JPH0291984A - Superconducting transistor - Google Patents

Abstract

PURPOSE:To obtain a sufficient gain by forming each layer with a semiconductor, and laminating superconductor films on a base at specified positions. CONSTITUTION:An emitter layer 6, a base layer 4 and a collector layer 2 are formed in a transistor with semiconductors so as to form heterojunctions. A superconductor film 7 is laminated on the layer 4 at a position around the layer 6 under the non-contact state. When this transistor is placed in an atmosphere below the critical temperature of the film 7, the density of superconductive electrons in the layer 4 is increased by an proximity effect. Carrier passing regions are continuously connected in a heterojunction pattern from the layer 6 to the layer 3. The regions are formed with the semiconductors. Therefore, a barrier layer other than a barrier layer 3 is not formed between the layers 4 and 2. The potential difference between the layer 4 and the layer 2 becomes small. The carrier passing rate is enhanced, and the sufficiently high current gain is obtained in the transistor.

Description

[Detailed Description of the Invention] [Summary] For the purpose of imparting sufficient gain to a transistor in which the Be-Ikku region has superconducting properties, the emitter layer, base layer, and collector layer constituting the transistor are made of semiconductors. and a superconductor film located around the emitter layer in a non-contact state is laminated on the base layer.

[Industrial Application Field] The present invention relates to a superconducting transistor, and more specifically,
This invention relates to a transistor whose base region has superconducting properties.

(Prior Art) Elements using Josephson junctions have high speed and low power consumption, and various transistors made of superconductivity have been proposed.

In a typical example of this transistor, as shown in FIG. 5, a semiconductor collector layer 51 and a barrier layer 52 are sequentially laminated on a semi-insulating substrate 53, and an n° semiconductor FW film is placed on top of this. A layer 54 is formed, and a base J155 made of a superconductor, a barrier 7156 made of aluminum oxide, and an emitter layer 57 made of a superconductor are laminated in this order.

Here, specific examples of materials applied to each layer are as follows:
The substrate 53 is made of InP, and the collector 151 is made of InP.
GaAs collector! The barrier layer 52 on the 151 side contains I
Both sides of nAlGaAs 1a are covered with non-doped InGaAs films, and the semiconductor thin film layer 54 is n'''.
niobium is used for the base layer 55 and emitter layer 57, and aluminum oxide is used for the barrier layer 56 on the emitter layer 57 side (However, In is indium, P is phosphorus, Ga is gallium, and As is Arsenic, AI is the element symbol for aluminum).

The principle of this transistor will be explained based on the potential diagram shown in FIG. 6. After carriers are brought into a state of having a certain excitation energy, that is, a state called a quasiparticle, and pass through the barrier N56 on the emitter side, passing through the base layer 55 and the n゛ semiconductor thin film layer 54;
Furthermore, it is configured to reach the collector layer 51 beyond the barrier layer 52 on the collector side.

In order for a transistor having this type of structure to operate, the quasiparticles injected into the base layer 55 need to flow into the collector layer 51 before recombining to form a Cooper pair. In order to provide a sufficient current gain to the current gain, it is necessary that the probability that the quasiparticles pass through the barrier layer 52 on the collector side is high.

[Problem to be solved by the invention]

However, in this type of transistor using a metal such as niobium as a base, the difference in potential between the base layer 55 and the collector layer 51 is extremely large, several eV, as shown in FIG. Therefore, even if carriers have the energy to pass through this barrier according to classical mechanics, they will be reflected by the barrier and return to the base layer 55 unless they have significantly greater energy than the barrier height due to quantum mechanical reflection. A phenomenon occurs in which carrier transmittance decreases.

Furthermore, even if the carrier has energy greater than the potential difference, if it travels obliquely to the barrier layer 52, it will be reflected by the barrier layer 52 and the base 11
155 or go back and forth many times until it exits to the collector Nc side, which impairs high speed performance.

Furthermore, since this transistor has the n゛ semiconductor thin film layer 54 between the base layer 55 and the collector layer 51,
A thin barrier A as shown in FIG. 6 appears at the junction between the superconducting metal forming the base layer 55 and the n° semiconductor film layer 54, reducing the energy of carriers.

Therefore, a sufficient gain cannot be obtained by the superconducting transistor as described above.

The present invention has been made in view of such problems, and an object of the present invention is to provide a superconducting transistor that can obtain a sufficient gain.

[Means to solve the problem]

The above-mentioned issues are related to the emitter layer that constitutes the transistor,
The problem is solved by a superconducting transistor characterized in that a base layer and a collector layer are formed of semiconductors, and a superconductor film positioned around the emitter layer in a non-contact manner is laminated on the base layer.

[For production]

An example of the potential diagram in the above invention is shown in FIG. 2.

Figure (a) shows the potential diagram of a transistor in an atmosphere at room temperature. The potential of its base layer exhibits the characteristics of a semiconductor, but if the transistor is placed in an atmosphere below the critical temperature of the superconductor film, The superconducting properties change as shown in Figure 1).

This is because, although the base layer itself is formed of a semiconductor, a proximity effect occurs in the base layer, which increases the density of superconducting electrons in the base layer. here,
The proximity effect is a phenomenon in which a semiconductor film bonded to a superconductor film has superconducting properties, and this superconducting electron density becomes an order parameter as shown in Part 3.

Further, in this transistor, each continuous layer formed of a semiconductor from an emitter layer to a collector layer is stacked to form a heterojunction.

Furthermore, since the base layer is made of a semiconductor, no barrier due to the junction between the metal and the semiconductor appears between the eyebrows of the base layer and the collector layer, and furthermore, the difference in potential between the base layer and the collector layer becomes small. Therefore, the carrier passage rate improves.

Therefore, in a transistor below the critical temperature,
Electrons in an excited energy state in the emitter layer pass through the base layer 4, which has superconducting properties, at high speed, while also easily reaching the collector layer from the base layer over the barrier on the collector side. Current gain can be obtained.

〔Example〕

(a) First Embodiment of the Present Invention FIG. 1 is a sectional view of a device showing an embodiment of the present invention. A collector barrier layer 3 and a base layer 4 made of semiconductor are laminated in this order, and the base layer 3
In the upper center of the tunnel barrier layer 5 made of semiconductor and n
An emitter N6 made of a type semiconductor is bonded in this order, and furthermore, a superconductor film 7 is formed on the base layer 3 to surround the tunnel barrier layer 5 and the emitter layer 6 in a non-contact state.

Examples of materials used for each layer of the present invention include InGaAs for the emitter layer 6, InAlGaAs for the tunnel barrier layer 5, and n-type 1nGaAs for the base layer 4.

InAlGaAs is used for the collector barrier layer 3, and n-type 1nGaAs is used for the collector layer 2, and these layers are formed by epitaxial growth, CVD, MBE, etc. to form a heterojunction.

However, In is the element symbol for indium, Ga is gallium, ^S is arsenic, and A1 is the element symbol for aluminum.

Note that reference numeral 9 in the figure indicates a hole or groove provided in the superconductor film 7 to surround the tunnel barrier layer 5 and the emitter layer 6.

Next, the operation of the above-mentioned embodiment will be explained.

The potential diagram in the above embodiment is shown in FIG. 2.

Figure (a) shows a potential diagram of the transistor 1 in an atmosphere at room temperature, and its base layer 4
Semiconductor characteristics appear in the potential, but when the transistor is placed in an atmosphere below the critical temperature of the superconductor 11ff7, it changes to superconducting characteristics as shown in FIG. 2(b).

This is because, although the base layer 4 itself is formed of a semiconductor, a proximity effect occurs in the base layer 4, so that the density of superconducting electrons in the base layer 4 increases. Here, the proximity effect is a phenomenon in which a semiconductor film bonded to a superconductor film has superconducting properties. In order to generate a proximity effect in the base region located in the gap, it is preferable to make these holes and gaps as small as possible. For example, this becomes noticeable when the holes and gaps are about 0.5 μm or less, and this superconducting electron density is The order parameters are as shown in the figure.

On the other hand, in this transistor 1, the carrier passage region is formed of a semiconductor, and each continuous layer from the emitter layer 6 to the collector layer 3 is stacked so as to form a heterojunction.

For this reason, no barrier other than the collector barrier appears between the base layer 4 and the collector layer 2, and since the base layer 4 is formed of a semiconductor, the base layer 4
The difference in potential between the collector layer 2 and the collector layer 2 becomes smaller, and the carrier passage rate improves.

Therefore, in a transistor below the critical temperature,
Electrons in an excited energy state at the emitter N6 pass through the base layer 4 having superconducting properties at high speed, while easily passing from the base layer 4 over the collector barrier layer 3 to reach the collector layer 2 where the potential difference is small. For,
The transistor can obtain sufficient current gain.

Note that the height of each barrier layer 3.5 can be appropriately controlled by changing the impurity concentration of the emitter layer 6 and collector layer 3.

(b) Second Embodiment of the Invention In the embodiment described above, the size of the hole (or groove) 9 surrounding the emitter layer 6 is made as narrow as possible to produce a proximity effect in the carrier passage region of the base layer 4. Therefore, the area of the tunnel barrier 115 and the emitter ji6 becomes smaller,
Base I? In some cases, it may not be possible to increase the current flowing through 54.

To solve this problem, for example, as shown in Figure 4,
A large number of small holes 18 are provided in the superconductor film 17 uniformly formed on the base [44] by etching. Then, a tunnel barrier layer 15 and an emitter layer 16 are formed on the base layer 4 to fit into each small hole 18 so as not to contact the superconductor 811, and then the plurality of emitter layers 16 are electrically connected. , the amount of carriers flowing into the base layer 4 can be increased to increase the current.

The reference numeral 20 in the figure is a substrate made of indolium phosphide (1nP), etc., on which a collector layer 12, a director barrier layer 13, and a base layer 14 are laminated in order. A conductor film 17 and the like are formed.

Further, reference numeral 21 denotes a protective film made of silicon dioxide or the like, and this protective film 1f121 is filled into a small gap formed between the superconductor layer 17, the tunnel barrier layer 15, and the emitter layer 16, and the collector It is configured to cover the exposed portions of the layer 12, the base layer 14, etc., and 22 indicates an electrode made of niobium or the like provided to connect the collector N12, the base layer 14, and the emitter layer 16 to the outside. ing.

Note that the materials of each layer in this example are the same as those in the first example.

(c) Other embodiments of the present invention To explain more specifically the composition and thickness of each layer in the above embodiments, the emitter layer 6.16 is an n-type Ino layer.
, 5sGao, aJs is formed to a thickness of 300 nm, the tunnel barrier layer 5.15 is formed of 1nAIGaAs to a thickness of 5 nm, and the base layer 4.14 is made of Inc., 5sGao,
aJs to a thickness of 1100n, collector barrier layer 3.
13 is made of single-hole AlGaAs with a thickness of 150n-, and the collector layer 2.12 is made of n-type 1no, 5sGao, aJs with a thickness of 500na. Among these, tunnel barrier [5, 15 is (Ino, 5sGao, n
Js) o, s (Ins, 5iAIo, 4sA
s) Mixed crystal so that o, s, collect barrier N
3.13 is (Ino, S:lGaO,47AS)
O, ea ([no, 5zAlo, n5As) o
, + <, and is a mixed crystal such that n-type 1n
The carrier concentration of GaAs is 1×lOL′1 piece/cT1
It is doped with impurities so that

In the embodiments described above, niobium (N
b), but oxide high-temperature superconductors such as indium barium copper oxygen (YBaCuO) and lanthanum
Strontium copper oxygen (LaSrCuO), bismuth strontium calcium copper oxygen (BtsrCla)
It can also be composed of CuO) or the like.

Also, in the above embodiment, an npn type transistor was explained, but is it also possible to create a proximity effect in the base of a pnp type transistor? be.

(Effects of the Invention) As described above, according to the present invention, the emitter, base,
In addition to forming the collector with a semiconductor, we also formed a superconductor film on the base that is located around the emitter layer in a non-contact manner, which makes it possible to reduce the difference in potential between the base layer and the collector layer, and to keep the temperature below the critical temperature A proximity effect can be produced in the base layer in an atmosphere, and reflection of carriers by the barrier on the collector side can be suppressed to increase current gain.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing one embodiment of the present invention, and FIG. 2 is a sectional view showing an embodiment of the present invention.
3 is a schematic diagram showing an example of an order parameter according to the present invention; FIG. 4 is a sectional view showing a second embodiment of the present invention; FIG.
The figure is a sectional view showing an example of a conventional device, and FIG. 6 is a schematic diagram showing an example of a potential diaphragm of the conventional device. (Explanation of symbols) 1...Transistor, 2.12...Collector layer, 3.13...Collector barrier layer, 4.14...Base layer, 5.15...Tunnel barrier layer, 6 .16...Emitter layer, 7.17...Superconductor film. Patent applicant Kei Okamoto, patent attorney representing Fujitsu Ltd. Schematic diagram No. 3 showing an example of order parameters according to the present invention
Figure 4 is a cross-sectional view showing a second embodiment of the present invention. Figure 1 is a cross-sectional view showing an embodiment of the present invention. Fig. 2 is a schematic diagram showing an example of a tensile diadem. Fig. 5 is a sectional view showing an example of a conventional device.

Claims (1)

[Claims] A superconducting transistor characterized in that an emitter layer, a base layer, and a collector layer constituting the transistor are formed of a semiconductor, and a superconductor film positioned around the emitter layer in a non-contact state is laminated on the base layer. .