Spin relaxation of two-dimensional holes in strained asymmetric SiGe quantum wells

TL;DR

This paper investigates how biaxial strain and asymmetry in SiGe quantum wells influence hole spin splitting and relaxation, revealing potential for spintronic devices with tunable spin properties at room temperature.

Contribution

It provides a detailed theoretical analysis of spin splitting and relaxation mechanisms in strained asymmetric SiGe quantum wells, including expressions up to third order in wavevector.

Findings

Spin splitting varies from 0.1 meV in Si to several meV in Ge QWs.

Gate electric fields can efficiently modify spin splitting.

Hole spin relaxation time can reach hundreds of picoseconds at room temperature.

Abstract

We analyze spin splitting of the two-dimensional hole spectrum in strained asymmetric SiGe quantum wells (QWs). Based on the Luttinger Hamiltonian, we obtain expressions for the spin-splitting parameters up to the third order in the in-plane hole wavevector. The biaxial strain of SiGe QWs is found to be a key parameter that controls spin splitting. Application to SiGe field-effect transistor structures indicates that typical spin splitting at room temperature varies from a few tenth of meV in the case of Si QW channels to several meV for the Ge counterparts, and can be modified efficiently by gate-controlled variation of the perpendicular confining electric field. The analysis also shows that for sufficiently asymmetric QWs, spin relaxation is due mainly to the spin-splitting related D'yakonov-Perel' mechanism. In strained Si QWs, our estimation shows that the hole spin relaxation time can be on the order of a hundred picoseconds at room temperature, suggesting that such structures are suitable for p-type spin transistor applications as well.