Manifestation of the upper Hubbard band in the electrical conductivity of two-dimensional p-GaAs-AlGaAs structures

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Abstract
The Hall effect and electrical conductivity were studied in the temperature range of 1.7–300 K in Be-doped p-GaAs/AlGaAs multilayer structures with 15-nm-wide quantum wells. Doping of the well itself and the adjacent barrier layer was used to create a situation when the upper Hubbard band (the A+ centers) was occupied with holes and electrical conduction proceeded over the states in this band. It is shown experimentally that the binding energy of A+ centers increases significantly in the 15-nm-wide wells compared to this energy in the bulk, which is explained by the fact that the well size and the hole radius at the A+ center are almost identical. The above radius was independently estimated from an analysis of the temperature dependence of the hopping conductivity.