Dependence of the Mobility and the Concentration of Two-Dimensional Electron Gas in Selectively Doped GaAs/N-AlxGa1-xAs Heterostructure on the AlAs Mole Fraction

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Abstract
The mobility and the concentration of two-dimensional electron gas (2DEG) were measured by Hall measurements (4.2 K, 77 K) and Shubnikov-de Haas measurements (4.2 K) in selectively doped GaAs/N–Al x Ga1-x As (0.1≦x≦0.4) heterostructures grown by MBE. The electron conduction in the Si-doped N–Al x Ga1-x As layer was eliminated by careful step etching of this layer. When x was increased from 0.1, the 2DEG mobility considerably increased, and it reached a maximum mobility (243,000 cm2/Vs at 4.2 K; 107,000 cm2/Vs at 77 K) at x=0.25-0.3. However, the sheet electron concentration of 2DEG was not sensitive to x, and showed broad peak (6×1011 cm-2) at around x=0.25.