A 4H-SiC avalanche photodetector and a method for preparing the same

Abstract

The present invention provides a 4H-SiC avalanche photodetector and a preparation method thereof, and relates to the technical field of semiconductor ultraviolet avalanche photodetectors. The epitaxial mesa structure in the 4H-SiC avalanche photodetector uses the perpendicular midline of the widest part of the epitaxial mesa structure in the <#imgabs0#> crystal direction as the interface, and the epitaxial mesa structures located on both sides of the interface have unequal average widths in the <#imgabs1#> crystal direction, forming an epitaxial mesa structure with non-centrosymmetry in the <#imgabs2#> crystal direction, so as to reduce the carrier shielding area, further increase the effective avalanche area of ​​the device, and improve the single-photon detection performance of the device.

Description

Technical Field

[0001] The present application relates to the technical field of semiconductor ultraviolet avalanche photodetectors, and in particular to a 4H-SiC avalanche photodetector and a preparation method thereof. Background Art

[0002] As the core component in the field of ultraviolet detection technology, ultraviolet photodetectors are widely used in military and civilian fields. In the field of weak ultraviolet light detection, detection devices with extremely high sensitivity are needed. Avalanche photodiodes based on wide bandgap semiconductor materials have the advantages of high gain, low power consumption, small size, and easy integration. They are one of the main components for detecting weak ultraviolet light and even single photons.

[0003] At present, ultraviolet photodetectors based on semiconductor materials mostly use third-generation semiconductor materials represented by silicon carbide and gallium nitride. Compared with the problems of wide response band, low quantum efficiency in ultraviolet band, and the need for additional filters of silicon-based photodetectors, third-generation semiconductor materials have the characteristics of high thermal conductivity, high chemical stability, wide band gap, and high ultraviolet visible suppression ratio, making them ideal materials for preparing ultraviolet photodetectors. As a representative material of the third-generation semiconductor, 4H-SiC has mature growth technology and few material defects, making it particularly suitable for preparing high-performance ultraviolet avalanche photodetectors.

[0004] In the past decade, 4H-SiC-based ultraviolet avalanche photodetectors have made great progress, but compared with silicon-based and InGaAs avalanche photodetectors, there is still a gap in single-photon detection. In addition to the limitations of the corresponding semiconductor processing technology and epitaxial growth quality, the uneven avalanche breakdown of the device is one of the main reasons that limit the further improvement of the single-photon detection performance of 4H-SiC ultraviolet avalanche photodetectors.

[0005] At present, in order to suppress the formation of material defects, 4H-SiC epitaxial growth is mostly carried out on a substrate with a 4° deviation from the (0001) crystal plane. Due to the anisotropy of the 4H-SiC crystal, a large number of carriers generated by avalanche will deviate to < >Directional aggregation causes local shielding of the device electric field, resulting in uneven avalanche gain on the device's photosensitive surface, limiting the device's single-photon detection performance.

[0006] Therefore, it is urgent to develop a new table structure to improve the avalanche uniformity of the photosensitive surface of the 4H-SiC avalanche photodetector, increase the effective avalanche area of ​​the detector, and improve its single-photon detection performance. Summary of the invention

[0007] In view of the above problems, the present application provides a 4H-SiC avalanche photodetector and a preparation method thereof, which is used to improve the existing 4H-SiC avalanche photodetector, which has uneven avalanche, small effective avalanche area, and low single-photon detection efficiency. The specific scheme is as follows:

[0008] In a first aspect, the present application provides a 4H-SiC avalanche photodetector, the 4H-SiC avalanche photodetector comprising:

[0009] substrate;

[0010] An epitaxial layer structure located on one side of the substrate; a portion of the epitaxial layer structure away from one side of the substrate is used as an epitaxial mesa structure;

[0011] Among them, the epitaxial mesa structure is the epitaxial mesa structure in < >The widest mid-perpendicular line in the crystal direction is the interface, and the epitaxial mesa structures on both sides of the interface are < >The average width in the crystal direction is not equal.

[0012] In a possible implementation, the substrate is a conductive substrate that is beveled at 4° from the (0001) crystal plane.

[0013] In a possible implementation, the size of the epitaxial mesa structure in the first direction gradually decreases;

[0014] The first direction is perpendicular to the plane where the substrate is located, and points from the substrate to the epitaxial layer structure.

[0015] In a possible implementation, the epitaxial layer structure includes:

[0016] A bottom electrode contact layer, a working layer, a top electrode contact layer and a top electrode are sequentially stacked on the substrate; the working layer, the top electrode contact layer and the top electrode form a whole that exposes the edge area of ​​the bottom electrode contact layer; the areas of the top electrodes on both sides of the interface are not equal;

[0017] The bottom electrode contact layer and the top electrode contact layer have different doping types. When one layer is P-type doped, the other layer is N-type doped.

[0018] In one possible implementation, the 4H-SiC avalanche photodetector further includes: a bottom electrode;

[0019] The bottom electrode is located at an edge region of the bottom electrode contact layer, or the bottom electrode is located at a side of the substrate away from the epitaxial layer structure.

[0020] In a possible implementation, when the bottom electrode contact layer is P-type doped and the top electrode contact layer is N-type doped, the [ ] The epitaxial mesa structure on one side of the crystal direction is [ ] The average width on the crystal direction is smaller than the average width on the other side, and the [ ]The area of ​​the top electrode on one side of the crystal direction is larger than that on the other side.

[0021] In a possible implementation, when the bottom electrode contact layer is N-type doped and the top electrode contact layer is P-type doped, the [ ] The epitaxial mesa structure on one side of the crystal direction is [ ] has an average width on one side of the crystal direction that is greater than the average width on the other side, and the [ ]The area of ​​the top electrode on one side of the crystal direction is smaller than that on the other side.

[0022] In a possible implementation, a lower edge position of the epitaxial mesa structure is lower than a contact surface between the bottom electrode contact layer and the working layer.

[0023] In a possible implementation, the working layer includes N sub-working layers stacked in sequence, where N≥2 and N is a positive integer.

[0024] A second aspect of the present application provides a method for preparing a 4H-SiC avalanche photodetector, the method for preparing the 4H-SiC avalanche photodetector comprising:

[0025] providing a substrate;

[0026] forming an epitaxial layer structure on one side of the substrate;

[0027] The epitaxial layer structure is processed so that a portion of the epitaxial layer structure away from the substrate side is used as an epitaxial mesa structure; wherein the epitaxial mesa structure is >The widest mid-perpendicular line in the crystal direction is the interface, and the epitaxial mesa structures on both sides of the interface are < >The average width in the crystal direction is not equal.

[0028] By means of the above technical solution, the present application provides a 4H-SiC avalanche photodetector and a method for preparing the same. The epitaxial mesa structure in the 4H-SiC avalanche photodetector is formed by the epitaxial mesa structure in the >The widest mid-perpendicular line in the crystal direction is the interface, and the epitaxial mesa structures on both sides of the interface are < >The average width of the crystal direction is not equal, forming a < >The epitaxial table structure has a non-centrosymmetric structure in the crystal direction to reduce the carrier shielding area, further increase the effective avalanche area of ​​the device, and improve the single-photon detection performance of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The above and other features, advantages and aspects of the embodiments of the present disclosure will become more apparent with reference to the following detailed description in conjunction with the accompanying drawings. Throughout the accompanying drawings, the same or similar reference numerals represent the same or similar elements. It should be understood that the drawings are schematic and the originals and elements are not necessarily drawn to scale.

[0030] Figure 1 One of the structural schematic diagrams of a 4H-SiC avalanche photodetector provided in an embodiment of the present invention;

[0031] Figure 2 A second structural schematic diagram of a 4H-SiC avalanche photodetector provided in an embodiment of the present invention;

[0032] Figure 3 A third structural schematic diagram of a 4H-SiC avalanche photodetector provided in an embodiment of the present invention;

[0033] Figure 4 A fourth structural schematic diagram of a 4H-SiC avalanche photodetector provided in an embodiment of the present invention;

[0034] Figure 5 One of the schematic diagrams of a surface of an epitaxial mesa structure facing away from a substrate provided in an embodiment of the present invention;

[0035] Figure 6 A second schematic diagram of a surface of an epitaxial mesa structure facing away from a substrate provided in an embodiment of the present invention;

[0036] Figure 7 A third schematic diagram of a surface of an epitaxial mesa structure facing away from a substrate provided in an embodiment of the present invention;

[0037] Figure 8 A fourth schematic diagram of a surface of an epitaxial mesa structure facing away from a substrate provided in an embodiment of the present invention;

[0038] Fig. 9 A fifth schematic diagram of a surface of an epitaxial mesa structure facing away from a substrate provided in an embodiment of the present invention;

[0039] Fig.10 A sixth schematic diagram of a surface of an epitaxial mesa structure facing away from a substrate provided in an embodiment of the present invention;

[0040] Fig.11 A schematic diagram of characterizing a water drop-shaped non-centrosymmetric epitaxial table structure 4H-SiC avalanche photodetector using a two-dimensional photon counting scanning technology provided by an embodiment of the present invention;

[0041] Fig.12A schematic diagram of characterizing a conventional circular epitaxial mesa structure 4H-SiC avalanche photodetector using a two-dimensional photon counting scanning technique provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0042] The embodiments of the present application are described below in conjunction with the drawings in the embodiments of the present application. The terms used in the implementation mode of the present application are only used to explain the specific embodiments of the present application, and are not intended to limit the present application. It is known to those skilled in the art that with the development of technology and the emergence of new scenarios, the technical solutions provided in the embodiments of the present application are also applicable to similar technical problems.

[0043] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0044] It should be noted that the directional words appearing in the present invention are based on the relative position relationship shown in the drawings and cannot be used as an absolute limitation to the present application.

[0045] refer to Figure 1 , Figure 1 One of the structural schematic diagrams of a 4H-SiC avalanche photodetector provided in an embodiment of the present invention; Figure 2 , Figure 2 A second structural diagram of a 4H-SiC avalanche photodetector provided by an embodiment of the present invention; Figure 3 , Figure 3 A third structural diagram of a 4H-SiC avalanche photodetector provided by an embodiment of the present invention; Figure 4 , Figure 4 The fourth structural diagram of a 4H-SiC avalanche photodetector provided by an embodiment of the present invention. A 4H-SiC avalanche photodetector provided by an embodiment of the present invention comprises:

[0046] Substrate 10. Figure 1 As shown, the substrate 10 may be a conductive substrate that is 4° off-cut from the (0001) crystal plane and polished. Figure 1 and Figure 2 In the expression .exist Figure 1 The middle figure shows a 4H-SiC substrate on which a 4H-SiC epitaxial layer is epitaxially grown.

[0047] The epitaxial layer structure is located on one side of the substrate 10; the part of the epitaxial layer structure away from the side of the substrate 10 is used as an epitaxial mesa structure.

[0048] Among them, the epitaxial mesa structure is the epitaxial mesa structure in < >The widest part in the crystal direction (i.e. Figure 2 X max ) is the interface, and the epitaxial mesa structures on both sides of the interface are < >The average width in the crystal direction is not equal.

[0049] Specifically, in the embodiments of the present invention, Figure 2-Figure 4 As shown, the epitaxial layer structure includes: a bottom electrode contact layer 11, a working layer 12, a top electrode contact layer 13 and a top electrode 15 which are sequentially stacked on the substrate 10; the working layer 12, the top electrode contact layer 13 and the top electrode 15 form a whole which exposes the edge area of ​​the bottom electrode contact layer 11; the areas of the top electrodes 15 located on both sides of the interface are not equal. The bottom electrode contact layer 11 and the top electrode contact layer 13 have different doping types, and when one layer is P-type doped, the other layer is N-type doped.

[0050] like Figure 3-Figure 4 As shown, the 4H-SiC avalanche photodetector further includes: a bottom electrode 16 .

[0051] like Figure 3 As shown, the bottom electrode 16 is located at the edge region of the bottom electrode contact layer 11, or, as shown Figure 4 As shown, the bottom electrode 16 is located on a side of the substrate 10 away from the epitaxial layer structure.

[0052] The novel 4H-SiC avalanche photodetector provided in the embodiment of the present invention is different from the conventional 4H-SiC avalanche photodetector in that the epitaxial mesa structure is improved, and the conventional epitaxial mesa structure with a central symmetric shape such as a circle or a rectangle is abandoned, and a non-central symmetric epitaxial mesa structure as shown in the embodiment of the present invention is designed. In other words, the epitaxial mesa structure is >The widest mid-perpendicular line in the crystal direction is the interface, and the epitaxial mesa structures on both sides of the interface are < >The average width of the crystal direction is not equal, forming a < >The epitaxial table structure has a non-centrosymmetric structure in the crystal direction to reduce the carrier shielding area, further increase the effective avalanche area of ​​the device, and improve the single-photon detection performance of the device.

[0053] Furthermore, the top electrode 15 can be biased at one end of the top surface of the epitaxial mesa structure so that the areas of the top electrodes 15 on both sides of the interface are unequal, thereby avoiding the high-gain area of ​​the photosensitive region, avoiding blocking the high-gain area of ​​the photosensitive region, increasing the proportion of the high-gain area of ​​the photosensitive region, and improving the single-photon detection performance of the device.

[0054] In general, the 4H-SiC avalanche photodetector with a non-centrosymmetric epitaxial table structure provided in the embodiment of the present invention, in the face of the avalanche unevenness in the photosensitive area caused by the unique properties of the material, alleviates the local electric field shielding effect caused by carrier aggregation by designing a non-centrosymmetric epitaxial table structure, increases the effective photosensitive area of ​​the device, can effectively improve the avalanche uniformity in the active area, increase the effective detection area, and optimize its detection performance.

[0055] In the embodiment of the present invention, including but not limited to using a photoresist to prepare a mask of a non-centrosymmetric pattern, etching starts from the top electrode contact layer 13 and etches into the bottom electrode contact layer 11 to form a non-centrosymmetric epitaxial mesa structure. The shape of the non-centrosymmetric epitaxial mesa structure can be a water drop shape, a trapezoid or a triangle. The shape of the non-centrosymmetric epitaxial mesa structure can also be other non-centrosymmetric shapes, as long as the epitaxial mesa structures located on both sides of the interface are within < >The average width in the crystal direction is not equal, as long as it has a carrier aggregation effect.

[0056] In an optional embodiment of the present invention, the top electrode contact layer 13 is a heavily doped 4H-SiC epitaxial layer with a doping concentration ranging from 1×10 18 / cm 3 -1×10 20 / cm 3 , thickness range is 0.1μm-0.5μm.

[0057] In an optional embodiment of the present invention, the working layer 12 is located on the bottom electrode contact layer 11, and the working layer 12 may include N sub-working layers stacked in sequence, where N≥2, and N is a positive integer.

[0058] In other words, the working layer 12 may be composed of one or N layers of 4H-SiC epitaxial layers with the same doping type and different doping concentrations. For example, the working layer 12 may be a lightly doped layer, a heavily doped layer and a lightly doped layer from top to bottom.

[0059] The doping concentration of the working layer 12 is in the range of 1×10 15 / cm 3 -1×10 20 / cm 3 The thickness of the working layer 12 is in the range of 0.3 μm to 3 μm.

[0060] In an optional embodiment of the present invention, Figure 2-Figure 4 As shown, the 4H—SiC avalanche photodetector further includes a passivation layer 14 .

[0061] Specifically, in the embodiment of the present invention, the passivation layer 14 is prepared by high temperature oxidation or thin film deposition, but not limited to the above. The passivation layer 14 is used to suppress the surface leakage of the 4H-SiC avalanche photodetector and improve the working stability of the 4H-SiC avalanche photodetector.

[0062] like Figure 3 As shown, the passivation layer 14 covers the upper surface area of ​​the device except the top electrode 15 and the bottom electrode 16, including the upper surface of the top electrode contact layer 13, the bottom electrode contact layer 11 and the sidewall of the non-centrosymmetric epitaxial mesa structure. The passivation layer 14 prepared by high temperature oxidation can be a 1nm-50nm silicon dioxide passivation layer, and the passivation layer 14 deposited by thin film can be a 200nm-2000nm silicon dioxide passivation layer, a silicon nitride passivation layer, an aluminum nitride passivation layer, a hafnium oxide passivation layer or a combination thereof.

[0063] In an optional embodiment of the present invention, Figure 2-Figure 4 As shown, the size of the epitaxial mesa structure in the first direction gradually decreases.

[0064] The first direction is perpendicular to the plane where the substrate 10 is located, and points from the substrate 10 to the epitaxial layer structure.

[0065] Specifically, the area of ​​each epitaxial layer in the non-centrosymmetric epitaxial mesa structure designed in the embodiment of the present invention is not greater than the area of ​​the adjacent lower epitaxial layer. That is, the part closer to the substrate 10 in the non-centrosymmetric epitaxial mesa structure has a larger orthographic projection area on the substrate 10, and the part farther away from the substrate 10 has a smaller orthographic projection area on the substrate 10. In other words, in the embodiment of the present application, the non-centrosymmetric epitaxial mesa structure is designed in a design manner of being wide at the bottom and narrow at the top.

[0066] The lower edge of the epitaxial mesa structure is lower than the contact surface between the bottom electrode contact layer 11 and the working layer 12. In other words, the lower edge of the epitaxial mesa structure is lower than the upper surface of the bottom electrode contact layer 11 and higher than the lower surface of the bottom electrode contact layer 11.

[0067] Among them, the formed inclined terrace is used to effectively suppress the fringe electric field of the 4H-SiC avalanche photodetector.

[0068] Optionally, the angle between the sidewall of the non-centrosymmetric epitaxial mesa structure and the plane where the substrate 10 is located is in the range of 2°-90°.

[0069] In an optional embodiment of the present invention, reference Figure 5 , Figure 5 One of the schematic diagrams of a surface of an epitaxial mesa structure facing away from a substrate provided by an embodiment of the present invention; Figure 6 , Figure 6 A second schematic diagram of a surface of an epitaxial mesa structure facing away from a substrate provided in an embodiment of the present invention; Figure 7 , Figure 7 The third schematic diagram of a surface of an epitaxial mesa structure facing away from the substrate provided in an embodiment of the present invention. It should be noted that: Figure 5-Figure 7 It can also be understood as a schematic diagram of the active area of ​​4H-SiC avalanche photodetector. Figure 5-Figure 7 The middle diagram shows the “active region”.

[0070] The bottom electrode contact layer 11 is a P-type doped 4H-SiC epitaxial layer, and the top electrode contact layer 13 is an N-type doped 4H-SiC epitaxial layer. At this time, the top electrode 15 forms an N-type ohmic contact with the top electrode contact layer 13, and the bottom electrode 16 forms a P-type ohmic contact with the bottom electrode contact layer 11. Alternatively, when the bottom electrode 16 is located on the side of the substrate 10 away from the epitaxial layer structure, the bottom electrode 16 forms an ohmic contact with the substrate 10 of the same doping type, and finally forms an epitaxial structure of a 4H-SiC avalanche photodetector with the working layer 12.

[0071] At this time, the designed non-centrosymmetric epitaxial terrace structure is located at the interface [ ] The epitaxial mesa structure on one side of the crystal direction is [ ] The average width on the crystal direction is smaller than the average width on the other side. That is to say, the designed non-centrosymmetric epitaxial mesa structure is located at the interface [ ] The epitaxial mesa structure on one side of the crystal direction is [ ] the average width in the crystal direction is smaller than that at the interface [ ] The epitaxial mesa structure on one side of the crystal direction is [ ]The average width in the crystal direction.

[0072] Optional, such as Figure 5 As shown, the shape of the designed non-centrosymmetric epitaxial mesa structure can be a water drop shape; alternatively, as Figure 6 As shown, the shape of the designed non-centrosymmetric epitaxial mesa structure can be a rounded trapezoid; alternatively, as Figure 7 As shown, the shape of the designed non-centrosymmetric epitaxial mesa structure can be a rounded triangle.

[0073] Further, such as Figure 5-Figure 7 As shown, the top electrode 15 is located on the top electrode contact layer 13, the surface area of ​​the top electrode 15 is smaller than the surface area of ​​the top electrode contact layer 13, and the [ ] The area of ​​the top electrode 15 on one side of the crystal direction is larger than that on the other side. That is, the area of ​​the top electrode 15 on the interface The area of ​​the top electrode 15 on the crystal direction side is larger than that of the top electrode 15 on the interface. ]The area of ​​the top electrode 15 on one side of the crystal direction.

[0074] Optional, such as Figure 5 As shown, the top electrode 15 may be in the shape of a semicircular ring; alternatively, Figure 6 As shown, the top electrode 15 may be in the shape of a semi-square ring; alternatively, Figure 7 As shown, the top electrode 15 may be in a circular shape. Obviously, the top electrode 15 may also be in other shapes, as long as the shape of the top electrode 15 at the interface is ensured. The area of ​​the top electrode 15 on the crystal direction side is larger than that of the top electrode 15 on the interface. ]The area of ​​the top electrode 15 on one side of the crystal direction is sufficient.

[0075] In general, for the designed non-centrosymmetric epitaxial mesa structure, when the bottom electrode contact layer 11 is P-type doped and the top electrode contact layer 13 is N-type doped, it is necessary to ensure that the [ ] The epitaxial mesa structure on one side of the crystal direction is [ ] The average width on the crystal direction is smaller than the average width on the other side, and the [ ]The area of ​​the top electrode 15 on one side of the crystal direction is larger than that on the other side.

[0076] In an optional embodiment of the present invention, reference Figure 8 , Figure 8 A fourth schematic diagram of a surface of an epitaxial mesa structure facing away from a substrate provided in an embodiment of the present invention; Fig. 9 , Fig. 9 A fifth schematic diagram of a surface of an epitaxial mesa structure facing away from a substrate provided in an embodiment of the present invention; Fig.10 , Fig.10 The sixth schematic diagram of a surface of an epitaxial mesa structure facing away from the substrate provided in an embodiment of the present invention. It should be noted that: Figure 8-Figure 10 It can also be understood as a schematic diagram of the active area of ​​4H-SiC avalanche photodetector. Figure 8-Figure 10 The middle diagram shows the “active region”.

[0077] The bottom electrode contact layer 11 is an N-type doped 4H-SiC epitaxial layer, and the top electrode contact layer 13 is a P-type doped 4H-SiC epitaxial layer. At this time, the top electrode 15 forms a P-type ohmic contact with the top electrode contact layer 13, and the bottom electrode 16 forms an N-type ohmic contact with the bottom electrode contact layer 11. Alternatively, when the bottom electrode 16 is located on the side of the substrate 10 away from the epitaxial layer structure, the bottom electrode 16 forms an ohmic contact with the substrate 10 of the same doping type, and finally forms an epitaxial structure of a 4H-SiC avalanche photodetector with the working layer 12.

[0078] At this time, the designed non-centrosymmetric epitaxial terrace structure is located at the interface [ ] The epitaxial mesa structure on one side of the crystal direction is [ ] The average width on the crystal direction is greater than the average width on the other side. That is to say, the designed non-centrosymmetric epitaxial mesa structure is located at the interface [ ] The epitaxial mesa structure on one side of the crystal direction is [ ] has an average width in the crystal direction greater than that at the interface [ ] The epitaxial mesa structure on one side of the crystal direction is [ ]The average width in the crystal direction.

[0079] Optional, such as Figure 8 As shown, the shape of the designed non-centrosymmetric epitaxial mesa structure can be a water drop shape; alternatively, as Fig. 9 As shown, the shape of the designed non-centrosymmetric epitaxial mesa structure can be a rounded trapezoid; alternatively, as Fig.10 As shown, the shape of the designed non-centrosymmetric epitaxial mesa structure can be a rounded triangle.

[0080] Further, such as Figure 8-Figure 10 As shown, the top electrode 15 is located on the top electrode contact layer 13, the surface area of ​​the top electrode 15 is smaller than the surface area of ​​the top electrode contact layer 13, and the [ ] The area of ​​the top electrode 15 on one side of the crystal direction is smaller than that on the other side. That is, the area of ​​the top electrode 15 on the interface is The area of ​​the top electrode 15 on the crystal direction side is smaller than that of the top electrode 15 on the interface. ]The area of ​​the top electrode 15 on one side of the crystal direction.

[0081] Optional, such as Figure 8 As shown, the top electrode 15 may be in the shape of a semicircular ring; alternatively, Fig. 9 As shown, the top electrode 15 may be in the shape of a semi-square ring; alternatively, Fig.10 As shown, the top electrode 15 may be in a circular shape. Obviously, the top electrode 15 may also be in other shapes, as long as the shape of the top electrode 15 at the interface is ensured. The area of ​​the top electrode 15 on the crystal direction side is smaller than that of the top electrode 15 on the interface. ]The area of ​​the top electrode 15 on one side of the crystal direction is sufficient.

[0082] In general, for the designed non-centrosymmetric epitaxial mesa structure, when the bottom electrode contact layer 11 is N-type doped and the top electrode contact layer 13 is P-type doped, it is necessary to ensure that the [ ] The epitaxial mesa structure on one side of the crystal direction is [ ] has an average width on one side of the crystal direction that is greater than the average width on the other side, and the [ ]The area of ​​the top electrode 15 on one side of the crystal direction is smaller than that on the other side.

[0083] In an optional embodiment of the present invention, the top electrode 15 and the bottom electrode 16 may be a metal composite structure of one or more of Ti, Al, Ni, Au, Pt, W, and Cr. A further optional composite structure of Ni / Ti / Al / Au may be selected, that is, a multilayer metal composite structure consisting of a 35nm thick Ni layer, a 50nm thick Ti layer, a 100nm thick Al layer, and a 100nm thick Au layer, which are sequentially connected to the upper surface of the top electrode contact layer 13, the upper surface of the bottom electrode contact layer 11, or the lower surface of the substrate 10. Among them, the outermost layers of the top electrode 15 and the bottom electrode 16 are Au layers.

[0084] Based on the 4H-SiC avalanche photodetector provided in the above embodiment of the present invention, the 4H-SiC avalanche photodetector with a water droplet-shaped non-centrosymmetric epitaxial mesa structure and the 4H-SiC avalanche photodetector with a traditional circular epitaxial mesa structure are characterized by using a two-dimensional photon counting scanning technology in the embodiment of the present application. Fig.11 , Fig.11 A schematic diagram of characterizing a 4H-SiC avalanche photodetector with a water droplet-shaped non-centrosymmetric epitaxial mesa structure using a two-dimensional photon counting scanning technology provided by an embodiment of the present invention; Fig.12 , Fig.12 A schematic diagram of characterizing a conventional circular epitaxial mesa structure 4H-SiC avalanche photodetector using a two-dimensional photon counting scanning technique provided by an embodiment of the present invention. Fig.11 and Fig.12 Gain represents the device avalanche gain.

[0085] like Fig.11 and Fig.12 As shown, by comparison, it can be seen that the water drop-shaped non-centrosymmetric epitaxial mesa structure has a larger effective detection area and better avalanche uniformity than the traditional circular epitaxial mesa structure. Under the action of biasing the top electrode 15 and the non-centrosymmetric epitaxial mesa structure, the shielding effect of carrier aggregation on the avalanche electric field can be improved, the inhomogeneity of the internal electric field can be alleviated, the effective photosensitive area of ​​the 4H-SiC avalanche photodetector can be increased, and the single-photon detection capability of the 4H-SiC avalanche photodetector can be further improved.

[0086] It should be noted that Figure 1 and Figure 2 Also shown is the >Crystal orientation, Figure 5-Figure 10 The figure also shows [ ] crystal direction. >Crystal orientation includes [ ] crystal orientation and [ ] crystal direction, [ ] crystal orientation and [ ] crystal directions are two parallel and opposite directions. >Crystal orientation and < >The same is true for crystal orientation, which will not be elaborated on here.

[0087] Based on the 4H-SiC avalanche photodetector provided in the above embodiment of the present invention, a method for preparing a 4H-SiC avalanche photodetector is further provided in another embodiment of the present invention. The method for preparing a 4H-SiC avalanche photodetector provided in the embodiment of the present invention comprises:

[0088] S101: providing a substrate 10.

[0089] S102 : forming an epitaxial layer structure on one side of the substrate 10 .

[0090] S103: Processing the epitaxial layer structure to make a portion of the epitaxial layer structure away from the substrate 10 as an epitaxial mesa structure; wherein the epitaxial mesa structure is the epitaxial mesa structure at < >The widest mid-perpendicular line in the crystal direction is the interface, and the epitaxial mesa structures on both sides of the interface are < >The average width in the crystal direction is not equal.

[0091] It should be noted that the embodiments of the present invention include but are not limited to using mask etching technology to process the epitaxial layer structure to form the required epitaxial mesa structure.

[0092] The above is a detailed introduction to a 4H-SiC avalanche photodetector and a preparation method thereof provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as a limitation on the present invention.

[0093] It should be noted that each embodiment in this specification is described in a progressive manner, and each embodiment focuses on the differences from other embodiments, and the same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part description.

[0094] It should also be noted that, in this article, relational terms such as first and second, etc. 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 the process, method, article or device that includes a series of elements is inherent to the elements, or also includes elements inherent to these processes, methods, articles or devices. In the absence of further restrictions, the elements defined by the sentence "including a..." do not exclude the presence of other identical elements in the process, method, article or device that includes the elements.

[0095] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one 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 invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A 4H-SiC avalanche photodetector, characterized in that: The 4H-SiC avalanche photodetector comprises: substrate; An epitaxial layer structure located on one side of the substrate; a portion of the epitaxial layer structure away from one side of the substrate is used as an epitaxial mesa structure; Among them, the epitaxial mesa structure is the epitaxial mesa structure in < >The widest mid-perpendicular line in the crystal direction is the interface, and the epitaxial mesa structures on both sides of the interface are < >The average width in the crystal direction is not equal.

2. The 4H-SiC avalanche photodetector according to claim 1, characterized in that: The substrate is a conductive substrate that is beveled at 4° from the (0001) crystal plane.

3. The 4H-SiC avalanche photodetector according to claim 1, characterized in that: The size of the epitaxial mesa structure in the first direction gradually decreases; The first direction is perpendicular to the plane where the substrate is located, and points from the substrate to the epitaxial layer structure.

4. The 4H-SiC avalanche photodetector according to claim 3, characterized in that: The epitaxial layer structure comprises: A bottom electrode contact layer, a working layer, a top electrode contact layer and a top electrode are sequentially stacked on the substrate; the working layer, the top electrode contact layer and the top electrode form a whole that exposes the edge area of ​​the bottom electrode contact layer; the areas of the top electrodes on both sides of the interface are not equal; The bottom electrode contact layer and the top electrode contact layer have different doping types. When one layer is P-type doped, the other layer is N-type doped.

5. The 4H-SiC avalanche photodetector according to claim 4, characterized in that: The 4H-SiC avalanche photodetector further includes: a bottom electrode; The bottom electrode is located at an edge region of the bottom electrode contact layer, or the bottom electrode is located at a side of the substrate away from the epitaxial layer structure.

6. The 4H-SiC avalanche photodetector according to claim 4, characterized in that: When the bottom electrode contact layer is P-type doped and the top electrode contact layer is N-type doped, the [ ] The epitaxial mesa structure on one side of the crystal direction is [ ] The average width on the crystal direction is smaller than the average width on the other side, and the [ ]The area of ​​the top electrode on one side of the crystal direction is larger than that on the other side.

7. The 4H-SiC avalanche photodetector according to claim 4, characterized in that: When the bottom electrode contact layer is N-type doped and the top electrode contact layer is P-type doped, the [ ] The epitaxial mesa structure on one side of the crystal direction is [ ] has an average width on one side of the crystal direction that is greater than the average width on the other side, and the [ ]The area of ​​the top electrode on one side of the crystal direction is smaller than that on the other side.

8. The 4H-SiC avalanche photodetector according to claim 4, characterized in that: The lower edge position of the epitaxial mesa structure is lower than the contact surface between the bottom electrode contact layer and the working layer.

9. The 4H-SiC avalanche photodetector according to claim 4, characterized in that: The working layer includes N sub-working layers stacked in sequence, where N≥2 and N is a positive integer.

10. A method for preparing a 4H-SiC avalanche photodetector, characterized in that: The preparation method of the 4H-SiC avalanche photodetector comprises: providing a substrate; forming an epitaxial layer structure on one side of the substrate; The epitaxial layer structure is processed so that a portion of the epitaxial layer structure away from the substrate side is used as an epitaxial mesa structure; wherein the epitaxial mesa structure is >The widest mid-perpendicular line in the crystal direction is the interface, and the epitaxial mesa structures on both sides of the interface are < >The average width in the crystal direction is not equal.

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