JP2506871B2 - Ultra high frequency generator - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a super high frequency generating device using a superconductor as a part of the device.

2. Description of the Related Art Conventionally, Gunn diodes, impat diodes and the like are known as high frequency generating elements. These make use of the negative resistance phenomenon of electrons in the semiconductor bulk and the transit time effect.

Problems to be Solved by the Invention In any of these high frequency generating elements, it is necessary to accelerate electrons in a high electric field, and the time until the electrons receive their energy is involved in the upper limit of the high frequency that can be generated.
Therefore, there is a criticality, and up to about 100 GHz has been obtained, but it is difficult to generate a higher frequency.

The present invention has been made in view of the above points, and uses a superconductor as a part of a diode structure, and uses recombination of electron-hole pairs injected into the superconductor to generate a high frequency. High frequency of 100HGHz or more can be easily generated.

Means for Solving the Problems In order to solve the above problems, the present invention has a first semiconductor on one side with a superconductor interposed, with an interlayer insulating film having a tunnelable thickness interposed therebetween. On the other side, the energy difference from the Fermi level to the conduction band edge is smaller than that of the first semiconductor and the Fermi level to the valence band is smaller than that of the first semiconductor through the interlayer insulating film having a tunnelable thickness. The structure has a structure in which the first semiconductor and the second semiconductor having a different conductivity type have a large energy difference up to the edge.

Action According to the present invention, when one semiconductor is an n-type semiconductor, electrons are tunnel-injected from the n-type semiconductor into the superconductor and holes are tunnel-injected from the other p-type semiconductor into the superconductor by the structure described above. Electrons and holes injected in the superconductor are set by setting the energy band structure so that the required voltage is lower than the voltage required for tunnel injected electrons or holes to tunnel to the other semiconductor. Is accumulated and recombined there to generate a high frequency wave having a wavelength corresponding to the energy band gap of the superconductor.

Embodiment One embodiment of the present invention will be described below with reference to the drawings.

On a gallium arsenide (GaAs) substrate, which is an n-type semiconductor,
About 20Å of silicon oxide (Si) by chemical vapor deposition (CVD)
O ₂ ) film is formed, and about 1 μm is formed on it by vacuum evaporation method.
To form a lead (Pb) thin film. Furthermore, chemical vapor deposition (CV
A silicon oxide (SiO ₂ ) film of about 20 Å is formed by D), and a germanium (Ge) film which is a p-type semiconductor of 5000 Å is formed on the silicon oxide (SiO ₂ ) film by vacuum evaporation, and ohmic electrodes are provided on GaAs and Ge.

The structure is shown in FIG. In FIG. 1, 1 is an n-type semiconductor GaAs substrate, 2 is a first SiO ₂ thin film formed thereon, 3 is a Pb thin film, and 4 is a second SiO ₂ film formed thereon. 5 is a p-type semiconductor Ge thin film. 6 is an ohmic electrode formed on the other surface of the GaAs substrate, and 7 is an ohmic electrode formed on the upper surface of the Ge thin film.

Pb is a superconductor that becomes superconducting at about 7.2K. Therefore, if an element having such a structure is cooled to a critical temperature or lower, for example, 7 K or lower, one superconductor is sandwiched between n-type semiconductor and p-type semiconductor separated by a thin interlayer insulating film. . The energy band diagram at this time is shown in FIG. The energy band gap of GaAs, Eg _1, is about 1.5 eV. E ₁ is the energy from the Fermi level to the conduction band edge, E ₁ ′ is the energy from the Fermi level to the valence band edge, and E ₁ + E ₁ ′ = Eg ₁ . n
By making the type impurity concentration extremely high, the band edge of the conduction band comes close to the Fermi level. Pb has an energy band gap of about 1.34 meV in the superconducting state. The energy band gap of Pb is 2
If it is Δ, the Fermi level is in the middle of the energy band gap. Ge energy band gap,
Eg ₂ is about 0.8 ev. E ₂ is the energy from the Fermi level to the edge of the conduction band, E ₂ ′ is the energy from the Fermi level to the edge of the valence band, and E ₂ + E ₂ ′ = Eg ₂ . By increasing the p-type impurity concentration, the valence band band edge comes close to the Fermi level. Therefore, the energy band diagram as shown in FIG. 2 is obtained. Number is a carrier electron at this time GaAs side, since the interlayer insulating SiO ₂ film is sufficiently thin, a very low voltage when the E ₁ -Δ> 0, when the _{E 1 -Δ <0, E 1} -Δ voltage Due to the tunnel effect, it easily enters the Pb superconductor. However, Pb superconductor is not tunnel-injected into Ge at this voltage because there is no energy level to tunnel to Ge. On the other hand, at this time, the holes, which are the majority carriers on the Ge side, still have E ₂ ′ because the interlayer insulating SiO ₂ film is sufficiently thin.
When −Δ> 0, the voltage is extremely low, and when E ₂ ′ −Δ <0, the voltage of E ₂ ′ −Δ easily tunnels into the Pb superconductor. However, tunneling cannot be performed from the Pb superconductor to GaAs at this voltage because there is no energy level to tunnel to GaAs. That is, at this time
A large amount of electrons and holes are injected and accumulated in the Pb superconductor. These electrons and holes recombine with an appropriate relaxation time. The energy difference between the electrons and holes at this time corresponds to the energy band gap of the Pb superconductor in the equilibrium state. The energy band gap of Pb superconductor is about 1.3 meV, the wavelength corresponding to this energy is about 1 mm, and the frequency is about 300 GHz. Therefore, by applying a higher voltage of E ₁ −Δ or E ₂ ′ −Δ to the device of this structure, electrons and holes are tunnel-injected inside the superconductor, where they recombine and generate a high frequency of about 300 GHz. To do.

In this state, the bias voltage between GaAs and Ge is increased.
When the Ge side is positive, an electron can tunnel from the superconductor to Ge only when a bias voltage of E ₂ −Δ is applied, and a current flows rapidly.

In this embodiment, since E ₂ −E ₁ is smaller than E ₁ ′ −E ₂ ′, current flows out at E ₂ −E ₁ , but if E ₁ ′ −E ₂ ′ is smaller, , E ₁ ′ -E ₂ ′ starts to flow current. Therefore, the state in which both electrons and holes are accumulated in the superconductor is E ₂ −E ₁ > 0 and E ₁ ′ −E ₂ ′> 0, in other words, the energy band structure of one semiconductor is This is the case where the energy difference from the Fermi level to the conduction band edge is smaller than that of the semiconductor and the energy difference from the Fermi level to the valence band edge is larger.

In this embodiment, Pb was used as the superconductor, but Ln ₁ Ba ₂
Cu ₃ oxide (however, Ln is Y, Nd, Sm, Eu, Gd, Tb, Dy, H
critical temperature 9 such as o, Er, Tm, Yb, Lu)
By using a superconductor having a critical temperature of about 30K, such as a superconductor having a temperature of about 0K or La _1.85- Ae _0.15- Cu ₁ oxide (where Ae is at least one of Ba, Sr, and Ca),
It is clear that at higher temperature, the same high frequency generating action can be obtained by voltage-hole recombination as in the present embodiment. In this case, the energy band gap of the Ln ₁ Ba ₂ Cu ₃ oxide as a superconductor is 20-30 meV, and an ultrahigh frequency of about 5-7 THz can be generated.

In the Ln ₁ Ba ₂ Cu ₃ oxide, a superconductor having a high critical temperature can be obtained even if Ba is replaced with Sr. Therefore,
It is clear that the same effect can be obtained by using a superconductor in which Ba is replaced with Sr.

Further, in this embodiment, as the semiconductor, n-type GaAs and p are used.
Type Ge, the energy band structure of the second semiconductor has a smaller energy difference from the Fermi level to the conduction band edge than the first semiconductor and the energy from the Fermi level to the valence band edge of the first semiconductor. It is sufficient if the difference is large, and the semiconductor is not limited to these semiconductors.

In this embodiment, a specific value is used as the thickness of the interlayer insulating film, but this thickness is arbitrary within the range where the tunnel effect occurs.

In this embodiment, SiO ₂ is used as the interlayer insulating film, but it is obvious that the present invention is not limited to this.

EFFECTS OF THE INVENTION As described above, according to the present invention, the first semiconductor is provided on one side of the superconductor with the tunnel insulating film having the tunnelable thickness interposed therebetween, and the other side of the tunnel is provided. The energy difference from the Fermi level to the conduction band edge is smaller than that of the first semiconductor and the energy difference from the Fermi level to the valence band edge is greater than that of the first semiconductor through the interlayer insulating film having a possible thickness. The present invention provides an element having a structure having a second semiconductor having a conductivity type different from that of a first semiconductor and generating an electromagnetic wave of extremely high frequency.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the structure of the present invention, and FIG. 2 is a schematic view showing an example of an energy band diagram of the element of the present invention. 1 ... n-type semiconductor substrate, 2 ... interlayer insulating film, 3 ... superconductor film, 4 ... interlayer insulating film, 5 ... p-type semiconductor film, 6,7
……electrode.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ichiro Yamashita 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-57-111068 (JP, A)

Claims (1)

(57) [Claims] 1. A superconductor is sandwiched between a first semiconductor and an interlayer insulating film having a tunnelable film thickness on one side, and an interlayer insulating film having a tunnelable film thickness on the other side. Conduction through the film to the first semiconductor, which has a smaller energy difference from the Fermi level to the conduction band edge than the first semiconductor and a larger energy difference from the Fermi level to the valence band edge than the first semiconductor. An ultra-high frequency generating element having a structure having a second semiconductor of a different type.