Structure and polarity of {111} CdTe on {100} GaAs

Abstract

Ultramicrotome techniques are used to prepare thin cross sections of a {111} epilayer of CdTe deposited by metalorganic chemical vapor deposition onto a {100} GaAs substrate. The structure of these samples is investigated by transmission electron microscopy using high-resolution (HRTEM) and diffraction contrast, and the polarity of the {111} layer by convergent beam electron diffraction (CBED) and characteristic x-ray emission under various electron channelling conditions, or ALCHEMI. Rutherford backscattering and channelling experiments on the bulk film confirm the presence of a multiply twinned lamellar structure as observed by electron beam techniques. Strong channeling confirms that the crystallinity is good, and that no significant concentration of defects occurs. HRTEM images of the {111} epilayer from the interface across the lamellar twins show few dislocations or crystal defects. Diffraction contrast indicates the presence of a periodic strain in the GaAs and parallel to the interface. CBED and ALCHEMI results confirm that the layer is B type, and that the lamellar twins do not invert phase.