Semiconductors doped with magnetically active atoms are expected to find application in spintronics. Si samples implanted with Mn⁺ (Si:Mn) or with V⁺ (Si:V) can order magnetically after processing at high temperature (HT) and also under enhanced hydrostatic pressure (HP). This work presents new results on structure-related properties of single crystalline Si implanted at 200 keV with V⁺ as well as that co-implanted additionally with Mn⁺ ions (Si:V, Mn), with dosages DV⁺ ≤ 5·10¹⁵ cm⁻² and DMn⁺ = 1·10¹⁵ cm⁻². The samples were processed for 1–5 h at HT ≤ 1270 K under HP ≤ 1.1 GPa. Secondary Ion Mass Spectrometry, Transmission Electron Microscopy, X-ray and related methods were applied for sample characterization. The HT- (HP) treatment affects, among others, solid phase epitaxial re-growth (SPER) of amorphous silicon created at implantation and distribution of implanted species

Bak-Misiuk, J.

Barcz, A.

Chow, L.

Misiuk, A.

Prujszczyk, M.

Romanowski, P.

Shalimov, A.

Surma, B.

Vanfleet, R.

Wnuk, A.

Наукова електронна бібліотека періодичних видань НАН України (Vernadsky National Library of Ukraine)

Физика и техника высоких давлений 2008, том 18, № 4105PACS: 61.72.Tt, 61.72.–y, 62.50.+p, 78.30.AmA. Misiuk1, A. Barcz1, L. Chow2, J. Bak-Misiuk3, P. Romanowski3,A. Shalimov4, A. Wnuk5, B. Surma5, R. Vanfleet6, M. Prujszczyk1PRESSURE-INDUCED STRUCTURAL TRANSFORMATIONSIN Si:V and Si:V, Mn1Institute of Electron TechnologyAl. Lotnikow 46, 02-668 Warsaw, PolandE -mail: misiuk@ite.waw.pl2Department of Physics, University of Central FloridaOrlando, FL 32816, USA3Institute of Physics, PAS02-668 Warsaw, Poland4Forschunszentrum Rossendorf-Dresden01328 Dresden, Germany5Institute of Electronic Materials Technology01-919 Warsaw, Poland6Department of Physics, Brigham Young UniversityProvo, UT 84602, USASemiconductors doped with magnetically active atoms are expected to find application inspintronics. Si samples implanted with Mn+ (Si:Mn) or with V+ (Si:V) can order mag-netically after processing at high temperature (HT) and also under enhanced hydrostaticpressure (HP). This work presents new results on structure-related properties of singlecrystalline Si implanted at 200 keV with V+ as well as that co-implanted additionally withMn+ ions (Si:V, Mn), with dosages DV+ ≤ 5·1015 cm–2 and DMn+ = 1·1015 cm–2. Thesamples were processed for 1–5 h at HT ≤ 1270 K under HP ≤ 1.1 GPa. Secondary IonMass Spectrometry, Transmission Electron Microscopy, X-ray and related methods wereapplied for sample characterization. The HT- (HP) treatment affects, among others, solidphase epitaxial re-growth (SPER) of amorphous silicon created at implantation and dis-tribution of implanted species.IntroductionMost investigations on semiconductors doped with magnetically active atoms,which are expected to be applied as diluted magnetic semiconductors (DMS), are stillФизика и техника высоких давлений 2008, том 18, № 4106focused on ferromagnetic Mn-doped III–V semiconductors, such as Ga1–xMnxAs,and on ZnO and similar oxides doped with transition metals (TM) [1,2].Recently, Si samples implanted with Mn+ (Si:Mn) [3] as well as with Cr+ or V+(Si:Cr and Si:V) have been also demonstrated to order magnetically after proc-essing at high temperature (HT) under enhanced hydrostatic pressure (HP) of inertgas ambient [4,5].The HT- (HP) treatment affects SPER of a-Si created at implantation. Specificlocal ordering near the implanted metal atoms in Si:TM materials (TM = V, Cr orMn) can be critical with respect to the formation of ferromagnetic ordering [6].Still, magnetic properties of the as-implanted as well as of processed Si:V, Si:Crand Si:Mn samples could be related in part to the so called quasi-ferromagnetismreported for Si implanted with non-magnetic species, such as He+ or Si+, andprocessed at relatively low temperatures [7].This work reports new results concerning structural and related properties of Si:V(implanted dose, DV+ ≤ 5·1015 cm–2) as well as of Si:V, Mn (DV+ = 5·1015 cm–2,DMn+ = 1·1015 cm–2), processed at up to 1270 K under HP up to 1.1 GPa.ExperimentalImplantation of 51V+ to a dose DV+ ≤ 5·1015 cm–2 into single crystalline (c-Si)Czochralski grown Cz–Si wafers with (001) orientation (to produce Si:V), some-times followed by 55Mn+ implantation (to produce Si:V, Mn), was performed atroom temperature at energy EV+,Mn+ = 200 keV. The projected range of implantedions, Rp, was about 170 nm.The Si:V and Si:V, Mn samples were processed for 1–5 h in Ar atmosphere atup to 1270 K under 105 Pa or HP = 1.1 GPa.The present results concern mostly Si:V prepared by V+ implantation with DV+ == 5·1015 cm–2 and Si:V, Mn prepared by V+ implantation with the same dose, thenfollowed by Mn+ implantation to a dose 1·1015 cm–2. If not otherwise stated, inwhat follows just such samples are labelled as Si:V and Si:V, Mn.The depth distribution of Mn was determined by Secondary Ions Mass Spec-trometry (SIMS, Cameca 6F instrument). X-Ray Reciprocal Space Mapping(XRRSM, MRD–PHILIPS diffractometer), Transmission Electron Microscopy(TEM) and photoluminescence (PL, at 10 K, excitation with Ar laser, λ = 488 nm)methods were applied to reveal structure of the samples. Magnetic properties of asimplanted Si:V were determined at 5 K using SQUID magnetometer.Results and discussionHeavy implantation of silicon with V+ produces strongly disordered areanear Rp. For the case of E = 200 keV and D = (1–2)·1015 cm–2, the total energyintroduced during implantation into Si is above the amorphization threshold.So in the case of DV+ ≥ 1015 cm–2, amorphization of Si takes place near Rpwith a creation of buried amorphous a-Si layer. Subsequent Mn+ implantationФизика и техника высоких давлений 2008, том 18, № 4107with DMn+ = 1·1015 cm–2 to produce Si:V, Mn, results in even more completeamorphization.Depth distributions of V and Mn in as-implanted Si:V, Mn are presented in Fig. 1.Depth distribution of V in Si:V prepared by implantation with DV+ = 1·1014 cm–2and DV+ = 1·1015 cm–2 is of the same character as that presented in Fig. 1.After implantation, the a-Si layer, enriched in V/Mn up to about 1 at.%, hasbeen formed in Si:V and Si:V, Mn at about 170 nm depth below the surface (Fig. 1).As seen in Fig. 2, magnetization observed for Si:V prepared by implantationwith DV+ in the 1·1012 cm–2–1·1015 cm–2 range, is dominated by the diamagne-tism of the silicon substrate. The Si:V (DV+ = 1·1015 cm–2) sample, processed at610 K, has been reported to order magnetically with magnetization slightly de-creasing with temperature increase, from 5 to 50 K [4].  Fig. 1. SIMS depth profiles of Mn and V in as-implanted Si:V, MnFig. 2. Magnetization M versus magnetic field for as-implanted Cz–Si:V (EV+ = 200keV): –□– – Si:V5 (DV+ = 1012 cm–2), –○– – Si:V6 (1013), –△– – Si:V7 (1014), –▽– –Si:V7 (1015). Measurements were made at 5 KAs revealed by TEM, the treatment of Si:V at 610 K results in a partial recov-ery of the initial crystallographic perfection (Fig. 3). In effect of processing at HT(HP), V and Mn atoms become to be distributed more uniformly through the a-Siarea, most probably because of enhanced, if compared to that in c-Si, diffusivityof Mn and V atoms within a-Si.At high temperatures, the a-Si layer is subjected to SPER, dependent on HT,processing time and on HP [4]. In Si:V and Si:V, Mn this results in a movementof the a–c interface toward the surface [8], detectable through either SIMS meas-urements (Figs. 4, 5) or cross-sectional TEM (compare Fig. 3).V atoms are excluded from the re-growth region, as the a-Si/c-Si interfacemoves toward the surface, because the solubility of V in crystalline Si is very low[9]. Through this process, a minimum in the V concentration profile was formedin Si:V at about 300 nm below the surface (Fig. 4). The same phenomenon is alsoФизика и техника высоких давлений 2008, том 18, № 4108    Fig. 3. High-resolution TEM image of Si:V (DV+ = 5·1015 cm–2) processed for 1 h at 610 Kunder 1.1 GPa. Width of re-growth region (left) equals to about 50 nmFig. 4. SIMS depth profiles of Mn and V in Si:V, Mn processed for 5 h at 1070 K under1.1 GPaobserved for Mn atoms, which are concentrated at the same positions as vana-dium. It is important to admit that, in the case of Si:Mn prepared by Mn+ implan-tation at 160 keV, D = 1·1016 cm–2, with substrate temperature, TSi ≤ 340 K, andprocessed for 1 h at 1070 K, most Mn atoms were shifted toward the Si surface[3]. This means that, in Si:V, Mn, Mn atoms are gettered at defects produced atSPER. This gettering is related to behavior of implanted vanadium.As mentioned, excess vanadium is accumulated at the a-c interface, and the Vconcentration reaches a point, at which excess V impurity cannot be pushed away.At higher temperatures (HT ≥ 900 K), the a-Si layer is converted into the partiallypolycrystalline state and VSi2 compound is formed [10]. Enthalpy of the VSi2formation equals 3.2 eV, so this silicide remains stable even at 1270 K and so,both in the case of Si:V and Si:V, Mn, it is located almost at the same depth, atabout 280 nm below the sample surface (Fig. 5).Fig. 5. SIMS depth profile of V in Si:Vprocessed for 5 h at 1270 K under 1.1 GPaФизика и техника высоких давлений 2008, том 18, № 4109The V concentration is peaking also at about 170 nm depth, near Rp (Figs. 4,5), so within the maximal V concentration induced by implantation itself. Thiseven more pronounced peak seems to be also related to a formation of VSi2. Thesimilar Mn concentration peak observed in Si:V, Mn processed at 1070 K or 1270 Kat this depth can be related to a formation of Mn4Si7 [11].Similarly as in the case of self-implanted silicon, Si:Si [12], processing of Si:Vor Si:V, Mn at 1270 K – 105 Pa/1.1 GPa does not result in a fully recovered crys-tallographic perfection of the implantation-damaged areas. This has been statedbasing on PL (Fig. 6) and XRRSM (Fig. 7) results. Processing of Si:V, Mn underHP results in an absence of the PL line at about 0.81 eV (Fig. 6,b), still clearlydetectable after processing under 105 Pa (Fig. 6,a). Usually this line is associatedwith the presence of dislocations in single-crystalline Si.а bFig. 6. PL spectra of Si:V, Mn processed for 5 h at 1270 K under 105 Pa (a) and 1.1 GPa (b)а bFig. 7. XRRSMs of Si:V processed for 5 h at 1270 K under 105 Pa (a) and 1.1 GPa (b)The favourable effect of HP at 1270 K on SPER is confirmed by X-ray map-ping. The intensity of diffusively scattered X-rays decreased in the case of Si:VФизика и техника высоких давлений 2008, том 18, № 4110processed at 1270 K under HP. The lattice parameters of c-Si, formed under 1.1GPa by SPER of a-Si, were distinctly more uniform (compare Fig. 7,a,b).After processing, the structure of Si:V and Si:V, Mn samples (these last withDV+/DMn+ = 5), is dependent first of all on the dose of implanted V+ and on tem-perature of processing. Enhanced pressure of Ar affects SPER and results in theimproved structure of re-crystallized a-Si, most probably due to the effect of HPon diffusivity of implantation-induced point and related defects [12].Local ordering near the implanted atoms in Si:TM materials (TM = V and/orMn) is critical for magnetic ordering. This ordering is also related to quasi-ferromagnetism, detected in silicon implanted with non-magnetic atoms [7,9].ConclusionsOur report presents the compositional and structural properties of single-crystal-line silicon implanted with medium dosage of vanadium (vanadium + manganese)ions and processed at up to 1270 K, also under enhanced pressure, up to 1.1 GPa.Understanding the mechanisms of SPER under HP and so of magnetic orderingin ion implanted Si-based materials, of the creation of specific crystalline mag-netically ordered phases and of the origin of quasi-ferromagnetism demands fur-ther research.One can hope that new Si–V and Si–V, Mn materials belonging to the DMSfamily will be developed.The authors thank Dr. W.K. Chu and Dr. Z.H. Zhang from the Department ofPhysics and Texas Centre for Superconductivity, University of Houston, Houston,TX 12345 for their help in preparation of the samples.1. H. Ono, Physica B376–377, 19 (2006).2. O.D. Jayakumar, I.K. Gopalakrishnan, S.K. Kulshrestha, Physica B381, 194 (2006).3. A. Misiuk, B. Surma, J. Bak-Misiuk, A. Barcz, W. Jung, W. Osinniy, A. Shalimov,Mater. Sci. Semicond. Process. 9, 270 (2006).4. A. Misiuk, L. Chow, A. Barcz, B. Surma, J. Bak-Misiuk, P. Romanowski, W. Osinniy,F. Salman, G. Chai, M. Prujszczyk, A. Trojan, in: High Purity Silicon 9, C.L. Claeys,R. Falster, M. Watanabe, P. Stallhofer (Eds.), ISBN 1-56677-504-3 (2006), p. 481–489.5. A. Misiuk, A. Barcz, L. Chow, B. Surma, J. Bak-Misiuk, M. Prujszczyk, Solid StatePhen. 131–133, 375 (2008).6. A. Wolska, K. Lawniczak-Jablonska, M. Klepka, M.S. Walczak, A. Misiuk, Phys. Rev.B75, 113201 (2007).7. T. Dubroca, J. Hack, R.E. Hummel, A. Angerhofer, Appl. Phys. Lett. 88, 182504(2006).8. P. Zhang, F. Stevie, R. Vanfleet, R. Needlakantan, M. Klimov, D. Zhou, L. Chow,J. Appl. Phys. 96, 1053 (2004).9. L. Chow, J.C. Gonzales-Pons, E. del Barco, R. Vanfleet, A. Misiuk, A. Barcz, E.S.Choi, G. Chai, in: Magnetic Materials, International Conference on Magnetic Materi-Физика и техника высоких давлений 2008, том 18, № 4111als (ICMM-2007), A. Ghoshray, B. Bandyopadhyay (Eds.), American Institute ofPhysics (2008), p. 248–251.10. S.P. Murarka, Silicides for VLSI Applications, Academic Press, New York (1983).11. J. Bak-Misiuk, E. Dynowska, P. Romanowski, A. Shalimov, A. Misiuk, S. Kret, P.Dluzewski, J. Domagala, W. Caliebe, J. Dabrowski, M. Prujszczyk, Solid State Phen.131–133, 327 (2008).12. A. Misiuk, B. Surma, J. Bak-Misiuk, Solid State Phen. 108–109, 351 (2005).

Pressure-induced structural transformations in Si:V and Si:V, Mn

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Pressure-induced structural transformations in Si:V and Si:V, Mn

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Наукова електронна бібліотека періодичних видань НАН України (Vernadsky National Library of Ukraine)