JPH02211677A - Superconductor element - Google Patents

Abstract

PURPOSE:To improve Nb-semiconductor junction interface characteristics by forming the joint surface of a semiconductor in a (110) face in the junction structure of Nb-semiconductor. CONSTITUTION:Nb shows (110) natural orientation growth, and the formation energy of the orientation growth is reduced maximally. Consequently, the joint surface of a semiconductor is formed in a (100) face, the joint surface of the semiconductor is shaped in a (110) face rather than the (100) growth of Nb, and the (110) growth of Nb is advantageous in the lattice consistency of both the semiconductor and Nb in the junction structure of the semiconductor and Nb, thus improving Nb-semiconductor junction interface characteristics. Accordingly, the discontinuous quantity of anti-potential ¦DELTA(r)¦ on the interface of Nb-Si is reduced, a superconductive wave function is easy to leak and a superconducting element having a large amplification factor can be realized in the superconducting element using Si as the semiconductor and including the junction structure of Nb and Si.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a superconducting element having a structure in which Nb, which is a superconducting material, and a semiconductor are bonded, and in particular, to a structure of a superconducting element suitable for improving these bonding interface characteristics. Regarding.

[Conventional technology]

Conventionally, superconducting elements including a bonded structure of Nb and Si have been discussed on the front page of the Dempa Shimbun on Saturday, August 6, 1988. As shown in FIG. 2, this superconducting element consists of a pair of Nb source superconducting electrodes 1 and a drain superconducting electrode 2 formed on a Si semiconductor substrate 3, which are separated from each other, and a gate electrode 4 located between them. It is composed of a gate insulating film 5 and an insulating film 6. When the source superconducting electrode 1 and the drain superconducting electrode 2 are in a superconducting state, a superconducting wave function leaks from them to the semiconductor substrate 3. Regarding the amount of seepage, see Solid State Physics, Volume 23 (1988), No. 15.
Discussed on pages 3 to 162. Figure 4 shows the pair potential 1Δ(r
) indicates the spatial change of 1.

The amount of seepage is the coherence length ξ in the semiconductor. 1Δ(r)l changes discontinuously at the Nb-Si interface. ξ. is proportional to the 1/3 power of the carrier concentration in a three-dimensional system. Therefore, in FIG. 2, if the carrier concentration in the channel portion is changed by applying an appropriate gate voltage to the gate electrode 4, ξ. can be controlled. ξ. is large, and when the superconducting wave functions seeping out from the source superconducting electrode and the drain superconducting electrode 2 overlap, a superconducting current flows between the two electrodes. ξ. If the superconducting wave functions are small and the superconducting wave functions do not overlap, no superconducting current will flow between the two electrodes. In other words, the superconducting current flowing through the channel can be controlled by the gate voltage.

Conventionally, regarding superconducting elements including a junction structure of Nb and InSb, IE Transactions on Magnetics, MNG21. ,
(1985) pp. 721-(:3) p. 724 (IEEE, Trans, Magneti
cs, MAG 21° (1985) pp721-72
4). In this superconducting element, as shown in FIG. 3, a Nb superconducting base 7 is formed on an InSb semiconductor 8 formed by MBE (molecular beam epitaxy). Applying an appropriate voltage VOR between the superconducting base 7 and the collector 9 bends the energy band of the semiconductor 8,
Further, by applying an appropriate voltage VER between the superconducting base 7 and the emitter 10, quasiparticles are injected from the emitter 10 into the superconducting base 7 via the tunnel barrier film 12.

Furthermore, conventionally, Nb (
100) oriented epitaxial growth is discussed in IEICE Technical Report 5CE8638, (1987) pages 35 to 40.

[Problem to be solved by the invention]

A superconducting element including the above-mentioned Nb and Si junction structure and Nb
Regarding superconducting elements including a junction structure of and InSb,
In both cases, no consideration is given to the junction interface characteristics between Nb and Si and Nb and In5b, and in the case of the former superconducting element, the amount of superconducting wave function seeping into Si is small, that is, the amount of change in drain current relative to the amount of change in gate voltage. , there was a problem that the amplification factor was small. This is N b −S
The lattice mismatch at the i junction is large, and in Fig. 4, the pair potential 1 at the N b -S i interface
This is thought to be due to the large amount of discontinuity in Δ(r).

In the latter superconducting element, quasiparticles flow into the semiconductor 8 made of InSb through the superconducting base 7 made of Nb, but the amount of this inflow is sensitive to the interface characteristics between Nb and InSb. In order to improve device characteristics, it is desirable that the amount of inflow be large, and therefore it is desirable that the lattice mismatch between both Nb and InSb be small.

Furthermore, conventionally, Nb (
100) oriented epitaxial growth has been discussed.

An object of the present invention is to optimize the junction plane orientation of the semiconductor in a structure in which Nb and a semiconductor are joined.
- To improve semiconductor junction interface characteristics.

[Means to solve the problem]

The above object is achieved by making the junction surface of the semiconductor a (110) plane in the Nb-semiconductor junction structure.

As the semiconductor, Si, GaAs, InSb, or the like can be used.

In addition, a semiconductor whose junction surface with Nb is the (110) plane, a pair of mutually separated source and drain superconducting electrodes made of Nb in contact with the semiconductor, and a gate electrode located between these and controlling the drain current. , a gate insulating film, or a superconducting element including a collector, a superconducting base made of the semiconductor and Nb, a tunnel barrier film, and an emitter.

[Effect]

Nb exhibits (110) natural oriented growth, and this oriented growth has the smallest formation energy. Therefore, in the junction structure of semiconductor and Nb, the junction plane of the semiconductor is set as the (100) plane,
Rather than growing Nb (100), growing Nb (110) with (l i O) on the semiconductor junction surface is more advantageous in terms of lattice matching between the two, and the characteristics of the Nb-semiconductor junction interface are improved. I will do it.

As a result, for example, Si is used as a semiconductor, and Nb and S
In a superconducting element including a junction structure with i, the pair potential IΔ(r
) 1 becomes smaller, the superconducting wave function easily leaks out, and a superconducting element with a large amplification factor can be realized.

In addition, in a superconducting element that uses InSb as a semiconductor and includes a junction structure of Nb and InSb,
The amount of quasiparticles flowing into Sb becomes large, and a superconducting element with a large collector current can be realized.

If the crystal structure of a semiconductor is a diamond type crystal structure or a zinc blende type crystal structure, the lattice positions are similar, so
The optimal semiconductor junction surface is the same for both (11
0) side. That is, the semiconductor is not limited to Sl or InSb.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to Examples. 1st
A first embodiment of the present invention will be described with reference to the drawings. This example relates to a method of forming a Nb film on a Si (110) substrate.

The Si surface is usually covered with several tens of Si natural oxide films. In order to remove inclusions between Nb-8i and improve the Nb-8i bonding interface characteristics, it is necessary to deposit Si before forming the Nb film.
This Si natural oxide film must be etched from the surface. Furthermore, ordinary HF etching is insufficient as a cleaning method because contaminants such as carbon may adhere to the Si surface and sufficient bonding interface properties may not be obtained. Therefore, the heating cleaning method described below was adopted, thereby obtaining a clean Si surface free from contamination with carbon, oxygen, and the like.

First, the Si substrate was boiled in nitric acid at about 120° C. for 10 minutes. After washing with pure water for 5 minutes, the S1 oxide film was etched by immersing it in 2% HF for 1 minute. It was washed with pure water for 5 minutes and boiled again with nitric acid. This was repeated three times. Next, in a mixture of ammonia water and hydrogen peroxide water at 90°C.
It was boiled for 10 minutes. After washing with pure water for 10 minutes, 2% H
The Si oxide film was etched with F. Next, it was boiled at 90° C. for 10 minutes in a mixture of hydrochloric acid and hydrogen peroxide, and finally washed with pure water for 10 minutes.

As a result of the above processing, the surface of the Si substrate is covered with a Si oxide film several times thicker, and it is considered that no contaminants such as carbon are attached thereto. Next, this Si substrate was heated at 850° C. for 30 minutes in an ultra-high vacuum of about 1xio-0 Torr to remove some Si oxide films on the surface of the Si substrate to obtain a clean Si surface. In this way, a clean Si surface was obtained by the heating cleaning method described above.

Next, Nb was evaporated onto this substrate while maintaining an ultra-high vacuum of 0 Torr for about 1-×10 min. The substrate heating temperature needs to be about 300'l: or less. At a heating temperature higher than that, NbSix is formed, and Nb −S i
The bonding interface properties deteriorate. SEM (SEM is an abbreviation for scanning electronic microscopy.) The tR festival revealed that the grain shape of Nb is approximately 2000 ellipsoidal in the long axis direction, and that the grain shape increases as the substrate heating temperature increases. It could be confirmed.

As shown in Figure 1, Nb has a lattice constant a=3.300,
Si is a = 5.420 people, inconsistency is 14%, G
a A s is a = 5.653 people and the inconsistency is 18
%, InSb is a=6.479 people, and the inconsistency is 1.
It is 9%. Therefore, from the perspective of lattice matching, I n S
b, Sj, and GaAs are advantageous in this order, but optimal Nb-semiconductor junction interface characteristics can be obtained by setting the (110) plane of each as the bonding surface with Nb.

Next, a second embodiment of the present invention will be described using FIGS. 5 and 6. The concentration of P with plane orientation (111) is approximately IX1.01
After applying a resist to the 8 mark-8 doped Si half-center substrate 3, patterning was performed by electron beam lithography, and then CF4
Reactive etching was carried out in a gas mixture of
obtain a). The thickness of the convex thin film portion of Sj is approximately 0.1 μm.
, have a height of about 0.2 μm, and are formed so that the (110) planes face each other. Next, after surface treatment was performed by the heating cleaning method described in the first embodiment of the present invention to obtain a clean surface, the substrate was heated at a temperature of about 240° C. in an ultra-high vacuum of about I x 10-” Torr. Nb is deposited by about 1,500 people at a deposition rate of about 2 people/S to form a source superconducting electrode 1 and a drain superconducting electrode 2, as shown in FIG. 6(b). About 1,000 people apply AZ-based resist. After that, reactive etching is performed in a mixed gas of CF4 and 02 to remove Nb on the upper part of the convex thin film.
is removed by etching back.

Next, about 20 5108 gates 1 to 5 are formed by CVD, and the gate electrode 4 is formed by PSG.
The superconducting element shown in FIG. 6(c) is obtained.

In the superconducting state, a superconducting wave function seeps into the semiconductor 3 from the source superconducting electrode 1 and the drain superconducting electrode 2. The tendency to seep out is controlled by the gate voltage applied to the gate electrode 4, and when the two seeped superconducting wave functions overlap, the source superconducting electrode 1. A train current flows between the drain superconducting electrodes 2 as a superconducting current. Therefore, the position where the superconducting wave function seeps out, which is controlled by the gate voltage, is dominated by the area on the opposing surface of the Si convex thin film part rather than the area on the S i (111) plane. Now, this facing surface is S
Since it is an i (110) plane, the Nb-Si junction interface characteristics are optimal, and the superconducting wave function is most likely to seep out.

Therefore, the amount of change in train current due to gate voltage also increases, and a superconducting element with a large amplification factor can be realized.

The shape of the Si convex thin film part is such that the thickness is such that the superconducting proximity effect occurs, that is, approximately 0.3 μm or less, and the height is such that the band bending of the Si semiconductor due to the gate voltage occurs, that is, approximately the length of the depletion layer. There is a need to.

Although Si is used as the semiconductor 3 in this embodiment, it goes without saying that the same effect can be obtained by using InSb, which has a small lattice mismatch with Nb.

〔Effect of the invention〕

As explained above, according to the present invention, in a junction structure between Nb and a semiconductor having a diamond-type crystal structure or a zinc blende-type crystal structure, the junction surface of the semiconductor is (110
) plane improves the Nb-semiconductor junction interface characteristics, making it possible to realize a superconducting element with excellent characteristics.

[Brief explanation of the drawing]

FIG. 1 is an atomic position diagram of Nb, Si, GaAs, and In5b (110) plane. FIGS. 2 and 3 are cross-sectional views of conventional superconducting elements including junction structures of Nb and Si and Nb and InSb, respectively. FIG. 4 is a diagram showing spatial changes in the pair potential in the Nb-Si junction. FIG. 5 is a sectional view of a superconducting element according to a second embodiment of the present invention. 6th
The figure is a diagram showing the manufacturing process of a superconducting element according to a second embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Source superconducting electrode, 2... Drain superconducting electrode, 3... Semiconductor substrate, 4... Gate electrode, 5...
・Gate insulating film, 6... Insulating film, 7... Superconducting base, 8... Semiconductor, 9... Collector, 10... Emitter, 11... Base electrode, 12... Tunnel barrier Film, 13... Semiconductor base Nb (//θ) plane S't (//ρ) plane CIL As (//θ) plane Rabbit

Claims (1)

[Claims] 1. In a superconducting element having a junction structure of Nb and a semiconductor having a diamond-type crystal structure or a zinc blende-type crystal structure, the junction plane of the semiconductor is a (110) plane. Features of superconducting elements. 2. The superconducting element according to claim 1, wherein the semiconductor is Si, GaAs or InSb. 3. A semiconductor whose junction surface with Nb is the (110) plane, a pair of mutually separated source and drain superconducting electrodes made of Nb in contact with the semiconductor, and a gate electrode located between these and controlling the drain current. 3. The superconducting element according to claim 1, wherein the superconducting element comprises a gate insulating film. 4. The superconducting element according to claim 1 or 2, comprising a collector, a superconducting base made of the semiconductor and the Nb, a tunnel barrier film, and an emitter.