Acceptor states in boron doped SiGe quantum wells

The temperature dependences of lateral conductivity and hole mobility in SiGe quantum well structures selectively doped with boron are presented. The boron A⁺ centers are found to exist and determine the low-temperature conductivity. The activation energy of conductivity at higher temperatures is shown to be determined by the energy distance between strain-split boron A⁰ centers. The model of two-stage excitation of free holes including the thermal activation of holes from the ground to split-off state and next tunneling into the valence band is proposed. The binding energy of A⁺ centers and the energy splitting of boron ground states by strain are found.