JPS6030114B2 - Josephson junction photodetector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photodetecting element comprising a Josephson junction,
More specifically, the present invention relates to a photodetecting element consisting of a tunnel-type Josephson junction.

In recent years, with the progress of optical communication technology and Josephson computer technology, the development of photodetecting elements with high sensitivity and high speed response has become an important technological development issue.

Conventional photodetecting elements include semiconductor photodetecting elements such as pin diodes and avalanche diodes (ADP) using semiconductor PN junctions, but recently, as shown in FIG. 3 at the bridge portion 2' of the microbridge-type Josephson junction element 2 made of a thin film.
500p generated by irradiating a ~5ps (picosecond) optical pulse and passing a constant bias current through the device.
Experimental examples have been reported in which voltage pulses with a half-width of less than s are observed (lEEETRANSACTIONS,
ONMAONETICS, VOL. MAC-1
7.No. 1, JANUARYI981).

An object of the present invention is to provide a photodetecting element comprising a tunnel-type Josephson junction, which is inspired by the operating mechanism of the ADP semiconductor photodetecting element described above.

Although this object is achieved by the configuration of the present invention as described in the claims, the configuration and effects of the present invention will be better understood from the following detailed description with reference to the accompanying drawings.

First, FIG. 2 shows an example of the structure of a conventional APD. When incident light is irradiated to the P+Pn+ junction from the P+ side and a reverse voltage is applied to the junction by the power source B, electrons are generated in the surface layer P+ and the junction P at the surface layer P+ and the junction P, as shown in the energy structure in Figure 3. The semiconductor C is excited from the filling zone F, and is accelerated by the exposed field at the junction to cause "avalanche" development, or avalanche development, producing N avalanche electrons for each excited electron. The excited electrons due to this avalanche generate a large number of conduction electrons, and the electrons caused by the light are amplified by N times.
The amount of incident light is detected with high sensitivity by detection by an external circuit consisting of. On the other hand, the present invention, as shown in FIG. superconductor layer 3
, a thin tunnel barrier 4 made of an oxide film of this superconductor layer or an insulator thin film such as Si02, and Pb, Pb0×
, Nb or the like, a second superconductor layer 5 having a thickness of 1000Δ or more that does not transmit light is sequentially formed, and a power source B is connected between the first and second superconductor layers 3 and 5, Current or voltage changes flowing through the tunnel barrier due to light incident on the tunnel barrier 4 from the substrate side through an optical waveguide 7 such as a fiber having a lens 6 are detected by an ammeter A and a voltmeter V. It is composed of

Now, assuming that the first superconductor layer 3 of NbN is thin and transmits light, and TcNbN<TcPb, the NbN thin film absorbs photons hw (photon) and generates electrons, as shown in FIG. The pair is NbN energy gap △(N
bN) is excited to a height approximately 100 times higher than that of

This excited electron is caused by inelastic scattering with the lattice, causing △ between ↑s
(NbN) reaches the upper limit, but during this time hw(phoMn
)>2Δ(NbN) is generated to destroy several ION solid electron pairs to generate quasi-particles, which acts just like the abalasoché development of ADP. Thereafter, the excitation ends at a recombination time of 7R, which is about 4 s for Pb-Bi. The change in 1-V characteristics due to light irradiation is shown in FIG. That is, before light irradiation, if the load straight line is L, the operating point that was at point A moves to point B by light irradiation, and the amount of current change at this time becomes the output current. A. The voltage change amount Vc is about △Pb (~2
Since V), V of Vcmi is obtained. Light sensitivity is 1
Approximately V/W can be obtained. In addition, the light response speed is about the relaxation time s for excited electrons and reaching the lower end of the superconductor, which is 100 s for the response speed of a conventional semiconductor photodetector element of 10 s.
About twice as fast. FIG. 7 is a perspective view of FIG. 4, showing a case where the first and second strip-shaped superconductor layers 3 and 5 intersect and a tunnel barrier 4 is formed in this intersecting region.

FIG. 8 shows a case where an insulating layer 9 with holes 8 is formed on the first superconductor layer 3, and a tunnel barrier 4 is formed in the holes.

In FIG. 9, the substrate 1 is formed as a cladding layer, and light is irradiated through the cladding layer 1' of this substrate.
A case is shown in which light is incident on the tunnel barrier 4.

When the substrate is formed as a cladding layer in this way, there is an advantage that it can be constructed from a thin film pattern circuit of the photodetecting element and the light input means.

[Brief explanation of drawings]

FIG. 1 is an enlarged perspective view of a microbridge type Josephson junction element, FIG. 2 is an explanatory diagram of the working mechanism of a conventional ADP semiconductor photodetector, and FIG. 3 is an explanatory diagram of the energy structure of ADP. FIG. 4 is an enlarged front view showing an example of the configuration of the photodetecting element of the present invention with a partial cross section, FIG. 5 is an explanatory diagram of the working mechanism of the present invention, and FIG. Graphs showing changes in the 1-V characteristics of the detection element, FIG. 7 is a perspective view of FIG. The front view shown. Codes in the diagram: 1... board, 3... first
superconductor layer, 4... tunnel barrier, 5...
...Second superconductor layer, B...Power supply, A...
Ammeter, V... Voltmeter. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9

Claims (1)

[Claims] 1. A substrate that transmits light, a first superconductor layer formed on this substrate and having a thickness that allows transmission of light, a tunnel barrier formed on this superconductor layer, and this tunnel barrier. a second superconductor layer formed above and having a thickness that does not transmit light; and a power source connected between the first and second superconductor layers, the light entering the tunnel barrier from the substrate side. 1. A Josephson junction photodetecting element, which detects a change in current or voltage of the tunnel barrier using light emitted from the tunnel barrier. 2. The Josephson junction photodetecting element according to claim 1, wherein the first superconductor layer is made of NbN, and the second superconductor layer is made of Pb. Child. 3. The Josephson junction photodetecting element according to claim 1 or 2, wherein the tunnel barrier is an oxide film of the first superconductor layer.