Epilayers were grown onto (001) GaAs substrates by means of molecular beam epitaxy. The samples could be divided into 2 groups. In one group, there was a linear relationship between the fundamental band-gap and the lattice constant. In the other group, the relationship was non-linear. Transmission electron microscopy showed that the occurrence of twins was related to a reduction in the gap energy.

T.Behr, S.Einfeldt, D.Hommel, C.R.Becker, G.Landwehr, H.Cerva: Journal of Crystal Growth, 1996, 159, 1123-7