A comparison of Si-doped (Al,Ga)As grown on on-axis GaAs(110) with As, and As-4 is reported, together with a low temperature photoluminescence study of cleaved edge overgrown quantum well structures. Approximately 90% of Si atoms are active as donors under both facet-free and facetted (110) growth conditions with As-2, whereas using As-4, the proportion is reduced to 40%-60%. It is shown that cleaving at the growth temperature (480 degrees C) rather than room temperature is essential if the cleaved interface is to be optically active.