Structure of the llO -Plane

It is very rare that the structure of a diamond film is really perfect and free of defects. Usually, there are many structural defects and impurities arising from the conditions of preparation. In some cases, however, a deliberate contamination with selected materials or certain structural features are even aimed at to make use of associated properties (e.g., electronic or optical characteristics). 

Within the lattice as well numerous defects exist They include vacancies, dislocations, stacking disorders, and twinning. Normally, these defects are already generated during nucleation of the crystallites, which means that the density of defects in a diamond film can be influenced by scrupulously controlling the conditions of preparation. 

The grain boundaries of individual crystallites constitute another highly defective structural element. Owing to the saturation of the surface and other lattice imperfections the portion of sp -carbon is particularly high here. Actually the grain boundaries can rather be considered as an sp sp -hybrid structure. 

The afore-mentioned boron plays a central role in the doping of diamond. It is the only acceptor available to date that is easy to incorporate into the crystal and at the same time provides satisfactory properties. The boron gives rise to a low acceptor level 0.37 eV above the valence band maximum, resulting in a p-doped material with semiconducting or, at higher boron concentrations, quasimetallic 

The somewhat bigger phosphorous, on the other hand, is a donor that introduces a level at 0.5-0.6eV below the conductance band. Thus an n-semiconductor arises from this kind of doping. At first, the incorporation of phosphorous posed serious problems as it is poorly soluble in carbon. By now, however, an in situ process has been estabhshed that directly introduces the dopant into the lattice during CVD production of the diamond film. Still, owing to its larger diameter, phosphorous does not fit in well as compared to boron or nitrogen, which causes a slight lattice distortion and, consequently, an additional alteration of the diamond s properties. 

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