Short-period (Si14/Ge1)N superlattice buffers for growth of Si0.75Ge0.25 alloy layers

Short-period (Si-14/Ge-1)(N) superlattices (SSLs) are used as buffer layers for the growth of 2000 and 5000 Angstrom Si0.75Ge0.25 alloy layers on Si(001) substrate. The grown layers have been characterized by X-ray diffraction (XRD), atomic force microscopy (AFM) and cross-sectional transmission electron microscopy (XTEM). From XTEM images, it is observed that the alloy layers are dislocation-free and dislocations are found in SSL layers and inside the substrate regions. A marked reduction in surface roughness is observed, when SSLs are used as buffer layers. The 2000 Angstrom alloy with 300degreesC grown (Si-14/Ge-1)(20) SSL buffer layer showed the smallest roughness (similar to10Angstrom). This sample also showed the lowest residual strain of about -0.09%. The residual strain of the upper alloy layers decreases with decreasing growth temperature of the buffer layers. A slight increase in roughness with decreasing growth temperature is seen for the samples of 5000 Angstrom alloy with (Si-14/Ge-1)(20) buffer layers.