Influence of δ doping position on subband properties in In_0.2Ga_0.8As/GaAs heterostructures

Subband properties of Si δ-doped pseudomorphic In_0.2Ga_0.8As/GaAs heterostructures have been investigated by solving the Schrödinger-Kohn-Sham equation and the Poission equation self-consistently, and by the density-density dynamical response function. The shift of the same Si δ-doped layer from the quantum-well center (the origin is at 0 Å) to the barrier (310 Å) has been studied to find its effect on subband electron densities and mobilities. The electron density of the first subband is greater than 3.6 x 10¹² cm^-2 when a δ-doped density of 4.5 x 1012 cm^-2 is placed in the well. It is only 2.06 x 10¹² cm^-2 for the doping position with a 85-Å spacer layer. The electron occupation of the second subband is 15.4% in the well-center-doped structure. It is up to the maximum of 42.3% at 130 Å. The electron mobility is not changed significantly for the first subband, but is varied noticeably for the second subband by moving the Si δ doping position in the well. The highest electron mobility is obtained at about 110 Å for the first subband, and at about 290 Å for the second subband. The calculated results are also compared to the corresponding experimental data.