JP3135002B2 - Light control type electron wave interference device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light control type electron wave interference device which controls a quantum wave interference current depending on the intensity of light applied to the device.

[0002]

2. Description of the Related Art Light-based systems such as optical transmission, optical switching, and optical computing are considered to hold the key to future large-capacity, ultra-high-speed information processing. Among them, an ultra-high-speed photodetector is required for optical communication, and a photodetector capable of being integrated at high density is required for optical switching.

[0003] In response to such demands, a method of controlling the quantum interference current with light is described in Yamanishi et al. Proceedings of the Japan Society of Applied Physics, 27p-z-1, proposed in the fall of 1989. Hereinafter, the principle of this method will be described.

An arm 71 on one side of an interferometer for irradiating an electron wave composed of a quantum wire 70 as shown in FIG. At this time, the photon energy of the incident light 72 is
By making the exciton energy gap sufficiently smaller than 0, carriers are virtually generated, that is, virtual transitions are generated. The virtual carriers generated in the arm 71 thus optically excited reduce the effective potential of the electron wave propagating in the arm 71 through the exchange interaction related to the exchange energy, and as a result, the electron propagating in the two arms 71 and 73. Quantum interference between waves can be controlled. On this occasion,
The virtually excited electron / hole carrier pair does not contribute to conduction because it is a coherent pair excitation.

The feature of this method is that since the structure is simple and the quantum wave interference is controlled by virtual excitation by light, the switching time of the device is not limited by the CR time constant or the recombination lifetime.

Next, another conventional technique will be described. FIG.
Is S. Data et al. , Appl. Phys
s. Lett. 48, p. 487, (1986) is a schematic sectional view showing the structure of a quantum interference device.

In this structure, two GaAs quantum well layers 80 and 81 are stacked in the z direction via an AlGaAs barrier layer 82. Since the barrier layer 82 is thin at both ends, considerable tunneling exists between the well layers 80 and 81. However, at the center, the barrier layer 82 is thick and has almost no tunneling. Now, the electron waves incident from the contact 83 on the left end are in a state where the phases are aligned because they are coherent in the two quantum wells 80 and 81 at first. Here, | A> represents an asymmetric wave function of an electron wave, and | S> represents its symmetric wave function. In the central portion of the electron wave propagating in the x direction, that is, in the portion between x = 0 and x = L, y
A magnetic field is applied in the direction such that a phase difference between the upper and lower channels 80 and 81 is generated by π. This is the well layers 80, 8
The phase difference between the band structure of No. 1 and the intensity of the applied magnetic field is π
Means to set it to occur. Then, the two electron waves that interfere with each other at the right end and whose wave functions are represented by | 1> and | 2> become energetically high and are reflected. That is, at the right end, the wave function of the electron becomes 1 again.
When it becomes one, its shape becomes the second state | A> instead of the ground state indicated by | S>, but it is reflected because it has only energy corresponding to | S> become.

On the other hand, if the magnetic field is controlled so that the phase difference is an integral multiple of 2π, the single electron wave can pass through the right end, and the same output current as the input current can be obtained. .

Therefore, the conductance shown on the vertical axis of FIG. 11 is a periodic function of the applied magnetic field, and thereby the passing current can be controlled in a wide range by modulating the magnetic field.

[0010]

However, the former structure of the prior art has the following problems. Now, considering that the quantum wire 70 is made of GaAs, which is a compound semiconductor, in order to cause virtual excitation from the valence band to the conduction band, a wavelength of 0.8 from the relationship with the energy interval.
It is necessary to use irradiation light of μm. However, since the lengths of the arms 71 and 73 of the interference device are at most 1 μm, condensing light on only one side of the two arms 71 and 73 in such a small area is a diffraction limit. It can be said that the relationship is very difficult.

The latter conventional example also has the following problems. First, high-speed modulation is difficult because the interference current is controlled by the magnetic field. The reason for this is that the impedance of the coil becomes too large for the high-frequency current required to modulate the magnetic field at high speed. Number 1
0 MHz is considered the upper limit frequency.

Second, re-growth is required to form the structure shown in FIG. First, a molecular beam epitaxy (MBE) method or metal organic chemical vapor deposition (MO-CV) is performed up to an AlGaAs barrier layer 82 between the two well layers 80 and 81.
After the growth by the method D), etching is performed to form a thick portion and a thin portion of the take-out barrier layer 82 in the atmosphere.

However, at this time, surface oxidation and adsorption of impurities are inevitable. Therefore, Ga grown on this
The As quantum well 81 has a rough heterointerface and contains many impurities and defects. As a result, the electrons traveling inside are scattered and disturbed in phase, so that the on / off ratio of the interference current is reduced.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a light-controlled electronic interference device that can perform high-speed modulation of an interference current, is easy to manufacture, and does not require any special measures for light irradiation. Is to do.

[0015]

According to the present invention, there is provided an electron wave interference device having two channels through which an electron wave propagates. The configuration of the function is changed so that the amount of magnetic flux crossing between the two channels is changed so that the phase difference between the two electron waves is controlled.

[0016]

FIG. 1 is a schematic diagram for explaining the principle of an electron wave interference device according to the present invention. In FIG. 1, the electrode 3
Channels 1a and 1b are provided at predetermined intervals between and. By applying a voltage between the electrodes, an electron wave propagates in each of these channels. These channels are produced, for example, by stacking quantum well layers made of a semiconductor with a barrier layer interposed therebetween.

The channel 1a of a plane interposed between these channels 1a and 1b, that is, a plane parallel to a virtual plane including the arrangement direction of the channels and the propagation direction of the electron wave.
A magnetic field is externally applied to the region between the first and second regions by means (not shown). The region is, in this example, a region between the two channels when the device is cut along a plane perpendicular to the film plane of the well layer and parallel to the propagation direction of the electron wave.

In the device as described above, the electron waves propagating through the channels 1a and 1b respectively interfere with each other. The phase difference between these electron waves is proportional to the product of the magnetic field applied to the channel portion and the cross-sectional area surrounded by the two channels. When the phase difference changes, the amount of current flowing between the electrodes changes. This will be described below.

In the device of FIG. 1, the transmission coefficient | T | ² of the electron wave between the electrodes is expressed as follows. | T | ² = cos ² (e / η · (d · l) / 2 · B) (1) where e represents an elementary charge of an electron. η = h / 2π, h
Indicates Planck's constant. d is the distance between the two channels 1a and 1b, l is the length of the channels 1a and 1b,
B indicates the magnitude of the external magnetic field. The direction of the applied external magnetic field is perpendicular to the plane of FIG. 4 and is a direction from the back to the near side.

As is clear from the equation (1), even if the magnitude of the magnetic field is constant, if the cross-sectional area (d · l) of the surface interposed between the two channels changes, these cross-sectional areas change. The phase difference between the electron waves propagating in the channel changes.

In the above example, channels 1a and 1a
distance d b is defined by the difference between the expected value of the position of the wave function [psi _a and [psi _b of the electron wave in each channel 1a and 1b. Therefore, the interval d is expressed as follows. d = The _{∫Ψ a * zΨ a dz-∫Ψ} b * zΨ b dz (2) present invention, by irradiating light, and changing the channel spacing d, changing the transmission coefficient. That is,
The present invention is to control an interference current using light.

As a method of changing the distance d,
There are a method using the exchange interaction and a method using the optical Stark effect. Hereinafter, each method will be described.

(1) Method Using Exchange Interaction FIG. 2 shows an energy band diagram of a semiconductor layer in the case where the channel of the device of FIG. 1 is constituted by a semiconductor layer having a quantum well structure. In FIG. 2, reference numerals 2a and 2b indicate quantum well layers constituting the channels 1a and 1b of FIG. 1, respectively. Between and on both sides of these quantum well layers, barrier layers 5a and 5b having a wider band gap than the quantum well layers are provided.
And 5c are provided.

The quantum well layers 2a and 2b have band structures inclined in directions opposite to each other. That is, each of the well layers 2a and 2b is formed such that the band gap gradually increases as the distance from the barrier layer 5b increases. In such a structure, for example, the well layer is formed of Al _x
When formed of Ga _1-x As, it can be realized by continuously changing the composition ratio x of Al. Here, as x increases, the band gap increases.

The well layers 2a and 2b have ground quantum levels E _ai and E _bi , respectively. In addition, these levels E _ai and E _bi respectively include the wave functions Ψ _ai and そ れ_ぞれ
_bi exists. Assuming that the energy levels of the valence band well layers 2a and 2b are E _av and E _bv respectively, these layers are irradiated with pump light having a photon energy ηω _p satisfying the following condition. ηω _p = E _ai −E _av −δ _a (3-1) ηω _p = E _bi −E _bv −δ _b (3-2) where δ _a and δ _b are detuning energies, respectively, as follows: Is shown in δ _a ≪ (E _ai −E _av ) (4-1) δ _b ≪ (E _bi −E _bv ) (4-2) By irradiation of light as described above, the well layers 2a and 2b
Carriers are virtually excited from the valence band. The conduction band carriers of the electron wave propagating through the well layers 2a and 2b have the energy levels of E _ai and E a by exchange action with the excited virtual carriers.
Shift from _bi to E _af and E _bf . At this time, since these well layers have an inclined band structure,
With the shift of the energy level, the peak position of the wave function also shifts. That is, the wave functions Ψ _ai and Ψ _bi change to wave functions Ψ _af and Ψ _bf by light irradiation. As a result, the channel interval d defined by the equation (2) changes.

Assuming that channel intervals when light is not irradiated and when light is irradiated are d _i and d _f , respectively, the transmission coefficient | T | ² when light is irradiated is expressed as follows. | T | ² = cos ² (e / η · (d _f · l) / 2 · B) = cos ² {e / η · (d _i · l) / 2 · B · (1 + δd / d _i )} ( 5) here, a δd = d _f -d _i. (5), the effect by which incident pump light to the device, shows that is equivalent to the effect of multiplying the magnitude of the magnetic field _{(l + δd / d i)} . That is, it can be seen that the transmission coefficient can be changed and the interference current can be controlled by light irradiation.

In order to change the channel interval d, a structure in which the band gaps of the semiconductor layers forming the channel are inclined in opposite directions as in the above-described example, that is, the barrier layer 5b
The structure in which the well layers 2a and 2b are symmetrical with respect to the center is particularly effective. However, the present invention is not limited to this structure. If at least one of the quantum well layers has a tilted potential shape, the channel spacing can be changed.

(2) Method Using Optical Stark Effect In a semiconductor layer having a quantum well structure having two quantum levels, the energy difference between these quantum levels is close to, that is, slightly smaller or slightly larger than the energy difference between these quantum levels. When light having energy is applied, mixing occurs between the two levels, and the energy level of the ground state shifts. At the same time, part of the excited state wave function mixes with the ground state wave function. Such a phenomenon is called an optical Stark effect. here,
An example in which the above-described channel spacing is changed using the optical Stark effect will be described.

FIG. 3 shows an energy band diagram of the semiconductor layer when the channel of the device shown in FIG. 1 is constituted by a semiconductor layer having a quantum well structure. In FIG. 3, reference numerals 12a and 1
Reference numeral 2b denotes quantum well layers constituting the channels 1a and 1b in FIG. 1, respectively. Between and on both sides of these quantum well layers, barrier layers 15a, 15b and 15c having a wider band gap than the quantum well layers are provided. These well layers have a tilted band structure as in the example of FIG.

The thickness and potential of each well layer are formed thin and deep enough to produce the quantum size effect. Therefore, two quantum levels E _a1 and E _a2 exist in the well layer 12a. Similarly, two quantum levels E _b1 and E _b2 exist in the well layer 12b.

Light that satisfies the following conditions is applied to these well layers.
Child energy ηω_pIrradiating pump light having ηω_p= E_a2-E_a1−δ_a (6-1) ηω_p= E_b2-E_b1−δ_b (6-2) δ_a≪ (E_a2-E_a1) (7-1) δ_b≪ (E_b2-E_b1(7-2) Then, the perturbation by the photoelectric field causes each quantum well
Door ground state wave function Ψ_a1And Ψ_b1Is below
The function φ shown in_a1And φ_b1Changes to φ _a1= 1 / (1 + c^Two _a)^1/2・ (Ψ_a1−Ψ_a2) (8-1) φ_b1= 1 / (1 + c^Two _b)^1/2・ (Ψ_b1−Ψ_b2(8-2) where c_aAnd c_bAre represented as
You. c_a= V_21a/ (E_a1-E_a2) (9-1) c_b= V_21b/ (E_b1-E_b2(9-2) In addition, V_21aAnd V_21bIs the perturbation potential due to the photoelectric field
Is the matrix element of the call V_21a= ∫Ψ_a2* (E · z · ε) Ψ_a1dz (10-1) V_21b= ∫Ψ_b2* (E · z · ε) Ψ_b1dz (10-2) where ε is a photoelectric field.

As can be seen from the above equations (8-1) and (8-2), the wave function in the ground state is deformed by the photoelectric field, and its peak position is determined by the well layer 12a and the well layer 12a.
b shifts in opposite directions. As a result, (5)
As described in the equation, the channel interval d changes, and the interference current can be controlled.

In the case where the optical Stark effect is used as in this embodiment, the inclined band structure as shown in FIG. 3 is not necessarily required. However, by adopting the inclined band structure, the channel interval d can be changed more effectively.

FIG. 4 is a schematic perspective view showing one embodiment of the quantum interference device of the present invention. This device was manufactured as follows.

First, on a semi-insulating GaAs substrate 41,
GaAs buffer layer 42 having a thickness of 0.5 μm and a thickness of 500
Ｎ n-AlAs barrier layer 43, 100 Ａｌ thick AlGa
The As quantum well layer 44, the 200-nm thick n-AlAs barrier layer 45, the 100-mm thick AlGaAs quantum well layer 46, and the 500-nm thick n-AlAs barrier layer 47 are formed by molecular beam epitaxy (MBE) or metalorganic chemistry. The layers were sequentially grown using a vapor phase deposition (MO-CVD) method. Furthermore,
On the barrier layer 47, a thickness of 5
A 00 ° n ⁺ -GaAs cap layer 48 was grown.
Here, the barrier layers 43, 45 and 47 contain Si
Was selectively doped at a density of about 10 ¹⁷ to 10 ¹⁸ cm ⁻³ . By this doping, a two-dimensional electron gas (2DEG) having a concentration of 10 ¹⁰ to 10 ¹¹ cm ⁻³ was stored in the quantum well layers 44 and 46.

Next, electrodes 51 and 52 made of an Au / Ge film were formed on both ends of the semiconductor layers stacked as described above. Thereafter, the laminate on which the electrodes are formed is heat-treated, and the Au / Ge film is diffused to form electrode portions 49 and 50.
Was formed. Here, the electrode portions 49 and 50 become a source portion and a drain portion, respectively, and a portion between them becomes a gate portion. Quantum well layers 44 and 4 in the gate section
Numeral 6 serves as first and second channels for propagating an electron wave between the electrode portions. The length l of these channels was 2 μm. In addition, in order to limit the width of these channels, hydrogen ions were implanted into a part of the direction orthogonal to the propagation direction of the electron wave to form an insulating region 53. Thus, the width W of the channel was formed to 0.5 μm.

FIG. 5 shows the energy levels near the channel of the device described above. Portions indicating the energy of each layer are denoted by the same reference numerals as in FIG. The quantum well layers 44 and 46 have a band gap that gradually changes in the thickness direction of the layers, and have a tilted band structure as shown in FIG. The energy bands of the well layers 44 and 46 are inclined in opposite directions. That is,
The band gaps of the well layers 44 and 46 are formed so as to gradually increase from the near side to the far side. Such a band structure corresponds to the well layers 44 and 4
6 is formed by changing the composition. Here, the well layers 44 and 46 were formed of Al _x Ga _{1 -x} As, and the composition ratio x of Al was continuously changed in the thickness direction.
The composition ratio x was set to 0.13 at the interface with the barrier layer 45, and set to 0 at each interface with the barrier layers 43 and 47.

With the above configuration, the well layers 44 and 46 have an energy difference of 100 meV at both ends. This is equivalent to an electric field F of 10 ⁵ V / cm being effectively applied in the thickness direction of the layer.

Next, the operation of the device shown in FIG. 4 will be described. In FIG. 4, a voltage is applied between the electrodes 51 and 52 by a power supply 54. Then, an electron wave is propagated from the electrode portion 49 to the electrode portion 50 through the well layers 44 and 46, respectively. A magnetic field B is externally applied to the device. Such a magnetic field is obtained, for example, by arranging the device 6 in a space inside the cylindrical permanent magnet 7, as shown in a perspective view in FIG. Here, when the well layers 44 and 46 are irradiated with light having the photon energy ηω _p , as described above, the peaks of the wave functions of the electron waves propagating through these layers due to the exchange interaction or the optical Stark effect. And the amount of current flowing between the electrode portions 49 and 50 changes. Such a change in the amount of current is measured by an ammeter 55 connected to the electrode.
It is detected by.

For example, as shown in FIG.
6, light having a wavelength of about 0.8 μm having a photon energy ηω _p1 close to the energy difference between the quantum levels E _av and E _{bv of} these valence bands and the quantum levels E _a1 and E _b1 of the conduction band. Upon irradiation, the wave function of the electron wave is deformed mainly by the exchange interaction between conduction carriers and virtual carriers.

The conduction bands of the well layers 44 and 46
Ground level E_a1And E_b1And the first excited level E_a2And
And E_b2Photon energy ηω close to the energy difference between_p2To
When irradiated with light having a wavelength of about 10 μm,
Due to the Stark effect, the wave function of the electron wave is deformed.
You. Here, by irradiating a sufficiently strong light,
Change δ in the interval between the peak positions of the wave function shown in equation (5)
d can be about 15 °. In this embodiment, the light
Of the peak position of the wave function without irradiation_iIs
Since the angle is about 300 °, from equation (5),
As a result, an effect equivalent to modulating the effective magnetic field by 5% can be obtained.

As shown in FIG. 11, the interference current is a periodic function of the magnetic field, and the intensity B ₀ of the magnetic field at which the current becomes zero is:
It is obtained from the equation (1) as follows. B ₀ = (2n + 1) · η / e · π / (l · d _i ) (11) where n is an integer. In equation (11), l = 2 μm,
By substituting d _i = 300 °, B ₀ = (2n + 1) × 34
3 Gauss. If n = 10, B ₀ = 720
3 Gauss. That is, in the device of FIG. 4, when the external magnetic field B is set to 7203 Gauss, no current flows between the electrode units 49 and 50 when no light is irradiated. On the other hand, when the well layers 44 and 46 are irradiated with light, the effective magnetic field is 5%, that is, 360 G
Auss changes, and the amount of current flowing between the electrode portions becomes maximum. The device according to the present invention can be used as a photodetector by monitoring the amount of current flowing between the electrode portions with an ammeter 55 by using light to be irradiated as light to be detected.

The present invention can also be applied to a device for controlling a current by light. This example will be described with reference to FIG. In FIG. 7, reference numeral 8 denotes a device as shown in FIG. A voltage is applied between the electrodes of the device 8 by the electrodes 9. This device 8 gate light L _G from the laser light source 11 such as a semiconductor laser is irradiated. By modulating this light L _G current supplied from the laser driving circuit 10 to the laser light source i _G, the drain current i _p of the device 8 is modulated. Pulse width 1p a gate light L _G
When s or less pulsed light, it is possible to modulate the drain current i _p at this speed, it is possible to realize a high-speed current modulator.

FIG. 8 is a block diagram illustrating an example in which the electron wave interference device of the present invention is used as a photodetector in an optical communication system. In FIG. 8, reference numeral 16 denotes an optical fiber for transmitting an optical signal. This optical fiber 16 includes
Optical node 17 _1, 17 _2, ..., via respective 17 _n, a plurality of terminals 18 _1, 18 _2, ..., 18 _n are connected. Each terminal has a terminal 19 ₁ , 19 ₂ ,.
19 _n are connected.

Each terminal has an optical signal transmitter including a modulation circuit 23 and a laser light source 22. Also,
Each terminal has an optical signal receiver including a photodetector 20 and a demodulation circuit 21. These transmitter and receiver, the control circuit 24 based on a command from the terminal 19 ₁
Is controlled by As the photodetector 20, the electron wave interference device of the present invention as described in FIG. 4 can be suitably used.

The present invention is not limited to the embodiments described above, but can be applied to various applications. For example, in the embodiment, the device A
Although it is fabricated using lAs and AlGaAs,
It may be manufactured using another III-V semiconductor such as nGaAs. Further, the device of the present invention has a ZnMnS
e, a II-VI group semiconductor such as CdMnTe, or
It can also be manufactured using an I-VII group semiconductor such as CuCl. The invention includes all such applications without departing from the scope of the claims.

[0047]

As described above, according to the present invention, it is possible to modulate the interference current at high speed only by irradiating light to both of the two channels, using a laminated structure that does not require regrowth. I have to. Since an optical pulse width of 1 ps or less has been obtained, the electron current can be modulated at this speed, and it is expected as a key device for future optical systems.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining the operation principle of an electronic interference device of the present invention.

FIG. 2 is a diagram showing a first example of an energy band structure of a channel in the device of the present invention.

FIG. 3 is a diagram showing a first example of an energy band structure of a channel in the device of the present invention.

FIG. 4 is a schematic perspective view showing one embodiment of the electron wave interference device of the present invention.

5 is a diagram showing an energy band structure around a well layer of the device of FIG.

FIG. 6 is a schematic sectional view showing an example of a means for applying a magnetic field to the device of the present invention.

FIG. 7 is a schematic diagram showing an apparatus for modulating current using the device of the present invention.

FIG. 8 is a block diagram showing an example of an optical communication system using the device of the present invention as a photodetector.

FIG. 9 is a schematic perspective view showing a first example of a conventional electron wave interference device.

FIG. 10 is a schematic sectional view showing a second example of a conventional electron wave interference device.

FIG. 11 is a diagram showing a relationship between the strength of an applied magnetic field and conductance in a second conventional example.

[Explanation of symbols]

 1a, 1b Channel 2a, 2b Well layer 41 Substrate 42 Buffer layer 43, 45, 47 Barrier layer 44, 46 Quantum well layer 48 Cap layer 49, 50 Electrode

Claims (4)

(57) [Claims] 1. An electron wave interference device having two channels through which an electron wave propagates, wherein the shape of the wave function of the electron wave is changed by irradiating light to the channel portion. An optically controlled electron wave interference device, wherein the amount of magnetic flux crossing between two channels is changed to control the phase difference between two electron waves. 2. The two channel quantum wells are configured such that the potential shapes of the quantum wells have a tilted structure and the tilt directions thereof are opposite to each other, so that light is irradiated to the two channel portions. 2. The electron wave interference device according to claim 1, wherein the peak positions of the wave functions of the two electron waves are shifted in opposite directions. 3. An electron wave propagating through the two channels by irradiating light having photon energies slightly detuned with respect to the energy difference between the quantum levels of the two channels by the optical Stark effect. The electron wave interference device according to claim 1, wherein the shape of the wave function is changed. 4. A virtual carrier is generated by irradiating light having photon energy slightly detuned with respect to the energy difference between the quantum levels of the two channels to generate virtual carriers and electrons of the channel. 2. The electron wave interference device according to claim 1, wherein the energy of the quantum level is shifted by an exchange interaction with the electron wave to change the shape of the wave function of the electron wave propagating through the two channels.