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In field-effect transistors (FETs), charge trapping in the gate oxide is known to cause low-frequency noise and threshold shifts. Here we calculate the effect of single trapped charges in a carbon nanotube FET, using the nonequilibrium Greens function method in a tight-binding approximation. We find that a single charge can shift and even rescale the entire transfer characteristic of the device. This can explain both the large “random telegraph signal” noise and the large variations between nominally identical devices. We examine the dependence on both the thickness and dielectric constant of the gate dielectric, suggesting routes to reduce electrical noise. [ABSTRACT FROM AUTHOR]

We present the results of first-principles study for the electronic structure and optical absorption spectrum of the alkaline-earth metal oxide BaO. The quasiparticle band structure is evaluated within the Hedin's GW approximation [Phys. Rev. 139, A796 (1965)]. Thereafter, the electronhole interaction is taken into consideration and the Bethe-Salpeter equation for the electron-hole two-particle Green function is solved. The calculated quasiparticle band gap of BaO is 4.1 eV, which is in good agreement with the experimental result. The calculated optical absorption spectrum of BaO is also in agreement with the experimental data. In particular, the calculated excitation energy for the lowest exciton peak in the optical absorption spectrum of BaO reproduces very well the corresponding experimental result. [ABSTRACT FROM AUTHOR]