Coexistence behavior of the CuPtB-type and the CuAu-I-type ordered structures in highly strained CdxZn1-xTe/GaAs heterostructures

Abstract

Ordered structures in highly strained CdxZn1-xTe/GaAs heterostructures epitaxial layers grown on (001)GaAs substrates were investigated by using selected area electron diffraction pattern (SADP) and cross-sectional high-resolution transmission electron microscopy (HRTEM) measurements. The SADP results showed two sets of (1/2 1/2 1/2) superstructure reflections with symmetrical intensities along the [110] axis, and the corresponding HRTEM images indicated a doublet periodicity in the contrast of the {111} lattice planes. Two structures, one corresponding to the CuPtB-type ordering for each direction of the doublet periodicity on the {111} lattice planes along the [110] axis and the other corresponding to superstructure spots related to the CuAu-I type ordering were observed in the SADP. The doublet periodicity of 200 lattice fringes, associated with the CuAu-I-type ordered structure was also observed in the HRTEM image, and many antiphase boundaries were observed in ordered regions. The formation of the two ordered structures in the CdxZn1-xTe epilayers might originate from the minimization of the relaxation energy due to the high strain effect resulting from the large lattice mismatch between the CdxZn1-xTe epilayer and the GaAs substrate. These results provide important information on the microstructural properties for improving the efficiencies of CdxZn1-xTe-based optoelectronic devices operating in the blue-green spectral region. (C) 2001 American Institute of Physics.