In the latest twenty years, the search for a source of spinpolarized electrons is an area of current active research [1][2][3][4][5][6][7], due to the feasibility of spin polarization and spin filtering within a two-dimensional electron gas which was proposed by Papp and Peeters [8,9] based on the combination of hybrid magnetic-electric barrier structure. The use of ferromagnetic metal (FM)-semiconductor (SC) junctions as spin polarization devices has been widely considered [10][11][12][13][14][15]. However, these systems suffer from rather poor spin-injection efficiency [3] arising from the conductance mismatch between the FM and SC materials [4]. Therefore, in order to obtain the large spin polarization, one must try to find the new method of spin injection.
Recently, extensive studies of spintronics have been directed towards the electron transport properties through a non-magnetic semiconductor after it is pointed out that the large spin polarization can be achieved in such a structure due to the spin-orbit coupling interaction [16][17][18][19][20][21][22]. Comparing to the tunneling through magnetic junctions, spin-dependent tunneling through non-magnetic semiconductors has several inherent merits. For example, it opens the door to orienting, detecting and manipulating electron spin through electrical ways and avoids the conductance mismatch between the FM and SC materials which would obviously reduce spin injection efficiency.
In these brief reports, we will investigate the spin-dependent tunneling through non-magnetic asymmetrical double barriers of strained heterostructure with zero-field, in which we take into account the effects of both Dresselhaus and Rashba spin-orbit interactions. It is shown that the large spin polarization can be achieved mainly due to the effect of Rashba spin-orbit coupling, although the magnetic field is zero in such a structure. It is also shown that both the transmission probability and the spin polarization show a periodic profile with the increase of the well width. These features could be engineered in the fabrication of tunable spin-dependent electric devices based on double-barrier non-magnetic semiconductors.
2. Theoretical method and formulas
The transmission of electrons with the initial wave vector, k ¼ ðk k ; k z Þ, through an asymmetrical double-barrier structure, InP/InAs/InP/InAs/InP, grown along zjj½0 0 1 is considered as shown