ACCOMMODATION OF LATTICE MISMATCH AND THREADING OF DISLOCATIONS IN GASB FILMS GROWN AT DIFFERENT TEMPERATURES ON GAAS(001)

Transmission electron microscopy has been used to investigate the accommodation of lattice mismatch and the threading mechanism of dislocations in GaSb films deposited at 420, 470 and 520 degrees C by molecular beam epitaxy (MBE) on GaAs (001) substrate. The lattice mismatch was relieved by regular 90 degrees dislocations generated during island growth of GaSb films. At high temperature, however, the lattice mismatch was partly accommodated by 60 degrees dislocation arrays which induce a local tilt of GaSb film with respect to the substrate. Even in the best case of misfit accommodation by very regular 90 degrees dislocations, the density of threading dislocations reaches 1 x 10(10) cm(-2). The main source of threading dislocations is attributed to the coalescence of randomly distributed GaSb islands. In particular, at low temperature many 90 degrees dislocations thread directly to the film surface, which is explained by the difference of 90 degrees dislocation spacings in two coalesced islands.