Electron Density Distribution of Wurtzite-Type Gallium Nitride by Maximum Entropy Method

The electron density distribution of wurtzite-type gallium nitride (-GaN) was obtained by the Maximum Entropy Method (MEM) using the Synchrotron Radiation powder data. Contribution of the very minor zinc blende-type phase (z-GaN) to the observed powder data was eliminated by the modified Rietveld method. In the obtained MEM electron density distribution map, there are two kinds of Ga-N covalent bonds. The electron density at the saddle point of Ga-N bond parallel to [001] axis is 0.5 [e/Angstrom(3)]. On the other hand, that of the other three equivalent Ga-N bonds are 0.8[e/Angstrom(3)]. Furthermore, it is found that the electron distribution of N atom shows asymmetric distortion. These features suggest asymmetric thermal vibrations of N atom which are restricted by Ga-N bonds.