Relaxation of a strained quantum well at a cleaved surface

Scanning probe microscopy of a cleaved semiconductor surface provides a direct measurement of the elastic field of buried, strained structures such as quantum wells or dots, but allowance must be made for relaxation at the surface. We have calculated this relaxation analytically for the exposed edge of a strained quantum well within classical elastic theory for a linear, isotropic, homogeneous medium. The surface bulges outward if the quantum well has a larger natural lattice constant and the dilation changes sign near the surface, which may enhance recombination. Results are given for a well of constant composition or an arbitrary variation along the growth direction and compared with cross-sectional scanning tunneling microscopy of InGaAs quantum wells in GaAs. Consistent values for the composition of the wells were obtained from counting In atoms, X-ray diffraction, and photoluminescence. The lattice constant on the surface and the normal relaxation were compared with the calculation. Qualitative agreement is good but the theory gives only about 80% of the observed displacement. Some of this difference can be explained by the larger size of indium atoms compared with gallium, and the different surface reconstruction and buckling behavior of InAs and GaAs (110) surfaces upon cleavag

Interplay between tip-induced band bending and voltage-dependent surface corrugation on GaAs(110) surfaces

Atomically resolved, voltage-dependent scanning tunneling microscopy (STM) images of GaAs(110) are compared to the results of a one-dimensional model used to calculate the amount of tip-induced band bending for a tunneling junction between a metal and a semiconductor. The voltage-dependent changes in the morphology of the atomic lattice are caused by the four surface states of the GaAs(110) surface contributing in varying relative amounts to the total tunneling current. Tip-induced band bending determines which of these states contributes to the total tunneling current at a given bias voltage, and thus has a profound influence on the voltage-dependent STM-images. It is shown that certain voltage regions exist, for which none of the surface states present at the GaAs(110) surface can contribute to the tunneling current. For these voltages, tunneling occurs between the tip and bulk states of the sample through a surface depletion layer several nm wide. Nevertheless, we observe atomic, surface like corrugation for these circumstance

Composition profiling at the atomic scale in III-V nanostructures by cross-sectional STM

Using cross-sectional STM we have studied the local composition in III/V nanostructures such as GaAs/InGaAs quantum wells, InGaNAs/InP quantum wells and quantum dots, and InAs/GaAs self-assembled quantum dots. We are able to determine the local composition by either simply counting the constituent atoms, measuring the local lattice constant or measuring the relaxation of the cleaved surface due to the elastic field of the buried strained nanostructures

Direct composition proriling in III-V nanostructures by cross-sectional STM

Using cross-sectional STM we have studied the local compo-sition in III–V nanostructures such as GaAs/InGaAs quantum wells, InGaNAs/InP quantum wells and quantum dots, and InAs/GaAs self-assembled quantum dots. We are able to determine the local composition by either simply counting the constituent atoms, measuring the local lattice constant or measuring the relaxation of the cleaved surface due to the elastic field of the buried strained nanostructures