In situ scanning tunneling microscopy of InAs quantum dots on GaAs( 0 0 1 ) during molecular beam epitaxial growth
Abstract Arrays of InAs quantum dots (QDs) have been studied using in situ scanning tunneling microscopy (STM) during their growth by molecular beam epitaxy on GaAs(0 0 1). At a substrate temperature of 400 °C under As 4 flux, both the QDs and the underlying step-terrace structure of the wetting layer (WL) are found to be static, with neither step-flow nor QD ripening observed. Higher resolution images of the mature WL show slightly different [1 1 0] periodicities to those observed in quenched STM studies.
Atomic Structure of Faceted Planes of InAs Quantum Dots on GaAs(001) Studied by Scanning Tunneling Microscopy
Three-dimensional island structure of the lattice mismatched InAs/GaAs(001) system was prepared by molecular beam epitaxy (MBE) and its images showing atomic structure on faceted planes were taken in situ by ultra-high vacuum scanning tunneling microscopy (UHV-STM). (113), (114) and (215) faceted planes are observed on 3D InAs islands. Based on high resolution STM images, atomic structural models of these faceted planes surfaces are proposed. The structure of the (113) planes is found to be different from those observed on nominal-flat InAs and GaAs (113) surfaces. The structural information will be useful for characterization of surface energy/stress of the islands, diffusion process on the surface, and interface properties. The result sheds a light on the formation mechanism and self-organization process of quantum dots.
MBE growth on vicinal GaAs(001) surfaces studied by scanning tunneling microscopy
We have imaged several different vicinal GaAs(001) surfaces, grown by molecular beam epitaxy (MBE), with the scanning tunneling microscope (STM). All the samples were grown under arsenic-rich conditions and had a (2 × 4)/c(2 × 8) surface reconstruction. The structure of the steps was found to be determined by the structure of the (2 × 4) unit cell. Atomic resolution images of the steps show that there is no step edge reconstruction and that the steps are built up from complete (2 × 4) unit cells. Vicinal GaAs(001) surfaces cut 2° towards (111)A and 2° towards (111)B and grown under step-flow growth conditions were compared. The A-type steps are relatively straight whereas the B-type steps are very ragged. Changing the angle of misorientation of the sample was not found to have a major effect on the step structure. A-type stepped surfaces grown under 2D nucleation growth conditions were found to be less regular than those grown under step-flow growth conditions. The results are discussed in terms of the growth mode of GaAs(001) and the prospects for growing sufficiently regular stepped surfaces for use in device structures such as quantum wires are considered.