Silicon carbide p-i-n ultraviolet photodetector with buried structure and preparation thereof

Abstract

Silicon carbide p-i-n ultraviolet photodetector with buried layer structure and preparation, relate to ultraviolet photodetector.Set with silicon carbide high-doped n+ type substrate, on the silicon surface of n+ type substrate, epitaxial homogeneous silicon carbide n type buffer layer, in the center of n type buffer layer, set cylindrical silicon carbide low-doped n type absorption layer upward, in n type absorption layer, set single or multiple cylindrical silicon carbide n type charge buried layer, on n type absorption layer, set silicon carbide high-doped p+ type ohmic contact layer, on p+ type ohmic contact layer, set silicon dioxide passivation isolation layer.On the surface of p+ type ohmic contact layer, set p+ type ring-shaped ohmic contact electrode, on the back of n+ type substrate, set n+ type ohmic contact electrode.n type absorption layer impedance is high, in high impedance n type absorption layer, introduce low impedance n type charge buried layer, can modulate the electric field of n type absorption layer, make the detector can occur avalanche breakdown under lower voltage, obtain higher quantum efficiency and gain.

Description

Technical Field

[0001] This invention relates to ultraviolet photodetectors, and more particularly to a silicon carbide pin ultraviolet photodetector with a buried layer structure and its fabrication method. Background Technology

[0002] With the increasing application of ultraviolet light in defense, industrial manufacturing, photolithography, medical and health disinfection, and environmental monitoring, the detection technology of ultraviolet light signals has gradually become a research hotspot in the field of optoelectronic devices. Different types and working principles of ultraviolet photodetectors have been developed, among which semiconductor material ultraviolet photodetectors with excellent characteristics such as low voltage, small size and long life have become the focus of research.

[0003] Currently, the mainstream semiconductor detection technology for ultraviolet signals mainly adopts silicon-based detectors. However, in harsh working environments such as high-energy photon radiation and high temperatures, the performance of silicon-based detectors will be significantly reduced, and detector damage may occur. In addition, the narrow bandgap of single-crystal silicon means that silicon-based detectors are affected by visible light during operation, requiring the use of filters to filter signals from other bands, increasing the cost and size of the detector. Wide-bandgap semiconductor photodetectors can accurately detect ultraviolet signals. Silicon carbide, as the main material of third-generation wide-bandgap semiconductors, has excellent properties such as wide bandgap, high breakdown electric field, high carrier saturation velocity, and high thermal conductivity (Jiafa Cai, Xiaping Chen, Rongdun Hong, Weifeng Yang, Zhengyun Wu, High-performance 4H-SiC-based pin ultraviolet photodiode and investigation of its capacitance characteristics[J]. Optics Communications, 2014, 333: 182-186.). Therefore, silicon carbide-based ultraviolet photodetectors have excellent properties such as high quantum efficiency, visible blindness, radiation resistance, and high temperature resistance. Silicon carbide-based ultraviolet photodetectors generally have four structures: Schottky, pin, MSM, and APD. Among them, pin-structured ultraviolet photodetectors have advantages such as low operating voltage, fast response speed, high responsivity, and stable operation. However, due to the low doping concentration of the absorption layer and high impedance of traditional pin-structured ultraviolet photodetectors, the avalanche breakdown voltage of the detector is very large, making it difficult for pin-structured ultraviolet photodetectors to operate in avalanche mode and achieve multiplier detection of weak ultraviolet signals (Zhang M, Wang KL, Jiang H, Hong R, Wu Z, Highperformance silicon carbide avalanche-pin ultraviolet photodiode with dual operation models[J]. Electronics Letters, 2016, 52(17):1474-1476.). Therefore, how to reduce the avalanche breakdown voltage of traditional pin-structured ultraviolet photodetectors so that the detector can operate in both low-voltage stable mode and avalanche multiplier detection mode has become a new direction in the research of silicon carbide ultraviolet photodetectors. Summary of the Invention

[0004] The purpose of this invention is to provide a silicon carbide pin ultraviolet photodetector with a buried layer structure and its fabrication method, while ensuring that the photocurrent and responsivity of the detector are reduced by less than 10% compared with traditional silicon carbide pin ultraviolet photodetectors. The avalanche breakdown voltage of the detector can be significantly reduced compared with traditional silicon carbide pin ultraviolet photodetectors.

[0005] The silicon carbide pin ultraviolet photodetector with a buried layer structure comprises, from bottom to top, a highly doped n+ type silicon carbide substrate, a homogeneous n-type silicon carbide buffer layer epitaxially formed on the silicon surface of the n+ type substrate, a cylindrical lightly doped n-type silicon carbide absorber layer formed upwards from the center of the n-type buffer layer, one or more cylindrical n-type charge buried layers of silicon carbide within the n-type absorber layer, a highly doped p+ type ohmic contact layer of silicon carbide on the n-type absorber layer, and a silicon dioxide passivation isolation layer on the p+ type ohmic contact layer. A p+ type annular ohmic contact electrode is formed on the upper surface of the p+ type ohmic contact layer, and an n+ type ohmic contact electrode is formed on the back side of the n+ type substrate. The n-type absorber layer in the detector has high impedance. Introducing a low-impedance n-type charge buried layer into the high-impedance n-type absorber layer can modulate the electric field of the n-type absorber layer, allowing the detector to undergo avalanche breakdown at a lower voltage. The aforementioned detector can significantly reduce the avalanche breakdown voltage of traditional silicon carbide pin photodetectors, enabling the detector to operate in a low-voltage stable mode, achieving stable responsivity and high response speed, and also to function as an avalanche photodetector at a lower avalanche breakdown voltage, achieving higher quantum efficiency and gain, and to be applied to the multiplication detection of weak ultraviolet signals.

[0006] The longitudinal cross-sectional width of the silicon carbide pin ultraviolet photodetector with a buried layer structure can be 50 μm to 800 μm; the n+ type substrate can be a commercially available n+ conductive substrate, and the doping concentration of the substrate can be on the order of 10. 18 / cm 3 ~10 19 / cm 3 The thickness can be 50μm to 800μm; the doping concentration of the n-type buffer layer, n-type absorber layer, n-type charge buried layer and p+ type ohmic contact layer can be on the order of 10. 18 / cm 3 ~10 19 / cm 3 10 14 / cm 3 ~10 16 / cm 3 10 17 / cm 3 ~10 18 / cm 3 and 10 18 / cm 3 ~1019 / cm 3 The thickness can be 100nm~1μm, 200nm~5μm, 10nm~200nm, and 100nm~500nm, respectively. The passivation layer on the surface of the p+ type ohmic contact layer can be a wide bandgap passivation isolation dielectric material such as silicon dioxide or hafnium oxide, and the thickness can be 10nm~2μm.

[0007] The method for fabricating the silicon carbide pin ultraviolet photodetector with a buried layer structure includes the following steps:

[0008] 1) Perform RCA standard cleaning on the highly doped silicon carbide n+ type substrate;

[0009] 2) Homoepitaxial growth of a silicon carbide n-type buffer layer on the Si surface of an n+ type substrate;

[0010] 3) Homoeically grow a cylindrical, lightly doped n-type absorber layer on a silicon carbide n-type buffer layer;

[0011] 4) Single or multiple cylindrical silicon carbide n-type charge buried layers are formed on the surface of the n-type absorber layer using deposition, photolithography, etching, ion implantation and high-temperature annealing techniques;

[0012] 5) Continue homoepitaxial growth of a cylindrical, lightly doped n-type absorber layer on the surface of the silicon carbide n-epitaxial layer;

[0013] 6) A cylindrical highly doped p+ type ohmic contact layer is epitaxially grown on a silicon carbide n-type absorber layer;

[0014] 7) A wide bandgap passivation isolation layer, such as silicon dioxide or hafnium oxide, is formed on the surface of the p+ type ohmic contact layer using thermal oxidation and PECVD deposition techniques;

[0015] 8) P+ type annular ohmic contact electrodes and n+ type ohmic contact electrodes were fabricated on the surface of a highly doped p+ type ohmic contact layer and the bottom of an n+ type substrate, respectively, using photolithography, magnetron sputtering and annealing techniques.

[0016] While conventional vertical pin sandwich structure silicon carbide ultraviolet photodetectors can achieve stable responsivity and high response speed for ultraviolet detection, the low doping concentration of the i-layer results in high impedance, leading to an excessively high avalanche breakdown voltage. This makes it difficult to achieve avalanche multiplication mode photodetectors with high quantum efficiency and gain.

[0017] Compared with existing technologies, this invention has the following outstanding advantages: The silicon carbide pin ultraviolet photodetector with a buried layer structure designed in this invention introduces an n-type charge buried layer within the n-type absorption layer. Because the n-type absorption layer has a low doping concentration and high impedance, it leads to a high avalanche breakdown voltage. Introducing a low-impedance n-type charge buried layer within the high-impedance n-type absorption layer modulates the electric field of the n-type absorption layer, enabling the detector to undergo avalanche breakdown at a lower reverse bias voltage, thus better suited for multiplication detection of weak ultraviolet signals. Therefore, the silicon carbide pin ultraviolet photodetector with a buried layer has two operating modes: the first is a low-voltage stable mode, where the detector operates at a low reverse bias voltage, achieving stable responsivity and high response speed in ultraviolet detection; the second is an avalanche multiplication mode, where the detector operates at a lower avalanche breakdown voltage, achieving high quantum efficiency and gain in ultraviolet detection. The silicon carbide pin ultraviolet photodetector with a buried layer structure designed in this invention has a significantly lower avalanche breakdown voltage compared to traditional pin photodetectors, enabling ultraviolet detection in dual operating modes. Compared to traditional avalanche photodetectors, it has a more stable spectral responsivity and faster response speed under low reverse bias, enabling stable ultraviolet detection. Attached Figure Description

[0018] Figure 1 This is a two-dimensional cross-sectional schematic diagram of the silicon carbide pin ultraviolet photodetector with a buried layer structure according to an embodiment of the present invention.

[0019] Figure 2 This is a three-dimensional cross-sectional schematic diagram of the silicon carbide pin ultraviolet photodetector with a buried layer structure according to an embodiment of the present invention.

[0020] Figure 3 The photocurrent curves of the silicon carbide pin ultraviolet photodetector with a buried layer structure and the traditional pin ultraviolet photodetector with a longitudinal sandwich structure described in the embodiments of the present invention are shown. Detailed Implementation

[0021] To make the structure of this invention clearer and easier to understand, the following embodiments will be used to further illustrate this invention in conjunction with the accompanying drawings.

[0022] See Figure 1 and 2 The buried silicon carbide pin ultraviolet photodetector has a commercially available highly doped silicon carbide n+ type substrate (1) from bottom to top. The substrate thickness can be 50 μm to 800 μm, and the doping concentration can be on the order of 10. 18 / cm 3 ~10 19 / cm 3The longitudinal cross-sectional width can be 50μm to 800μm; a homogeneous silicon carbide n-type buffer layer (2) is epitaxially formed on the silicon surface of an n+ type substrate, with a thickness of 100nm to 1μm and a doping concentration on the order of 10. 18 / cm 3 ~10 19 / cm 3 A cylindrical silicon carbide low-doped n-type absorber layer (3) is provided upward from the center of the n-type buffer layer. The thickness can be 200 nm to 5 μm, and the doping concentration can be on the order of 10. 14 / cm 3 ~10 16 / cm 3 In the n-type absorber layer, one or more cylindrical silicon carbide n-type charge buried layers (5) are provided, with a thickness of 10 nm to 200 nm, a cross-sectional width of 25 μm to 400 μm, and a doping concentration on the order of 10. 17 / cm 3 ~10 18 / cm 3 A cylindrical silicon carbide highly doped p+ type ohmic contact layer (4) is provided on the n-type absorber layer. The width can be 50 μm to 800 μm, the thickness can be 100 nm to 500 nm, and the doping concentration can be on the order of 10. 18 / cm 3 ~10 19 / cm 3 A passivation isolation dielectric layer (8) is provided on the p+ type ohmic contact layer. The dielectric layer material can be a wide bandgap passivation material such as silicon dioxide or hafnium oxide, and the thickness can be 10nm to 2μm. A p+ type annular ohmic contact electrode (6) is provided on the upper surface of the p+ type ohmic contact layer, and an n+ type ohmic contact electrode (7) is provided on the back side of the n+ type substrate. The detector n-type absorption layer has an n-type charge buried layer with high impedance. Introducing a low-impedance n-type charge buried layer into the high-impedance n-type absorption layer can modulate the electric field of the n-type absorption layer, so that the detector can undergo avalanche breakdown at a lower voltage.

[0023] The method for fabricating the silicon carbide pin ultraviolet photodetector with a buried layer structure includes the following steps:

[0024] 1) Perform RCA standard cleaning on the highly doped silicon carbide n+ type substrate (1);

[0025] 2) Homoepitaxial growth of silicon carbide n-type buffer layer on the Si surface of n+ type substrate (2);

[0026] 3) Homoeically grow a cylindrical, lightly doped n-type absorber layer on a silicon carbide n-type buffer layer (3);

[0027] 4) Single or multiple cylindrical silicon carbide n-type charge buried layers are formed on the surface of the n-type absorber layer using deposition, photolithography, etching, ion implantation and high temperature annealing techniques (5);

[0028] 5) Continue to grow a cylindrical, lightly doped n-type absorber layer on the surface of the silicon carbide n-epitaxial layer (3);

[0029] 6) A cylindrical highly doped p+ ohmic contact layer is epitaxially grown on the silicon carbide n-type absorber layer (4);

[0030] 7) A wide bandgap passivation isolation layer, such as silicon dioxide or hafnium oxide, is formed on the surface of the p+ type ohmic contact layer using thermal oxidation and PECVD technology (8);

[0031] 8) P+ type annular ohmic contact electrode (6) and n+ type ohmic contact electrode (7) were fabricated on the surface of the highly doped p+ type ohmic contact layer and the bottom of the n+ type substrate, respectively, using photolithography, magnetron sputtering and annealing techniques.

[0032] Specific embodiments are given below.

[0033] 1) Perform RCA standard cleaning on the silicon carbide highly doped n+ type substrate (1) sample, as follows:

[0034] a. Clean with toluene, acetone and ethanol at least twice in sequence, then rinse with deheated and cold deionized water.

[0035] b. Boil in solution No. 3 at 250℃ for 20 minutes, then rinse with hot and cold deionized water. The volume ratio of solution No. 3 is H2SO4∶H2O2=4∶1.

[0036] c. Immerse the sample in diluted hydrofluoric acid (hydrogen fluoride:deionized water = 1:10 by volume) for 3 minutes or more, then rinse with hot and cold deionized water.

[0037] d. Place the sample in solution No. 1 and boil for 10 minutes or more, then rinse with hot and cold deionized water. Solution No. 1 is prepared by volume ratio of NH3·H2O∶H2O2∶H2O=1∶1∶4.

[0038] e. Place the sample in solution No. 2 and boil for 10 minutes or more, then rinse with hot and cold deionized water. Solution No. 1 is prepared by volume ratio of HCl:H2O2:H2O = 1:1:4.

[0039] f. Immerse the sample in diluted hydrofluoric acid (hydrogen fluoride:deionized water = 1:10 by volume) for 3 minutes or more, then rinse with hot and cold deionized water, and dry the substrate with nitrogen gas for later use.

[0040] 2) Homoeic epitaxial growth with a doping concentration on the order of 10 on the (0001) Si surface of a silicon carbide n+ type substrate after RCA standard cleaning was performed. 18 / cm 3 ~10 19 / cm 3 A silicon carbide n-type buffer layer with a thickness of 100 nm to 1 μm (2);

[0041] 3) Homoepitaxial growth with a doping concentration on the order of 10 on the silicon carbide n-type buffer layer. 14 / cm 3 ~10 16 / cm 3 A cylindrical silicon carbide n-type absorber layer with a thickness of 100 nm to 2 μm (3);

[0042] 4) A mask is formed using photolithography, etching, and deposition techniques. Phosphorus ions are then implanted into the n-type absorber layer, and high-temperature annealing is used to activate the phosphorus ions. This forms one or more cylindrical silicon carbide n-type charge buried layers (5) on the surface of the n-type absorber layer. The width can be 25 μm to 400 μm, the thickness can be 10 nm to 200 nm, and the doping concentration can be on the order of 10. 17 / cm 3 ~10 18 / cm 3 ;

[0043] 5) Continue homoepitaxial growth on the surface of the silicon carbide n-epitaxial layer, with a doping concentration on the order of 10. 14 / cm 3 ~10 16 / cm 3 A cylindrical silicon carbide n-type absorber layer with a thickness of 100 nm to 3 μm (3);

[0044] 6) Epitaxial growth of a doping concentration on the order of 10 on the silicon carbide n-type absorber layer. 18 / cm 3 ~10 19 / cm 3 A cylindrical, highly doped p+ type ohmic contact layer with a thickness of 100nm to 500nm;

[0045] 7) The sample was cleaned using RCA standard to remove surface impurities. A layer of oxide was grown on the positive surface of the sample (upper surface of the i-type absorber layer) as a sacrificial layer using alternating dry oxygen, wet oxygen, and dry oxygen oxidation. The sample with the grown sacrificial layer was then etched in buffered hydrofluoric acid to remove the sacrificial layer. A thermally oxidized silicon dioxide passivation isolation layer with a thickness of 10 nm to 60 nm was grown using alternating dry oxygen, wet oxygen, dry oxygen, and nitrogen oxidation. Alternatively, after removing the sacrificial layer, a wide bandgap passivation material such as silicon dioxide or hafnium oxide with a thickness of 10 nm to 2 μm can be grown using PECVD technology (8).

[0046] 8) Photolithography is used to expose and develop the photoresist. Buffered hydrofluoric acid is used to etch the oxide layer on the upper part of the p+ type ohmic contact layer to form an electrode window. A layer of alloy is prepared by magnetron sputtering to form a p+ type ring ohmic contact electrode (6). A layer of photoresist is prepared on the front side of the sample for protection and isolation. Buffered hydrofluoric acid is used to etch the oxide layer on the bottom surface of the substrate. An alloy layer is prepared by magnetron sputtering to form an n+ type ohmic contact electrode (7). The two electrodes are annealed so that the p+ type ring electrode and n+ type electrode of the sample form good ohmic contact with the p+ type ohmic contact layer and the n+ type substrate, respectively.

[0047] Figure 3 The photocurrent curves of the silicon carbide pin ultraviolet photodetector with a buried layer structure described in the embodiments of the present invention and the conventional pin ultraviolet photodetector with a vertical sandwich structure are given. From Figure 3 It can be seen that, compared with traditional pin ultraviolet photodetectors, the breakdown voltage of silicon carbide pin ultraviolet photodetectors with buried layer structure can be reduced by nearly half, while the reduction in photocurrent is less than 5%.

[0048] The detector of this invention features a high-impedance n-type absorption layer. By introducing a low-impedance n-type charge-buried layer into this high-impedance n-type absorption layer, the electric field of the n-type absorption layer can be modulated, allowing the detector to undergo avalanche breakdown at a lower voltage. This detector significantly reduces the avalanche breakdown voltage of traditional silicon carbide pin photodetectors, enabling it to operate in a low-voltage stable mode with stable responsivity and high response speed, while also functioning as an avalanche photodetector at a lower breakdown voltage, achieving higher quantum efficiency and gain, and thus being applied to the multiplication detection of weak ultraviolet signals.

[0049] The above embodiments are merely preferred embodiments of the present invention and should not be considered as limiting the scope of the present invention. All equivalent variations and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A silicon carbide pin ultraviolet photodetector with a buried layer structure, characterized in that... The structure consists of a silicon carbide heavily doped n+ type substrate from bottom to top. A homogeneous silicon carbide n-type buffer layer is epitaxially formed on the silicon surface of the n+ type substrate. A cylindrical silicon carbide lightly doped n-type absorber layer is formed upward from the center of the n-type buffer layer. Multiple cylindrical silicon carbide n-type charge buried layers are formed in the n-type absorber layer for modulating the electric field. A silicon carbide heavily doped p+ type ohmic contact layer is formed on the n-type absorber layer for collecting photogenerated carriers. A silicon dioxide passivation isolation layer is formed on the p+ type ohmic contact layer. A p+ type annular ohmic contact electrode is formed on the upper surface of the p+ type ohmic contact layer. An n+ type ohmic contact electrode is formed on the back side of the n+ type substrate. The detector has multiple n-type charge buried layers in its n-type absorption layer. These multiple n-type charge buried layers are distributed in a combination of longitudinal and transverse directions. The n-type absorption layer has high impedance. By introducing low-impedance n-type charge buried layers into the high-impedance n-type absorption layer, the electric field of the n-type absorption layer is modulated, so that the detector can undergo avalanche breakdown under a lower reverse bias voltage, which is used for multiplication detection of weak ultraviolet signals. The n-type buried charge layer has a width of 25 μm to 400 μm, a thickness of 10 nm to 200 nm, and a doping concentration on the order of 10. 17 / cm 3 ~10 18 / cm 3 .

2. The silicon carbide pin ultraviolet photodetector with a buried layer structure as described in claim 1, characterized in that... The p+ type ohmic contact layer has a width of 50 μm to 800 μm, a thickness of 100 nm to 500 nm, and a doping concentration on the order of 10. 18 / cm 3 ~10 19 / cm 3 .

3. The silicon carbide pin ultraviolet photodetector with a buried layer structure as described in claim 1, characterized in that... The thickness of the silicon dioxide passivation isolation layer is 10 nm to 2 μm.

4. The silicon carbide pin ultraviolet photodetector with a buried layer structure as described in claim 1, characterized in that... The material of the silicon dioxide passivation isolation layer is replaced with a wide bandgap passivation isolation material.

5. The silicon carbide pin ultraviolet photodetector with a buried layer structure as described in claim 4, characterized in that... The wide bandgap passivation isolation material is hafnium oxide.

6. The silicon carbide pin ultraviolet photodetector with a buried layer structure as described in claim 1, characterized in that... The thickness and doping concentration of the n+ type substrate are on the order of 50 μm to 800 μm and 10 μm, respectively. 18 / cm 3 ~10 19 / cm 3 The thickness and doping concentration of the n-type buffer layer are on the order of 100 nm to 1 μm and 10, respectively. 18 / cm 3 ~10 19 / cm 3 The thickness and doping concentration of the n-type absorber layer are on the order of 200 nm to 5 μm and 10 μm, respectively. 14 / cm 3 ~10 16 / cm 3 .

7. The method for fabricating a silicon carbide pin ultraviolet photodetector with a buried layer structure as described in any one of claims 1 to 6, characterized in that... Includes the following steps: 1) Perform RCA standard cleaning on the highly doped silicon carbide n+ type substrate; 2) Homoepitaxial growth of a silicon carbide n-type buffer layer on the Si surface of an n+ type substrate; 3) Homoeically grow a cylindrical, lightly doped n-type absorber layer on a silicon carbide n-type buffer layer; 4) Multiple cylindrical silicon carbide n-type charge buried layers are formed on the surface of the n-type absorber layer using deposition, photolithography, etching, ion implantation and high-temperature annealing techniques; 5) Continue homoepitaxial growth of a cylindrical, lightly doped n-type absorber layer on the surface of the silicon carbide n-epitaxial layer; 6) Epitaxially grow a cylindrical highly doped p+ type ohmic contact layer on a silicon carbide n-type absorber layer; 7) A silicon dioxide or hafnium oxide wide bandgap passivation isolation layer is formed on the surface of the p+ type ohmic contact layer using thermal oxidation and PECVD technology; 8) P+ type annular ohmic contact electrodes and n+ type ohmic contact electrodes were fabricated on the surface of a highly doped p+ type ohmic contact layer and the back side of an n+ type substrate, respectively, using photolithography, magnetron sputtering and annealing techniques.

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