The N-for-As, P-for-As and Sb-for-As anion exchange reactions at GaAs surfaces, and the N-for-P anion exchange reaction at the Gap surface have been investigated with the aim at the formation of a thin high-gap surface layer for passivation of GaAs and GaP. Among the investigated anion exchange reactions, the P-for-As results in the formation of a ternary alloys GaPyAs1-y not effective for GaAs passivation. The Sb-for-As anion exchange does not occur and results in segregation of Sb at the GaAs surface. The Sb overlayer is effective in the chemical passivation of GaAs. The N-for-As anion exchange by a remote N-2-H-2 (a mixture of 97% N-2-3% H-2) radiofrequency plasma nitridation procedure forms a very thin (similar to5 Angstrom) GaN layer that is successful in the electronic and chemical passivation of GaAs(100) surfaces. The N-2-H-2 (a mixture of 97% N-2-3% H-2) nitridation has been found completely different from the pure N-2 nitridation which, in contrast, do not provide GaAs passivation, because the formation of Ga-N bonds accompanies with AsN and the segregation of elemental As at the GaN/GaAs interface. GaAs-GaN based Schottky structures have also been deposited and characterized by I-V measurements. A chemical and kinetic mechanism for the anion exchange reactions which takes into account also the competitive formation of PAs, AsN, and PN isoelectronic compounds is proposed. (C) 2004 Elsevier B.V. All rights reserved.