Monolayer and bilayer growth on Ge(111)

Journal of Crystal Growth 81(1987) 65—66 North-Holland, Amsterdam

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MONOLAYER AND BILAYER GROWTH ON Ge(111) J. AARTS, W.M. GERITS and P.K. LARSEN Philips Research Laboratories, P.O. Box 80.000, 5600 JA Eindhoven, The Netherlands

Intensity oscillations in Reflection High Energy Electron Diffraction (RHEED) patterns, have by now been seen on various semiconductor surfaces. Although monolayer growth has been observed for (001) surfaces of Si and Ge [1,2], bilayer growth might be expected for (111) surfaces in order to minimize the number of dangling bonds on the growing surface. In this communication we demonstrate that for Ge(111) RHEED measurements clearly point to single layer growth at low temperatures, going over into bilayer growth at higher temperatures. In fig. 1, intensity oscillations of the specular beam during growth of Ge(1 11) are given for three temperatures. The measurements were made with an electron energy of 12 kV, at an angle of incidence of 0.5°, in the [211] azimuth. The oscillations observed at 20°Cfirst display an asymmetric waveform; a relatively small intensity maximum and shallow minimum are followed by a large maximum and a deep minimum. The shallow minimum gradually disappears, leading, after a number of oscillations, to a waveform with a period which is doubled with respect to the initial oscillations. Upon increasing the temperature to 180°C two maxima are still visible, but above 200°Conly one doubled period is observed. The Ge flux was calibrated by measuring the wellestablished monolayer-type oscillations on a (001) surface, which established that the period at the beginning of growth at 20°Con the (111) surface also corresponds to a monolayer of atoms. At low temperatures we therefore find monolayer growth while at higher temperatures (> 200°C)the growth takes place in double layers; this may well be explained by the temperature dependence of the surface diffusion That surface diffusion can account for the observations was confirmed in an experiment in

which 1/4 layers were deposited at 20°C, after which the sample was annealed at 2500 C for 5 mm. After cooling again to 20°C, the intensity of the specular beam was measured and the cycle repeated. The intensity changes found in this way demonstrate perfect double layer oscillations: obviously the atoms deposited in a monolayer are rearranged into a (fraction of) a double layer upon annealing. Results similar to these have been found on Si(111) [3].

I T20°C

~

-~

T=18o0C

4

—

T~T=240Dc

0

2

4

time (mm) from 1.a RHEED Fig. Ge(111) surface, intensity (211) oscillations azimuth of for the three specular substrate beam temperatures. The angle of incidence is 0.5° and the electron energy 12 keV.

0022-0248/87,/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)

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J. Aarts eta!.

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Monolayer and bilayer growth on Ge(1I1)

References

[2] J. Aarts, W. Gerits and P.K. Larsen, AppI. Phys. Letters 48 (1986) 933.

[1] T. Sakamoto, N.J. Kawai, T. Nakagawa, K. Ohta and T. Kojima, AppI. Phys. Letters 47 (1985) 617.

[3] J. Aarts, W. Gerits and P.K. Larsen, unpublished, 1986.