Photoconductive material, method for producing the same, and terahertz wave generator

Abstract

The application provides a photoconductive material and a preparation method thereof and a terahertz wave generator, and belongs to the technical field of photoelectricity. The photoconductive material comprises a substrate, a buffer layer covering the upper surface of the substrate, and a doped layer covering the upper surface of the buffer layer, wherein the doped layer comprises multiple groups of alternating layers formed by alternating doped CdTe:In layers and doped InSb:Be layers, and the doped CdTe:In layer covers the upper surface of the buffer layer. The application uses the aforementioned doped layer to use a fiber laser emitter with a wider wavelength as an excitation source, and the effective mass of the aforementioned doped layer is smaller and the mobility is higher, so that the power of a subsequent integrated device can be improved.

Description

Technical Field

[0001] The present invention relates to the field of optoelectronic technology, and in particular to a photoconductive material and a preparation method thereof, and a terahertz wave generator. Background Art

[0002] Due to their unique properties, terahertz waves have important applications in time-resolved measurement, materials science, biomedicine, safety testing, and other fields. Photoconductive materials are crucial for the fabrication of terahertz devices. These materials must possess short carrier lifetimes, high mobility, and high resistivity, enabling devices to achieve higher frequencies, stronger radiation intensity, and higher breakdown voltages.

[0003] Currently used photoconductive materials mainly include semi-insulating gallium arsenide (GaAs), etc. However, the excitation wavelength of semi-insulating GaAs is short, and sapphire lasers are expensive and difficult to integrate.

[0004] Therefore, it is necessary to find a new photoconductive material with higher performance. Summary of the Invention

[0005] In view of this, in order to at least partially solve the above-mentioned technical problems, the present invention provides a photoconductive material and a preparation method thereof, and a terahertz wave generator.

[0006] According to an embodiment of one aspect of the present invention, a photoconductive material is provided, comprising: a substrate; a buffer layer covering the upper surface of the substrate; a doping layer covering the upper surface of the buffer layer, comprising a plurality of alternating layers formed by alternating doped CdTe:In layers and doped InSb:Be layers; the doped CdTe:In layer covering the upper surface of the buffer layer.

[0007] In some embodiments, the substrate is GaAs or InP.

[0008] In some embodiments, the thickness of the doped CdTe:In layer in each set of alternating layers is 0.5-8 nm; the thickness of the doped InSb:Be layer is 6-16 nm.

[0009] In some embodiments, the thickness of the doped CdTe:In layer in each set of alternating layers is 1-3 nm, and the thickness of the doped InSb:Be layer is 10-14 nm.

[0010] In some embodiments, the number of alternating layers in the multiple groups of alternating layers is 30-120.

[0011] In some embodiments, in the doped layer, the total thickness of the plurality of doped InSb:Be layers is ≥0.8 μm.

[0012] In some embodiments, the buffer layer is an InSb buffer layer, and the thickness of the InSb buffer layer is 30-80 nm.

[0013] According to another embodiment of the present invention, a terahertz wave generator is provided, in which the aforementioned photoconductive material is used as a photoconductive material layer in a photoconductive antenna.

[0014] According to another aspect of the embodiments of the present invention, a method for preparing a photoconductive material is provided, comprising: growing a buffer layer on a substrate by vapor phase epitaxy; growing a doped CdTe:In layer on the buffer layer by vapor phase epitaxy, and growing a doped InSb:Be layer on the doped CdTe:In layer, wherein alternating layers consisting of a doped CdTe:In layer and a doped InSb:Be layer constitute a group, and multiple groups of alternating layers are located on the buffer layer to form doped layers, thereby forming a photoconductive material.

[0015] In some embodiments, the temperature for growing the buffer layer is 280-320° C.; the temperature for growing the doping layer is 300-340° C.

[0016] In some embodiments, the Te / Cd beam ratio used in growing the doped CdTe:In layer is 3-7, and the In doping concentration is 1E16-5E17 cm -3 .

[0017] In some embodiments, the Sb / In beam ratio used in growing the doped InSb:Be layer is 8-15, and the Be doping concentration is 1E16-4E16 cm -3 .

[0018] According to the photoconductive material of the embodiment of the present invention, the InSb in the doping layer used in the present invention has a relatively small bandgap, which can be adapted for use as an excitation source for a 1.3-1.55 μm fiber exciter, helping to reduce the cost of subsequent device adaptation. The addition of beryllium (Be) to InSb can increase the resistivity of the photoconductive material. CdTe, on the other hand, has a large bandgap and does not absorb the light emitted by the aforementioned fiber laser, further increasing the overall resistivity of the photoconductive material. At the same time, the addition of In to CdTe can generate electron traps in the CdTe material, reducing the carrier lifetime and improving the frequency characteristics of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above and other objects, features and advantages of the present invention will become more apparent from the following description of the embodiments of the present invention with reference to the accompanying drawings.

[0020] Figure 1 A schematic structural diagram of a photoconductive material according to an embodiment of the present invention is shown;

[0021] Figure 2A schematic diagram showing alternating layers of photoconductive material according to an embodiment of the present invention;

[0022] Figure 3 A flow chart showing a method for preparing a photoconductive material according to an embodiment of the present invention is shown.

[0023] In the accompanying drawings, the meanings of the reference numerals are as follows:

[0024] 1. Substrate;

[0025] 2. Buffer layer;

[0026] 3. Doping layer;

[0027] 31. Doped CdTe: In layer;

[0028] 32. Doped InSb:Be layer. DETAILED DESCRIPTION

[0029] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present invention. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of embodiments of the present invention. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of the concept of the present invention.

[0030] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. The term "comprising" used herein indicates the existence of features, steps, operations, but does not exclude the existence or addition of one or more other features.

[0031] When expressions such as "at least one of A, B or C, etc." are used, they should generally be interpreted in accordance with the meaning commonly understood by those skilled in the art (for example, "a system having at least one of A, B or C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.).

[0032] In addition to semi-insulating GaAs, the commonly used photoconductive materials suitable for terahertz wave generators currently include low-temperature GaAs materials and low-temperature InGaAs materials. Low-temperature GaAs materials mainly refer to GaAs materials with a growth temperature of 200~300℃, and low-temperature InGaAs materials mainly refer to InGaAs materials with a growth temperature of 350~380℃. Although low-temperature GaAs materials have improved the resistivity to a certain extent, due to the large bandgap of GaAs itself, a sapphire laser with a wavelength of about 800nm ​​is required as an excitation source. This sapphire laser is expensive and not conducive to the subsequent integration of terahertz devices. Although the bandgap of low-temperature InGaAs materials is small, the 1.3-1.55μm fiber laser commonly used in communications can be used as an excitation source, which can reduce the cost of the device to a certain extent and reduce the difficulty of integration. However, there is still the problem of insufficient mobility.

[0033] In the process of realizing the concept of the present invention, it was discovered that by covering the buffer layer with alternating doped layers of doped CdTe:In layers and doped InSb:Be layers, the InSb material in the doped InSb:Be layer has a smaller bandgap width, which can be adapted to a 1.3~1.55μm fiber exciter as an excitation source, helping to reduce the cost of subsequent devices. The CdTe material in the doped CdTe:In layer has a large bandgap width and does not absorb the light emitted by the aforementioned excitation source, which helps to increase the resistivity of the photoconductive material. Incorporating Be into the InSb material can further increase the resistivity, and incorporating In into the CdTe material can reduce the carrier lifetime, thereby improving device performance.

[0034] Specifically, according to an embodiment of one aspect of the present invention, a photoconductive material is provided. Figure 1 FIG. 1 shows a schematic structural diagram of a photoconductive material according to an embodiment of the present invention. Figure 1 As shown, the photoconductive material of the present invention includes: a substrate 1, a buffer layer 2 and a doping layer 3.

[0035] The substrate 1 provides mechanical support and high thermal stability. The buffer layer 2 serves as a transition layer with a significant lattice difference between the substrate 1 and the doped layer 3. The buffer layer 2 covers the upper surface of the substrate 1 and also provides good surface flatness, providing a smooth growth foundation for the doped layer 3 thereon. The doped layer 3 covers the upper surface of the buffer layer 2 and comprises multiple alternating layers formed by doped CdTe:In layers 31 and doped InSb:Be layers 32. The doped CdTe:In layers 31 cover the upper surface of the buffer layer 2.

[0036] It can be understood that InSb and CdTe are semiconductors with different band gaps, where the band gap width of InSb is approximately 0.17 eV and the band gap width of CdTe is approximately 1.5 eV. InSb has a high electron mobility, so the electrons photogenerated or injected in the doped InSb:Be layer 32 can move at a very high speed. The band gap width of the low-temperature InGaAs material commonly used in related art is 0.75 eV, and the energy required to excite the photogenerated carriers in the InSb in the doped layer 3 of the present invention is lower, which ensures that InSb can also use a 1.3-1.55 μm fiber laser (low cost and easy to integrate devices) as an excitation source. CdTe corresponds to a minimum excitation wavelength of 794 nm, so it does not absorb the light of the fiber laser. CdTe only acts as an additional electron trap layer, which helps to reduce the electron lifetime.

[0037] According to embodiments of the present invention, the alternating structure formed by two semiconductor materials with different band gap widths helps enhance photogenerated carrier generation and improve carrier mobility. Furthermore, doping InSb with Be can correct the intrinsic n-type nature of InSb, thereby increasing the resistivity of the photoconductive material. Simultaneously, doping CdTe with In can create deep-level electron traps in the CdTe, significantly shortening the lifetime of photogenerated carriers and improving the device's frequency characteristics, thereby increasing the on / off ratio.

[0038] It should be noted that the lattice constants of InSb and CdTe are nearly identical. Therefore, relaxation does not occur between the multiple alternating layers of the doped layer 3 of the present invention until the required light absorption thickness is met. Furthermore, the high-quality doped InSb:Be layer 32 and the doped CdTe:In layer 31 are grown at similar temperatures, achieving both good doping effects and a high-quality doped layer 3.

[0039] In some embodiments, substrate 1 is GaAs or InP. GaAs is high quality and relatively stable, making it suitable for large-scale production. InP has higher electron mobility and better thermal conductivity than GaAs, but is also relatively more expensive. Both GaAs and InP are high-quality, low-defect-density single-crystalline substrates. After being covered with a buffer layer 2, a doped layer 3 with high crystal quality, low interface states, and low defect density can be subsequently formed.

[0040] In some embodiments, the buffer layer 2 is an InSb buffer layer. Based on the lattice mismatch between the substrate 1 and the doped layer 3 (also understood as an epitaxial layer), the InSb buffer layer is first grown on the substrate 1 to form a surface that matches the InSb lattice. This prevents defects such as dislocations caused by the lattice mismatch from entering the subsequent doped layer 3.

[0041] In some embodiments, the thickness of the InSb buffer layer is 30-80 nm. This configuration helps cover any surface damage on the substrate 1 and provides a surface with a suitable lattice transition, facilitating the formation of a higher-quality doped layer 3. If the buffer layer 2 is too thin, achieving a smooth surface may be difficult and dislocations may be introduced into the doped layer 3. If the buffer layer 2 is too thick, costs may increase.

[0042] Optionally, the thickness of the InSb buffer layer may be 30 nm, 40 nm, 50 nm, 60 nm, 70 nm or 80 nm, etc.

[0043] In some embodiments, the thickness of the doped CdTe:In layer 31 in each set of alternating layers is 0.5-8 nm. It is understood that the doped CdTe:In layer 31 primarily provides deep-level defects, acting as electron traps, formed by Cd vacancies induced by In doping. Designing the doped CdTe:In layer 31 too thin makes it difficult to form a continuous layered structure, affecting electron capture effectiveness. Excessively thicker layers also hinder significant improvement in electron capture efficiency and increase costs.

[0044] Optionally, the thickness of the doped CdTe:In layer 31 in each group of alternating layers may be 0.5 nm, 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm or 8 nm, etc.

[0045] In some embodiments, the thickness of the doped InSb:Be layer 32 is 6 to 16 nm. It is understood that the doped InSb:Be layer 32 primarily provides efficient photon absorption and a high-mobility carrier channel. A thicker thickness facilitates sufficient light absorption depth. If the thickness is too thin, light absorption is insufficient, reducing conversion efficiency. If the thickness is too thick, the time it takes for electrons to migrate to the doped CdTe:In layer 31 is increased, thereby weakening the doped CdTe:In layer 31's ability to rapidly capture electrons, adversely affecting frequency characteristics.

[0046] Optionally, the thickness of the doped InSb:Be layer 32 in each group of alternating layers may be 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm or 16 nm, etc.

[0047] It can be understood that the doped InSb:Be layer 32 and the doped CdTe:In layer 31 are set differently, using the thicker doped InSb:Be layer 32 to generate a large number of photogenerated carriers and using the doped CdTe:In layer 31 to form electron traps or recombination centers, which is conducive to achieving high-frequency characteristics.

[0048] Preferably, the thickness of the doped CdTe:In layer 31 in each set of alternating layers is 1-3 nm. This configuration generally satisfies the requirements for electron capture and increased resistivity. However, if the doped CdTe:In layer 31 is too thick, costs increase, the series resistance increases, and the bias voltage required for subsequent devices increases.

[0049] Preferably, the thickness of the doped InSb:Be layer 32 in each set of alternating layers is 10-14 nm. This configuration ensures sufficient light absorption while taking into account the average time it takes for carriers to reach the adjacent doped CdTe:In layer 31.

[0050] In some embodiments, the number of alternating layers in the multiple sets of alternating layers is 30 to 120. This arrangement can significantly improve light absorption efficiency, generate a higher concentration of photogenerated carriers, maintain faster carrier dynamics, and thus maintain a shorter carrier lifetime. Too few alternating layers will result in insufficient light absorption, making the resulting carrier concentration less than desired. Too many alternating layers will result in thicker layers, which increase light absorption less significantly, leading to lower costs and increased difficulty in growing the doped layer 3.

[0051] Optionally, the number of alternating layers may be, for example, 30, 40, 50, 60, 70, 80, 90, 100, 110 or 120.

[0052] For example, Figure 2 Schematic diagram of alternating layers of photoconductive material according to one embodiment of the present invention is shown. Figure 2 As shown, 100 alternating layers can be formed in the doped layer 3. Of course, 80 alternating layers can also be formed in the doped layer 3 as needed. The number of alternating layers can be adjusted as needed, and the present invention does not impose any particular limitation on the number of alternating layers.

[0053] In some embodiments, in the doped layer 3, the total thickness of the multiple doped InSb:Be layers 32 is ≥0.8 μm. This configuration allows the laser to be fully absorbed when passing through the doped layer 3, avoiding energy waste caused by photons penetrating the doped layer 3, and in the process of passing through, more photons are converted into electron-hole pairs, providing a basis for the subsequent generation of large transient currents. Furthermore, for long-wavelength pump sources (i.e., the 1.3~1.55 μm fiber exciter mentioned above in the present invention), because they penetrate deeper into the doped InSb:Be layer 32, such a thickness can achieve better compatibility with the fiber exciter and can be compatible with existing integrated devices, which will help promote the application of the photoconductive material prepared by the present invention.

[0054] Optionally, the total thickness of all doped InSb:Be layers 32 in the doping layer 3 may be, for example, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, etc.

[0055] According to another embodiment of the present invention, a terahertz wave generator is provided, using the above-mentioned photoconductive material as a photoconductive material layer in a photoconductive antenna.

[0056] It can be understood that after forming a metal electrode of a specific shape on the aforementioned photoconductive material, a photoconductive antenna is formed, which is then assembled into a terahertz wave generator. When light with energy greater than that of the photoconductive material impinges on the photoconductive material layer, additional photogenerated carriers are generated in the photoconductive material. The metal electrode creates an electric field in the photoconductive material. The newly generated photogenerated carriers are accelerated by the applied electric field, resulting in a transient photocurrent, which radiates outward as terahertz waves.

[0057] According to an embodiment of the present invention, the aforementioned photoconductive material as a photoconductive material layer helps to generate terahertz waves with a wider spectrum, higher intensity and higher signal-to-noise ratio, and helps to improve the detection effect in fields such as terahertz time-domain spectroscopy systems and terahertz imaging.

[0058] According to yet another embodiment of the present invention, a method for preparing a photoconductive material is provided. Figure 3 FIG. 1 is a flow chart showing a method for preparing a photoconductive material according to an embodiment of the present invention. Figure 3 As shown, the preparation method includes operations S301 to S302.

[0059] In operation S301 , a buffer layer 2 is grown on a substrate 1 by vapor phase epitaxy.

[0060] In operation S302, a doped CdTe:In layer 31 is grown on the buffer layer 2 by vapor phase epitaxy, and a doped InSb:Be layer 32 is grown on the doped CdTe:In layer 31. An alternating layer consisting of one doped CdTe:In layer 31 and one doped InSb:Be layer 32 is a group. Multiple groups of alternating layers are located on the buffer layer 2 to form a doped layer 3, thereby forming a photoconductive material.

[0061] It is understood that the buffer layer 2 and doping layer 3 can be grown using vapor phase epitaxy (VPE), which can be, for example, molecular beam epitaxy (MBE) or metal-organic chemical vapor deposition (MOCVD). The specific methods for growing the buffer layer 2 and doping layer 3 can be the same or different. Preferably, both are grown using MBE.

[0062] According to an embodiment of the present invention, the vapor phase epitaxy method can achieve sub-nanometer thickness control, meeting the fine requirements for the doped layer 3. In particular, the MBE method can achieve atomic-level thickness control and has high precision for the thinner doped CdTe:In layer 31. Growing the buffer layer 2 on the substrate 1 using the vapor phase epitaxy method effectively alleviates the lattice mismatch and reduces the threading dislocation density. In addition, when doping the doped layer 3, the vapor phase epitaxy method can accurately control the doping concentration and improve the doping uniformity. Combining the vapor phase epitaxy method with the process of growing photoconductive materials makes it easy to stably grow an alternating structure of a thinner doped layer 3.

[0063] In some embodiments, the temperature for growing the buffer layer 2 is 280-320°C, and the temperature for growing the doping layer 3 is 300-340°C. This configuration facilitates the growth of a higher-quality buffer layer 2. Setting the temperature for growing the buffer layer 2 slightly lower than that for growing the doping layer 3 allows the buffer layer 2 to be formed through three-dimensional nucleation at a low temperature, which helps eliminate twins generated by large lattice mismatch. This provides a foundation for the nucleation and growth of the doping layer 3, forming a relatively flat doping layer 3 with fewer defects, and improving the crystal quality of the doping layer 3.

[0064] Optionally, the temperature for growing the buffer layer 2 may be, for example, 280° C., 290° C., 300° C., 310° C., or 320° C.

[0065] Optionally, the temperature for growing the doped layer 3 may be, for example, 300° C., 310° C., 320° C., 330° C., or 340° C.

[0066] In some embodiments, the Te / Cd beam ratio used to grow the doped CdTe:In layer 31 is 3 to 7. Growing CdTe in a Te-rich atmosphere helps to suppress the formation of Te vacancies, reduce intrinsic defects, and improve the quality of the doped CdTe:In layer 31. It can be understood that in X-ray diffraction analysis, the lower the half-width, the higher the quality of the doped CdTe:In layer 31; in atomic force microscopy analysis, the lower the roughness, the higher the quality of the doped CdTe:In layer 31. Based on the structures analyzed by X-ray diffraction analysis and atomic force microscopy, the Te / Cd beam ratio is adjusted within the aforementioned range, so that the quality of the doped CdTe:In layer 31 is relatively better. The doping concentration of In is 1E16-5E17cm -3 This configuration helps provide an electron trap. If the concentration of In is too high, the resistivity will be low.

[0067] Optionally, the Te / Cd beam ratio used for growing the doped CdTe:In layer 31 may be, for example, 3, 4, 5, 6 or 7.

[0068] Preferably, the doping concentration of In is 5E16-1E17 cm -3This further allows In to replace Cd and contribute excess electrons. Adjusting the In doping concentration within the above range keeps the n-type doping within a suitable range, thereby achieving higher electron mobility.

[0069] In some embodiments, the Sb / In beam ratio used to grow the doped InSb:Be layer 32 is 8 to 15. If the Sb is too high, Sb clusters will form; if the Sb is too low, In clusters will form. Both situations will result in poor crystal quality of the doped InSb:Be layer 32, which is reflected in an increase in the half-height width in X-ray diffraction analysis, the appearance of grooves on the surface in atomic force microscopy analysis, and a decrease in mobility. The Be doping concentration is 1E16 to 4E16 cm -3 Such a setting helps to avoid excessively high p-type doping concentration and thus avoid overcompensation.

[0070] Optionally, the Sb / In beam ratio used for growing the doped InSb:Be layer 32 may be, for example, 8, 9, 10, 11, 12, 13, 14 or 15.

[0071] Preferably, the doping concentration of Be is 2-3E16cm -3 This further keeps the p-type doping within an appropriate range, thereby avoiding overcompensation and preventing the mobility from being too low.

[0072] In one specific embodiment, the preparation process of the photoconductive material can be as follows: on a GaAs substrate, a 30-80 nm low-temperature InSb buffer layer is first grown at a temperature of 280-320°C using the MBE method, and then a doped CdTe:In layer and a doped InSb:Be layer are alternately grown at 300-340°C. The doped CdTe:In layer covers the upper surface of the low-temperature InSb buffer layer. The Te / Cd beam ratio used to grow the doped CdTe:In layer is 3-7, and the Sb / In beam ratio used to grow the doped InSb:Be layer is 8-15, thereby obtaining a photoconductive material.

[0073] The present invention is further illustrated below by way of examples and their results. In the detailed description that follows, for ease of explanation, numerous specific details are set forth to provide a comprehensive understanding of the embodiments of the present invention. However, it is apparent that one or more embodiments may be implemented without these specific details. Furthermore, the details in the following embodiments may be arbitrarily combined into other feasible embodiments, unless conflicting.

[0074] It should be noted that the following specific examples are for illustration only and the scope of protection of the present invention is not limited thereto. The raw materials used in the following examples are commercially available or prepared by generally recognized processing methods.

[0075] Example 1

[0076] Using a GaAs substrate, the oxide layer was first removed at 600°C in an As atmosphere. The substrate temperature was then lowered to 300°C, the In and Sb baffles were opened, and a 50nm thick InSb low-temperature buffer layer was grown using MBE.

[0077] The substrate temperature was raised to 320°C, and doped CdTe:In layers and doped InSb:Be layers were grown alternately for 80 times to obtain a doped layer. The thickness of the doped CdTe:In layer was 1 nm, and the In doping concentration was 7E16 cm -3 , Te / Cd beam ratio is 5. The thickness of the doped InSb:Be layer is 12nm, and the In doping concentration is 2E16cm -3 , the Sb / In beam ratio is 10, so that the total thickness of the doped InSb:Be layer reaches 0.96μm, thereby obtaining a photoconductive material.

[0078] Example 2

[0079] This embodiment 2 uses a method substantially the same as that of embodiment 1, except that the number of alternating layers in this embodiment 2 is 100, so that the total thickness of the doped InSb:Be layer reaches 1.2 μm.

[0080] In the photoconductive material consisting of a buffer layer and a doping layer grown sequentially on the obtained GaAs substrate, the carrier mobility is increased by about 1.5 times through the combination of multiple alternating doped CdTe:In layers and doped InSb:Be layers. The increase in the mobility of the photoconductive material helps to improve the far-field power level of the terahertz wave generator.

[0081] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A photoconductive material, characterized in that: include: substrate; a buffer layer covering the upper surface of the substrate; The doping layer covers the upper surface of the buffer layer and includes a plurality of alternating layers formed by alternating doped CdTe:In layers and doped InSb:Be layers. Wherein, the doped CdTe:In layer covers the upper surface of the buffer layer.

2. The photoconductive material according to claim 1, wherein The substrate is GaAs or InP.

3. The photoconductive material according to claim 1, wherein The thickness of the doped CdTe:In layer in each group of alternating layers is 0.5-8 nm; the thickness of the doped InSb:Be layer is 6-16 nm.

4. The photoconductive material according to claim 1, wherein The thickness of the doped CdTe:In layer in each group of alternating layers is 1-3 nm, and the thickness of the doped InSb:Be layer is 10-14 nm.

5. The photoconductive material according to any one of claims 1 to 4, characterized in that The number of alternating layers in the multiple groups of alternating layers is 30-120.

6. The photoconductive material according to any one of claims 1 to 4, characterized in that In the doped layer, the total thickness of the plurality of doped InSb:Be layers is ≥0.8 μm.

7. The photoconductive material according to any one of claims 1 to 4, characterized in that The buffer layer is an InSb buffer layer, and the thickness of the InSb buffer layer is 30-80 nm.

8. A terahertz wave generator, characterized in that: The photoconductive material according to any one of claims 1 to 7 is used as a photoconductive material layer in a photoconductive antenna.

9. A method for preparing a photoconductive material according to any one of claims 1 to 7, characterized in that: include: growing a buffer layer on the substrate by vapor phase epitaxy; A doped CdTe:In layer is grown on the buffer layer by vapor phase epitaxy, and a doped InSb:Be layer is grown on the doped CdTe:In layer. An alternating layer consisting of one doped CdTe:In layer and one doped InSb:Be layer constitutes a group. Multiple groups of alternating layers are located on the buffer layer to form a doped layer, thereby forming the photoconductive material.

10. The preparation method according to claim 9, characterized in that The temperature for growing the buffer layer is 280-320° C. The temperature for growing the doped layer is 300-340°C, wherein the Te / Cd beam ratio used for growing the doped CdTe:In layer is 3-7, and the In doping concentration is 1E16-5E17cm -3 ; The Sb / In beam ratio used in growing the doped InSb:Be layer is 8-15, and the Be doping concentration is 1E16-4E16cm -3 .

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