JP3171278B2 - Quantum box semiconductor 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 semiconductor device, and more particularly to a quantum box semiconductor device for controlling carrier transition between quantum boxes having a zero degree of freedom of carriers.

[0002] Advances in semiconductor fine processing technology have made it possible to manufacture semiconductor devices in submicron or smaller sizes. In a semiconductor region miniaturized to a size of about the de Broglie wavelength of electrons in a solid, quantum mechanical properties of carriers appear. As a result, the energy levels of electrons and holes are quantized.

One of the new functions using these quantized levels is resonance tunneling. This phenomenon is a phenomenon in which carriers selectively make a tunnel transition only when two adjacent energy levels coincide with each other. A resonant hot electron transistor (RHE) using this as an emitter is used.
T) has been prototyped.

[0004]

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

However, at room temperature, the influence of thermal vibration of the lattice cannot be avoided, and sharp characteristics cannot be obtained in many cases due to the energy distribution of the carriers and the blur of the energy level.

Therefore, a quantum wire (one-dimensional carrier) in which the degree of freedom of the carrier is further restricted and the level is localized.
And quantum boxes (0-dimensional carriers) have been proposed, and application to devices has been studied.

For example, TI's Mark Read et al.
Japanese Patent Application Laid-Open Nos. 61-123174 and 61-816 disclose a semiconductor device using two-dimensional resonant tunneling.
No. 62, JP-A-61-82470, JP-A-61-82
No. 471, JP-A-61-82472 and JP-A-61-82472.
-82473). This is a logic element that performs electron tunneling control using the change in the external potential of electrons.

[0008]

In the conventional quantized semiconductor device described above, the potential of a region including a potential well or the external field potential of a region including a quantum box in which 0-dimensional electrons are placed is generally reduced. Modulated. 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 proximity arrangement of the quantized semiconductor device is restricted.

An object of the present invention is to provide a quantum box semiconductor device having a novel configuration. Another object of the present invention is to provide a quantum box semiconductor device using a driving method capable of high integration.

[0010]

According to the present invention, there is provided a quantum box semiconductor device formed in a semiconductor so as to be close to a carrier having a quantum box structure formed in the semiconductor and to be tunnel-injected from the carrier emitter. A plurality of carrier collectors having a quantum box structure, and control means for controlling a quantum box size of the carrier collector by an external voltage, wherein the plurality of carrier collectors are formed in quantum boxes of different sizes in advance, and the control is performed. The means has means for applying the same external voltage to a plurality of carrier collectors, and causes resonant tunneling injection from the carrier emitter to different carrier collectors depending on the 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 using the change in the quantum level.

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

FIG. 1A shows a state where no external voltage is applied to the carrier collector 8A. For simplicity, 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, but the present invention is of course not limited to this.

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

As shown in the middle part of FIG. 1A, a voltage is now applied to the carrier collector 8A by an external voltage applying means, for example, an additional electrode, and the surrounding depletion layer region is enlarged, whereby the quantum in the direction indicated by arrow 1 is increased. If you shrink the box size,
The quantum level 6Ab of the carrier collector 8A shifts to a higher 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, causing the source 2 to move from the carrier emitter 7
The carrier injected to the carrier transitions to the carrier collector 8A.

Therefore, if the quantum levels of the carrier collector 8A and the drain 4A are made to match by 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 carrier that has transited to the carrier collector 8A can immediately flow into the drain 4A in a hot state.

At room temperature, the transition probability has a certain width because the quantum level is blurred due to the effects 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 energetically higher than the quantum level 5 of the carrier emitter 7 as shown in the lower part of FIG. Becomes As a result, from 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 hardly affected by charges such as impurities in the surroundings.

FIG. 1B shows a plurality of carrier collectors (three carrier collectors 8A, 8B and 8 in the figure) of the present invention.
C is shown). Now, for the sake of explanation,
The size of each carrier collector is set as follows: 8A <8B <8C. The carrier is electron e.

The size 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 located at the highest energy level coincides with the quantum level 5 of the carrier emitter 7 according to the quantum box size ratio. The electrons e injected into the carrier emitter 7 are subjected to resonance tunnel injection into the carrier collector 8A.

When the external voltage is further increased, the carrier collector 8A becomes non-resonant, and the carrier collector 8B having the next highest energy level is brought into a resonance state, and electrons from the quantum level 5 to the quantum level 6B are changed. 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 a non-resonant state, coincides with the carrier emitter level 5 to perform resonance tunneling. Occurs.

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

The state described in principle with reference to FIG.
For example, 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, when a second semiconductor having a high impurity concentration and a wide bandgap is laminated on or under the first semiconductor having a low impurity concentration and a narrow bandgap, a modulation doping structure is formed. A well layer is formed at the heterojunction interface of the first semiconductor by band bending, 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 surroundings with a depletion layer.

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

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

[0029]

FIG. 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 configuration in FIG. 2 is, for example, as shown in FIG.

FIG. 2 shows quantum box carrier collectors 48, 50, and 52 (sizes are different from each other) close to the quantum box carrier emitter 46, similarly to the case of FIG.
8 <50 <52).

The emitter / collector distance is several to several tens of nm, which enables tunnel injection even by size reduction due to depletion of the collector. Each size of the emitter and the collector is about several tens nm.

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

The quantum level of each drain 40, 42, 44 is controlled by a respective gate electrode (not shown) so that the quantum level coincides with the respective carrier collectors 48, 50, 52.

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

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

Next, the n ⁺ type GaAs contact layer 68
A source electrode 30 and drain electrodes 32 and 34 made of AuGe / Au (thickness 20 nm / 200 nm) are formed thereon.
36 is formed using vapor deposition and a normal lift-off method.

Thereafter, heat treatment is performed to alloy the electrodes. The alloyed region is formed by a two-dimensional electron gas layer 70 in the depth direction.
Has been reached. Therefore, the two-dimensional electron gas layer 7 is formed from the source electrode 30 and the drain electrodes 32, 34, 36.
An electrical connection to zero 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, as shown in FIG. 3, n ⁺ -type GaAs contact layers 68 and n are formed by selective dry etching. Type A
A part of the lGaAs electron supply layer 66 is dug to separate regions corresponding to a source region, a carrier emitter, a carrier collector, and a drain region.

Undoped G just 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 is controlled.
A Schottky gate electrode 54 made of an Al film having a thickness of 300 nm is deposited on the region corresponding to. The electrode 54 has carrier collectors 48, 5 and 5 as indicated by the dotted lines in FIG.
0 and 52 are formed continuously so as to control the 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. 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 but performed only on the side surface.

As described above, when the voltage is applied to the electrode 54 formed only on the side surface to reduce the size of the quantum box, the quantum level becomes smaller than the size reduction ratio of the carrier collector as compared with the case where the electrode is formed on the entire surface. Since the shift ratio increases, the output rises for the same gate voltage change,
There is an advantage that the fall becomes sharper and the multi-channel output separation via a plurality of carrier collectors becomes clearer.

In the present embodiment, the quantum box sizes of the carrier collectors 48, 50 and 52 formed as described above satisfy the relationship of collector 50 <collector 48 <collector 52.

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

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

Of course, the carrier emitter size can be made larger or equal to other quantum boxes. These shift only 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 close to the respective quantum box regions 46, 48, 50 and 52 as to enable tunnel injection 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 energetically higher than the quantum level 51 of the carrier collector 50, 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 the quantum level 4
Even lower than 9.

Now, a negative voltage is applied to the source electrode 30 to increase the quantum level of the source 38. When the quantum level coincides with the quantum level 47 of the carrier emitter 46, resonance tunneling occurs, and electrons are generated by the carrier emitter. Injected into 46.

A negative voltage is also applied to the drain electrode 34,
The quantum level of the drain 42 is made to match the quantum level 51 of the carrier collector 50 in advance. However, the quantum level 47
Since the quantum level 51 is at a lower position in terms of 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 energetically. First, the quantum level 51 of the carrier collector 50 coincides with the quantum level 47 of the carrier emitter 46 to be in a resonance state, and electrons transition from the carrier emitter to the carrier collector.

The electrons injected into the quantum level 51 by tunnel injection have the same quantum level of the quantum level 51 and that of the drain 42, so that the drain 4 is immediately subjected to resonance tunneling.
2 to form a drain current. This is shown in FIG.
Shown in

On the other hand, the quantum level of the other carrier collector is still lower in energy than the quantum level 47 of the carrier emitter 46 as shown in the middle and lower parts of FIG. No current flows. Note that the quantum levels of the drains 40 and 44 are the carrier collectors 48 and 5
The two quantum levels 49 and 53 are matched.

As the bias of the Schottky gate electrode 54 is gradually increased, the quantum level of the carrier collector increases, and a current flows through 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 shows the relationship between the Schottky gate voltage and the drain current flowing. The drain current does not become completely zero due to lattice vibration at room temperature or transition between sub-levels, etc., and it is difficult to sharply cut off the current. However, it is possible to switch the current channel at high speed only by the magnitude of the gate voltage It is.

Such a multi-channel quantum box semiconductor device is suitable for application to a highly integrated device such as a neural network. In the above embodiment, three channels are arranged around the carrier emitter 46. However, the number of channels can be increased or decreased as needed. The quantum box can be formed by an ion implantation method in addition to the above-described etching method.

In the above embodiment, the two-dimensional electron gas layer 7
0 was formed by modulation doping of AlGaAs / GaAs, 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 and may not be quantized.

In the above embodiment, the traveling carriers are electrons. However, it is clear from the principle of the present invention that holes can be used. Although the present invention has been described 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 level in the quantum box can be changed by effectively changing the size of the quantum box of the carrier collector constituting the multi-channel by an external voltage. By appropriately changing the quantum level of each carrier collector with a voltage, an arbitrary channel can be selected and a current through resonance tunneling can be selectively passed.

Since the quantum level is controlled by changing the size of the quantum box, the size of the quantum box is hardly affected by charges due to surrounding impurities and the like, and the size can be further reduced. Therefore, a highly integrated high-speed switching circuit can be formed.

[Brief description of the drawings]

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

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

FIG. 3 is a schematic configuration diagram in the XY section of FIG. 2;

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

FIG. 5 is a graph showing a change in current of each channel due to the operation shown in FIG. 4;

[Explanation of symbols]

Reference Signs List 1 external voltage applying means to quantum box 2 source of quantum wire structure 3 potential barrier between carrier emitter and 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 Reference Signs List 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 Reference Signs List 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 Region 74, 76, 78 Two-dimensional electron gas drain region

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 21/337 H01L 21/338 H01L 27/095 H01L 29/778 H01L 29/80-29/812 H01L 29 / 68

Claims (4)

(57) [Claims] 1. A carrier emitter having a quantum box structure formed in a semiconductor, a plurality of carrier collectors having a quantum box structure formed in the semiconductor so close to the carrier that tunnel injection can be performed, and the carrier collector Control means for controlling the quantum box size by an external voltage, wherein the plurality of carrier collectors are previously formed in quantum boxes of different sizes, and the control means controls the plurality of carrier collectors with the same external voltage. A multi-channel quantum box semiconductor device, comprising: means for applying a voltage to the carrier emitter to cause resonance tunnel injection from the carrier emitter to a different carrier collector according to a voltage. 2. A quantum well or quantum wire structure source for supplying carriers to the carrier emitter and a quantum well or quantum wire structure drain for extracting carriers from the carrier collector, respectively. Multi-channel quantum box semiconductor device. 3. The multi-channel quantum box semiconductor device according to claim 1, wherein the source, the carrier emitter, the carrier collector, and the drain are formed in a two-dimensional electron gas region generated by modulation doping of a heterojunction. 4. The control means includes a Schottky electrode formed on the plurality of carrier collectors.
The multi-channel quantum box semiconductor device according to any one of the above items.