The diffusion and desorption of Ga atoms in MBE-grown AlGaAs layers and GaAs QWs on channeled substrate planar structures have been studied by scanning electron microscopy, photoluminescence and cathodoluminescence. The (m11)A side facets of ridges and grooves act as sources for additional Ga which increases the growth rate on the (100) sections of ridges and grooves, leading to lower Al compositions and thicker quantum wells on narrow stripes. The adatom flux is increased for growth temperatures above 700°C and an As4:(Ga,Al) flux ratio below 1. Growth interruption after the QW leads to a complete desorption of Ga at the (311)A facets, leaving an embedded (100) QW. © 1989.