Understanding disorder in InAs quantum wells on metamorphic III-V buffer layers for topological Josephson junction

Semiconductor and superconductor heterostructures are prime candidates for quantum devices based on mesoscopic and topological superconductivity. In these structures, the semiconductor and the superconductor should be placed near each other in the lattice to form an ohmic contact. InAs heterostructures that have a narrow bandgap with the Fermi level close to the conduction band are a prime candidate. Here, we present the study of the structural properties of InAs quantum well – Al superconducting layer heterostructures grown by molecular beam epitaxy. We report the modification of the growth conditions of the metamorphic buffer layer and quantum well active region and study disorder using various techniques. We extract background impurity, surface impurities, alloy scattering and surface roughness as a function of growth conditions. We find samples that have high indium content in their graded buffer layer show that the surface roughness decreases with the layer growth temperature. In addition, roughness along certain directions shows a higher mobility than those with anisotropic roughnesses. The growth temperature of the quantum wells was also studied at the range of 445°C to 465°C and its effect on the 2DEG mobility will be presented. A thin capping layer of 1 - 6 nm of In0.81Al0.19As was used to study the effect of surface scattering on the quantum well and the mobility as a function of its thickness.