JP3070070B2 - Polarized electron beam generator - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization method for generating a polarized electron beam comprising a group of electrons whose spin directions are localized in one of two types by receiving light energy. The present invention relates to an electron beam generating element.

2. Description of the Related Art A polarized electron beam composed of an electron group in which the spin direction is unevenly distributed in one of two types is used for investigating a magnetic structure inside a nucleus and a magnetic structure on a material surface in a high energy elementary particle experiment. Has been used as an effective means. In generating such a polarized electron beam, for example, a crystal surface of a compound semiconductor such as a gallium-arsenic system is irradiated with a circularly polarized laser, and the spin direction is biased in one direction due to a selective transition accompanying conservation of angular momentum. It is common practice to extract polarized electron beams.

Problems to be Solved by the Invention By the way, according to the conventional polarized electron beam generating element as described above, the degree of polarization of the generated polarized electron beam is theoretically 50%, that is, the upspin and downspin. The ratio was estimated to be the maximum at 1: 3 or 3: 1, and an electron beam with a sufficiently high degree of polarization could not be obtained.

On the other hand, it is conceivable to use a polarized electron beam generating element in which a unidirectional anisotropy is given to the valence band by applying a stress in a certain direction to the semiconductor crystal. However, it is difficult to obtain strain and stably apply strain, and there is a problem that a device for applying strain stress from the outside hinders extraction of electrons.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a polarized electron beam generating element capable of stably and easily obtaining an electron beam having a sufficiently high degree of polarization. To provide.

Means for Solving the Problems The gist of the present invention for achieving the above object is that a polarized electron beam composed of a group of electrons whose spin directions are unevenly distributed in one of two types is converted into light energy. A polarized electron beam generating element that generates compound electrons by receiving the compound semiconductor layers having mutually different lattice constants and being hetero-bonded to each other with a lattice strain of about 0.1% or more.

In this way, the lattice constants are different from each other and 0.1
% Or more due to hetero-bonding between the compound semiconductor layers accompanied by lattice distortion, which causes band splitting of the valence band. Therefore, when energy is injected by receiving light such as laser light, Since the electron group unevenly distributed in one spin direction is exclusively excited and emitted, an electron beam having a sufficiently high degree of polarization can be obtained. Further, as described above, due to the hetero bond between the compound semiconductor layers having different lattice constants and having a lattice strain of about 0.1% or more,
Since the strain is stably applied from the inside, a polarized electron beam having a stable degree of polarization can be easily obtained without being disturbed by the external strain applying device.

Embodiment Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

In FIG. 1, a polarized electron beam generating element 10 includes a first compound semiconductor layer 14 and a second compound semiconductor layer 16 sequentially grown on a semiconductor substrate 12 by a well-known MOCVD crystal growth method. I have. An oxidation treatment film (not shown) is formed on the surface of the second compound semiconductor layer 16 using H ₂ O ₂ .

The semiconductor substrate 12 has a thickness of about 350 μm,
For example, gallium-arsenic p having a carrier concentration of about 5 × 10 ¹⁸ by doping zinc Zn as an impurity.
It is a type semiconductor single crystal plate (P-GaAs). In addition, the first
The compound semiconductor layer 14 has a thickness of about 2 μm. For example, an indium-gallium-phosphorous p-type semiconductor single crystal layer (P-type) having a carrier concentration of about 5 × 10 ¹⁸ by doping zinc Zn as an impurity. Ga _0.5 In _0.5 P).
The second compound semiconductor layer 16 has a thickness of about 0.05 μm, and has a carrier concentration of about 5 × 10 ¹⁸ by doping zinc Zn as an impurity, for example, to form a gallium-arsenic p-type semiconductor single crystal. Layer (P-GaAs). Therefore, the first compound semiconductor layer 14 and the second compound semiconductor layer 16
A hetero bond with a lattice strain of about 0.1% is formed between the two due to the difference in the lattice constant.

The polarized electron beam generator 10 configured as described above is provided, for example, in a polarized electron beam generator (electron gun) 20 shown in FIG. In FIG. 2, in addition to the polarized electron beam generator 20, a polarization ratio measuring device 22 for measuring the polarization of electrons contained in an electron beam generated therefrom is shown.
And a knitted pole electron transfer device 24 for transferring the polarized electron beam generated from the polarized electron beam generator 20 to the polarization rate measuring device 22.

The polarized electron beam generator 20 includes a vacuum housing 30 for forming a high vacuum chamber, a turbo molecular pump 32 and an ion pump 34 for setting the vacuum housing 30 to a high vacuum of about 10 ⁻⁹ torr, Vacuum housing 30 for electron beam generator 10
And a liquid nitrogen container 38 surrounding the container holder 36 for adsorbing residual gas, and electrons from the surface of the polarized electron beam generating element 10. Multiple electrodes 40 for extraction
And a cesium emitter 42 and an oxygen emitter that emit cesium and oxygen toward the surface of the polarized electron beam generator 10.
44, and a laser light irradiation device 46 for irradiating the surface of the polarized electron beam generating element 10 with laser light.

The laser light irradiation device 46 includes a tunable laser light source 50 that selectively outputs laser light having a wavelength of 700 to 850 nm, a polarizer 52 that passes only linearly polarized light, and a quarter that converts linearly polarized light to circularly polarized light. A wavelength element 54 and a mirror 56 for irradiating circularly polarized laser light toward the surface of the polarized electron beam generating element 10.
And

The polarimeter 22 is a tank filled with Freon gas.
A high-pressure tank (Mott scattering tank) 64, which is arranged in the chamber 60 and is supported by the high-voltage insulator 62 and to which 100 kV is applied from the anode 63, and is connected to the high-pressure tank 64 and has a high vacuum of about ^10-6 A turbo molecular pump 66, an accelerating electrode 68 for accelerating the polarized electron beam, a gold foil 70 supported by a disc (not shown) and collided with the polarized electron beam, and colliding with gold nuclei in the gold foil 70. A pair of surface barrier type detectors 72 for detecting electrons scattered by θ = 120 °, and a surface barrier type detector 72 amplified by a preamplifier (not shown).
An LED 74 that converts a signal from the LED 74 into light, and a light receiver 76 that receives the light output of the LED 74 and converts it into an electric signal.

FIG. 3 shows an example of a circuit for calculating the degree of polarization based on two-channel signals from the surface barrier type detector 72. In the figure, a signal from the surface barrier type detector 72 is amplified by a preamplifier 84 and then converted into an optical signal by an LED 74, respectively. The optical receiver 76 receives the optical signal, converts it into an electric signal, and supplies it to the arithmetic and control circuit 80 via the interface 78. The arithmetic control circuit 80 calculates the degree of polarization of the electron group included in the polarized electron beam based on the input signal from an arithmetic expression stored in advance and causes the display 82 to display the calculated degree.

Returning to FIG. 2, the polarized electron transfer device 24 is sandwiched between a pair of small conductance tubes 90 provided in a conduit connecting the vacuum housing 30 and the high-pressure tank 64 and having a low conductance, and a pair of conductance tubes 90. Pump installed at a different position
92 and a spherical capacitor device 94 for electrostatically bending the polarized electron beam extracted from the polarized electron beam generating element 10 at a right angle.
And a Helmholtz coil 96 for magnetically bending the polarized electron beam toward the high-pressure tank 64 at a right angle.
If the vacuum housing 30 and the high-pressure tank 64 are in a relative positional relationship that does not require bending the polarized electron beam, the spherical capacitor device 94 and the Helmholtz coil 96 become unnecessary.

When a polarized electron beam is generated in the above apparatus, the polarized electron beam generating element 0 is first fixed to the lower end of the container holder 36, and then the inside of the vacuum housing 30 is set to a high vacuum of about 10 ^-9. By heating to a temperature of about 600 ° C. for about 15 minutes with a heater, the oxide on the surface of the polarized electron beam generating element 10 is removed and cleaned. Then the cesium emitter
Cesium and oxygen are alternately emitted from 42 and the oxygen emitter 44 toward the surface of the polarized electron beam generating element 10 to adsorb only a small amount of cesium and oxygen. Thereby, electron affinity (an energy gap corresponding to the difference between the energy level of electrons at the bottom of the conduction band and the vacuum level) on the surface of the polarized electron beam generating element 10 is made negative.
Then, the polarized electron beam generating element 10 is
After cooling to ゜ K, the laser light irradiation device 46 irradiates circularly polarized laser light. When the energy of the circularly polarized laser light is injected, a group of electrons having a high degree of polarization is generated from the surface of the polarized electron beam generating element 10, and the group of electrons is extracted by the electrode 40 as a polarized electron beam. The polarized electron beam is applied to the gold foil 70 in the high-pressure tank 64 by the polarized electron transfer device 24.
And the polarization rate is measured by the circuit shown in FIG.

According to experiments performed by the present inventors, it has been found that a conventionally used polarized electron beam generating element (P-GaAs on a P-GaAs substrate) is used.
The growth rate of the tank: equivalent to that of the polarized electron beam generating element 10 from which the first compound semiconductor tank 14 has been removed) is "43".
On the other hand, in the polarized electron beam generator 10 configured as described above, a polarization ratio of “68” was obtained.

As described above, according to the polarized electron beam generating device 10 of the present embodiment, the difference in lattice constant between the first compound semiconductor layer 14 and the second compound semiconductor layer 16 is about 0.1%. Since the hetero bond with distortion is formed, band splitting of the valence band is generated,
When the degeneracy of the valence band of the first compound semiconductor layer 14 is released, an electron group having a relatively uniform spin direction is generated.

Further, according to the polarized electron beam generating element 10 of the present embodiment, the heterojunction between the first compound semiconductor layer 14 and the second compound semiconductor tank 16 having mutually different lattice constants allows stable distortion from the inside. Is given, so that a polarized electron beam having a stable degree of polarization can be easily obtained without being hindered by an external strain applying device.

Here, in the polarized electron beam generating element 10, the first
Strain was internally generated due to the hetero bond between the two layers of the compound semiconductor layer 14 and the second compound semiconductor tank 16,
The difference in lattice constant between three or more layers may be used.

Further, in the polarized electron beam generator 10, the first compound semiconductor layer 14 is made of Ga _0.5 In _0.5 P and the second compound semiconductor bath 16 is made of GaAs.
Other types of compound semiconductors such as a Ga _1-x Al _x As system, a Ga _x In _1-x As _{1-y Py} system, and an In _1-xy Ga _x Al _y P system can be used as needed. In short, the first compound semiconductor layer 14 and the second compound semiconductor bath 16 only need to have different lattice constants and be hetero-coupled with a lattice strain of about 0.1% or more.

The above is merely an example of the present invention, and the present invention can be variously modified without departing from the gist thereof.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view illustrating the configuration of a polarized electron beam generating element according to one embodiment of the present invention. FIG. 2 is a diagram showing a polarized electron beam generator and a polarization rate measuring device provided with the polarized electron beam generator of FIG. FIG. 3 is a diagram showing a measuring circuit of the polarization rate measuring device of FIG. 10: polarized electron beam generator 14: first compound semiconductor layer 16: second compound semiconductor layer

──────────────────────────────────────────────────続 き Continued on the front page (56) References Maruyama et al. , "Enhanced Electron Spin-Polarizion in Photomission from Thin GaAs", SLAC-PUB-4779, July 1989 (58) Fields studied (Int. Cl. ⁷ , DB name) File (JOIS)

Claims (1)

(57) [Claims] 1. A polarized electron beam generating element for generating a polarized electron beam composed of a group of electrons whose spin directions are localized in one of two types by receiving light energy, wherein the polarized electron beams are different from each other. 1. A polarized electron beam generator comprising a compound semiconductor layer having a lattice constant and hetero-bonded to each other with a lattice strain of about 0.1% or more.