High sensitivity detector with internal gain
By setting the charge collection area and the charge control area at intervals, the longitudinal electric field distribution is optimized, and the high gain and high sensitivity of the photodetector are achieved, solving the problem that gain improvement affects responsiveness and noise performance in the prior art.
Patent Information
- Application Number
- CN202421352656.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-06-13
- Publication Date
- 2025-06-10
- Estimated Expiration
- 2034-06-13
AI Technical Summary
When existing photodetectors improve internal gain, they can easily affect the device's responsiveness and noise performance, resulting in insufficient detection sensitivity to meet application needs.
By setting charge collection and charge control areas with opposite conductivity types at intervals, the longitudinal electric field distribution between the doubling region and the absorption region is optimized to ensure that the charge control area is in a depleted state at the appropriate operating voltage, forming an avalanche multiplication effect.
The high gain of the photodetector is achieved while maintaining the advantages of high bandwidth, high detection efficiency and low dark current at low operating voltage, improving the sensitivity and signal-to-noise ratio of the detector.
Smart Images
Figure CN222967333U_ABST
Abstract
Description
Technical Field
[0001] The utility model belongs to the field of photodetectors and relates to a highly sensitive detector with internal gain. Background Technique
[0002] At present, most photodetectors are mainly based on the photoelectric effect or the impact ionization effect. That is, when light or high-energy particles irradiate the surface of the detector, the energy of photons or high-energy particles is absorbed by the material, causing electrons to be released from the material and generating charge carriers. Compared with conventional photodetectors, avalanche photodetectors (APDs) utilize the avalanche impact ionization effect to amplify the photo-generated carriers. When the device is under a high reverse bias voltage, the absorption layer absorbs the incident light to generate photo-generated carriers, so that the internal photo-generated carriers collide with the lattice under the action of a strong electric field and ionization occurs, resulting in an avalanche effect. The photocurrent generated by a single carrier is amplified to a macroscopic level that can be detected, thus having a high-frequency response characteristic and a high internal gain, and being widely used in systems such as optical fiber communication, laser detection and ranging, quantum imaging, biomolecular detection, medical imaging, and optical fiber sensing. In high-bandwidth detectors, in order to achieve a certain signal-to-noise ratio, the backend processing circuit usually needs to include a preamplifier with sufficiently low noise, which increases the difficulty and cost of circuit design. For high-frequency detection of weak signals, in order to reduce the difficulty of circuit design, increasing the signal strength of the detector itself can make it easier to detect a high signal-to-noise ratio. However, for the detection scenario of weak light, the signal value is often relatively weak.
[0003] Please refer to Figure 1 and Figure 2 , which shows a schematic diagram of the typical structure of a punch-through photodetector. Generally, an APD device includes a substrate layer 1 and a P-type epitaxial layer 10 stacked in sequence from bottom to top. A first charge region 12 and a second charge region 14 are disposed adjacent to each other in the P-type epitaxial layer 10. The first charge region 12 has an end that extends into the epitaxial layer 10 lower than the end of the second charge region 14. The second charge region 14 has a conductivity type opposite to that of the first charge region 12, so that the interface between the first charge region 12 and the second charge region 14 provides a PN junction. As Figure 1As shown, the first charge region 12 is a P-type well region, and the second charge region 14 is an N-type well region. The electrons generated by the excitation of the absorption region adjacent to the first charge region 12 are multiplied during the process of traveling to the anode electrode. In the low electric field region near the cathode electrode, the electron ionization coefficient is greater than the hole ionization coefficient, ensuring that hole multiplication hardly occurs at the position where the hole current is high. Therefore, the above-mentioned silicon-based avalanche photodetector can effectively reduce the ionization coefficient ratio of effective holes and electrons in the multiplication region. Although increasing the doping concentration of the second charge region 14 in the above device structure can increase the probability of avalanche multiplication, increasing the doping concentration of the second charge region 14 will cause the thickness of the multiplication region to become thinner, and most of the voltage drops occur in the multiplication region. Achieving high gain of the APD in this way will affect the responsiveness of the device and degrade the noise performance.
[0004] Therefore, it is necessary to provide an improved photodetector to achieve controllable internal gain of the detector, thereby increasing the signal value of the detector itself and further reducing the requirements for circuit design and manufacturing.
[0005] It should be noted that the above introduction of the technical background is only for the convenience of clearly and completely explaining the technical solutions of the present application and facilitating the understanding of those skilled in the art. It cannot be considered that the above technical solutions are well-known to those skilled in the art just because these solutions are described in the background art part of the present application. Summary of the Utility Model
[0006] In view of the above-mentioned disadvantages of the prior art, the purpose of the present utility model is to provide a highly sensitive detector with internal gain, which is used to solve the problems in the prior art that the responsiveness of the detector is affected while increasing the internal gain of the device, excessive noise is generated, and the detection sensitivity cannot meet the application requirements.
[0007] To achieve the above purpose and other related purposes, the present utility model provides a highly sensitive detector with internal gain, including a stacked substrate layer and an epitaxial structure. The epitaxial structure includes a charge collection region, a charge control region, and an absorption region arranged in sequence from the surface of the epitaxial structure away from the substrate layer towards the inside. The charge collection region is used to collect photo-generated carriers. The charge control region has a conductivity type opposite to that of the charge collection region. The charge collection region and the charge control region are spaced apart by a predetermined distance to introduce a multiplication region between the charge collection region and the charge control region, and allow free carriers entering the multiplication region to trigger an avalanche multiplication effect when the charge control region is in a depleted state.
[0008] Optionally, the epitaxial structure is configured as a P-type epitaxial layer, and the center distance between the charge collection region and the charge control region in the P-type epitaxial layer ranges from 0.5 μm to 3 μm, where the doping concentration of the charge collection region is 1e16 cm -3 -1e20 cm -3 。
[0009] Optionally, it further includes: a guard ring, arranged to surround the charge collection region, and the guard ring has a diffusion depth greater than that of the charge collection region.
[0010] Optionally, the depth of the charge collection region extending from the surface of the P-type epitaxial layer away from the substrate layer towards the inside is 0.5 μm to 1 μm.
[0011] Optionally, it further includes an upper electrode layer located on the surface of the charge collection region, and the upper electrode layer is electrically connected to the charge collection region: a lower electrode layer, and the lower electrode layer is electrically connected to the substrate layer; wherein, by modulating the working voltage applied between the upper electrode layer and the lower electrode layer, the center distance between the multiplication region and the charge control region is changed, and the range of the working voltage is 5V - 200V.
[0012] Optionally, it further includes:
[0013] a passivation layer, covering the P-type epitaxial layer and arranged on the periphery of the charge collection region;
[0014] an incident window, defined between the passivation layers, and an antireflection film is arranged in the incident window.
[0015] Optionally, through holes are provided in the passivation layer, and the upper electrode layer forms an ohmic contact with the charge collection region by filling the through holes.
[0016] Optionally, it further includes: an N-type deep well, located on the periphery of the guard ring and arranged in the P-type epitaxial layer, and a contact electrode is arranged above the N-type deep well, and the contact electrode is used to electrically lead out the N-type deep well.
[0017] Optionally, it further includes: a P-type deep well, located on the periphery of the guard ring, and the P-type deep well is floatingly arranged on the upper surface layer of the P-type epitaxial layer.
[0018] Optionally, the material of the P-type epitaxial layer includes one of silicon, germanium, and silicon carbide.
[0019] As described above, the highly sensitive detector with internal gain of the present utility model replaces the conventional structure of arranging two charge regions adjacent to each other by arranging charge regions with opposite conduction types at intervals, optimizes the longitudinal electric field distribution between the multiplication region and the absorption region, so that when an appropriate working voltage is applied to both ends of the device, the charge control region is in a depleted state, and a multiplication region is provided below the charge collection region to cause an avalanche multiplication effect for the free carriers entering it, thereby enabling the photodetector to maintain high gain and having the advantages of high bandwidth, high detection efficiency, and low dark current at a low working voltage. BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Figure 1 and Figure 2 show a schematic diagram of a typical structure of a reach-through avalanche photodetector.
[0021] Figure 3 show a cross-sectional schematic diagram of the highly sensitive detector in an embodiment of the present utility model.
[0022] Figure 4 show a cross-sectional schematic diagram of another structure of the highly sensitive detector in an embodiment of the present utility model.
[0023] DESCRIPTION OF REFERENCE NUMERALS
[0024] 1 Substrate layer
[0025] 10 P-type epitaxial layer
[0026] 12 First charge region
[0027] 14 Second charge region
[0028] 15 Guard ring
[0029] 100 Substrate layer
[0030] 110 P-type epitaxial layer
[0031] 120 Charge control region
[0032] 130 Multiplication region
[0033] 140 Charge collection region
[0034] 150 Guard ring
[0035] 160 N-type deep well
[0036] 180 Antireflection film
[0037] 112 Absorption region
[0038] 200 Upper electrode layer
[0039] 210 Passivation layer
[0040] 300 Lower electrode layer
[0041] 190 Lower electrode contact layer
[0042] 40 Contact electrode
[0043] 560 P-type deep well Detailed implementation manners
[0044] The following uses specific specific examples to illustrate the implementation manners of the present utility model. Those skilled in the art can easily understand other advantages and effects of the present utility model from the content disclosed in this specification. The present utility model can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present utility model.
[0045] Please refer to Figures 3 to 4 . It should be noted that the diagrams provided in this embodiment only illustrate the basic concept of the present utility model in a schematic manner. Therefore, only the components related to the present utility model are shown in the diagrams, rather than being drawn according to the number, shape, and size of the components in actual implementation. The type, quantity, and ratio of each component in actual implementation can be arbitrarily changed, and the component layout type may also be more complex.
[0046] The semiconductor field vocabulary used in this article is the commonly used technical vocabulary of those skilled in the art. For example, for P-type and N-type impurities, to distinguish the doping concentration, simply P+ type represents the P-type with heavy doping concentration, P type represents the P-type with medium doping concentration, P- type represents the P-type with light doping concentration, N+ type represents the N-type with heavy doping concentration, N type represents the N-type with medium doping concentration, and N- type represents the N-type with light doping concentration.
[0047] To achieve the above and other related purposes, this embodiment provides a highly sensitive detector with internal gain. Please refer to Figure 3 , which shows a schematic cross-sectional structure diagram of a highly sensitive detector with internal gain, including a stacked substrate layer 100 and an epitaxial structure. In the epitaxial structure, an absorption region 112, a charge control region 120, a multiplication region 130, and a charge collection region 140 are stacked in sequence from the substrate layer. The charge collection region 140 is configured to provide a PN junction at its interface for collecting photo-generated carriers. The charge control region 120 has a conductivity type opposite to that of the charge collection region. The charge collection region 140 and the charge control region 120 are spaced apart at a predetermined distance. When an appropriate working voltage is applied to both ends of the device, a multiplication region 130 is introduced between the charge collection region and the charge control region, and it is allowed to cause an avalanche multiplication effect of free carriers entering the multiplication region when the charge control region is in a substantially depleted or depleted state.
[0048] For optical signal detection, the absorption region 112 utilizes the carrier energy level transition to achieve photon absorption of the target detection light, converts the incident photons into photo-generated carriers to achieve photoelectric conversion, and the multiplication region 130 utilizes the impact ionization characteristic of the material under high electric field to cause the photo-generated carriers to undergo impact ionization to generate new hole-electron pairs of the second and third order, so as to achieve gain. By alternately arranging the charge control region 120 and the charge collection region 140, the longitudinal electric field distribution between the multiplication region and the absorption region is adjusted. Without increasing / decreasing the thickness of the absorption region, when an appropriate reverse bias voltage is applied between the charge control region and the charge collection region to completely deplete the charge collection region 140, there is sufficient spacing between the charge control region and the charge collection region to ensure that a high electric field region is formed in the multiplication region below the charge collection region. This high electric field region can increase the impact ionization collision rate of both electrons and holes, and the secondary hole-electron pairs will not penetrate to its periphery to cause breakdown, thereby achieving high gain. Compared with Figure 1 and Figure 2 the shown reach-through type APD device, by alternately arranging the charge collection region and the charge control region, the spatial electric field distribution between the multiplication region and the absorption region is optimized. Since the multiplication region is used to cause the photo-generated carriers entering therein to undergo impact ionization under the action of the high electric field in the multiplication region, an avalanche multiplication effect occurs to generate a large number of free carrier pairs, thereby amplifying the signal, while preventing an excessive electric field from generating an excessive tunneling dark current or generating a harmful avalanche multiplication.
[0049] The high-sensitivity detector can be configured as a planar structure avalanche photodetector or a mesa structure avalanche photodetector, and the material and size of the epitaxial structure can be set in a conventional manner in the art.
[0050] The high-sensitivity detector further includes an upper electrode layer 200 and a lower electrode layer 300. The upper electrode layer 200 is located on the surface of the charge collection region, the upper electrode layer 200 is electrically connected to the charge collection region 140, the lower electrode layer 300 is electrically connected to the substrate layer 100, and the depletion region thickness of the PN junction defined below the charge collection region is changed by modulating the operating voltage applied between the upper electrode layer and the lower electrode layer.
[0051] In one implementation, the epitaxial structure is configured as an epitaxial layer of a single material. Figure 3 Fig. shows a schematic structural diagram of the high-sensitivity detector with internal gain in Embodiment 1 of the present invention. A P-type epitaxial layer is provided on the substrate layer. The charge control region 120 and the charge collection region 140 are alternately arranged in the P-type epitaxial layer for adjusting the longitudinal electric field distribution between the absorption region and the multiplication region 130. In some embodiments, such asFigure 3 As shown, the charge collection region 140 is an N++ type well region, the charge control region 120 is a P+ type well region, the absorption region 112 is an intrinsic region or a P-type lightly doped implantation region, the substrate layer 100 can be selected as a P-type heavily doped substrate, and the substrate layer 100 is electrically connected to the lower electrode layer to collect the holes collected to the lower electrode layer. The center distance between the charge collection region and the charge control region in the P-type epitaxial layer 110 ranges from 0.5 μm to 3 μm.
[0052] In a preferred embodiment, the charge collection region 140 and the charge control region 120 are arranged at a predetermined interval to allow a high electric field region to be formed in the multiplication region 130 below the charge collection region when the charge control region is in a fully depleted state, while ensuring that the depletion region electric field overlaps with the absorption region in the breakdown mode of the APD, separating the multiplication region from the drift region, avoiding most of the voltage drop falling on the multiplication region and affecting the drift rate of photo-generated carriers, and achieving high gain and high responsivity. In this embodiment, the doping concentration of the charge collection region 140 is 1e16 cm -3 -1e20 cm -3 , the doping concentration of the charge control layer 140 is 1e14 cm -3 -1e18 cm -3 , the doping concentration of the absorption region 112 is 1e10 cm -3 -1e15 cm -3 . Further, by modulating the operating voltage applied between the upper electrode layer and the lower electrode layer, the center distance between the multiplication region and the charge control region is changed, where the range of the operating voltage is 5V - 200V, so as to ensure that the APD amplifies the photocurrent signal at a relatively high receiving sensitivity operating voltage, improve the detection efficiency, facilitate the detection of weak optical signals, and provide higher sensitivity and signal-to-noise ratio compared with conventional photodetectors. The charge control region has a transverse width along the parallel plane of the surface of the P-type epitaxial layer, and the transverse width can be determined according to the size of the pixel. For example, for a photodetector with a pixel pitch of 1 mm, the transverse width of the charge control region can be 500 μm - 900 μm.
[0053] In some embodiments, the material of the P-type epitaxial layer includes one of silicon, germanium, and silicon carbide. The charge collection region 140 is arranged to extend inward from the surface of the P-type epitaxial layer away from the substrate layer to a predetermined depth to form a shallow junction on the surface of the P-type epitaxial layer, thereby improving the collection efficiency of photo-generated carriers in the N++ type charge collection region. The charge control region 120 and the charge collection region 140 in the P-type epitaxial layer are arranged at a predetermined interval to ensure that the high electric field region is located below the charge collection region when the charge collection region 140 and the P-type epitaxial layer 110 are in a reverse depletion state.
[0054] In this embodiment, the thickness range of the P-type epitaxial layer is 20 μm - 100 μm, and the diffusion depth of the charge control region 120 extending from the surface of the P-type epitaxial layer away from the substrate layer into its interior is 0.5 μm - 3 μm.
[0055] In Figure 3 the implementation shown, a guard ring 150 is further provided in the P-type epitaxial layer. The guard ring 150 is located around the charge collection region and is used to make the electric field distribution more uniform. Please refer to Figure 3 , in one embodiment, the guard ring 150 is disposed adjacent to and around the charge collection region 140 to prevent premature breakdown at the edge and improve the reverse breakdown voltage performance of the device. The diffusion front of the guard ring 150 is lower than that of the charge collection region, that is, the guard ring 150 has a diffusion depth greater than that of the charge collection region. The guard ring 150 and the charge collection region 140 can be formed by introducing different dopants. For example, phosphorus can be used as the dopant for the guard ring 150, and arsenic can be used as the dopant for the charge collection region 140. Preferably, the depth of the charge collection region extending from the surface of the P-type epitaxial layer away from the substrate layer into the interior reaches 0.5 μm - 1 μm.
[0056] The high-sensitivity detector further includes a passivation layer covering the surface of the P-type epitaxial layer away from the substrate layer to passivate the device surface of the photodetector, thereby reducing the dark current. In this embodiment, the high-sensitivity detector is configured as a front-illuminated avalanche photodetector, which includes an incident window located on the side of the P-type epitaxial layer away from the substrate layer for detecting optical signals and / or high-energy particles such as electrons, X-rays, γ-rays, α-rays, and β-rays. An antireflection film 180 is provided in the incident window. Further, through holes are provided in the passivation layer 210, and the through holes expose the charge collection region 140. As Figure 3 shown, the upper electrode layer 200 contacts the charge collection region by filling the through holes; preferably, the upper electrode layer 200 can form an ohmic contact with the exposed surface of the charge collection region to ensure good electrical performance of the device. In a specific embodiment, the material of the passivation layer 210 can be selected as SiO 2 , and the material of the antireflection film 180 can be selected as SiN x .
[0057] In other implementations, the epitaxial structure can be configured as a composite epitaxial stack, where the material layers where the multiplication region and the absorption region are located can be made of different materials. For example, the charge collection region, the multiplication region, and the charge control region can be provided in a silicon epitaxial layer, and the absorption region can be selected from Ge, SiGe alloy, SiGe quantum dots, SiGe quantum wells, or similar materials to enhance light absorption in the near-infrared band.
[0058] As shown Figure 3 in the figure, an N-type deep well 160 is further provided in the P-type epitaxial layer 110. The N-type deep well 160 can be configured as an N-type collection ring around the guard ring. The depletion region formed by the N-type deep well and the P-type epitaxial layer is used to collect the dark current in the peripheral region of the device, prevent interference with the effective multiplication signal, and at the same time form an electric field to reduce the formation of diffusion current, thereby affecting the detector bandwidth. A contact electrode 40 is provided above the N-type deep well 160. The contact electrode 40 is electrically connected to the N-type deep well 160 through a through hole penetrating the passivation layer to realize the electrical lead-out of the N-type deep well. In a specific embodiment, the doping concentration of the N-type deep well 160 is 1e14 cm -3 -1e19 cm -3 , and the depth of the N-type deep well 160 extending from the surface of the P-type epitaxial layer away from the substrate layer into its interior is 1.5 μm - 2 μm.
[0059] In another embodiment, as Figure 4 shown in the figure, a P-type deep well 560 is further provided in the P-type epitaxial layer 110, located outside the guard ring. The P-type deep well 560 is floatingly disposed in the P-type epitaxial layer, for example, the upper surface layer of the P-type epitaxial layer, to reduce the influence of substrate noise on the dark current and photocurrent, improve the stability of the device, and at the same time form an electric field to reduce the formation of diffusion current, thereby affecting the detector bandwidth; preferably, the doping concentration of the P-type deep well 560 is 1e14 cm -3 -1e19 cm -3 , and the depth of the P-type deep well 560 extending from the surface of the P-type epitaxial layer away from the substrate layer into its interior is 1.5 μm - 2 μm.
[0060] A lower electrode contact layer 190 is provided on the surface of the substrate layer away from the epitaxial structure. An lower electrode layer 300 is provided on the lower electrode contact layer 190. The lower electrode layer and the lower electrode contact layer form an ohmic contact to ensure good electrical performance of the device. In this embodiment, the lower electrode layer 300 is used as the cathode electrode. As Figure 3 and Figure 4 shown in the figure, the lower electrode layer 300 can be disposed on the side of the substrate layer away from the P-type epitaxial layer. In another embodiment, the lower electrode layer 300 can be located on the same side as the P-type epitaxial layer and disposed outside it.
[0061] As an example, the substrate layer 100 can be configured as a P-type heavily doped substrate with a doping concentration of 1e17 cm -3 -1e20 cm -3 , and the doping concentration of the lower electrode contact layer 190 is 1e17 cm -3 -1e20 cm-3 , the thickness range of the lower electrode contact layer 190 is 0.1 μm - 1.5 μm.
[0062] As an example, the upper electrode layer 200 and the lower electrode layer 300 may include a single layer composed of one selected from the following or a stacked layer composed of a plurality of them: Al, Au, or similar metals.
[0063] As an example, the high-sensitivity detector is applied in the fields of optical communication, infrared signal detection, and other suitable technical fields.
[0064] The above embodiments merely illustrate the principles and effects of the present invention by way of example, rather than limiting the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.
Claims
1. A high-sensitivity detector with internal gain, characterized in that: The invention comprises a stacked substrate layer and an epitaxial structure, wherein the epitaxial structure comprises a charge collection region, a charge control region and an absorption region arranged in sequence from a surface of the epitaxial structure away from the substrate layer toward the inside, the charge collection region is used to collect photogenerated carriers, the charge control region has a conductivity type opposite to that of the charge collection region, the charge collection region and the charge control region are arranged at a predetermined interval to introduce a multiplication region therebetween, and free carriers entering the multiplication region are allowed to trigger an avalanche multiplication effect when the charge control region is in a depleted state.
2. The high-sensitivity detector according to claim 1, characterized in that: The epitaxial structure is configured as a P-type epitaxial layer, and the center distance between the charge collection region and the charge control region in the P-type epitaxial layer ranges from 0.5 μm to 3 μm.
3. The high-sensitivity detector according to claim 2, characterized in that: Also includes: A guard ring is disposed to surround the charge collection region, and the guard ring has a diffusion depth greater than that of the charge collection region.
4. The high-sensitivity detector according to claim 2, characterized in that: The charge collection region extends inward from the surface of the P-type epitaxial layer away from the substrate layer to a depth of 0.5 μm-1 μm.
5. The high-sensitivity detector according to claim 2, characterized in that: Also includes: An upper electrode layer, located on the surface of the charge collection region, and the upper electrode layer is electrically connected to the charge collection region: a lower electrode layer, the lower electrode layer being electrically connected to the substrate layer; Wherein, the distance between the multiplication region and the charge control region is changed by modulating the working voltage applied between the upper electrode layer and the lower electrode layer, and the working voltage ranges from 5V to 200V.
6. The high-sensitivity detector according to claim 5, characterized in that: Also includes: A passivation layer, covering the P-type epitaxial layer and disposed at the periphery of the charge collection region; An incident window is defined between the passivation layers, and an anti-reflection film is disposed in the incident window.
7. The high-sensitivity detector according to claim 6, characterized in that: The passivation layer is provided with a through hole, and the upper electrode layer forms an ohmic contact with the charge collection region by filling the through hole.
8. The high-sensitivity detector according to claim 3, characterized in that: Also includes: An N-type deep well is located at the periphery of the guard ring and is arranged in the P-type epitaxial layer. A contact electrode is arranged above the N-type deep well, and the contact electrode is used to realize the electrical extraction of the N-type deep well.
9. The high-sensitivity detector according to claim 3, characterized in that: Also includes: The P-type deep well is located at the periphery of the protection ring, and the P-type deep well is arranged in a floating manner on the upper surface layer of the P-type epitaxial layer.
10. The high-sensitivity detector according to claim 2, characterized in that: The material of the P-type epitaxial layer includes one of silicon, germanium and silicon carbide.