Ge quantum dots on a large band gap semiconductor: the first growth stages on 4H–SiC(0 0 0 1)

The Ge growth on SiC(0 0 0 1) follows a Stranski–Krastanov mode for Si-rich <f>(3×3)</f> and <f>(√ of 3×√ of 3)R30°</f> reconstructed surfaces. For Ge deposit in particular temperature conditions, a new <f>(4×4)</f> superstructure takes place and the reflection high energy electron diffraction (RHEED) specular spot intensity presents one oscillation proving a wetting layer formation. An island nucleation is then ascertained by the oscillation vanishing and by the appearance of a <f>k⊥</f>-modulated RHEED pattern. On the other hand, on a <f>(6√ of 3×6√ of 3)R30°</f> C-rich surface, a direct Ge island nucleation is observed from the first growth stage. Indeed, for <f>1 ML</f> Ge, the RHEED diagram consists in spots and rings, and the atomic force microscopy analysis indicates a high density (<f>∼8×1010 cm-2</f>) of small islands (<f>∅∼30 nm</f>, <f>h∼3 nm</f>). The RHEED spot analysis shows a preferential epitaxial relationship with the substrate Ge(1 1 1)//SiC(0 0 0 1). The Ge–C bonding being energetically unfavourable, Ge tends to form islands immediately rather than wetting the graphite-terminated surface. The Ge growth mode on C-rich surface is thus of Volmer–Weber type. [Copyright &y& Elsevier]