Spin transport and spin manipulation in GaAs (110) and (111) quantum wells

Abstract

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.Spin dephasing via the spin-orbit interaction is a major mechanism limiting the electron spin lifetime in zincblende III-V quantum wells (QWs). QWs grown along the non-conventional crystallographic directions [111] and [110] offer new interesting perspectives for the control of spin-orbit (SO) related spin dephasing mechanisms due to the special symmetries of the SO fields in these structures. In this contribution, we show that the combination of such special symmetries with the transport of carriers by the type II modulation accompanying a surface acoustic wave allows the transport of spin polarized carriers over distances of tens of μm in GaAs(110) QWs. In the case of GaAs(111), the Rashba contribution to the SO field generated by an electric field perpendicular to the QW plane is used to compensate the Dresselhaus contribution at low temperatures, leading to spin lifetimes of up to 100 ns. The compensation mechanism is less effective at high temperatures due to nonlinear terms of the Dresselhaus contribution. Perspectives to overcome this limitation via the combination of (111) structures with the transport of spins by surface acoustic waves are discussed.

Electric control of spin transport in GaAs (111) quantum wells

“…The bias voltage, V b , applied between an Al Schottky contact on top of the n-doped layer and the p-doped substrate, generates the vertical electric field E z required for the control of the SO-interaction. From previous measurements in a similar sample, we expect to reach E c z at a reverse voltage bias V b ≈ −1.5 V. 15,19 To confine the electric field along the z-direction, we processed the top doped layer and part of the top undoped (Al,Ga)As spacer into mesa structures of 300 µm diameter defined by wet chemical etching.…”

“…The shape of the measured PL profile deviates from the expected one, symmetric to y = 0, due to terraces at the sample surface, which originate from the growth on a surface tilted by an angle δθ with respect to the [111] direction. 19 We have also performed time-resolved µ-PL experiments using a time-gated CCD camera. Figure 2 pulse (vertical scale) for V b = 1 V. Panel (b) displays the corresponding spatial profiles at the times marked with dashed lines in panel (a).…”

“…Our result is τ p ≈ 3 ps, in agreement with previously estimated values in a similar QW based on measurements of Dyakonov-Perel' spin dephas- ing time under homogeneous carrier concentration. 15,19 We have repeated the previous experiment for several voltage biases and laser powers, P laser , to extract the dependence of τ r and D a on E z and carrier density. Figure 4 shows (a) τ r and (b) D a as a function of V b obtained from measurements performed at P laser = 40 µW (squares) and 80 µW (circles).…”

“…The corresponding value of E c z ≈ 18 kV/cm agrees well with PL results recorded in a similar sample using a larger illumination area. 15,19 It is noteworthy that the ρ z profile for r = 0 in Fig. 5(c) is asymmetric with respect to the compensation bias V b = −1.8 V. The asymmetry arises from the fact that, in a time-integrated PL measurement, ρ z depends on the ratio between the carrier recombination time, τ r , and the spin dephasing time, τ s , according to:…”

“…We exclude thermal effects as the cause of this shift: higher temperatures would allow the occupation of energy states with larger k-vectors, whose contribution to the cubic terms of Ω SO reduces E c z . 12,15,18,19 We attribute the enhancement of E c z to a partial screening of the electric field generated by the top gate. This screening comes from the accumulation of photoexcited electrons and holes at opposite walls of the QW as a response to the gate field.…”