Bismuth content dependence of the electron spin relaxation time in GaAsBi epilayers and quantum well structures

Abstract

Time-resolved optical orientation experiments have been performed in dilute bismidestructures. Bulk layers with bismuth fractions in the range 1-3.8% and quantum wells with bismuth fractions in the range 2.4-7% were investigated. A clear decrease of the electron spin relaxation time is evidenced in both cases when the bismuth content increases. These results can be well interpreted by the increased efficiency of the spin relaxation mechanisms due to the bismuth induced larger spin-orbit interaction in these alloys.The incorporation of small concentrations of bismuth (Bi) into GaAs yields a significant reduction of the band gap energy 0F 1 , 2 . As a consequence the dilute bismide alloys, GaAs 1−x Bi x , are interesting for potential optical telecommunication or photovoltaic applications 3,4 . As Bismuth is a heavy atom, dilute bismides are also characterized by a much larger spin-orbit interaction compared to GaAs 5 . Indeed, an increase of the valence band spin-orbit (SO) split-off energy Δ was clearly evidenced in GaAsBi with values reaching ~800 meV and above (i.e. twice the GaAs value) for a bismuth composition of about 10% 6 .This remarkable property has triggered massive efforts to improve alloy growth, as the condition Δ > could lead to a significant reduction of Auger or Inter Valence Band Absorption loss mechanisms in the NIR telecommunication range as suggested by Sweeney's group et al 7 , 8 . This system has also been proposed as a good candidate for spintronic applications by Fluegel et al. as the enhanced SO coupling in this material allows for a composition-dependent SO engineering and hence possible electron spin tuneability and manipulation 5 .For these reasons, the role of the SO interaction on the electron Landé g-factor in bulk GaAsBi was studied both theoretically and experimentally 9 , 10 . It was shown that the introduction of a Bi fraction of the order of 0.03 led to an increase of the g-factor by a factor of 3. Similar observations were made on the exciton g-factors in quantum wells in the low temperature range 11 .Besides, the elctrons spin relaxation time is a key parameter for spin manipulations as the spin memory should last longer than the manipulation time in order to make use of the electron spin as the information vector. Tong et al. predicted theoretically that the electron spin relaxation time in GaAsBi decreases drastically when the Bi content increases 12 . The experimental investigation of the electron spin relaxation rate in a bulk sample with a bismuth fraction of 2.2% confirmed these predictions 9 . The result was in good agreement with the characterization of the product . (where is the electron Landé factor) determined by Pursley et al. via Hanle effect measurements 13 . However, a measurement of the bismuth dependence of the electron spin relaxation time is still lacking although it is essential to assess the potential of dilute bismides for spintronic applications. In this work we have measured the electron spin dynamics by time-and polarization-resolved photoluminescen...

GaAsBi: From Molecular Beam Epitaxy Growth to Devices

“…The g ‐factor describes the response of the electron spins to externally applied magnetic field while the τ s must be longer than the manipulation time to be able to utilize electron spins as an information vector. [ 82,83 ] In 2006, Fluegel et al proposed the possibility of Bi alloying as a means to manipulate the spin orbit gap of GaAsBi for spintronic application. [ 12 ] This is based on the giant spin–orbit splitting energy observed in GaAsBi with the incorporation of Bi.…”

“…This value is twice compared with the g ‐factor of GaAs which is −0.41 at 100 K. Furthermore, the τ s decreases from 370 to 100 ps when the temperature increases from 100 to 300 K. The product of g · τ s obtained by Mazzucato et al is consistent with the earlier report by Pursley et al measured by Hanle effect measurements. Recently, electron spin dynamics of GaAsBi bulk (1–3.8% Bi) and quantum wells (2.4–7% Bi) were studied by Azaizia et al [ 83 ] For both structures, a clear decrease in τ s with the increase in Bi concentration were observed. These are also attributed to increased efficiency of the DP mechanism due to stronger spin–orbit interaction.…”

Optical properties and dynamics of excitons in Ga(Sb, Bi)/GaSb quantum wells: evidence for a regular alloy behavior

“…Table 2 summarizes typically observed carrier relaxation dynamics in Ga(As,Bi)/GaAs QWs of a comparable well width to these studied in this work. One can see that PL lifetime ranges from hundreds of ps [34], few ns [35,36], up to tens of ns [26] at cryogenic temperature and, what is more important, shows a strong spectral dispersion over the PL emission band. The spectral dispersion is roughly represented by a parameter (ps meV −1 ) that describes the change in the observed PL lifetime with the change in the emission energy.…”

GaAsBi: From Molecular Beam Epitaxy Growth to Devices

“…GaAsBi bulk (1-3.8% Bi) and quantum wells (2.4-7% Bi) were studied by Azaizia et al [85] For both structures, a clear decrease of τs with the increase of Bi concentration were observed.…”

“…The g-factor describes the response of the electron spins to externally applied magnetic field while the τs must be longer than the manipulation time to be able to utilize electron spins as an information vector. [84,85] In 2006, Fluegel et al proposed the possibility of Bi alloying as a means to manipulate the spin orbit gap of GaAsBi for spintronic application. [12] This is based on the giant spin-orbit splitting energy observed in GaAsBi with the incorporation of Bi.…”