JP2523517B2 - Superconducting light guide detector - Google Patents

Description

TECHNICAL FIELD The present invention relates to a superconducting light guide detection element, and more particularly to a superconducting light guide detection element having high detection sensitivity and suitable for integration.

[Conventional technology]

For an element that detects light by making light incident on a weakly coupled element using a superconductor, see Physical Levy, B.
Volume 18, (1978) pp. 6035 to 6040 (Phys.Re
vB, Vol. 18, (1978) pp. 6035-6040).

[Problems to be solved by the invention]

In the above-mentioned conventional technology, CdS or the like is used as the barrier material, and one using lead or indium as the material of the superconducting conductive electrode is known, but the incident light is irradiated to a large area including the element and its periphery, and thus CdS is used. The excitation of the inside carrier by light was not limited to just under the superconducting electrode. Therefore, in this case, the light transmissivity of the superconducting electrode is not particularly known, and the film thickness of the electrode is not particularly limited.

In other words, the above-mentioned prior art has not paid any attention to the light transmissivity of the superconducting thin film, and therefore it cannot be said that the photodetection sensitivity is sufficient as the photodetection element. Therefore, the area of the photodetector becomes large, and unnecessary heat generation due to absorption of light makes it unsuitable for high integration of the device.

An object of the first invention is to use a superconducting thin film having both light transmissivity and superconductivity at a liquid helium temperature, and combining this with a semiconductor to realize a superconducting light guide detecting element which realizes a high-speed switching operation as a photodetecting device. It is possible to make.

In addition, the above-mentioned conventional technology does not take into consideration that the light incident on the semiconductor is used as efficiently as possible, and when extremely weak light is used, electrons and holes are sufficiently excited in the semiconductor. Therefore, the superconducting current due to the superconducting proximity effect did not flow, and sufficient sensitivity could not be obtained.

A second object of the present invention is to improve absorption efficiency by reflecting light transmitted through the semiconductor layer by a layer provided below the semiconductor layer that is excited by absorbing light, and, by extension, weaken the light of the device. It is to provide a structure of a superconducting light guide detection element capable of realizing switching.

[Means for solving problems]

The above-mentioned first object is achieved by determining the film thickness of the superconducting thin film in consideration of the film thickness dependence of both the light transmittance and the superconducting transition temperature. In order for the carriers in the semiconductor excited by light to efficiently change the superconducting characteristics, it is desirable that light passes through the superconductor and enters the semiconductor. As the film thickness of the superconductor decreases, the light transmittance increases, but the superconducting transition temperature decreases. On the other hand, in order to maintain superconductivity so that the device operates in liquid helium, it is necessary to select a film thickness such that the transition temperature is 4.2K or higher. Therefore, by selecting the thickness of the superconducting thin film used for the superconducting light guide detecting element so as to satisfy the above two requirements at least in the part where light is incident, the superconducting light guide having high detection sensitivity and suitable for high integration can be obtained. A detection element can be realized.

The second object of the present invention is, in a superconducting light guide detection element, to efficiently reflect light having a wavelength such that the semiconductor has a large absorptivity under a semiconductor layer that is excited by absorbing light. This is accomplished by providing a layer and the presence of this reflective layer does not interfere with the operation of the device.

[Work]

In the first invention, light transmittance is 10% or more, superconducting transition temperature
The thickness of the superconducting electrode is 4.2K or more, that is, as shown in FIGS. 3 and 4, Nb alone is ~ 28 nm, NbN
Then, by producing a thin film having a thickness of 5 to 35 nm, it becomes possible to obtain a superconducting conductive electrode having both light transmissivity and superconductivity in liquid helium.

As shown in FIG. 1, two electrodes composed of the above-mentioned thin film are arranged so as to face each other on a flat semiconductor, penetrate the above-mentioned thin film, and further excite atoms of the semiconductor to form electron-hole pairs. When the light having a wavelength and intensity sufficient to generate the light is made incident, the carrier concentration in the semiconductor is increased. If a carrier concentration before light incidence is appropriately adjusted by applying a voltage to the control electrode in advance, the superconducting current flows due to the superconducting proximity effect. Therefore, the superconducting current between the two electrodes can be controlled by light to realize switching. Furthermore, the film thickness of the superconducting electrode,
By changing the type of semiconductor and the impurity concentration thereof, it is possible to change the sensitivity of the photodetection element in various ways with respect to the wavelength and intensity of light. Alternatively, the sensitivity can be changed by changing the voltage applied to the control electrode.

By using the above photodetection element, it has become possible to apply a superconducting element to an optoelectronic circuit and increase the speed thereof.

In the second invention, at the interface between the two kinds of media, the first
Let i _{0 be} the critical angle of the light that enters the second medium from the medium
If the refractive indices of the first medium and the second medium are n ₁ and n ₂ , respectively, and the extinction coefficient of the second medium is k, the reflectance R in the case of vertical incidence is Is represented. In the above equation, R has n ₁ , n ₂ and k such that R ≧ 0.5 for light having a wavelength at which electrons and holes in the first medium are excited, and the transmittance of the first medium Is 50%
By selecting the combination of the first medium and the second medium and the film thickness of the first medium as described above, as shown in FIG. 6, two electrodes 602 made of a superconductor are formed on a flat semiconductor layer 605. Are arranged so as to face each other, a layer of a light reflection film 604 as a second medium is provided on the back side of the semiconductor layer 605 via an insulating film 603 as a first medium, and light having a wavelength as described above is made incident. If
A part of the incident light is reflected at the interface between the first medium and the second medium, the carrier concentration in the semiconductor can be increased very effectively, and the sensitivity of the superconducting light guide detection element can be improved. .

In this case, it is necessary that the presence of the light reflecting layer cannot prevent the superconducting coupling between the two superconducting electrodes. For example, when the impurity concentration on the reflection film side of the semiconductor layer is so high that the semiconductor on the light reflection film side degenerates at an extremely low temperature, it is desirable to provide an insulating film between the semiconductor layer and the light reflection film. This is because the electrons and holes in the light-reflecting film enter the semiconductor by diffusion, and act to shorten the life of the superconducting pair produced in the semiconductor layer by the proximity effect.
This is because the element will not operate stably.

Therefore, when an insulating film is not used, it is necessary to reduce the impurity concentration on the reflective film layer side of the semiconductor to sufficiently reduce the tunnel of carriers through the Schottky barrier. The above is the case where a metal is used for the light reflecting film, but in the case where a pn junction is formed between the semiconductor and the light reflecting film which is the second semiconductor by using a second semiconductor for this. Is the same.

〔Example〕

Examples of the first and second inventions will be described in detail below.

[Embodiment 1] FIG. 1 is a sectional view showing a part of a superconducting light guide detection element in an embodiment of the first invention. Boron was diffused at a concentration of 4 × 10 ²⁵ m ⁻³ into a semiconductor substrate 1 made of 2-inch Si having a (100) orientation, and anisotropic etching was performed only in the vertical direction from the back surface to a Si thickness of 70 nm. Next, the SiO ₂ gate insulating film 3 having a thickness of 40 nm was formed by thermal oxidation. Thickness on it
A 0.7 μm Al thin film was formed by a resistance heating vapor deposition method and processed by an Ar sputter etching method to form a control electrode 4.
A 15 nm thick Nb thin film was formed on the surface by the DC magnetron sputtering method. In that case, the substrate temperature was kept at 25 ° C. This was processed by electron beam drawing using an electron beam resist and reactive ion etching to obtain a light transmissive superconducting electrode 2 having a spacing of 0.2 μm. As described above, the superconducting light guide detection element of the present invention could be manufactured. The device was cooled to the temperature of liquid helium and GaAl _x A was added as shown in FIG.
s _{1-x The} light source 501 is a light emitting diode, and the light having a wavelength of 650 nm is dispersed by the diffraction grating 502. The lens 503 and the optical fiber.
By making it enter the element 505 through 504, it operated as a superconducting light guide detecting element.

Although Nb was used as the material of the superconducting electrode in this example, similar effects could be obtained when NbN was used instead of Nb.

Although Si is used as the semiconductor substrate 1 in the present embodiment, Ge, InAs, InSb, GaAs, GaAs _x As _1-x , InP may be used instead.
Further, although a GaAl _x As _1-x light emitting diode is used as the light source 501, other light emitting diodes, semiconductor lasers, solid-state lasers, gas lasers, white light, or the like may be used instead.

[Embodiment 2] Next, FIG. 2 shows a partial sectional view of a superconducting light guide detection element according to a second embodiment of the present invention. Boron was diffused at a concentration of 1 × 10 ²⁴ m ⁻³ into a semiconductor substrate 11 made of 2-inch Si having a (100) orientation, and a 50 nm-thick Nb thin film was formed on the surface by DC magnetron sputtering. This was processed by reactive ion etching using CF ₄ gas, and the interval was 0.2μ.
m superconducting electrode 12 was used. A 100 nm-thick SiO ₂ film was formed by the oxidative vapor phase epitaxy method, and similarly processed by reactive ion etching to obtain a light-transmissive gate insulating film 13. Finally, a 15 nm Nb thin film was formed by the DC magnetron sputtering method and processed by the lift-off method to form the light transmissive superconducting control electrode 14. By the above, the superconducting light guide detection element of the present invention could be prepared. The device was cooled to the temperature of liquid helium, and as shown in FIG. 5, light having a wavelength of 650 nm was made to enter the device 5 as in the first embodiment, thereby operating as a superconducting light guide detection device.

Although Nb was used as the material of the superconducting electrode in this example, similar effects could be obtained when NbN was used instead of Nb.

In addition, although Si is used as the semiconductor substrate in this embodiment,
Instead of this, Ge, InAs, InSb, GaAs, GaAl _x As _1-x , InP, etc. were used as the light source, and GaAl _x As _1-x light emitting diode was used as the light source. , A semiconductor laser, a solid-state laser, a gas laser, white light or the like may be used.

[Embodiment] Hereinafter, the second invention will be described in detail with reference to an embodiment. FIG. 6 is a sectional view showing a part of the superconducting light guide detection element according to the third embodiment. Si semiconductor substrate 601 whose surface is collected and oxidized
A thin film of Al having a thickness of 50 nm was formed on the top by a sputtering method and processed by an Ar sputter etching method to form a light reflection film 604. Then, an insulating film 603 made of SiO _{2 and having} a thickness of 30 nm and made of SiO ₂ is formed by a chemical vapor deposition method, and subsequently, a semiconductor layer 605 made of an InSb thin film and having a thickness of 300 nm is formed by a sputtering method. Si is added to the semiconductor layer 605 as an impurity at a concentration of 5 × 10 ²² m ⁻³ during sputtering. Finally, a 15-nm-thick Nb thin film was formed by the DC magnetron sputtering method, and this was processed by electron beam drawing using a electron beam resist and reactive ion etching to form a superconducting electrode 602 having a facing portion interval of 200 nm. As described above, the superconducting light guide detection element of this embodiment can be realized. After cooling this element to the liquid helium temperature, as shown in FIG. 7, after the light emitted from the light beam 701 composed of the photodiode is condensed by the lens 702, it is dispersed using the diffraction grating 703 to emit the light of 650 nm. When light was made incident on this element 705 using the fiber 704, it operated as a photodetection element.

In this example, Nb was used as the material of the superconducting electrode, SiO ₂ was used as the material of the insulating film, and Al was used as the material of the reflective film.Instead, NbN, Pb alloy, MoN, Nb ₃ Si, was used as the superconducting material. nb ₃ Al or the like, SiO the material of the insulating film, Si ₃ N ₄ or the like, Cu as the material of the reflective film, may be used Ag or the like.

[Embodiment 4] FIG. 8 is a sectional view showing a part of a superconducting light guide detection element according to this embodiment. Boron is diffused at a concentration of 5 × 10 ²⁶ m ⁻³ into a 2-inch Si semiconductor substrate 801 having a (100) orientation, and anisotropic etching is performed from the back surface only in the vertical direction to reduce the Si thickness.
It was set to 70 nm. Next, an insulating film 803 made of SiO _{2 and having a} thickness of 20 nm was formed by thermal oxidation. A 700 nm-thick Al thin film was formed thereon by a resistance heating vapor deposition method and processed by an Ar sputter etching method to form a light reflective control electrode 804. A 15 nm thick Nb thin film was formed on the surface by the DC magnetron sputtering method. This was processed by electron beam writing using an electron beam resist and reactive ion etching to obtain a superconducting electroconductive electrode 802 having an interval between facing portions of 200 nm. As described above, the superconducting light guide detection element according to the present embodiment can be realized.
After cooling this element to the liquid helium temperature, as shown in FIG. 7, the light emitted from the photodiode 701 is condensed by the lens 702, and then dispersed using the diffraction grating 703 to emit 650 nm light using the optical fiber 704. When it was incident on the element 705, it operated as a photodetection element.

In this embodiment, Nb is used as the material of the superconducting conductive electrode, Si is used as the material of the semiconductor, SiO ₂ is used as the material of the insulating film, and Al is used as the material of the light reflective control electrode, but instead of these, Nb is used as the superconducting material.
InAs, In for semiconductor materials such as N, Pb alloy, MoN, Nb ₃ Si, Nb ₃ Al
P, InSb, GaAs, GaP, CdS, etc., SiO, Si ₃ N ₄ etc. as the material of the insulating film,
Cu, Ag or the like may be used as the material of the reflective film.

〔The invention's effect〕

As described above, according to the first aspect of the invention, the superconducting light guide detecting element that realizes the high-speed switching operation can be manufactured by using the light-transmitting superconducting thin film made of Nb alone or NbN.

According to the second aspect of the invention, the light incident on the semiconductor layer is reflected by the mirror surface layer provided under the semiconductor layer so that the light is efficiently absorbed by the semiconductor, whereby carriers necessary for flowing a superconducting current can be obtained. Since the concentration can be easily obtained, it is possible to provide a method for improving the sensitivity of the superconducting light guide detection element.

[Brief description of drawings]

1, 2, 6, and 8 are sectional views showing a part of a superconducting light guide detection element according to different embodiments of the present invention, and FIG. 3 is a thickness of a superconducting Nb thin film and its superconducting transition. Figure 4 shows the relationship between temperature and light transmittance. Figure 4 shows superconducting NbN.
FIG. 5 is a view showing the relationship between the thickness of the thin film and its superconducting transition temperature and light transmittance, and FIGS. 5 and 7 are schematic views of different devices for confirming the switching operation. 1 ... Semiconductor substrate, 2 ... Light transmissive superconducting electrode, 3 ...
Gate insulating film, 4 ... Control electrode, 11 ... Semiconductor substrate, 12
...... Superconducting electrode, 13 …… Light-transmissive gate insulating film, 14 ……
Light-transmissive superconducting controller, 501 ... Light source, 502 ... Diffraction grating, 503 ... Lens, 504 ... Optical fiber, 505 ... Element, 601,801 ... Semiconductor substrate, 602,802 ... Superconducting electrode,
603, 803 ... Insulating film, 604, ... Control electrode, 605 ... Reflective film, 606 ... Semiconductor layer, 701 ... Light source, 702 ... Lens, 7
03 ... Diffraction grating, 704 ... Optical fiber, 705 ... Photodetector, 804 ... Light reflective control electrode.

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-61-35574 (JP, A) JP-A-58-141582 (JP, A) JP-A-62-199070 (JP, A)

Claims (9)

(57) [Claims] 1. A semiconductor layer and at least an electrode composed of two superconductors provided on the surface of the semiconductor layer on the light incident side. The thickness of the two electrodes composed of the superconductor is equal to that of the electrodes. Light transmittance is 10% or more and the electrode is 4.
A superconducting light guide detection element, which is set so as to make a superconducting transition at 2 K or more, and detects light as a change in a current generated between the two superconducting electrodes by the light incident on the semiconductor layer. 2. The superconducting light guide detection element according to claim 1, wherein the superconductor forming the electrode is Nb, Nb.
A superconducting light guide detection element, characterized in that it is at least one material selected from N. 3. The superconducting light guide detecting element according to claim 2, wherein the superconducting conductive electrode made of Nb has a film thickness of 28 nm.
The thickness of the NbN superconducting electrode selected below is 5
A superconducting light guide detection element characterized by being selected in the range of up to 35 nm. 4. The superconducting light guide detecting element according to claim 1, wherein at least a control electrode for applying a voltage between the two superconducting conductive electrodes is provided in the semiconductor layer via an insulating film. Characteristic superconducting light guide detection element. 5. The superconducting light guide detection element according to claim 4, wherein the material forming the control electrode is a superconductor, and the control electrode has a thickness for transmitting light incident on the semiconductor layer. A superconducting photodetector characterized by having a thickness. 6. The superconducting light guide detection element according to claim 5, wherein the control electrode is made of Nb alone or
A superconducting light guide detection element characterized by being selected from NbN and having a thickness of 28 nm or less for Nb and 5 to 35 nm for NbN. 7. A semiconductor layer, at least an electrode composed of two superconductors provided on the surface of the semiconductor layer on the light incident side, and insulation on the back side of the surface of the semiconductor layer provided with the superconducting conductive electrode. The two electrodes made of the opposite film provided via the film have a thickness that allows the light incident on the semiconductor layer to pass therethrough, and the reflective film reflects the light incident on the semiconductor layer. A superconducting light guide detection element, which is formed as described above and detects light as a change in a current generated between the two superconducting electrodes by the light incident on the semiconductor layer. 8. The superconducting light guide detection element according to claim 7, wherein the reflective film has a larger optical refractive index at the wavelength of the incident light than a metal or a material forming the semiconductor layer. A superconducting light guide detection element characterized by using the second semiconductor material having. 9. The superconducting light guide detection element according to claim 7 or 8, wherein the impurity concentration in the semiconductor layer is non-uniform, and the impurity concentration in at least the reflective film side of the semiconductor layer. Is a superconducting light guide detection element characterized by being selected so small that carriers in that portion freeze at extremely low temperatures.