Argon gas cluster ion beams (GCIBs) are now routinely employed for depth profiling of soft organic materials to preserve the structure and reduce ion beam damage due to the low average energy/atom (E/n). The benefits of using GCIBs for depth profiling of inorganic materials are less clear due to issues of preferential sputtering effects and new artefacts being introduced. In this work, GCIBs were employed to depth profile through GaAs and InP at varying incident energies and cluster sizes between 75 and 1000 Ar atoms with and without sample rotation. As a result, the surface topography and chemical composition of ion beam-induced GaAs and InP etch craters were examined to add meaningful interpretations to the XPS depth profile data. Additionally, the effects monatomic Ar⁺ beam at varying incident energies between 0.5 and 3.0 keV were examined and compared to GCIB.  Preferential sputtering of As and P were observed in the XPS depth profiles of GaAs and InP respectively for all GCIB conditions. However, for GaAs, the correct GaAs_1.00 stoichiometry could be obtained through employing a 500 eV monatomic Ar⁺ ion beam at 60° incident angle. With 8 keV GCIBs, a higher average E/n and sample rotation gave the least preferential sputtering and a stoichiometry of GaAs_0.91 was obtained using an 8 keV Ar₇₅⁺ cluster beam. For InP, varying the incident energy of monatomic Ar⁺ ion and E/n for each GCIB made little difference with P preferential sputtering occurring for all energies,

GCIB bombardment of GaAs generated Ga rich ripple morphologies and a lower average E/n yielded nanoparticles in between ripple morphologies. On the other hand, nanocone morphology were developed with GCIB bombardment of InP. Sample rotation led to the development of GaAs nano mounds and InP nano-islands.

The GaAs and InP stoichiometries and morphologies observed for different ion beam conditions are discussed in light of existing theories for monatomic Ar⁺ bombardment and expanded upon for GCIB bombardment. Mechanistic models for GaAs and InP have been developed to explain the formation of the GaAs nanoparticles at low E/n GCIB and InP nanodots formed with sample rotation. Molecular dynamics modelling was performed to compare with the experimental data and provide support for proposed mechanisms.