JPH065879A - Quantum-box semiconductor device - Google Patents

Abstract

PURPOSE:To provide a current selectively through resonance tunneling in a desired selective channel by adjusting a voltage to change a quantum level adequately for each carrier collector. CONSTITUTION:A negative voltage is applied to a source electrode 30. Then, a quantum level at a source 38 increases and becomes equal to a quantum level 47 at a carrier emitter 47 so that resonance tunneling takes place and electrons are injected into the carrier emitter 46. A negative voltage is previously applied to a drain electrode 34 to make a quantum level at a drain 42 equal to a quantum level 51 at a carrier collector 50. Also, a negative voltage is applied to a Schottky gate electrode 54 to increase a quantum level in energy for each collector. When the quantum level 51 at the carrier collector 50 becomes equal to the quantum level 47 at the carrier emitter 46, the electron resonance takes place at first, and electrons make the transition from the carrier emitter to the carrier collector. The electrons that tunnel into the quantum level 51 are put in resonance because the quantum level 51 is equal to that of the drain 42, and then the electrons flow into the drain 42 to form a drain current.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device, and more particularly to a quantum box semiconductor device for controlling carrier transition between quantum boxes having 0-dimensional freedom of carriers.

With the advancement of semiconductor fine processing technology, it has become possible to manufacture semiconductor devices with a size of submicron or less. Quantum mechanical properties of carriers appear in a semiconductor region miniaturized to a size of about de Broglie wavelength of electrons in a solid. As a result, the energy levels of electrons and holes are quantized.

Resonant tunneling is one of the new functions utilizing these quantized levels. This phenomenon is such that carriers are selectively tunnel-transitioned only when two adjacent energy levels coincide with each other, and a resonant hot electron transistor (RHE) using this as an emitter
T) has been prototyped.

[0004]

2. Description of the Related Art In the case of RHET, carriers (electrons) normally transit between the levels of two quantum well layers adjacent to each other. That is, the degree of freedom of the carrier is two-dimensional.

However, at room temperature, the effect of thermal vibration of the lattice cannot be avoided, and sharp characteristics are often not obtained due to the carrier energy distribution and the energy level blurring.

Therefore, the quantum wires (one-dimensional carriers) in which the degrees of freedom of carriers are further restricted and the levels are localized
Also, a quantum box (0-dimensional carrier) has been proposed, and its application to a device is under consideration.

[0007] For example, Mark Lead et al.
A semiconductor device utilizing three-dimensional resonant tunneling has been disclosed (Japanese Patent Laid-Open Nos. 61-123174 and 61-816).
62, JP-A-61-82470, JP-A-61-82.
471, JP-A-61-82472 and JP-A-61.
-82473). This is a logic element that controls the tunneling of electrons by utilizing the external potential change of electrons.

[0008]

In the conventional quantized semiconductor device described above, the potential of the region including the potential well or the external field potential of the region including the quantum box in which the zero-dimensional electrons are placed is totally changed. It is modulating. For this reason, the electric field for controlling the operation of the quantized semiconductor device spreads to a region other than the quantum level, so that the adjacent arrangement of the quantized semiconductor device is limited.

An object of the present invention is to provide a quantum box semiconductor device having a novel structure. Another object of the present invention is to provide a quantum box semiconductor device by a driving method that enables high integration.

[0010]

A quantum box semiconductor device of the present invention is formed in a semiconductor such that a carrier emitter having a quantum box structure formed in a semiconductor and a tunnel emitter from the carrier emitter are close to each other. And a control means for controlling the quantum box size of the carrier collector by an external voltage.

[0011]

When the size of the quantum box is changed, the quantum level allowed in the quantum box changes. The resonance tunnel phenomenon can be controlled by utilizing this change in the quantum level.

FIG. 1 schematically shows the principle of the present invention. Figure 1
(A) is a potential diagram showing the quantum states of the carrier emitter 7 and the carrier collector 8A (one of a plurality of carrier collectors) adjacent to the carrier emitter 7. As the quantum box size becomes smaller, its potential distribution is tailed as shown in the figure, and it becomes difficult to change sharply.

The upper part of FIG. 1A shows a state where no external voltage is applied to the carrier collector 8A. The figure shows a case where the level 6Aa of the carrier collector 8A is lower in energy than the quantum level 5 of the carrier emitter 7 for simplicity, but the present invention is not limited to this.

In the upper part of FIG. 1A, the source 2 is indicated by an arrow from the left side of the carrier emitter 7 as a means for supplying carriers to the emitter 7 and the right side of the carrier collector 8A. In the figure, a drain 4A that draws carriers from the collector 8A is indicated by an arrow.

As shown in the middle part of FIG. 1A, a voltage is applied to the carrier collector 8A by an external voltage applying means, for example, an additional electrode, and the depletion layer region around the carrier collector 8A is expanded to expand the quantum in a direction indicated by an arrow 1. If you reduce the box size,
The quantum level 6Ab of the carrier collector 8A shifts to the high energy side. At the same time, the bottom of the potential rises.

Carrier emitter 7 and carrier collector 8
When the quantum levels of A become energetically equal, a resonance tunneling phenomenon occurs and the source 2 to the carrier emitter 7
The carriers injected into the carrier transit to the carrier collector 8A.

Therefore, if the quantum levels of the carrier collector 8A and the drain 4A are matched with each other by an appropriate means,
At this time, carriers flow from the source 2 to the drain 4A.
Of course, if the drain 4A is not quantized, the carriers that have transited to the carrier collector 8A can immediately flow into the drain 4A in a hot state.

At room temperature, the transition level has a certain width because the quantum level is blurred due to the influence of lattice vibration and other carrier scattering mechanisms. Next, when the external voltage is further increased, the quantum level 6Ac of the carrier collector 8A becomes higher in energy than the quantum level 5 of the carrier emitter 7, as shown in the lower part of FIG. Becomes As a result, the carrier emitter 7 to the carrier collector 8A
The transition to stops again.

The level control of the quantum box of the present invention is possible by applying an external voltage to the quantum box and is not necessarily related to the external potential around the quantum box. It is unlikely to be affected by charges such as surrounding impurities.

FIG. 1B shows a plurality of carrier collectors of the present invention (three carrier collectors 8A, 8B, 8 in the figure).
(Indicates C). Now, for convenience of explanation,
The size of each carrier collector is set to 8A <8B <8C. The carrier is an electron e.

The sizes of the carrier collectors 8A, 8B and 8C can be controlled as shown in FIG. 1A when no external voltage is applied. When an external voltage is applied, the quantum level 6A of the carrier collector 8A, which is the highest in terms of energy, first coincides with the quantum level 5 of the carrier emitter 7 due to the quantum box size ratio, and the source 2 The electrons e injected into the carrier emitter 7 are resonance tunnel injected into the carrier collector 8A.

When the external voltage is further increased, the carrier collector 8A becomes non-resonant, and instead the carrier collector 8B having the next highest energy level becomes in a resonance state, and electrons from the quantum level 5 to the quantum level 6B are replaced. Tunnel injection occurs.

When the external voltage is further increased, the carrier collector 8B also becomes non-resonant, and the quantum level 6C of the carrier collector 8C, which has been in the non-resonant state until then, coincides with the carrier emitter level 5 to cause resonant tunneling. Occurs.

In this way, the carriers of one carrier emitter 7 are made into a plurality of conductive channels with a relatively sharp threshold value (composed of a carrier collector and a drain).
Can be arbitrarily switched.

The state described in principle with reference to FIG.
For example, the modulation doping of a heterojunction used in a high mobility transistor (HEMT) can be used, and it can be embodied by fine processing and appropriate electrode formation.

That is, a modulation doping structure is formed by stacking a second semiconductor having a high impurity concentration and a wide bandgap on or below a first semiconductor having a low impurity concentration and a narrow bandgap. A well layer is formed by band bending at the heterojunction interface of the first semiconductor, and electrons are integrated in the well layer. Since this is a two-dimensional electron gas, a one-dimensional or zero-dimensional state can be created by isolating the surrounding area with a depletion layer.

Utilizing such a 0-dimensional state, FIG.
By controlling the quantum box size as shown in (A) and (B), the resonance state can be controlled without forming a particular potential gradient outside the quantum box.

Hereinafter, the present invention will be described in more detail based on examples.

[0029]

2 is a plan view of a functional layer region of a multi-channel quantum box semiconductor device according to an embodiment of the present invention. The XY cross-sectional structure of FIG. 2 is as shown in FIG. 3, for example.

As in the case of FIG. 1B, FIG. 2 shows quantum box carrier collectors 48, 50 and 52 (sizes of 4 are different in size, which are close to the quantum box carrier emitter 46).
8 <50 <52) is arranged.

The emitter / collector distance is from several nm to several tens of nm which can be tunnel-injected even if the size is reduced by depleting the collector. The size of each of the emitter and collector is about several tens of nm.

A source 38 is provided near the carrier emitter 46.
However, drains 40, 42 and 44 are arranged near the collectors 48, 50 and 52, respectively. In the figure, each drain region has a one-dimensional channel (quantum wire) structure, but it does not necessarily have to be quantized.

The quantum levels of each drain 40, 42, 44 are controlled by their respective gate electrodes (not shown) to match the quantum levels with their respective carrier collectors 48, 50, 52.

The source 38 is connected to the two-dimensional electron gas region 72, and the source electrode 30 is provided on the region 72. On the other hand, each drain 40, 42, 44 is also 2
Connected to the three-dimensional electron gas regions 74, 76 and 78, drain electrodes 32, 34 and 36 are provided on the respective regions. A common gate electrode 54 is provided on the carrier collectors 48, 50 and 52.

Such a structure is manufactured, for example, as described above. First, as shown in FIG. 3, a 500 nm-thick undoped Ga layer is formed on a semi-insulating GaAs substrate 60.
As layer 62 and undoped AlG having a thickness of 10 nm thereon
an aAs spacer layer 64, on which an n-type AlGaAs electron supply layer 6 having a thickness of 45 nm and an impurity concentration of 1 × 10 ¹⁸ cm ^−3.
6, with a thickness of 45 nm and a carrier concentration of 1 × 10 ¹⁸ c
A multilayer structure in which the m ³ n ⁺ type GaAs contact layer 68 is continuously formed by the MBE method is obtained.

Then, an n ⁺ type GaAs contact layer 68 is formed.
On top, a source electrode 30 and a drain electrode 32, 34 made of AuGe / Au (thickness 20 nm / 200 nm),
36 is formed by vapor deposition and a normal lift-off method.

Then, heat treatment is performed to alloy the electrodes. The alloyed region has a two-dimensional electron gas layer 70 in the depth direction.
Has reached. Therefore, from the source electrode 30 and the drain electrodes 32, 34, 36 to the two-dimensional electron gas layer 7
An electrical connection to 0 is made through the alloyed region.

The undoped GaAs channel layer 62 and the n-type AlGaAs electron supply layer 66 form a modulation-doped heterojunction. In the two-dimensional electron gas layer 70 is formed on the heterojunction interface region between the undoped GaAs channel layer 62, the sheet carrier concentration of about 2.3 × 10 ¹¹ cm ^-2, the electron mobility becomes 800000cm ² / V · sec about .

In order to form the carrier emitter 46 and the carrier collectors 48, 50 and 52 in the two-dimensional electron gas layer 70, the n ⁺ type GaAs contact layers 68 and n are formed by selective dry etching as shown in FIG. Type A
A part of the 1GaAs electron supply layer 66 is dug to separate the regions corresponding to the source region, carrier emitter, carrier collector, and drain region.

Undoped G immediately below the etched region
In the aAs channel layer 62, the two-dimensional electron gas layer 70 disappears from the heterojunction interface region due to depletion. Finally, in order to control the quantum box size of the carrier collectors 48, 50, 52 by an external voltage, the contact layer 68
A Schottky gate electrode 54 made of an Al film having a thickness of 300 nm is deposited on the corresponding region of. The electrode 54 has carrier collectors 48, 5 as shown by the dotted lines in FIG.
It is formed continuously so as to control 0, 52 as a whole.

As shown in FIG. 3, the Schottky gate electrode 54 is formed of an Al film deposited not only on the surface of the island region of the contact layer but also on the side surface thereof. FIG. 3B shows another form of the Schottky gate electrode 54. In this case, the Al film is deposited on the contact layer 6
8 is not performed on the upper surface of the island region, but is performed only on the side surface.

In this way, when the voltage is applied to the electrode 54 formed only on the side surface to reduce the quantum box size, the quantum level is smaller than the carrier collector size reduction ratio as compared with the case where the electrode is formed on the entire surface. Since the shift ratio is large, the output rises for the same gate voltage change,
It has the advantages of a sharper fall and more clear multi-channel output separation via multiple carrier collectors.

The quantum box sizes of the carrier collectors 48, 50 and 52 formed as described above in the present embodiment have a relationship of collector 50 <collector 48 <collector 52.

That is, regarding the quantum level of each carrier collector when the external voltage is not applied, the collector 52 is at the lowest energy position, and then the collector 4
8, collector 50 in that order.

Now, for simplicity, the carrier emitter 46
Is formed to be smaller than the carrier collector 50. At this time, the quantum level of the carrier emitter 46 is at the highest energy level between the quantum boxes.

Of course, the carrier emitter size can be made larger or equal to that of the other quantum boxes. These only shift the quantum level energy relative to the voltage applied to the gate electrode 54, and do not essentially affect the operation of the semiconductor device.

The quantum levels of the quantum wire regions 38, 40, 42 and 44 formed so as to be close to the quantum box regions 46, 48, 50 and 52, respectively, so that they can be tunnel-injected, are higher than the quantum box levels. It is in a low energy position.

FIG. 4A shows the potential state of each region when no voltage is applied to the gate electrode 54. The quantum level 47 of the carrier emitter 46 is higher in energy than the quantum level 51 of the carrier collector 50, and the quantum level 49 of the carrier collector 48 is lower than the quantum level 51.
The quantum level 53 of the carrier collector 52 is equal to the quantum level 4
Even lower than 9.

Now, when a negative voltage is applied to the source electrode 30 to raise the quantum level of the source 38 and it coincides with the quantum level 47 of the carrier emitter 46, resonance tunneling occurs and electrons are generated in the carrier emitter. Injected at 46.

A negative voltage is also applied to the drain electrode 34,
The quantum level of the drain 42 is matched with the quantum level 51 of the carrier collector 50 in advance. However, the quantum level 47
Since the quantum level 51 is lower in energy,
No drain current flows.

Next, when a negative voltage is applied to the Schottky gate electrode 54, the quantum level of each collector rises in terms of energy. First, the quantum level 51 of the carrier collector 50 coincides with the quantum level 47 of the carrier emitter 46 and becomes a resonance state, and electrons transit from the carrier emitter to the carrier collector.

Since the quantum level 51 and the drain 42 have the same quantum level, the electron injected into the quantum level 51 is immediately tunneled to the drain 4 by resonance tunneling.
2 to form a drain current. This is shown in FIG.
Shown in.

On the other hand, the quantum levels of the other carrier collectors are still lower in terms of energy than the quantum level 47 of the carrier emitter 46, as shown in the middle and lower stages of FIG. No current flows. The quantum levels of the drains 40 and 44 are carrier collectors 48 and 5,
It is made to agree with the quantum levels 49 and 53 of 2.

As the bias of the Schottky gate electrode 54 is gradually increased, the quantum level of the carrier collector rises, and a current flows to the drain 40 of the carrier collector 48 and then to the drain 44 of the carrier collector 52. Is clear. When the drain current flows through each carrier collector, the other drain currents are almost zero.

FIG. 5 illustrates the relationship between the Schottky gate voltage and the flowing drain current. The drain current does not become completely zero due to lattice vibrations at room temperature and transitions between sublevels, and it is difficult to sharply cut off the current, but it is possible to switch the channel of the flowing current at high speed only by the magnitude of the gate voltage. Is.

Such a multi-channel quantum box semiconductor device is suitable for application to highly integrated devices such as neural networks. In the above embodiment, the channels arranged around the carrier emitter 46 are three systems, but the number can be increased or decreased if necessary. In addition to the etching method described above, the quantum boxes can be formed using an ion implantation method.

In the above embodiment, the two-dimensional electron gas layer 7
0 was formed by AlGaAs / GaAs modulation doping, but other materials, combinations such as InAlAs /
Obviously, InGaAs or the like can be used. further,
The source 38 and the drains 40, 42, 44 may have a quantum well structure or may not be quantized.

Further, in the above embodiments, the traveling carrier is an electron, but it is also clear from the principle of the present invention that a hole can be used. Although the present invention has been described above with reference to the embodiments, the present invention is not limited thereto. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0059]

As described above, according to the present invention,
The quantum levels in the quantum boxes can be changed by effectively changing the size of the quantum boxes of the carrier collectors forming the multi-channel with an external voltage. By changing the quantum level of each carrier collector with an appropriate voltage, an arbitrary channel can be selected and a current due to resonant tunneling can be selectively passed.

Since the quantum level is controlled by changing the size of the quantum box, it is less susceptible to charges due to impurities in the surroundings, and the size can be further reduced. Therefore, it is possible to form a highly integrated high-speed switching circuit.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is a plan view showing an operation area of the embodiment of the present invention.

FIG. 3 is a schematic configuration diagram in an XY cross section of FIG.

FIG. 4 is a schematic diagram for explaining the operation of the embodiment shown in FIGS.

5 is a graph showing a change in current of each channel due to the operation shown in FIG.

[Explanation of symbols]

1 means for applying external voltage to quantum box 2 source of quantum wire structure 3 potential barrier between carrier emitter / collector 4 drain of quantum wire structure 5 quantum level of carrier emitter 6 quantum level of carrier collector 7 carrier emitter 8 carrier collector 30 Source electrode 32, 34, 36 Drain electrode 38 Source 40, 42, 44 Drain 46 Carrier emitter 47 Carrier emitter quantum level 48, 50, 52 Carrier collector 49, 51, 53 Carrier collector quantum level 54 Schottky gate electrode 60 semi-insulating GaAs substrate 62 undoped GaAs channel layer 64 undoped AlGaAs spacer layer 66 n-type AlGaAs electron supply layer 68 n ⁺ type GaAs contact layer 70 two-dimensional electron gas layer 72 two-dimensional electron gas source region Area 74, 76, 78 Two-dimensional electron gas drain area

Claims (5)

[Claims] 1. A quantum box structure carrier emitter (7) formed in a semiconductor, and a plurality of quantum box structure quantum well structures formed in the semiconductor as close as possible to tunnel injection from the carrier emitter (7). A multi-channel quantum box semiconductor device having carrier collectors (8A, 8B, ...) And control means (1) for controlling the quantum box size of the carrier collectors (8A, 8B, ...) With an external voltage. 2. A source (2) of a quantum well or quantum wire structure for supplying carriers to the carrier emitter (7) and the carrier collector (8A, 8).
2. The multi-channel quantum box semiconductor device according to claim 1, further comprising a quantum well or a quantum wire structure drain (4A, 4B, ...) For extracting carriers from B ,. 3. The plurality of carrier collectors (8A, 8)
B) are formed in quantum boxes of different sizes in advance, and the control means (1) has means for applying the same external voltage to a plurality of carrier collectors, and the carrier emitter (7) changes the voltage. 3. The multi-channel quantum box semiconductor device according to claim 1, wherein resonant tunnel injection is caused in different carrier collectors accordingly. 4. A two-dimensional electron gas region in which the source (2), carrier emitter (7), carrier collector (8A, 8B, ...) And drain (4A, 4B, ...) Appear by modulation doping of a heterojunction. The multi-channel quantum box semiconductor device according to claim 1, which is formed by. 5. The multi-channel quantum box semiconductor device according to claim 1, wherein the control means (1) includes a Schottky electrode formed on the plurality of carrier collectors (8A, 8B, ...). .