Wachstum und Charakterisierung von Ge-Nanostrukturen auf Si(113) durch Adsorbat-modifizierte Epitaxie
|Other Titles:||Growth and characterization of Ge nano-structures on Si(113) by adsorbate-mediated epitaxy||Authors:||Clausen, Torben||Supervisor:||Falta, Jens||1. Expert:||Falta, Jens||2. Expert:||Wollschläger, Joachim||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  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>.
|Keywords:||nano-structures, quantum dots, Ge, Si(113), surfactant, Ga, Sb, epitaxy||Issue Date:||11-Dec-2006||URN:||urn:nbn:de:gbv:46-diss000105300||Institution:||Universität Bremen||Faculty:||FB1 Physik/Elektrotechnik|
|Appears in Collections:||Dissertationen|
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