Using double crystal X-rays diffraction(DCXRD)and atomic force microscopy(AFM),the results of GexSi1-x grown UHV/CVD from Si2H6 and SiH4 are analyzed and compared.Adsorbates can migrate to the energy-favoring position due to the slow growth rate from SiH4.In this case,a Si buffer that isolates the effect of substrate on epilayer could not be grown,which results in a pit penetrating into epilayer and buffer.The FWHM is 0.055° in DCXRD from SiH4.The presence of diffraction fringes is an indication of an excellent crystalline quality,The roughness of the surface is improved if grown by Si2H6:however,the crystal quality of the Gex2Si1-x material became worse than that from SiH4 due to much larger growth rate from Si2H6.The content of Ge is obtained from DCXRD,which indicates the growth rate from Si2H6 is largest,then GeH4 and that from SiH4 is least.