JP3002010B2 - Superconducting transistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting transistor using an oxide superconducting material.

[0002]

2. Description of the Related Art Quasiparticle injection type superconducting transistors are:
It comprises a collector region composed of a semiconductor, a base region composed of an oxide superconductor formed on the collector region, and an emitter region composed of a superconductor or a metal provided on the base region via an insulating layer.

In this quasiparticle injection type superconductor transistor, quasiparticles injected from an emitter region pass through a base region formed of a superconductor, reach a collector region, and flow to an external electrode.

In this superconductor transistor, as a quasiparticle collector junction for trapping quasiparticles with high efficiency,
Semiconductor-superconductor contacts with low barrier heights are used. Considering the operation of this device as a transistor, a base region made of a superconductor and a collector region made of a semiconductor come into contact with each other, and a barrier having a height of っ て as measured from the Fermi level is formed at the contact portion. I do. A positive potential V is applied to the collector region with respect to the base region. Considering a process in which electrons in a quasiparticle state in a superconductor are incident on the semiconductor side, the electrons are at an energy level higher by E than the Fermi energy of the superconductor. Here, E is the excitation energy of the quasiparticle and E> △, so that the electrons can freely move to the semiconductor side over the barrier. On the other hand, an electric field exists in the semiconductor in a direction in which the electrons are extracted from the junction. Therefore, the electrons in the quasi-particle state incident on the collector region are captured by the collector region and flow out.

[0005]

However, in a conventional quasiparticle injection type superconducting transistor using an oxide superconducting material, in order to form a base region made of an oxide superconductor directly on a semiconductor to be a collector region, The semiconductor layer at the collector-base interface is oxidized, and an insulating layer is formed at the interface. This insulating layer forms a high-resistance layer between the collector and the base, increases the barrier between the collector and the base, lowers the quasiparticle transmittance, and operates as a transistor when using oxide superconducting material. There was a problem that it was difficult to create the image.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a superconducting transistor in which a semiconductor-oxide superconductor contact with a low barrier at a base-collector junction can be obtained. Is the subject.

[0007]

A superconducting transistor according to the present invention has a collector region made of a semiconductor made of tin oxide and a BiBa _1-x K _x epitaxially grown on the (001) plane of the tin oxide. O ₂ It is characterized by comprising a base region composed of an oxide superconductor having a composition, and an emitter region composed of a superconductor or a metal provided on the base region via an insulating layer.

[0008]

The (001) plane of tin oxide is BiBa_1-xK_xO_Two When
Since the lattice constant is close and familiar, this tin oxide
BiBa without forming an oxidation reaction layer on it_1-xK_xO_Two
Is epitaxially grown to provide good base-collector contact
A joint is formed. Therefore, a good collector-base
Frank davitson-type ohmic contact
Lowering the height of the barrier between base and collector
And the transmittance of the quasiparticles to the collector is increased.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing the structure of a quasiparticle injection type superconducting transistor according to the present invention.

As shown in FIG. 1, this quasi-particle-injection type superconducting transistor uses a semiconductor substrate such as GaAs as a substrate 1 and has a semiconductor doped with impurities for activating the semiconductor. An activation region 2 is provided. From this activation region 2, a collector current is taken out.

A few atomic layers of tin (Sn) 3 are formed on the substrate 1 by MBE (molecular beam epitaxy) or the like.
Activated oxygen is introduced onto the Sn layer 3, and a collector region 4 made of SnO ₂ as an oxide semiconductor is provided by a reactive evaporation method.

Then, a base region 5 is formed by epitaxially growing an oxide superconductor BiBa _1-x K _x O ₂ (hereinafter referred to as BKBO) on the (001) plane of the SnO ₂ . The (001) plane of SnO ₂ is BK
Since the lattice constant of BO is close to that of BO and familiar, BKBO is epitaxially grown without forming an oxidation reaction layer on SnO ₂ , and a good base-collector junction is formed.

On the base region 5, MgO, SrTiO
_After an insulating layer 6 of ₃ or the like having a predetermined thickness is formed by the MBE method, an emitter region 7 of BKBO is formed to obtain a superconducting transistor according to the present invention.

Next, an example of manufacturing a superconducting transistor according to the present invention will be described.

As a substrate 1, a GaAs substrate is used.
An n + -type activation region 2 doped with Se and Te impurities at a high concentration is formed in a predetermined region of the aAs substrate 1.

Subsequently, the Sn layer 3 is replaced with several atomic layers, ie,
A Sn layer 3 having a thickness of 0.3 to 1 nm is formed on the surface of the substrate 1 by the MBE method.
00 ° C., the film formation rate is 0.1 to 0.3 nm / sec, and the degree of vacuum is 1 to 5 × 10 ⁻¹⁰ Torr. By providing the Sn layer 3, the SnO ₂ layer formed in the next step and the GaAs
Matching with the s substrate 1 is performed.

Thereafter, a film thickness of 100 to 2
A 00 nm SnO ₂ layer 4 is formed by a reactive evaporation method. At this time, the substrate temperature is 400 to 450 ° C., and the deposition rate is 0.5.
Å3Å / sec, O ₂ gas pressure is 4-6 × 10 ^-3 Torr
r, and Sn metal was used as the evaporation source.

After that, a film thickness of 10 to 20 nm made of BKBO is formed on the SnO ₂ layer 4 by magnetron sputtering.
Is formed. At this time, the target is Ba
_0.6 K _0.5 BiO _x powder was mixed with N ₂ and O _{2 under the} conditions shown in FIG.
Was used. Film formation at substrate temperature 400
° C, Ar + O ₂ (O ₂ : 40-50) as a sputtering gas
%), A gas pressure of 4 to 8 Pa, an input voltage of 50 W, a film formation rate of 0.8 to 12 nm / min, and as-grown.
Thus, a superconducting thin film having Tc = 16K is formed.

Then, a tunnel junction insulating layer 6 having a thickness of 0.5 to 7 nm is formed on the base region 5 made of BKBO by MBE. At this time, the film forming condition is a substrate temperature 30
The film formation rate was 0 to 400 ° C., the degree of vacuum was 1 to 5 × 10 ⁻¹⁰ Torr, and the deposition limit was MgO.

Finally, an emitter region 7 made of BKBO is formed on the insulating layer 6 in the same manner as the base region 5 described above, whereby the superconducting transistor shown in FIG. 1 is formed.

[0022]

As described above, according to the present invention, by using an oxide semiconductor as a semiconductor in the collector region, a good ohmic contact can be made between the collector and the base. And the transmittance of quasiparticles to the collector increases.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a superconducting transistor according to the present invention.

FIG. 2 is a view showing conditions for preliminarily firing powder used for forming a superconducting thin film used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 3 Sn layer 4 Collector region (oxide semiconductor) 5 Base region 6 Insulating layer 7 Emitter region

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kazuhiko Takahashi 2-18-18 Keihanhondori, Moriguchi City Sanyo Electric Co., Ltd. (72) Inventor Junnobu Yoshizato 2-18-18 Keihanhondori, Moriguchi City Sanyo Electric Co., Ltd. (56) References JP-A-2-111082 (JP, A) JP-A-1-2097981 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 39/22 H01L 39 / 24 H01L 39/00

Claims (1)

(57) [Claims] 1. A collector region composed of a semiconductor made of tin oxide, and BiBa _1-x K _x O ₂ formed by epitaxial growth on a (001) plane of the tin oxide. A superconducting transistor comprising: a base region formed of an oxide superconductor having a composition; and an emitter region formed of a superconductor or a metal provided on the base region via an insulating layer.