PN junction type CZT detector with one ohmic surface and one Schottky surface and preparation method of PN junction type CZT detector

Abstract

The invention discloses a PN junction type CZT detector with one ohmic surface and one Schottky surface and a preparation method thereof, and relates to the technical field of semiconductors, and the detector comprises a detector main body, a cathode and an anode. Wherein the upper surface of the detector main body is the anode, and the anode is an Au / In composite electrode; the cathode is arranged on the lower surface of the detector main body, and the cathode is an Au / Cr composite electrode. One side of the detector adopts Schottky contact, the other side of the detector adopts ohmic contact, the anode serves as a collecting electrode to form Schottky contact, a potential barrier bent downwards is formed, hole injection is resisted, and leakage current is reduced; the cathode serves as a pressing electrode to form ohmic contact; according to the structure, a negative voltage is applied to a cathode, under an ideal condition, a bias voltage is directly applied to a p-n junction, namely a Schottky contact, through an ohmic junction, and along with gradual reduction of a potential barrier, the voltage is gradually applied to a bulk resistor, and the bulk resistor is downwards exhausted from the junction until the bulk resistor is completely exhausted.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and particularly relates to a PN junction type CZT detector with one ohmic side and one Schottky side and a preparation method thereof. Background Art

[0002] Cadmium zinc telluride (CdZnTe, CZT) is a new type of semiconductor detector material with a relatively high average atomic number. When detecting X / γ rays, the CZT material has a relatively large photoabsorption cross-section when interacting with rays. When the rays pass through the crystal, more energy is deposited into the CZT crystal, and electrical signals are generated through the photoelectric effect. Compared with Si (Z = 14) crystals, the CZT material has a higher average atomic number, which also makes the CZT detector have a higher detection efficiency; compared with Ge materials, the CZT crystal has a relatively large bandgap width, high resistivity and does not require the assistance of a refrigeration system, and can obtain a low level of leakage current and a relatively high energy resolution under normal temperature conditions, making the CZT detector have a broader application prospect. In addition, the CZT detector can be made very small, has a good spatial resolution, and is more convenient to use. Due to these advantages, CZT detectors are widely used in fields such as national defense security detection, medical diagnosis, industrial flaw detection, and aerospace astronomical observation.

[0003] Although CZT detectors have advantages such as high energy resolution, high spatial resolution, and the ability to work at room temperature, there are still problems such as poor hole transport performance and crystal defect problems, resulting in leakage current, breakdown voltage, anti-polarization, and resolution not meeting the relevant usage 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] In order to solve the above problems, the present invention provides a PN junction type CZT detector with one ohmic side and one Schottky side and a preparation method thereof, which has low leakage current, high breakdown voltage, anti-polarization, and high energy resolution. One side of the PN junction detector of the present invention uses Schottky contact, and the other side uses ohmic contact. The anode forms a Schottky contact as the collecting electrode, forming a downward-bending potential barrier to resist hole injection and reduce leakage current; the cathode forms an ohmic contact as the pressure-applying electrode; a negative voltage is applied at the cathode. Ideally, the bias voltage is directly applied to the p-n junction, that is, the Schottky contact, through the ohmic junction. As the potential barrier gradually decreases, the voltage is gradually applied to the bulk resistance and starts to deplete downward from the junction until it is completely depleted.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

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

[0008] Wherein, the upper surface of the detector body is the anode, and the anode is an Au / In composite electrode, forming a Schottky contact with the CZT substrate to collect charge signals;

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

[0010] In the detector structure of the present invention, In forms a Schottky contact with a downward - bent potential barrier with the detector body, Cr forms an ohmic contact with the detector body, a negative voltage is applied at the cathode, the bias voltage is directly applied to the p - n junction (at the Schottky contact) through the ohmic junction. As the potential barrier decreases, the voltage is gradually applied to the bulk resistance, and the depletion region expands downward from the junction until it is completely depleted. A larger voltage is borne at the ohmic contact, improving the charge collection efficiency.

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

[0012] The upper surface and the lower surface are squares with side lengths of 0.1 - 0.5 mm;

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

[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 thickness of the In layer is 100 - 200 nm, and the thickness of the first Au contact layer is 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] According to the above - mentioned preparation method of a PN - junction type CZT detector with one ohmic side and one Schottky side, the following steps are included:

[0019] (1) Deposit an In layer on the upper surface of the detector body using electron beam evaporation or sputtering technology and then perform heat treatment, and then deposit the first Au contact layer. After heat preservation, the anode is obtained;

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

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

[0022] The conditions for heat preservation are: low-temperature heat preservation at 50 - 60 °C for 10 - 15 min.

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

[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 a Schottky contact on one side and an ohmic contact on the other side. Among them, the Schottky contact is composed of an In-Au electrode, and In diffuses to form an n + heavily doped layer, forming a p-n junction with the P-type substrate, effectively blocking hole injection and reducing leakage current, thereby improving energy resolution; the ohmic contact is composed of a Cr-Au electrode, and Cr is easy to form a low-resistance and high-thermal-stability ohmic contact with CZT;

[0026] (2) In the detector of the present invention, an ohmic junction is formed between Cr and the P-type substrate at the cathode, preventing hole polarization and being able to bear a higher voltage, significantly improving the breakdown voltage and charge collection efficiency;

[0027] (3) The detector of the present invention adopts a planar electrode design, simplifies the process difficulty, and reduces the manufacturing cost; the gold-plated protective layer has stable chemical properties, reduces the corrosion of the electrode surface, and ensures the long-term reliability of electrical conductivity; when a negative voltage is applied to the cathode in this structure, the bias voltage is directly applied to the p-n junction through the ohmic junction, and the depletion region gradually expands from the junction to complete depletion, 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, high energy resolution, etc., and is suitable for fields such as nuclear radiation detection, medical imaging, and space detection. Description of the Drawings

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. The drawings in this description are only the embodiments of the present invention.

[0030] Figure 1 This is a two-dimensional cross-sectional view of the structure of the detector proposed by the present invention;

[0031] Figure 2 This is a test data graph of the leakage current of the detector prepared in Example 1 of the present invention. Specific embodiments

[0032] The following describes embodiments of the present invention. Examples of the embodiments are shown in the accompanying drawings. The embodiments described with reference to the accompanying drawings are exemplary and are intended to explain the present invention, rather than being construed as a limitation of the present invention.

[0033] Example 1

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

[0035] Among them, the upper surface of the CZT substrate 3 is the anode, and the anode is an Au / In composite electrode, forming 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, and the cathode is an Au / Cr composite electrode, forming an ohmic contact with the CZT substrate to apply 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 the upper and lower surfaces being squares, the side length of the square being 0.5 mm, and the thickness being 2 mm;

[0038] The anode consists of an In layer 2 and a first Au contact layer 1 from bottom to top. The thickness of the In layer 2 is 150 nm, and the thickness of the first Au contact layer 1 is 100 nm. An n + heavily doped layer is formed by In diffusion, forming a p-n 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) Deposit an In layer on the upper surface of the CZT substrate using electron beam evaporation technology, anneal it in a vacuum environment at 100 °C for 2 min, then deposit the first Au contact layer, and keep it at a low temperature of 60 °C for 15 min to obtain the anode;

[0042] (2) After sequentially depositing a Cr layer and a second Au contact layer on the lower surface of the detector body obtained in step (1) by electron beam evaporation technology, keep it in a vacuum environment at 150 °C for 30 min, take it out after the wafer naturally cools for 60 min, and the cathode can be obtained;

[0043] Figure 2 This is the leakage current test data graph of the CZT detector prepared in this embodiment. It can be clearly seen 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 lower, and there is no breakdown phenomenon when the voltage is applied at 300 V, and it is more resistant to high voltage; when the detector of the present invention works, a negative voltage is applied to the cathode, and the ohmic contact will not block the injection of electrons from the cathode, and can effectively recombine the positive charges accumulated in the cathode region, thereby suppressing the polarization effect. The Schottky contact has a lower leakage current due to the existence of the potential barrier.

[0044] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A PN junction type CZT detector with one ohmic side and one Schottky side, characterized in that, It includes a detector body, a cathode and an anode; Among them, 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.

2. The PN junction type CZT detector with one ohmic side and one Schottky side according to claim 1, characterized in that, The detector body is a cuboid, made of cadmium zinc telluride, with a resistivity greater than 10 9 Ω·cm; The upper surface and the lower surface are square, and the side length is 0.1 - 0.5 mm; The height of the cuboid is 0.2 - 2 mm.

3. The PN junction type CZT detector with one ohmic side and one Schottky side according to claim 1, wherein, The anode is a square planar electrode, and the side length is 0.1 - 0.5 mm; The anode consists of an In layer and a first Au contact layer from bottom to top. The thickness of the In layer is 100 - 200 nm, and the thickness of the first Au contact layer is 50 - 100 nm.

4. The PN junction type CZT detector with one ohmic side and one Schottky side according to claim 1, wherein The cathode is a square planar electrode, and the side length is 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.

5. The preparation method of a PN junction type CZT detector with one ohmic side and one Schottky side according to any one of claims 1-4, characterized in that, It includes the following steps: (1) Deposit an In layer on the upper surface of the detector body using electron beam evaporation or sputtering technology and then perform heat treatment, and then deposit the first Au contact layer. After heat preservation, the anode is obtained; (2) Deposit a Cr layer and a second Au contact layer on the lower surface of the detector body obtained in step (1) in sequence using electron beam evaporation or sputtering technology, and then perform heat treatment to obtain the cathode.

6. The preparation method of a PN junction type CZT detector with one ohmic side and one Schottky side according to claim 5, characterized in that, The conditions for the heat treatment in step (1) are: annealing in a vacuum environment at 80 - 120 °C for 1 - 2 min; The conditions for the heat preservation are: low-temperature heat preservation at 50 - 60 °C for 10 - 15 min.

7. The preparation method of a PN junction type CZT detector with one ohmic side and one Schottky side according to claim 5, characterized in that, The conditions for the heat treatment in step (2) are: heat preservation in a vacuum environment at 80 - 180 °C for 30 - 60 min, and take it out after the wafer naturally cools for 30 - 90 min.

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