Faculty of Engineering and Natural Sciences
Imaging of Quantum Dots and Dopant Atoms by Cross-sectional Scanning Tunneling Microscopy (X-STM)
C. Çelebi, Sabancı University
Self-assembled semiconductor quantum dots are interesting nano-objects from fundamental and technological points of view because they form nearly ideal 0D systems where the quantum mechanical effects become extremely important. Epitaxially grown InAs quantum dots are employed successfully, for example, in single electron transistors, mid-infrared lasers and detectors and single-photon sources. For such device applications, in order to prevent unwanted effects occurring at the surface, the quantum dots are necessarily capped after they are grown. However, the use of capping materials such as InP, GaAs and InGaAs with different lattice mismatch values strongly affects the dot parameters at the atomic level and hence change dramatically the spatial confinement of the charge carriers.
Another interesting aspect is to investigate the behavior of dopant atoms including the interaction of their bound charge with the surrounding semiconducting host crystal. The dopants are essential components in semiconductors not only because they provide extrinsic charges or magnetic moments, but also they offer a unique potential to be used as the functioning parts of nanoscale or quantum information devices. Prior to utilizing single dopants in such novel devices, their electronic and magnetic structures have to be unraveled in detail.
A real breakthrough in understanding the atomic scale properties of quantum dots and single dopants embedded in semiconductors can be achieved by Scanning Tunneling Microscopy (STM). Especially, the Cross-sectional STM (X-STM) technique gives direct access to the nanostructures and to the dopant atoms near the cleaved facet of the sample structures and can therefore enables one to image them with atomic resolution. By means of X-STM measurements, the compositional profile and the interface morphology of quantum dots and the local electron or hole distribution around dopant atoms can be studied with ever increasing precision. In my presentation, I will give an overview on X-STM analysis of capped InAs quantum dots and will discuss particularly the spatial mapping of single donor (e.g. Si in GaAs) and single acceptor (e.g. Mn in GaAs) wave-functions near various semiconductor/vacuum interfaces.
Cem Çelebi, VITA-Cem Çelebi completed his BSc. degree from Physics Engineering at Hacettepe University in 2000. After completing the military service in 2002, he obtained his MSc. in 2004 from Nanophysics program at University of Antwerp in Belgium. He received his PhD. in 2009 from Eindhoven University of Technology in Netherlands. His main research interests are STM studies of nanostructures, magnetic impurities in semiconductors, the physics governing the electronic and magnetic properties of epitaxially grown low dimensional systems including quantum dots, quantum wires and quantum wells.
 C. Çelebi et al. Phys. Rev. B, 77, 075328, (2008)
 C. Çelebi et al. Appl. Phys. Lett., 89, 02311, (2006)
July 16, 2009, 13:40, FENS G035