The SOinteraction is associated with the fact that an electron moving in the lattice potential of a IIIV semiconductor experiences an effective, wave vector (k) dependent magnetic field B_{SO}(k), which acts on its spin. In GaAs QWs, the SOinteraction is governed by two major contributions. The first is related to the bulk inversion asymmetry (BIA) of the zincblende lattice. In the case of (111) QWs, the linear in k components of the effective magnetic field associated with this contribution, B_{BIA}(k), lies in the QW plane and has the orientation dependence on k sketched in Figure 1. The second important contribution arises from structural inversion asymmetries (SIA) due to external fields. In the case of an electric field E_{Z }applied across the QW, the associated effective magnetic field B_{SIA}(k, E_{z}) is proportional to k and E_{z} and also lies in the QW plane (cf. Figure 1). Since the linear terms of both contributions have exactly the same symmetry, if one applies a compensation electric field, E_{c}, for which the condition B_{BIA}(k) + B_{SIA}(k, E_{c}) = 0 is satisfied, then the total SOinteraction will simultaneously vanish for all k vectors. We have provided the experimental verification of this BIA/SIA compensation mechanism by demonstrating the electrically driven transition from a BIAdominated spin dephasing regime to a SIAdominated one.
The studies were carried out in (111) QWs embedded in the intrinsic region of an nip diode, where bias voltage, V_{b}, applied between the top ndoped layer and the pdoped substrate generates the vertical electric field E_{Z}. We have studied the electron spin dynamics by exciting outofplane spin polarized electrons in the QWs using a circularly polarized, pulsed laser beam, and by detecting the circular polarization of the photoluminescence (PL) emitted when the carriers recombine. Figure 2 shows the dependence of the electron spin lifetime on reverse bias in a sample including 20 QWs: the spin lifetime increases with increasing reverse bias from barely 1 ns to up to 60 ns (black squares). For large reverse voltages, the overlap between the electron and hole wave functions reduces significantly, thereby reducing the PL intensity and hindering the optical detection of the spin dynamics. We could overcome this limitation by carrying out experiments under pulsed reverse bias. Here, laser and bias pulses with the same repetition frequency are synchronized, so that the laser pulse hits the sample at a time shortly after the application of a reverse bias pulse of amplitude V_{b}. The photoexcited carriers are then driven towards opposite interfaces of the QW by the vertical electric field, where they remain stored until the bias pulse is removed. Then the stored carriers quickly recombine, giving rise to a short PL burst. We extract the spin dynamics from the circular polarization of these PL bursts after voltage pulses of different durations. By repeating this procedure for different V_{b}, we determined the electric field dependence of the spin lifetime indicated by the open squares in Figure 2. The observation of a maximum spin lifetime maximum in the voltage dependence unambiguously establishes the BIA/SIA compensation as the mechanism for biasinduced spin lifetime enhancement in (111) QWs. Furthermore, the observed peak spin lifetimes exceeding 100 ns are among the longest values reported for undoped GaAs structures.
3  Autor  A. HernándezMínguez , K. Biermann , R. Hey , P. V. Santos 
Titel 
Spin transport and spin manipulation in GaAs (110) and (111) quantum wells 

Source  Phys. Status Solidi B , 251 , 1736 ( 2014 )  
DOI : 10.1002/pssb.201350202  Cite : Bibtex RIS 
2  Autor  A. HernándezMínguez , K. Biermann , R. Hey , P. V. Santos 
Titel 
Electrical suppression of spin relaxation in GaAs(111)B quantum wells 

Source  Phys. Rev. Lett. , 109 , 266602 ( 2012 )  
DOI : 10.1103/PhysRevLett.109.266602  Download: PDF  Cite : Bibtex RIS 
1  Autor  K. Biermann , A. HernándezMínguez , R. Hey , P. V. Santos 
Titel 
Electrically tunable electron spin lifetimes in GaAs(111)B quantum wells 

Source  J. Appl. Phys. , 112 , 083913 ( 2012 )  
Download: PDF  Cite : Bibtex RIS 