Method for improving the hardness of zinc selenide grown by chemical vapor deposition reaction

Abstract

The present invention discloses a method for improving the hardness of zinc selenide grown by chemical vapor deposition reaction, comprising: injecting solid metal zinc into a crucible, boiling it to make zinc vapor, and then feeding it into a reaction chamber; introducing a mixed gas of hydrogen selenide and hydrogen sulfide into the reaction chamber until the grain growth is completed. The present invention improves the hardness reduction derived from the grain growth or grain growth shape produced by the long-term process of CVD-ZnSe growth without damaging the optical properties, so that the ZnS particles are micro-dispersed and grown in the ZnSe crystal, and the excessive growth of the grains is suppressed; at the same time, the ZnS particles grown in this dispersed manner suppress the growth of dendrites, induce epitaxial growth, and improve the characteristics of the crystal organization, thereby increasing the physical properties such as volume hardness.

Description

Technical Field

[0001] The invention belongs to the technical field of infrared materials, and in particular relates to a method for improving the hardness of zinc selenide grown by chemical vapor deposition reaction. Background Art

[0002] Infrared materials generally used in infrared applications include polycrystalline materials such as silicon (Si), germanium (Ge), sapphire, magnesium fluoride (MgF2), zinc sulfide (ZnS), zinc selenide (ZnSe), and chalcogenide glass, etc. ZnSe and ZnS produced by CVD reaction are the most widely used infrared materials. Among them, CVD-ZnSe has the best optical properties (transmittance, wave transmission range, dispersion coefficient, absorption coefficient, etc.) and can be used universally, but its hardness is lower than that of ZnS in physical properties, and scratches and other defects are easily found on the surface, which limits its use in harsh environments.

[0003] The above mechanical properties of ZnSe, especially the hardness, are caused by the characteristics of the internal grain size and structure of ZnSe. In other words, the growth rate of ZnSe grown by CVD reaction is relatively slow. To obtain a material with a thickness of 30 mm, it is necessary to grow continuously at high temperature for about 350 to 400 hours. The ZnSe grains generated at this time are formed by nucleation and grain growth. The reaction at high temperature for a long time makes the generated grains interact with each other at high temperature and continuously grow into large crystals. The small crystals disappear, and only large crystals are left. The physical properties of large crystal materials grown in this way, especially the hardness, are relatively low. In addition, the ZnSe CVD reaction is a hot wall process. The reaction occurs on the surface of the substrate and grows in the thickness direction. Its structural feature is dendrite structure. This vertically growing dendrite structure usually has poor hardness. Summary of the invention

[0004] The object of the present invention is to provide a method for improving the hardness of zinc selenide grown by chemical vapor deposition reaction, by inhibiting excessive growth of grains and dendrite growth, thereby improving its hardness within a range that does not damage the optical properties.

[0005] The technical solution adopted by the present invention is: a method for improving the hardness of zinc selenide grown by chemical vapor deposition reaction, comprising the following steps:

[0006] Step 1, injecting solid metal zinc into a crucible, boiling it to produce zinc vapor and injecting it into a reaction chamber;

[0007] Step 2: introducing a mixed gas of hydrogen selenide and hydrogen sulfide into the reaction chamber until the grain growth is completed.

[0008] The present invention is also characterized in that:

[0009] In step 2, the molar ratio of hydrogen sulfide to hydrogen selenide is 0.03 to 0.04.

[0010] In step 2, only hydrogen selenide is introduced into the mixed gas 30 to 50 hours before the completion of grain growth, and hydrogen sulfide is mixed and introduced starting from 30 to 50 hours before the completion of grain growth and continuously for 10 hours. During the 10 hours, the proportion of hydrogen sulfide in the mixed gas continues to increase. At the end of 10 hours, the proportion of hydrogen sulfide in the mixed gas is 100%, and this proportion is maintained until the grain growth is completed.

[0011] The grain growth process is a 300-hour reaction process.

[0012] The introduction ratio and duration of hydrogen selenide and hydrogen sulfide in the mixed gas of step 2 are adjusted by a gas flow controller.

[0013] The beneficial effects of the present invention are as follows: the hardness improvement method of zinc selenide grown by chemical vapor deposition reaction of the present invention improves the hardness reduction derived from the grain growth or grain growth shape produced by the long-term process in CVD-ZnSe growth without damaging the optical properties, so that ZnS particles are micro-dispersed and grown in ZnSe crystals, and excessive grain growth is suppressed; at the same time, the ZnS particles grown in such a dispersed manner suppress dendrite growth, induce epitaxial growth, improve the characteristics of the crystal organization, and thus increase physical properties such as volume hardness. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic structural diagram of the chemical vapor deposition reaction device used in the present invention. DETAILED DESCRIPTION

[0015] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0016] The present invention provides a method for improving the hardness of zinc selenide grown by chemical vapor deposition reaction, and uses the CVD method to prepare infrared material ZnSe, such as Figure 1 As shown, solid metal zinc (Zn) is injected into a crucible and boiled to produce zinc vapor which is then fed into a reaction chamber. The molar fractions of the reaction gases H2Se and H2S are adjusted by a gas flow controller and added to the reaction zone in a stoichiometrically balanced manner. ZnSe and ZnS are grown according to the following reaction formula.

[0017] H2Se+Zn→ZnSe+H2

[0018] H2S+Zn→ZnS+H2

[0019] When the reaction gas H2Se is added, a small amount of H2S gas is added into the reaction chamber, so that the ZnS particles are micro-dispersed and grown in the ZnSe crystal structure. The grown micro ZnS particles can generate ZnS particles in the ZnSe crystal structure, which can inhibit the growth of ZnSe crystals (the grain size becomes smaller), thereby achieving the effect of blocking the decline of mechanical properties such as hardness of ZnSe. In this way, the fine and dispersed ZnS particles also have a large resistance to deformation caused by potential migration in the ZnSe crystal structure, which is effective in improving mechanical properties such as hardness. At the same time, the ZnS dispersed in the ZnSe crystal is also effective in inhibiting the growth of dendrites that reduce mechanical properties, especially hardness, and inducing epitaxial growth, thereby preventing the decline of mechanical properties caused by the dendrite structure.

[0020] In addition, in harsh environments, the surface of the crystal material is severely damaged. At this time, according to needs, only H2Se gas can be introduced to grow ZnSe crystals, and then H2S gas can be mixed to grow ZnSe and ZnS crystals on the surface of the ZnSe crystals. When the mixed gas of H2Se and H2S is introduced, the S / Se ratio is gradually increased, and finally only ZnS crystals are generated on the outer surface. In this way, the characteristic that ZnS has a higher hardness than ZnSe can be utilized to achieve the effect of improving the surface hardness, while maintaining the hardness of the sub-outer layer within the range that does not damage the optical performance. The central ZnSe crystals in the innermost layer can also offset the reduction in transmission characteristics caused by some of the outermost ZnS crystals alone, thereby completing the surface hardness enhancement work under specific environments.

[0021] Through the above-mentioned method, the hardness improvement method of zinc selenide grown by chemical vapor deposition reaction of the present invention adopts a proper mixture of the reaction gases H2Se and H2S to improve the volume hardness without reducing the relatively excellent optical properties, and can also harden only the surface as needed, significantly reducing its surface damage in harsh environments.

[0022] Example

[0023] A. Enhance the volume hardness of ZnSe

[0024] 1) Changes in physical properties of ZnSeS grown by continuous reaction for 300 hours with a S / Se molar ratio of 0.005.

[0025] - Knoop hardness increase is about 10kg / mm 2 (120→130kg / mm 2 , measured under 50g pressure head)

[0026] -Infrared transmittance is unchanged compared to pure ZnSe.

[0027] 2) 300 hours reaction time, S / Se molar ratio is 0.01.

[0028] - Knoop hardness increase is about 30kg / mm 2 (120→150kg / mm 2 , measured under 50g pressure head)

[0029] -No change in infrared transmittance.

[0030] 3) 300 hours reaction time, S / Se molar ratio 0.03.

[0031] - Knoop hardness increase is about 60kg / mm 2 (120→180kg / mm 2 , measured under 50g pressure head)

[0032] -No change in infrared transmittance.

[0033] 4) 300 hours reaction time, S / Se molar ratio 0.035.

[0034] - Knoop hardness increase is about 65kg / mm 2 (120→180kg / mm 2 , measured under 50g pressure head)

[0035] -No change in infrared transmittance.

[0036] 5) 300 hours reaction time, S / Se molar ratio 0.04.

[0037] - Knoop hardness increase is about 70kg / mm 2 (120→180kg / mm 2 , measured under 50g pressure head)

[0038] -No change in infrared transmittance.

[0039] 6) 300 hours reaction time, S / Se molar ratio 0.05.

[0040] - Knoop hardness increase is about 80kg / mm 2 (120→200kg / mm 2 , measured under 50g pressure head)

[0041] -Infrared transmittance slightly decreased (3% to 5%).

[0042] The above-mentioned S / Se molar ratio of about 0.03 to 0.04 is most appropriate.

[0043] B. Enhance surface hardness

[0044] 300 hours reaction process

[0045] 1) Only H2Se gas was added in the first 270 hours, and the S / Se molar ratio was continuously increased from 0 to 100 in the following 10 hours, reaching 100% H2S, and then the H2S gas continued to maintain 100% for the remaining 20 hours.

[0046] -The thickness of the surface ZnS is about 1mm

[0047] -Surface Knoop hardness is about 200kg / mm 2

[0048] -The infrared transmission range does not change much, but the transmittance decreases slightly (2% to 3%).

[0049] 2) Only H2Se gas was introduced in the first 250 hours, and then the S / Se molar ratio was continuously increased from 0 to 100 within 10 hours to reach 100% H2S, and then 100% H2S gas was maintained for the remaining 40 hours.

[0050] -The thickness of the surface ZnS is about 2mm

[0051] -Surface Knoop hardness is about 220kg / mm 2

[0052] -Infrared transmission range and transmittance (3% to 5%) are reduced.

[0053] In the above range of 250 to 270 hours, reaction conditions close to the desired properties are selected in consideration of factors such as hardness and transmittance characteristics.

Claims

1. A method for improving the hardness of zinc selenide grown by chemical vapor deposition reaction, characterized in that: The following steps are involved: Step 1, injecting solid metal zinc into a crucible, boiling it to produce zinc vapor and injecting it into a reaction chamber; Step 2: introducing a mixed gas of hydrogen selenide and hydrogen sulfide into the reaction chamber until grain growth is completed. The grain growth process is a 300-hour reaction process. The introduction ratio and duration are adjusted by a gas flow controller. The molar ratio of hydrogen sulfide to hydrogen selenide is 0.03-0.04.

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