JPH07320634A - Polarized electron beam generating apparatus - Google Patents

Abstract

PURPOSE:To compose a polarized electron beam generating apparatus by which stable quantum efficiency can be obtained from a polarized electron beam generating element for a long duration. CONSTITUTION:In a polarized electron beam generating apparatus, the quantity of polarized electron beam to be emitted is measured by a monitor 90 and the incidence angle theta of excited laser beam 20 against a polarized electron beam generating element 10 is so controlled automatically by a controlling apparatus 70 as to make the measured quantity of the polarized electron beam generating element 10 become the same as an aiming value. Consequently, even in the case the surface condition of the polarized electron beam generating element 10 is deteriorated during emission of polarized electron beam, almost the same quantity of polarized electron beam can be obtained and thus stable quantum efficiency can be kept for a long duration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a polarized electron beam generator for generating a polarized electron beam whose spin directions are unevenly distributed.

[0002]

2. Description of the Related Art A polarized electron beam composed of an electron group whose spin directions are unevenly distributed in one of two types is used, for example, in the field of high energy elementary particles to study the magnetic structure inside the nucleus and in the field of condensed matter physics. Is used as an effective means for investigating the magnetic structure of the material surface. Such a polarized electron beam can be extracted by irradiating a polarized electron beam generating element having a semiconductor photoelectric layer having band splitting in the valence band with excitation light by a polarized electron beam generator. According to such a polarized electron beam generating element, an energy level difference is generated between the heavy-hole subband and the light-hole subband in the valence band, while the spin directions of the electrons extracted by the excitation of both subbands are Since they are in opposite directions, if light energy that excites only the subband with a higher energy level, that is, the one with a smaller energy gap with the conduction band, is injected into the semiconductor photoelectric layer, it is localized in one spin direction. The electron group is exclusively excited and emitted to obtain a polarized electron beam.

As the above polarized electron beam generating element, for example, a GaAsP semiconductor having a bandgap rather than that disclosed in Japanese Patent Application Laid-Open No. 4-329235 previously filed by the present applicant. There is a strained GaAs semiconductor obtained by crystal growth of a GaAs semiconductor having a small lattice constant and a slightly different lattice constant as a semiconductor photoelectric layer. According to this, G having a lattice constant different from that of GaAsP semiconductor
When the aAs semiconductor is hetero-coupled, lattice distortion is imparted to the GaAs semiconductor, so that band splitting occurs in its valence band. In addition, for example, a superlattice in which two kinds of semiconductor thin films having different band gaps (for example, GaAs and Al _0.35 Ga _0.65 As) are alternately laminated, in particular, the band gap of one semiconductor thin film is between the band gap of the other semiconductor thin film. There is also a polarized electron beam generating element in which a semiconductor photoelectric layer is formed by a so-called quantum well that is adapted to enter. According to such a structure, sub-bands are formed in the valence band and the conduction band by the tunnel effect in the layer functioning as the well layer (GaAs when the above-mentioned two types of semiconductor thin films are used), so that the strained Band splitting occurs in the valence band without imparting lattice distortion due to lattice mismatch to the semiconductor photoelectric layer like a semiconductor.

[0004]

By the way, when the polarized electron beam generating element as described above is used, oxygen and cesium are attached for the purpose of facilitating extraction of the polarized electron beam (that is, obtaining high quantum efficiency). As a result, the surface is brought into the NEA (Negative Electron Affinity) state, but it is known that the quantum efficiency gradually decreases when the polarized electron beam is taken out for a long time. It is considered that this is because the surface condition of the polarized electron beam generating element is deteriorated (for example, the amount of cesium attached to the surface is reduced by evaporation, or the surface is contaminated). Since the polarized electron dose is proportional to the product of the quantum efficiency and the irradiation dose of the excitation light, it can be reduced with the decrease in the quantum efficiency, but in the experiment using the polarized electron beam as described above, It is required that the polar electron dose be stable for a long time. Therefore, conventionally, for example, to increase the intensity of the excitation light according to the decrease of the quantum efficiency, or irradiating the polarized electron beam generating element through the slit with the excitation light, the slit according to the decrease of the quantum efficiency. The polarized electron dose was stabilized by widening the diaphragm to increase the irradiation area.

However, the former method requires a large-scale control circuit to control the intensity of the excitation light, and the intensity control changes the injection current when a semiconductor laser is used as the excitation light. Therefore, there is a problem in that the wavelength of the excitation light changes due to fluctuations in the oscillation conditions. That is, the optical resonator length of the laser is L,
The refractive index of the optical resonator is n _r , and the wavelength of the laser in vacuum is λ ₀
Then, the optical resonance condition of the laser is m (λ ₀ / n _r ) =
The wavelength given by 2L and satisfying this equation is the oscillation wavelength of the laser. However, in the optical resonator, the refractive index n _r is slightly increased due to the temperature increase due to the increase of the injection current, that is, the increase of the carrier density. Therefore, when the intensity of the excitation light is increased, the wavelength satisfying the above formula, that is, the excitation The wavelength of light slightly changes to the long wavelength side. This means that a polarized electron beam generating element having an optical resonator structure for increasing the absorption amount of excitation light by a semiconductor photoelectric layer and improving quantum efficiency (e.g.
Proposed in No. 280822, a reflective layer forming an optical resonator for resonating excitation light with the surface of a second semiconductor (that is, a semiconductor photoelectric layer) is provided on the back side of the second semiconductor to generate a polarized electron beam. In devices, etc.), the wavelength of the excitation light deviates from the resonance wavelength, which is a big problem. On the other hand, the latter method requires a large-area and uniform polarized electron beam generating element, and only a part of the excitation light is actually irradiated to the polarized electron beam generating element, which is a strong method. There is a problem that a laser light source is required and the efficiency is low.

The present invention has been made in view of the above circumstances, and an object of the present invention is to obtain a polarized electron beam from a polarized electron beam generating element capable of obtaining a stable polarized electron dose for a long time. Providing a generator.

[0007]

In order to achieve such an object, the gist of the present invention is to provide a semiconductor photoelectric layer having band splitting in the valence band and a semiconductor photoelectric layer provided on the back side of the semiconductor photoelectric layer, Irradiating the excitation light to a polarized electron beam generating element provided with a reflection layer that constitutes an optical resonator that resonates the excitation light with which the semiconductor photoelectric layer is irradiated with the surface of the semiconductor photoelectric layer. A polarized electron beam generator for extracting a polarized electron beam in which the spin direction is unevenly distributed from the surface of the semiconductor photoelectric layer by (a) a measuring device for measuring the extracted polarized electron dose, b) incident angle control means for automatically controlling the incident angle of the excitation light to the polarized electron beam generating element so that the measured polarized electron dose and a predetermined target value match. Has been prepared.

[0008]

In this way, in the polarized electron beam generator for extracting the polarized electron beam from the polarized electron beam generating element having the optical resonator structure, the amount of the polarized electron beam extracted can be measured. The angle of incidence of the excitation light on the polarized electron beam generating element is automatically controlled so that the measured polarized electron dose coincides with a predetermined target value. Therefore, similar quantum efficiency can be obtained even when the surface condition of the polarized electron beam generating element deteriorates during extraction of the polarized electron beam, and a stable polarized electron dose can be obtained for a long time.

That is, the quantum efficiency of the polarized electron beam generating device having the optical resonator structure is highest when the resonance wavelength of the optical resonator and the wavelength of the excitation light coincide with each other. It decreases as the difference between and increases. on the other hand,
Since the optical path of the optical resonator is changed by inclining the incident angle of the excitation light, the optical resonator length, that is, the resonance wavelength is changed according to the incident angle. for that reason,
If the above-mentioned target value is set to a value smaller than the maximum polarized electron dose (that is, the value obtained by the incident angle at which the wavelength of the excitation light and the resonance wavelength match), the measured polarized electron dose will decrease. In this case, the incident angle control means changes the incident angle of the excitation light to bring the resonance wavelength closer to the wavelength of the excitation light to increase the quantum efficiency, and conversely, the polarized electron dose measured for some reason. When is increased, the incident angle is changed so that the difference between the wavelength of the excitation light and the resonance wavelength is increased, the quantum efficiency is reduced, and in any case, a stable polarized electron dose is obtained. .

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows a main configuration of a polarized electron beam generating element 10 used in a polarized electron beam generator 24 of one embodiment of the present invention. In the figure, a polarized electron beam generating element 10 includes a substrate 12 and a semiconductor multilayer film reflection layer 14 which is sequentially crystal-grown on the substrate 12 by a well-known MOCVD (metal organic chemical vapor deposition) apparatus. A first semiconductor 16 and a second semiconductor 18 are provided.

The substrate 12 has a thickness of about 350 μm.
Therefore, since Zn is doped as an impurity,
Rear concentration is 5 × 10¹⁸(Cm^-3) P-Ga
As, and the surface is the (100) plane. Also, the above half
The conductor multilayer reflective layer 14 is made of p-Al having a thickness of 63 nm.
_0.6 Ga_0.4 As and p-Al with a thickness of 58 nm_0.15Ga
_0.85Alternate 30 with As so that the former is on the substrate 12 side.
Circularly polarized pump laser with wavelength λ
Equipped with a reflection characteristic with a sufficiently wide bandwidth for the light 20
I am. Zn is impure in these two types of semiconductors.
Carrier concentration is 5 × 1
0¹⁸(Cm^-3) It is said to be about. In addition, semiconductor multilayer film
The film thickness of the two types of semiconductors of the reflective layer 14 is different from the refractive index thereof.
It is determined according to the wavelength of the light to be emitted.

The first semiconductor 16 has a thickness of 2000n.
with a thickness of about m, Zn as an impurity
Carrier concentration of 5 × 10
¹⁸(Cm ^-3) P-GaAs_0.74P_0.26And
It The second semiconductor 18 has a thickness of about 180 nm.
And is doped with Zn as an impurity.
Carrier concentration is 5 × 10¹⁸(Cm^-3)
P-GaAs which is determined_{0. 87}P_0.13Is. Note that FIG.
The thickness of each semiconductor in
Not a thing.

Since the lattice constant of the second semiconductor 18 is larger than that of the first semiconductor 16, the second semiconductor 18 is hetero-coupled on the first semiconductor 16 under the condition that the second semiconductor 18 has a lattice strain due to a two-dimensional compressive stress. To be Due to this lattice distortion, band splitting occurs in the valence band of the second semiconductor 18, causing an energy level difference between the heavy hole subband and the light hole subband, while the electrons extracted by the excitation of both subbands. Have opposite spin directions to each other, so that when the light energy (excitation laser light) 20 that excites only the higher energy level, that is, the heavy-hole subband is incident on the surface 22 of the second semiconductor 18, The electron group unevenly distributed in the spin direction is excited and emitted from the surface 22 thereof. That is,
In this embodiment, the second semiconductor 18 corresponds to a semiconductor photoelectric layer. The difference in lattice constant between the two semiconductors 16 and 18, that is, the mixed crystal ratio of P (phosphorus), is determined so that the energy level difference is larger than the thermal noise. No oxidation protection film or the like is provided on the surface 22 of the second semiconductor 18.

FIG. 2 is a diagram showing the construction of a polarized electron beam generator 24 for taking out a polarized electron beam from the polarized electron beam generating element 10 constructed as described above. The polarized electron beam generator 24 includes a vacuum housing 26 for forming a high vacuum chamber, a turbo molecular pump 28 and an ion pump 30 for maintaining the vacuum housing 26 in a high vacuum of about 10 ⁻¹⁰ torr, and a polarized gas. The polar electron beam generating element 10 is held in the vacuum housing 26 and its polarized electron beam generating element 10 is held.
A sample holder 34 rotatably mounted in the housing 32, a motor 36 for rotating the sample holder 34, and a plurality of electrodes for extracting electrons from the surface 22 of the polarized electron beam generating element 10. 38, a cesium emitter 40 and an oxygen emitter 42 that emit cesium and oxygen toward the surface 22 of the polarized electron beam generating element 10, and the surface 22 of the polarized electron beam generating element 10 are irradiated with laser light. And a laser beam irradiation device 44 for The laser light irradiation device 44 includes, for example, a laser light source 46 that outputs laser light having a wavelength of 810 nm, a polarizer 48 that passes only linearly polarized light, and a quarter that converts linearly polarized light into circularly polarized light.
A wavelength element 50 and a mirror 52 for irradiating the surface 22 of the polarized electron beam generating element 10 with circularly polarized laser light are provided.

The sample holder 34 is constructed by screwing a bottomed cylindrical sample holding member 56 to a rotating member 54, as shown in detail in FIG. A counterbore 58 is provided on the bottom surface of the sample holding member 56 facing the inside of the vacuum housing 26 to accommodate the polarized electron beam generating element 10. The polarized electron beam generating element 10 has its peripheral edge. It is fixed in the counterbore portion 58 by a holding plate 60 that holds the portion and a cap 62 that holds the holding plate 60 and that is screwed to the sample holding member 56 and has an L-shaped cross section.
Further, inside the sample holding member 56, a heater 64 for heating the polarized electron beam generating element 10 housed in the spot facing portion 58 is provided. The rotating member 54 is the motor 3
A worm wheel 68 that meshes with a worm 66 that is rotated by 6 is provided. By the rotation of the worm 66, the worm 66 rotates about an axis perpendicular to the plane of the drawing around the center of the surface 22 of the polarized electron beam generating element 10. Made, Figure 1
The incident angle θ of the excitation laser light 20 at is changed.
The rotation of the motor 36 is controlled by the control device 70. 2 and 3 show the state in which the rotating member 54 is in the non-rotating position, and the excitation laser beam 20 is incident on the surface 22 of the polarized electron beam generating element 10 in a direction perpendicular to the surface 22. Therefore, the incident angle θ = 0.

The housing 32 is a vacuum housing 2.
6 is fixed to an intermediate member 76 fixed by screws 72 and nuts 74. The vacuum housing 26 and the intermediate member 76 are provided with circumferential projecting portions 78, 80 on the inner circumferential side at the ends facing each other. A metallic bellows 82 is attached to an end portion on the inner circumferential side of the circumferential projection 80 of the intermediate member 76, and the bellows 82 is a disc-shaped member having the sample holding member 56 fitted in the central portion thereof. It is connected to 84.
A metal packing 86 is provided between the vacuum housing 26 and the intermediate member 76, and the circumferential protrusion 8 is provided.
0, the bellows 82, and the disc-shaped member 84 are welded to each other, so that the inside of the vacuum housing 26 is maintained at an ultrahigh vacuum.

When a polarized electron beam is generated in the above apparatus, since no oxidation protection film is provided on the surface 22 of the polarized electron beam generating element 10, the polarized electron beam stored in a vacuum desiccator immediately after growth is maintained. The polar electron beam generating element 10 is used. First, the polarized electron beam generating element 10 is attached to the sample holding member 5
After fixing to the counterbore 58 of 6, the inside of the vacuum housing 26 is set to a high vacuum of about 10 ^-10 torr, and the heater 64
The surface 22 of the polarized electron beam generating element 10 is cleaned by heating to a temperature of about 20 ° C. for about 15 minutes. Then, cesium and oxygen are alternately emitted from the cesium emitter 40 and the oxygen emitter 42 toward the surface 22 of the polarized electron beam generating element 10 to adsorb a small amount of cesium and oxygen. As a result, the electron affinity (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 22 of the polarized electron beam generating element 10 becomes negative (that is, the NEA state). Then, at room temperature, the laser light irradiation device 4
Circularly polarized laser light 20 is irradiated from 4 as excitation light. When the energy of the circularly polarized laser light 20 is injected into the second semiconductor 18 of the polarized electron beam generating element 10, an electron group in which the spin direction is unevenly distributed from the surface 22 of the polarized electron beam generating element 10 to one side. The generated electron group is extracted by the electrode 38 as a polarized electron beam. This polarized electron beam is electrostatically bent at a right angle by the spherical condenser device 88 and taken out in the direction of the arrow in the figure.

The extracted polarized electron beam is detected as a current by the monitor 90, and the control device 70 controls the rotation of the motor 36 based on the current value signal obtained by the monitor 90. That is, the rotation of the motor 36 is started at the same time when the irradiation of the circularly polarized laser light 20 is started,
By rotating the sample holder 34, the polarized electron beam generating element 10 is tilted with respect to the axis of the vacuum housing 26, and the incident angle θ of the circularly polarized laser light 20 on the surface 22 thereof.
The polarized electron dose is measured by the monitor 90 while changing. Then, the motor 36 is held in a state where a predetermined current value, that is, the polarized electron dose is detected, that is, the sample holder 34 is held at the rotation angle, and the polarized electron beam is taken out. An experiment using a polarized electron beam is performed in this state. Further, the detection by the monitor 90 is continued during this experiment, and the rotation of the motor 36 is controlled so that the polarized electron beam of a constant value is always taken out. It

FIG. 4 is a view for explaining the rotation control by the control device 70, that is, the control function of the incident angle θ. Set the target current value I ₀ by the target value setting unit 92, the comparison unit 94 corresponding to the comparison means, current values I detected by the monitor 90 is compared with the set current value I ₀ and the difference [Delta] I (= I _0- I) is calculated. Based on this difference ΔI, the control unit 96 corresponding to the control means has the following control equation.
The angle operation amount Δθ is calculated according to (1), the motor 36 is rotated, and the incident angle θ of the excitation laser light 20 is changed. As a result, the difference ΔI and the angle operation amount Δθ are calculated again based on the current value I detected by the monitor 90, and the motor 36 is rotated until the angle operation amount Δθ becomes 0, that is, the difference ΔI becomes 0. The detected current value I is made to match the set current value I ₀ by the PID control. In this embodiment, the motor 36,
The rotating member 54 and the worm 66 correspond to the incident angle changing means, the control device 70 corresponds to the incident angle control means, and the monitor 90 corresponds to the measuring device.

[0020]

[Equation 1]

Here, the polarized electron beam generator 2 of this embodiment is used.
4, the polarized electron dose extracted as described above is measured by the monitor 90, and the polarized electron beam generating element 10
The incident angle θ of the excitation laser beam 20 to the is automatically controlled so that the measured polarized electron dose coincides with a predetermined target value. Therefore, similar quantum efficiency can be obtained even when the state of the surface 22 of the polarized electron beam generating element 10 deteriorates during extraction of the polarized electron beam, and a stable polarized electron dose can be obtained for a long time. To be

That is, since the polarized electron beam generating element 10 includes the semiconductor multilayer reflection layer 14 on the substrate 12,
The excitation laser light 20 incident from the surface 22 is reflected by the semiconductor multilayer film reflection layer 14, and the light from the inside is also reflected by the surface 22 of the second semiconductor 18 at a reflectance of about 30%, so that the second semiconductor 18 is reflected. An optical resonator that resonates the pump laser light 20 is formed between the and the semiconductor multilayer film reflective layer 14. Excitation laser beam 2 that can be resonated in this optical resonator
The resonance wavelength of 0 is determined by the thickness and refractive index of the second semiconductor 18 and the first semiconductor 16, and the thickness and refractive index of each layer of the semiconductor multilayer reflective layer 14. When the light having the resonance wavelength is reflected by the surface 22 of the second semiconductor 18 constituting the optical resonator and the semiconductor multilayer film reflective layer 14 and returns, the light has the same phase and resonates to cause the second semiconductor 18 to resonate. The second semiconductor 1 is repeatedly passed.
The amount of light energy absorbed by 8 increases and the quantum efficiency improves.

Therefore, as represented by ● in FIG.
A peak of quantum efficiency will be formed at a position where the wavelength λ ₀ of the excitation laser light 20 matches the above-mentioned resonance wavelength (about 810, 830, 860 nm in this embodiment).
In the figure, ◯ represents the quantum efficiency of the conventional polarized electron beam generating element that does not include the semiconductor multilayer film reflective layer 14. Further, in the above resonance, it is necessary to consider the change of the phase with the progress of light, the change of the phase in the semiconductor multilayer reflection layer 14, and the change of the phase on the surface 22 of the second semiconductor 18. . Therefore, the quantum efficiency of the polarized electron beam generating element 10 having the optical resonator structure is highest when the resonance wavelength of the optical resonator and the wavelength λ ₀ of the pump laser light 20 match, and the wavelength of the pump laser light 20 is the highest. It decreases as the difference between λ ₀ and the resonance wavelength increases.

On the other hand, the optical path of the optical resonator is the excitation laser light 20.
The optical resonator length, that is, the resonance wavelength, is changed according to the incident angle θ because the incident angle θ is changed. FIG. 6 is a diagram showing a curve by extracting only the vicinity of the above resonance wavelength from FIG. 5, and a quantum corresponding to the incident angle θ = θ ₀ when the wavelength λ ₀ of the pump laser light 20 matches the resonance wavelength. The efficiency distribution is a solid line, θ =
The distribution corresponding to θ ₁ (<θ ₀ ) is a broken line, and θ = θ ₂ (>
The distributions corresponding to θ ₀ ) are indicated by the alternate long and short dash lines. Since the optical path of the optical resonator becomes shorter as the incident angle θ becomes smaller, the resonance wavelength shifts to the shorter wavelength side as indicated by the broken line, and conversely, as the incident angle θ becomes larger, the optical path becomes longer. It shifts to the long wavelength side as described above. The wavelength of the pump laser light 20 is λ _0.
The quantum efficiency at the time is a value indicated by the intersection of the vertical line on the horizontal axis passing through λ ₀ and the distribution curve, and is E ₀ when θ = θ ₂ , for example.

The above quantum efficiency E₀Is a polarized electron beam generator
It is not the maximum quantum efficiency obtained by 10.
If the value is sufficient to
Set as quantum efficiency (that is, target value of polarized electron dose)
Is determined. When generating a polarized electron beam,
Target current value I corresponding to standard quantum efficiency₀Is the target value setter 9
2, the polarized electron beam generator 22 is
The incident angle of the excitation laser light 20 is θ = θ₂In the state of
Extraction of the subsidiary wire is started. Extracting polarized electron beam
(That is, during the experiment), the table of the polarized electron beam generating element 10 is shown.
Since the state of the surface 22 gradually deteriorates, the quantum efficiency becomes overall.
However, as shown by the broken line in FIG. 7, for example,
Even when the child efficiency is reduced to some extent, the required quantum
Efficiency E₀Of the resonance wavelength
It exists in the vicinity. Therefore, the distribution shown by the broken line in the figure
To shift to the left, that is, the incident angle θ is θ₀To
The rotation of the motor 36 is controlled so that it approaches.
Always constant quantum efficiency E ₀Will be obtained,
A constant polarized electron dose can be obtained with a constant excitation laser light 20 intensity.
It will be done.

That is, in the present embodiment, the target value is set to a value smaller than the maximum polarized electron dose that can be taken out, so that when the measured polarized electron dose decreases, the motor 36 rotates. Excited laser light 2
The incident angle θ of 0 is changed, the resonance wavelength is brought close to the wavelength λ ₀ of the pump laser light 20, and the quantum efficiency is increased, so that the extracted polarized electron dose is increased. Contrary to the case described above, when the quantum efficiency becomes high for some reason, the incident angle θ is changed so that the difference between the wavelength λ ₀ of the pump laser light 20 and the resonance wavelength becomes large. As a result, the quantum efficiency is reduced, and in any case, a stable polarized electron dose can be obtained.

Since the polarized electron beam generating element 10 is usually designed so that the wavelength λ ₀ of the pump laser light 20 coincides with the resonance wavelength when the incident angle θ = 0, the above-mentioned embodiment is used. In general, the extraction of the polarized electron beam is started from the state where the incident angle θ is larger than θ ₀ . Therefore, as shown in FIG. 7, the wavelength λ ₀ of the pump laser light 20 is
The intersection of the curve and the distribution curve occurs in the lower left part of the distribution curve, and the incident angle θ is changed to a smaller direction.
Can be approached to ₀ . Therefore, in this embodiment,
When ΔI is positive, the polarized electron dose is lower than the target value, so the motor 36 is rotated in a direction in which the incident angle θ becomes smaller, and conversely, when the incident angle θ becomes too small, Δ
When I is negative, the motor 36 is set to rotate in the direction in which the incident angle θ increases. However, even if the rotation direction of the motor 36 is not set in this way, for example, if the first rotation direction is arbitrarily set and the motor 36 is rotated, ΔI has the same sign and absolute value as before rotation. If it becomes smaller than before, in the same rotation direction,
When ΔI has a different sign from that before the rotation or an absolute value is larger than that before the rotation, the rotation may be controlled in the opposite rotation direction.

Further, according to the present embodiment, the incident angle θ of the excitation laser light 20 is continuously controlled even while the polarized electron beam is being taken out. Even when the wavelength λ ₀ of the excitation laser light 20 changes, a polarized electron beam of a constant value is always taken out.

Further, in this embodiment, since the first semiconductor 16 of the polarized electron beam generating element 10 is made relatively thick to about 2000 nm and the optical resonator length is made large, the resonance wavelength interval becomes small. There is. Therefore, the quantum efficiency greatly changes due to a slight change in the resonance condition, so that the polarized electron dose can be controlled to be constant with a small change in the incident angle.

Note that the incident angle θ is gradually changed to θ ₀
After matching with, the rotation of the motor 36, that is, the incident angle θ
Since the quantum efficiency cannot be improved even if the change is made, if it is detected that the incident angle θ coincides with θ ₀ and then the decrease in the quantum efficiency is detected, for example, the control device 70
A warning or the like may be given by. And
In such a case, cesium is again adsorbed on the surface 22 of the polarized electron beam generating element 10, or the surface 22 is cleaned by once heating it to a temperature of about 420 ° C. by the heater 64 as at the start of use. Then, the cesium and oxygen are adsorbed alternately, so that the surface 22 is re-exposed to the NEA.
To be in a state.

FIG. 8 shows a polarized electron beam generator 24 of the present invention.
It is a figure which shows the principal part structure of the other polarized electron beam generation element 98 used for. The polarized electron beam generating element 98 is a well-known MBE (Molecular Beam Epitaxy) apparatus, in which a buffer layer 100 and a semiconductor multilayer, which are sequentially crystal-grown on a substrate 12 made of p-GaAs similar to that of the above-described embodiment. The film reflection layer 102, the barrier layer 104, the semiconductor photoelectric layer 106, and the passivation film 108 are provided.

The buffer layer 100 has a thickness of about 50 nm.
Thickness, Be doped as impurities
Therefore, the carrier concentration is 5 × 10¹⁸(Cm^-3) It is assumed to be
P-GaAs. The buffer layer 100 is a substrate
By making the surface of 12 flat on the atomic scale,
A semiconductor multilayer reflective layer 102 or the like grown on the
It is to improve the degree. Also, a semiconductor multilayer film reflective layer
102 is p-Al having a thickness of 60.6 nm._0.6Ga_0.4
As and p-Al with a thickness of 56.1 nm_0.2Ga _0.8As
And 30 alternately so that the latter is on the buffer layer 100 side.
It is a stack of pairs and has a sufficiently wide reflection band.
It In both of these two types of semiconductors, Be is an impurity.
The carrier concentration is 5 × 10 by being doped.¹⁸(C
m^-3) It is said to be about. It should be noted that the above two types of semiconductor films
The thickness is 1 when the wavelength λ of the excitation laser light 20 is 775 nm.
The thickness is determined to be / 4 wavelength.

The barrier layer 104 has a thickness of about 2020 nm and is made of p-Al _0.35 Ga _{0.65 with a} carrier concentration of about 5 × 10 ¹⁸ (cm ⁻³ ) by being doped with Be as an impurity. It is As. In addition, the semiconductor photoelectric layer 106 has a thickness of 1.98 nm of p-GaA.
s and p-Al _0.35 Ga _0.65 As having a thickness of 3.11 nm are alternately arranged so that the latter is on the barrier layer 104 side, for example, 1
One pair is laminated and the total thickness is 56 nm, and the carrier concentration is about 5 × 10 ¹⁸ (cm ⁻³ ) in each case by doping with Be as an impurity. The thickness of these thin films and the mixed crystal ratio of Al are such that the separation of the band difference between the heavy hole and the light hole is larger than the thermal noise, and the excited electrons are p-A which is the barrier layer.
It is set so that it can pass through _0.35 Ga _0.65 As by the tunnel effect. In this example, the band difference separation is 44 eV.

The semiconductor photoelectric layer 106 is a semiconductor thin film.
Stacked superlattices, especially what are called quantum wells
, P-GaAs with a thickness less than the de Broglie wavelength is
Working as a well layer Heavy holes and lights in this well layer
Quantum levels with different hole quantum levels are formed,
Due to the tunnel effect, over the barrier layer and adjoining well layers
The penetrating electrons and holes affect each other,
Subbands are formed in the child band and conduction band, that is, the band sp
Litting occurs. The above semiconductors
The number of stacked photoelectric layers 106 was determined as follows.
Of. The semiconductor photoelectric layer 106 has the superlattice structure as described above.
Of the excitation laser light 20 that gives a high polarization rate
The wavelength is about λ = 775 nm, and the semiconductor photoelectric layer 106
Refractive index n of _SLIs 3.445 from the following equation (2). did
Therefore, the thickness of the semiconductor photoelectric layer 106 is half the standing wave.
11 pairs so that it is an integral multiple of the wavelength (that is, 56 nm).
Oh, they are stacked.

[0035]

[Equation 2]

The thickness t _B of the barrier layer 104 is
An optical resonator is set to be formed between the semiconductor multilayer reflective layer 102 and the surface of the semiconductor photoelectric layer 106 when the wavelength λ of the excitation laser light 20 is 775 nm. That is, in order to satisfy the resonance condition when λ = 775 nm, the following equation (3) should be satisfied when m is an integer, and when m = 18, the thickness t _B = 202 of the barrier layer 104.
It is set to 0 nm. The barrier layer 10
4 is a substrate 12 for electrons excited by the semiconductor photoelectric layer 106.
It plays the role of a potential barrier to prevent it from flowing to the side.

[0037]

[Equation 3]

The passivation film 108 is
The semiconductor photoelectric layer 106 is As having a thickness of about 2 μm.
Is provided to prevent the tunnel effect from being lost due to the oxidation of the Al _0.35 Ga _0.65 As Al barrier layer and to prevent the electrons from being difficult to be taken out due to the oxidation of GaAs which is the well layer. There is something. The passivation film 108 is vaporized and removed by high-temperature treatment in vacuum during use.

Also in the polarized electron beam generating element 98 configured as described above, the semiconductor multilayer film reflective layer 102 is provided and an optical resonator is configured between the semiconductor photoelectric layer 106 and the semiconductor multilayer film reflective layer 102. Therefore, when used in the polarized electron beam generator 24, the polarized electron dose taken out is monitored by the monitor 9 as in the polarized electron beam generating element 10.
The incident angle θ of the excitation laser beam 20 is automatically controlled by the measurement of
Similar quantum efficiency can be obtained even when the surface condition of No. 8 deteriorates, and a stable polarized electron dose can be obtained for a long time.

Although one embodiment of the present invention has been described in detail with reference to the drawings, the present invention can be implemented in other modes.

For example, as the incident angle changing means, instead of rotating the sample holder 34 by rotating the motor 36, the mirror 52 of the laser light irradiation device 44 may be rotated. In this case, in order to correct the deviation of the irradiation position of the excitation laser light 20 due to the rotation of the mirror 52, for example, the mirror 52 needs to be moved in the horizontal direction in FIG. 2 according to the rotation angle. Further, the vacuum chamber 26 may be provided with a mirror, a prism, or the like, and the positional deviation may be corrected by the rotation thereof. Further, in the embodiment, only the rotating member 54 is configured to be rotated within the housing 32, but the entire housing 32 may be configured to be rotated with respect to the vacuum housing 26. good.

Although so-called PID control is performed in the embodiment, either one or both of integral control and differential control may not necessarily be performed. That is, the control equation (1)
In, the second and third terms on the right side are not necessarily required.

Further, in the embodiment, the polarized electron dose (that is, the current value I) is continuously measured during the operation, the incident angle is continuously changed, and a constant polarized electron dose is always obtained. However, if the allowable range of the fluctuation range of the polarized electron dose is relatively large, for example, the polarized electron dose is The incident angle may be changed only when the dose is below the polar electron dose.

In the embodiment, the sample holder 34
In the non-rotational position, the excitation laser light 20 is incident from a direction perpendicular to the surface 22 of the polarized electron beam generating element 10 or the like, and the polarized electron beam is bent by the spherical condenser 88 and taken out. Excitation laser light 20
The state in which the light is incident on the surface 22 from an oblique direction may be configured to be the non-rotational position. This makes it possible to rotate the incident angle θ in both directions of increasing and decreasing, and for example, the wavelength λ ₀ of the pump laser light 20 and the target quantum efficiency in the lower left part of the distribution curve of FIG. It is also possible to obtain the intersection with E ₀ and set it so that the quantum efficiency is improved by the rotation in the direction in which the incident angle θ increases.

Further, the polarized electron beam generator 24 described above is constructed so as to take out the polarized electron beam at room temperature, but it is taken out at a low temperature by providing the housing 32 with a cooling facility such as liquid nitrogen. It may be configured as follows.

Further, the semiconductor multilayer film reflection layers 14, 102,
The composition (mixed crystal ratio of P and Al), type, thickness, and the like of the first semiconductor 16, the second semiconductor 18, the barrier layer 104, the semiconductor photoelectric layer 106, and the like can be appropriately changed. For example, a strained compound semiconductor such as AlGaAs, GaAs, InGaAs, InGaAsP can be used, and a strained superlattice in which the well layer is strained may be used instead of the semiconductor photoelectric layer 106. When a material such as AlGaAs which is easily oxidized is used as the second semiconductor 28 or the semiconductor photoelectric layer 106, in order to prevent the oxidation, the relatively thick As shown in the polarized electron beam generating element 98 is used. The passivation film 108 and the protective layer made of p-GaAs,
It is better to be provided on the second semiconductor 2 and the semiconductor photoelectric layer 106.

Further, a chalcopyrite type semiconductor or the like which originally has band splitting in the valence band is used as the second
It can also be used as the semiconductor 18. Or I
n _0. As ₅ Ga _0.5 P, the band splitting may be a compound semiconductor is used that occurs by a plurality of atoms are regularly lattice arrangement.

In the above embodiment, the substrate 12 is made of Ga.
Although As was used, it is also possible to use other compound semiconductors such as AlGaAs or Si substrates.

Further, in the above-mentioned embodiment, the case where each semiconductor layer is formed by using the MOCVD method or the MBE method has been described, but it is of course possible to use another epitaxial growth technique.

Although not illustrated one by one, the present invention can be variously modified without departing from the spirit thereof.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a polarized electron beam generating element used in an embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of a polarized electron beam generator using the polarized electron beam generator of FIG.

FIG. 3 is an enlarged view of a main part of the polarized electron beam generator of FIG.

FIG. 4 is a functional block diagram showing a function of controlling an incident angle by a control device of the polarized electron beam generator of FIG.

5 is a diagram showing the relationship between the quantum efficiency obtained by the polarized electron beam generator of FIG. 2 and the wavelength of excitation laser light.

FIG. 6 is a diagram for explaining a change in quantum efficiency distribution due to a change in incident angle.

FIG. 7 is a diagram for explaining the action of stabilizing the polarized electron dose by changing the incident angle.

FIG. 8 is a diagram showing the configuration of another example of the polarized electron beam generating element used in one embodiment of the present invention.

[Explanation of symbols]

 10, 98: Polarized electron beam generating element 14, 102: Semiconductor multilayer film reflective layer (reflective layer) 18: Second semiconductor (semiconductor photoelectric layer) 20: Excitation laser light (excitation light) 24: Polarized electron beam generator 70: Control device (incident angle control means) 90: Monitor (measurement device) 106: Semiconductor photoelectric layer

Claims (1)

[Claims] 1. A semiconductor photoelectric layer having band splitting in the valence band, and excitation light provided on the back side of the semiconductor photoelectric layer and irradiating the semiconductor photoelectric layer is resonated with the surface of the semiconductor photoelectric layer. A polarized electron beam having a spin direction unevenly distributed is extracted from the surface of the semiconductor photoelectric layer by irradiating the polarized electron beam generating element provided with a reflection layer forming an optical resonator with the excitation light. A polarized electron beam generator, wherein the measuring device for measuring the extracted polarized electron dose and the excitation light so that the measured polarized electron dose coincides with a predetermined target value. And an incident angle control means for automatically controlling the incident angle to the polarized electron beam generating element.