An X-ray standing wave study of ultrathin InAs films in GaAs(001) grown byatomic layer epitaxy

X-ray standing wave and X-ray diffraction measurements were used to determi ne the structure of nominal 1 monolayer and 1/2 monolayer InAs films buried in GaAs(001). The films were grown by atomic layer epitaxy using trimethyl gallium, tertiarybutylarsine and trimethylindium. For the full monolayer sa mple the standing wave measurement shows that the indium atoms reside 1.577 +/- 0.014 Angstrom above the GaAs(004) substrate planes. A calculation bas ed on the macroscopic elastic theory suggests that this corresponds to a si ngle InxGa1-xAs layer with x = 0.794 +/- 0.068. The coherent fraction of 0. 766 +/- 0.051 indicates a reasonably abrupt interface, as confirmed by the In-excitonic photoluminescence full width at half maximum of 5.74 +/- 0.01 meV. The half monolayer sample is less strained, as expected, with the indi um atoms at 1.502 +/- 0.030 Angstrom above the substrate planes, correspond ing to an InxGa1-xAs layer with x = 0.446 +/- 0.145, and a coherent fractio n of 0.88 +/- 0.12. This study exemplifies the complimentary nature of XSW and XRD. (C) 1998 Elsevier Science B.V. All rights reserved.