Effect of GaAs (100) substrate misorientation on the electrical parameters and surface morphology of metamorphic In$_{0.7}$Al$_{0.3}$As/In$_{0.75}$Ga$_{0.25}$As/In$_{0.7}$Al$_{0.3}$As HEMT nanoheterostructures

The results of studies of the effect of GaAs (100) substrate misorientation on the electrical parameters and surface morphology of high electron mobility In$_{0.7}$Al$_{0.3}$As/In$_{0.75}$Ga$_{0.25}$As/In$_{0.7}$Al$_{0.3}$As/GaAs nanoheterostructures are reported. Using molecular-beam epitaxy, two identical structures with a stepped compositional profile of the metamorphic In$_x$Al$_{1-x}$As ($\Delta x$ = 0.05) buffer are grown on substrates of two types: a singular GaAs substrate with the orientation (100) $\pm$ 0.5$^\circ$ and a GaAs (100) substrate misoriented by (2 $\pm$ 0.5$^\circ$) in the $[0\overline{11}]$ direction. It is found that, in the case of the misoriented substrate, the concentration of the two-dimensional electron gas is $\sim$ 40% higher. Broadening of the photoluminescence spectra and a shift of the peaks to lower photon energies, as experimentally observed in the case of the misoriented substrate, are attributed to the increased roughness of the heterointerfaces and strengthened fluctuations of the quantum-well width.