The initial stages of carbon alloying into the Si(001) surface are studied by scanning tunneling microscopy (STM) and density functional theory. Carbon increases the surface roughness compared to the clean surface and induces a c͑4 3 4͒ reconstruction. To explain experimental observations, we propose a novel surface reconstruction model that involves pairing of Si dimers mediated by the presence of a complex of a C dimer and four nearest neighbor subsurface C atoms. The model is backed by total energy and thermal stability simulations. Its calculated surface charge density agrees well with the filled state STM images. [S0031-9007(98)08302-1]
Magnetoresistivity measurements on p-type Si/SiGe quantum wells reveal the coexistence of a metallic behavior and weak localization. Deep in the metallic regime, pronounced weak localization reduces the metallic behavior around zero magnetic field without destroying it. In the insulating phase, a positive magnetoresistivity emerges close to B=0, possibly related to spin-orbit interactions.
The photoluminescence emission of SiGe quantum dot arrays prepared by templated self-assembly, combining extreme-ultraviolet interference lithography and molecular beam epitaxy, were studied. The PL spectra obtained from areas with ordered dots show a pronounced SiGequantum-dot-related signal. The corresponding no-phonon and assisted transversal optical phonon recombinations are well resolved due to the narrow-size distribution of the fabricated quantum dot arrays. Additionally, the dependence of the photoluminescence emission on dot size and Ge concentration is discussed as well as effects of laser power excitation.
Deposition of submonolayer coverages of C on Si͑100͒ prior to Ge growth leads to the formation of Ge quantum dots below the critical thickness for Ge islanding on bare Si͑100͒. In situ scanning tunneling microscopy reveals a high density of irregularly shaped islands for Ge coverages from 2.5 to 4 ML. Island sizes are broadly distributed between 10 and 25 nm. Keeping the C coverage constant and increasing the Ge coverage from 2.5 to 4 ML, the islands increase in height but their density remains constant (ϳ10 11 cm Ϫ2). At a Ge coverage of 5.8 ML, formation of larger ͑105͒-faceted islands is observed. Their density is reduced by a factor of 4 compared to smaller Ge coverages. Transmission electron microscopy shows that the nonfaceted islands are preserved after Si capping.
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