We have investigated the influence of substrate type (GaAs vs. germanium) and of group-V precursor (AsH3 vs. TBAs) on the epitaxial quality of (In)(AI)GaAs layers. We evaluated these layers in terms of morphology, background contamination and doping characteristics. For final benchmarking of the individually optimised processes, we produced p-on-n single junction GaAs solar cells and compared their relative performance. This type of device is an excellent performance monitor for epitaxial layers as the fundamental operating mechanism is drift of minority carriers. The solar cell grown with TBAs on a germanium-substrate has a conversion efficiency under the AM1.5 solar spectrum, which compares favourably with the highest reported value for a p-on-n GaAs solar cell on Ge (Prog. Photovolt. Res. Appl. 8 (2000) 377). (C) 2002 Elsevier Science B.V. All rights reserved.