Formation of InAs/InGaAsP quantum-dashes on InP(001)

Self-assembled InAs/InGaAsP/InP(001) nanostructures are investigated using cross-sectional scanning tunneling microscopy. Atomically resolved images at both the (110) and the (1¯10) cleavage surface show InAs quantum dashes with almost binary composition and a truncated pyramidal shape. The quaternary matrix material directly above the InP substrate already shows a tendency toward decomposition, which gradually increases along the [001] growth direction, in particular above quantum dash layers. This decomposition, in turn, leads to an enhanced vertical correlation in the nucleation of further quantum dash layers.