The electronic properties of two-dimensional honeycomb structures of molybdenum disulfide (MoS 2 ) subjected to biaxial strain have been investigated using first-principles calculations based on density functional theory. On applying compressive or tensile bi-axial strain on bi-layer and mono-layer MoS 2 , the electronic properties are predicted to change from semiconducting to metallic. These changes present very interesting possibilities for engineering the electronic properties of two-dimensional structures of MoS 2 .

Silicon dominates the electronics industry, but its poor optical properties mean that III-V compound semiconductors are preferred for photonics applications. Photoluminescence at visible wavelengths was observed from porous Si at room temperature in 1990, but the origin of these photons -highly-localized defect states or quantum confinement effects? -has been the subject of intense debate ever since. Since then attention has shifted from porous Si to Si nanocrystals, but the same fundamental question about the origin of the photoluminescence has remained. Here we show, based on measurements in high magnetic fields, that defects are the dominant source of light from Si nanocrystals. Moreover, we show that it is possible to control the origin of the photoluminescence in a single sample: passivation with hydrogen removes the defects, resulting in photoluminescence from quantum-confined states, but subsequent UV illumination reintroduces the defects, making them the origin of the light again.

The electronic properties of hydrogenated silicene and germanene, so called silicane and germanane, respectively, are investigated using first-principles calculations based on density functional theory. Two different atomic configurations are found to be stable and energetically degenerate. Upon the adsorption of hydrogen, an energy gap opens in silicene and germanene. Their energy gaps are next computed using the HSE hybrid functional as well as the G0W0 many-body perturbation method. These materials are found to be wide band-gap semiconductors, the type of gap in silicane (direct or indirect) depending on its atomic configuration. Germanane is predicted to be a direct-gap material, independent of its atomic configuration, with an average energy gap of about 3.2 eV, this material thus being potentially interesting for optoelectronic applications in the blue/violet spectral range.

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Germanium possesses higher electron and hole mobilities than silicon. There is a big leap, however, between these basic material parameters and implementation for high-performance microelectronics. Here we discuss some of the major issues for Ge metal oxide semiconductor field effect transistors ͑MOSFETs͒. Substrate options are overviewed. A dislocation reduction anneal Ͼ800°C decreases threading dislocation densities for Ge-on-Si wafers 10-fold to 10 7 cm −2 ; however, only a 2 times reduction in junction leakage is observed and no benefit is seen in on-state current. Ge wet etch rates are reported in a variety of acidic, basic, oxidizing, and organic solutions, and modifications of the RCA clean suitable for Ge are discussed. Thin, strained epi-Si is examined as a passivation of the Ge/gate dielectric interface, with an optimized thickness found at ϳ6 monolayers. Dopant species are overviewed. P and As halos are compared, with better short channel control observed for As. Area leakage currents are presented for pϩ/n diodes, with the n-doping level varied over the range relevant for pMOS. Germanide options are discussed, with NiGe showing the most promise. A defect mode for NiGe is reported, along with a fix involving two anneal steps. Finally, the benefit of an end-of-process H 2 anneal for device performance is shown.