MICROCHARACTERIZATION OF COMPOSITION MODULATIONS IN EPITAXIAL ZNSE1-XTEX

Molecular beam epitaxial growth of the ZnSe1-xTex (x = 0.44-0.47) allo y on vicinal (001) GaAs substrates tilted four, six, and nine degree-[ 111]A or B results in partial phase separation of the alloy with a ver tical modulation between different compositions. Transmission electron microscopy images of samples grown on four degree-tilted substrates s howed superlattice-like structures, with periods in the range 13.4-28. 9 Angstrom. Lattice images reveal diffuse interfaces between light and dark bands. Period variations were detected in isolated regions of so me samples. We present evidence that the modulation develops at the gr owth surface, and remains stable in the bulk at temperatures up to 450 degrees C. Satellite spot pairs with approximate indices (h k 1 + del ta) were present near the zinc-blende spots in electron diffraction pa tterns and x-ray diffraction data, as expected from material with a si nusoidal composition profile. The orientation of the spots reveals tha t the modulation vector is parallel to the growth direction, rather th an to [001]. The [111]A- and B-tilted samples showed significant modul ation, while the five degree-[110] and on-axis material showed no dete ctable modulation. The modulation wavelength did not strongly depend o n growth temperature in the range examined (285-335 degrees C). Sample s showing composition modulation did not exhibit significantly altered low-temperature luminescence spectra from material: with no modulatio n.