| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 1688069 | Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms | 2006 | 5 Pages |
In this 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 growth temperatures and Al fractions. For this purpose AlxGa1−xAs films were produced by metal organic chemical vapour deposition and analysed 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 ordering is observed for high growth temperatures and for samples with an Al fraction of 50%. Furthermore, 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 close to the ordering degree 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.The lowest detection limit is estimated to be S = 0.0009 ± 0.0006, which makes it possible to measure CuAu-I-type reflections of alternating Al0.5005Ga0.4995As and Al0.4995Ga0.5005As monolayers. For the highest ordered sample, (1 1 0) Al0.50Ga0.50As grown at 750 °C with S = 0.053 ± 0.014, the alloy consists of alternating Al0.527Ga0.473As and Al0.473Ga0.527As monolayers along the [0 0 1] direction.
