The GaP surfaces were passivated withCH

3

CSNH

2

solution of certain concentration at 90℃ temperature.The effect of passivation for different treatment time on the surface structure

morphology and electronic features was investigated using scanning electron microscopy(SEM)and X-ray photoelectron spectroscopy(XPS).First

the treatment time of about 20min.was determined to obtain a uniform passivation film on the GaP surface.This means that the wet chemical reactions were completed in a certain interval of time when the GaP wafer was dipped in the CH

3

CSNH

2

solution.It is found that the oxide overlayer on the GaP surface has been removed basically.The chemical reaction between the Ga atoms and the S

2-

ions dissociated from theCH

3

CSNH

2

solution has taken place under the condition of certain temperature.The XPS measuremnet results indicate that the gallium sulfide and phosphor us sulfide have been formed on the surface during the passivation.After passivation the XPS peaks of Ga 3d and P2p are shifted to higher binding energy by about 0.1-0.5eV.0.2~0.4eV from those of the bulk GaP and their full widths at half maximum(FWHMs)are increased

respectively.The P 2p band has been resolved into two component bands by a curve fitting technique.The fitted band peaked at 129.2eV corresponds to free atom state of P

whereas the other fitted band peaked at 128.5eV corresponds to compound state of P.These chemical shift are consistent with electronegativity and binding energy of sulfur.The passivated surfaces were further sputtered by Ar

+

ion for 2min under the condition of voltage SKV

current density 100uA/cm

2

.It shows that the Ga 3d

P2p

S2p peaks are located at the binding energies of 18.5eV

129.0eV

158.1eV

respectively.Hence it reveals that a thin Soverlayer film has been formed on the GaP surface

which can prevent the oxidation from environment.It possesses a good chemical stability.The XPS measurements identify the presence of both Ga-S and P-S bonding.