Surface Cusp Formation in Si Homoepitaxy

ABSTRACTWe report a study of the surface morphology and microstructure of Si epitaxial layers grown by MBE on (001) Si at temperatures at which epitaxy breakdown is observed. For films grown in the 400 - 450 °C temperature range the epitaxy breakdown is very sluggish and characterized by a columnar growth and the formation of surface cusps. We have used atomic force microscopy to study the shape, size and distribution of those surface cusps. Surface cusps are of square shape with sides predominantly oriented along <110> directions and are typically of 50 nm size and 5 nm depth. The cusps can be very regular in size and their surface density (typically of 109-1010 cm-2) is dependent on the growth temperature. The epitaxial Si in this temperature regime exhibits a residual strain of the order of -5 × 10−5 in the growth direction. Photoluminescence (PL) from cusped Si films is characterized by a broad PL at low energy possibly due to impurities incorporation at low growth temperatures. We have observed that Ge self-assembled dots can be grown on cusped surfaces. Large area AFM measurements reveal that surface cusps are “decorated” by clusters of large dome-like Ge dots, while a lower density of smaller dome and pyramid shape islands are seen away from the cusps.