Quantitative analysis of variant III CuAu-I-type ordering of AlxGa1−xAs on (1 1 0), (1 1 1)A and (0 0 1) GaAs substrates using X-ray diffraction

In the present paper variant III of the CuAu-I-type ordering of AlxGa1−xAs on (1 1 0), (1 1 1)A and (0 0 1) GaAs substrates is determined for different temperatures and Al fractions. For this purpose AlxGa1−xAs films were produced by metal organic chemical vapor deposition and analyzed using X-ray diffraction at the European Synchrotron Radiation Facility in Grenoble. It is found that the ground state of AlxGa1−xAs is given by the CuAu-I-type structure, followed by the disordered phase. Generally, a higher degree of order is observed for high growth temperatures and for samples with an Al fraction of 50%. With respect to the substrate orientation the ordering is found to be strongest for samples grown on (1 1 0) substrates with a maximum long-range order parameter S of 0.053±0.014, followed by the samples grown on (1 1 1)A and (0 0 1) substrates with an S of 0.011±0.005 and 0.0025±0.0017, respectively. Because of symmetrical considerations, a total S of 0.033±0.015 is expected for the (1 1 1)A samples. This is more than half the ordering of the (1 1 0) samples, reflecting the (1 1 0)-like surface configuration of the (1 1 1)A face at higher temperatures. For the (0 0 1) samples the variant III CuAu-I-type ordering is observed for the first time.