ZnS has been of great interest for optoelectronic development as a potential light emitting material. Most Ⅱ-Ⅵ compounds have been grown on GaAs substrates. However silicon is the most important semiconductor for electronic industry because of its availability in large-area wafer with excellent quality and low cost

and silicon-based devices are so highly developed. In this work

the ZnS epilayers directly grown on (111) Si substrates have been successfully obtained at lower temperature (300～400℃) by low-pressure metalorganic chemical vapor deposition (LP MOCVD). The growth of ZnS on Si substrates has been investigated primarily by X-ray diffraction. The Si substrates were degreased in organic solutions and cleaned using 1HNO

3

:1H

2

SO

4

solution and 3HCl:1H

2

O

2

:1H

2

O solution

then etched with HF solution to remove the native oxide layer

then immediately flushed with N

2

gas and loaded into the reactor. No high temperature preheat treatment of the Si substrates was used to obtain ZnS in this work. The two-step growth method with changing Ⅱ/Ⅵ flow rate was used to obtain ZnS epilayers on Si substrates. The growth mechanism was discussed. A thin amorphous or an unstable crystal structure was deposited at a lower Ⅱ/Ⅵ flow rate for the first layer. The subsequent step was done at a higher and optimum growth Ⅱ/Ⅵ flow rate. The Zn and S atoms would rearrange themselves through a solid-phase epitaxial process in which the relatively lattice-matched regions may act as seeds for subsequent single-crystal growth. The X-ray diffraction spectra of ZnS epilayers show that the epilayer qualityincreases with decreasing the growth temperature. The crystallinity was further investigated in terms of the X-ray FWHM (full width at half maximum) of ZnS epilayers. The FWHM decreases with decreasing growth temperature. The lowest FWHM of ZnS epilayer grown at 300℃ on Si by the two-step method of changing Ⅱ/Ⅵ flow rate is 540 arc·sec.