Structural and optical characterization of InAs/GaSb type-II superlattices: Influence of the change in InAs and GaSb layer thicknesses for fixed InSb-like interfaces

In this article, we report on the molecular beam epitaxy growth and characterization of a 140 period InAs/GaSb type-II superlattice structure designed for mid infrared detection. Thickness of a period was systematically altered in each sample by changing the thickness of InAs (GaSb) layers from 9 to 7 monolayers (ML) for a fixed GaSb (InAs) layer at 9 ML (7 ML). The same InSb-like strain compensation interface was used for all samples. High resolution X-ray diffraction analysis, spectral responsivity and external quantum efficiency (QE) measurements were performed to express the effects of layer thickness variations on both structural and photodetector features. The decrease in the InAs thickness resulted in the increased mismatch from 0 to + 1626 ppm and the blue shift in the 50% cut-off wavelength (λ_c) from 5.41 to 4.36 μm at 77 K. The additional decrease in GaSb thickness caused further increase in the mismatch up to + 1791 ppm. The steepness of the photoresponse at the absorption band edge was quantified and presented comparatively with different photodetector parameters and material properties for a complete picture. The highest optical response was obtained from sample having 8 ML InAs and 9 ML GaSb with λ_c = 4.76 μm and QE = 23.7% at 4 μm. - Highlights: • Detailed growth conditions for InAs/GaSb SLs designed for infrared detection • Precisely engineering the λ_c and the ∆a_⊥/a by controlling the SL layer thicknesses • InAs layer thickness changes are more effective than the GaSb on the λ_c and ∆a_⊥/a