Ultraviolet photocathode with high quantum efficiency and preparation method and application thereof

Abstract

The invention discloses an ultraviolet photocathode with high quantum efficiency and a preparation method and application thereof, and relates to the technical field of photoelectric device manufacturing. According to the preparation method of the ultraviolet photocathode with high quantum efficiency provided by the invention, the ultraviolet photocathode containing cesium and tellurium is grown by adopting a molecular beam epitaxy method, and by controlling the temperature of the cesium beam source furnace and the distance between the beam source furnace and the substrate, the evaporation rate of an elementary substance and the growth rate of a compound in the beam source furnace can be controlled; according to the preparation method, the photoelectric cathode with a regular crystal structure and excellent quality is prepared by matching a growth structure of a compound crystal, and the quantum efficiency of the obtained cathode is greater than 30% when the wavelength of an illumination signal is 254nm, so that the preparation method has a good application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of optoelectronic device manufacturing, and specifically, to a high quantum efficiency ultraviolet photocathode and its preparation method and application. Background Art

[0002] A photoemission detector is a device that can convert a light signal into an electrical signal. Among them, the photocathode is its core device, and a photocathode that can respond to the spectral range of 10 nm to 400 nm in the photocathode is called an ultraviolet photocathode. Conventional ultraviolet photocathodes are usually directly prepared on a quartz glass substrate by thermal evaporation. However, when preparing a photocathode by thermal evaporation, slow heating and cooling are required during the manufacturing process, which takes a long time, and the growth process is approximately controlled by experience, making it difficult to meet the technical requirements of automation and mass production. At the same time, the yield is low, and the quantum efficiency of the obtained ultraviolet photocathode is difficult to meet the growing demand. Summary of the Invention

[0003] To solve the deficiencies of the prior art, the present invention provides a preparation method for a high quantum efficiency ultraviolet photocathode. An ultraviolet photocathode including two elements, cesium and tellurium, or further including a third element is grown by molecular beam epitaxy. During the growth process, by controlling the temperatures of different source furnaces and the distance between the source furnace and the substrate, an ultraviolet photocathode with a good crystal structure is formed, improving its quantum efficiency.

[0004] Another object of the present invention is to provide a high quantum efficiency ultraviolet photocathode.

[0005] Another object of the present invention is to provide an application of a high quantum efficiency ultraviolet photocathode.

[0006] The above objects of the present invention are achieved by the following technical solutions:

[0007] A preparation method for a high quantum efficiency ultraviolet photocathode includes the following steps:

[0008] Heat the molecular beam epitaxy source furnace, and perform co-deposition of tellurium and cesium on the substrate to form a compound film, thereby obtaining a high quantum efficiency ultraviolet photocathode; the temperature of the cesium source furnace is 50 - 110 °C higher than the temperature of the tellurium source furnace, the temperature of the cesium source furnace is 300 - 450 °C, and the distance between the molecular beam epitaxy source furnace and the substrate is 100 - 900 mm.

[0009] When the temperature of the cesium source furnace is 50 - 110 °C higher than the temperature of the tellurium source furnace and the temperature of the cesium source furnace is 300 - 450 °C, that is, the temperature of the tellurium source furnace is 190 - 340 °C. The preparation method provided by the present invention uses molecular beam epitaxy to grow a compound (when only containing two elements, cesium and tellurium, the obtained compound is Cs2 Te) ultraviolet photocathode, by controlling the temperatures of the cesium source furnace and the tellurium source furnace and the temperature difference, realizes the control of the evaporation rate of the single element and the growth rate of the compound in the beam source furnace, matches the growth structure of the compound crystal, and thus grows Cs with a more regular crystal structure. 2 Te, improving the quantum efficiency of the ultraviolet photocathode. Specifically, in the present invention, after controlling the temperature of the cesium source furnace to be 300 - 450 °C and the temperature of the tellurium source furnace to be 190 - 340 °C, due to the higher temperature, the movement of molecules is more intense, and sufficient collisions and reactions can occur between cesium and tellurium atoms to form Cs. 2 Te compound and uniformly deposit it on the substrate. However, the increase in temperature will lead to an increase in the movement distance of the gas molecular beam per unit time. In order to ensure that the cesium and tellurium molecular beams have sufficient time to collide and react with each other before reaching the substrate, the distance between the molecular beam epitaxy beam source furnace and the substrate should be controlled to be 100 - 900 mm. The inventors of the present application surprisingly found through experiments that when the temperature is further increased, even if the distance between the substrate and the beam source furnace is further increased, it is difficult to form a uniform and regular crystal thin film. This may be because at too high a temperature, cesium and tellurium elements tend to maintain a gaseous state, and the tendency for them to react to form crystals decreases.

[0010] It should be noted that in molecular beam epitaxy, the distances between the beam source furnaces of different elements and the substrate are kept consistent.

[0011] Since the evaporation source has a large size in molecular beam epitaxy and the evaporation angle can be 0 - 90°, therefore, the preparation method provided by the present invention can also achieve batch production.

[0012] In a specific embodiment of the present invention, the step of cleaning the substrate is further included before deposition. More specifically, the step of cleaning the substrate includes: starting a DC power supply with a current of 0.01 - 1 A and a voltage of 500 - 6000 V in an inert gas atmosphere with a pressure of 0.1 - 50 Pa to bombard the substrate with inert gas plasma. More specifically, the time for cleaning the substrate is 1 - 10 h. More specifically, the inert gas includes at least one of argon and neon. More specifically, the partial pressure of gas moisture in the inert gas is lower than 10% of the background pressure.

[0013] Preferably, the distance between the molecular beam epitaxy beam source furnace and the substrate is 500 - 700 mm.

[0014] Preferably, the temperature of the cesium source furnace is 75 - 85 °C higher than the temperature of the tellurium source furnace, and the temperature of the cesium source furnace is 350 - 410 °C.

[0015] When the temperature of the cesium source furnace is 75 - 85 °C higher than that of the tellurium source furnace and the temperature of the cesium source furnace is 350 - 410 °C, that is, the temperature of the tellurium source furnace is 265 - 335 °C. When the temperatures of the two source furnaces are within the above ranges respectively, the obtained crystal structure is more regular, and thus the quantum efficiency is higher.

[0016] Preferably, the beam currents of the cesium source furnace and the tellurium source furnace are (2 - 5):1.

[0017] By controlling the beam current, the control of the element ratio in the compound can be achieved.

[0018] Preferably, before the co - deposition, there is also a step of heating the temperature of the third element source furnace to 270 - 430 °C. The third element includes at least one of rubidium, potassium, and sodium. The co - deposition includes co - depositing cesium, tellurium, and the third element on the substrate.

[0019] Using at least one element of rubidium, potassium, and sodium to jointly construct a photocathode with Cs and Te can obtain a higher quantum efficiency.

[0020] More preferably, the temperature of the third element source furnace is 320 - 380 °C.

[0021] Controlling the temperature of the third element source furnace within the above range can obtain an ultraviolet photocathode with a more regular crystal structure, and thus a higher quantum efficiency.

[0022] More preferably, during the process of co - depositing cesium, tellurium, and the third element on the substrate, the beam currents of the cesium source furnace, the tellurium source furnace, and the third element source furnace are (0.5 - 2):1:(0.5 - 2).

[0023] Preferably, the thickness of the ultraviolet photocathode with high quantum efficiency is 400 - 600 nm.

[0024] Controlling the thickness of the ultraviolet photocathode within the above range can obtain a higher quantum efficiency.

[0025] Preferably, the deposition time is 600 - 4200 s.

[0026] Controlling the deposition time within the above range can obtain an ultraviolet photocathode with a suitable thickness and a higher quantum efficiency.

[0027] More preferably, the growth rate of the compound thin film is 0.01 - 1 nm / s.

[0028] More preferably, the deposition is carried out under the condition of a vacuum degree > 1×10 -6 Pa.

[0029] In a specific embodiment of the present invention, the substrate is quartz glass. More specifically, the number of substrates is 30 to 40 pcs (pieces).

[0030] Preferably, the temperature of the substrate is 120 to 180 °C.

[0031] More preferably, the rotation speed of the substrate is 10 to 20 rpm.

[0032] In a specific embodiment of the present invention, the deposition also includes an in-situ monitoring operation, which is achieved by at least one of Reflection High Energy Electron Diffraction (RHEED) and Crystal Growth Monitor (BFM).

[0033] In-situ monitoring enables the present invention to monitor the crystal structure and quality of the photocathode in real time, which is beneficial to further improving the quantum efficiency.

[0034] The present invention also protects a high-quantum-efficiency ultraviolet photocathode prepared by the above preparation method.

[0035] The present invention also protects the application of the above high-quantum-efficiency ultraviolet photocathode in a photodetector.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] By using the method provided by the present invention, a photocathode with a regular crystal structure and excellent quality can be prepared. The quantum efficiency of the obtained cathode is > 30% when the wavelength of the light signal is 254 nm, and it has good application prospects. Specific Embodiment

[0038] The following further illustrates the present invention in conjunction with specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the raw material reagents used in the embodiments of the present invention are conventionally purchased raw material reagents.

[0039] Example 1

[0040] A method for preparing a high-quantum-efficiency ultraviolet photocathode includes the following steps:

[0041] Start a DC power supply in an argon atmosphere with a pressure of 5 Pa, the current magnitude is 0.5 A, and the voltage is 3000 V to form plasma to bombard the substrate for cleaning. The cleaning time of the substrate is 5 h, and the partial pressure of gas moisture in argon is 0; after cleaning, adjust the temperature of the cesium source furnace to 380 °C and the temperature of the tellurium source furnace to 300 °C, so that cesium and tellurium are co-deposited on the substrate to form a Cs 2 Te compound film, namely obtaining a high-quantum-efficiency ultraviolet photocathode; wherein, the beam currents of the cesium source furnace and the tellurium source furnace are 3:1, and the deposition is carried out at a vacuum degree of 5×10-7 It is carried out under the condition of [[Pa]], the substrate is 36 pcs of quartz glass, the temperature is 160 °C, the rotation speed is 15 rpm, the distance between the substrate and the beam source furnace is 600 mm, the deposition time is 2500 s, the growth rate of the compound thin film is 0.2 nm / s, and the thickness of the obtained compound thin film is 500 nm.

[0042] Example 2

[0043] A preparation method of a high quantum efficiency ultraviolet photocathode, the difference from Example 1 is only that:

[0044] Adjust the temperature of the cesium source furnace to 380 °C, the temperature of the tellurium source furnace to 300 °C, and the temperature of the rubidium source furnace to 350 °C, so that cesium, tellurium and rubidium are co-deposited on the substrate to form an RbCsTe thin film, where the beam currents of the cesium source furnace, tellurium source furnace and rubidium source furnace are 1.5:1:1.5.

[0045] Example 3

[0046] A preparation method of a high quantum efficiency ultraviolet photocathode, the difference from Example 2 is only that:

[0047] Adjust the temperature of the rubidium source furnace to 270 °C.

[0048] Example 4

[0049] A preparation method of a high quantum efficiency ultraviolet photocathode, the difference from Example 2 is only that:

[0050] Adjust the temperature of the rubidium source furnace to 430 °C.

[0051] Example 5

[0052] A preparation method of a high quantum efficiency ultraviolet photocathode, the difference from Example 1 is only that:

[0053] Adjust the temperature of the cesium source furnace to 450 °C and the temperature of the tellurium source furnace to 340 °C.

[0054] Example 6

[0055] A preparation method of a high quantum efficiency ultraviolet photocathode, the difference from Example 1 is only that:

[0056] Adjust the temperature of the cesium source furnace to 300 °C and the temperature of the tellurium source furnace to 250 °C.

[0057] Comparative Example 1

[0058] A preparation method of an ultraviolet photocathode, the difference from Example 1 is only that:

[0059] Adjust the temperature of the cesium source furnace to 40 °C.

[0060] Comparative Example 2

[0061] A method for preparing an ultraviolet photocathode, which is only different from Example 1 in that:

[0062] The temperature of the tellurium source furnace is adjusted to 40 °C.

[0063] Comparative Example 3

[0064] A method for preparing an ultraviolet photocathode, which is only different from Example 1 in that:

[0065] The temperature of the cesium source furnace is adjusted to 300 °C, and the temperature of the tellurium source furnace is adjusted to 380 °C.

[0066] Comparative Example 4

[0067] A method for preparing an ultraviolet photocathode, which is only different from Example 1 in that:

[0068] The temperature of the cesium source furnace is adjusted to 450 °C, and the temperature of the tellurium source furnace is adjusted to 220 °C.

[0069] Comparative Example 5

[0070] A method for preparing an ultraviolet photocathode, which is only different from Example 1 in that:

[0071] The temperature of the cesium source furnace is adjusted to 600 °C.

[0072] Comparative Example 6

[0073] A method for preparing an ultraviolet photocathode, which is only different from Example 1 in that:

[0074] The temperature of the tellurium source furnace is adjusted to 450 °C.

[0075] Comparative Example 7

[0076] A method for preparing an ultraviolet photocathode, which is only different from Example 1 in that:

[0077] The distance between the substrate and the target is adjusted to 50 mm.

[0078] Comparative Example 8

[0079] A method for preparing an ultraviolet photocathode, which is only different from Example 1 in that:

[0080] The distance between the substrate and the target is adjusted to 1000 mm.

[0081] Performance Test

[0082] Quantum efficiency test: The ultraviolet photocathodes obtained from the examples and comparative examples were placed in a specially designed test vacuum chamber to test their quantum efficiency at 254 nm.

[0083] The specific test data are shown in Table 1 below:

[0084] Table 1. Quantum efficiency of ultraviolet photocathodes obtained from examples and comparative examples

[0085]

[0086]

[0087] From the data in Table 1 above, it can be seen that by using the method provided by the present invention, a photocathode with a regular crystal structure and excellent quality can be prepared. The quantum efficiency of the obtained cathode is > 30% when the wavelength of the light signal is 254 nm, showing good application prospects.

[0088] From the data of Examples 1-2 in Table 1 above, it can be seen that when the compound film further includes the third element rubidium, the obtained ultraviolet photocathode has a higher quantum efficiency.

[0089] From the data of Examples 2-4, it can be seen that when the compound film further includes the third element, when the temperature of the third element source furnace is within the preferred range of 320-380 °C in the present invention (Example 2), the crystal structure of the obtained ultraviolet photocathode is more regular, and thus the quantum efficiency is higher.

[0090] From the data of Examples 1, 5-6, it can be seen that when the temperature of the cesium source furnace is within the preferred range of 350-410 °C in the present invention and the temperature of the cesium source furnace is 75-85 °C higher than the temperature of the tellurium source furnace (Example 1), the crystal structure of the obtained ultraviolet photocathode is also more regular, and thus has a higher quantum efficiency.

[0091] From the data of Comparative Examples 1-6, it can be seen that when the temperatures of the cesium source furnace and the tellurium source furnace are not appropriate, an ultraviolet photocathode with a regular crystal structure cannot be grown, and the quantum efficiency of the obtained cathode is low.

[0092] From the data of Example 1 and Comparative Examples 7, 8, it can be seen that when the distance between the substrate and the target is not appropriate, an ultraviolet photocathode with a regular crystal structure cannot be grown, the quantum efficiency of the obtained cathode is low, and the uniformity in the same furnace is poor.

[0093] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a high quantum efficiency ultraviolet photocathode, characterized in that: The steps include: The molecular beam epitaxy beam source furnace is heated to co-deposit tellurium and cesium on a substrate to form a compound film, thereby obtaining an ultraviolet photocathode with high quantum efficiency; the temperature of the cesium source furnace is 50-110° C. higher than that of the tellurium source furnace, the temperature of the cesium source furnace is 300-450° C., and the distance between the molecular beam epitaxy beam source furnace and the substrate is 100-900 mm.

2. The method for preparing a high quantum efficiency ultraviolet photocathode according to claim 1, characterized in that: The temperature of the cesium source furnace is 75-85°C higher than that of the tellurium source furnace, and the temperature of the cesium source furnace is 350-410°C.

3. The method for preparing a high quantum efficiency ultraviolet photocathode according to claim 2, characterized in that: The beam current of the cesium source furnace and the tellurium source furnace is (2-5):

1.

4. The method for preparing a high quantum efficiency ultraviolet photocathode according to claim 1, characterized in that: The method also includes a step of heating the temperature of a third element source furnace to 270-430° C. before the co-deposition. The third element includes at least one of rubidium, potassium, and sodium. The co-deposition includes depositing cesium, tellurium, and the third element together on a substrate.

5. The method for preparing a high quantum efficiency ultraviolet photocathode according to claim 4, characterized in that: The temperature of the third element source furnace is 320-380°C.

6. The method for preparing a high quantum efficiency ultraviolet photocathode according to claim 5, characterized in that: In the process of making cesium, tellurium and the third element co-deposit on the substrate, the beam currents of the cesium source furnace, the tellurium source furnace and the third element source furnace are (0.5-2): (0.5-2):

1.

7. The method for preparing a high quantum efficiency ultraviolet photocathode according to any one of claims 1 to 6, characterized in that: The thickness of the ultraviolet photocathode with high quantum efficiency is 400-600nm.

8. The method for preparing a high quantum efficiency ultraviolet photocathode according to claim 7, characterized in that: The growth rate of the compound film is 0.01-1 nm / s.

9. An ultraviolet photocathode with high quantum efficiency prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the ultraviolet photocathode with high quantum efficiency according to claim 9 in a photodetector.

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