CROSS REFERENCE TO RELATED APPLICATION

This is a Sect. 371 National Stage of PCT International Application No. PCT/CN2018/082551, filed on 10 Apr. 2018, which claims priority of a Chinese Patent Application No. 201711101757X filed on 10 Nov. 2017, the contents of both applications hereby being incorporated by reference in their entireties for all purposes.

BACKGROUND

Field of Disclosure

The present disclosure relates to the technical field of optical detectors, in particular, to a single photon detector with a modified superconducting nanowire and a method for making the same.

Description of Related Arts

Superconducting Nanowire Single Photon Detector (SNSPD) is a highly sensitive photon detector using superconducting nanowires for photon detection. Compared with traditional semiconductor photon detectors, the SNSPDs have high detection efficiency, low dark count rate and high timing resolution. At present, SNSPDs have been widely used in the applications of quantum information, single-photon source characterization, integrated circuit defect detection, high-speed optical communication and molecular fluorescence detection.

The current SNSPDs are mainly fabricated with 3-6 nm high-quality niobium nitride (NbN) thin film. A typical width of the nanowire is about 100 nm. The SNSPDs generally operate at a temperature of 1.4-4.2K, and are biased at a current slightly below the critical current. A single photon has high enough energy to break up hundreds of Cooper pairs in the superconducting nanowire to form hot spots. These hot spots will result in transient resistance states causing the current to drop, creating a voltage pulse across a load resistor. The detection of incident photons is realized by the reading out of this voltage pulse, with a photon counter.

In practical applications, the most important performance metrics of the single photon detector is the detection efficiency η (the probability that an incident photon results in an electrical output pulse). In reality, η is less than 100%, and is closely related to the wavelength of the incident photon. In the actual photon counting measurements, due to absorption, reflection or transmission in the experimental environment, the photon will be lost before reaching the detector. This probability that an incident photon is finally received by a detector is defined as the optical coupling efficiency (ηcoupling). The material, geometric structure, and optical cavity structure of the detector determine the optical absorption efficiency (ηabsorption) the detector. Finally, when the photons are absorbed by the detector, there is an intrinsic detection efficiency (ηregistering) is the probability that an SNSPD generates a response pulse after a photon is absorbed. Considering the above factors, the detection efficiency (ηside) of the entire system can be expressed as:
ηside=ηcoupling×ηabsorption×ηregistering

At present, many studies are devoted to improving the detection efficiency of SNSPD. For example, the nanowire is made into a meander wire structure to enhance the optical coupling efficiency. The meander SNSPD is implanted into an optical cavity structure to improve the optical absorption efficiency, or the width of the nanowire is reduced to increase the intrinsic detection efficiency. However, these studies are all optimizing the SNSPD geometry structure, and there are few reports on the methods that can directly modify the superconducting properties of the material to improve the intrinsic detection efficiency.

For current SNSPD devices, critical temperature (Tc) of the nanowire is thickness dependent. Tcdrops fast when the thickness is less than 10 nm. It is believed that, low Tcnanowire or its thin film can help to improve the intrinsic detection efficiency to a certain extent, due to a larger hotspot generation in the nanowire. However, the method to modify the nanowire's properties by reducing the film thickness will result in a decrease in the optical absorption of the nanowires, as well as a significant reduction in the Tc. The excessive reduction of Tcwill greatly limit the operating temperature range of the SNSPD devices.

Therefore, it is necessary to provide a method for making a superconducting nanowire single photon detector to improve the intrinsic detection efficiency without sacrificing the optical absorption. Such a method should maintain the optical absorption, and the uniformity of the superconducting thin film. It is believed that, a high uniform superconducting thin film usually demonstrates a small superconducting transition temperature width. As the Tcof the material is adjusted properly, the detection performance of the device would be improved, with a limited effect on the operating temperature.

SUMMARY

The present disclosure provides a single photon detector with a modified superconducting nanowire and a method for making the same, to solve the problem that reducing the Tcof the material will cause the light absorption and material uniformity of the device to deteriorate, and the superconducting transition temperature width to become widened.

The present disclosure provides a method for making a single photon detector with a modified superconducting nanowire. The method includes: preparing a substrate; modifying a superconducting nanowire with stress on a surface of the substrate; fabricating a superconducting nanowire single photon detector based on the superconducting nanowire with stress.

As a preferred solution of the present disclosure, during the preparation of the superconducting nanowire with stress on the surface of the substrate, the stress is introduced into the superconducting nanowire based on ion implantation.

As a preferred solution of the present disclosure, the preparing of the superconducting nanowire with stress on the surface of the substrate includes: preparing a superconducting thin film layer on the surface of the substrate; implanting ions from a surface of the superconducting thin film layer to introduce stress into the superconducting thin film layer; performing photolithography and reactive ion etching on the obtained superconducting thin film layer to obtain the superconducting nanowire structure with stress.

As a preferred solution of the present disclosure, the preparing of the superconducting nanowire with stress on the surface of the substrate includes: preparing a superconducting thin film layer on the surface of the substrate; performing photolithography and reactive ion etching on the superconducting thin film layer to obtain a superconducting nanowire structure; implanting ions on a surface of the superconducting nanowire structure to introduce stress into the superconducting nanowire structure, to obtain the superconducting nanowire with stress.

As a preferred solution of the present disclosure, the ions in the ion implantation process are inert gas ions.

As a preferred solution of the present disclosure, in the ion implantation process, an implantation dose ranges from 1×1014to 1×1016cm−2, an implantation energy ranges from 10 to 100 keV, and an implantation temperature ranges from 0 to 600° C.

As a preferred solution of the present disclosure, an ion implantation area in the ion implantation process covers a surface of a stress layer to be introduced and/or ions in the ion implantation process penetrate into the stress layer to be introduced.

As a preferred solution of the present disclosure, a material of the superconducting nanowire is NbN, Nb, TaN, TiN, NbTiN or WSi.

As a preferred solution of the present disclosure, between the preparing of the substrate and the preparing of the superconducting nanowire with stress on the surface of the substrate, the method further includes: preparing an optical reflective film on the surface of the substrate, the optical reflective film is prepared between the substrate and the superconducting nanowire.

The present disclosure further provides a superconducting nanowire single photon detector, which includes: a substrate; and a superconducting nanowire located on a surface of the substrate, wherein the superconducting nanowire contains stress.

As a preferred solution of the present disclosure, the superconducting nanowire single photon detector further includes an optical reflective film located between the substrate and the superconducting nanowire.

As a preferred solution of the present disclosure, the optical reflective film includes alternately stacked SiO2thin film layers and Si thin film layers, alternately stacked SiO2thin film layers and TiO2thin film layers, or alternately stacked SiO2thin film layers and Ta2O5thin film layers.

As a preferred solution of the present disclosure, a material of the superconducting nanowire is NbN, Nb, TaN, TiN, NbTiN or WSi.

As a preferred solution of the present disclosure, the superconducting nanowire includes a plurality of linear portions arranged in parallel and spaced apart, and a connecting portion connecting the plurality of linear portions sequentially end to end.

As described above, the single photon detector with a modified superconducting nanowire and the method for making the same have the following beneficial effects:

1) In the single photon detector with the modified superconducting nanowire provided by the present disclosure, while the thickness of the device material layer film is guaranteed, the Tcof the device material is reduced, while the uniformity of the device material and small superconducting transition width are well preserved.

2) The single photon detector with the modified superconducting nanowire provided by the present disclosure can reduce the Tcof the device material, thereby improving the intrinsic detection efficiency of the device.

