The development of two-dimensional chemically assisted ion beam etching model of GaAs by Cl-2/Ar+ allowed the authors to analyze the role of some critical. parameters of etch process on the morphology of trench and mesa structures. In a fact, the simulation results show that the etch rate variation with substrate temperature T-s reveals three regimes: For T-s < 350 K, the etch rate of GaAs is mainly controlled by ion assisted etching component. For 3 50 < T-s < T-M where T-M corresponds to the maximum of etch rate, a high variation of etch rate is observed. In this range of temperature, the etch rate is controlled by the chemical component and mainly by the exponential rise of desorption coefficient of GaClx, lambda(3), with T-s. For T-s > T-M a fast decrease of the etch rate is observed because of the high decrease of the coverage rate of Cl, xi, on the gallium sites with the substrate temperature. On the other hand, the increase of the Cl-2 flow rate allows to improve the anisotropy and contributes to the elimination of both the microtrenching and the transfer of the facets from the mask into the substrate. (c) 2007 American Vacuum Society.