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Adviser : Dr. Hon-Kuan Reporter : Jheng-Jie Syu

NDL. STUT.

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Adviser : Dr. Hon-Kuan Reporter : Jheng-Jie Syu

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  1. NDL STUT Low-temperature Al-induced crystallization of hydrogenatedamorphous Si1−xGex (0.2≤x≤1) thin filmsShanglong Peng, Xiaoyan Shen, Zeguo Tang, Deyan He *Department of Physics, Lanzhou University, Lanzhou 730000, ChinaReceived 14 August 2006; received in revised form 20 June 2007; accepted 17 July 2007Available online 25 July 2007 Adviser : Dr. Hon-Kuan Reporter : Jheng-Jie Syu Date : 11/11/2008

  2. NDL STUT Outline • Introduction • 2. Experimental details • 3. Results and discussions • 4. Conclusions

  3. NDL STUT 1.Introduction • Low-temperature formation of microcrystalline (mc-) or polycrystalline (poly-) Si1−xGex films on inexpensive substrates such as glass has been expected to realize advanced systems in displays and three-dimensional ultra large-scale integrated circuits. • Some low-temperature approaches such as solid phase crystallization and laser annealing have been carried out to crystallize amorphous (a-) Si1−xGex films. However,poly-Si1−xGex films with small grain (∼1 μm) were often obtained by these techniques[2.3]. [3]-(2003)-Laser-crystallized microcrystalline SiGe alloys for thin film solar cells [2]-(1999)-Solid-phase crystallization of amorphous SiGe films deposited by LPCVD on SiO2 and glass Fig. 4. TEM bright field images of LIC SiGe films deposited at 4500C and laser crystallized at (a) 250C (b) and 7400C. Fig. 3. Plain-view TEM images of the samples with (a) x = 0 and (b) x = 0:38 crystallized at 5500C on silicon dioxide.

  4. NDL STUT Outline • Introduction • 2. Experimental details • 3. Results and discussions • 4. Conclusions

  5. NDL STUT 2. Experimental details • Al films (200–300 nm thick) were firstly deposited by vacuum thermal evaporation on corning 7059 glass substrates. • Hydrogenated a-Si1−xGex films (1000–1200 nm thick) were then grown on the Al-coated glass substrates using a radio frequency (13.56 MHz) capacitively-coupled PECVD system. • The reaction gases were SiH4 (Ar dilution), Ar and GeH4 (H2 dilution) with a total flow in the range of 40–50 sccm. The substrate temperature was fixed at 250 °C. The base pressure and the deposition pressure were 3.0×10− 4 Pa and 150 Pa, respectively. The applied radio frequency power was 30 W. • The annealing temperatures were 300, 350, 400 and 450 °C,respectively, and the annealing time was kept constant for 3 h.

  6. NDL STUT Outline • Introduction • 2. Experimental details • 3. Results and discussions • 4. Conclusions

  7. NDL STUT 3. Results and discussions The peaks at 28°, 47° and 55° can be seen when the sample was annealed at a temperature of 350 °C ,which correspond to the diffraction from (111), (220), and (311) planes of the crystallized Si1−xGex films, respectively. • Further increase in the peak intensity and reduction in the full width at half maximum can be found with the increase of the annealing temperature, indicating an enhancement in the film crystallinity. 28° 47° 55° 25° Fig. 1. XRD patterns of hydrogenated a-Si1−xGex (x=0.2) film as-deposited and annealed at several temperatures for 3 h.

  8. NDL STUT 3. Results and discussions • We found that the three XRD peaks of (111), (220), and (311) in Fig. 2(a) are much stronger than those in Fig. 2(b), confirming that the Ge-rich sample is easier to be crystallizedat the same annealing temperature. • The small shift of the peak position was observed, which results from the increase of the lattice constantwith theincrease of the Ge fraction. Fig. 2. XRD patterns of hydrogenated a-Si1−xGex films with x=0.5 (a) and x=0.2 (b) annealed at 400 °C for 3 h.

  9. NDL STUT 3. Results and discussions • Increasing the annealing temperature to 400 °C, not only the Al layer disappeared, but also the structure of the SiGe film changed dramatically. We believe that Al atoms diffuse into the SiGe film and induce the film to crystallize by forming a mixture of Al and SiGe. • In the following phase the Si grains go on growing laterally onlyuntil they touch adjacent grains and form a continuous poly-Si film on the glass substrate. • It was reported that crystallization of a-SiGe needs much longer annealing time at low annealing temperature below 420 °C (the eutectic temperature of binary of Al–Ge). Fig. 3. Cross-section SEM images of hydrogenated a-Si1−xGex (x=0.2) film annealed at 300 °C (a) and 400 °C (b) for 3 h.

  10. NDL STUT 3. Results and discussions • The three Raman broad peaks located at 300, 400 and 500 cm− 1 can be clearly seen, which respectively correspond to the Ge–Ge, Si–Ge and Si–Si stretching mode s. • The Raman peaks of the Ge–Ge and Si–Ge modes shift to higher frequency (blue shift) with the increase of the Ge fraction, however, the peak of the Si–Si mode shifts to low frequency (red shift) in the Ge composition range under study. Fig. 4. Raman spectra of the as-deposited hydrogenated a-Si1−xGex films with x=1, 0.5, 0.4, 0.33 and 0.2.

  11. NDL STUT 3. Results and discussions • It was reported that the increase of the crystalline phase leads to high-frequency shifts of Ge–Ge and Si–Ge peaks. • Furthermore, it is known that the intensities of the peaks for crystallized Si1−xGex alloys depend on the composition x because the number of Si–Si, Si–Ge and Ge–Ge bonds scales like (1−x)2,2x(1−x) and x2 and therefore the relative intensities[17]. Fig. 5. Raman spectra of hydrogenated a-Si1−xGex films with x=0.5, 0.4, 0.33 and 0.2 annealed at 350 °C for 3 h.

  12. NDL STUT 3. Results and discussions • The Raman shift of the Si–Si,Si–Ge and Ge–Ge phonon modes for the unstrained Si1−xGex layer varies linearly with the Ge fraction according to the following relationships [19–21]: • The little deviations may be due to the presence of tensile strain and the interaction of lattice phonons caused by residual Al-doping (Fano interaction). Fig. 6. Experimental frequency shifts (squares and dashed lines) of the Si–Si (a), Si–Ge (b) and Ge–Ge (c) modes as a function of Ge fraction x for the hydrogenated a-Si1−xGex films annealed at 350 °C for 3 h. The corresponding calculated frequency shifts (lines) for fully unstrained SiGe films (Eqs. (1)–(3)) are presented in comparison with the experimental data.

  13. NDL STUT Outline • Introduction • 2. Experimental details • 3. Results and discussions • 4. Conclusions

  14. NDL STUT 4. Conclusions • It is shown that the crystallization of hydrogenated a-Si1−xGex films begins at the Al/a-Si1−xGex interface and the Al-induced layer exchange significantly promotes the crystallization of the films. • The Ge–Ge and Si–Ge peaks shift to a higher frequency with the increase of the Ge fraction. • With the increase of the Ge fraction and annealing temperature,there is an enhancement in film crystallinity and grain size.

  15. NDL STUT references [1] T. Aoki, H. Kanno, A. Kenio, T. Sadoh, M. Miyao, Thin Solid Films 508(2006) 44. [2] J. Olivares, A. Rodriguez, J. Sangrador, T. Rodriguez, C. Ballesteros, A.Kling, Thin Solid Films 337 (1999) 51. [3] C. Eisele, M. Berger, M. Nerding, H.P. Strunk, C.E. Nebel, M. Stutzmann,Thin Solid Films 427 (2003) 176. [4] M. Miyao, T. Sadoh, S.Yamaguchi, S.K. Park, Tech. Rep. IEICE 101 (2001) 1. [5] M. Gjukic, M. Buschbeck, R. Lechner,M. Stutzmann, Appl. Phys. Lett. 85(2004) 2134. [6] G. Radnoczi, A. Robertsson, H.T.G. Hentzell, S.F. Gong, M.A. Hasan,J. Appl. Phys. 69 (1991) 6394. [7] I. Chambouleyron, F. Fajardo, A.R. Zanatta, Appl. Phys. Lett. 79 (2001)3233. [8] T.J. Konno, R. Sinclair, Philos. Mag., B 66 (1992) 749. [9] M.S. Ashtikar, G.L. Sharma, J. Appl. Phys. 78 (1995) 913. [10] L. Hultman, A. Robertsson, H.T.G. Hentzell, I. Engstrom, P.A. Psaras,J. Appl. Phys. 62 (1987) 3647. [11] D. Dimova-Malinovska, O. Angelov, M. Sendova-Vassileva, M. Kamenova, J.C. Pivin, Thin Solid Films 451 (2004) 303.

  16. NDL STUT references [12] R. Lechner, M. Buschbeck, M. Gjukic, M. Stutzmann, Phys. Status Solidi,C 1 (2004) 1131. [13] E.V. Jelenkovic, K.Y. Tong, Z. Sun, C.L. Mak, W.Y. Cheung, J. Vac. Sci.Technol., A, Vac. Surf. Films 15 (1997) 2836. [14] W.K. Choi, L.K. The, L.K. Bera, W.K. Chim, A.T.S. Wee, Y.X. Jie,J. Appl. Phys. 91 (2002) 444. [15] R.J. Jaccodin, J. Electrochem. Soc. 110 (1963) 524. [16] S. Gall, M. Muske, I. Sieber, O. Nast, W. Fuhs, J. Non-Cryst. Solids 299(2002) 741. [17] M.A. Renucci, J.B. Renucci, M. Cardona, in: M. Balkanski (Ed.),Proceedings of the Second International Conference on Light Scattering inSolids, Paris, France, July 19–23, Flammarion, Paris, 1971, p. 326. [18] M.I. Alonso, K. Winer, Phys. Rev., B 39 (1989) 10056. [19] W.J. Brya, Solid State Commun. 12 (1973) 253. [20] J.C. Tsang, P.M. Mooney, F. Dacol, J.O. Chu, J. Appl. Phys. 75 (1994) 8098. [21] A. Perez-Rodrigue, A. Cornet, J.R. Morante, Microelectron. Eng. 40(1998) 223. [22] N. Nakano, L. Marville, R. Reif, J. Appl. Phys. 72 (1992) 3641.

  17. NDL STUT Thanks for your attention.

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