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We report first-principles molecular dynamics (MD) simulations that unveil the interface structures of amorphous mixed oxide (Al2O3)1−x(SiO2)x and GaN polar surfaces. The MD allows us to perform the melt and quench (simulated annealing) simulations to forge distinct amorphous samples. We find that the dangling bonds are completely absent at all the obtained interfaces. This annihilation is due to the diffusion of appropriate species, O for (Al2O3)1−x(SiO2)x/GaN(0001) and Al and Si for (Al2O3)1−x(SiO2)x/GaN(000 1 ¯), from the amorphous to the interface and the subsequent formation of strong bonds with both ionicity and covalency at the interface. This absence of the dangling bond indicates the superiority of (Al2O3)1−x(SiO2)x films to Al2O3 or SiO2 as a gate oxide for the GaN–metal–oxide–semiconductor field effect transistor. [ABSTRACT FROM AUTHOR]

A study on size-dependent subband structures of silicon nanowires (SiNWs) aligned along [100] direction, ranging from 0.77 to 2.69 nm in width, is performed by the first-principles calculation. Combined with a compact model adopting Landauer’s formula, on-currents of ballistic SiNW field effect transistors (FETs) are estimated and assessment of size-dependent performance is conducted. Size-dependent injection velocity strongly depends on Fermi level measured from the conduction band edge when carriers are degenerate. It is also supposed that the Fermi level has a peak value at a certain wire width. Despite variation in the size-dependent Fermi level and injection velocity, large SiNW FETs show large on-currents owing to their larger gate capacitances resulting from longer periphery. The on-current in the case of a multichannel SiNW FET reveals that size-dependent subband structures of nanowires have a serious effect on performance. As the results, although the normalized on-current decreases with decrease in wire width in the assessed multichannel FETs because both the saturation velocities and the normalized capacitances decrease, there can be a maximum in the normalized on-current in a larger wire owing to the maximized Fermi level and injection velocity. [ABSTRACT FROM AUTHOR]

Realization of an abrupt HfO2/Si interface without unintentional oxidation of the silicon substrate is a crucial task for the development of modern field-effect transistors. Here, we present a theoretical model which suggests that deposition of a dopant material on the HfO2 layer turns it into an oxygen absorber, suppressing the formation of SiOx at the interface. Tantalum is predicted as an effective dopant in HfO2 for this purpose. [ABSTRACT FROM AUTHOR]

Abstract: We have investigated theoretically the cause of the substantial threshold voltage (V th) shifts observed in Hf-related high-k gate stacks with p+poly-Si gates, by focusing on the ionic nature of HfO2. The oxygen vacancy (Vo) level in ionic HfO2 is located in a relatively higher part of the band gap. This high position of the Vo level results in a significant elevation of the Fermi level for p+poly-Si gates, if the p+poly-Si gate is in contact with the high-k HfO2. Vo formation in the HfO2 induces a subsequent electron transfer across the interface, causing a substantial V th shifts in p+poly-Si gate MISFETs. Moreover, our theory also systematically reproduces other recent experimental results. [Copyright &y& Elsevier]

The solubility of silicon in high-permittivity (high-κ) oxides significantly affects the performance of field-effect transistors. Our comparative study of silicon impurities in La2O3 and HfO2 reveals that the stability of silicon at substitutional sites strongly depends on its coordination number. When substituted for lanthanum, a silicon atom fits comfortably in La2O3, thanks to the formation of a SiO4 tetrahedral structure. In addition, the substitutional silicon acts as a donor impurity in La2O3, increasing oxygen content in the oxide. This contributes to absorbing silicon and oxygen from the interface region, leading to the formation of lanthanum silicate at the La2O3/silicon interface. [ABSTRACT FROM AUTHOR]

Charged defects in a gate insulating oxide significantly degrade electric properties of the field-effect transistors. We report on our analysis of the effects of Mg incorporation into HfO2 upon reduction in the positive charges associated with oxygen vacancies VO+2. Our comprehensive study using first-principles calculations revealed that a Mg atom substituted for Hf is stable in charge negative MgHf-2 and strongly binds with VO+2, neutralizing the defect. This contributes to the suppressing of the electron traps at the defect site, improving the reliability of Hf-based gate oxides. [ABSTRACT FROM AUTHOR]