The effects of fluorine ion bombardment on the channel transport properties of AlGaN/GaN heterostructures have been investigated. Ion bombardment of the heterostructure was carried out within a CF4 plasma in a reactive ion etching system at various self-bias voltages. Hall mobility and sheet electron concentration for the two-dimensional electron gas showed strong dependence on bombardment duration and postbombardment annealing. A systematic study of the behavior of implanted fluorine ions in the annealed heterostructure reveals diffusion followed by accumulation of the ions at the heterointerface. Implications of such behavior on the performance of high electron mobility transistors are briefly discussed. (C) 2007 American Vacuum Society.