
Effect of subsurface boron on photoluminescence from silicon nanocrystals Navneethakrishnan Salivati a,1, Nimrod Shuall b, Joseph M. McCrate a, John G. Ekerdt a,⁎ a b
Department of Chemical Engineering, University of Texas at Austin, Austin, TX 78712, USA D.C. Sirica Ltd., Nesher, 36680, Israel
a r t i c l e
i n f o
Article history: Received 29 April 2010 Accepted 18 January 2011 Available online 26 January 2011 Keywords: Silicon nanocrystals Temperature programmed desorption Passivation Photoluminescence Boron
a b s t r a c t Silicon (Si) nanocrystals (NCs) less than 5 nm in diameter are grown on SiO2 surfaces using hot wire chemical vapor deposition in an ultrahigh vacuum chamber and the dangling bonds are passivated using atomic deuterium. The passivated NCs are subsequently exposed to BDx radicals formed by dissociating deuterated diborane (B2D6) over a hot tungsten filament and photoluminescence quenching is observed. Temperature programmed desorption spectra reveal the presence of additional D2 desorption peaks beyond those found for surfaces that have only been passivated by atomic deuterium. The additional peaks appear at lower temperatures and this can be attributed to deuterium desorption from surface Si atoms bonded to subsurface boron atoms. The subsurface boron likely enhances nonradiative Auger recombination leading to photoluminescence quenching. © 2011 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
Silicon (Si) nanocrystals (NCs) are promising candidates for light emitting devices because they exhibit size-dependent light emission [1–5]. However, in order to exploit the potential of such materials, the role of surface passivation and doping needs to be fully understood [6–10]. Photoluminescence (PL) intensity from Si NCs increases as the concentration of mono-, di- and trideuteride species on the NC surface increases and as the surface deuteride species lead to unreconstructed Si-dimer bonds and passivated (occupied) dangling bonds [6,7]. The insertion of dopants into Si NCs has been shown to quench PL and this has been attributed to an increase in nonradiative Auger recombination [8–10]. In a previous manuscript, the influence of deuteride and NDx surface chemistry on the PL emitted from ammonia (ND3)-passivated Si NCs was examined [7]. Although the NC surface was covered by mono-, di- and trideuteride species and nitrogen containing species, such as Si-ND2 and Si2ND, intense PL was observed from ND3 passivated Si NCs. In this paper we use a combination of temperature programmed desorption (TPD) and PL measurements to show that the presence of subsurface B atoms has a significant negative impact on the opto-electronic properties of Si nanocrystals and quenches the PL signal of a deuterium-passivated NC.
The experimental apparatus consists of a load lock, growth chamber, a PL chamber, and an analytical chamber, all connected to each other via an intermediate transfer chamber under a base pressure of 5×10− 9 Torr. More details of the system are available elsewhere [11,12] and the hot wire chemical vapor deposition (HWCVD) experimental procedure has been described earlier [6,7]. Si(100) wafers with 10 nm of thermal oxide were cut into squares of 1.6 cm× 1.6 cm and inserted into the growth chamber and heated to the growth temperature of 875 K. A hot tungsten filament situated 3 cm away from the substrate is used in HWCVD; a constant filament current of 4 A was used that led to an estimated filament temperature of 1775 K [6,7]. Disilane (Voltaix; 4% in He) partial pressure during HWCVD was 1.6 × 10− 7 Torr and the particle size was controlled by varying the HWCVD time. After growth, the samples were cooled to 375 K under vacuum, and subsequently the hot filament was turned on (4 A filament current) and the samples were subjected to various doses of deuterium (D2) (Voltaix; 99.99%) followed by doses of diborane (B2D6) (Voltaix; 1% in He) under a D2 or B2D6 partial pressure of 5 × 10−6 Torr. The samples were then transferred in situ to the PL chamber where PL was measured at a substrate temperature of 310 K. A 405 nm continuous wave diode laser with an output power of 20 mW was used for excitation and a QE65000 Ocean optics spectrometer (wavelength range 300 nm to 1050 nm) was used for detection. A 450 nm long pass filter was used to cut off the scattered laser illumination. The sample was next transferred to the analytical chamber, where X-ray photoelectron spectroscopy (XPS) and TPD spectra were collected
⁎ Corresponding author at: The University of Texas at Austin, Department of Chemical Engineering C0400, Austin, TX 78712 USA. Tel.: +1 512 471 4689; fax: +1 512 471 7060. E-mail address: [email protected] (J.G. Ekerdt). 1 Current address: Intel Corporation, Hillsboro, OR 97124. 0039-6028/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.susc.2011.01.022
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N. Salivati et al. / Surface Science 605 (2011) 799–801
in that order. A differentially pumped Thermo Electron Smart IQ+ mass spectrometer covered by a nose cone with a 0.5 cm opening was used to collect TPD measurements. The TPD ramp rate was 3 K/s. The analytical chamber is also equipped for XPS using a VG Microtech 8025 XPS system with a CLAM2 cylindrical analyzer employing Al Kα radiation and a pass energy of 100 eV. A fresh sample was grown and used for each PL-TPD run. 3. Results and discussion We use the same nomenclature for the deuteride states on the surface of the NC as described earlier [6,7]. The mono- and dideuteride are denoted by β1 and β2, which desorb around 780 K and 680 K, respectively; the trideuteride, denoted by β3 appears as a broad low temperature feature before the dideuteride feature. D2 and B2D6 exposures are reported in Langmuir (1 L = 10−6 Torr s). Scanning electron microscopy (SEM) images of the nanocrystals grown using HWCVD can be found in Ref. [6]. The particle number density is estimated to be in the range of 8 × 1011 cm− 2. Initially, Si NCs grown using 15 min of HWCVD (~4 nm in diameter) were subjected to various hot wire doses of B2D6 at 375 K without first passivating the surfaces with deuterium and were moved to the transfer chamber where PL was measured at 310 K. No PL was observed from diborone-only passivated Si NCs. In order to understand the reason for the lack of PL, Si NCs were first subjected to a 3600 L hot wire dose of D2, which results in a deuterium passivated surface [6], and these NCs were subsequently subjected to various hot wire doses of B2D6. The PL results displayed in Fig. 1 show that PL intensity decreases as the B2D6 dose is increased and is completely quenched with a 600 L dose. It was difficult to see a measurable B signal in XPS at these hot wire doses; however, at higher doses (3000 L B2D6) a weak B signal (not shown) was observed at 188 eV. D+ 2 TPD spectra are shown in Fig. 2. The dotted line is from a control experiment in which the Mo ring used to mount the sample was subjected to a 600 L hot wire dose of B2D6. The mono-, di- and trideuteride features for a surface that was only exposed to atomic deuterium are labeled β1, β2 and β3, respectively, in Fig. 2 [6,13]. Additional low temperature features are observed in the D+ 2 TPD from NCs exposed to the same hot wire D2 dose and then to hot wire doses of B2D6. As the B2D6 dose is increased, the β1 and β2 features broaden, and the lower temperature peaks labeled β1⁎ and β2⁎ develop at a 300 L B2D6 dose. STM studies by Wang et al. have shown that B on Si(100) prefers to go subsurface [14]. In the TPD spectra, Kim et al. have observed similar low temperature desorption features, they labeled as β1⁎ and β2⁎, in addition to the conventional β1 and β2 features for B-treated Si(100) surfaces [15,16]. These low temperature features arise due to a B-induced decrease in the Si⁎–D bond strength, where Si⁎ represents surface Si atoms bonded to second-layer B atoms. The decreased Si⁎–D
Fig. 1. PL intensity from Si NCs grown using 15 min of HWCVD and exposed to a 3600 L hot wire dose of D2. This was followed by various hot wire doses of B2D6.
Fig. 2. Comparison of D+ 2 TPD from Si NCs exposed to hot wire doses (3600 L) of D2 followed by hot wire doses of B2D6. The dotted line corresponds to the signal recorded after a 600 L hot wire dose of B2D6 on the Mo sample transfer ring.
bond strength has been associated with increased Si⁎ dimer strain as the Si–B bond length (2.0–2.1 Å), is considerably shorter than the Si–Si bond length (2.35 Å) and also to the Si⁎–B backbond charge transfer, which takes place because of the higher electronegativity of B [15,17]. The lower temperature β1⁎ and β2⁎ desorption features over Si NCs in Fig. 2 are likely associated with the same phenomena that result with surface Si(100) atoms bonded to subsurface B atoms. In addition to the β1⁎ and β2⁎ desorption features that appear following BDx exposure, three desorption peaks appear below 600 K as the B2D6 dose is increased (Fig. 2); the new features, as a set, are labeled β3⁎. Comparable β3⁎ features were not reported on Si(100) [15,16]. We have previously reported that, unlike Si(100), the monodeuteride (β1), dideuteride (β2) and trideuteride (β3) do not fill sequentially on Si NCs [6,13]. The β3⁎ features may also form on Si(100) under the appropriate atomic D exposure conditions. The β3⁎ features are tentatively attributed to D2 desorption from boron-weakened trideuteride species. The reason for multiple β3⁎ features was not revealed in this study; it is possible that back-bonded B atoms may have affected the trideuteride stability differently at the various NC edge and surface sites. Based on the TPD results and drawing analogies to Si(100), it can be concluded that BDx radicals formed by the dissociation of B2D6 at the hot filament lead to subsurface B, with the surface Si atoms back-bonded to these B atoms. These subsurface B atoms can act as a p-type dopant and enhance the nonradiative Auger recombination of excitons, which quenches the PL intensity [8–10]. Si NCs grown using 11 min (~3 nm in diameter) and 10 min of HWCVD (particle size is below resolution of the SEM) were deuterium
Fig. 3. PL from Si NCs of different sizes after deuterium passivation and then followed by exposure to hot wire doses of B2D6. The PL was quenched for each NC size; 300 L B2D6 quenched the 11 min and 10 min HWCVD samples, and 600 L B2D6 quenched the 15 min HWCVD sample.
N. Salivati et al. / Surface Science 605 (2011) 799–801
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bonds and deuterium desorption is observed at lower temperatures. The presence of subsurface B is detrimental for PL.
Acknowledgements The authors thank the Welch Foundation (Grant No. F-1502) and Sirica Corporation for funding.
References
Fig. 4. D+ 2 TPD from Si NCs exposed to hot wire doses of D2 followed by hot wire doses of B2D6.
passivated and then exposed to hot wire doses of B2D6. As the particle size is reduced, PL shifts to a lower wavelength (Fig. 3) as reported previously [6]. Complete PL quenching is observed at a B2D6 dose of 300 L for the 3 nm size NC. Less deuterium exposure is needed to fully passivate the smaller Si NCs [6] and less BDx exposure is also needed for complete PL quenching. D+ 2 TPD spectra (Fig. 4) indicate the presence of the β1⁎, β2⁎ and β3⁎ desorption features that signify the presence of subsurface B for the smaller Si NCs as well. The PL quenching observed with diborane is in sharp contrast with an earlier work with ammonia [7]. Boron prefers to go subsurface while nitrogen stays at the surface. The quenching of PL from Si NCs is observed even at low doses of B2D6, indicating that the presence of subsurface B atoms is extremely detrimental for PL. 4. Conclusion TPD experiments reveal that surface Si atoms are back-bonded to the subsurface B atoms. The back-bonded B atoms weaken the surface Si⁎–D
[1] Z.H. Lu, D.J. Lockwood, J.M. Baribeau, Nature 378 (1995) 258. [2] J.D. Holmes, K.J. Ziegler, R.C. Doty, L.E. Pell, K.P. Johnston, B.A. Korgel, J. Am. Chem. Soc. 123 (2001) 3743. [3] L.Y. Chen, W.H. Chen, F.C.N. Hong, Appl. Phys. Lett. 86 (2005) 193506. [4] A. Anopchenko, A. Marconi, E. Moser, S. Prezioso, M. Wang, L. Pavesi, G. Pucker, P. Bellutti, J. Appl. Phys. 106 (2009) 033104. [5] A. Marconi, A. Anopchenko, M. Wang, G. Pucker, P. Bellutti, L. Pavesi, Appl. Phys. Lett. 94 (2009) 221110. [6] N. Salivati, N. Shuall, E. Baskin, V. Garber, J.M. McCrate, J.G. Ekerdt, J. Appl. Phys. 106 (2009) 063121. [7] N. Salivati, N. Shuall, J.M. McCrate, J.G. Ekerdt, J. Phys. Chem. C. 114 (2010) 16924. [8] A. Mimura, M. Fujii, S. Hayashi, K. Yamamoto, Solid State Commun. 109 (1999) 561. [9] X.J. Hao, E.C. Cho, C. Flynn, Y.S. Shen, G. Conibeer, M.A. Green, Nanotechnology 19 (2008) 424019. [10] M. Fujii, S. Hayashi, K. Yamamoto, J. Appl. Phys. 83 (1998) 7953. [11] W.T. Leach, J.H. Zhu, J.G. Ekerdt, J. Cryst. Growth 240 (2002) 415. [12] W.T. Leach, J.H. Zhu, J.G. Ekerdt, J. Cryst. Growth 243 (2002) 30. [13] N. Salivati, J.G. Ekerdt, Surf. Sci. 603 (2009) 1121. [14] a Y. Wang, R.J. Hamers, Appl. Phys. Lett. 66 (1995) 2057; b Y. Wang, R.J. Hamers, J. Vac. Sci. Technol. A 13 (1995) 1431; c Y. Wang, R.J. Hamers, E. Kaxiras, Phys. Rev. Lett. 74 (1995) 403. [15] H. Kim, G. Glass, S.Y. Park, T. Spila, N. Taylor, J.R. Abelson, J.E. Greene, Appl. Phys. Lett. 69 (1996) 3869. [16] H. Kim, G. Glass, T. Spila, N. Taylor, S.Y. Park, J.R. Abelson, J.E. Greene, J. Appl. Phys. 82 (1997) 2288. [17] B.E. Weir, R.L. Headrick, Q. Shen, L.C. Feldman, M.S. Hybertson, M. Needels, M. Schluter, T.R. Hart, Phys. Rev. B 46 (1992) 12861.