JP4477901B2 - Spin filter and spin state separation method - Google Patents

Description

  The present invention relates to a spin filter and a spin state separation method for separating spin states of carriers propagating in a semiconductor.

  With the progress of semiconductor epitaxial technology and microfabrication technology, the miniaturization of semiconductor devices has shown remarkable progress, but the miniaturization is approaching the limit.

  Therefore, in addition to the “charge” possessed by electrons, the property of “spin” is also used at the same time, and the field of spintronics has been attracting attention as a new device having an unprecedented function.

  To realize a spin device that controls spin in a semiconductor, (1) generation of spin-polarized carriers, (2) spin transport, storage, arithmetic operations, and (3) detection of a final spin state. It is necessary to establish an operation method.

  Among these, as the most established technique for generating spin-polarized electrons in a semiconductor, there is a method of exciting spin-polarized electrons from a valence band to a conduction band by circularly polarized light.

  In the case of this method, it is impossible to obtain 100% spin-polarized electrons due to the limitation of the light selection rule, and holes are generated in pairs with electrons. There has been a problem that the spin relaxation time cannot be made sufficiently long.

  A method of injecting spin from a ferromagnetic electrode into a semiconductor is also known, but in this case, it is difficult to obtain a large degree of spin polarization in the semiconductor due to the difference in conductance between the metal and the semiconductor. Has been pointed out theoretically.

  As a method of overcoming such a difference in conductance, a method of inserting a tunnel barrier between a ferromagnet and a semiconductor has been proposed, but at present, a large spin polarization can be obtained even by using this method. Not.

  Under such circumstances, a spin filter using a non-uniform magnetic field using the Stern-Gerlach effect, which is well known in quantum mechanics, has been proposed from the viewpoint of establishing the operation method shown in the above (1) to (3). (For example, refer nonpatent literature 1).

FIG. 4 is a diagram conceptually showing the Stern-Gerlach effect. Stern-Gerlach (1922) developed an upward and downward spin by removing silver (Ag) atoms with spin 1/2 from the oven furnace through a slit and passing through this non-uniform magnetic field gradient. Have successfully separated atoms e ₁ and e ₂ each having a (see, for example, JJ Sakurai, “Modern Quantum Mechanics”, The Benjamin / Cummings Publishing Company, p2 (1994)).

Non-Patent Document 1 proposes a spin filter combining a one-dimensional or two-dimensional electron gas of GaAs (gallium arsenide) and a non-uniform magnetic field using the Stern-Gerlach effect.
J. Wroebel, T. Dietl, K. Fronc, A. Lusakowski, M. Czeczott, G. Grabecki, R. Hey, and KH Ploog, Physica E 10, 91 (2001).

  However, in the conventional spin filter described above, the electron velocity in the semiconductor is high, and the interaction time through the inhomogeneous magnetic field is shortened, so that a sufficient spin deflection angle can be obtained to separate different spin states. It was difficult to construct a practical spin filter.

  The present invention has been made in view of such circumstances, and an object thereof is a spin filter capable of obtaining a spin deflection angle sufficient to separate different spin states of carriers propagating in a semiconductor. And providing a spin state separation method.

In order to achieve the above object, an invention according to claim 1 is a spin filter for separating carriers for each spin state taken by carriers propagating in a semiconductor, wherein a movable region in one spatial dimension direction of the carrier is different from the other. A semiconductor channel in which carriers are confined in a two-dimensional region that is negligibly small compared to a movable region in two spatial dimension directions, and a space including the semiconductor channel by generating surface acoustic waves in the semiconductor channel A spatial potential modulating means for modulating the potential of the carrier, a carrier generating means for generating a carrier propagating in the semiconductor channel in accordance with the potential modulated by the spatial potential modulating means, and a carrier generated by the carrier generating means passes. For regions containing at least part of the semiconductor channel And having a nonuniform magnetic field applying means for applying a uniform magnetic field.

According to a second aspect of the present invention, in the first aspect of the present invention, the semiconductor channel is formed by confining the carriers in a semiconductor quantum well structure.

According to a third aspect of the present invention, in the first or second aspect of the present invention, the semiconductor channel is formed using a III-V group compound semiconductor.

According to a fourth aspect of the present invention, in the first or second aspect of the present invention, the semiconductor channel is configured by using a group IV semiconductor in which a thin film having a piezoelectric field effect is provided on a surface. .

The invention according to claim 5 is the invention according to any one of claims 1 to 4 , further comprising spin state detecting means for detecting a spin state of carriers generated by propagating through the semiconductor channel. To do.

The invention according to claim 6 is a spin state separation method for separating carriers for each spin state taken by carriers propagating in a semiconductor, wherein the movable region with respect to one spatial dimension direction of the carrier is in the other two spatial dimension directions. Modulating the potential of the space containing the semiconductor channel by generating surface acoustic waves in a semiconductor channel in which carriers are confined in a two-dimensional region that is negligibly small compared to the movable region with respect to According to the method, carriers propagating in the semiconductor channel are generated, and a non-uniform magnetic field is applied to a region including at least a part of the semiconductor channel through which the generated carriers pass.

According to a seventh aspect of the present invention, in the sixth aspect of the invention, the spin state of carriers generated by propagating through the semiconductor channel is further detected.

  According to the present invention, the Stern-Gerlach effect is realized in a semiconductor by propagating through the semiconductor by combining the modulation of the potential of the space including the semiconductor and the application of a local inhomogeneous magnetic field to a predetermined region of the semiconductor. It is possible to obtain a spin deflection angle sufficient to separate different spin states of the carriers to be separated.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

<Basic matters>
First, basic matters that are preconditions for carrying out the present invention will be described. The basic matters described below are common to all embodiments of the present invention.

In III-V compound semiconductors such as GaAs, AlGaAs (aluminum gallium arsenide), InAs (indium arsenic), InP (indium phosphide), etc., surface acoustic waves (SAW: Surface) generated by the piezoelectric field effect caused by crystal distortion Acoustic Wave) modulates the potential of the space containing the semiconductor. As a result, in the semiconductor, electrons accumulate in the potential minimum portion of the conduction band, while holes are attracted to the potential maximum portion of the valence band. For this reason, the electron-hole pair excited by irradiating with light having appropriate energy is spatially separated. This spatial separation is expected to reduce the overlap of wave functions that give electron and hole quantum mechanical states, and to significantly increase the lifetime of electron-hole pairs. According to a recent report, the relaxation length of electron-hole pairs reaches several hundred μm (1 μm = 10 ⁻⁶ m) (C. Rocks, S. Zimmermann, A. Wixforth, JP Kotthaus, G. Bohm). , and G. Weimann, Phys. Rev. Lett. 78, 4099 (1997); F. Alsina, JAH Stotz, R. Hey, and PV Santos, submitted to Phys. Rev. Lett. (Aug. 2003)) .

  In addition, due to the spatial separation of electrons and holes due to the spatially modulated potential (SAW potential) generated by the generation of the surface acoustic wave described above, it is possible to irradiate circularly polarized light and to align the spin directions. It has been reported that the spin relaxation length is 10 times longer than usual (T. Sogawa, PV Santos, SK Zhang, S. Eshlaghi, AD Wieck, and KH Ploog, Phys. Rev. Lett. 87, 276601 ( 2001)).

  Although no experimental and theoretical clarification of spin relaxation during surface acoustic wave propagation has been made so far, the spin relaxation rate is predicted to increase with the power or the third power of electron energy (G. Fishman and G. Lampel, Phys. Rev. B16, 820 (1977)). In this sense, spin relaxation is greatly suppressed by the presence of the surface acoustic wave, and it can be expected to have a long spin relaxation length of several tens of μm or more at low energy.

By the way, the electron density can be lowered to about 4 × 10 ⁸ [cm ⁻³ ] using very weak excitation light. In the case where the semiconductor is GaAs, the carrier concentration (electron density) is very small as E _F = 0.014 [MeV = 10 ⁶ ev] in terms of Fermi energy. Normally, carriers do not propagate at such a low carrier concentration. However, it is known that when a SAW potential exists, carriers propagate through the semiconductor at the propagation speed of the SAW potential. The propagation speed v _SAW of this SAW potential is about 3000 [m / sec], which is significantly lower than the normal electron velocity. Therefore, when the SAW potential exists, it is possible to transport the semiconductor at a low carrier concentration.

As described above, carrier propagation by surface acoustic waves has the following characteristics compared to carrier propagation in a normal semiconductor:
・ The carrier relaxation length is as long as several hundreds of micrometers.
-The relaxation length of the spin is 10 times longer than that of a normal semiconductor.
-Carrier propagation speed is very slow, about 3000m / sec.
・ Transportation with low carrier concentration is possible.

  In an embodiment of the present invention described below, carrier propagation of surface acoustic waves having these characteristics is used.

<Device configuration of spin filter>
FIG. 1 is a block diagram showing an outline of a functional configuration of a spin filter according to an embodiment of the present invention. The spin filter 1 shown in FIG. 1 includes a semiconductor channel 3 that propagates carriers, a surface acoustic wave generator 5 as a spatial potential modulation unit that generates a surface acoustic wave in the semiconductor channel 3 to modulate a spatial potential, and a semiconductor channel. 3 includes a carrier generation unit 7 (carrier generation unit) that generates one or a plurality of carriers, and a non-uniform magnetic field application unit 9 (non-uniform magnetic field application unit) that generates a non-uniform magnetic field to be applied to the semiconductor channel 3. Have.

The semiconductor channel 3 has a two-dimensional region in which the movable region in one spatial dimension direction of the carrier is so small that it can be ignored as compared with the movable regions in the other two spatial dimension directions. The generated carriers behave as a two-dimensional electron gas in this region (hereinafter, this two-dimensional region is referred to as a “two-dimensional electron gas channel”). The two-dimensional electron gas channel confines carriers in a two-dimensional region by forming a semiconductor quantum well structure, for example. As is well known, such a semiconductor quantum well structure having a narrow width in the one-dimensional direction of space, for example, is formed by laminating both surfaces of a GaAs thin film with Al _0.3 Ga _0.7 As, or an In _0.53 Ga _0.47 As thin film. It is possible to configure such that both sides are laminated with InP. More generally, of course, the semiconductor channel 3 can be appropriately configured by using a semiconductor epitaxial growth technique or a fine processing technique. The validity of configuring such a semiconductor channel 3 will be described later together with a discussion of the possibility of verifying the Stern-Gerlach effect in the spin filter of this embodiment.

  The carrier generation unit 7 irradiates a predetermined region of the semiconductor channel 3 with light having energy larger than the band gap width. As a result, as described in the above <Basic matter>, the relaxation length is reduced. Extremely long carriers can be generated. In addition to the light source described above, means for injecting carriers into a predetermined region of the semiconductor channel 3 through the electrodes can be applied as the carrier generating unit 7.

  The non-uniform magnetic field applying unit 9 is configured using, for example, one or a plurality of ferromagnetic bodies 91. Needless to say, the non-uniform magnetic field application unit 9 is installed so as to apply a non-uniform magnetic field to a local region after carriers are generated in the semiconductor channel 3.

FIG. 2 is an explanatory diagram showing a more specific configuration example of the spin filter 1 according to the present embodiment. In the spin filter 11 shown in the figure, two comb-shaped electrodes 51 (IDT: also called InterDigital Transducer) are provided in the semiconductor channel 3 and an angular frequency ω _SAW is supplied from an AC power source 53 connected to the comb-shaped electrode 51. By applying an RF (Radio Frequency) signal, a surface acoustic wave having a wavelength λ _SAW is generated. Therefore, in the spin filter 11, the two comb electrodes 51 and the AC power supply 53 form the surface acoustic wave generating unit 5. The distance between the two comb electrodes 51 is designed to be λ _SAW / 2.

で与えられる（πは円周率）。例えば、キャリアが伝搬する二次元電子ガスチャネル３１としてＧａＡｓを用いる場合、ｖ_SAW＝２８６６[m/sec]とおくことができ、ω_SAW／２π＝５２０[MHz]とすると、λ_SAW＝５.５[μm]程度の波長を持つ表面弾性波が発生する。 The relationship between the wavelength λ _SAW of the surface acoustic wave generated by the comb-shaped electrode 51 and the angular frequency ω _SAW of the RF signal is that the velocity of the surface acoustic wave is v _SAW (the propagation direction is positive).

(Π is the pi). For example, when GaAs is used as the two-dimensional electron gas channel 31 through which the carrier propagates, v _SAW = 2866 [m / sec] can be set, and when ω _SAW / 2π = 520 [MHz], λ _SAW = 5. A surface acoustic wave having a wavelength of about 5 [μm] is generated.

Carriers carried by the surface acoustic wave through the two-dimensional electron gas channel 31 are generated in a predetermined region C closer to the comb-shaped electrode 51 than the ferromagnetic material 91 that generates a non-uniform magnetic field. FIG. 2 shows the case where the predetermined region C of the semiconductor channel 3 is irradiated with the light l ₀ to generate carriers (the carrier generator 7 itself is not shown). The energy of photons contained in the light l ₀ this is irradiated has a greater energy than the band gap of the semiconductor channel 3.

FIG. 3 is an arrow view showing the main part of the spin filter as viewed from the direction of arrow A in FIG. Region C shown by the broken line in FIG. 3, which is an irradiation region of the light l ₀ which is emitted from the carrier generating unit 7. As described above, the carrier may be injected through the electrode instead of irradiating the light l ₀ to generate the carrier.

  In the spin filter 11, the inhomogeneous magnetic field application unit 9 is configured using two ferromagnetic materials 91, but is not necessarily limited to this configuration. For example, one or a plurality of ferromagnetic materials 91 may be used, and more generally, any material that can apply a non-uniform magnetic field to the semiconductor channel 3 may be used.

  In addition to the above configuration, the spin filter 11 shown in FIGS. 2 and 3 further includes spin state detection means for detecting spin states separated by a non-uniform magnetic field. Carriers that pass through the inhomogeneous magnetic field are separated by the Stern-Gerlach effect, and carriers that take different spin states (upward and downward) are spatially separated and propagated. Branch waveguides 301 and 303 of the semiconductor channel 3 branching into a Y shape are provided so that the propagation direction can be detected. These branch waveguides 301 and 303 are made of the same semiconductor material as the semiconductor channel 3.

  The branching waveguides 301 and 303 are respectively provided with metal electrodes 311 and 313 that promote carrier recombination by shorting the SAW potential. Optical waveguides 321 and 323 are further connected to these metal electrodes 311 and 313, respectively, and can be detected as circularly polarized light by recombining spin-polarized electrons.

  In the case of the spin filter 11 shown in FIG. 2, spin state detection means including the branched waveguides 301 and 303, the metal electrodes 311 and 313, and the optical waveguides 321 and 323 are configured. The configuration of the spin state detection means is as follows. However, the present invention is not limited to this case. In other words, any configuration can be adopted as long as different spin states can be spatially separated and then the separated spin states can be locally measured along the y-axis direction in FIGS. Good. In this sense, the branching waveguides 301 and 303 are not essential. Further, it is not necessary to use the optical waveguides 321 and 323. For example, light may be detected from the side surfaces of the branching waveguides 301 and 303 (in this case, the metal electrodes 311 and 313 are also unnecessary).

で与えられる。 In the spin filter 11 described above, the conditions for separating 100% spin-polarized electrons are as follows: the spin deflection angle is φ _SG , the width of the semiconductor channel 3 (thickness in the y-axis direction) is W, and the electrons are inhomogeneous magnetic fields. When the distance in the x-axis direction affected by is L,

Given in.

ここで、ｓ_yはｙ方向のスピン固有値であり、±１／２のいずれかの値をとる。また、ｇはｇ因子、μ_Bはボーア磁子、Ｂ_yはｙ方向の磁場成分である。この式（２）からも明らかなように、エネルギーの空間勾配によって求められる力は、磁場の勾配によって存在するスピン上向き（ｓ_y＝１／２）と下向き（ｓ_y＝−１／２）の場合、それぞれ逆向きとなる。 In the spin filter 11, when the electrons in the semiconductor channel 3 pass through the magnetic field, the following energy is obtained by the Zeeman effect in the magnetic field.

Here, s _y is a spin eigenvalue in the y direction and takes any value of ± 1/2. Also, g is g-factor, mu _B is the Bohr magneton, B _y is the magnetic field component in the y-direction. As is clear from this equation (2), the force determined by the spatial gradient of energy is spin upward (s _y = 1/2) and downward (s _y = −1 / 2) that exist due to the gradient of the magnetic field. In each case, the directions are reversed.

ここで、Δｐ_yは電子のｙ軸方向の運動量変化、ｐ_xは電子のｘ軸方向の運動量成分、
Ｆ_yΔｔは電子がｙ軸方向に受ける力積（電子にｙ方向の力Ｆ_yが時間Δｔ＝Ｌ／ｖ_SAWだけ作用）、∂Ｂ_y／∂yはｙ軸方向の磁場の勾配の強さをそれぞれ表す。 Considering the effective mass m ^* of electrons in the semiconductor channel 3 and the electron propagation velocity v _SAW due to surface acoustic waves, the spin deflection angle φ _SG caused by this Stern-Gerlach effect is given by the following equation.

Here, Delta] p _y momentum change of the electron in the y-axis direction, p _x is the electron x-axis direction of the momentum components,
F _y Δt is the impulse that the electron receives in the y-axis direction (the force F _y in the y direction acts on the electron for the time Δt = L / v _SAW ), and ∂B _y / ∂y is the strength of the magnetic field gradient in the y-axis direction. Represents each.

This equation (3) shows that the spin deflection angle φ _SG increases as the surface acoustic wave velocity v _SAW decreases and the magnetic field gradient ∂B _y / ∂y increases.

Here, the strength of the magnetic field gradient of the inhomogeneous magnetic field generated using one or a plurality of ferromagnetic materials 91 is estimated, and it is examined whether or not a sufficient spin deflection angle φ _SG can be obtained in the semiconductor channel 3.

Saturation magnetization M _s of the ferromagnetic, ferromagnetic Then d _f a z-axis direction of the thickness of the Figure 2, the distance r field in remote locations B and (r) the field gradient dB (r) / dr is , Respectively (see M. Johnson, BR Bennet, MJ Yang, and BV Shanabrook, Appl, Phys. Lett. 71, 974 (1997)):

Here, permalloy (NiFe) is taken as an example of a ferromagnetic material, saturation magnetization M _s = 860 [emu / cm ³ = 4π × 10 ⁻⁴ T], thickness d _f = 250 [nm = 10 ⁻⁹ m], When the distance from the ferromagnet is r = 2.5 [μm] and the strength of the magnetic field gradient is estimated, it is 8.6 × 10 ⁴ [T / m]. Further, when calculated as r = 3.5 [μm], 4.4 × 10 ⁴ [T / m] is obtained as the strength of the magnetic field gradient.

Equations (4) and (5) are approximate equations assuming a point magnetic charge on the surface of the magnetic material, but are approximate equations sufficient for calculating an approximate magnetic field gradient. Assuming that the strength of the magnetic field gradient is 5 × 10 ⁴ [T / m]. In addition to this assumption, it is assumed that L = 2 [μm] and the two-dimensional electron gas channel 31 through which carriers propagate is GaAs. In this case, g = −0.44, m ^* = 0.067 × m (m = 9.1 × 10 ⁻³¹ [kg]: free electron mass), and the propagation velocity is approximately v _SAW = 3000 [m / sec], if these values are substituted into equation (3), φ _SG = 22 [deg] is obtained as an expected approximate spin deflection angle. In order for the spin deflection angle to satisfy the conditional expression (1), the width of the semiconductor channel 3 (thickness in the y-axis direction) may be set to W = 0.8 [μm]. It is easy with the current technology to set W to about 1 [μm]. In this sense, it can be seen that the spin filter 11 of this embodiment is a sufficiently realizable device.

  Note that the device length of the spin filter 11 must be longer than the spin relaxation length of the generated carriers, but when using surface acoustic waves as in the spin filter 11, as described above, a normal semiconductor is used. Since the spin relaxation time can be made 10 times longer than that of the device, a device having a size that can be sufficiently realized in this sense can be formed.

Incidentally, according to the method of Wroebel et al. (See Non-Patent Document 1), even if the Fermi energy is reduced to 1 [MeV] in order to reduce the electron velocity v _F , the electron velocity is still v _F = 73000 [m. / sec] is large, the spin deflection angle is only about φ _SG = 0.035 [deg], and it is extremely difficult to observe this in a spatially separated manner.

  Next, the possibility of measuring the Stern-Gerlach effect in this embodiment will be discussed.

を満たす。ここで簡単のため、図２の座標系において、磁場のｘ軸成分がゼロ（∂Ｂ_x／∂ｘ＝０）を仮定すると、ｙ軸方向の磁場勾配∂Ｂ_y／∂ｙがゼロでなければ、キャリアの伝搬方向に垂直なｚ軸方向にもゼロでない磁場勾配∂Ｂ_z／∂ｚ＝−（∂Ｂ_y／∂y）が存在する（この場合、ｚ方向の磁場成分の大きさ|∂Ｂ_z／∂ｚ|は最大となる）。 Stern-Gerlach's experiment was originally performed using silver (Ag) atoms with spin 1/2, but in the case of charged atoms or electrons, the Lorentz force due to the magnetic field must be considered. Therefore, it has been predicted that the Stern-Gerlach effect itself cannot be verified. The reason is as follows. According to electromagnetism, the magnetic field is generally

Meet. For simplicity, assuming that the x-axis component of the magnetic field is zero (∂B _x / ∂x = 0) in the coordinate system of FIG. 2, the magnetic field gradient ∂B _y / ∂y in the y-axis direction must be zero. For example, there is a non-zero magnetic field gradient ∂B _z / ∂z = − (∂B _y / ∂y) in the z-axis direction perpendicular to the carrier propagation direction (in this case, the magnitude of the magnetic field component in the z direction | ∂B _z / ∂z | is the maximum).

Due to the presence of the magnetic field gradient ∂B _z / ∂z in the z-axis direction, carriers are subjected to a force in the z direction, resulting in uncertainty in the spin deflection angle. That is, carriers with electric charges receive Lorentz force, which causes uncertainty in the spin deflection angle, which is an essential problem in observing the Stern-Gerlach effect.

  However, with the recent development of semiconductor epitaxial growth technology and microfabrication technology, it has been shown that the essential problems can be solved by confining carriers in a very narrow space such as a semiconductor quantum well (BM Garraway and S. Stenholm, Phys. Rev. A 90, 63 (1999)).

ここで、ｅは電気素量（１.６×１０^-19 [C]）であり、ΔＢ_z＝（∂Ｂ_y／∂ｙ）×ｄは磁場の不確定性を与えている。
この条件式（６）によれば、二次元電子ガスチャネル３１のｚ軸方向の厚さｄを小さくとってキャリアをｚ軸方向に閉じ込めることができれば、Stern-Gerlach効果が生じ、これによってキャリアの有するスピン状態の分離が可能となる。 The condition for observing the Stern-Gerlach effect is | Δφ _SG / φ _SG | <1, but this left side (the uncertainty of the spin deflection angle due to the Lorentz force) is the z direction of the two-dimensional electron gas channel 31. Where d is given by the following equation.

Here, e is the elementary electric charge (1.6 × 10 ⁻¹⁹ [C]), and ΔB _z = (∂B _y / ∂y) × d gives the uncertainty of the magnetic field.
According to this conditional expression (6), if the thickness d in the z-axis direction of the two-dimensional electron gas channel 31 is reduced and the carriers can be confined in the z-axis direction, the Stern-Gerlach effect is generated, thereby It is possible to separate spin states.

  Therefore, the case where GaAs is used as the two-dimensional electron gas channel 31 will be calculated. Substituting the g factor (−0.44) of GaAs into equation (6) yields d <4.5 [nm], and the two-dimensional electron gas channel 31 is formed using a semiconductor quantum well having such a thickness. It can be seen that the Stern-Gerlach effect can be observed.

Equation (6) shows that it is more preferable to use a semiconductor material having a large absolute value of g factor in order to reduce the uncertainty of the spin deflection angle. In fact, in the case of GaAs, since the absolute value of g factor is small as g = −0.44, it is necessary to limit the thickness d of the two-dimensional electron gas channel 31, but in In _0.53 Ga _0.47 As, the g factor is g. Since it is as large as −4, the conditional expression (6) is approximately d <45 [nm], and a semiconductor quantum well can be easily formed as compared with the case of GaAs.

Table 1 below shows the case where various semiconductor materials are applied as the two-dimensional electron gas channel 31, the g factor for each semiconductor material, the ratio m ^* / m of effective mass to free electron mass, the spin deflection angle φ _SG , And the uncertainty of the spin deflection angle (absolute value thereof) | Δφ _SG / φ _SG |.

In preparing Table 1, the surface acoustic wave velocity in a semiconductor other than Si (silicon) is set to v _SAW = 2866 [m / sec], while the surface acoustic wave velocity in Si is set to v _SAW = 5080 [m / sec].

The other physical quantities in the equation (6) were calculated as d = 3 [nm], L = 2 [μm], and ∂B _y / ∂y = 5 × 10 ⁴ [T / m].

  By the way, since a group IV semiconductor such as Si or Ge (germanium) does not cause a piezoelectric field effect, a surface acoustic wave cannot be generated as it is. Therefore, for example, if the surface of the semiconductor channel 3 is coated with a thin film capable of generating a piezoelectric field effect such as Si or ZnO (zinc oxide) on sapphire, it is possible to generate surface acoustic waves. In this case, the comb-shaped electrode 51 is provided on the thin film coated on the semiconductor, but the other configuration is the same as that shown in FIG.

  According to the embodiment of the present invention described above, a spin filter using the Stern-Gerlach effect is configured by combining a surface acoustic wave and a locally inhomogeneous magnetic field, and the spin state of carriers is separated by 100%. It becomes possible to do.

This is due to the following characteristics of the carrier carried by surface acoustic waves:
-The carrier propagation speed is as slow as about 3000 m / sec.
-Electron-hole pairs are transported over several hundred μm.
-Since electron kinetic energy can be reduced and transported, spin relaxation can be suppressed as compared with ordinary semiconductors.

  Such a spin filter can be realized by applying the current semiconductor epitaxial growth technology and microfabrication technology. That is, according to the present embodiment, it is possible to configure a spin filter that satisfies the conditions for verifying the Stern-Gerlach effect and can also satisfy the design conditions as a device of a realistic size.

Recently, a group III-V dilute semiconductor in which a part of a group III semiconductor (Al, Ga, In, etc.) is substituted with Mn (manganese) can be synthesized. In this case, carriers are holes, Spin relaxation was also fast due to the influence of spin-orbit interaction. Further, there is a problem that the ferromagnetic transition temperature (Curie temperature) T _C is 110 K, which is not more than room temperature. On the other hand, in this embodiment, since the spin relaxation becomes gentle as described above, it becomes possible to separate the 100% spin state even at room temperature.

  In the spin filter 11 described above, the case where the spin state detection means is added to the configuration of the spin filter 1 (see FIG. 1) has been described. It is also possible to use 100% spin-polarized electrons by connecting to other devices.

  As described above, the present invention can include various embodiments and the like without departing from the scope of the claims.

It is a block diagram which shows the function structure of the spin filter which concerns on one Embodiment of this invention. It is explanatory drawing which shows one specific structural example of the spin filter of FIG. It is an arrow line view which shows the spin filter principal part seen from the arrow A direction of FIG. It is explanatory drawing which shows the experiment of Stern-Gerlach conceptually.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 11 Spin filter 3 Semiconductor channel 5 Surface acoustic wave generation part 7 Carrier generation part 9 Inhomogeneous magnetic field application part 31 Two-dimensional electron gas channel 51 Comb electrode 53 AC power supply 91 Ferromagnetic material 301, 303 Branching waveguide 311, 313 Metal 313, 323 Optical waveguide

Claims (7)

A spin filter for separating carriers for each spin state taken by carriers propagating in a semiconductor,
A semiconductor channel in which carriers are confined in a two-dimensional region in which the movable region in one spatial dimension direction of the carrier is negligibly small compared to the movable regions in the other two spatial dimension directions;
Spatial potential modulation means for modulating the potential of the space containing the semiconductor channel by generating surface acoustic waves in the semiconductor channel;
Carrier generating means for generating carriers propagating in the semiconductor channel according to the potential modulated by the spatial potential modulating means;
A spin filter comprising: a non-uniform magnetic field applying unit that applies a non-uniform magnetic field to a region including at least a part of a semiconductor channel through which carriers generated by the carrier generating unit pass. The semiconductor channel spin filter according to claim 1, characterized in that it comprises confining the carriers in the semiconductor quantum well structure. The semiconductor channel, according to claim 1 or 2 spin filter according to characterized in that it is constructed using a group III-V compound semiconductor. The semiconductor channel, according to claim 1 or 2 spin filter, wherein the thin film having a piezoelectric field effect is constituted by using a Group IV semiconductor formed provided on the surface. The spin filter of any one of claims 1 to 4, further comprising a spin state detecting means for detecting the spin state of the carrier caused by propagating the semiconductor channel. A spin state separation method for separating carriers for each spin state taken by carriers propagating in a semiconductor,
A surface acoustic wave is generated in a semiconductor channel in which carriers are confined in a two-dimensional region in which the movable region in one spatial dimension direction of the carrier is negligibly small compared to the movable regions in the other two spatial dimension directions . To modulate the potential of the space containing the semiconductor channel ,
Generate carriers that propagate in the semiconductor channel according to the modulated potential,
A spin state separation method comprising applying a non-uniform magnetic field to a region including at least a part of a semiconductor channel through which the generated carriers pass. The spin state separation method according to claim 6 , further comprising detecting a spin state of carriers generated by propagating through the semiconductor channel.

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