We have produced epitaxial Si1−x−yGexCy/Si heterostructures by rapid thermal chemical vapor deposition using methylsilane SiCH6). These layers were grown in the SiH4/GeH4/SiCH6/H2 system between 550 and 600 °C at 1.5 Torr. Suitable process conditions were found that allow very efficient substitutional carbon incorporation. No carbon cross contamination was observed. Crystal quality, chemical composition, and lattice strain were deduced from Nomarski microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, secondary ion mass spectrometry, and x-ray diffraction. Defect-free alloy layers with compositions of up to 20 at.% Ge and 2.2 at. % C were produced. The lattice parameter was tailored so that the strain in these layers gradually moved from compressive to tensile. A tensile strain of up to 0.35% was achieved.
Intrinsic zinc oxide (i-ZnO) and aluminium-doped ZnO (ZnO:Al) are components of high-efficiency copper indium gallium diselenide solar cells. This paper examines both of these materials grown by two different techniques, namely radio frequency sputtering and electrodeposition (ED) for comparison and a better understanding. X-ray diffraction showed all materials to be polycrystalline and hexagonal (wurtzite) ZnO. Scanning electron microscopy indicated crystallites with different orientations for ED materials compared to agglomerated nanocrystallites of the sputtered layers. The band-gap energy was determined to be in the range 3.27-3.45 eV. The transmission was 85% for both ED materials and 95% for the sputtered layers. Glass/FTO/i-ZnO/Al structures were rectifying, and glass/FTO/ZnO:Al/Al contacts were ohmic for both ZnO:Al layers. Addition of Al decreases the bulk resistivity for both i-ZnO layers by 1-2 orders of magnitude. The photovoltage response to pulsed illumination showed a slow relaxation hysteresis, and all materials showed n-type electrical conduction.
High mobility electron gases and modulationdoped field effect transistors fabricated in Si/Si1−x Ge x by rapid thermal chemical vapor deposition Formation of βSiC at the interface between an epitaxial Si layer grown by rapid thermal chemical vapor deposition and a Si substrate Chemical vapor deposition has been applied to the fabrication of a relaxed SiGe buffer on (100) Si substrates. Our structures consist of a O%-x% graded layer and a uniform Si 1 -",Ge x capping layer, with x between 32% and 52%. First, the variation of the threading dislocation density with grading rate has been determined. Our results clearly show an abrupt transition between two domains: steep gradings correspond to a high dislocation density, and smooth gradings to low dislocation densities. Second, the surface morphology has been studied at different steps of the buffer fabrication. In addition to the classical (110) crosshatch morphology, we report for the first time (1OO)-oriented undulations. This new morphology, only found on steep gradings, is attributed to a Stranski-Krastanov growth mode caused hy large surface strains. Finally, we propose a new picture of the role of the grading: a steep grading, with a large surface strain, induces very undulated growths; in this case, small dislocation loops and a high density of threading dislocation are generated. Our calculations allow us to derive a simple criterion: grading rates lower than 137% Gel j-Lm will guarantee a relaxation of the low mismatched type. Following this, very low threading dislocation densities (l0 3 cm -2) were indeed achieved.
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