Energy-filtered electron diffraction and high-resolution electron microscopy on short-range ordered structure in GaAs_0.5Sb_0.5

Characteristic intensity distribution of diffuse scattering in III-V alloy semiconductor GaAs_0.5Sb_0.5 epitaxially grown was observed by the energy-filtered electron diffraction method with [1̄10] incidence. The diffuse scattering situates at the one-third positions between the fundamental reflections extending parallel to the q₀₀₂ direction in the reciprocal space. A high-resolution electron microscope image shows weak contrast modulation corresponding to the diffuse scattering. The image processed with the Fourier transform by selecting the diffuse scattering and a fundamental reflection shows small regions consisting of bright dots being elongated along the (111) planes and aligning on the (002) planes, which are considered to result from the ordering of As and Sb during the growth process. The effect of including the fundamental reflection for imaging the ordered regions in the image processing method is also discussed. Finally, based on the results obtained by energy-filtered electron diffraction and high-resolution electron microscopy, a simple structure model for the short-range ordered structure in GaAs_0.5Sb_0.5 is proposed.