JPS62195189A - Superconducting three-terminal device - Google Patents

Abstract

PURPOSE:To improve a signal amplification factor by a method wherein a base layer is composed of an Nb or NbN layer provided on a collector layer composed of diamond structure Sn, GaSb, InSb, InAs, CdS, CdSe, PbTe and In1-xGaxAs mixed crystal or InSb1-yAsy mixed crystal. CONSTITUTION:An Nb layer is formed by CVD on a single crystal substrate 1 made of p-type GaSb, non-doped (n-type) InSb, p-type InAs, n-type CdS, n-type CdSe or n-type PbTe. Then a base pattern 2 composed of the Nb layer is formed from the Nb layer by reactive ion etching. Further, after an insulating layer 3 made of SiO2 is deposited over the whole surface of the substrate by vacuum evaporation, windows are formed in the insulating layer 3 on the base layer 2 and an emitter electrode 5 made of Nb is formed on the base layer 2 with a barrier layer 4 between by lifting-off and a base electrode 6 made of Nb is formed on the base layer 2 by lifting-off. Finally, a collector electrode 7 is formed in the window which is formed in the insulating layer 3 and exposes the substrate 1. With this constitution, a current transfer factor can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a superconducting device that performs signal amplification and switching operations similar to semiconductor bipolar transistors.

[Conventional technology]

As a switching device using superconductivity, Josephson tunneling devices (Josephson devices) have been considered for application to integrated circuits due to their high speed performance. However, the Josephson element is a two-terminal element and does not itself have a signal amplification effect, so when configuring a memory circuit or logic circuit, the circuit is not only more complicated than when semiconductor transistors are used. However, large-scale integration was difficult due to the small operating margin.

Therefore, various three-terminal devices using superconductors have been proposed to achieve signal amplification and switching operations similar to those of semiconductor transistors. For example, as shown in FIG. 3, an emitter junction 22 for injecting quasi-particles into the superconductor layer 21 (superconductor-normal metal, superconductor-superconductor tunnel junction via a barrier layer, or a superconductor-semiconductor contact) and the superconductor 21
A superconducting three-terminal device comprising a collector junction 23 (mainly composed of a superconductor-semiconductor contact) for capturing quasiparticles from
JP-A No. 60-231375) is also known. These devices can operate similar to semiconductor bipolar transistors by controlling the flow of quasiparticles injected from the emitter to the collector. In addition, these devices are hot electron transistors (e.g., Niss, M, 5ZE) in which carriers travel pallistically through a thin base layer.
“Physics of Semiconductor Devices
r Devices)”, (John Riley End Sump Inc.) (John Villagey &
5ons Inc,), N, Y,, pp, 5
It is thought that a superconductor is used in the base layer of the base layer (see 87-613), but in addition to the fact that the velocity of the quasiparticle in the base is close to the Fermi velocity (~1010l1/5ee), the base transit time is short. Since a superconducting current flows from the outside into the base with zero resistance, the signal delay represented by the product of the base resistance and the base-collector capacitance is extremely small, and hot electrons with a semiconductor or normal metal base layer are It can be expected to have superior high-frequency characteristics (high-speed switching characteristics) compared to transistors and normal bipolar transistors.

On the other hand, a problem with this type of device is that the collector capture rate (current transfer rate α) of quasiparticles is generally lower than that of bipolar transistors. The factors that inhibit the capture of quasiparticles into the collector are scattering of quasiparticles in the base superconductor,
It can be roughly divided into two types: recombination, and reflection and scattering at the superconductor-semiconductor interface. Among these, for the former recombination in the base, its characteristic time (relaxation time) is 10~
1.00 psec and the base travel time of the quasiparticle (-0,1
(psec) can be ignored. Regarding the scattering of quasiparticles, there are factors such as electron-phonon scattering, electron-electron collisions, lattice defects, scattering due to impurities, etc., but when the quasiparticle injection energy is low at an extremely low temperature, the former two are can be almost ignored.

On the other hand, polycrystalline thin films formed on semiconductor single crystals by sputtering or electron beam evaporation are conventionally used as base superconducting layers, but in the initial stage of deposition, the crystal grain size is very small, less than 100 Å, and The number of layers containing semiconductor constituent atoms as impurities due to diffusion etc. is 100 to 50.
In such an initial deposited layer, scattering of quasiparticles due to grain boundaries and impurities is significant, reducing the probability of quasiparticles reaching the collector interface. .

Next, since a potential barrier (Schottky barrier) is normally formed at the superconductor-semiconductor interface, quantum mechanical reflection of quasiparticles occurs. The transmittance is increased by using narrow gap semiconductors such as InSb and InAs. On the other hand, when a superconductor thin film is conventionally deposited on these semiconductor single crystals by sputtering, electron beam evaporation, etc., a layer with disordered crystallinity or interdiffusion may appear on the semiconductor surface due to irradiation with high-energy particles or thermal radiation. A layer is formed. This means that the flatness of the semiconductor-superconductor interface decreases, and this potential disturbance increases scattering of quasiparticles at the interface region, reducing the effective transmittance below the quantum mechanical theoretical value. There is a problem.

Due to the reduction in the current transfer rate α due to these causes, the conventional device has the disadvantage that only a lower current gain (β=α/1−α) can be obtained than that of a semiconductor bipolar transistor.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a superconducting device that solves the above-described drawbacks of conventional devices, has a sufficiently large signal amplification factor comparable to that of semiconductor bipolar transistors, and operates at high speed and with low power consumption.

[Structure of the invention]

The present invention includes a base layer made of a superconductor, an emitter layer made of a normal metal, a superconductor, or a semiconductor that is in contact with one side of the base layer and into which quasiparticles are injected into the base layer, and the base layer. a collector layer made of a semiconductor that is in contact with the other side of the base layer and captures quasiparticles from the base layer, wherein the base layer has a diamond structure S
n.

GaSb, InSb, InAs, CdS, CdSe.

P b T e HI nl -x GB
The most important feature is that it is a layer.

Nb has a body-centered cubic crystal structure, and in Figure 4 (in the table,
diamond structure Sn, GaSb, InSb as shown in the diagram (ao indicates lattice constant).

It has a lattice constant that is close to 1/2 of the lattice constant of the same cubic system narrow gap (E g < 1 eV) semiconductors such as InAs, CdS, CdSe, and PbTe. When considering the growth of Nb crystals as shown in Figure 5 (A,) on these semiconductor single crystals, the lattice constant mismatch is at most 1.
It is 1% or less, and heteroepitaxial growth on a semiconductor single crystal is possible. Furthermore, if Nb for the base is deposited using a method such as MOCVD (metal-organic chemical vapor deposition) that causes very little disturbance due to high-energy particle irradiation or thermal radiation on the substrate, it is possible to deposit Nb for the base using a method such as MOCVD (metal-organic chemical vapor deposition). A device in which the crystal can be grown from the initial stage of deposition, and the structure of the base-collector interface has very little disturbance by using the semiconductor single crystal as the collector layer, which is further epitaxially grown on the substrate semiconductor single crystal or single crystal Nb. You can get the configuration.

On the other hand, NbN has a Bl (NaCu type) structure and is a cubic system, and its lattice constant is 7 times close to the lattice constant of the semiconductor described above, and is 45° It is possible to perform heteroepitaxial growth in the direction of Nb, and a device configuration similar to that in the case of Nb can be obtained.

As described above, the present invention differs from conventional devices in the manufacturing method, structure, and crystallinity of the base superconductor.

[Embodiments of the invention]

Embodiment 1 FIG. 1 is a schematic sectional view illustrating a first embodiment of the present invention.

P-type GaSb, non-doped (n-type) InSb, p-type In
As, n-type CdS, n-type Cd S e, or n-type P
Each Nb layer was formed to a thickness of 500 nm on the (100) plane of a single crystal substrate 1 made of bTe by an RF-excited CVD method. At this time, a susceptor made of graphite was used, the susceptor temperature was set at 400 to 650°C, Nbcas was used as the reaction gas, and H2 was used as the carrier gas. Total gas flow rate is 2Q/ll1in, reaction gas pressure is 0.1
It was taken as atmospheric pressure. At this time, an Nb layer is deposited on the substrate 1 by a thermal decomposition reaction expressed by the formula: 2NbCL+5H2→2Nb+10HCa.

The Nb thin film deposited on each of the substrates 1 showed a good Laue pattern, and was confirmed to be a single crystal thin film. In addition, the superconducting transition temperature Tc is 9.4, and the ratio of resistivity at room temperature and IOK (residual resistance ratio ρ (300K) / ρ (10K)
) was 100-200. On the other hand, the Nb thin film deposited at room temperature by DC magnetron sputtering on the same semiconductor single crystal substrate is polycrystalline and has a Tc of 9.0 to 9.2K.
, the residual resistance ratio was 4-6.

Next, a base pattern 2 made of the Nb layer is formed from the Nb layer on each substrate 1 by reactive ion etching (R, IE).
was formed. For etching, a (CF4+5%02) mixed gas was used, the total gas pressure was 8 Pa, and the RF discharge power was 20
Etching was performed under W conditions. Furthermore, after depositing an insulating layer 3 made of SiO on the entire surface of the substrate by vacuum evaporation, a window is opened in the insulating layer 3 on the base layer 2, and an emitter electrode 5 made of Nb is attached via a barrier layer 4. Each base electrode 6 was formed by a lift-off method.

After cleaning the Nb surface in (Ar+10% CF4) mixed gas plasma, the barrier layer was prepared using (Ar+8% O2).
It was formed by plasma oxidation using RF discharge in a mixed gas.

Finally, a collector electrode 7 made of Au was formed in a window formed in the insulating layer 3 on the semiconductor substrate 1 and communicating with the substrate 1.

The current transfer rate α of the three-terminal element thus produced with the base grounded was measured at 4.2. FIG. 6 graphically shows α when the base-collector voltage is zero. As can be seen from the figure, the emitter base voltage 30Q+nV (p
-10 mV for GaSb) for quasiparticle injection,
In the case of a device made of polycrystalline Nb base, the range is 0.05 to 0.0.
25 was obtained, whereas in the element whose base was made of epitaxially grown Nb single crystal, α was found to be significantly improved from 0.25 to a maximum of 0.7. Here, in the case of p-GaSb, the reason why a large α was obtained even when the injection voltage was low is because a low potential barrier close to rhiomic is formed due to the decrease in interface state density at the base-collector interface. .

Example 2 Similar to Example 1, p-type GaSb, non-doped InSb
, p-type InAs, n-type CdS, n-type CdSe.

Alternatively, a 500% NbN layer is deposited on the (100) plane of an n-type PbTe single crystal substrate using the RF-excited CVD method.
Formed to the thickness of a person. NbCa and N are used as reaction gases.
H2 was used as the carrier gas, the susceptor temperature was 600° C., the total gas flow rate was 3 Q/min, and the reaction gas pressure was 0.15 atm. In this case, NbC et al + NH
3+H2-→NbN+5H (A NbN layer is formed by the reaction of Jl.

The NbN thin film formed on each of the above substrates showed a good rawe pattern, and was confirmed to be a single crystal thin film. Also,
Tc was 16.5-17.2.

Next, an element having the same structure as that shown in FIG. 1 was manufactured using the same process as in Example 1. Moreover, on each of the above substrates (A r + N
2) Polycrystalline NbN (Tc = 14 to 1
A device having a base layer of 5.5K) was also fabricated.

The current transfer rate of these elements in a state where the base-collector voltage is zero was measured at 4.2. As a result, while an α of 0.01 to 0.20 was obtained for a device using a polycrystalline base, an α of 0.2 to 0.75 was obtained for a device based on epitaxially grown single crystal NbN. Improved.

Embodiment 3 FIG. 2 is a schematic sectional view showing a third embodiment of the present invention.

n+ type Ga doped with Se by metal organic chemical vapor deposition (MOCVD) on the (100) plane of a semi-insulating InP single crystal substrate 8, 1. I no, Ils As layer 9
(thickness 5000 people) and n-type Gal+, 1. I no,
Collector layer 10 (1000 layers thick) consisting of 65 As
was continuously grown epitaxially. In this case, as the organic metal, trimethyl gallium (TMG, (CHa
) aGa) and trimethylindium (TM In, (C
H3) 3 In) using H2 as a carrier gas,
In addition, the supply of group Ⅰ elements is as follows: arsine A s H3 with H2
Mixed gas diluted to 0%, Se for doping is H2Se
dilution gas was used. Substrate temperature during crystal growth is 650℃
, the total carrier gas flow rate was 4Q/min.

Next, a base layer 1 made of Nb or NbN is continuously formed on this semiconductor thin film by the same CVD method as in Example 1-2.
1 has grown to a depth of 500 people. Base layer 1 in this case
The mismatch in lattice constant between Nb and superconductor layer 11 is 10% for Nb and 4% for NbN, and a single crystal layer is also obtained.

Next, MOC is continuously formed on the single crystal Nb and NbN layers 11.
The n+ type GaAs layer 12 was epitaxially grown to a thickness of 5000 nm by the VD method. In this case, the substrate temperature is still 650°C, and the carrier gas flow rate is 2Q/mi.
It was set as n. The multilayer film thus formed was taken out and subjected to chemical etching and RIE to form the emitter junction (in this case, Nb (or NbN)-'n'' type Ga A
s Schottky junction) and base pattern processing, an insulating layer 13 made of SiO is deposited in the same manner as in Example 1, and a base electrode 14 made of Nb and a base electrode 14 made of Au are deposited in the window provided in the insulating layer 13. Emitter electrode 15 was formed by a lift-off method. Finally, the n
An ohmic collector electrode 16 made of Au was formed in another window reaching the +-type Ga, 15Inn, and BgAs layers 9.

The current transfer coefficient α at 4.2 of the device fabricated as described above has a value of 0.65 to 0.85 when the emitter-base bias is 20111V, and the Nb formed by sputtering on the base layer Or 0 when using NbN polycrystal
．． A significant improvement was seen from 0.07 to 0.25.

Example 4 Using a non-doped InSb single crystal as a substrate, similarly to Example 3, MOCVD was used to epitaxially grow InS bl-, As, and diamond structure Sn. In the former case, TMI
First, using n, SbH, and AsH3 as source gases, an n+ type I n S b with a thickness of 5,000 people was prepared. ,,, As.

,, layer as a buffer layer, a collector layer consisting of a 1000 nm thick n-type I n S bo,3Aso,v was formed.

In the case of Sn, (CH3)4Sn was used as the source gas and SbH3 diluted with H2 was used for doping, and the n+ layer was grown to a thickness of 5000 layers and the n-type Sn layer as the collector layer was grown to a thickness of 1000 layers. Continuously on top of this, as in Examples 1 and 2, C
Nb and NbN layers were epitaxially grown using the VD method to form a single crystal base layer (thickness: 500 nm). next,
Elements were produced using the same process as Examples 1 to 3. The emitter junction in this case was formed by depositing an electrode made of normal conducting Au through a barrier layer made of an underlying Nb (or NbN) plasma oxide film.

The current transfer coefficient of these elements is 0.4-0.7
5 (I n S b, -y 10 mV between emitter-base for Asy collector, 150 mV for Sn collector
mV), which exceeded the values for polycrystalline Nb (or NbN)-based devices from 0.01 to 0.35.

〔Effect of the invention〕

As explained above, according to the present invention, diamond-structured Sn, GaSb, I'nSb, and InAs.

By selecting one of CdS, CdSe, PbTe, In1-xGaxAs mixed crystal, and InS bl-y mixed crystal as the substrate (base), it is possible to epitaxially grow Nb or NbN monomers with the same cubic crystal but with small lattice constant mismatch. A crystal thin film can be obtained, and by using this single crystal Nb or NbN as the base layer of the device and the underlying semiconductor single crystal as the collector layer, the scattering factors of quasiparticles due to disorder of the base crystal and interface structure are reduced. It has the advantage of providing a large current transfer rate comparable to that of semiconductor bipolar transistors, that is, a large current gain. Similarly, due to the reduction in interface state density at the base-collector interface, a low potential barrier can be formed by selecting the semiconductor material and polarity, reducing the operating voltage.
That is, there is an advantage that lower power consumption of the element can be achieved.

[Brief explanation of drawings]

1 and 2 are schematic cross-sectional views showing examples of the present invention, FIG. 3 is a schematic diagram of a conventional superconducting three-terminal device according to the present invention, and FIG. 4 is a schematic diagram of a conventional superconducting three-terminal device according to the present invention. lattice constant a
. 5 is a diagram for explaining the lattice matching state between the Nb or NbN single crystal and the semiconductor single crystal shown in FIG. 4, and FIG. 6 is a diagram showing the superconducting two-terminal device according to the present invention and the conventional one. It is a chart showing the current transfer rate α of a superconducting three-terminal device. In the figure, 1 is a semiconductor single crystal substrate, 2 is a base layer (epitaxially grown Nb or NbN single crystal layer), 3 is an insulator (SiO), 4 is a barrier layer, and 5 is an emitter electrode (NbN
), 6 is a base electrode (Nb), 7 is a collector electrode (Au
), 8 is a semiconductor single crystal substrate (InP), 9 is n''-G
ao, □6 I n. , B HA s layer, 10 is the collector layer (n Gao, 1sI n., Il, As layer)
, 11 is a base layer (epitaxially grown Nb or NbN
layer), 12 is an n+-Ga As layer, and 13 is an insulating layer (
14 is a base electrode (Nb), 15 is an emitter electrode (Au), 16 is an ohmic collector electrode (Au
). JI! P2 Figure 831-A 艷い三月 1 (Gi 1 Crystal, 1 (-talience (r??
P) Sai3 figure Sai4 Dako5 figure (A) ■ 0 ■ o OoNbA) (B) Δ Δ Δ Δ ■ ・ ΔN Float (Vac = O)

Claims (1)

[Claims] 1. A base layer made of a superconductor, and a normal conducting metal in contact with one side of the base layer and injecting quasiparticles into the base layer;
In a superconducting three-terminal device comprising an emitter layer made of a superconductor or a semiconductor, and a collector layer made of a semiconductor that is in contact with the other side of the base layer and captures quasiparticles from the base layer, the base layer Layer has diamond structure Sn, GaSb, InSb, InAs, CdS, CdS
e, Nb or NbN epitaxially grown on the collector layer consisting of PbTe, In_1_-_xGa_xAs mixed crystal or InSb_1_-_yAs_y mixed crystal.
A superconducting three-terminal device characterized by consisting of layers.