Influence of the Si cap layer on the SiGe islands morphology

Transmission electron microscopy (TEM), atomic force microscopy (AFM), and EDX methods were used to study morphology and chemical composition of SiGe/Si(001) islands grown at 700 degrees C and covered at 550 degrees C and 700 degrees C by Si layers of different thickness. The samples were grown in ultra high vacuum chemical vapor deposition process (UHVCVD) controlled with in situ reflection of high-energy electron diffraction (RHEED). The islands transformed from initial pyramid and dome shapes to lens shape for 1.4 nm and 3.7 nm cap layer thickness at 550 degrees C and 700 degrees C, respectively. An increase of lateral to vertical ratio was observed during the transformation. For the higher depositing temperature the ratio was bigger and was increasing continuously with cap layer thickness. Also, with increasing Si cap layer thickness, the Ge concentration was decreasing, which was more observable for higher capping temperature.