Role of surface morphology for InAs quantum dot or dash formation on InGaAsP/InP (100)

We investigate the formation of self-assembled InAs quantum structures on lattice-matched InGaAsP on InP (100) substrates grown by chemical beam epitaxy. The surface morphology of the InGaAsP buffer layer plays a key role for the formation of InAs quantum dots (QDs) or dashes (QDashes). QDash formation is always accompanied by a rough buffer layer surface. Growth conditions such as higher growth temperature, larger As flux, and compressive buffer layer strain promote the formation of QDs. However, once, the buffer layer has a rough morphology, QDashes always form during InAs deposition. On the other hand, well-shaped and symmetric QDs are reproducibly formed on smooth InGaAsP buffer layers for the same InAs growth conditions. Hence, not the growth conditions during InAs deposition, but rather the surface morphology of the buffer layer determines the formation of QDs or QDashes, which both exhibit high optical quality.