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arXiv:1001.3228 · Physical Review B

Spin dynamics of electrons and holes in InGaAs/GaAs quantum wells at millikelvin temperatures

L. V. Fokina, I. A. Yugova, Dmitri R. Yakovlev, Михаил Михайлович Глазов, Ilya A. Akimov, A. Greilich, D. Reuter, Andreas Dirk Wieck, M. Bayer

Published May 4, 2010• 30 citations
arXivHTMLPDF

Abstract

The carrier spin dynamics in a $n$-doped (In,Ga)As/GaAs quantum well has been studied by time-resolved Faraday rotation and ellipticity techniques in the temperature range down to 430 milliKelvin. These techniques give data with very different spectral dependencies, from which nonetheless consistent information on the spin dynamics can be obtained, in agreement with theoretical predictions. The mechanisms of long-lived spin coherence generation are discussed for the cases of trion and exciton resonant excitation. We demonstrate that carrier localization leads to a saturation of spin relaxation times at 45 ns for electrons below 4.5 K and at 2 ns for holes below 2.3 K. The underlying spin relaxation mechanisms are discussed.

DOI
10.1103/physrevb.81.195304

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Acta Physica Sinica•Jan 1, 2011•0 citations
The carrier spin dynamics in a nnn-doped (In,Ga)As/GaAs quantum well has been studied by time-resolved Faraday rotation and ellipticity techniques in the temperature range down to 430 milliKelvin. These techniques give data with very different spectral dependencies, from which nonetheless consistent information on the spin dynamics can be obtained, in agreement with theoretical predictions. The mechanisms of long-lived spin coherence generation are discussed for the cases of trion and exciton resonant excitation. We demonstrate that carrier localization leads to a saturation of spin relaxation times at 45 ns for electrons below 4.5 K and at 2 ns for holes below 2.3 K. The underlying spin relaxation mechanisms are discussed.
Systematic investigation of the spin dephasing times in GaAs/(Al,Ga)As quantum wells and its depending on parameters like temperature, magnetic fields and doping will be shown in Chapter 3.In Chapter 4 are presented results of investigation of the nuclear spin systems in quantum well heterostructures.The chapter 5 presents the results of studying the carrier spin dynamics in a n-doped (In,Ga)As/GaAs quantum wells by time-resolved Faraday rotation and ellipticity techniques in the temperature range down to 430 mil-liKelvin.In Chapter 6 is devoted to experimental and theoretically studying of optical control of the spin coherence of quantum well electrons by short laser pulses with circular or linear polarization.For that purpose the coherent electron spin dynamics in a n-doped CdTe/(Cd,Mg)Te quantum well structure was measured by time-resolved pump-probe Kerr rotation, using resonant excitation of the negatively charged exciton (trion) state.on the eigenstates |s z ; ↑ and |s z ; ↓ yields the states themselves independent of time.Along the field axis (longitudinal direction) these quantum-mechanical spin states are thus stationary.Any loss of coherence is induced by coupling of those states with the environment.Applying the time-evolution operator on the spin states perpendicular
Carrier spin coherence in a p-doped GaAs/(Al,Ga)As quantum well with a diluted hole gas is studied by picosecond pump-probe Kerr rotation. For resonant optical excitation of the positively charged exciton the spin precession shows two types of oscillations: Electron spin beats decaying with the charged exciton radiative lifetime of 50 ps, and long-lived hole spin beats with dephasing times up to 650 ps, which decrease with increasing temperature, underlining the importance of hole localization. The mechanism of hole spin coherence generation is discussed.
Pulsed optical excitation of the negatively charged trion has been used to generate electron spin coherence in an n-doped (In,Ga)As/GaAs quantum well. The coherence is monitored by resonant spin amplification detected at times exceeding the trion lifetime by 2 orders of magnitude. Still, even then signatures of the hole spin dynamics in the trion complex are imprinted in the signal leading to an unusual batlike shape of the magnetic field dispersion of spin amplification. From this shape information about the spin relaxation of both electrons and holes can be derived.
The excitation of electron spin polarization and coherence by picosecond light pulses and their dynamics in a wide remotely doped quantum well are studied theoretically and experimentally. Assuming that all electrons in the quantum well are localized, the theory considers the resonant interaction of light pulses with the four-level system formed by the electron spins of the ground state and the hole spins of the trion excited state. The theory describes the effects of spontaneous emission, a transverse magnetic field and hole spin relaxation on the dynamics detected by the Kerr rotation of a probe pulse. Time resolved Kerr rotation experiments were carried out on a remotely doped 14nm14\phantom{\rule{0.3em}{0ex}}\mathrm{nm}14nm GaAs quantum well in the frequency range of optical transitions to the heavy hole (HH) trion and to the light-hole (LH) trion degenerate with the HH exciton. The experiments on the resonant excitation of the HH trion show a very slow heavy hole spin relaxation and, consequently, a weak electron spin polarization after the trion relaxation. In contrast, the resonant excitation of the LH trion/HH exciton results in a fast hole spin relaxation that increases electron spin polarization.
Pump‐probe time‐resolved Kerr rotation technique has been used for experimental investigation of hole spin coherence in 15‐nm wide GaAs/AlGaAs quantum well structure in regime of diluted two‐dimensional hole gas. Due to the spectral width of 1.5 ps laser pulses which correspond to ∼1 meV, selective excitation of trion and exciton states has been performed. In the case of resonant excitation of exciton only the electron spin beats have been observed in the presence of magnetic field. In the case of resonant excitation of the positively charged exciton two component decay of time‐resolved Kerr rotation (TRKR) signal appeared. From the period of the quantum beat oscillation related to long decay component (up to 650 ps) of TRKR signal we obtained in‐plain hole g‐factor of ∼0.048±0.005.
Based on the rate equations of a two-level system, time-resolved Faraday rotation spectroscopy model was developed. It was found that the carrier recombination has strong effect on the decay of Faraday rotation signal. The model was also used to fit the Faraday rotation spectra measured in GaAs quantum wells. The electron spin relaxation time was obtained as 73.5 ps. However, the spin relaxation time was obtained only as 51.3 ps with the single exponent to fit the Faraday rotation spectra. Thus, the conventional method with the single exponent to fit the Faraday rotation spectra is inaccurate.