CN115528128B - A single photon avalanche diode and its preparation method - Google Patents

Abstract

The present disclosure relates to a single photon avalanche diode and a method of making the same, the single photon avalanche diode comprising: a substrate layer, a device layer, and an aperiodic grating; the device layer is embedded in the substrate layer, and the aperiodic grating is arranged on the surface of the device layer which is not covered by the substrate layer; the aperiodic grating is used for diffracting and resonantly coupling incident light rays; the device layer is used for generating an electric signal by photoelectrically responding an incident light signal. Therefore, the single photon avalanche diode with the aperiodic grating is formed by arranging the substrate layer, the device layer and the aperiodic grating, light is coupled to the device layer based on diffraction and resonance coupling effects of the aperiodic grating on incident light, photon absorption efficiency is improved, light absorption effect is enhanced, and high-sensitivity photoelectric detection of the single photon avalanche diode is facilitated.

Description

A single photon avalanche diode and its preparation method

Technical Field

The present disclosure relates to the field of semiconductor optoelectronic technology, and in particular to a single-photon avalanche diode and a preparation method thereof.

Background technique

The silicon-based single photon avalanche diode (SPAD) is a single photon device that works in Geiger mode. Due to its single photon counting sensitivity and ultrafast time resolution, it can be used to detect and accurately measure photons in the visible spectrum (wavelength 400nm-600nm). However, due to the low absorption efficiency of silicon materials for photons with wavelengths in the near infrared (NIR) region (wavelength 800nm-1000nm), the performance of single photon avalanche diodes in the near infrared region still needs to be improved.

Among them, most of the existing technologies improve the photon absorption efficiency by increasing the depletion layer thickness, but an overly thick depletion layer requires a higher electric field strength, which makes the operating voltage higher, resulting in a larger device power. At the same time, an overly thick depletion layer will increase the jitter time of the device, resulting in a decrease in photon resolution. In addition, the existing technology also uses periodic metal gratings to improve device performance, but the traditional periodic metal grating structure is limited by its symmetry, so that some resonances cannot be coupled into the incident light, resulting in a weakened light absorption effect.

Summary of the invention

In order to solve the above technical problems or at least partially solve the above technical problems, the present disclosure provides a single-photon avalanche diode and a method for preparing the same.

The present disclosure provides a single-photon avalanche diode, comprising: a substrate layer, a device layer, and a non-periodic grating;

The device layer is embedded in the substrate layer, and the non-periodic grating is arranged on the surface of the device layer that is not covered by the substrate layer;

The non-periodic grating is used to cause incident light to undergo diffraction and resonance coupling;

The device layer is used for generating an electrical signal by performing a photoelectric response based on an incident light signal.

Optionally, the substrate layer comprises silicon layers and silicon dioxide layers arranged alternately to form a resonant cavity; or, the substrate layer is a silicon layer;

Wherein, the device layer is coated with a silicon layer.

Optionally, the non-periodic grating is a non-periodic metal grating.

Optionally, the non-periodic grating includes light shielding portions arranged at intervals, and a hollow portion is provided between two adjacent light shielding portions;

Wherein, in the extension direction perpendicular to the shading portion, the widths of at least two of the shading portions are unequal, and/or the widths of at least two of the hollow portions are unequal.

Optionally, the single photon avalanche diode further comprises a passivation layer;

The passivation layer is arranged between the non-periodic grating and the device layer, and is used for protecting the device layer.

The present disclosure also provides a method for preparing a single-photon avalanche diode, which is used to prepare any of the above-mentioned diodes; the method comprises:

providing a substrate layer;

Embedding a device layer on a surface of one side of the substrate layer;

A non-periodic grating is formed on the surface of the device layer not covered by the substrate layer.

Optionally, providing a substrate layer comprises:

providing a silicon layer;

Or the providing of the substrate layer comprises:

providing a silicon layer;

On one side of the silicon layer, silicon dioxide layers and silicon layers are alternately formed and end with the silicon layer.

Optionally, forming a non-periodic grating on a surface of the device layer not covered by the substrate layer comprises:

forming a light shielding layer on the surface of the device layer not covered by the substrate layer;

Performing patterning on the light shielding layer to retain the light shielding portion to form the non-periodic grating;

Wherein, the non-periodic grating includes the shading portions arranged at intervals, and a hollow portion is arranged between two adjacent shading portions; in the extension direction perpendicular to the shading portions, the widths of at least two of the shading portions are unequal, and/or the widths of at least two of the hollow portions are unequal.

Optionally, forming the light shielding layer includes:

Forming a preset area on the surface of the device layer not covered by the substrate layer by a photolithography process, and forming the light shielding layer in the preset area by electron beam evaporation or sputtering;

The patterning of the light shielding layer comprises:

Using photoresist as a mask, etching the light shielding layer to form the light shielding portion and the hollow portion;

The residual photoresist is washed away to obtain the non-periodic grating.

Optionally, forming a non-periodic grating on a surface of the device layer not covered by the substrate layer comprises:

A mask plate with a preset pattern is used to shield the surface of the device layer that is not covered by the substrate layer, so as to form the non-periodic grating by mask deposition.

Compared with the prior art, the technical solution provided by the embodiments of the present disclosure has the following advantages:

The single-photon avalanche diode provided by the embodiment of the present disclosure includes: a substrate layer, a device layer and a non-periodic grating; the device layer is embedded in the substrate layer, and the non-periodic grating is arranged on the surface of the device layer that is not covered by the substrate layer; the non-periodic grating is used to diffract and resonantly couple the incident light; the device layer is used to generate an electrical signal by photoelectric response based on the incident light signal. Thus, by setting the substrate layer, the device layer and the non-periodic grating, a single-photon avalanche diode with a non-periodic grating is formed, and based on the diffraction and resonant coupling of the incident light by the non-periodic grating, the light is coupled to the device layer to improve the photon absorption efficiency, enhance the light absorption effect, and facilitate the single-photon avalanche diode to achieve high-sensitivity photoelectric detection.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

FIG1 is a schematic diagram of a single photon avalanche diode structure with a periodic grating structure provided by the prior art;

FIG2 is a schematic diagram of another single photon avalanche diode structure with a periodic grating structure provided by the prior art;

FIG3 is a schematic diagram of a single photon avalanche diode structure with a periodic grating structure provided by the prior art;

FIG4 is a schematic diagram of the structure of a single photon avalanche diode provided in an embodiment of the present disclosure;

FIG5 is a schematic structural diagram of a single-photon avalanche diode with a normal-incident structure provided by an embodiment of the present disclosure;

FIG6 is a schematic structural diagram of another single-photon avalanche diode with a normal-incident structure provided by an embodiment of the present disclosure;

FIG7 is a schematic structural diagram of a single-photon avalanche diode with a back-incident structure provided by an embodiment of the present disclosure;

FIG8 is a schematic structural diagram of another single-photon avalanche diode with a back-incident structure provided by an embodiment of the present disclosure;

FIG9 is a schematic flow chart of a method for preparing a single-photon avalanche diode provided in an embodiment of the present disclosure.

Among them, the existing technology: 01, P-type silicon substrate; 02, N-type buried layer; 03, P-type heavily doped (P+) layer; 04, N-type heavily doped (N+) layer; 05, silicon nitride dielectric layer; 06, periodic grating; 07, incident light; 08, width; 09, period; 10, silicon dioxide layer;

This scheme: 110, substrate layer; 111, P-type silicon layer; 112, silicon dioxide layer; 120, device layer; 121, N-type buried layer; 122, P-type heavily doped (P+) layer; 123, N-type heavily doped (N+) layer; 130, non-periodic grating; 140, passivation layer; 150, incident light.

Detailed ways

In order to more clearly understand the above-mentioned objectives, features and advantages of the present disclosure, the scheme of the present disclosure will be further described below. It should be noted that the embodiments of the present disclosure and the features in the embodiments can be combined with each other without conflict.

In the following description, many specific details are set forth to facilitate a full understanding of the present disclosure, but the present disclosure may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present disclosure, rather than all of the embodiments.

First, the solution of the embodiment of the present disclosure proposed for improvement is briefly described in combination with the relevant background.

In the field of semiconductor optoelectronics, silicon-based single-photon avalanche diodes are often used to detect and accurately measure photons in the visible spectrum (wavelength 400nm-600nm) due to their single-photon counting sensitivity and ultrafast time resolution. However, due to the low absorption efficiency of silicon materials for photons with wavelengths in the near-infrared region, the performance of single-photon avalanche diodes in the near-infrared region still needs to be improved.

In conjunction with the above, it should be noted that the photon detection efficiency (PDE) is an important indicator for evaluating the performance of single-photon avalanche diodes. At present, the common method used to improve the photon detection efficiency is mostly to increase the photon absorption efficiency by increasing the thickness of the depletion layer, but an overly thick depletion layer requires a higher electric field strength. The higher the electric field strength, the higher the operating voltage, which ultimately leads to a higher device power. At the same time, an overly thick depletion layer will also increase the jitter time of the single-photon avalanche diode, resulting in a decrease in photon resolution.

For example, FIG1 is a schematic diagram of a single-photon avalanche diode structure with a periodic grating structure provided by the prior art. As can be seen from FIG1, FIG1 shows the overall structure of the device, the P-type silicon substrate 01 is the bottom substrate of the device, the N-type deep buried layer 02, the P-type heavily doped (P+) layer 03 and the N-type heavily doped (N+) layer 04 are all located inside the P-type silicon substrate 01 and form the structure shown in the figure, the periodic grating 06 is a metal grating and is located above the silicon nitride dielectric layer 05, and the incident light 07 is irradiated from the top of the device. Among them, when light is incident on the P-type heavily doped (P+) layer 03 and the N-type deep buried layer 02, the two will form a PN junction at the junction where they contact based on the photoelectric response, that is, a depletion region (also called an absorption region) is formed. It should be noted that 08 represents the width of the periodic grating 06, and 09 represents the period of the periodic grating 06. One period represented by 09 is the sum of a width value and a slit value. It is not difficult to understand that each width in the structure shown is equal, which means that each period in the figure is the same, thereby forming a periodic grating 06.

For example, Fig. 2 is a schematic diagram of another single-photon avalanche diode structure with a periodic grating structure provided by the prior art. Referring to Fig. 2, Fig. 2 shows a P-type silicon substrate 01 as the bottom substrate of the device, a silicon dioxide layer 10 is arranged on the top, and another P-type silicon substrate 01 is arranged on the surface where the silicon dioxide layer 10 is located, and an N-type buried layer 02, a P-type heavily doped (P+) layer 03 and an N-type heavily doped (N+) layer 04 are arranged in the top P-type silicon substrate 01, combined with a periodic grating 06 and a silicon nitride dielectric layer 05, to form the structure shown in the figure.

In combination with the above, the use of periodic grating structures in the prior art to increase light absorption is a way to improve the performance of existing single-photon avalanche diodes. This method mainly confines light to a very small area on the device surface by generating surface plasmons (surface plasmonpolariton, SPP), and then increases the coupling between the incident light of the device and the absorption layer (the area that absorbs photons) through grating diffraction to increase photon absorption. However, due to the symmetry limitations of traditional periodic gratings, some resonances cannot be coupled into the incident light, resulting in a weakened light absorption effect of the device, which is not conducive to high-sensitivity photoelectric detection. Therefore, the light absorption efficiency of traditional periodic gratings needs to be improved.

Exemplarily, FIG3 is a schematic diagram of another single-photon avalanche diode structure with a periodic grating structure provided by the prior art. Combined with the above, it can be seen from FIG3 that FIG3 shows the overall structure of the device, the P-type silicon substrate 01 is still the substrate at the bottom of the device, the N-type deep buried layer 02, the P-type heavily doped (P+) layer 03 and the N-type heavily doped (N+) layer 04 are all located inside the P-type silicon substrate 01, the periodic grating 06 is located above the silicon nitride dielectric layer 05, and the incident light 07 is incident from the back of the device to form the illustrated structure. The device in FIG3, on the basis of having a periodic grating structure, allows light to be incident from its back. Compared with the structure in FIG1 where the incident light is directly incident from the front of the device, although the structure shown in FIG3 reduces the shielding of the incident light, the light absorption effect still needs to be strengthened.

In summary, the prior art has the following defects:

First, the photon absorption efficiency is improved by increasing the thickness of the depletion layer, which results in higher device power and longer jitter time, ultimately leading to lower photon resolution.

Second: using periodic metal gratings to improve device performance, due to its symmetry limitations, some resonances cannot be coupled into the incident light, resulting in a weakened light absorption effect.

In response to at least one of the above defects, the disclosed embodiments propose a single-photon avalanche diode and a method for preparing the same, wherein the single-photon avalanche diode comprises: a substrate layer, a device layer, and a non-periodic grating; the device layer is embedded in the substrate layer, and the non-periodic grating is arranged on the surface of the device layer that is not covered by the substrate layer; the non-periodic grating is used to diffract and resonantly couple incident light; the device layer is used to generate an electrical signal by photoelectrically responding to the incident light signal. Thus, by providing a substrate layer, a device layer, and a non-periodic grating, a single-photon avalanche diode having a non-periodic grating is formed, and based on the diffraction and resonant coupling of the incident light by the non-periodic grating, light is coupled to the device layer, which improves the photon absorption efficiency and enhances the light absorption effect, which is beneficial for the single-photon avalanche diode to achieve high-sensitivity photoelectric detection.

In some embodiments, based on the incident direction of the incident light, the non-periodic grating is combined with different types of substrate layers so that the resonant coupling generated by the non-periodic grating can better couple the light into the depletion layer of the device, thereby effectively increasing the light absorption. At the same time, the formed device structure also avoids the problems of decreased time resolution and increased device power caused by the increase in the depletion layer thickness in the prior art.

The single photon avalanche diode and the method for preparing the same provided by the embodiments of the present disclosure are exemplarily described below in conjunction with the accompanying drawings.

In some embodiments, Figure 4 is a structural schematic diagram of a single-photon avalanche diode provided in an embodiment of the present disclosure. Referring to Figure 4, the single-photon avalanche diode includes: a substrate layer 110, a device layer 120 and a non-periodic grating 130; the device layer 120 is embedded in the substrate layer 110, and the non-periodic grating 130 is arranged on the surface of the device layer 120 not covered by the substrate layer 110; the non-periodic grating 130 is used to diffract and resonantly couple incident light; the device layer 120 is used to generate an electrical signal by performing photoelectric response based on the incident light signal.

The substrate layer 110 is a substrate for supporting the hierarchical structure disposed thereon. Exemplarily, the substrate layer 110 may be a substrate composed of a P-type silicon layer, an N-type silicon layer, or other types of silicon layers, which are not limited herein.

The device layer 120 is a structure for photoelectric response, and its specific composition structure is related to the type of silicon layer provided in the substrate layer 110, and the specific content is described later. In addition, the device layer 120 is provided in the substrate layer 110 in an embedded manner, and the device layer 120 is embedded in the exposed surface formed by the substrate layer 110, and is used to set the non-periodic grating 130 on the surface of the exposed surface.

Exemplarily, the material of the non-periodic grating 130 may be gold, silver, aluminum or other types of materials, which are not limited here. It should be noted that based on the preparation cost and the comprehensive effect of forming diffraction and resonance coupling, the non-periodic grating 130 is usually made of silver, which can be called a non-periodic metal grating, which has a better effect of forming diffraction and resonance coupling and a lower preparation cost.

It is not difficult to understand that the period of the non-periodic grating 130 is non-uniform. Combined with the structure of the periodic grating in the prior art described above, compared with the periodic gratings in Figures 1, 2 and 3, the width of the non-periodic grating 130 provided in the embodiment of the present disclosure is different, and correspondingly, its position may also be different, thereby forming a non-periodic grating structure. Specifically, when the width of the non-periodic grating 130 changes, its position remains unchanged; when the position of the non-periodic grating 130 changes, its width remains unchanged.

Among them, the working process of the single-photon avalanche diode can be specifically as follows: the incident light irradiates the single-photon avalanche diode, and the non-periodic grating arranged on the surface of the device will produce strong near-field diffraction, so that the device has a stronger resonant coupling effect, thereby increasing the coupling between the incident light and the absorption layer in the device layer. While enhancing the light absorption effect, it also improves the responsiveness of the electrical signal generated by the photoelectric response in the device layer based on the incident light signal.

The single-photon avalanche diode provided by the embodiment of the present disclosure includes: a substrate layer, a device layer and a non-periodic grating; the device layer is embedded in the substrate layer, and the non-periodic grating is arranged on the surface of the device layer that is not covered by the substrate layer; the non-periodic grating is used to diffract and resonantly couple the incident light; the device layer is used to generate an electrical signal by photoelectric response based on the incident light signal. Thus, by setting the substrate layer, the device layer and the non-periodic grating, a single-photon avalanche diode with a non-periodic grating is formed, and based on the diffraction and resonant coupling of the incident light by the non-periodic grating, the light is coupled to the device layer to improve the photon absorption efficiency, enhance the light absorption effect, and facilitate the single-photon avalanche diode to achieve high-sensitivity photoelectric detection.

In some embodiments, the substrate layer 110 includes silicon layers and silicon dioxide layers that are alternately arranged to form a resonant cavity; or, the substrate layer 110 is a silicon layer; wherein the device layer 120 is encapsulated with a silicon layer.

Among them, when the substrate layer 110 is an alternately arranged silicon layer and silicon dioxide layer, it forms a silicon on insulator (SOI) substrate, which can be referred to as an SOI substrate. Exemplarily, the bottom layer of the substrate layer 110 is a silicon layer, and a silicon dioxide layer is formed above the silicon layer, and then alternately arranged in this way. It should be noted that the layer that covers the device layer 120 is a silicon layer. Here, there is no specific limitation on the number of alternately arranged silicon layers and silicon dioxide layers. Exemplarily, at least two silicon layers can be arranged, and a silicon dioxide layer is arranged between the silicon layers, and the silicon layer above the silicon dioxide layer is used to cover the device layer 120. The device formed in this way corresponds to a structure of a device with normal incidence (i.e., the incident light is incident along the direction of the non-periodic grating pointing to the substrate layer).

When the substrate layer 110 is only a silicon layer, it forms a substrate covering the device layer 120. The device thus formed corresponds to a back-incident device structure (ie, the incident light is incident along the direction of the substrate layer pointing to the non-periodic grating).

Exemplarily, FIG5 is a schematic diagram of the structure of a single-photon avalanche diode of a normal-incident structure provided in an embodiment of the present disclosure. Referring to FIG5 , it is shown that the substrate layer 110 is an SOI substrate, and two layers of P-type silicon layers 111 and a layer of silicon dioxide layer 112 are provided. Correspondingly, the device layer 120 includes an N-type buried layer 121, a P+ layer 122, and an N+ layer 123, and the P+ layer 122 and the N+ layer 123 are both embedded in the N-type buried layer 121, and the N+ layer 123 is arranged on opposite sides of the P+ layer 122. It should be noted that the position of the non-periodic grating 130 introduces randomness, that is, the position of the grating is changed, and the incident light 150 is incident from the front of the device, thereby forming a normal-incident structure.

In combination with the previous embodiment, FIG6 is a schematic diagram of the structure of another single-photon avalanche diode of a normal-incident structure provided in an embodiment of the present disclosure. Referring to FIG6 , the figure shows that the substrate layer 110 is an SOI substrate, and two layers of P-type silicon layers 111 and a layer of silicon dioxide layer 112 are provided. Correspondingly, the device layer 120 includes an N-type buried layer 121, a P+ layer 122, and an N+ layer 123, and the P+ layer 122 and the N+ layer 123 are both embedded in the N-type buried layer 121, and the N+ layer 123 is arranged on opposite sides of the P+ layer 122. It should be noted that the width of the non-periodic grating 130 introduces randomness, that is, the width of the grating is changed, and the incident light 150 is still incident from the front of the device, thereby forming another normal-incident structure.

According to the embodiment, by applying the non-periodic grating 130 structure to the device surface, introducing the randomness of the non-periodic grating 130 structure (including changes in width and position), the generated hybrid plasma resonance coupling couples light to the depletion region (the region that absorbs photons, also called the absorption region), effectively improving the photon detection efficiency and sensitivity of the device. In addition, the breaking of the existing grating periodicity stimulates and enhances the dark mode of light absorption and the diffraction effect of the grating to a certain extent, improving the light absorption effect and photon absorption efficiency of the device.

At the same time, it should be noted that when the device is at normal incidence, the embodiment of the present disclosure adopts an SOI substrate to replace the traditional silicon substrate. For example, the SOI substrate is not limited to a single layer of P-type silicon layer 111 and silicon dioxide layer 112, and can be set according to actual application requirements so that the device can absorb more photons in the required wavelength range. In addition, the resonant cavity formed by the SOI substrate enables the device with the same depletion region thickness to obtain a higher photon detection efficiency without reducing the photon time resolution, thereby avoiding increasing the power consumption of the device. Specifically, light can be captured in a relatively narrow resonance range by using an optically guided mode, and the light that passes through the bottom of the silicon dioxide layer 112 is reflected back by setting the silicon dioxide layer 112, thereby increasing the light absorption in the absorption zone of the device. For example, adjusting the thickness of the silicon dioxide layer 112 can make the light act in the near-infrared band, that is, the light in the near-infrared band can be reflected and absorbed by the absorption zone.

In combination with the above, when the thickness of the silicon dioxide layer 112 is a preset value, it can achieve the reflective effect of the anti-reflection film, wherein the calculation formula of the anti-reflection film is:

Δ=kλ/n

Wherein, Δ is the thickness value, k is an integer, n is the refractive index, and λ is the wavelength of the incident light. For example, when n=λ/4, 3λ/4, 5λ/4 and other values, the reflective effect of the anti-reflection film can be achieved. It should be noted that since the calculation formula is related to the wavelength of the incident light, when the device needs to enhance the absorption of light in the near-infrared band, the formula can be calculated to obtain the corresponding thickness of the silicon dioxide layer 112. For example, when the wavelength of the incident light is 850 nm, the thickness of the silicon dioxide layer 112 can be obtained as 212 nm according to the calculation formula.

Exemplarily, FIG7 is a schematic diagram of the structure of a single-photon avalanche diode of a back-incident structure provided by an embodiment of the present disclosure. Referring to FIG7, the figure shows that the substrate layer 110 is a P-type silicon layer 111, and correspondingly, the device layer 120 includes an N-type buried layer 121, a P+ layer 122, and an N+ layer 123. The P+ layer 122 and the N+ layer 123 are both embedded in the N-type buried layer 121, and the N+ layer 123 is arranged on opposite sides of the P+ layer 122. It should be noted that the position of the non-periodic grating 130 introduces randomness, that is, the position of the grating is changed, and the incident light 150 is incident from the back of the device, thereby forming a back-incident structure.

In combination with the previous embodiment, illustratively, FIG8 is a schematic diagram of the structure of another back-incident single-photon avalanche diode provided in an embodiment of the present disclosure. Referring to FIG8 , the substrate layer 110 is shown as a P-type silicon layer 111, and correspondingly, the device layer 120 includes an N-type buried layer 121, a P+ layer 122, and an N+ layer 123. The P+ layer 122 and the N+ layer 123 are both embedded in the N-type buried layer 121, and the N+ layer 123 is arranged on opposite sides of the P+ layer 122. It should be noted that the width of the non-periodic grating 130 introduces randomness, that is, the width of the grating is changed, and the incident light 150 is incident from the back of the device, thereby forming another back-incident structure.

The back-incident structure adopted in the embodiment of the present disclosure overcomes the defect of placing metal wiring and the like on the surface of the device in the traditional front side illuminated (FSI) process, which blocks part of the incident light and leads to reduced photon absorption efficiency; and on the basis of the back-incident structure, a non-periodic grating is further combined, and the non-periodic grating 130 is combined with the back side illuminated (BSI) process, and the substrate layer 110 is thinned by the BSI process so that the incident light is incident from the back side of the device. On the one hand, the BSI process reduces the blocking of the incident light 150 and improves the filling factor of the photosensitive area (corresponding to the P+ layer); on the other hand, the reflection of the non-periodic grating 130 is used to confine the light to the depletion region, thereby enhancing light absorption, thereby achieving the effect of improving the photon absorption efficiency.

In addition, referring to Figures 5 to 8, it can be seen that when light is incident, the N-type buried layer 121 and the P+ layer 122 will form a PN junction at the junction where they contact based on the photoelectric response, that is, a depletion region (also called an absorption region) is formed. In the actual working process, the P+ layer 122 formed by doping the boron element (also a P-type semiconductor material) in the silicon layer and the N-type buried layer 121 formed by doping the phosphorus element (also an N-type semiconductor material) form a PN junction (depletion region) at the position where they contact each other to generate a photoelectric response. Based on this, it is also necessary to prepare corresponding electrodes on the P+ layer 122 and the N+ layer 123 of the device. Correspondingly, the P+ layer 122 can be used as the lead-out layer of the anode, and the N+ layer 123 can be used as the lead-out layer of the cathode.

In some embodiments, in conjunction with the above, the non-periodic grating 130 is a non-periodic metal grating.

The size of the non-periodic metal grating is nanometer-scale. It should be noted that when the non-periodic metal grating is a back-incident structure, its metal material can also play a reflective effect, and the metal material of the non-periodic metal grating is not limited here.

In some embodiments, referring to Figures 5-8, the non-periodic grating 130 includes shading portions that are spaced apart, and a hollow portion is provided between two adjacent shading portions; wherein, in an extension direction perpendicular to the shading portions, the widths of at least two shading portions are not equal, and/or the widths of at least two hollow portions are not equal.

The light shielding parts and hollow parts in the non-periodic grating 130 are arranged alternately, that is, each light shielding part is adjacent to at least one hollow part. It is not difficult to understand that the width and position of the non-periodic grating 130 are variable, and when the width changes, the position remains unchanged, and the widths of at least two light shielding parts in the non-periodic grating 130 are not equal; when the position changes, the width remains unchanged, and the widths of at least two hollow parts in the non-periodic grating 130 are not equal.

In combination with the above, and with reference to FIG. 1, FIG. 2 and FIG. 3, in the existing periodic grating structure, exemplarily, when the period of the periodic grating is 250nm and the width is 200nm, the duty cycle of the formed grating structure is 80%; it should be noted that in the actual working process, according to the law obtained from a large number of simulation calculation results, it can be known that the duty cycle in the periodic grating structure is usually ≥ 80%. Correspondingly, when the position of the non-periodic grating 130 changes, the upper limit of the change of the non-periodic grating 130 in the horizontal direction can be set to 50nm, thereby, the change of the position of the non-periodic grating 130 can achieve the maximum change without causing the overlap of the grating structure in the non-periodic grating 130. In addition, when the width of the non-periodic grating 130 changes, its width can increase or decrease by 10nm, 15nm or other values, and can also be other values in other embodiments, which are not limited here.

In some embodiments, referring to FIGS. 5 to 8 , a passivation layer 140 is further included; the passivation layer 140 is disposed between the non-periodic grating 130 and the device layer 120 to protect the device layer 120 .

Among them, the passivation layer 140 is a structure that prevents the device from being affected by external factors and plays a role in protecting the device layer 120. It should be noted that the passivation layer 140 can be a film layer of an insulating material. Exemplarily, the passivation layer 140 can be a silicon nitride layer with a thickness of 15nm. In other embodiments, it can also be a material layer of other types and thickness values, which is not limited here.

The single-photon avalanche diode provided by the embodiment of the present disclosure includes: a substrate layer, a device layer and a non-periodic grating; the device layer is embedded in the substrate layer, and the non-periodic grating is arranged on the surface of the device layer that is not covered by the substrate layer; the non-periodic grating is used to diffract and resonantly couple the incident light; the device layer is used to generate an electrical signal by photoelectric response based on the incident light signal. Therefore, based on the diffraction and resonant coupling of the incident light by the non-periodic grating, coupling the light to the device layer improves the photon absorption efficiency, enhances the light absorption effect, and facilitates the single-photon avalanche diode to achieve high-sensitivity photoelectric detection. That is, by providing the substrate layer, the device layer and the non-periodic grating, a single-photon avalanche diode with high photon detection efficiency and responsiveness is formed.

On the basis of the above-mentioned embodiments, the embodiments of the present disclosure further provide a method for preparing a single-photon avalanche diode, which can be used to prepare any of the diodes provided in the above-mentioned embodiments and has corresponding beneficial effects.

In some embodiments, FIG9 is a flow chart of a method for preparing a single photon avalanche diode provided by an embodiment of the present disclosure. Referring to FIG9 , the method includes:

S21. Provide a substrate layer.

In combination with the above, when the substrate layer is an SOI substrate formed by alternating P-type silicon layers and silicon dioxide layers, and a single P-type silicon layer, an N-type deep buried layer, a P+ layer, and an N+ layer can be formed therein. Based on this, it can be seen that when the substrate layer is an SOI substrate formed by alternating N-type silicon layers and silicon dioxide layers, and a single N-type silicon layer, a P-type deep buried layer, an N+ layer, and a P+ layer can be formed therein, and the type of silicon layer is not limited here.

In addition, in the specific steps of preparing a separate P-type silicon layer as a substrate layer, illustratively, a P-crystal-oriented silicon wafer can be first used as the P-type silicon layer and subjected to conventional cleaning, and then an N-type deep buried layer region is defined on the P-type silicon layer by photolithography, and an N-type deep buried layer (also referred to as a deep N-well) is formed by doping with an N-type semiconductor, and P-type heavy doping is performed in the N-type deep buried layer to form a P+ layer (also referred to as a P-well) as a photosensitive region of the device and also as the anode of the device, and N-type heavy doping is performed in the N-type deep buried layer to form an N+ layer (also referred to as an N-well) as the cathode of the device.

S22, forming a device layer by embedding on one side surface of the substrate layer.

The device layer may include an N-type deep buried layer, a P+ layer and an N+ layer, wherein the P+ layer and the N+ layer are embedded in the N-type deep buried layer, and the N+ layer is disposed on two opposite sides of the P+ layer; or the device layer may include a P-type deep buried layer, an N+ layer and a P+ layer, wherein the N+ layer and the P+ layer are embedded in the P-type deep buried layer, and the P+ layer is disposed on two opposite sides of the N+ layer. Thus, the N-type deep buried layer and the P+ layer form a PN junction, or the P-type deep buried layer and the N+ layer form a PN junction to absorb photons.

S23. Form a non-periodic grating on the surface of the device layer that is not covered by the substrate layer.

Among them, the non-periodic grating is covered on the surface of the single-photon avalanche diode to trigger the high absorption of the material, and when it is a non-periodic grating of metal material, its size is usually nanometer-level. The introduction of non-periodicity, that is, randomness, can further enhance the diffraction effect of the grating and increase the light absorption efficiency.

The method for preparing a single-photon avalanche diode provided by the embodiment of the present disclosure is to set a substrate layer, then embed a device layer on one side surface of the substrate layer, and finally form a non-periodic grating on the surface of the device layer not covered by the substrate layer. Thus, improvements are made on the basis of the periodic grating structure to form a single-photon avalanche diode with a non-periodic grating. Based on the diffraction and resonant coupling of the incident light by the non-periodic grating, the light is coupled to the depletion region in the device layer for absorption, thereby improving the photon absorption efficiency and enhancing the light absorption effect, avoiding the problems of decreased time resolution and increased device power due to the increase in the thickness of the depletion layer in the prior art, and facilitating the single-photon avalanche diode to achieve high-sensitivity photoelectric detection.

In some embodiments, providing a substrate layer includes: providing a silicon layer; or providing a substrate layer includes: providing a silicon layer; alternately forming silicon dioxide layers and silicon layers on one side of the silicon layer and ending with the silicon layer.

In combination with the above, it can be known that the substrate layer can be only a silicon layer, or an SOI substrate. When it is set as an SOI substrate, the substrate at the bottom of the device is a silicon layer, and then silicon dioxide layers and silicon layers are alternately arranged, and the final layer covering the device layer is a silicon layer. The number of layers set is not limited and will not be repeated here.

For example, during the actual operation of the device, when light is incident on an SOI substrate consisting of two silicon layers and one silicon dioxide layer, part of the light passes through the first silicon layer covering the reaction layer, and then enters the bottom of the silicon dioxide layer and is reflected to the depletion region to the maximum extent, and the remaining very small part of the light enters the bottom silicon layer. Therefore, in order to ensure a better reflection effect and reduce the transmittance of the incident light, that is, to make the resonant coupling effect of the silicon layer and the silicon dioxide layer to form a resonant cavity better, the required number of layers of SOI substrate can be set according to actual needs.

In some embodiments, a non-periodic grating is formed on the surface of the device layer not covered by the substrate layer, including: forming a shading layer on the surface of the device layer not covered by the substrate layer; patterning the shading layer to retain the shading portion to form a non-periodic grating; wherein the non-periodic grating includes shading portions arranged at intervals, and a hollow portion is arranged between two adjacent shading portions; in an extension direction perpendicular to the shading portions, the widths of at least two shading portions are unequal, and/or the widths of at least two hollow portions are unequal.

In some embodiments, forming a light-shielding layer includes: forming a preset area on the surface of the device layer not covered by the substrate layer based on a photolithography process, and forming a light-shielding layer in the preset area by electron beam evaporation or sputtering; patterning the light-shielding layer, including: etching the light-shielding layer using a photoresist as a mask to form a light-shielding portion and a hollow portion; and washing away residual photoresist to obtain a non-periodic grating.

Specifically, before preparing the non-periodic grating, a layer of silicon nitride film can be grown by plasma enhanced chemical vapor deposition (PECVD), and then the silicon nitride film outside the photosensitive area (corresponding to the area outside the P+ layer) can be removed by photolithography, etching and other processes. After that, the position of the metal grating can be defined in the photosensitive area by photolithography, and then the metal is evaporated by electron beam evaporation or sputtering, and the metal is etched using the photoresist as a mask, and finally the residual photoresist is washed off to obtain the non-periodic metal grating. The process steps for preparing the non-periodic metal grating are not limited here.

In some embodiments, forming a non-periodic grating on a surface of the device layer not covered by the substrate layer includes: using a mask plate with a preset pattern to block the surface of the device layer not covered by the substrate layer to form the non-periodic grating by mask deposition.

It should be noted that, in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

The above description is only a specific embodiment of the present disclosure, so that those skilled in the art can understand or implement the present disclosure. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present disclosure. Therefore, the present disclosure will not be limited to the embodiments described herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims (9)

1. A single photon avalanche diode, comprising: a substrate layer, a device layer, and an aperiodic metal grating;

the device layer is embedded in the substrate layer, and the aperiodic metal grating is arranged on the surface of the device layer which is not covered by the substrate layer;

the aperiodic metal grating is used for enabling incident light to be diffracted and resonantly coupled;

the device layer is used for generating an electric signal based on photoelectric response of an incident light signal;

the non-periodic metal grating is of a back incidence structure and is also used for reflecting incident light rays to the device layer.

2. The single photon avalanche diode according to claim 1, wherein the substrate layer is a silicon layer.

3. The single photon avalanche diode according to claim 1 or 2, wherein the aperiodic metal gratings comprise light shielding parts arranged at intervals, and a hollowed-out part is arranged between two adjacent light shielding parts;

the width of at least two shading parts is unequal in the extending direction perpendicular to the shading parts, and/or the width of at least two hollowed-out parts is unequal.

4. The single photon avalanche diode according to claim 3, further comprising a passivation layer;

the passivation layer is arranged between the aperiodic metal grating and the device layer and is used for protecting the device layer.

5. A method for the preparation of a single photon avalanche diode according to any of claims 1-4; the method comprises the following steps:

providing a substrate layer;

forming a device layer in a embedded manner on one side surface of the substrate layer;

forming an aperiodic metal grating on the surface of the device layer, which is not covered by the substrate layer;

the non-periodic metal grating is of a back incidence structure and is also used for reflecting incident light rays to the device layer.

6. The method of claim 5, wherein the providing a substrate layer comprises:

a silicon layer is provided.

7. The method of claim 5 or 6, wherein forming the non-periodic metal grating on the surface of the device layer not covered by the substrate layer comprises:

forming a shading layer on the surface of the device layer, which is not covered by the substrate layer;

patterning the light shielding layer, and reserving a light shielding part to form the aperiodic metal grating;

the non-periodic metal grating comprises light shielding parts which are arranged at intervals, and hollowed-out parts are arranged between two adjacent light shielding parts; in the extending direction perpendicular to the light shielding parts, the widths of at least two light shielding parts are unequal, and/or the widths of at least two hollowed-out parts are unequal.

8. The method of claim 7, wherein forming the light shielding layer comprises:

forming a preset area on the surface of the device layer, which is not covered by the substrate layer, based on a photoetching process, and forming the shading layer in the preset area by utilizing an electron beam evaporation or sputtering mode;

the patterning the light shielding layer comprises the following steps:

etching the light shielding layer by taking photoresist as a mask to form the light shielding part and the hollowed-out part;

and washing off residual photoresist to obtain the aperiodic metal grating.

9. The method of claim 5 or 6, wherein forming the non-periodic metal grating on the surface of the device layer not covered by the substrate layer comprises:

and shielding the surface of the device layer, which is not covered by the substrate layer, by using a mask plate with a preset pattern, and forming the aperiodic metal grating through mask deposition.