Effect of design and growth conditions of metamorphic In(Ga,Al)As/GaAs heterostructures on electrical properties of In$_{0.75}$Ga$_{0.25}$As/InAlAs two-dimensional channel

Undoped metamorphic structures with In$_{0.75}$Ga$_{0.25}$As quantum well and various design of (In,Al)As barriers were grown on GaAs substrates by molecular beam epitaxy. Electrical properties of such structures were studied by using a 4-point Van der Pauw method and contactless technique based on the analysis of propagation of surface acoustic waves along the interface of the piezoelectric LiNbO$_3$ and the sample. Increasing the thickness of the bottom barrier layer of the In$_{0.75}$Ga$_{0.25}$As quantum well as well as optimizing the growth temperature and As$_4$/III ratio allowed achieving concentration and mobility of 2D carriers in 30 nm–thick In$_{0.75}$Ga$_{0.25}$As QW of below 3.4 $\cdot$ 10$^{11}$ cm$^{-2}$ and above 2 $\cdot$ 10$^5$ cm$^2$/(V $\cdot$ s), respectively, at $T$ = 1.7 K.