Low-temperature hopping conduction over the upper hubbard band in p-GaAs/AlGaAs multilayered structures

The low-temperature 2D variable range hopping conduction over the states of the upper Hubbard band is investigated in detail for the first time in mul tilayered Be-doped p-type GaAs/AlGaAs structures with quantum wells of 15-n m width. This situation was realized by doping the layer in the well and a barrier layer close to the well for the upper Hubbard band (A(+) centers) i n the equilibrium state filled with holes. The conduction was of the Mott h opping type in the entire temperature range (4-0.4 K). The positive and neg ative magnetoresistance branches as well as of non-Ohmic hopping conduction at low temperature are analyzed. The density of states and the localizatio n radius, the scattering amplitude, and the number of scatterers in the upp er Hubbard band are estimated. It is found that the interference pattern of phenomena associated with hopping conduction over the A(+) band is qualita tively similar to the corresponding pattern for an ordinary impurity band, but the tunnel scattering is relatively weak. (C) 2001 MAIK "Nauka/Interper iodica".