Hole transport due to shallow acceptors along boron doped SiGe quantum wells

Lateral conductivity and magnetotransport measurements were performed with SiGe single quantum well (QW) structures doped with boron in the QW. The co nductivity at low temperatures (T) is shown to be due to hopping over B cen ters while at higher T, it is due to two-stage excitation: thermal activati on of holes from the ground to strain-split B states are followed by hole t unneling into the valence band. The tunneling is due to a potential drop ac ross the QW which is due to hole capture at surface states of the Si cap la yer making the surface charged. The external potential applied across the Q W essentially changes the lateral conductivity as well as the activation en ergy. The calculations of band profile, free carrier concentration in the Q W and acceptor population, as well as an effect on the transverse electric field were carried out taking into account the charging of surface states. (C) 2000 Elsevier Science B.V. All rights reserved.