The Hanle effect and electron spin polarization in InAs/GaAs quantum dots up to room temperature

Abstract

Abstract. The Hanle effect in InAs/GaAs quantum dots (QDs) is studied under optical orientation as a function of temperature over the range of 150-300 K, with the aim to understand the physical mechanism responsible for the observed sharp increase of electron spin polarization with increasing temperature. The deduced spin lifetime T s of positive trions in the QDs is found to be independent of temperature, and is also insensitive to excitation energy and density. It is argued that the measured T s is mainly determined by the longitudinal spin flip time (T 1 ) and the spin dephasing time (T 2 * ) of the studied QD ensemble, of which both are temperature-independent over the studied temperature range and the latter makes a larger contribution. The observed sharply rising QD spin polarization degree with increasing temperature, on the other hand, is shown to be induced by an increase in spin injection efficiency from the barrier/wetting layer and also by a moderate increase in spin detection efficiency of the QD.PACS numbers: 73.21.La, 78.67.Hc, 72.25.Fe IntroductionSpins in semiconductor quantum dots (QDs) are the subject of extensive current research due to their weak interaction with the solid state environment, resulting in long spin lifetimes and the proposal for their application in spintronics and quantum information technology [1][2][3]. To this end, studies of spin injection and detection are important tasks to advance both our understanding of the relevant physical processes and to guide the design of improved structures for spintronic applications. Spin-related properties of QDs have in past years been investigated extensively, mainly at low temperatures, largely thanks to the availability of modern single-dot optical spectroscopy such as micro-photoluminescence (-PL) and scanning near-field optical microscopy (SNOM) [4][5][6][7][8][9][10]. Unfortunately, applications of these techniques for studies of QDs have been extremely restricted at elevated temperatures due to drastically decreasing emission intensity with increasing temperature. As a result, detailed studies and understanding of spin properties of QDs at temperatures close to room temperature (RT), highly relevant for practical applications, remain very limited.Recently, we reported a dramatic increase in electron spin polarization degree of InAs/GaAs QDs at high temperatures [11]. Polarization values up to 35% in the QD ground state at RT have been found, indicating at least equally high spin detection efficiency. In this work we carry out detailed studies of the Hanle effect [12], i.e. the depolarization effect in a transverse magnetic field, in InAs/GaAs QDs. Our aim is to determine the temperature dependence of the QD electron spin lifetime

Room-temperature polarized spin-photon interface based on a semiconductor nanodisk-in-nanopillar structure driven by few defects

“…To approach the maximum value of , on the other hand, τ needs to be much shorter than τ s . This requires introduction of non-radiative recombination such that τ  ≈  τ nr ≪  τ s 53 , which simultaneously minimizes η , as η  =  τ / τ r ≪1 under the same condition. Such an anti-correlation between P e and η can be clearly visualized from the simulations shown by the gray dashed lines in Fig.…”

Spin injection and helicity control of surface spin photocurrent in a three dimensional topological insulator

“…2a,b ) in the bare GaAs substrates (Samples Substrate 1 and Substrate 2 or in short Sub.1 and Sub.2) under the normal incidence of circularly polarized light. As P PL of the excitons with spin-depolarized holes is governed by the exciton electron spin polarization and X is contributed by both heavy-hole and light-hole excitons with a 3:1 intensity ratio but with opposite P PL for a given (refs 24 , 25 ), the corresponding | | in the exciton ground state should be twice as large as | P PL |, that is, | |∼20%. Taking into account possible spin losses during capture of conduction band (CB) electrons and valence-band holes in forming the excitons, we can therefore conclude that the spin polarization degree of the photo-generated CB electrons in the GaAs substrates must be >20% but <50% (50% is the theoretical maximum spin polarization degree, , that CB electrons can acquire under the 100% circularly polarized optical excitation with the photon energy above the GaAs bandgap but without involving the spin-orbit split-off valence band state.…”

“…4 . It is well known from optical orientation that above-bandgap optical excitation of GaAs (without involving the spin-orbit split-off holes) with a given circular polarization, say σ − , predominately generates spin-up electrons and spin-down holes 24 25 . As holes experience stronger spin relaxation in GaAs and slower injection due to a lower mobility as compared with electrons, it is reasonable to view that spin injection is mainly associated with electrons as illustrated in Fig.…”

Ultrafast spin tunneling and injection in coupled nanostructures of InGaAs quantum dots and quantum well

“…1,2 Therefore, semiconductor QDs provide excellent platforms for initializing, manipulating, and probing the spin states of electron, hole or exciton, [3][4][5][6][7] and realization of spin-functional photonic devices. [8][9][10][11][12] Efficient spin injection, namely, the spatial transfer of spin-polarized carriers or excitons into QDs, is prerequisite for these applications.…”