A study of the nitridation process on GaAs (001) surface by rf-N plasma irradiation

The nitridation process of a GaAs (001) surface caused by N-radical irradiation is studied. In the nucleation stage, the adsorption of N atoms is observed by scanning tunneling microscopy. Hexagonal GaN, whose [I 1201 axis aligns parallel to the [ 1 lo] of GaAs substrates, is formed by excess Ga atoms generated by a higher As .desorption rate. When nitridation proceeds toward the subsurface region due to the replacement of As atoms with N atoms, cubic GaN is formed. The stoichiometries of the surface and of the interface between the nitride layers and substrate play an important role in controlling the crystal structure of nitride layers. However, comparing with the GaN growth experiments, our results appear to be contradictory in the dependence on the stoichiometries. It will result in the difference of the mechanism between the nitridation and the growth.