Highly strained AlAs-type interfaces in InAs/AlSb heterostructures

Abstract

Spontaneously formed Al-As type interfaces of the InAs/AlSb system grown by molecular beam epitaxy for quantum cascade lasers were investigated by atomic resolution scanning transmission electron microscopy. Experimental strain profiles were compared to those coming from a model structure. High negative out-of-plane strains with the same order of magnitude as perfect Al-As interfaces were observed. The effects of the geometrical phase analysis used for strain determination were evidenced and discussed in the case of abrupt and huge variations of both atomic composition and bond length as observed in these interfaces. Intensity profiles performed on the same images confirmed that changes of chemical composition are the source of high strain fields at interfaces. The results show that spontaneously assembled interfaces are not perfect but extend over 2 or 3 monolayers.

Elastic properties of AlAs-like and InSb-like strained interfaces in [InAs/AlSb] heterostructures

“…The difference between these two values is smaller than the precision of experimental measures done at interfaces by analyzing atomic resolved (Scanning)-TEM images. 4 Heterostructures with larger or smaller values of m and/or n presented similar results (not shown).…”

“…Experimentally, spontaneously formed interfaces are not perfect and extend over 2 or 3 monolayers, but they could reach the same level of strain as expected for a perfect tensile Al-As type interface. 4 Using a modified growth procedure, interfaces with a high compressive stress were also achieved. 5 High and localized strains also exist in various mismatched heterostructures, thanks to the same interfacial configuration as here ([InAs/GaSb] 6 and [ZnTe/CdSe] 7 ) or to a nanowire geometry [8][9][10] for instance.…”

“…calculated with (2) from d is 6.9% (linear elasticity) and 8.2% (DFT). Similarly to Al-As interfaces, the precision of (scanning)-TEM images analysis 4 is not sufficient to capture the difference between these two strain values. No significant change occurs when AlSb is reduced to the smallest thickness, i.e., when p !…”

Unintentional As incorporation into AlSb and interfacial layers within InAs/AlSb superlattices

“…In 2016, A. Ponchet's group cooperated with Baranov's group to investigate the extent of InAs/AlSb interfaces. They performed strain and elemental analysis by applying atomically resolved Z-contrast images by high-angle annular dark-field imaging in a scanning transmission electron microscope (HAADF-STEM) [7]. They demonstrated a high content of Al-As bonds at the interface.…”

“…As a result, large localized strain may exist at the interfaces; and the strain strongly influence the electronic properties of an InAs/AlSb based QCL. Recent transmission electron microscopy (TEM) studies indicated that Al-As bonds are more favorable at both interfaces, however, the interfacial structures can be complex, extending up to 3 monolayers (ML) [5]- [7]. An illustration of InSb-type and AlAs-type interface is plotted Figure 1.1.…”