this report describes the progress in the fifth six-month period of a program to develop deposited dielectrics for gaas device applications. three applications of the dielectrics have been investigated on this program: (1) isolation of control electrodes, (2) passivation of the gaas surface, and (3) encapsulation of completed circuits. the dielectrics studied have included silicon oxynitride and mixtures of silicon nitride with germanium nitride during this reporting period the activities performed emphasized a parametric study of plasma-enhanced deposition (ped) of silicon nitride. the overall process involves cleaning of the sample, anodic oxidation of the gaas surface, stripping of the anodic oxide, an optional final wet-chemical surface preparation step, pre-deposition plasma-enhanced treatment of the walls of the deposition system or 'preburn' (which may involve a concurrent sample surface treatment), optional plasma etching of the sample surface, and deposition of the dielectric. we have analyzed the effects of variations in (1) oxide stripping and final wet-chemical preparation procedures, (2) preburn, (3) plasma etches, and (4) deposition procedures on the electrical properties of the gaas/silicon nitride interface. none of the procedures investigated yielded interfaces useful for fabrication of practical gaas insulated-gate transistors or integrated circuits. in addition, we have performed preliminary studies to determine appropriate parameters for the plasma-enhanced deposition of germanium nitride and mixtures of silicon nitride with germanium nitride. (author)