Electron transport in phemt AlGaAs/InGaAs/GaAs РНЕМТ quantum wells at different temperatures: influence of one-side $\delta$-Si doping

The influence of the concentration of $\delta$ doping with Si on the electron transport properties of Al$_{0.25}$Ga$_{0.75}$As/In$_{0.2}$Ga$_{0.8}$As/GaAs pseudomorphic quantum wells is studied in a broad temperature range of 4.2–300 K. A decrease in the doping efficiency at an electron concentration of $>$ 1.8 $\times$ 10$^{12}$ cm$^{-2}$ is found. This is caused by the effects of incomplete impurity ionization, which is also reflected on the temperature dependence of the electron concentration. A nonmonotonic variation in the electron mobility with increasing donor concentration, which is not associated with filling of the upper subband of size quantization, is observed. An increase in the mobility is associated with a rise in the Fermi momentum and screening, while its subsequent drop with increasing Si concentration is caused by the tunnel degradation of the spacer layer with a decrease in the conduction-band potential in the region of the $\delta$-Si layer.