Reverse mass transport during capping of In0.5Ga0.5As/GaAs quantum dots

Abstract

The rates of indium mass transport between the wetting layer, the quantum dots, and the capping layer are derived from the indium distributions probed by cross-sectional scanning tunneling microscopy of the In 0:5 Ga 0:5 As=GaAs quantum dot system. During capping, a lateral backsegregation from the quantum dots toward the wetting layer is found, reversing the Stranski-Krastanov growth mode during quantum dot formation. This lateral back-segregation critically affects the resulting indium distribution in the wetting layer, the apparent segregation coefficients as well as the quantum dot shape. Furthermore, the strain effect on the segregation coefficient is quantified. V

Suppressing the Effect of the Wetting Layer through AlAs Capping in InAs/GaAs QD Structures for Solar Cells Applications

“…All segregation models to describe the decay profiles due to surface segregation in InGaAs QWs [25,27] cannot be applied for the case of WLs in InAs QDs systems. The reason is that the segregation profiles in the case of QWs are always much smaller, being necessary to add an extra amount of In to correctly fit the segregation tails of the WL profiles in QD systems [35]. This added amount of In can only come from the decomposition of the QDs, where it has been found that there is a relationship between the size of the QDs and the In content in the WL.…”

“…Second, the proposed surface migration of In toward the QDs that removes the WL, like what occurs during the QD formation, is opposite to the process observed during QD capping. In fact, it is broadly admitted that a massive transport of In atoms occur from the dots to the WL during capping due to a decomposition of QD [34,35].…”

Spatial structure of In0.25Ga0.75As/GaAs/GaP quantum dots on the atomic scale

“…Such a truncated pyramidal shape is typical for capped quantum dots and was already found for other material systems like InAs/GaAs. [10][11][12][13][14] The average quantum-dot base length is found to be 12 nm, and quantum-dot heights up to 10 ML are observed.…”

Increased InAs quantum dot size and density using bismuth as a surfactant

“…It should be noted that the dimensions of the buried QDs will be different from those of the uncapped QDs that are presented here; unlike the surface QDs, buried QD dimensions are influenced by surface segregation of the In atoms and alloying of the InAs in the QD with the surrounding GaAs. [27][28][29] Furthermore, the uncapped QDs could ripen even after growth has stopped, during the time it takes for the substrate to cool, unlike the buried QDs, which are immediately capped with GaAs. However, since the different sets of uncapped QDs were grown under nominally identical growth conditions, a comparison of AFM images can illuminate general trends in the QD distribution, under the influence of the Bi surfactant.…”