Abstract
Crystal structures of two kinds of optically active semiconductors and both of which are defect wurtzite structures but show different reduced ratios, have been studied using powder X-ray diffraction and Rietveld analysis. The final reliability factors are as follows: for and for The structure of with is called the ideal defect wurtzite structure; the bond lengths are nearly the same and the bond angles are almost to be the ideal bond angle of tetrahedral bonding 109.47°. Meanwhile, the structure of with is called the layered defect wurtzite structure; the nearest and layers are waved and very close to each other as if they merged into one atomic layer. The average bond length along the c axis is 5.89% longer than that between the atoms in the merged and layers; the average bond angle whose one side is the bond along the c axis is 13.11% smaller than 109.47°. Based on these structural results, the anomalous dependence of the optical band gap on composition is discussed from the view of bonding nature. The additional ionic bonding between the merged (001) layers in the layered defect wurtzite structure makes the c parameter smaller but the band gap larger than those of the ideal defect wurtzite structure although the ionic bonding nature is dominant for the both defect wurtzite structures.
- Received 17 April 2000
DOI:https://doi.org/10.1103/PhysRevB.62.16549
©2000 American Physical Society