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Spin storage in quantum dot ensembles and single quantum dots

Abstract

This thesis deals with the investigation of spin relaxation of electrons and holes in small ensembles of self-assembled quantum dots using optical techniques. Furthermore, a method to detect the spin orientation in a single quantum dot was developed in the framework of this thesis. A spin storage device was used to optically generate oriented electron spins in small frequency selected quantum dot ensembles using circularly polarized optical excitation. The spin orientation can be determined by the polarization of the time delayed electroluminescence signal generated by the device after a continuously variable storage time. The degree of spin polarized initialization was found to be limited to 0.6 at high magnetic fields, where anisotropic effects are compensated. The spin relaxation was directly measured as a function of magnetic field, lattice temperature and s-shell transition energy of the quantum dot by varying the spin storage time up to 30 ms. Very long spin lifetimes are obtained with a lower limit of T{sub 1}=20 ms at B=4 T and T=1 K. A strong magnetic field dependence T{sub 1}{proportional_to}B{sup -5} has been observed for low temperatures of T=1 K which weakens as the temperature is increased. In addition, the temperature dependence has been determined with  More>>
Authors:
Publication Date:
Oct 15, 2009
Product Type:
Thesis/Dissertation
Report Number:
INIS-DE-1000
Resource Relation:
Other Information: TH: Diss. (Dr.rer.nat.); Related Information: Selected Topics of Semiconductor Physics and Technology v. 113
Subject:
77 NANOSCIENCE AND NANOTECHNOLOGY; CHARGE STATES; ELECTROMAGNETIC RADIATION; ELECTRONS; EXCITATION; EXCITED STATES; HOLES; LIFETIME; MAGNETIC FIELDS; PAULI PRINCIPLE; PHOTON COLLISIONS; POLARIZATION; POLARIZED BEAMS; QUANTUM DOTS; RELAXATION; RELAXATION TIME; SPIN ORIENTATION; TEMPERATURE DEPENDENCE; TEMPERATURE RANGE 0000-0013 K; TUNNEL EFFECT
OSTI ID:
21380818
Research Organizations:
Technische Univ. Muenchen, Garching (Germany). Walter-Schottky-Inst. fuer Physikalische Grundlagen der Halbleiterelektronik; Technische Univ. Muenchen, Garching (Germany). Fakultaet fuer Physik
Country of Origin:
Germany
Language:
English
Other Identifying Numbers:
Other: ISBN 978-3-941650-13-8; TRN: DE10FE311
Availability:
Commercial reproduction prohibited; INIS; OSTI as DE21380818
Submitting Site:
DEN
Size:
220 pages
Announcement Date:
Dec 22, 2010

Citation Formats

Heiss, Dominik. Spin storage in quantum dot ensembles and single quantum dots. Germany: N. p., 2009. Web.
Heiss, Dominik. Spin storage in quantum dot ensembles and single quantum dots. Germany.
Heiss, Dominik. 2009. "Spin storage in quantum dot ensembles and single quantum dots." Germany.
@misc{etde_21380818,
title = {Spin storage in quantum dot ensembles and single quantum dots}
author = {Heiss, Dominik}
abstractNote = {This thesis deals with the investigation of spin relaxation of electrons and holes in small ensembles of self-assembled quantum dots using optical techniques. Furthermore, a method to detect the spin orientation in a single quantum dot was developed in the framework of this thesis. A spin storage device was used to optically generate oriented electron spins in small frequency selected quantum dot ensembles using circularly polarized optical excitation. The spin orientation can be determined by the polarization of the time delayed electroluminescence signal generated by the device after a continuously variable storage time. The degree of spin polarized initialization was found to be limited to 0.6 at high magnetic fields, where anisotropic effects are compensated. The spin relaxation was directly measured as a function of magnetic field, lattice temperature and s-shell transition energy of the quantum dot by varying the spin storage time up to 30 ms. Very long spin lifetimes are obtained with a lower limit of T{sub 1}=20 ms at B=4 T and T=1 K. A strong magnetic field dependence T{sub 1}{proportional_to}B{sup -5} has been observed for low temperatures of T=1 K which weakens as the temperature is increased. In addition, the temperature dependence has been determined with T{sub 1}{proportional_to}T{sup -1}. The characteristic dependencies on magnetic field and temperature lead to the identification of the spin relaxation mechanism, which is governed by spin-orbit coupling and mediated by single phonon scattering. This finding is qualitatively supported by the energy dependent measurements. The investigations were extended to a modified device design that enabled studying the spin relaxation dynamics of heavy holes in self-assembled quantum dots. The measurements show a polarization memory effect for holes with up to 0.1 degree of polarization. Furthermore, investigations of the time dynamics of the hole spin relaxation reveal surprisingly long lifetimes T{sub 1}{sup h} in the microsecond range, therefore, comparable with electron spin lifetimes. The longest measured value is T{sub 1}{sup h} =270 {mu}s at B=1.5 T and T=8 K. Based on this spin detection technique in small ensembles, electron spin resonance experiments with the goal to study coherence properties were attempted. After optical charge generation and storage, a spin-conditional absorption of a circularly polarized light pulse tuned to the singly charged quantum dot s-shell absorption converts the spin information of the resident electron to charge information. Subsequently, time-gated photoluminescence directly reveals the charge state of the quantum dot (1e, 2e) and, therefore, the spin orientation of the resident electron. Schottky diode devices suitable for this single dot spin readout scheme were fabricated and characterized with time-gated photoluminescence. The electric field regimes applicable for reset, optical charging and reliable charge storage were identified. Furthermore, the fidelity of charge readout was investigated as a function of excitation wavelength, applied electric field and optical excitation power. Additional measurements using resonant excitation showed that a single quantum dot can be selectively charged with a single electron via optical excitation in its p-shell. The tunneling escape of this optically initialized electron has been determined, proving the feasibility of reliable charge detection in time-resolved measurements. Extrapolated to reasonable storage fields F=20 kV/cm the tunneling time of the electron exceeds seconds. The electron spin relaxation in a single quantum dot has been determined as a function of temperature at B=12 T. (orig.)}
place = {Germany}
year = {2009}
month = {Oct}
}