JPH03262161A - Resonant tunnel transistor - Google Patents

Abstract

PURPOSE:To enable a resonant tunnel electron current to be controlled with a small base current by a method wherein a first and a second potential barrier layer are provided sandwiching a base layer between them, an emitter electrode is formed into a pointed structure, and the tip of the emitter electrode is connected to the second potential barrier layer. CONSTITUTION:In this transistor, a potential barrier layer 35 formed of a silicon oxide film is provided to the side of a base layer 33 opposed to a pointed recess 31a coming into contact with the base layer 33, and a second potential barrier layer 37 formed of a silicon oxide film is provided coming into contact with the base layer 33 on the pointed recess 31a side. A proper electrode material is filled into the pointed recess 31a to form an emitter electrode which is formed in a pointed structure and whose tip is connected to the second potential barrier layer 37. Therefore, as the emitter electrode has a pointed structure, an electrical field can be concentrated on the tip of the emitter electrode, so that a resonant tunnel phenomenon can be induced with a small base current, and a resonant tunnel electron current is improved in injection efficiency, in result a resonant tunnel electron current can be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a resonant tunnel transistor.

(Prior art) Resonant tunnel transistors that utilize resonant tunneling are known as one of the new devices that utilize the tunneling effect in superlattice heterojunctions. “Structural Device” (1
988) p. 397, published by the Industrial Research Association).

FIG. 5 is a cross-sectional view schematically showing the general structure of a conventional resonant tunneling transistor that includes two potential barrier layers (two in total above and below the base layer 17).
Diagram M6 is a diagram showing an energy band diagram of such a resonant tunnel transistor.

This resonant tunnel transistor includes, on a substrate 11, a collector electrode 13, a first potential barrier layer 15, a base layer 17 consisting of a quantum well layer, a second potential barrier layer 19, and an emitter electrode 21 in this order. (It had a laminated structure. Roughly speaking, in this resonant tossinel transistor, for example, AuGe, etc. A wiring lead-out batt 23 made of metal was provided.In the energy band diagram of FIG. 6, what is indicated by 17a is a resonant tunnel level.

Here, the first and second potential barrier layers 15, 19
The thickness of the base layer 17 is, for example, about several tens of λ to allow electrons to pass through the barrier layer due to tunneling phenomenon, and the thickness of the base layer 17 is set to prevent scattering of electrons by the Hose layer 17. In order to keep the number of participants small, it was supposed to be around 10 people.

In this resonant tunnel transistor, the Hose layer 1
Only when the potential of 7 is at a certain value (this certain value exists discretely), the resonant tunnel level formed in the base layer 17 and the electron level in the emitter electrode layer 21 become equal and resonance occurs. A tunneling phenomenon occurs, and electrons are transported from the emitter electrode side to the collector electrode side. On the other hand, when the potential of the base layer is other than the above-mentioned certain value, the resonant tunneling phenomenon does not occur and the amount of electron transport decreases. However, when electrons are transported by the resonant tunneling phenomenon, the collector current can be controlled with a very small base current, so a higher current gain can be obtained compared to bipolar transistors and the like.

Further, in a GaAs-based resonant tunnel transistor, the structural part consisting of the potential barrier layer 15/base layer 17/potential barrier 19 in such a conventional resonant tunnel transistor is A 12 G a A
s / Ga As / AβGaAs (for example, literature: Yoshihisa Takeuchi, co-edited by Okoshiba Mikoshiba, "Physics and Applications of Tunnel Phenomenon", Baifukan (+989) p.
, 49), and for InGaAS-based ones,
A fl A s / I n +. GaxAs/Aρ
△S or I n A II A s / l: n G
It was composed of a A s / I n Aρ△S (for example, literature = "Spectrum" round cover (+989) p
, 94). In addition, in the case of Sl-based products, 5il-G
ex /Sl/Si.

Ge, (for example, literature: IEEE I
EDM) Technical Digest (1989) p, 65
1).

Further, in such a resonant tunnel transistor, a collector layer 13, a first potential barrier layer 5, a base layer 1
7. Second potential barrier layer 19 and emitter layer 21
The hetero-O junction formed between each layer must have a steep Peter interface. Therefore, when forming a potential barrier layer and a base layer composed of a mixed crystal layer, the composition must be controlled with high precision.Therefore, molecular beam epitaxy technology, which allows crystal growth on the order of atomic layers, is widely used. It was used.

(Problems to be Solved by the Invention) However, in the conventional resonant tunnel transistor shown in FIG. Because this was not the intended structure, ■...it was not possible to lower the voltage that could cause the resonant tunneling phenomenon, and ■...the resonant tunneling electron current (corresponding to the collector current during the resonant tunneling phenomenon) was increased. The problem was that I couldn't do it. In other words, it was not possible to control the resonant tunneling electron current with a low base potential (low tunnel level).

In addition, in a structure using a mixed crystal layer such as a conventional resonant channel transistor, even if molecular beam epitaxy technology is used,
It is extremely difficult to optimize the composition of each layer such as the potential barrier layer and the Hess layer, and it has been difficult to obtain a technically satisfactory resonant tunnel transistor.

The present invention has been made in view of these points, and therefore, an object of the present invention is to provide a resonant tunneling transistor that can control the resonant tunneling electron current with a lower base current than the conventional one.

(Means for Solving the Problems) According to this invention, in order to achieve the object of this invention,
a base layer, first and second potential barrier layers sandwiching the base layer, a collector electrode connected to the first potential barrier layer, and a collector electrode connected to the second potential barrier layer. A resonant tunnel transistor comprising an emitter electrode is characterized in that the emitter electrode is constituted by an electrode having a needle-like structure, and the tip of this electrode is connected to a second potential barrier layer.

In carrying out the present invention, it is preferable that the base layer described above is made of silicon, and the first and second potential barrier layers mentioned above are made of silicon oxide films.

Roughly speaking, in carrying out the present invention, a needle-shaped recess is provided on one of the front side and the back side of the silicon substrate, and the second potential barrier layer is formed with a silicon oxide film formed on the wall surface of the recess. Preferably, the emitter electrode is formed of an electrode material embedded in the recessed portion having the second potential barrier layer.

(Function) According to this configuration, since the emitter electrode is needle-shaped, the electric field can be concentrated at the tip of the emitter electrode, so resonance tunneling occurs at a lower base potential than when the emitter electrode is not needle-shaped. In addition, the resonant tunneling electron current can be increased by increasing the injection efficiency of the resonant tunneling electron current.

Furthermore, when the base layer is made of silicon and the first and second potential barrier layers are made of silicon oxide films,
It is easier to obtain desired silicon and silicon oxide films than in the case of mixed crystal layers. For example, a base layer and a potential barrier layer can be easily obtained by forming a silicon thin film as a base layer and then thermally oxidizing the silicon thin film to form a silicon oxide film on the surface of the thin film.

Further, a needle-shaped recess is provided on one of the front side and the back side of the silicon substrate, and a silicon oxide film formed on the wall surface of this recess constitutes a second potential barrier layer. When the emitter electrode is formed of an electrode material embedded in a recess having a barrier layer, it is easy to form the second potential barrier layer and the emitter electrode having a needle-like structure. Furthermore, since the base layer can be formed from the portion of the silicon substrate remaining at the tip of the portion where the needle-shaped recess is provided, the formation of the base layer is also facilitated.

(Embodiments) Hereinafter, embodiments of the resonant tunnel transistor of the present invention will be described with reference to the drawings. Note that each figure used in the explanation schematically shows the dimensions, shapes, and arrangement relationships of each component to the extent that the present invention can be understood.

First, the structure of the resonant tunnel transistor of the embodiment will be explained with reference to FIG. Here, FIG. 1 is a cross-sectional view schematically showing a resonant tunnel transistor of an example.

The resonant tunnel transistor of this embodiment has a structure in which a plurality of resonant tunnel transistors of the present invention are arranged in an array in order to improve the current gain. 1st
Although the figure also shows an array configuration, the approximate area of one resonant tunnel transistor in this figure is the area indicated by S.

In the resonant tunnel transistor of this embodiment, a needle-shaped recess 31afJX is formed on one of the front and back surfaces of an n-type silicon substrate 31 as a silicon substrate, for example.
It is a provision. In this embodiment, since a plurality of resonant tunnel transistors are provided in an array on the substrate, a corresponding number of needle-shaped recesses 31a are provided. Each needle-shaped recess 31a has a shape that becomes narrower from the opening of the recess toward the bottom, and is shaped so that the tip of an emitter electrode (described later) embedded in the recess has an acicular shape as sharp as possible. It's good to say that. Its actual shape, dimensions, etc. are determined depending on the processing method used and the required characteristics.

Furthermore, in the resonant tunnel transistor of this embodiment, the base layer 33 is formed by the wall of the bottom portion of the needle-shaped recess 31a, that is, the portion remaining in the region of the silicon substrate 31 where the recess 31a is provided. The thickness of the wall of the bottom portion of the recess 31a is set to be about 10 nm, which is not limited to this, so that it can function as a base layer of a resonant tunnel transistor. Therefore, the needle-shaped recesses 31a are formed so that the base layer 33 has such a thickness (details will be explained in the manufacturing method section). Note that the base layer 33 can be doped with a suitable impurity such as arsenic, if necessary.

Furthermore, in the resonant tunnel transistor of this embodiment, a first potential barrier layer 35 made of a silicon oxide film is provided on the opposite side of the base layer 33 from the needle-shaped recess 31a side, and is in contact with the base layer 33. Further, a second potential barrier layer 37 made of a silicon oxide film and in contact with the base layer 33 is provided on the needle-shaped recess 31a side of the heath layer 33. In reality, the first and second potential barrier layers 35 and 37 are each composed of a silicon oxide film obtained by thermally oxidizing the surface of the silicon substrate 31, including the inner wall surface of the acicular recess 31a. The thickness of the silicon oxide film constituting each of the first and second potential barrier layers 35 and 37 needs to be thick enough to allow electrons to pass through this oxide film due to the tunneling phenomenon. In the example, the thickness is about 3 to 5 nm.

Furthermore, in the resonant tunneling transistor of this embodiment, a suitable electrode material is embedded in the needle-shaped recess 31a provided with the second potential barrier layer 37. The tip of the electrode is the second
emitter electrode 3 connected to potential barrier layer 37 of
It consists of 9.

Furthermore, a collector electrode 41 is provided on the first potential barrier layer 35 .

Although the constituent materials of the emitter electrode 39 and the collector electrode 41 are not limited to these, Au, Ni, etc.
, Cu, Au, A9, M9 and the like.

Next, the voltage-current (V-I) characteristics of the resonant tunnel transistor of the embodiment having the above-described configuration are measured. FIG. FIG.

In this VI characteristic measuring circuit 51, the base layer 33 (
A silicon substrate 31 is interposed therebetween. ) and emitter electrode 39
(The provided variable voltage power supply 51a changes the voltage between the base layer 33 and the emitter electrode 39 and the voltage between the emitter electrode 39 and the collector electrode 41. the voltage between the layers 33;
Measure the relationship with collector current.

FIG. 3 is a V-I characteristic showing the relationship between the voltage between the emitter electrode 39 and the base layer 33 on the horizontal axis and the collector current on the vertical axis. The characteristics indicated by ■ in FIG. 3 are the VI characteristics of the resonant tunnel transistor of the example, and II
The characteristic shown in is the VI characteristic of the conventional resonant tunnel transistor (hereinafter referred to as a comparative example) shown in FIG. As can be seen from FIG. 3, in both the transistors of the example and comparative example, when the voltage applied between the emitter electrode layer 39 and the base layer 33 reaches a certain value, a rapid increase in collector current is observed. When the voltage is increased or decreased from , a sudden phenomenon of collector current is observed.

In other words, when the potential of the base layer 33 becomes equal to the intrinsic energy of the base layer 33 (resonant tunneling level), a resonant tunneling effect occurs and the collector current increases rapidly, and when the potential deviates from the above potential, the resonance condition weakens and the collector current decreases. Decrease. However, in the comparative example and the example, it can be seen that when the potential of the base layer 33 is the same, the resonant tunneling transistor of the example can control a higher resonant tunneling electron current.

Next, in order to deepen the understanding of the resonant tunnel transistor of the present invention, an example of a method for manufacturing the resonant tunnel transistor of the embodiment will be described. FIGS. 4(A) to 4(C) are explanatory diagrams, and show the state of the resonant tunnel transistor at the main steps in the manufacturing process with cross-sectional views at positions corresponding to FIG. 1. This is a process diagram.

First, an n-type silicon substrate 31 whose main surface is a (100) plane.
(Figure 4 (A)).

Next, a focused ion beam (Focus
ed Ion Beam: 0 using FIB) technology
．． The silicon in this region is etched by irradiation with gallium ions focused to a diameter of 1 nm, forming a needle-shaped recess 31a (FIG. 4(B)). Note that this etching is performed until the silicon substrate is approximately 1 inch thick on the other side of the silicon substrate 31.
This is done so that a thickness of approximately 0 nm remains.

Note that the formation of the needle-shaped recesses 31a is not limited to the FIB method, but may be performed, for example, by reactive ion etching using a silicon oxide film (SiO2 film) as a mask.

After forming the needle-shaped recesses 31a% by the method described above, the silicon substrate is exposed to a dry oxygen atmosphere at a temperature of, for example, 950'C for a predetermined period of time. By this thermal oxidation, first and second potential barrier layers 35,37@ each having a film thickness of about 3 to 5 nm are formed (FIG. 4(C)).

Next, an emitter electrode layer 39 and a collector electrode layer 41 are formed using known film forming techniques, photolithography techniques, and etching techniques to obtain the resonant tunnel transistor of the embodiment shown in FIG. 1.

Although the embodiments of the resonant tunnel transistor of the present invention have been described above, the present invention is not limited to the above-described embodiments, and may be modified as described below.

In the above-described embodiments, a configuration in which a plurality of resonant tunnel transistors of the present invention are provided in an array on the same substrate has been described, but the effects of the present invention can be obtained even with a single resonant tunnel transistor of the present invention. it is obvious.

Further, in the above-described embodiment, the present invention was applied to a resonant tunnel transistor in which the base layer 33 was formed from the wall of the bottom portion of the needle-shaped recess 31a provided in the silicon substrate 31. However, the present invention is not only applicable to transistors having such a configuration. For example, even if the emitter electrode of a conventional stacked resonant tunnel transistor using a mixed crystal layer shown in FIG. Ru. Further, in this case, the base layer 17 is made of silicon,
Of course, the present invention can also be applied to a structure in which each of the potential barrier layers 15 and 19 is made of a silicon oxide film.

(Effects of the Invention) As is clear from the above explanation, according to the resonant tunnel transistor of the present invention, since the emitter electrode is needle-shaped, the electric field can be concentrated at the tip of the emitter electrode. Compared to the non-acicular case, resonant tunneling can occur at a lower base potential,
Furthermore, the resonant tunneling electron current can be increased by increasing the injection efficiency of the resonant tunneling electron current. Therefore, it becomes possible to control the resonant tunneling electron current at a low Hoesmi level.

Furthermore, when the base layer is made of silicon and the first and second potential barrier layers sandwiching the base layer are made of silicon oxide films, compared to the conventional case in which these layers are made of mixed crystal layers. , it becomes easier to manufacture transistors. actual,
A desired transistor can be formed without using crystal growth techniques as in the case of using a mixed crystal layer. Furthermore, since the base layer/potential barrier layer is composed of silicon/silicon oxide film, the consistency of the interface is good.
Therefore, a good petrojunction can be obtained.

Therefore, it can be expected that the characteristics of the resonant tunnel transistor will be improved.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view for explaining the resonant tunnel transistor of the example, FIG. 2 is a diagram for explaining the V-I characteristic measurement system, and FIG. 3 is a cross-sectional view of the resonant tunnel transistor of the example and comparative example. 4(A) to 4(C) are process diagrams showing an example of a manufacturing method; FIG. 5 is a cross-sectional view schematically showing a conventional resonant tunnel transistor; The figure shows an energy band diagram of a resonant tunnel transistor. 31...Silicon substrate, 31a...Acicular recess 33...Base layer 35...First potential barrier layer 37...Second potential barrier layer 39...Emitter electrode 41... - Collector electrode 51...V-I characteristic measuring circuit 51a...Variable voltage power supply. "-1

Claims (3)

[Claims] (1) A base layer, first and second potential barrier layers sandwiching the base layer, a collector electrode connected to the first potential barrier layer, and a collector electrode connected to the second potential barrier layer. 1. A resonant tunnel transistor comprising an emitter electrode having a needle-like structure, the emitter electrode having a needle-like structure, the tip of which is connected to a second potential barrier layer. (2) The resonant tunnel transistor according to claim 1, wherein the base layer is made of silicon, and the first and second potential barrier layers are made of silicon oxide films. (3) In the resonant tunneling transistor according to claim 1, a needle-shaped recess is provided on one of the front side and the back side of the silicon substrate, and the silicon oxide film formed on the wall surface of the recess is used as the second 1. A resonant tunnel transistor, wherein the emitter electrode is formed of an electrode material embedded in a recessed portion having the second potential barrier layer.