Abstract
The growth of germanium at low temperature by ultrahigh vacuum chemical vapor deposition on Si(001) is investigated in real time by reflection high-energy electron diffraction. These observations are complementarily checked by atomic force microscopy, Rutherford backscattering spectrometry, transmission electron microscopy, and x-ray diffraction experiments. It can be seen that the currently observed Stranski-Krastanov-related two-dimensional (2D) to three-dimensional transition is avoided at
330
°
C
and that the major part of the relaxation process occurs during the deposition of the first two monolayers. Then, the measured in-plane lattice parameter evolves slowly and approaches that of bulk Ge after deposition of 50 monolayers. The corresponding relaxation equals 83%. The resulting surface is flat, with a rms roughness of
0.55
nm
. The relaxation is found to be mainly due to misfits dislocations located at the
Ge
∕
Si
interface. Regrowth experiments at
600
°
C
show that the low-temperature films are not stable for thicknesses below
27
nm
. In spite of the nearly complete relaxation observed for
7.5
nm
, a much higher thickness is needed to enable a continuous 2D growth at
600
°
C
. Finally, a
500
-
nm
-thick film, obtained with a low-temperature Ge buffer and with a Ge regrowth at high temperature, exhibits a channeling-to-random Rutherford backscattering spectrometry ratio
(
χ
min
)
of 4%, which indicates a good crystalline quality.