- Email: [email protected]
Near-surface recrystallization of the amorphous implanted layer of ion implanted 6H-SiC
Nuclear Instruments and Methods in Physics Research B xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
Near-surface recrystallization of the amorphous implanted layer of ion implanted 6H-SiC R.J. Kuhudzai a,⇑, N.G. van der Berg a, J.B. Malherbe a, T.T. Hlatshwayo a, C.C. Theron a, A.V. Buys b, A.J. Botha b, E. Wendler c, W. Wesch c a b c
Physics Department, University of Pretoria, Pretoria, South Africa Laboratory for Microscopy and Microanalysis, University of Pretoria, South Africa Institut Für Festköperphysik, Friedrich-Schiller-Universität Jena, Jena, Germany
a r t i c l e
i n f o
Article history: Available online xxxx Keywords: Ion implantation SiC Amorphisation Recrystallization Crystal growth SEM
a b s t r a c t The recrystallization and subsequent crystal growth during annealing of amorphous surface layers on 6HSiC produced by ion implantation is investigated. Amorphous surface layers were produced by ion implantation of 360 keV ions of iodine, silver, xenon, cesium and strontium into single crystalline 6H-silicon carbide samples. The ion fluence for all the implantations were in the order of 1016 cm 2. Vacuum annealing of the damaged silicon carbide samples was then performed. The microstructure of SiC surfaces before and after annealing was investigated using a high resolution field emission scanning electron microscope (SEM). SEM analysis was complimented by Atomic Force Microscopy (AFM). SEM images acquired by an in-lens detector using an accelerating voltage of 2 kV show nano-crystallites developed for all implanted samples after annealing. Larger and more faceted crystallites along with elongated thin crystallites were observed for iodine and xenon implanted 6H-SiC. Crystallites formed on surfaces implanted with strontium and cesium were smaller and less faceted. Strontium, silver and cesium implanted samples also exhibited more cavities on the surface. AFM was used to evaluate the effect of annealing on the surface roughness. For all the amorphous surfaces which were essentially featureless, the root mean square (rms) roughness was approximately 1 nm. The roughness increased to approximately 17 nm for the iodine implanted sample after annealing with the surface roughness below this value for all the other samples. AFM also showed that the largest crystals grew to heights of about 17, 20, 45, 50 and 65 nm for Sr, Cs, Ag, Xe and I implanted samples after annealing at 1200 °C for 5 h respectively. SEM images and AFM analysis suggest that iodine is more effective in promoting crystal growth during the annealing of bombardment-induced amorphous SiC layers than the rest of the ions we implanted. In samples of silicon carbide co-implanted with iodine and silver, few cavities were visible on the surface indicating that iodine influenced the recrystallization. Surface crystallites that grew on the iodine implanted surfaces were more resistant to thermal etching and decomposition than those that grew on the silver implanted samples at temperatures of up to 1400 °C for 30 h. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction The extent of radiation damage retained after ion implantation into single crystalline SiC and the annealing of that damage has been an area of interest to researchers in the semiconductor and nuclear materials field. Research has been undertaken in the quest to understand the impact of damage retained on the fundamental properties of SiC, given its promising future in a wide number of applications ranging from, electronic and optical to nuclear ⇑ Corresponding author. Tel.: +27 124204777; fax: +27 123625288.
cladding in high temperature reactors [1–3]. The majority of the work found in published papers focuses on the analysis of solid phase epitaxy (SPE) emanating from the bulk crystalline and the amorphous layer interface. Several Rutherford backscattering spectroscopy (RBS) in channelling mode studies [2–9] have shown that heavy ion bombardment of single crystal SiC at room temperature with ion energies in the order of hundreds of keV and to fluences 1 1015 cm 2 or higher results in an amorphous surface layer. In these studies, they have shown that SPE commences after vacuum annealing at 1000 °C – the minimum annealing temperature reported. Studies by Pacaud et al. [10] showed that SPE starts at temperatures even as low as 500 °C. Once SiC has been
E-mail address: [email protected] (R.J. Kuhudzai). http://dx.doi.org/10.1016/j.nimb.2014.02.072 0168-583X/Ó 2014 Elsevier B.V. All rights reserved.
Please cite this article in press as: R.J. Kuhudzai et al., Near-surface recrystallization of the amorphous implanted layer of ion implanted 6H-SiC, Nucl. Instr. Meth. B (2014), http://dx.doi.org/10.1016/j.nimb.2014.02.072
2
R.J. Kuhudzai et al. / Nuclear Instruments and Methods in Physics Research B xxx (2014) xxx–xxx
amorphized, very high annealing temperatures (typically above 1500 °C) are needed to completely recrystallize it into a single crystal. A recent review [1] discusses the problems for full SPE growth of the amorphous layer. Very little information is available on a totally independent recrystallization process taking place simultaneously on or near the front surface of the samples as the annealing proceeds. For amorphous surface layers produced by heavy ion implantation with fluences of up to 1016 cm 2, the front surface is shielded from the underlying crystalline bulk as the concentration of implanted ions inhibits SPE and thus the recrystallization here does not follow the pattern of the underlying crystalline bulk [11]. Snead et al. [12], investigated the recrystallization of 6H-SiC amorphised by neutron irradiation. In their case, neutron irradiation provided them the opportunity to analyse the recrystallization behaviour of amorphous SiC without the influence of an impurity species. Snead et al., observed star shaped crystallites forming on the surface starting at 800 °C with the previously amorphous layer completely crystallised at 1150 °C. For ion implanted SiC [5,13], surface crystallites were also observed after recrystallization of silver and iodine implanted SiC for annealing cycles at 1100 °C. The kinetics of the recrystallization of amorphous SiC layers have been explained by using the classical nucleation and growth theory of Avrami-Johnson-Mehl [14–16]. Our group has been characterising radiation damage produced by ions of the significant fission products produced in fuel particles of high temperature nuclear reactors. RBS and channelling studies on 360 keV xenon ions to a fluence of 1 1016 cm 2 implanted at room temperature, reveal an amorphous layer extending to a depth of 200 nm from the surface [17]. The amorphous layers produced by implantation of, iodine, strontium, silver and cesium ions, also of energy 360 keV, into 6H-SiC wafers, were up to depths of 220, 240, 260 and 190 nm, respectively [6,7,9,18]. In this paper we investigate the effect of these ions on the growth of crystals on the surface of the damaged SiC as annealing proceeds. This growth can reveal how these different ions interact with SiC and ultimately the effect of any interaction on the release of fission products from SiC coated fuel particles.
2. Experimental 6H-SiC wafers of thickness 0.3 mm and diameter 50 mm from Intrinsic SemiconductorsÒ, were individually implanted with 360 keV ions of 131Xe+, 127I+ and 133Cs+ up to a fluence of 1 1016 cm 2. Implantations for 109Ag+ and 88Sr + were up to a fluence of 2 1016 cm 2. Two additional wafers of 6H-SiC were co-implanted with 133Cs+ and 127I+ ions and 109Ag+ and 127I+ ions respectively. The implantations were carried out at room temperature. The flux was maintained at a rate below 1013 cm 2 s 1 to minimise the increase in the substrate temperature, reducing the probability of simultaneously annealing some of the radiation damage produced during the room temperature implantations. During the implantations the temperature of the samples rose to about 55 °C. The angle of incidence of the ions was set at an angle of 7° relative to the normal to avoid channelling effects during implantation. For the annealing cycles, the samples were placed inside small graphite crucibles and annealed in a computer controlled high temperature air cooled vacuum WebbÒ graphite furnace. The annealing was performed at 1100 °C for 15 min and at 1200 °C for 5 h. The pressure was maintained below 5 10 5 mbar throughout the annealing cycles. The microstructure of SiC surfaces before and after annealing was investigated using a high resolution Zeiss Ultra 55 field emission scanning electron microscope fitted with an in-lens detector. A 2 kV accelerating voltage was employed during all SEM imaging.
The working distance was maintained at approximately 2 mm for all the imaging experiments. SEM images were complimented by AFM using Bruker’s Dimension Icon scanning probe microscope. All AFM measurements were performed in contact mode using a Si probe of tip radius 610 nm. Since the AFM images on their own did not exhibit any additional features not already visible in the SEM images, no AFM images are shown. However, the RMS roughness values obtained from the AFM images were used to quantify the increase in surface topography after annealing.
3. Results and discussion Fig. 1(a) shows a typical SEM image of the as-received un-implanted 6H-SiC wafer. The surface had only some polishing marks (P) observable on it and the surface roughness was found to be approximately 0.5 nm. Fig. 1(b) shows the as-implanted surfaces of the xenon implanted sample. The surfaces of all the other as-implanted samples (not shown) are similar to the xenon one. As the sample surfaces were amorphous after implantation, the surfaces were flat and featureless with the polishing marks less pronounced after ion bombardment. The surface roughness was about 1 nm for all the samples. The increase in RMS roughness, as measured by AFM, after ion bombardment is due to sputter-induced roughening [19]. The images showing the effect of annealing at 1100 °C for 15 min on implanted samples are shown in Fig. 2. In Fig. 2a, for the strontium implanted sample, the surface is no longer featureless. The previously amorphous surface layer appears now to have been recrystallized into a polycrystalline material as some crystallites are observed on the surface although it is difficult to clearly ascertain their size. Fig. 2b shows the SEM image of the cesium implanted sample; evidence of some recrystallization can be seen from the contrast which seems to be depicting crystallites on the surface. These crystallites are not as developed as those observed on the strontium implanted sample. Elongated thin crystallites (L) appear on the annealed surface of the silver implanted sample (Fig. 2c), with some extending to a length of about 1 lm. There seem to be no preferred orientation as these needle type crystallites develop randomly on the surface. Star-like crystallites (S) were observed on the surface of the xenon implanted sample (Fig. 2d). These crystallites look similar to those observed by Snead et al. [6] on annealing of neutron amorphised SiC. They appear to nucleate from certain points or centres on the surface and grow parallel to the surface. Again there appears to be no preferred orientation for growth. The surface of the iodine implanted sample (Fig. 3a) is characterised by pockets of closely packed (densely packed regions) of nano crystallites (C) as well as elongated thin crystallites (L). Some of these long crystallites extend to lengths of about 1 lm. In this case the thin crystallites seem to branch out from certain growth centres (G) unlike those observed for the silver implantation. The crystals are more developed than in the silver case, where needles seem to grow in a sea of amorphous zones while for the iodine implanted sample, thin long crystallites grow along with pockets of closely packed nano crystallites. The case of expedited growth in the presence of iodine is supported by the image showing the sample co-implanted with silver and iodine (Fig. 3b). In this case, the long thin crystallites are more pronounced than in the case of silver implantation alone, and the seemingly amorphous zones observed on silver implanted samples are now crystalized with close packed nano crystallites now being visible. A similar trend is observed in Fig. 3c which shows the annealed SiC sample co-implanted with cesium and iodine ions. In this image the long thin crystallites (size) are now visible which were not fully developed for the sample only implanted with cesium. At 1100 °C for 15 min, all
Please cite this article in press as: R.J. Kuhudzai et al., Near-surface recrystallization of the amorphous implanted layer of ion implanted 6H-SiC, Nucl. Instr. Meth. B (2014), http://dx.doi.org/10.1016/j.nimb.2014.02.072
R.J. Kuhudzai et al. / Nuclear Instruments and Methods in Physics Research B xxx (2014) xxx–xxx
a
P
3
b
Fig. 1. SEM images of (a) as received 6H-SiC, and (b) the as-implanted image of 6H-SiC implanted with Xe ions. The ion energy was 360 keV and the implantation was performed at room temperature.
a
b
c
d L
S
Fig. 2. SEM images of 6H-SiC wafers implanted with ions of (a) Sr, (b) Cs, (c) Ag and (d) Xe. All the samples were annealed at 1100 °C for 15 min. The ion energy was 360 keV and all implantations were performed at room temperature. Ion fluences for all samples were 1 1016 cm 2 .
the surfaces look to have under gone recrystallization although iodine implanted sample seems to have the most developed crystal structures. Micrographs of the implanted samples annealed 1200 °C for 5 h are shown in Figs. 4 and 5. For the strontium implanted sample (Fig. 4a), the polycrystalline surface observed looks similar to the one observed after the 15 min anneal at 1100 °C. However, the nano crystallites on the surface are now more visible and larger. Cavities (O) on the surface are observable at this annealing cycle. The grain size of some of these crystallites is estimated to be about 100 nm with a few nano crystallites having grown to approximately to a diameter of 150 nm. AFM analysis shows the surface roughening to approximately 5 ± 1 nm, with the height of some of the larger crystals approximately 17 nm. The recrystallization of the amorphous SiC into crystals occurs according to a step-flow mechanism [20]. For the crystals to grow materials must be provided from nearby areas resulting in the formation of cavities. Crystal surfaces with higher surface energies grow proportionally faster than surfaces with lower surface energies via surface diffusion, according to Wulf’s law [21], thereby lowering the total energy of the system.
The cesium implanted sample is shown in Fig. 4b. In this case the polycrystalline surface is composed of short thin crystallites approximately 300 nm long, and irregular close packed nano crystallites approximately 100 nm in diameter. The surface is also not continuous as cavities are also prominent on this surface. Surface roughness, as measured by AFM, was found to be approximately 6.3 ± 1 nm. The largest crystals on the surface grew to heights of about 20 nm. From the image of the silver implanted sample (Fig. 4c), the recrystallized surface is characterised by a number of cavities (O). The larger cavities on this annealed surface extend to diameters beyond 200 nm and to depths of 45 nm. The top surface is far from being a continuous layer. Although larger crystallites (of diameter larger than 200 nm and height of 45 nm) develop on the surface, their growth via surface diffusion leaves behind large cavities or pits. On annealing the xenon implanted 6H-SiC (Fig. 4d), the surface is characterised by long, thin crystallites branching out from growth centres. These elongated thin crystallites extend to a lengths 700–900 nm on average. Large faceted crystals (approximately 200–300 nm in diameter) characterised by
Please cite this article in press as: R.J. Kuhudzai et al., Near-surface recrystallization of the amorphous implanted layer of ion implanted 6H-SiC, Nucl. Instr. Meth. B (2014), http://dx.doi.org/10.1016/j.nimb.2014.02.072
4
R.J. Kuhudzai et al. / Nuclear Instruments and Methods in Physics Research B xxx (2014) xxx–xxx
b
a G
C
L
c
Fig. 3. SEM images of 6H-SiC wafers implanted with ions of (a) iodine, (b) co-implanted with ions of Ag and I, and (c) co-implanted with ions of Cs and I. All the samples were annealed at 1100 °C for 15 min. The ion energy was 360 keV and all implantations were performed at room temperature. Ion fluencies for all samples were 1 1016 cm 2.
b
a
O
O
c
d
G
O
Fig. 4. SEM images of 6H-SiC wafers implanted with ions of (a) Sr, (b) Cs, (c) Ag and (d) Xe. All the samples were annealed at 1200 °C for 5 h. The ion energy was 360 keV and all implantations were performed at room temperature. Ion fluences for all samples were 1 1016 cm 2.
multiple twinning (visible under higher magnification) have also grown under annealing. These crystals grow to heights reaching approximately 50 nm. The surface appears to be quite continuous, with the large cavities observed for the silver implanted samples not seen in this case. Although the growth mechanism appears be the same, i.e. of larger crystals growing through a crystal surface diffusion supply mechanism, the surface layer does not break up in
the xenon implanted sample. Large faceted crystals with a few cavities can be seen on the iodine implanted sample, (Fig. 5a). In the case of iodine these crystals easily grow to diameters of about 200 nm and in some cases 400 nm. These crystallites reach heights of approximately 65 nm above the sample surface. Again the thin and elongated crystals branching out from certain growth points are visible. It is quite clear that the largest crystals grow on the
Please cite this article in press as: R.J. Kuhudzai et al., Near-surface recrystallization of the amorphous implanted layer of ion implanted 6H-SiC, Nucl. Instr. Meth. B (2014), http://dx.doi.org/10.1016/j.nimb.2014.02.072
R.J. Kuhudzai et al. / Nuclear Instruments and Methods in Physics Research B xxx (2014) xxx–xxx
a
b
c
d
5
e
Fig. 5. SEM images of 6H-SiC wafers implanted with ions of (a) I, (b) co-implanted with ions of Ag and I, and (c) co-implanted with ions of Cs and I. All the samples were annealed at 1200 °C for 5 h. (d) implanted with Ag and (e) implanted with I. The samples in (d) and (e) were annealed at 1400 ºC for 30 h. The ion energy was 360 keV and all implantations were performed at room temperature. Ion fluences for all samples were 1 1016 cm 2.
iodine amorphised surfaces. Fewer cavities are also observed for annealed samples implanted with iodine and xenon as compared to the cesium, strontium and silver implanted samples. Images of annealed samples of the co-implantation experiment of iodine and silver and iodine and cesium are shown in Fig. 5b and c respectively. Annealing results in the growth of large faceted crystals, (larger than 200 nm in diameter). Crystals of this magnitude are not seen for the annealed single silver (Fig. 4c) and cesium, (Fig. 4b) ion implanted samples. It appears iodine catalyses crystal growth on the surface during annealing on amorphised SiC surfaces. The larger crystallites and fewer but larger cavities observed for the iodine implanted surfaces compared to the other implanted samples could suggest some form of stronger binding or chemical interaction or catalytic action between the iodine and SiC. Malherbe [1] discussed the suggestions previously made that iodine and other halogen elements can aid crystal growth in SiC [22– 24]. According to Malherbe [1] this process is probably related to compound formation in the amorphous SiC with free Si and C due to the bombardment process. It is known that iodine reacts with silicon above 600 °C to form SiI4 which reacts further with silicon at high temperatures (above 800 °C) to form SiI2 [25,26]. The SiI2 again decomposes above 1000 °C. These processes are pressure
dependent when performed in fluid conditions. Within a solid, the above temperatures might be different. These processes might explain the report by Ramesh et al. [20] that pure 3C-SiC is obtained when heating Si and activated carbon powder in an iodine atmosphere in a commercial microwave oven. These chemical reactions between iodine and free Si, released in the SiC by the ion bombardment process, might lead to the recrystallization driven topography development. Annealing for a longer time (30 h) at a higher temperature (1400 °C) seems to support the case for some sort of stronger binding for in the presence of iodine. (Fig. 5d and e) show SEM images of SiC implanted with Ag and I respectively after annealing for 30 h at 1400 °C. From these images, the crystals on the Ag implanted surface are not as faceted anymore. They appear to be not as defined as in the images of the samples annealed at the lower temperature (1200 °C for 5 h Fig. 4c). This may indicate that decomposition due to thermal etching is already taking place. In the case of the iodine implanted sample, the large crystals still exhibit well defined facets indicating that the thermal etching is not as advanced at this stage as in the case of silver. Similar results have been observed after annealing at 1500 °C for 30 h using Rutherford backscattering spectroscopy [27]. The authors reported an increase in the detected surface carbon signal which was more
Please cite this article in press as: R.J. Kuhudzai et al., Near-surface recrystallization of the amorphous implanted layer of ion implanted 6H-SiC, Nucl. Instr. Meth. B (2014), http://dx.doi.org/10.1016/j.nimb.2014.02.072
6
R.J. Kuhudzai et al. / Nuclear Instruments and Methods in Physics Research B xxx (2014) xxx–xxx
pronounced for the silver implanted sample than in the case of iodine implanted SiC. At these temperatures, the decomposition of SiC is accompanied by the evaporation of silicon leaving carbon on the surface [28]. The appearance of cavities on the surfaces after annealing might have implications for the nuclear industry. Modern nuclear fuel elements are coated with a SiC layer to retain radioactive fission products within the fuel elements. Recently it was proposed that these cavities might act as migration paths for implanted silver in SiC [5]. It is therefore expected that iodine and xenon are more likely to be retained in SiC while the large cavities observed on silver and cesium implanted samples could provide paths for their release. 4. Conclusion The recrystallization and the crystal growth on the surface after annealing of the bombardment-induced amorphous SiC layers were investigated using SEM and AFM. Growth of surface crystallites was observed to be greatest on surfaces that had been implanted with iodine ions. The faceted crystals on the surface of the iodine implanted SiC grew to heights of about 65 nm and to diameters as large as 400 nm. Large faceted crystals of diameters extending to 300 nm and heights of 50 nm grew on surfaces implanted with xenon. The surfaces implanted with iodine and xenon remained fairly continuous with few cavities observed after annealing at 1200 °C for 5 h. After annealing the samples implanted with silver, strontium and cesium, SEM showed some cavities developed on their surfaces. Crystal growth was less pronounced on surfaces that had been implanted with cesium and strontium with crystals heights of 20 and 17 nm, respectively. Although crystals on the silver implanted surfaces grew to heights of about 45 nm, the surface however, was quite porous exhibiting large cavities with diameters of about 200 nm distributed across the surface. Large crystals similar to those that grew on the iodine implanted samples were observed for the samples co-implanted with cesium and iodine. These findings show that iodine plays a major role in the growth of the surface crystals as the cesium single element implanted surfaces did not exhibit crystals on this same scale. A similar trend was observed on the surfaces co-implanted with iodine and silver ions. Over all the surfaces were less porous in the presence of iodine for the co-implanted samples as compared to single element implantation with silver or cesium
indicating iodine enhanced the recrystallisation process. Surface crystallites that grew on the iodine implanted surfaces were found to be more stable and resistant to thermal etching and decomposition than those that grew on the silver implanted samples at temperatures of up to 1400 °C for 30 h. References [1] J.B. Malherbe, J. Phys. D Appl. Phys. 46 (2013) 473001. [2] A. Benyagoub, Nucl. Instr. Meth. Phys. Res. B 266 (12–13) (2008) 2766. [3] J.B. Malherbe, E. Friedland, N.G. van der Berg, Nucl. Instr. Meth. Phys. Res. B 266 (8) (2008) 1373. [4] E. Wendler, A. Heft, W. Wesch, Nucl. Instr. Meth. Phys. Res. B 141 (1–4) (1998) 105. [5] T.T. Hlatshwayo, J.B. Malherbe, N.G. van der Berg, L.C. Prinsloo, A.J. Botha, E. Wendler, W.E. Wesch, Nucl. Instr. Meth. Phys. Res. B 274 (2012) 120. [6] E. Friedland, N.G. van der Berg, J.B. Malherbe, R.J. Kuhudzai, A.J. Botha, E. Wendler, W. Wesch, Nucl. Instr. Meth. Phys. Res. B 268 (2) (2010) 2892. [7] E. Friedland, N.G. van der Berg, J.B. Malherbe, E. Wendler, W. Wesch, J. Nucl. Mater. 425 (1–3) (2012) 205. [8] T.T. Hlatshwayo, J.B. Malherbe, N.G. van der Berg, A.J. Botha, P. Chakraborty, Nucl. Instr. Meth. Phys. Res. B 273 (2012) 61. [9] E. Friedland, J.B. Malherbe, N.G. van der Berg, T. Hlatshwayo, A.J. Botha, E. Wendler, W. Wesch, J. Nucl. Mater. 389 (19) (2009) 326. [10] Y. Pacaud, J. Stoemenos, G. Brauer, R. Yankov, V. Heera, M. Voelskow, R. Kogler, W. Skorupa, Nucl. Instr. Meth. Phys. Res. B 120 (1–4) (1996) 177. [11] I.T. Bae, M. Ishimaru, Y. Hirotsu, K.E. Sickafus, J. Appl. Phys. 96 (3) (2004) 1451. [12] L.L. Snead, S.J. Zinkle, J.C. Hay, M.C. Osborne, Nucl. Instr. Meth. Phys. Res. B 141 (1–4) (1998) 123. [13] J.B. Malherbe, N.G. van der Berg, A.J. Botha, E. Friedland, T.T. Hlatswayo, R.J. Kuhudzai, E. Wendler, W. Wesch, P. Chakraborty, E.F. da Silveira, Nucl. Instr. Meth. Phys. Res. B 315 (2013) 136. [14] S. Inoue, K. Yoshii, M. Umeno, H. Kawabe, Thin Solid Films 151 (1987) 403. [15] L. Calcagno, P. Musumeci, F. Roccaforte, C. Bongiorno, G. Foti, Appl. Surf. Sci. 184 (1–4) (2001) 123. [16] A. Höfgen, V. Heera, F. Eichhorn, W. Skorupa, J. Appl. Phys. 84 (9) (1998) 4769. [17] T.T Hlatswayo, Private communication. [18] E. Friedland, N. van der Berg, T. Hlatshwayo, R. Kuhudzai, J. Malherbe, W.E. Wendler, W. Wesch, Nucl. Instr. Meth. Phys. Res. B 286 (2012) 102. [19] J.B. Malherbe, CRC Crit. Rev. Solid State Mater. Sci. 19 (1994) 129. [20] W.K. Burton, N. Cabrera, F.C. Frank, Philos. Trans. R. Soc. 243A (1931) 299. [21] G. Wulff, Z. Krist, Z. Kristallogr. 34 (1901) 449. [22] P.D. Ramesh, B. Vaidhyanathan, M. Ganguli, K.J. Rao, J. Mater. Res. 9 (1994) 3025. [23] G.D. Papasouliotis, S.V. Sotirchos, J. Mater. Res. 14 (1999) 3397. [24] H. Pedersen, S. Leone, A. Henry, V. Darakchieva, E. Janzén, Surf. Coat. Technol. 201 (22–23) (2007) 8931. [25] T.F. Ciszek, H. Wang, M.R. Page, R.E. Bauer, M.D. Landry, IEEE 21 (2002) 206. [26] T.H. Wang, T.F. Ciszek, J. Electrochem. Soc. 147 (2000) 1945. [27] T.T. Hlatshwayo, N.G. van der Berg, M. Msimanga, J.B. Malherbe, R.J. Kuhudzai, J. Nucl. Instr. Meth. Phys. Res. B, submitted for publication. [28] N.G. van der Berg, J.B. Malherbe, A.J. Botha, E. Friedland, Appl. Surf. Sci. 258 (15) (2012) 5561.
Please cite this article in press as: R.J. Kuhudzai et al., Near-surface recrystallization of the amorphous implanted layer of ion implanted 6H-SiC, Nucl. Instr. Meth. B (2014), http://dx.doi.org/10.1016/j.nimb.2014.02.072
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
Near-surface recrystallization of the amorphous implanted layer of ion implanted 6H-SiC R.J. Kuhudzai a,⇑, N.G. van der Berg a, J.B. Malherbe a, T.T. Hlatshwayo a, C.C. Theron a, A.V. Buys b, A.J. Botha b, E. Wendler c, W. Wesch c a b c
Physics Department, University of Pretoria, Pretoria, South Africa Laboratory for Microscopy and Microanalysis, University of Pretoria, South Africa Institut Für Festköperphysik, Friedrich-Schiller-Universität Jena, Jena, Germany
a r t i c l e
i n f o
Article history: Available online xxxx Keywords: Ion implantation SiC Amorphisation Recrystallization Crystal growth SEM
a b s t r a c t The recrystallization and subsequent crystal growth during annealing of amorphous surface layers on 6HSiC produced by ion implantation is investigated. Amorphous surface layers were produced by ion implantation of 360 keV ions of iodine, silver, xenon, cesium and strontium into single crystalline 6H-silicon carbide samples. The ion fluence for all the implantations were in the order of 1016 cm 2. Vacuum annealing of the damaged silicon carbide samples was then performed. The microstructure of SiC surfaces before and after annealing was investigated using a high resolution field emission scanning electron microscope (SEM). SEM analysis was complimented by Atomic Force Microscopy (AFM). SEM images acquired by an in-lens detector using an accelerating voltage of 2 kV show nano-crystallites developed for all implanted samples after annealing. Larger and more faceted crystallites along with elongated thin crystallites were observed for iodine and xenon implanted 6H-SiC. Crystallites formed on surfaces implanted with strontium and cesium were smaller and less faceted. Strontium, silver and cesium implanted samples also exhibited more cavities on the surface. AFM was used to evaluate the effect of annealing on the surface roughness. For all the amorphous surfaces which were essentially featureless, the root mean square (rms) roughness was approximately 1 nm. The roughness increased to approximately 17 nm for the iodine implanted sample after annealing with the surface roughness below this value for all the other samples. AFM also showed that the largest crystals grew to heights of about 17, 20, 45, 50 and 65 nm for Sr, Cs, Ag, Xe and I implanted samples after annealing at 1200 °C for 5 h respectively. SEM images and AFM analysis suggest that iodine is more effective in promoting crystal growth during the annealing of bombardment-induced amorphous SiC layers than the rest of the ions we implanted. In samples of silicon carbide co-implanted with iodine and silver, few cavities were visible on the surface indicating that iodine influenced the recrystallization. Surface crystallites that grew on the iodine implanted surfaces were more resistant to thermal etching and decomposition than those that grew on the silver implanted samples at temperatures of up to 1400 °C for 30 h. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction The extent of radiation damage retained after ion implantation into single crystalline SiC and the annealing of that damage has been an area of interest to researchers in the semiconductor and nuclear materials field. Research has been undertaken in the quest to understand the impact of damage retained on the fundamental properties of SiC, given its promising future in a wide number of applications ranging from, electronic and optical to nuclear ⇑ Corresponding author. Tel.: +27 124204777; fax: +27 123625288.
cladding in high temperature reactors [1–3]. The majority of the work found in published papers focuses on the analysis of solid phase epitaxy (SPE) emanating from the bulk crystalline and the amorphous layer interface. Several Rutherford backscattering spectroscopy (RBS) in channelling mode studies [2–9] have shown that heavy ion bombardment of single crystal SiC at room temperature with ion energies in the order of hundreds of keV and to fluences 1 1015 cm 2 or higher results in an amorphous surface layer. In these studies, they have shown that SPE commences after vacuum annealing at 1000 °C – the minimum annealing temperature reported. Studies by Pacaud et al. [10] showed that SPE starts at temperatures even as low as 500 °C. Once SiC has been
E-mail address: [email protected] (R.J. Kuhudzai). http://dx.doi.org/10.1016/j.nimb.2014.02.072 0168-583X/Ó 2014 Elsevier B.V. All rights reserved.
Please cite this article in press as: R.J. Kuhudzai et al., Near-surface recrystallization of the amorphous implanted layer of ion implanted 6H-SiC, Nucl. Instr. Meth. B (2014), http://dx.doi.org/10.1016/j.nimb.2014.02.072
2
R.J. Kuhudzai et al. / Nuclear Instruments and Methods in Physics Research B xxx (2014) xxx–xxx
amorphized, very high annealing temperatures (typically above 1500 °C) are needed to completely recrystallize it into a single crystal. A recent review [1] discusses the problems for full SPE growth of the amorphous layer. Very little information is available on a totally independent recrystallization process taking place simultaneously on or near the front surface of the samples as the annealing proceeds. For amorphous surface layers produced by heavy ion implantation with fluences of up to 1016 cm 2, the front surface is shielded from the underlying crystalline bulk as the concentration of implanted ions inhibits SPE and thus the recrystallization here does not follow the pattern of the underlying crystalline bulk [11]. Snead et al. [12], investigated the recrystallization of 6H-SiC amorphised by neutron irradiation. In their case, neutron irradiation provided them the opportunity to analyse the recrystallization behaviour of amorphous SiC without the influence of an impurity species. Snead et al., observed star shaped crystallites forming on the surface starting at 800 °C with the previously amorphous layer completely crystallised at 1150 °C. For ion implanted SiC [5,13], surface crystallites were also observed after recrystallization of silver and iodine implanted SiC for annealing cycles at 1100 °C. The kinetics of the recrystallization of amorphous SiC layers have been explained by using the classical nucleation and growth theory of Avrami-Johnson-Mehl [14–16]. Our group has been characterising radiation damage produced by ions of the significant fission products produced in fuel particles of high temperature nuclear reactors. RBS and channelling studies on 360 keV xenon ions to a fluence of 1 1016 cm 2 implanted at room temperature, reveal an amorphous layer extending to a depth of 200 nm from the surface [17]. The amorphous layers produced by implantation of, iodine, strontium, silver and cesium ions, also of energy 360 keV, into 6H-SiC wafers, were up to depths of 220, 240, 260 and 190 nm, respectively [6,7,9,18]. In this paper we investigate the effect of these ions on the growth of crystals on the surface of the damaged SiC as annealing proceeds. This growth can reveal how these different ions interact with SiC and ultimately the effect of any interaction on the release of fission products from SiC coated fuel particles.
2. Experimental 6H-SiC wafers of thickness 0.3 mm and diameter 50 mm from Intrinsic SemiconductorsÒ, were individually implanted with 360 keV ions of 131Xe+, 127I+ and 133Cs+ up to a fluence of 1 1016 cm 2. Implantations for 109Ag+ and 88Sr + were up to a fluence of 2 1016 cm 2. Two additional wafers of 6H-SiC were co-implanted with 133Cs+ and 127I+ ions and 109Ag+ and 127I+ ions respectively. The implantations were carried out at room temperature. The flux was maintained at a rate below 1013 cm 2 s 1 to minimise the increase in the substrate temperature, reducing the probability of simultaneously annealing some of the radiation damage produced during the room temperature implantations. During the implantations the temperature of the samples rose to about 55 °C. The angle of incidence of the ions was set at an angle of 7° relative to the normal to avoid channelling effects during implantation. For the annealing cycles, the samples were placed inside small graphite crucibles and annealed in a computer controlled high temperature air cooled vacuum WebbÒ graphite furnace. The annealing was performed at 1100 °C for 15 min and at 1200 °C for 5 h. The pressure was maintained below 5 10 5 mbar throughout the annealing cycles. The microstructure of SiC surfaces before and after annealing was investigated using a high resolution Zeiss Ultra 55 field emission scanning electron microscope fitted with an in-lens detector. A 2 kV accelerating voltage was employed during all SEM imaging.
The working distance was maintained at approximately 2 mm for all the imaging experiments. SEM images were complimented by AFM using Bruker’s Dimension Icon scanning probe microscope. All AFM measurements were performed in contact mode using a Si probe of tip radius 610 nm. Since the AFM images on their own did not exhibit any additional features not already visible in the SEM images, no AFM images are shown. However, the RMS roughness values obtained from the AFM images were used to quantify the increase in surface topography after annealing.
3. Results and discussion Fig. 1(a) shows a typical SEM image of the as-received un-implanted 6H-SiC wafer. The surface had only some polishing marks (P) observable on it and the surface roughness was found to be approximately 0.5 nm. Fig. 1(b) shows the as-implanted surfaces of the xenon implanted sample. The surfaces of all the other as-implanted samples (not shown) are similar to the xenon one. As the sample surfaces were amorphous after implantation, the surfaces were flat and featureless with the polishing marks less pronounced after ion bombardment. The surface roughness was about 1 nm for all the samples. The increase in RMS roughness, as measured by AFM, after ion bombardment is due to sputter-induced roughening [19]. The images showing the effect of annealing at 1100 °C for 15 min on implanted samples are shown in Fig. 2. In Fig. 2a, for the strontium implanted sample, the surface is no longer featureless. The previously amorphous surface layer appears now to have been recrystallized into a polycrystalline material as some crystallites are observed on the surface although it is difficult to clearly ascertain their size. Fig. 2b shows the SEM image of the cesium implanted sample; evidence of some recrystallization can be seen from the contrast which seems to be depicting crystallites on the surface. These crystallites are not as developed as those observed on the strontium implanted sample. Elongated thin crystallites (L) appear on the annealed surface of the silver implanted sample (Fig. 2c), with some extending to a length of about 1 lm. There seem to be no preferred orientation as these needle type crystallites develop randomly on the surface. Star-like crystallites (S) were observed on the surface of the xenon implanted sample (Fig. 2d). These crystallites look similar to those observed by Snead et al. [6] on annealing of neutron amorphised SiC. They appear to nucleate from certain points or centres on the surface and grow parallel to the surface. Again there appears to be no preferred orientation for growth. The surface of the iodine implanted sample (Fig. 3a) is characterised by pockets of closely packed (densely packed regions) of nano crystallites (C) as well as elongated thin crystallites (L). Some of these long crystallites extend to lengths of about 1 lm. In this case the thin crystallites seem to branch out from certain growth centres (G) unlike those observed for the silver implantation. The crystals are more developed than in the silver case, where needles seem to grow in a sea of amorphous zones while for the iodine implanted sample, thin long crystallites grow along with pockets of closely packed nano crystallites. The case of expedited growth in the presence of iodine is supported by the image showing the sample co-implanted with silver and iodine (Fig. 3b). In this case, the long thin crystallites are more pronounced than in the case of silver implantation alone, and the seemingly amorphous zones observed on silver implanted samples are now crystalized with close packed nano crystallites now being visible. A similar trend is observed in Fig. 3c which shows the annealed SiC sample co-implanted with cesium and iodine ions. In this image the long thin crystallites (size) are now visible which were not fully developed for the sample only implanted with cesium. At 1100 °C for 15 min, all
Please cite this article in press as: R.J. Kuhudzai et al., Near-surface recrystallization of the amorphous implanted layer of ion implanted 6H-SiC, Nucl. Instr. Meth. B (2014), http://dx.doi.org/10.1016/j.nimb.2014.02.072
R.J. Kuhudzai et al. / Nuclear Instruments and Methods in Physics Research B xxx (2014) xxx–xxx
a
P
3
b
Fig. 1. SEM images of (a) as received 6H-SiC, and (b) the as-implanted image of 6H-SiC implanted with Xe ions. The ion energy was 360 keV and the implantation was performed at room temperature.
a
b
c
d L
S
Fig. 2. SEM images of 6H-SiC wafers implanted with ions of (a) Sr, (b) Cs, (c) Ag and (d) Xe. All the samples were annealed at 1100 °C for 15 min. The ion energy was 360 keV and all implantations were performed at room temperature. Ion fluences for all samples were 1 1016 cm 2 .
the surfaces look to have under gone recrystallization although iodine implanted sample seems to have the most developed crystal structures. Micrographs of the implanted samples annealed 1200 °C for 5 h are shown in Figs. 4 and 5. For the strontium implanted sample (Fig. 4a), the polycrystalline surface observed looks similar to the one observed after the 15 min anneal at 1100 °C. However, the nano crystallites on the surface are now more visible and larger. Cavities (O) on the surface are observable at this annealing cycle. The grain size of some of these crystallites is estimated to be about 100 nm with a few nano crystallites having grown to approximately to a diameter of 150 nm. AFM analysis shows the surface roughening to approximately 5 ± 1 nm, with the height of some of the larger crystals approximately 17 nm. The recrystallization of the amorphous SiC into crystals occurs according to a step-flow mechanism [20]. For the crystals to grow materials must be provided from nearby areas resulting in the formation of cavities. Crystal surfaces with higher surface energies grow proportionally faster than surfaces with lower surface energies via surface diffusion, according to Wulf’s law [21], thereby lowering the total energy of the system.
The cesium implanted sample is shown in Fig. 4b. In this case the polycrystalline surface is composed of short thin crystallites approximately 300 nm long, and irregular close packed nano crystallites approximately 100 nm in diameter. The surface is also not continuous as cavities are also prominent on this surface. Surface roughness, as measured by AFM, was found to be approximately 6.3 ± 1 nm. The largest crystals on the surface grew to heights of about 20 nm. From the image of the silver implanted sample (Fig. 4c), the recrystallized surface is characterised by a number of cavities (O). The larger cavities on this annealed surface extend to diameters beyond 200 nm and to depths of 45 nm. The top surface is far from being a continuous layer. Although larger crystallites (of diameter larger than 200 nm and height of 45 nm) develop on the surface, their growth via surface diffusion leaves behind large cavities or pits. On annealing the xenon implanted 6H-SiC (Fig. 4d), the surface is characterised by long, thin crystallites branching out from growth centres. These elongated thin crystallites extend to a lengths 700–900 nm on average. Large faceted crystals (approximately 200–300 nm in diameter) characterised by
Please cite this article in press as: R.J. Kuhudzai et al., Near-surface recrystallization of the amorphous implanted layer of ion implanted 6H-SiC, Nucl. Instr. Meth. B (2014), http://dx.doi.org/10.1016/j.nimb.2014.02.072
4
R.J. Kuhudzai et al. / Nuclear Instruments and Methods in Physics Research B xxx (2014) xxx–xxx
b
a G
C
L
c
Fig. 3. SEM images of 6H-SiC wafers implanted with ions of (a) iodine, (b) co-implanted with ions of Ag and I, and (c) co-implanted with ions of Cs and I. All the samples were annealed at 1100 °C for 15 min. The ion energy was 360 keV and all implantations were performed at room temperature. Ion fluencies for all samples were 1 1016 cm 2.
b
a
O
O
c
d
G
O
Fig. 4. SEM images of 6H-SiC wafers implanted with ions of (a) Sr, (b) Cs, (c) Ag and (d) Xe. All the samples were annealed at 1200 °C for 5 h. The ion energy was 360 keV and all implantations were performed at room temperature. Ion fluences for all samples were 1 1016 cm 2.
multiple twinning (visible under higher magnification) have also grown under annealing. These crystals grow to heights reaching approximately 50 nm. The surface appears to be quite continuous, with the large cavities observed for the silver implanted samples not seen in this case. Although the growth mechanism appears be the same, i.e. of larger crystals growing through a crystal surface diffusion supply mechanism, the surface layer does not break up in
the xenon implanted sample. Large faceted crystals with a few cavities can be seen on the iodine implanted sample, (Fig. 5a). In the case of iodine these crystals easily grow to diameters of about 200 nm and in some cases 400 nm. These crystallites reach heights of approximately 65 nm above the sample surface. Again the thin and elongated crystals branching out from certain growth points are visible. It is quite clear that the largest crystals grow on the
Please cite this article in press as: R.J. Kuhudzai et al., Near-surface recrystallization of the amorphous implanted layer of ion implanted 6H-SiC, Nucl. Instr. Meth. B (2014), http://dx.doi.org/10.1016/j.nimb.2014.02.072
R.J. Kuhudzai et al. / Nuclear Instruments and Methods in Physics Research B xxx (2014) xxx–xxx
a
b
c
d
5
e
Fig. 5. SEM images of 6H-SiC wafers implanted with ions of (a) I, (b) co-implanted with ions of Ag and I, and (c) co-implanted with ions of Cs and I. All the samples were annealed at 1200 °C for 5 h. (d) implanted with Ag and (e) implanted with I. The samples in (d) and (e) were annealed at 1400 ºC for 30 h. The ion energy was 360 keV and all implantations were performed at room temperature. Ion fluences for all samples were 1 1016 cm 2.
iodine amorphised surfaces. Fewer cavities are also observed for annealed samples implanted with iodine and xenon as compared to the cesium, strontium and silver implanted samples. Images of annealed samples of the co-implantation experiment of iodine and silver and iodine and cesium are shown in Fig. 5b and c respectively. Annealing results in the growth of large faceted crystals, (larger than 200 nm in diameter). Crystals of this magnitude are not seen for the annealed single silver (Fig. 4c) and cesium, (Fig. 4b) ion implanted samples. It appears iodine catalyses crystal growth on the surface during annealing on amorphised SiC surfaces. The larger crystallites and fewer but larger cavities observed for the iodine implanted surfaces compared to the other implanted samples could suggest some form of stronger binding or chemical interaction or catalytic action between the iodine and SiC. Malherbe [1] discussed the suggestions previously made that iodine and other halogen elements can aid crystal growth in SiC [22– 24]. According to Malherbe [1] this process is probably related to compound formation in the amorphous SiC with free Si and C due to the bombardment process. It is known that iodine reacts with silicon above 600 °C to form SiI4 which reacts further with silicon at high temperatures (above 800 °C) to form SiI2 [25,26]. The SiI2 again decomposes above 1000 °C. These processes are pressure
dependent when performed in fluid conditions. Within a solid, the above temperatures might be different. These processes might explain the report by Ramesh et al. [20] that pure 3C-SiC is obtained when heating Si and activated carbon powder in an iodine atmosphere in a commercial microwave oven. These chemical reactions between iodine and free Si, released in the SiC by the ion bombardment process, might lead to the recrystallization driven topography development. Annealing for a longer time (30 h) at a higher temperature (1400 °C) seems to support the case for some sort of stronger binding for in the presence of iodine. (Fig. 5d and e) show SEM images of SiC implanted with Ag and I respectively after annealing for 30 h at 1400 °C. From these images, the crystals on the Ag implanted surface are not as faceted anymore. They appear to be not as defined as in the images of the samples annealed at the lower temperature (1200 °C for 5 h Fig. 4c). This may indicate that decomposition due to thermal etching is already taking place. In the case of the iodine implanted sample, the large crystals still exhibit well defined facets indicating that the thermal etching is not as advanced at this stage as in the case of silver. Similar results have been observed after annealing at 1500 °C for 30 h using Rutherford backscattering spectroscopy [27]. The authors reported an increase in the detected surface carbon signal which was more
Please cite this article in press as: R.J. Kuhudzai et al., Near-surface recrystallization of the amorphous implanted layer of ion implanted 6H-SiC, Nucl. Instr. Meth. B (2014), http://dx.doi.org/10.1016/j.nimb.2014.02.072
6
R.J. Kuhudzai et al. / Nuclear Instruments and Methods in Physics Research B xxx (2014) xxx–xxx
pronounced for the silver implanted sample than in the case of iodine implanted SiC. At these temperatures, the decomposition of SiC is accompanied by the evaporation of silicon leaving carbon on the surface [28]. The appearance of cavities on the surfaces after annealing might have implications for the nuclear industry. Modern nuclear fuel elements are coated with a SiC layer to retain radioactive fission products within the fuel elements. Recently it was proposed that these cavities might act as migration paths for implanted silver in SiC [5]. It is therefore expected that iodine and xenon are more likely to be retained in SiC while the large cavities observed on silver and cesium implanted samples could provide paths for their release. 4. Conclusion The recrystallization and the crystal growth on the surface after annealing of the bombardment-induced amorphous SiC layers were investigated using SEM and AFM. Growth of surface crystallites was observed to be greatest on surfaces that had been implanted with iodine ions. The faceted crystals on the surface of the iodine implanted SiC grew to heights of about 65 nm and to diameters as large as 400 nm. Large faceted crystals of diameters extending to 300 nm and heights of 50 nm grew on surfaces implanted with xenon. The surfaces implanted with iodine and xenon remained fairly continuous with few cavities observed after annealing at 1200 °C for 5 h. After annealing the samples implanted with silver, strontium and cesium, SEM showed some cavities developed on their surfaces. Crystal growth was less pronounced on surfaces that had been implanted with cesium and strontium with crystals heights of 20 and 17 nm, respectively. Although crystals on the silver implanted surfaces grew to heights of about 45 nm, the surface however, was quite porous exhibiting large cavities with diameters of about 200 nm distributed across the surface. Large crystals similar to those that grew on the iodine implanted samples were observed for the samples co-implanted with cesium and iodine. These findings show that iodine plays a major role in the growth of the surface crystals as the cesium single element implanted surfaces did not exhibit crystals on this same scale. A similar trend was observed on the surfaces co-implanted with iodine and silver ions. Over all the surfaces were less porous in the presence of iodine for the co-implanted samples as compared to single element implantation with silver or cesium
indicating iodine enhanced the recrystallisation process. Surface crystallites that grew on the iodine implanted surfaces were found to be more stable and resistant to thermal etching and decomposition than those that grew on the silver implanted samples at temperatures of up to 1400 °C for 30 h. References [1] J.B. Malherbe, J. Phys. D Appl. Phys. 46 (2013) 473001. [2] A. Benyagoub, Nucl. Instr. Meth. Phys. Res. B 266 (12–13) (2008) 2766. [3] J.B. Malherbe, E. Friedland, N.G. van der Berg, Nucl. Instr. Meth. Phys. Res. B 266 (8) (2008) 1373. [4] E. Wendler, A. Heft, W. Wesch, Nucl. Instr. Meth. Phys. Res. B 141 (1–4) (1998) 105. [5] T.T. Hlatshwayo, J.B. Malherbe, N.G. van der Berg, L.C. Prinsloo, A.J. Botha, E. Wendler, W.E. Wesch, Nucl. Instr. Meth. Phys. Res. B 274 (2012) 120. [6] E. Friedland, N.G. van der Berg, J.B. Malherbe, R.J. Kuhudzai, A.J. Botha, E. Wendler, W. Wesch, Nucl. Instr. Meth. Phys. Res. B 268 (2) (2010) 2892. [7] E. Friedland, N.G. van der Berg, J.B. Malherbe, E. Wendler, W. Wesch, J. Nucl. Mater. 425 (1–3) (2012) 205. [8] T.T. Hlatshwayo, J.B. Malherbe, N.G. van der Berg, A.J. Botha, P. Chakraborty, Nucl. Instr. Meth. Phys. Res. B 273 (2012) 61. [9] E. Friedland, J.B. Malherbe, N.G. van der Berg, T. Hlatshwayo, A.J. Botha, E. Wendler, W. Wesch, J. Nucl. Mater. 389 (19) (2009) 326. [10] Y. Pacaud, J. Stoemenos, G. Brauer, R. Yankov, V. Heera, M. Voelskow, R. Kogler, W. Skorupa, Nucl. Instr. Meth. Phys. Res. B 120 (1–4) (1996) 177. [11] I.T. Bae, M. Ishimaru, Y. Hirotsu, K.E. Sickafus, J. Appl. Phys. 96 (3) (2004) 1451. [12] L.L. Snead, S.J. Zinkle, J.C. Hay, M.C. Osborne, Nucl. Instr. Meth. Phys. Res. B 141 (1–4) (1998) 123. [13] J.B. Malherbe, N.G. van der Berg, A.J. Botha, E. Friedland, T.T. Hlatswayo, R.J. Kuhudzai, E. Wendler, W. Wesch, P. Chakraborty, E.F. da Silveira, Nucl. Instr. Meth. Phys. Res. B 315 (2013) 136. [14] S. Inoue, K. Yoshii, M. Umeno, H. Kawabe, Thin Solid Films 151 (1987) 403. [15] L. Calcagno, P. Musumeci, F. Roccaforte, C. Bongiorno, G. Foti, Appl. Surf. Sci. 184 (1–4) (2001) 123. [16] A. Höfgen, V. Heera, F. Eichhorn, W. Skorupa, J. Appl. Phys. 84 (9) (1998) 4769. [17] T.T Hlatswayo, Private communication. [18] E. Friedland, N. van der Berg, T. Hlatshwayo, R. Kuhudzai, J. Malherbe, W.E. Wendler, W. Wesch, Nucl. Instr. Meth. Phys. Res. B 286 (2012) 102. [19] J.B. Malherbe, CRC Crit. Rev. Solid State Mater. Sci. 19 (1994) 129. [20] W.K. Burton, N. Cabrera, F.C. Frank, Philos. Trans. R. Soc. 243A (1931) 299. [21] G. Wulff, Z. Krist, Z. Kristallogr. 34 (1901) 449. [22] P.D. Ramesh, B. Vaidhyanathan, M. Ganguli, K.J. Rao, J. Mater. Res. 9 (1994) 3025. [23] G.D. Papasouliotis, S.V. Sotirchos, J. Mater. Res. 14 (1999) 3397. [24] H. Pedersen, S. Leone, A. Henry, V. Darakchieva, E. Janzén, Surf. Coat. Technol. 201 (22–23) (2007) 8931. [25] T.F. Ciszek, H. Wang, M.R. Page, R.E. Bauer, M.D. Landry, IEEE 21 (2002) 206. [26] T.H. Wang, T.F. Ciszek, J. Electrochem. Soc. 147 (2000) 1945. [27] T.T. Hlatshwayo, N.G. van der Berg, M. Msimanga, J.B. Malherbe, R.J. Kuhudzai, J. Nucl. Instr. Meth. Phys. Res. B, submitted for publication. [28] N.G. van der Berg, J.B. Malherbe, A.J. Botha, E. Friedland, Appl. Surf. Sci. 258 (15) (2012) 5561.
Please cite this article in press as: R.J. Kuhudzai et al., Near-surface recrystallization of the amorphous implanted layer of ion implanted 6H-SiC, Nucl. Instr. Meth. B (2014), http://dx.doi.org/10.1016/j.nimb.2014.02.072