Influence of the domain size on the band gap of ordered (GaIn)P

The domain size and the band-gap energy of ordered epitaxial (GaIn)P layers have been determined by means of transmission electron microscopy and phot oluminescence measurements, respectively. With decreasing domain size the s ymmetry of the ordered layers is reduced from the trigonal space group R3m (CuPtB type) to the monoclinic Pm space group. Pseudopotential band-structu re calculations reveal an increase of the band-gap energy of ordered (GaIn) P with diminishing domain size. This would affect the determination of the degree of order by methods, which rely on the band-gap energy of perfectly ordered (GaIn)P. By correlating the theoretical with the experimental band- gap energies we demonstrate that the order parameter eta of layers with sma ll domains is higher if the dependence of the band-gap energy on the domain size is considered. Hence, for the determination of the degree of order no t only the band-gap energy, but also the domain size have to be taken into account. (C) 1999 American Institute of Physics. [S0021-8979(99)06207-6].