Bi: Perfect surfactant for Ge growth on Si?111??

1392 Appl. Phys. Lett., Vol. 74, No. 10, 8 March 1999 Schmidt et al. FIG. 1. XSW data obtained after **on** **Si****111**-) ) in **111** and 220 Bragg reflecti**on**, reflectivity , **on**s regarding basic theory and analysis of XSW can be found in the literature. 13 The output parameters of an XSW analysis are the coherent positi**on** c and coherent fracti**on** f c . These are defined as the phase and amplitude of the corresp**on**ding Fourier coefficient of the atomic distributi**on** functi**on** and **111** 1 **111** c 2 argA **111** N1 0 , 2 2N **111** f c A**111**sin 2 N sin 2 2. If **on**gly differ from that of **on** the surface and occupy sites at identical height with respect to the surface, depending **on** the surface roughness. C**on**clusively, **on**e expects a large **on** and a small **on**. Figure 1 displays **on** **Si****111**-)) at 485 °C. The **on** and fracti**on** are also shown. The results obtained in **111** Bragg reflecti**on** are in perfect agreement with the expected values **111** Eq. 1 yields c **111** 0.34 which is physically equivalent to c 1.34) and **111** f c 0.28 in perfect agreement with the experimental results **on** is expected to shift according to the number of **111** lattice plane spacing between **Si**: c 1 **111** (N) (N1)00. From measurements at low **on**al offset due to the **on**d length to be 00.020.01. 11 Thus, **111** 16 we obtain c 0.690.01, again perfectly reproducing the experimental results. **111** The coherent **on** f **on** of 15 BL **Si****111**-)) surface, i.e., **111** f **on** the surface. These islands are due to excess **on** the surface. FIG. 2. CTR data and best fit solid lines after depositi**on** of 11.5 BL and 35 BL **on** **Si****111**-)), Q1 corresp**on**ds to the **111** Bragg reflecti**on**. The measurements of crystal truncati**on** rods CTR is a sensitive tool **on** of film thicknesses and the roughness of interfaces and surfaces 15,16 and has even been successfully employed **on** of ultrathin buried **on**, **Si**Q R int **Si** 1e iQa **Si** F **on** reflect the sample geometry, i.e., scattering c**on**tributi**on**s from the **Si** substrate, the **Si****111** and **111** planes is found in the factor: F**Si**,**Si**,**Si**,**Si**(Q) denotes the atomic scattering factor of the corresp**on**ding element. N**on**integer values of N, we used the weighted average of Nn and Nn1; a**Si**,**Si** substrate and the **Si**-**on** functi**on**: Rxe 2 2 2 ax y, with qQ2/a. Figure 2 shows CTR measured after depositi**on** of 11.5

Appl. Phys. Lett., Vol. 74, No. 10, 8 March 1999 Schmidt et al. FIG. 3. STM image after depositi**on** of 10 BL **on** **Si****111**-)) at 485 °C. The inset shows a zoom of 400400 Å 2 . and 35 BL **on** **Si****111**-)) at 485 °C. The results **on** of **on**ly 11.5 BL **on** from pseudomorphically strained to relaxed film **on** of 10 BL **on** to single steps at the edges of neighboring terraces a periodic surface height modulati**on** is found in the image with an amplitude of 0.5 Å. This feature is even more clearly visible in the inset of Fig. 3 and indicated by superimposing the array of white dots. This frame represents an area of 400 400 Å2 of the same surface. The additi**on**al fine structure visible in this image is due to the )) surface structure, resolved here. The valleys of the periodic surface height modulati**on** white dots are aligned in 11¯0] like orientati**on**s and the distance between neighboring rows of minima indicated by white dots is approximately 105 Å. These observati**on**s indicate the presence of a periodic dislocati**on** net- work at the **Si**-**on** of this dislocati**on** network enables the relaxati**on** of the pseudomorphically strained **on** of the periodicity of the dislocati**on** network shows a laterally completely relaxed **on** spectroscopy AES was employed to determine the desorpti**on** temperature of **on** **Si****111**. At substrate temperatures exceeding 500 °C rapid **on** was observed, resulting in complete removal of **Si****111** surfaces the same effect is found at 550 °C. Hence a large **on** during **on** to successfully per**on**clusi**on**, **on** **Si****111**. A layer of **on** and alters the **on** of more than 10 BL **on** proceeds by the **on** of a highly periodic dislocati**on** network at the **Si**-**on** leads to the **on**s, the **on** Hoegen, F. K. LeGoues, M. Copel, M. C. Reuter, and R. M. Tromp, Phys. Rev. Lett. 67, 1130 1991. 3 J. Falta, M. Copel, F. K. LeGoues, and R. M. Tromp, Appl. Phys. Lett. 62, 2962 1993. 4 J. Falta, T. Schmidt, A. Hille, and G. Materlik, Phys. Rev. B 54, R17288 1996. 5 S. Maruno, S. Fujita, H. Watanabe, Y. Kusumi, and M. Ichikawa, Appl. Phys. Lett. 68, 2213 1996. 6 M. Horn v**on** Hoegen, A. Al Falou, H. Pietsch, B. H. Müller, and M. Henzler, Surf. Sci. 298, 291993. 7 G. Meyer, B. Voigtländer, and N. M. Amer, Surf. Sci. 274, L541 1992. 8 B. Voigtländer and A. Zinner, J. Vac. Sci. Technol. A 12, 1932 1994. 9 H. Minoda, S. Sakamoto, and K. Yagi, Surf. Sci. 372, 11997. 10 J. C. Woicik, G. E. Franklin, C. Liu, R. E. Martinez, I.-S. Hw**on**g, M. J. Bedzyk, J. R. Patel, and J. A. Golovchenko, Phys. Rev. B 50, 12246 1994. 11 T. Schmidt, J. Falta, and G. Materlik unpublished. 12 E. Vlieg, A. E. M. J. Fischer, J. F. van der Veen, B. N. Dev, and G. Materlik, Surf. Sci. 178, 361986. 13 J. Zegenhagen, G. Materlik, and W. Uelhoff, J. X-Ray Sci. Technol. 2, 214 1990. 14 The lateral atom density of a completely relaxed **on**, Phys. Rev. B 33, 3830 1986. 16 I. K. Robins**on**, R. T. Tung, and R. Feidenhans’l, Phys. Rev. B 38, 3632 1988. 17 J. Falta, D. Bahr, G. Materlik, B. H. Müller, and M. Horn v**on** Hoegen, Appl. Phys. Lett. 68, 1394 1996. 18 D. Bahr, J. Falta, G. Materlik, B. H. Müller, and M. Horn v**on** Hoegen, Physica B 221, 961996. 19 T. Schmidt, J. Falta, and G. Materlik unpublished. 1393