17.4 Spintronics
471
source
drain
gate
Fig. 17.8 Scheme of spin transistor after the proposal of [1549]. Source and drain are ferromagnets with their magnetization shown schematically as arrows. The channel under the gate transports electrons whose spin rotates in the electric
field under the gate
17.4.2 Spin LED
In a spin LED (for LEDs see Sect. 23.3), the injection of spin-polarized carriers into the active layer
leads to circularly polarized luminescence. The spin alignment can be achieved with semimagnetic
semiconductors grown on top of the active layer or via spin injection from a ferromagnetic metal
into the semiconductor (for metal–semiconductor junctions cf. Sect. 21.2). In Fig. 17.9a, a Fe/AlGaAs
interface is shown.
Ideally, the spin-polarized electrons from the ferromagnetic metal tunnel into the semiconductor and
transfer to the recombination region. Subsequently, the emission is circularly polarized (Fig. 12.30b).
The degree of circular polarization is
P σ =
I σ + − I σ −
I σ + + I σ −
,
(17.2)
with I σ ± being the intensity of the respective polarization. The degree of polarization depends on the
magnetization of the metal. For the saturation magnetization of Fe, the maximum polarization is about
(a)
Fe
AlGaAs
[001]
(110)
(b)
Fe/
AlGaAs/
GaAs
M Fe
Fig. 17.9 a Transmission electron microscopy image of the (110) cross section of the Fe/AlGaAs interface of a spin
LED. The vertical lines in Fe are the (110) planes with 0.203 nm distance. b Magnetic-field dependence of the circular
polarization ratio P σ at T = 4.5 K (17.2) (filled and empty circles) and the out-of-plane component of the Fe-film
magnetization (dashed line, scaled to the maximum of P σ ). Reproduced from [1551] by permission of the MRS Bulletin
471
source
drain
gate
Fig. 17.8 Scheme of spin transistor after the proposal of [1549]. Source and drain are ferromagnets with their magnetization shown schematically as arrows. The channel under the gate transports electrons whose spin rotates in the electric
field under the gate
17.4.2 Spin LED
In a spin LED (for LEDs see Sect. 23.3), the injection of spin-polarized carriers into the active layer
leads to circularly polarized luminescence. The spin alignment can be achieved with semimagnetic
semiconductors grown on top of the active layer or via spin injection from a ferromagnetic metal
into the semiconductor (for metal–semiconductor junctions cf. Sect. 21.2). In Fig. 17.9a, a Fe/AlGaAs
interface is shown.
Ideally, the spin-polarized electrons from the ferromagnetic metal tunnel into the semiconductor and
transfer to the recombination region. Subsequently, the emission is circularly polarized (Fig. 12.30b).
The degree of circular polarization is
P σ =
I σ + − I σ −
I σ + + I σ −
,
(17.2)
with I σ ± being the intensity of the respective polarization. The degree of polarization depends on the
magnetization of the metal. For the saturation magnetization of Fe, the maximum polarization is about
(a)
Fe
AlGaAs
[001]
(110)
(b)
Fe/
AlGaAs/
GaAs
M Fe
Fig. 17.9 a Transmission electron microscopy image of the (110) cross section of the Fe/AlGaAs interface of a spin
LED. The vertical lines in Fe are the (110) planes with 0.203 nm distance. b Magnetic-field dependence of the circular
polarization ratio P σ at T = 4.5 K (17.2) (filled and empty circles) and the out-of-plane component of the Fe-film
magnetization (dashed line, scaled to the maximum of P σ ). Reproduced from [1551] by permission of the MRS Bulletin