Hole spin dynamics and valence‐band spin excitations in two‐dimensional hole systems

T Korn,C Schüller

doi:10.1002/pssb.201350186

Abstract

AbstractIn recent years, the spin dynamics and spin–orbit interaction in GaAs‐based two‐dimensional hole systems (2DHS) have created a lot of attention. This is due to the complex structure of the valence band, with its p‐like character, which leads to strong spin–orbit coupling. In this paper, we review our recent studies on hole spin dynamics and valence‐band spin excitations in GaAs‐based, p‐modulation‐doped quantum wells (QWs). In 2DHS with low carrier concentration, we demonstrate that maximizing the heavy‐hole–light‐hole band splitting by changing the QW width leads to long hole spin dephasing times at low temperatures. Different mechanisms for initializing a resident hole spin polarization by optical excitation are presented. To accurately determine hole spin dynamics parameters, the resonant spin amplification technique is utilized. The strong anisotropy of the hole g factor, and electrical g factor control are investigated, using this technique. In highly doped 2DHS, we use resonant inelastic light scattering (RILS) to study the spin splitting of the valence band. We observe a low‐energy spin‐density excitation (SDE), which is a measure of the spin splitting of the hole ground state. By varying the laser energy in the RILS experiment, we can resonantly probe the k dependence of the spin splitting. The spectral shape of the SDE depends on the orientation of the light polarizations relative to the crystal axes and reflects the in‐plane anisotropy of the valence‐band spin splitting.

Highlights

The spin dynamics and spin–orbit coupling in semiconductor heterostructures have been investigated intensely in recent years, in part due to possible applications in semiconductor spintronics [1,2,3]
We review our recent studies on hole spin dynamics and valence-band spin excitations in GaAs-based, p-modulation-doped quantum wells (QWs)
In 2DHS with low carrier concentration, we demonstrate that maximizing the heavy-hole–light-hole band splitting by changing the QW width leads to long hole spin dephasing times at low temperatures

Summary

Introduction

The spin dynamics and spin–orbit coupling in semiconductor heterostructures have been investigated intensely in recent years, in part due to possible applications in semiconductor spintronics [1,2,3]. A lot of studies have focussed on direct-gap semiconductors, such as the GaAs/AlGaAs material system, as it gives a lot of flexibility in the design and symmetry of heterostructures, and high-quality growth of such structures via molecular beam expitaxy (MBE) is a mature technique They are well-suited as model systems, as optical spectroscopy techniques can be used to study the spin dynamics [4]. For k > 0, the spin–orbit interaction leads to a kdependent valence-band spin splitting even in the absence of an external magnetic field This spin splitting originates either from bulk inversion asymmetry (Dresselhaus field), or from a growth-axis asymmetry of a heterostructure (Rashba field), which may be caused, e.g., by asymmetric modulation doping or a growth-axis electric field. By changing the excitation energy and the light polarization relative to the crystal axes, we show the dependence of the spin splitting on the magnitude and crystallographic orientation of the hole wave vector

Hole spin dynamics

Findings

Conclusions