PREGROWTH TREATMENT DEPENDENCE OF SURFACE-MORPHOLOGY FOR GAAS GROWN ON EXACTLY ORIENTED (111)A SUBSTRATES BY MOLECULAR-BEAM EPITAXY

We investigate the dependence of growth layer surface morphology on su rface treatment processes, i.e., etching, mounting, and loading wafers before molecular-beam epitaxial growth. The surface morphology of a G aAs growth layer on exactly oriented (111)A GaAs is found to be strong ly dependent on stoichiometry and roughness of the surface before grow th. Device-quality layers with a good surface morphology were obtained only on the exactly oriented (111)A GaAs wafers etched with NH4OH:H2O 2:H2O (2:1:96) etchant, loaded into a growth chamber with little resid ual As4, and mounted without In. It is very important to use the NH4OH etchant (2:1:96) with (111)A GaAs, because it maintains the surface s toichiometry and smoothness.