RHEED, XPS, HRTEM and channeling studies of molecular beam epitaxy growth of CdTe On (001) GaAs

Abstract

MBE growth of CdTe on (001) GaAs can be achieved either in the (001) or the (111) orientation. We present a study of CdTe/(001) GaAs interfaces by reflection high energy diffraction (RHEED), X-ray photo emission spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM) and channeling.A detailed phase diagram of the GaAs-Te precursor surfaces is reported. The surfaces are analyzed by RHEED and XPS and CdTe growth is characterized on each of them. The (2×1) and (6×1)100 GaAs-Te superstructures allow (001) CdTe growth, while the Te poor (6×1), (6×1)111 and incommensurate (∗ × 3) ones (∗ indicating incommensurate phase in the [110] direction) induce (111) CdTe growth. XPS reveals three different Te adsorption sites (identified as TeAs, TeGa and TeTe) with concentrations depending on the Te-precursor surface.By HRTEM we observe, in the case of (001)CdTe/(001)GaAs, that the lattice mismatch is accommodated by a square array of Lomer-type edge dislocations with their 12a〈110〉 Burgers vector in the interface plane. Moreover, the defect concentration within the layer is greatly reduced by use of thin ZnTe buffer layers.In the case of (111) CdTe growth, ion channeling shows that (111) CdTe grown on (001) GaAs presents a (111)B face and confirms the epitaxial relationship [112]CdTe ⫫ [110]GaAs. By HRTEM we reveal that growth proceeds by formation of flat islands. Twinning is present parallel to the interface: it can be eliminated by using GaAs substrates tilted around the [110] axis.