Wachstum und Charakterisierung von Ge-Nanostrukturen auf Si(113) durch Adsorbat-modifizierte Epitaxie

Abstract

In the work presented here Ge nano-structures on Si(113) substrates have been grown by adsorbate-mediated epitaxy at sample temperatures between 400 degrees C and 700 degrees C. The Ge nano-islands and nano-layers have been investigated regarding their atomic reconstruction, morphology, strain state, chemical composition and defect structure. Various in-situ and ex-situ experimental techniques have been used, as there are low-energy electron diffraction (LEED), low-energy electron microscopy (LEEM), x-ray photoemission electron microscopy (XPEEM), spot profile analysis low-energy electron diffraction (SPA-LEED), grazing incidence x-ray diffraction (GIXRD), scanning tunneling microscopy (STM), atomic force microscopy (AFM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM).On a clean Si(113) surface Ge preferentially nucleates at surface step edges and forms a wetting layer exhibiting a Ge-(2x2) surface reconstruction. With increasing growth temperature the Ge islands are elongated in the [33-2] direction. Simultaneously, the average island size increases with decreasing island density. From the Arrhenius-like behaviour of the island density, a Ge adatom diffusion barrier height of about 0.53 eV is deduced. At 600 degrees C the Si concentration of the islands amounts to about 41% and the residual lattice strain of the islands is found to about 23%.The adsorption of Gallium on a clean Si(113) substrate leads to the formation of well ordered surface facets in the [1-10] direction with a periodicity of about 43 nm in the [33-2] direction. From reciprocal space maps both facet angles are determined to be about 9.8 degrees with respect to the [113] direction. Thus the facet orientations are identified to be (112) and (115), showing (6x1) and (4x1) surface reconstructions, respectively. Ge deposition on the faceted Si(113) leads to a high density of ordered 3D Ge nano-islands beaded at the surface facets. The size of these islands is about 25 nm in the [33-2] direction and about 40 nm in the [1-10] direction. The islands are strongly relaxed and they contain no appreciable Si concentration.The Antimony surfactant-mediated epitaxy allows to grow smooth Ge films on Si(113) substrates. These Ge films exhibit surface roughnesses of only some Angström at a thickness of about 5 nm. The films are strongly relaxed with a residual Ge strain of about 31% (500 degrees C) to 37% (600 degrees C) and contain only a low Si concentration of about 4% Si (500 degrees C) to 10% Si (600 degrees C). The relaxation results from the formation of misfit dislocations at the Ge/Si(113) interface with a bimodal distance distribution of about 7 nm and 12.5 nm. Most likely, the misfit dislocations are 60 degrees dislocations with a Burgers vector of 1/2 * a_0 * <10-1>.