The electronic properties of heterostructures with selective doping on the basis of III-V compounds have been intensively studied for more than 30 years. These investigations remain of current importance because the highest low temperature mobility of the two dimensional electron gas being 3500 m 2 /V s was achieved in such structures [1]. However, even such a highly mobile system is far from the ideal one and its transport properties at low temperatures are mainly determined by the scattering of the charge carriers on the random potential of the ionized centers of the dopant [2]. This mechanism of scattering of the charge carriers in semiconductor structures is suppressed by so called selective doping [3]. The essence of this method for increasing the mobility (μ) is the spatial separation of the charge carrier transport and doping regions.In a conventional GaAs/AlGaAs heterojunction, the charge transport and doping regions are separated by a layer of undoped AlGaAs with the thickness d S that is called a spacer [4]. The higher d S , the less scat tering on the dopant induced random potential and, respectively, the higher μ in the quantum well. How ever, an increase in d S inevitably leads to the decrease in the density of the free charge carriers. This means that it is impossible to simultaneously get high mobil ity and density values in the selectively doped GaAs/AlGaAs heterostructure. To solve this problem, it was proposed to use AlAs/GaAs superlattices as lat eral barriers to the GaAs quantum well [5].A schematic of a GaAs quantum well with AlAs/GaAs superlattice barriers is shown in Fig. 1. The scattering of the charge carriers on the random potential of ionized dopants in this modulated struc ture is suppressed owing not only to the spatial separa tion of the doping and transport regions but also to the screening effect of the X electrons located in the AlAs layers. This method of suppressing scattering on the dopant induced random potential makes it possible to simultaneously get the high mobility and high density of the two dimensional electrons in GaAs quantum wells with AlAs/GaAs superlattice barriers. This expands the possibilities of experimental study of the electronic properties of low dimensional semicon ductor systems [6][7][8][9][10][11].The quality of selectively doped heterostructures, as a rule, is estimated according to the mobility value which is determined by the transport relaxation time of the momentum τ tr = (m*/e)μ, where m* and e are the electron effective mass and charge, respectively. This is apparently related to the simplicity of measur ing the quantity μ in the experiment. Another impor tant parameter characterizing the processes of the charge carrier scattering in the disordered electron systems is the quantum lifetime τ q , which determines the half width of Landau levels. The times τ tr and τ q are identical only in the case of scattering on a short range potential. In the general case, they are not equivalent and are determined by the relations 1/τ q = Low temperature depend...

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