Thermodynamic stability of GaAs sulfur passivation

The solid-state part of the Ga-As-S-O quaternary equilibrium phase diagram has been established from thermodynamic calculations. It is shown that GaS forms a chemically stable interface with GaAs, while As2S3 tends to react with GaAs and the reaction results in elemental As segregation at the GaAs/native sulfide interface. A recently developed chemical vapor deposition of GaS provides, hence, an ideal chemical passivation of GaAs.