Investigation of positively charged acceptor states in Si and Ge under uniaxial stress by phonon induced conduction

Abstract

We use superconducting Al-tunnel junctions as tunable phonon generators in the meV-range to determine ground state splitting at zero stress of positively charged states associated with single ac-' ceptors in Si and double acceptors in Ge. From the stress and energy dependence of the conductivity induced by high frequency phonon irradiation of the corresponding two-and three-hole states we find that the splitting is below 0.1 meV for the ground states of Si: B+ and Ge: Be+, and 1 meV and 1.2 meV for Si : Ga+ and Si : A]+, respectively. These level separations are comparable to those found previously for the ground states of the corresponding acceptor bound excitons A%. For the deeper acceptors Si: In+, Si: T1+, and Ge: Zn+ the results are qualitatively different.

Activated and Metallic Conduction in p -Type Modulation-Doped Ge - Sn Devices

“…The hole density is not thermally activated and does not correspond to transport in an impurity band of boron dopant close to the valence-band edge. Even if an impurity band associated with the upper Hubbard state was present from positively charged acceptor states in the boron modulation doping, not the Sn-vacancy traps, this is approximately 1 meV below the valence-band edge [46] and is unlikely to be operating in this system due to the approximately 10.7 meV Fermi energy with the conductivity not being described by hopping transport through these states. The triplet state of the upper Hubbard band can be on the order of meV above the valence-band edge but below the mobility edge and this is unlikely to be playing a role in the transport of the Ge 0.92 Sn 0.08 QWs.…”