The structure of layers of GaSb grown on InAs
substrates has been investigated by means of high-resolution x-ray diffraction.
The samples were grown in Oxford using the metal–organic vapour phase epitaxy
facility to produce high-quality single-crystal layers with thicknesses between
60 and 3000 Å. The x-ray scattering experiments were performed with a Philips
MRD diffractometer in Oxford and with the XMaS facility at the ESRF. The
results show that the scattering for layers with a thickness below Tc' ~ 1250 Å
is different from the scattering for those with larger thicknesses. The
scattering from the thinner layers shows that the in-plane lattice constant of
the GaSb is very close to that of the InAs substrate and that the strain does
not vary through the film, while the measured diffuse scattering is in good
agreement with calculations of the scattering from isolated 60o dislocations.
The thicker layers show no diffuse scattering but single-Gaussian Bragg peaks
and the scattering is that expected from a mosaic layer with a large
concentration of 60o dislocations. Analysis of the peak parameters shows that
the average in-plane lattice constant is intermediate between those of bulk
GaSb and bulk InAs and that there is a changing strain through the film. The
critical thickness Tc for GaSb on InAs is calculated as about 204 Å. We argue
that between 204 and 1250 Å there are only a few dislocations, but thicker
films are relaxed by spontaneous creation of a dislocation network. The results
demonstrate the power of high-resolution x-ray scattering for studying
non-destructively the structures of thin films containing dislocations, and
show that there is a marked change in the scattering for layers above the
critical thicknesses Tc and Tc'.
Source:IOPscience
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