A PN junction CZT detector with one ohmic and one Schottky side and its fabrication method

Abstract

This invention discloses a PN junction-type CZT detector with one ohmic and one Schottky contact and its fabrication method, relating to the field of semiconductor technology. The detector includes a detector body, a cathode, and an anode. The upper surface of the detector body serves as the anode, which is an Au / In composite electrode. The lower surface of the detector body serves as the cathode, which is an Au / Cr composite electrode. In this invention, the detector uses a Schottky contact on one side and an ohmic contact on the other. The anode acts as a collecting electrode, forming a Schottky contact that creates a downwardly bent potential barrier to resist hole injection and reduce leakage current. The cathode acts as a voltage-applying electrode, forming an ohmic contact. In this structure, a negative voltage is applied to the cathode. Ideally, the bias voltage is applied directly to the p-n junction, i.e., the Schottky contact, through the ohmic junction. As the potential barrier gradually decreases, the voltage is gradually applied to the bulk resistance, which begins to deplete downwards from the junction until it is completely depleted.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, specifically to a PN junction-type CZT detector with one side ohmic and the other side Schottky, and its fabrication method. Background Technology

[0002] Cadmium zinc telluride (CdZnTe, CZT) is an emerging semiconductor detector material with a high average atomic number. When detecting X-rays and gamma rays, CZT exhibits a large photoelectric absorption cross-section when interacting with the radiation. As the radiation passes through the crystal, more energy is deposited into the CZT crystal, generating an electrical signal through the photoelectric effect. Compared to Si (Z=14) crystals, CZT has a higher average atomic number, resulting in higher detection efficiency for CZT detectors. Compared to Ge, CZT crystals have a larger bandgap, higher resistivity, and do not require a cooling system. They can achieve low leakage current and high energy resolution at room temperature, making CZT detectors more promising for various applications. Furthermore, CZT detectors can be made very small, offering good spatial resolution and ease of use. Given these advantages, CZT detectors are widely used in defense security detection, medical diagnostics, industrial flaw detection, and aerospace astronomical observation.

[0003] Although CZT detectors have advantages such as high energy resolution, high spatial resolution, and room temperature operation capability, they still have problems such as poor hole transport performance and crystal defects, which cause their leakage current, breakdown voltage, anti-polarization and resolution to fail to meet relevant application requirements.

[0004] Therefore, providing a CZT detector with low leakage current, high breakdown voltage, anti-polarization and high energy resolution is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a PN junction CZT detector with low leakage current, high breakdown voltage, anti-polarization, and high energy resolution, featuring an ohmic contact on one side and a Schottky contact on the other, along with its fabrication method. The PN junction detector of this invention employs a Schottky contact on one side and an ohmic contact on the other. The anode serves as the collecting electrode, forming a Schottky contact that creates a downward-bending potential barrier to resist hole injection and reduce leakage current. The cathode serves as the voltage-applying electrode, forming an ohmic contact. In this structure, a negative voltage is applied at the cathode. Ideally, the bias voltage is applied directly to the PN junction, i.e., the Schottky contact, through the ohmic junction. As the potential barrier gradually decreases, the voltage is gradually applied to the bulk resistance, which begins to deplete downwards from the junction until it is completely depleted.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A PN junction CZT detector with one ohmic and one Schottky side includes a detector body, a cathode and an anode;

[0008] The upper surface of the detector body is the anode, which is an Au / In composite electrode that forms a Schottky contact with the CZT substrate to collect charge signals.

[0009] The lower surface of the detector body is the cathode, which is an Au / Cr composite electrode that forms an ohmic contact with the CZT substrate and applies a negative bias voltage.

[0010] In the detector structure of this invention, In forms a Schottky contact with the detector body that bends downwards due to the potential barrier, and Cr forms an ohmic contact with the detector body. A negative voltage is applied to the cathode, and the bias voltage is applied directly to the pn junction (Schottky contact) through the ohmic junction. As the potential barrier decreases, the voltage is gradually applied to the bulk resistance, and the depletion region extends downwards from the junction until it is completely depleted. The ohmic contact carries a larger voltage, which improves the charge collection efficiency.

[0011] Preferably, the detector body is a cuboid, made of cadmium zinc telluride material, and has a resistivity greater than 10⁻⁶. 9 Ω·cm;

[0012] The upper and lower surfaces are square with a side length of 0.1-0.5 mm;

[0013] The height of the cuboid is 0.2-2mm.

[0014] Preferably, the anode is a square planar electrode with a side length of 0.1-0.5 mm;

[0015] The anode consists of an In layer and a first Au contact layer from bottom to top. The In layer has a thickness of 100-200 nm, and the first Au contact layer has a thickness of 50-100 nm.

[0016] Preferably, the cathode is a square planar electrode with a side length of 0.1-0.5 mm;

[0017] The cathode consists of a second Au contact layer and a Cr layer from bottom to top. The thickness of the Cr layer is 5-20 nm, and the thickness of the second Au contact layer is 50-100 nm.

[0018] The fabrication method of the PN junction CZT detector with one ohmic and one Schottky side as described above includes the following steps:

[0019] (1) After depositing an In layer on the upper surface of the detector body using electron beam evaporation or sputtering technology, heat treatment is performed, followed by deposition of the first Au contact layer, and the anode is obtained after heat preservation.

[0020] (2) After depositing the Cr layer and the second Au contact layer on the lower surface of the detector body obtained in step (1) by electron beam evaporation or sputtering, the cathode is obtained by heat treatment.

[0021] Preferably, the heat treatment conditions in step (1) are: annealing in a vacuum environment at 80-120°C for 1-2 minutes to allow In to diffuse and form n. + Heavily doped layer;

[0022] The insulation conditions are: low temperature insulation at 50-60℃ for 10-15 minutes.

[0023] Preferably, the heat treatment conditions in step (2) are: heat treatment in a vacuum environment at 80-180°C for 30-60 minutes, and then take out the wafer after it has cooled naturally for 30-90 minutes.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The detector of the present invention adopts a composite electrode design with one side being a Schottky contact and the other side being an Ohmic contact. The Schottky contact is composed of an In-Au electrode, and In diffuses to form n + The heavily doped layer forms a pn junction with the p-type substrate, effectively blocking hole injection and reducing leakage current, thereby improving energy resolution; the ohmic contact is composed of Cr-Au electrodes, and Cr easily forms a low-resistance, high-thermal-stability ohmic contact with CZT.

[0026] (2) The detector of the present invention forms an ohmic junction between the cathode and the P-type substrate through Cr, which prevents hole polarization and can carry higher voltage, significantly improving the breakdown voltage and charge collection efficiency.

[0027] (3) The detector of the present invention adopts a planar electrode design, which simplifies the process and reduces the manufacturing cost; the gold-plated protective layer has stable chemical properties, reduces electrode surface corrosion, and ensures long-term reliability of electrical conductivity; when a negative voltage is applied to the cathode, the bias voltage is directly applied to the pn junction through the ohmic junction, and the depletion region gradually expands from the junction to complete depletion, thus optimizing the electric field distribution and charge collection performance.

[0028] (4) The detector of the present invention has the advantages of low leakage current, high breakdown voltage, anti-polarization and high energy resolution, and is suitable for fields such as nuclear radiation detection, medical imaging and space exploration. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings in this description are merely embodiments of the present invention.

[0030] Figure 1 A two-dimensional cross-sectional view of the detector structure is provided for this invention;

[0031] Figure 2 The image shows the test data of the detector leakage current prepared in Embodiment 1 of the present invention. Detailed Implementation

[0032] Embodiments of the present invention are described below, examples of which are shown in the accompanying drawings. The embodiments described with reference to the drawings are exemplary and intended to explain the present invention, but are not to be construed as limiting the present invention.

[0033] Example 1

[0034] like Figure 1 The present invention provides a PN junction type CZT detector with one side ohmic and the other side Schottky, comprising a P-type CZT substrate 3 (resistivity 1e9-1e11), a cathode and an anode;

[0035] The upper surface of the CZT substrate 3 is the anode, which is an Au / In composite electrode that forms a Schottky contact with the CZT substrate to collect charge signals; the anode is a square planar electrode with a side length of 0.5 mm.

[0036] The lower surface of the CZT substrate 3 is the cathode, which is an Au / Cr composite electrode that forms an ohmic contact with the CZT substrate and applies a negative bias voltage; the cathode is a square planar electrode with a side length of 0.5 mm;

[0037] The CZT substrate 3 is a cuboid with a square upper and lower surface. The square has a side length of 0.5 mm and a thickness of 2 mm.

[0038] The anode consists of an In layer 2 and a first Au contact layer 1 from bottom to top. The In layer 2 has a thickness of 150 nm, and the first Au contact layer 1 has a thickness of 100 nm. In is diffused to form the inductance layer. + The heavily doped layer forms a pn junction with the p-type substrate, effectively blocking hole injection and reducing leakage current, thereby improving energy resolution;

[0039] The cathode consists of a second Au contact layer 5 and a Cr layer 4 from bottom to top. The thickness of the Cr layer 4 is 5 nm, and the thickness of the second Au contact layer 5 is 50 nm.

[0040] The preparation method specifically includes the following steps:

[0041] (1) After depositing an In layer on the upper surface of the CZT substrate using electron beam evaporation, the substrate was annealed in a vacuum environment at 100°C for 2 min, and then the first Au contact layer was deposited. The anode was obtained by holding the substrate at 60°C for 15 min.

[0042] (2) After depositing the Cr layer and the second Au contact layer on the lower surface of the detector body obtained in step (1) by electron beam evaporation, keep it at 150°C in a vacuum environment for 30 minutes, and take it out after the wafer has cooled naturally for 60 minutes to obtain the cathode.

[0043] Figure 2 The leakage current test data of the CZT detector prepared for this embodiment clearly shows that the leakage current at the Schottky contact is about one order of magnitude lower than that at the ohmic contact. The leakage current is even lower, and there is no breakdown when the voltage is applied at 300V, indicating that it is more resistant to high voltage. When the detector of this invention is working, only a negative voltage needs to be applied to the cathode. The ohmic contact does not block the injection of electrons from the cathode, and can effectively recombine the positive charge accumulated in the cathode region, thereby suppressing the polarization effect. The Schottky contact has a lower leakage current due to the presence of the potential barrier.

[0044] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A PN junction CZT detector with one ohmic and one Schottky side, characterized in that, It includes a detector body, a cathode, and an anode; the detector body is made of cadmium zinc telluride. The upper surface of the detector body is the anode, and the anode is an Au / In composite electrode; The lower surface of the detector body is the cathode, and the cathode is an Au / Cr composite electrode; The anode is a square planar electrode with a side length of 0.1-0.5 mm; the anode consists of an In layer and a first Au contact layer from bottom to top, the In layer has a thickness of 100-200 nm, and the first Au contact layer has a thickness of 50-100 nm. The cathode is a square planar electrode with a side length of 0.1-0.5 mm; the cathode consists of a second Au contact layer and a Cr layer from bottom to top, the thickness of the Cr layer is 5-20 nm, and the thickness of the second Au contact layer is 50-100 nm. The Au / In composite electrode diffuses In to form n + The heavily doped layer forms a pn junction with the p-type substrate, forming a Schottky contact, and the Au / Cr composite electrode forms an ohmic contact with the detector body.

2. The PN junction CZT detector with one ohmic and one Schottky side as described in claim 1, characterized in that, The detector body is a cuboid with a resistivity greater than 10⁻⁶. 9 Ω·cm; The upper and lower surfaces are square with a side length of 0.1-0.5 mm; The height of the cuboid is 0.2-2mm.

3. The method for fabricating a PN junction CZT detector with one ohmic and one Schottky side as described in claim 1 or 2, characterized in that, Includes the following steps: (1) After depositing an In layer on the upper surface of the detector body using electron beam evaporation or sputtering technology, heat treatment is performed, followed by deposition of the first Au contact layer, and the anode is obtained after heat preservation. (2) After depositing the Cr layer and the second Au contact layer on the lower surface of the detector body obtained in step (1) by electron beam evaporation or sputtering, the cathode is obtained by heat treatment.

4. The method for fabricating a PN junction CZT detector with one ohmic and one Schottky side according to claim 3, characterized in that, The heat treatment conditions described in step (1) are: annealing in a vacuum environment at 80-120℃ for 1-2 minutes; The insulation conditions are: low temperature insulation at 50-60℃ for 10-15 minutes.

5. The method for fabricating a PN junction CZT detector with one ohmic and one Schottky side according to claim 3, characterized in that, The heat treatment conditions in step (2) are: heat treatment in a vacuum environment of 80-180℃ for 30-60 minutes, and take out the wafer after it has cooled naturally for 30-90 minutes.

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