N. Fujita

Diffusion of nitrogen in silicon

We use local density functional theory to investigate the diffusion of nitrogen dimers in silicon. We investigate several trajectories for the diffusing dimer finding an alternative one whose barrier is 2.69eV and in close agreement with experimental diffusion data carried out at high temperature. We suggest that recent reports of a low barrier of 1.45eV found from studies of dislocation unlocking are to be understood from the interaction of nitrogen dimers with interstitials or vacancies released by the dislocation.

Nitrogen related shallow thermal donors in silicon

In this letter, the authors investigate the electrical properties of nitrogen related shallow thermal donor (STD) candidates and their concentrations under different doping conditions by means of density functional theory. Experimentally, the existence of STDs containing one nitrogen atom and both even and odd numbers of oxygen atoms has been proposed. However, so far first principles studies have not presented a candidate for the latter. Here, they show that the NO defect possesses a shallow donor level. Adding one or two more oxygen atoms results in the donor level to become shallower. The fraction of shallow nitrogen related donors to N dimers increases in material with low concentration of nitrogen.

A Theoretical Study of Copper Contaminated Dislocations in Silicon

Recently, the interaction of copper with dislocations in p-type Si/SiGe/Si structures has been investigated experimentally and a new dislocation related DLTS-level at Ev +0.32 eV was detected after intentional contamination with copper. To determine the origin of this newly detected level, in this work we present first density functional calculations of substitutional copper at 90◦ and 30◦ partial dislocations in silicon. Defect–dislocation binding energies are determined and electrical gap levels are calculated and compared with the experimental data. As a result, the observed level at Ev + 0.32 eV is tentatively assigned to the single acceptor level of substitutional copper at the dislocation.

First-Principle Study on the Identification of Nitrogen-Oxygen Defect Domplexes in Silicon

Local density functional theory is used to investigate theinteraction of nitrogen with oxygen in Cz-Si. The binding energyof O with N2 and the positions of four local vibrational modesof the N2O ce ...

Theoretical Investigations of the Diffusion of Nitrogen-Pair Defects in Silicon

The formation of oxygen precipitates and microvoids as well as the movement and growth of dislocations are strongly affected by the presence of nitrogen. However, the diffusion mechanism of nitrogen is unclear with several conflicting reports in the literature. Here, ab initio density functional theory is used to investigate diffusion mechanisms of the nitrogen-pair defect in silicon. We find a new metastable nitrogen-pair defect structure, which is lower in energy than any structures previously considered as intermediate structures in the minimum energy paths. Thus, by including this new metastable structure, we suggest a more likely, alternative reaction path whose barrier is 2.69 eV. This is compared with experimental barriers.

Theoretical Aspects on the Formation of the Tri-interstitial Nitrogen Defect in Silicon

In this paper we investigate the formation of interstitial nitrogen trimers N3 which have been suggested as a fast-diffusing species in silicon recently. Out-diffusion profiles of nitro- gen show the involvement of at least two independent nitrogen related defects in the diffusion process depending on the nitrogen concentration at different depths of the sample. When the nitrogen concentration is small it is proposed that nitrogen trimers are formed in a two step process. We present the structural properties of such a defect using density functional theory and examine the energetics of the two proposed reactions leading to the formation of N3.