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Transport properties of bulk semiconductors are strongly influenced by intrinsic and extrinsic defects. Introduction of extrinsic defects via p- and n-type doping is crucial to building semiconductor devices. An example of p-type doping is boron-implanted silicon. Here, boron ions impinge on and penetrate a silicon sample. The doping profile, that is, the concentration distribution of the boron ions as a function of implantation depth, should be as sharp as possible since sharp profiles allow the fabrication of small devices and fast computers.

Since ion implantation breaks bonds in the silicon sample, these broken bonds have to be ``repaired'' since they act as carrier traps otherwise. A standard way to repair the damage done, is to anneal the sample. A major problem that arises upon annealing, is that boron diffuses at least 100 times faster in boron-implanted silicon than in bulk silicon. This fast initial diffusion -- the so-called transient enhanced diffusion -- leads to broad doping profiles and limits the size reduction that can be obtained in submicron Si-based devices.

Interstitial and extended {311} defects in silicon are believed to be the reason for the transient enhanced diffusion in silicon. Our work is an ab-initio description of di-interstitial defects, that for the first time identifies the structure of the characteristic P6 di-interstitial defect. In the medium and long-term, we will understand formation mechanisms of extended defects in Si and their interaction with other impurities such as boron or carbon.

Paper on di-interstitial defects in silicon.

To cite this page:
Defects in Silicon
<http://www.physics.ohio-state.edu/~aulbur/sidefect/sidefect.html>