Morphology, Defect Spectrum, and Photoluminescence of Thin Si0.7Ge0.3 Layers: I. Structural and Morphological Characterization

Abstract

Morphology and atomic structure of thin ⟨100⟩-oriented nominally undoped and boron-doped layers, deposited by atmospheric-pressure chemical vapor deposition (APCVD) at on silicon wafers are studied in the first part of this paper. Nominal concentration of boron was for all doped samples. Local strain in the layers was estimated through X-ray diffraction data and depends on the layer thickness and presence of the dopant. Submicrometer scale morphology has been observed on the surface of the layers by atomic force microscopy. Anisotropic grain shape is clearly observed in all undoped samples, whereas round-shaped grains are found on boron-doped layers. Transverse sizes of the nonhomogeneities and surface roughness depend on the thickness and presence of dopant in the layers. For all studied samples, the average surface roughness is equal to or even higher than the nominal layer thickness, indicating that the layers are actually formed with spatially isolated submicrometer-scaled grains. Boron-doped samples have higher average surface roughness compared to nominally undoped layers with the same nominal thickness that is explained within the framework of kinetic approach of morphology formation [ J. Tersoff and F. K. LeGoues , Phys. Rev. Lett. , 72 , 3570 (1994) ] via significant lowering of potential barrier for surface roughening in the boron-doped layers.