Strain relaxation of GaNxAs1-x on GaAs (001) grown by molecular-beam epitaxy

A series of samples consisting of a strained layer of GaNxAs1-x of different thickness, covered by a GaAs cap layer of 100 nm were grown by molecular-beam epitaxy. The samples have been characterized by high-resolution x-ray diffraction and simulations based on the dynamical theory in order to determine the strain relaxation in GaNxAs1-x layers. It is found that there is a huge difference between the critical thickness determined by x-ray diffraction and the theoretical calculations according to the Matthews and Blakeslee model. The critical thickness of GaNxAs1-x on GaAs is ten times smaller than the theoretical value. The strain relaxation is a crucial point that affects the quality of GaNAs. Photoluminescence measurements are in good agreement with the x-ray diffraction results. The optical properties degraded rapidly when the GaNxAs1-x thickness exceeded the critical thickness determined above. (C) 1999 American Institute of Physics. [S0021-8979(99)07821-4].