温度对Si衬底上低压MOCVD外延生长ZnS薄膜质量的影响

用低压MOCVD系统在(111)Si衬底上,用两步生长方法(改变/流量比)在300～400℃时外延生长了ZnS单晶薄膜。随着衬底温度的降低,ZnS薄膜结晶质量提高,并在300℃生长时获得结晶完整性较好的(111)ZnS单晶薄膜。文中讨论了衬底温度对薄膜质量的影响。

Effect of Substrate Temperature on the Epilayer Quality of ZnS Grown on the Si Substrate by LP-MOCVD

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 1HNO₃:1H₂SO₄ solution and 3HCl:1H₂O₂:1H₂O solution, then etched with HF solution to remove the native oxide layer, then immediately flushed with N₂ 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.