Abstract
Monoatomic growth steps on vicinal (100) faces of gallium arsenide, grown epitaxially from gallium solution close to thermal equilibrium, are normally straight, equidistant and usually nucleated at dislocation emergence points. Beyond a critical temperature (T c = 765°C) for epitaxy termination, the steps display a sudden onset of roughening and bunching which suggest interpretation in terms of a roughening phase transition. No such roughening is found for alloys of GaAs with AlAs up to 800°C.