The growth of III-V bismuthides is complicated by the low incorporation efficiency of Bi in GaAs, leading either to the formation of metallic Bi droplets or low layer composition fractions. Typically growth is performed between 280 and 350 degrees C and at near stoichiometric Ga:As fluxes in order to encourage Bi incorporation. However most work reported to date also utilises As-2 as the As overpressure constituent. It is found in this work that growth with As-4 allows high Bi composition films with the standard 1:20 Ga:As-4 beam equivalent pressure ratio (BEPR) utilised for higher temperature buffer layer growth. The Bi fraction versus Bi:As-4 BEPR is found to be initially linear, until a maximum value is obtained for a given temperature after which the continued oversupply of Bi results in the formation of droplets. (C) 2011 Elsevier B.V. All rights reserved.