JPH04273478A - Quantum ring device - Google Patents

Abstract

PURPOSE:To acquire a quantum ring device which uses Ahoronov-Bohm effect by applying magnetic field or electric field to a ring which is formed of a conductive substance and constitutes a closed loop and by changing energy state of carrier in the ring. CONSTITUTION:A ring 1 is electrically isolated. When magnetic field is applied to the ring 1 from a magnetic field applying means 2 or electric field is applied to the ring 1 from an electric field applying means 3, energy state of carrier in the ring 1 changes instantly through Aharonov-Bohm effect. The change of energy state of carrier is acquired as a signal by a signal pick-up means 5 of photoabsorption, light emitting recombination, etc.; thereby an electronic/ optical device is realized.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to electronic/optical devices, and more particularly to electronic/optical devices that utilize the Ahranoff-Bohm effect.

For example, in computers and communication devices, devices with higher speed, lower power consumption, multiple functions, and new functions are desired.

0003

2. Description of the Related Art Many conventional electronic and optical devices employ a transistor structure or a diode structure. In recent years, with advances in crystal growth technology, thin film formation technology, and microfabrication technology, the miniaturization, speeding up, high integration, and low power consumption of these conventional electronic and optical devices have been achieved almost to the limit. It is also conceivable. However, parasitic effects that differ from the essential functions of these devices stand in the way. Specific examples of this parasitic effect include parasitic capacitance of wiring and tunnel effect due to high electric field.

For example, when switching the current to charge the capacitor C in the next stage to raise or lower the potential, R is inevitably caused by the resistance R and capacitance C in the charging path
The C time constant comes into play. Furthermore, there are parameters determined by the material used, such as band gap and dielectric constant, and it is often difficult to avoid high electric fields and high current densities.

[0005] In recent years, devices that utilize a quantum mechanical effect called the Ahranoff-Bohm effect have been studied. The Ahranov-Bohm effect was discovered as a phenomenon in which the movement of electrons passing on both sides of an infinitely long solenoid, with no magnetic flux leaking outside, is affected by magnetic flux.

In other words, the electromagnetic influence on the motion of elementary particles is due to scalar potential, vector potential, etc., rather than electric or magnetic fields, and even if no electric or magnetic field exists in the path of the charged particle, the potential This shows that the motion of charged particles can be affected if

Referring to FIG. 2, a conventional device utilizing the Ahranoff-Bohm effect will be described. Figure 2
(A) shows a device using a metal ring. Experiments using this device were reported by Webb et al. in Physical Review Letters, Vol. 54, No. 25 (June 1985), No. 2.
It is reported on page 696. A ring 51 made of a thin gold film and having a diameter of several hundred nm is connected to the outside through lead wires 52 and 53. A magnetic flux φ is applied through this ring 51.

In the experiment, the magnetic resistance between the lead wires 52 and 53 was measured when the magnetic flux φ was changed. According to the measurement results, the magnetoresistance fluctuated periodically with respect to magnetic flux changes. The periodic fluctuation included a fast component and a slow component, and the fast component showed a one-period change in magnetic resistance when the magnetic flux showed a change in h/e. That is, it was observed that the magnetic resistance of the ring 51 changed due to the Ahranoff-Bohm effect.

This experiment suggests that by connecting a pair of lead wires to a minute ring, it is possible to utilize changes in conductance due to the Ahranoff-Bohm effect.

[0010] FIG. 2(B) is by Datta et al., Physical Review Letters, Vol. 55, No. 21 (November 1985).
The device used in the experiment reported on page 2344 is shown in cross section. In this experiment, a single crystal semiconductor is used as the conductor. Compared to metals, single crystal semiconductors are
Carrier scattering is low, the mean free path is long, and a high signal/noise ratio can be obtained.

In the illustrated configuration, a GaAs buffer layer 62 is epitaxially grown on a semi-insulating GaAs substrate 61, and an AlGa buffer layer 62 is grown thereon to function as a barrier layer.
An As layer 63 is grown epitaxially. AlG
aAs has a wider bandgap than GaAs;
A potential barrier can be formed for the carriers inside. On this AlGaAs layer 63, a GaAs layer 64 functioning as a conductor and an AlGaAs layer 64 functioning as a barrier layer are formed.
A layer 65, a GaAs layer 66 functioning as a conductor, and an AlGaAs layer 67 functioning as a barrier layer are epitaxially grown in this order. Further, n+ type alloying is performed from the surface of the epitaxial layer to form conductive regions 68, 6.
9 is formed. In this way, conductive regions shown by hatched areas are formed. This conductive region is centered on the central AlGa
A ring surrounding the As region 65 (in this specification,
It can be seen that a closed loop-shaped conductor (called a ring) is formed. A voltage is applied from a DC power supply 70 to the alloying regions 68 and 69, which are two points in this ring, and magnetic flux is applied in a direction perpendicular to the plane of the paper.

[0012] While changing the magnetic flux, the measured conductance of the ring showed periodic fluctuations. Akharanov
The period theoretically predicted from the Bohm effect is h/eA (
However, A is the area of the part surrounded by the ring). The values obtained from the experimental data were almost in agreement with the theoretical values.

[0013] Thus, the possibility of a new device using the Ahranoff-Bohm effect has been experimentally confirmed.

[0014]

[Problems to be Solved by the Invention] A conventional device using the Ahranov-Bohm effect connects a lead wire to a conductive ring and measures changes in conductance by applying magnetic flux to the ring. Ta.

An object of the present invention is to provide a novel quantum ring device using the Ahranov-Bohm effect.

[0016]

[Means for Solving the Problems] The quantum ring device of the present invention includes a ring formed of a conductive material and forming a closed loop, and a magnetic field or an electric field applied to the ring to change the energy state of carriers in the ring. means for changing the
and signal extraction means for extracting a change in the energy state of the carrier as a signal.

[0017] Note that the ring may be of any loop shape, and does not necessarily mean a circle or a similar shape.

[0018]

[Operation] Carriers such as electrons and holes exist in the ring formed of a conductive material. When a magnetic or electric field is applied to the ring, the energy state of the carriers in the ring changes. An electronic/optical device is realized by extracting this change in the energy state of the carrier as a signal by a signal extracting means.

As means for extracting changes in the energy state of carriers, for example, light absorption, luminescent recombination, etc. can be used.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic perspective view showing a basic embodiment of the present invention. A ring 1 made of a conductive material such as a metal or a semiconductor is disposed, and means 2 for applying a magnetic flux within the ring 1 or means 3 for applying an electric field to the ring 1 are functionally coupled to the ring 1. It is located. Further, a signal extraction means 5 is arranged near the ring 1 to extract a change in the energy state of carriers within the ring as a signal.

Furthermore, a light receiving means 6 for introducing light into the ring 1 may be provided. In this embodiment, ring 1 is electrically isolated. When a magnetic field is applied to the ring 1 from the magnetic field application means 2 or an electric field is applied to the ring 1 from the electric field application means 3, the energy state of carriers within the ring 1 changes instantaneously due to the Ahranoff-Bohm effect. For example, by luminescently recombining electrons and holes whose energy levels have changed, a wavelength-tunable light-emitting device can be realized. In this case, the signal extraction means 5 is constituted by a waveguide means such as a window, a lens, a fiber, or the like.

The carrier within the ring 1 may be one that originally existed within the ring 1, or may be one that is supplied by some carrier supply mechanism. Further, in order to form electron-hole pairs, the ring 1 may be irradiated with light from the outside by the light receiving means 6, for example.

Furthermore, the light receiving device may be configured such that the light introduced from the light receiving means 6 is absorbed only when the energy level of carriers within the ring 1 changes. Although FIG. 1 shows a configuration including one ring, a configuration using a plurality of rings can also be adopted. It is also possible to arrange a large number of rings on a single substrate to form an integrated device. Also, instead of an isolated ring,
It is also possible to use a ring that is connected to other devices or other rings by wiring. Further, the magnetic field applying means and the electric field applying means can be used simultaneously. Furthermore, the form of signal input and signal output is not limited to light.

Next, a more specific embodiment of the present invention will be described with reference to FIG. FIG. 3(A) shows a cross-sectional view, and FIG. 3(B) shows a plan view. In the figure, semi-insulating GaA
An electron transit layer 12 made of undoped GaAs and an electron supply layer 13 made of n-type AlGaAs are epitaxially grown on the s-substrate 11. For example, the thickness of the electron transit layer 12 is about 200 nm, and the thickness of the electron supply layer 1 is about 200 nm.
The doping concentration of 3 is approximately 1E18 cm-3. In this way, a so-called two-dimensional electron gas structure is constructed. A ring-shaped gate electrode 14 as shown in FIG. 3(B) is formed on the electron supply layer 13. In addition, GaAs
When the gate voltage is 0, no carriers exist on the electron transit layer side of the hetero interface between the electron transit layer 12 made of AlGaAs and the electron supply layer 13 made of AlGaAs, and the gate 1
By applying a positive voltage to electrode 4, two-dimensional electron gas 15 is accumulated under the electrode.

In this way, the two-dimensional electron gas 15 is formed in a shape corresponding to the gate electrode 14, forming a ring. A magnetic flux φ is applied perpendicularly to this ring (in the vertical direction in the figure). The change ε in the absorption edge due to the magnetic flux φ can be approximated by the formula shown in the figure. However, in the formula, h is Planck's constant, m is the effective mass of electrons or holes, L is the circumference of the ring,
φo is the magnetic flux quantum, Eto is the fundamental energy of transverse motion within the ring, Eg is the band gap, and Eo is the fundamental energy of the two-dimensional electron gas.

The diameter of the ring is, for example, 0.3 μm, and the width of the ring is, for example, about 0.1 μm. Note that a gate electrode for controlling electrostatic potential for controlling the Ahranoff-Bohm effect is provided above or to the side of the gate electrode 14 shown in the figure. The control voltage is
For example, it is 30mV.

[0027] When such a device is used to generate a light emission phenomenon due to the Ahranoff-Bohm effect, the emission wavelength is, for example, about 2.5 μm. Note that although a device that generates two-dimensional electron gas in an enhancement mode has been described, a depletion type device can also be configured. For example, a gate electrode is formed on the entire surface except for the ring-shaped region, and a reverse bias voltage is applied to the gate electrode so that no two-dimensional electron gas exists under the gate electrode.

According to this embodiment, the carriers in the ring are composed of two-dimensional electron gas, and a device with extremely low scattering and a long mean free path can be realized. below,
Examples of other forms will be described.

FIG. 4 shows an embodiment using two rings. FIG. 4A shows a configuration including two isolated rings 21, 22. For example, when magnetic flux is applied to the ring 21 by the magnetic flux applying means 25, the energy level of carriers within the ring 21 changes, and this change in the energy level of the carriers affects the ring 22.

Alternatively, as shown in the figure, by slightly changing the sizes of the rings 21 and 22, the magnetic flux applying means 2
Apply magnetic flux from 5. Then, due to the difference in the dimensions of the rings, a difference occurs in the change in carrier energy level between the rings 21 and 22. By extracting the differences in the changes in these energy levels by the signal extracting means and comparing them, more accurate signal detection becomes possible. for example,
A device that measures the magnetic flux applied by the magnetic flux applying means 25 can be configured.

FIG. 4(B) shows two electrically connected
An example using two rings is shown. The ring 21 and the ring 22 are arranged concentrically in parallel, and the conductive means 2 is inserted between them.
Connected by 4. The rings 21 and 22 have different areas. When a magnetic field is applied to the ring pair 21 and 22 from the magnetic flux applying means 25, the ring 2
Since the dimensions of ring 1 and ring 22 are different, changes in the energy level of carriers within the ring are also different. for example,
When the magnetic flux is gradually increased, the carriers are first localized in the ring 21 and then the carriers are localized in the ring 22. By detecting the movement of carriers within such a ring pair, an electronic/optical device can be constructed. The movement of carriers within the ring pair can also be carried out using, for example, light absorption, light emission, or detection means that is capacitively coupled to one of the rings. In addition, various detection methods can be used.

FIG. 5 shows an embodiment using multiple rings. A large number of rings 32 are arranged on the surface of the support substrate 31. Each of these rings can function similarly to the previous embodiments. Furthermore, when emitting light by means of rings, for example, a number of rings can be coupled together to obtain an amplified light output. Although a configuration in which a large number of isolated rings are integrated is shown, some or all of these rings may be connected to each other.

FIG. 6 shows an example in which a so-called quantum dot structure is used as a means for forming a quantum ring. Carriers can exist only in a disk-shaped region, resulting in a so-called quasi-zero-dimensional structure. By applying a magnetic field,
The circular motion of carriers within the dot is modulated, and the energy eigenvalue also changes. Therefore, it can be said that a quantum ring is essentially formed. This structure can be used to realize the various applications listed above. Although a disk-shaped region is taken as an example here, the shape is not essential as long as it is a simply connected micro region.

In contrast to FIG. 6, FIG. 7 shows a method of constructing a quantum ring using a so-called quantum antidot structure. In this case, carriers can exist only in regions other than the disk-shaped portion. By applying a magnetic field, the wave function, or trajectory, around the disk is modulated, and the energy level changes. Therefore, the same effect as quantum dots can be obtained.

[0035] The present invention has been explained in accordance with the embodiments above, but
The present invention is not limited to these. Any device may be used as long as it is made of a conductive material and changes the energy state of carriers in a ring constituting a closed loop using a magnetic field or an electric field and extracts it as a signal. Various forms of the signal are possible, such as light, current, and voltage. Furthermore, the quantum ring device using the Ahranoff-Bohm effect of the present invention can be used in combination with other types of devices. It will be obvious to those skilled in the art that various other changes, improvements, combinations, etc. are possible.

[0036]

[Effects of the Invention] As explained above, according to the present invention,
By changing the energy state of carriers within the ring using magnetic flux or electric field, a novel type of quantum ring device utilizing the Ahranov-Bohm effect is provided.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a basic embodiment of the present invention.

FIG. 2 shows a conventional technique. FIG. 2(A) is a schematic diagram for explaining an experiment using a metal ring, and FIG. 2(B) is a cross-sectional view for explaining an experiment using a single crystal semiconductor ring.

FIG. 3 shows an embodiment of the invention. FIG. 3(A) is a cross-sectional view;
FIG. 3(B) is a plan view.

FIG. 4 shows an embodiment of the invention using two rings. FIGS. 4A and 4B are schematic diagrams of embodiments using two rings, respectively.

FIG. 5 is a schematic perspective view of an embodiment of the invention using multiple rings.

FIG. 6 is a schematic perspective view showing an embodiment of the present invention using a so-called quantum dot structure.

FIG. 7 is a schematic perspective view showing an embodiment of the present invention using a so-called quantum antidot structure.

[Explanation of symbols]

1 Ring 2 Magnetic field application means 3 Electric field application means 5 Signal extraction means 6 Light receiving means

Claims (5)

[Claims] 1. A ring (1) formed of a conductive material and constituting a closed loop; and means (2) for applying a magnetic field or an electric field to the ring to change the energy state of carriers in the ring. 3), and signal extraction means (5) for extracting the change in the energy state of the carrier as a signal.
) and quantum ring devices. 2. The quantum ring device according to claim 1, wherein said signal extraction means includes light guiding means for guiding the generated light. 3. The quantum ring device according to claim 1, further comprising light receiving means (6) for receiving light from the outside to the ring. 4. The quantum ring device according to claim 1, further comprising at least one other ring coupled to the ring. 5. At least two rings (21, 22) formed of a conductive material, each forming a closed loop.
), a conductive member (24) electrically connecting the at least two rings, and applying a magnetic field or an electric field to at least one of the at least two rings to change the energy state of the carrier in the ring. , means (25) for changing the distribution state of carriers in a plurality of coupled rings.