X-ray diffraction analysis of lateral composition modulation in InAs/GaSb superlattices intended for infrared detector applications

Lateral compositional modulation in a (InAs)₁₃ (GaSb)₁₃ superlattice grown by molecular beam epitaxy for infrared detector applications has been investigated using high-resolution X-ray diffraction. X-ray diffraction reciprocal space maps exhibit distinct lateral satellite peaks about the vertical superlattice peaks; however, the pattern is tilted with respect to the [001] direction. This tilt is directly related to the stacking of the layers as revealed by cross-sectional scanning tunnelling microscopy (XSTM) images. XSTM shows the morphology of the structure to consist of InAs- and GaSb-rich regions with a modulation wavelength of ∼1200 Å and a lateral composition wavelength of 554 ± 3 Å. The modulation only occurs along one in- plane direction, resulting in InAs ´nanowires´ along the [11~0] direction, which are several microns long. The possible causes of the lateral composition modulation and its impact on device performance are discussed.