Effect of the Growth Conditions on the Perfection of Thick AlxGa1 - xAs Epitaxial Films.

It is shown that by zone recrystallization in the presence of a temperature gradient it is easy to prevent the supercooling characteristic of other methods of liquid epitaxy. By zone recrystallization in the presence of a gravitational field it is possible to obtain films with dislocation numbers less than 10**4cm** minus **2. The dislocation density concentration in thick Al//xGa//1// minus //xAs films obtained by zone recrystallization in the presence of either a temperature gradient or a gravitational field, if x less than 0. 2, depends mainly on the growth rate and zone thickness and weakly correlates with the dislocation density in the substrate.