Atomic scale study of intrinsic and Mn doped quantum dots in III-V semiconductors

In this thesis, a Cross Sectional Scanning Tunneling Microscope (X-STM) is used to investigate nanostructures in IIIV semiconductors and single Mn impurities in bulk GaAs. The atomic resolution which can be achieved with X-STM makes it possible to link structural properties of nanostructures to growth conditions and to properties obtained in other experiments. Furthermore, X-STM is very well suited to investigate the effect of a quantum dot on single Mn acceptors both in terms of potential confinement and in terms of strain. In recent years, quantum dots have emerged as essential components of new generation optical devices. The use of Sb has proven to be a way of tuning the emission wavelength of quantum dots. X-STM measurements have been performed on samples with InAs/GaAs and InAs/InP quantum dots where Sb has been used in different ways during capping to tune their emission wavelength. We have found that Sb can act as a strain reducing layer for the InAs/GaAs quantum dots if it is used in the capping layer in the form of GaAsSb which results in reduced quantum dot decomposition during capping. The same reduction of quantum dot decomposition has been achieved by soaking the quantum dots with Sb before capping. In this case the Sb has been found to act as a surfactant which limits the in plane mass transport of material from the quantum dots. Similar results have been obtained for InAs/InP (311B) quantum dots. Another subject that has been investigated with X-STM is the incorporation and the behavior of single Mn acceptors in and around InAs/GaAs quantum dots. Single Mn doped quantum dots are potential building blocks for future spintronic devices in which electric, magnetic and optical properties can be utilized. X-STM measurements have shown that segregation of Mn during growth makes it very difficult to incorporate Mn in InAs/GaAs quantum dots. Furthermore, Mn acceptors in and around the quantum dots have been investigated with Scanning Tunneling Spectroscopy (STS). For Mn outside the quantum dots, we have found that the wavefunction is strongly influenced by coupling between the quantum dot states and the Mn states. There is a much smaller influence of strain field of the quantum dot. For Mn atoms inside the quantum dot, the shape seems to be determined by the potential confinement.