JP2008013414A - Zinc selenide polycrystal and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zinc selenide polycrystal by which a matter to be treated can be appropriately processed when a lens formed by the zinc selenide polycrystal is used for an optical component for a carbon dioxide laser and to provide its manufacturing method. <P>SOLUTION: When the zinc selenide polycrystal is synthesized by a CVD method, a zinc vapor from a metal zinc 6 generated in a zinc vapor generating chamber 4 is supplied to a reaction chamber 12 together with a carrier gas. A gaseous hydrogen is supplied to a hydrogen selenide synthesizing chamber 5 in a state housing a starting material of an acceptor impurity in a molten bath 10 housing a metal selenium 9 and an H<SB>2</SB>Se gas synthesized in a hydrogen selenide synthesizing chamber 5 is supplied to the reaction chamber 12 together with an unreacted gaseous hydrogen. Thus, the zinc selenide polycrystal wherein the acceptor impurity is doped is synthesized when the zinc selenide polycrystal is synthesized by the reaction of a zinc vapor and the hydrogen selenide in the reaction chamber 12. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention uses a carbon dioxide laser as a heat source and locally heats an object to be processed (for example, a part of an automobile or home appliance) by the heat of laser light to perform laser processing such as drilling or cutting. The present invention relates to a polycrystal of zinc selenide (ZnSe) constituting an optical component to be used and a method for producing the same.

  Conventionally, carbon dioxide laser processing has been used as a technique for melting and processing an object to be processed by heat. This carbon dioxide laser has a high output and is excellent in processing such as drilling and cutting. Carbon dioxide laser light in the 10.6 μm band is mainly used.

  Further, when processing an object to be processed, an optical component such as a lens for guiding the irradiated laser beam to the target is required. For example, as the lens, infrared light of a carbon dioxide laser (wavelength is 9 μm). Zinc selenide lenses that can transmit (˜11 μm) are widely used.

For this zinc selenide lens, zinc selenide polycrystal synthesized by chemical vapor deposition (CVD) using zinc and hydrogen selenide (H ₂ Se) gas as raw materials is used. Here, as a method for synthesizing the zinc selenide polycrystal, for example, zinc vapor and hydrogen selenide synthesized by the reaction of selenium vapor from metal selenium and hydrogen gas are supplied to the reaction chamber, Discloses a method of growing zinc selenide polycrystals on a substrate provided in a reaction chamber by reacting zinc vapor with hydrogen selenide. (For example, refer nonpatent literature 1).
JITENDRA S GOELA, 1 other person, “JOURNAL OF MATERIALS SCIENCE” (USA), Springer Netherlands, December 1988, Volume 23, p.4331-4339

However, in the zinc selenide polycrystal synthesized by the conventional CVD method, there are free electrons due to slight residual impurities, vacancies, defects and the like present in the zinc selenide polycrystal. Further, the zinc selenide polycrystalline, its physical properties, to form an n-type semiconductor layer, the electrical resistance shows an electrical conductivity of about ^{10 10 ~10 12 Ωcm.} When a lens formed of a zinc selenide polycrystal is used as an optical component for a carbon dioxide laser, free electrons existing in the zinc selenide polycrystal absorb the carbon dioxide laser beam incident on the zinc selenide lens. The kinetic energy of the free electrons increases. Then, the temperature of the zinc selenide lens rises, the change in the refractive index of the zinc selenide lens occurs due to the temperature rise, and the focal distance of the zinc selenide lens may change or the zinc selenide lens may burn out. is there. As a result, it may be difficult to appropriately process the workpiece.

  Therefore, the present invention has been made in view of the above-described problems, and appropriately processes a workpiece when using a lens formed of zinc selenide polycrystal as an optical component for a carbon dioxide laser. It is an object to provide a zinc selenide polycrystal and a method for producing the same.

  In order to achieve the above object, the invention described in claim 1 is a polycrystal of zinc selenide, wherein the crystal is doped with an acceptor impurity. According to this configuration, the doped acceptor impurity acts as an acceptor and generates holes in the zinc selenide polycrystal. Accordingly, free electrons existing in the zinc selenide polycrystal can be combined with the holes to reduce the free electrons existing in the zinc selenide polycrystal. Then, for example, when a lens formed of zinc selenide polycrystal is used as an optical component for a carbon dioxide gas laser, it is incident on the zinc selenide lens as compared with the case of using the conventional zinc selenide polycrystal. Since free electrons that absorb carbon dioxide laser light are reduced, the temperature rise of the zinc selenide lens can be effectively suppressed, and the change in the refractive index of the zinc selenide lens due to the temperature rise is effectively reduced. It becomes possible to suppress. Therefore, compared with the case where the conventional zinc selenide polycrystal is used, the focal length variation of the zinc selenide lens and the occurrence of burnout of the zinc selenide lens can be effectively prevented. Can be processed appropriately.

  Invention of Claim 2 is the zinc selenide polycrystal of Claim 1, Comprising: The density | concentration of the acceptor impurity in a zinc selenide polycrystal is 0.001 ppb or more and 0.01 ppm or less, It is characterized by the above-mentioned. And According to this configuration, the effect of reducing free electrons can be sufficiently exerted while suppressing absorption of carbon dioxide laser light by the doped acceptor impurity.

  The invention according to claim 3 is the zinc selenide polycrystal according to claim 1 or 2, wherein the acceptor impurity is at least one element selected from the group consisting of lithium, sodium, and potassium. It is characterized by including. According to this configuration, a zinc selenide polycrystal doped with an acceptor impurity can be obtained with an inexpensive and simple configuration.

  The invention according to claim 4 is a method for producing a zinc selenide polycrystal, wherein when the zinc selenide polycrystal is grown by a CVD method, an acceptor impurity is doped into the zinc selenide polycrystal. And

  According to this configuration, the doped acceptor impurity acts as an acceptor and generates holes in the zinc selenide polycrystal. Accordingly, free electrons existing in the zinc selenide polycrystal can be combined with the holes to reduce the free electrons existing in the zinc selenide polycrystal. Then, for example, when a lens formed of a zinc selenide polycrystal is used as an optical component for a carbon dioxide gas laser, it is incident on the zinc selenide lens as compared with the case where the conventional zinc selenide polycrystal is used. Since free electrons that absorb carbon dioxide laser light are reduced, the temperature rise of the zinc selenide lens can be effectively suppressed, and the change in the refractive index of the zinc selenide lens due to the temperature rise is effectively reduced. It becomes possible to suppress. Therefore, compared with the case where the conventional zinc selenide polycrystal is used, the focal length variation of the zinc selenide lens and the occurrence of burnout of the zinc selenide lens can be effectively prevented. Can be processed appropriately. Further, the acceptor impurity can be uniformly doped in the entire zinc selenide polycrystal.

Invention of claim 5, a zinc selenide polycrystalline method according to claim 4, the raw material of an acceptor impurity, selenide lithium (Li 2 _Se), sodium selenide (Na 2 _Se) And at least one selected from the group consisting of potassium selenide (K ₂ Se). According to this configuration, when the acceptor impurity is doped into the zinc selenide polycrystal, it is possible to effectively avoid the disadvantage that impurities other than the acceptor impurity are mixed into the zinc selenide polycrystal.

  The invention according to claim 6 is a method for producing a zinc selenide polycrystal, a step of synthesizing the zinc selenide polycrystal by a CVD method, and heat-treating the synthesized zinc selenide polycrystal, thereby accepting the acceptor. And a step of doping impurities into the polycrystal of zinc selenide.

  According to this configuration, the doped acceptor impurity acts as an acceptor and generates holes in the zinc selenide polycrystal. Accordingly, free electrons existing in the zinc selenide polycrystal can be combined with the holes to reduce the free electrons existing in the zinc selenide polycrystal. Then, for example, when a lens formed of a zinc selenide polycrystal is used as an optical component for a carbon dioxide gas laser, it is incident on the zinc selenide lens as compared with the case where the conventional zinc selenide polycrystal is used. Since free electrons that absorb carbon dioxide laser light are reduced, the temperature rise of the zinc selenide lens can be effectively suppressed, and the change in the refractive index of the zinc selenide lens due to the temperature rise is effectively reduced. It becomes possible to suppress. Therefore, compared with the case where the conventional zinc selenide polycrystal is used, the focal length variation of the zinc selenide lens and the occurrence of burnout of the zinc selenide lens can be effectively prevented. Can be processed appropriately. Further, the acceptor impurity can be uniformly doped in the entire zinc selenide polycrystal. In addition, acceptor impurities can be easily doped into the zinc selenide polycrystal by thermal diffusion.

The invention according to claim 7, a zinc selenide polycrystalline method according to claim 6, the raw material of an acceptor impurity, selenide lithium (Li 2 _Se), sodium selenide (Na 2 _Se) And at least one selected from the group consisting of potassium selenide (K ₂ Se).

  According to this configuration, lithium selenide, sodium selenide, and potassium selenide have high vapor pressure at the temperature of the heat treatment, and are liable to become a gas. Therefore, contact of the acceptor impurity raw material with the synthesized zinc selenide polycrystal The amount can be increased. Therefore, acceptor impurities can be more easily doped into the zinc selenide polycrystal by thermal diffusion. Further, when doping acceptor impurities into the zinc selenide polycrystal, it is possible to effectively avoid the disadvantage that impurities other than the acceptor impurity are mixed into the zinc selenide polycrystal.

  The invention according to claim 8 is a zinc selenide polycrystal, characterized by having zinc vacancies and introducing selenium between crystal lattices. According to this configuration, zinc vacancies and selenium, which is an interstitial atom, act as an acceptor and generate holes in the zinc selenide polycrystal. Accordingly, free electrons existing in the zinc selenide polycrystal can be combined with the holes to reduce the free electrons existing in the zinc selenide polycrystal. Then, for example, when a lens formed of a zinc selenide polycrystal is used as an optical component for a carbon dioxide gas laser, it is incident on the zinc selenide lens as compared with the case where the conventional zinc selenide polycrystal is used. Since free electrons that absorb carbon dioxide laser light are reduced, the temperature rise of the zinc selenide lens can be effectively suppressed, and the change in the refractive index of the zinc selenide lens due to the temperature rise is effectively reduced. It becomes possible to suppress. Therefore, compared with the case where the conventional zinc selenide polycrystal is used, the focal length variation of the zinc selenide lens and the occurrence of burnout of the zinc selenide lens can be effectively prevented. Can be processed appropriately.

  The invention according to claim 9 is a method for producing a zinc selenide polycrystal, wherein, when the zinc selenide polycrystal is grown by a CVD method, zinc and an amount of selenium larger than the amount of zinc are reacted. It is characterized by that.

  According to the same configuration, in the synthesized zinc selenide polycrystal, zinc vacancies are generated and selenium is present as interstitial atoms, and these zinc vacancies and interstitial atoms are present. Selenium acts as an acceptor and generates holes in the zinc selenide polycrystal. Accordingly, free electrons existing in the zinc selenide polycrystal can be combined with the holes to reduce the free electrons existing in the zinc selenide polycrystal. Then, for example, when a lens formed of a zinc selenide polycrystal is used as an optical component for a carbon dioxide gas laser, it is incident on the zinc selenide lens as compared with the case where the conventional zinc selenide polycrystal is used. Since free electrons that absorb carbon dioxide laser light are reduced, the temperature rise of the zinc selenide lens can be effectively suppressed, and the change in the refractive index of the zinc selenide lens due to the temperature rise is effectively reduced. It becomes possible to suppress. Therefore, compared with the case where the conventional zinc selenide polycrystal is used, the focal length variation of the zinc selenide lens and the occurrence of burnout of the zinc selenide lens can be effectively prevented. Can be processed appropriately.

  The invention according to claim 10 is a method for producing a zinc selenide polycrystal, comprising a step of synthesizing a zinc selenide polycrystal by a CVD method and a heat treatment of the synthesized zinc selenide polycrystal. Zinc polycrystal is characterized by generating zinc vacancies and introducing selenium between crystal lattices.

  According to the same configuration, in the synthesized zinc selenide polycrystal, zinc vacancies are generated and selenium is present as interstitial atoms, and these zinc vacancies and interstitial atoms are present. Selenium acts as an acceptor and generates holes in the zinc selenide polycrystal. Accordingly, free electrons existing in the zinc selenide polycrystal can be combined with the holes to reduce the free electrons existing in the zinc selenide polycrystal. Then, for example, when a lens formed of zinc selenide polycrystal is used as an optical component for a carbon dioxide gas laser, it is incident on the zinc selenide lens as compared with the case of using the conventional zinc selenide polycrystal. Since free electrons that absorb carbon dioxide laser light are reduced, the temperature rise of the zinc selenide lens can be effectively suppressed, and the change in the refractive index of the zinc selenide lens due to the temperature rise is effectively reduced. It becomes possible to suppress. Therefore, compared with the case where the conventional zinc selenide polycrystal is used, the focal length variation of the zinc selenide lens and the occurrence of burnout of the zinc selenide lens can be effectively prevented. Can be processed appropriately.

  According to the present invention, when a zinc selenide lens is used as a lens for processing an object to be processed by a carbon dioxide gas laser and guides irradiated laser light to a target, the focal point of the zinc selenide lens is It is possible to effectively prevent the fluctuation of the distance and the burnout of the zinc selenide lens, and it becomes easy to process the workpiece appropriately.

(First embodiment)
Hereinafter, a preferred embodiment of the present invention will be described. FIG. 1 is a schematic diagram showing the overall configuration of an apparatus for carrying out the method for synthesizing zinc selenide polycrystal according to the first embodiment of the present invention. The apparatus 1 includes a carrier gas container 2 containing a carrier gas and a hydrogen gas container 3 containing hydrogen gas. The apparatus 1 further includes a zinc vapor generation chamber 4 connected to the carrier gas container 2 and a hydrogen selenide synthesis chamber 5 connected to the hydrogen gas container 3. In the zinc vapor generation chamber 4, a molten bath 7 containing metal zinc 6 is installed, and a heater 8 is provided around the zinc vapor generation chamber 4. In the hydrogen selenide synthesis chamber 5, a molten bath 10 containing metal selenium 9 is installed, and a heater 11 is provided around the hydrogen selenide synthesis chamber 5. The apparatus 1 also includes a reaction chamber 12 connected to both the zinc vapor generation chamber 4 and the hydrogen selenide synthesis chamber 5 and a cold trap 15 connected to the reaction chamber 12. A substrate 13 is installed in the reaction chamber 12, and a heater 14 is provided around the reaction chamber 12. As shown in FIG. 1, the hydrogen selenide synthesis chamber 5 is connected to the reaction chamber 12 via a flow rate adjustment valve 16 for adjusting the flow rate of the synthesized hydrogen selenide to the reaction chamber 12. ing.

  When synthesizing zinc selenide polycrystals for optical components such as lenses used for processing with a carbon dioxide laser by the CVD method, the temperature of the carrier gas is controlled from the carrier gas container 2 by the heater 8. In addition, the hydrogen gas is supplied from the hydrogen gas container 3 to the hydrogen selenide synthesis chamber 5 whose temperature is controlled by the heater 11. Then, in the zinc vapor generation chamber 4, zinc vapor from the metal zinc 6 is generated, and the zinc vapor is supplied to the reaction chamber 12 together with the carrier gas supplied to the zinc vapor generation chamber 4. On the other hand, in the hydrogen selenide synthesis chamber 5, selenium vapor from the metal selenium 9 reacts with the hydrogen gas supplied to the hydrogen selenide synthesis chamber 5 to synthesize and segregate hydrogen selenide. The hydrogen selenide gas is supplied to the reaction chamber 12 together with unreacted hydrogen gas.

  Then, in the reaction chamber 12 controlled in temperature by the heater 14, the zinc vapor supplied to the reaction chamber 12 reacts with hydrogen selenide to grow zinc selenide polycrystal on the substrate 13, The deposited layer 17 made of the zinc selenide polycrystal is formed. Further, the excess gas in the reaction chamber 12 is discharged through the cold trap 15.

  The zinc selenide single crystal is generally used for an active element such as a light-emitting device and is used with an increased electrical resistance, whereas the zinc selenide polycrystal of the present embodiment is laser-processed as described above. The zinc selenide polycrystal of the present invention is essentially a property of a zinc selenide single crystal for a light emitting device because it is used for an optical component when performing electrical resistance. Are different.

  Here, the present embodiment is characterized in that a zinc selenide polycrystal doped with an acceptor impurity is synthesized during synthesis by the above-described CVD method. The doped acceptor impurity acts as an acceptor and generates holes in the zinc selenide polycrystal. Therefore, the free electrons existing in the zinc selenide polycrystal are combined with the generated holes, so that the free electrons existing in the zinc selenide polycrystal are reduced.

Examples of the acceptor impurity include Group 1 elements such as lithium, sodium, and potassium. In order to synthesize a zinc selenide polycrystal doped with an acceptor impurity, a raw material of an acceptor impurity, for example, lithium selenide (in the above-described CVD method, in a molten bath 10 containing the above metal selenium 9 ( While supplying Li ₂ Se), sodium selenide (Na ₂ Se), potassium selenide (K ₂ Se), etc., hydrogen gas is supplied to the hydrogen selenide synthesis chamber 5 and hydrogen selenide synthesis chamber The H ₂ Se gas synthesized in 5 is supplied to the reaction chamber 12 together with unreacted hydrogen gas. Then, when the zinc selenide polycrystal is synthesized in the reaction chamber 12 by the reaction of zinc vapor and hydrogen selenide, the acceptor impurity is taken into the zinc selenide polycrystal, and the acceptor impurity is doped. A zinc selenide polycrystal will be synthesized.

  The concentration of acceptor impurities in the zinc selenide polycrystal is preferably 0.001 ppb or more and 0.01 ppm or less. This is because if the concentration of the acceptor impurity is less than 0.001 ppb, it is difficult to sufficiently obtain the effect of reducing the above-mentioned free electrons, and if the concentration of the acceptor impurity is greater than 0.01 ppm, the carbonation due to the acceptor impurity is difficult. This is because the absorption effect of the gas laser beam is larger than the above-described effect of reducing free electrons, and the absorption of the carbon dioxide laser beam is promoted.

  Also, the amount of acceptor impurity raw material accommodated in the molten bath 10 can be reliably doped with the acceptor impurity, and the effect of reducing free electrons by impurity absorption when the acceptor impurity is excessively doped. From the viewpoint of preventing inconvenience of canceling out, it is preferable that the amount is 0.5 wt% or more and 5 wt% or less with respect to the weight of the metal selenium contained in the molten bath 10.

According to the present embodiment described above, the following effects can be obtained.
(1) In this embodiment, the acceptor impurity is doped into the crystal of zinc selenide polycrystal. Therefore, the doped acceptor impurity acts as an acceptor and generates holes in the zinc selenide polycrystal. Therefore, free electrons present in the zinc selenide polycrystal due to slight residual impurities, vacancies, and defects are combined with the holes, reducing the free electrons present in the zinc selenide polycrystal. It becomes possible to make it. Then, when a lens formed of zinc selenide polycrystal is used as an optical component for a carbon dioxide laser, the carbon dioxide laser incident on the zinc selenide lens is used as compared with the case of using the conventional zinc selenide polycrystal. Since free electrons that absorb light are reduced, the temperature increase of the zinc selenide lens can be effectively suppressed, and the change in the refractive index of the zinc selenide lens due to the temperature increase is effectively suppressed. It becomes possible. Therefore, compared to the case of using the conventional zinc selenide polycrystal, it is possible to effectively prevent the fluctuation of the focal length of the zinc selenide lens and the occurrence of burnout of the zinc selenide lens. Can be processed appropriately.

  (2) In this embodiment, when the zinc selenide polycrystal is grown by the CVD method, the acceptor impurity is doped into the zinc selenide polycrystal. Therefore, the acceptor impurity can be uniformly doped in the entire zinc selenide polycrystal.

  (3) In this embodiment, the acceptor impurity includes at least one element selected from the group consisting of lithium, sodium, and potassium. Therefore, a zinc selenide polycrystal doped with acceptor impurities can be obtained with an inexpensive and simple configuration.

  (4) In this embodiment, the concentration of the acceptor impurity in the zinc selenide polycrystal is set to 0.001 ppb or more and 0.01 ppm or less. Accordingly, it is possible to sufficiently exhibit the effect of reducing free electrons while suppressing the absorption of the carbon dioxide laser beam by the doped acceptor impurity.

(5) In this embodiment, when lithium, sodium, or potassium is used as the acceptor impurity, the acceptor impurity and selenium compound (that is, Li ₂ Se, Na ₂ Se, K ₂ Se) is used. Therefore, when doping the acceptor impurity into the zinc selenide polycrystal, it is possible to effectively avoid the disadvantage that impurities other than the acceptor impurity are mixed into the zinc selenide polycrystal.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. In the first embodiment described above, when the zinc selenide polycrystal is grown by the CVD method, the acceptor impurity is doped into the zinc selenide polycrystal. After synthesizing the zinc selenide polycrystal by the CVD method, the above-described zinc selenide polycrystal is doped with the acceptor impurities such as lithium, sodium, and potassium by heat treatment.

  More specifically, first, zinc selenide polycrystal is synthesized by the above-described CVD method. At this time, unlike the first embodiment, the acceptor impurity raw material is not accommodated in the molten bath 10 and only the metal selenium 9 is accommodated to synthesize zinc selenide polycrystal.

Next, the synthesized zinc selenide polycrystal is subjected to ultrasonic cleaning with acetone and ethanol, and then etched using sodium hydroxide (NaOH). Next, the zinc selenide polycrystal is housed in a quartz tube washed with hydrofluoric acid together with acceptor impurity raw materials (for example, Li ₂ Se, Na ₂ Se, K ₂ Se), and a predetermined pressure (1 × 10 ^−3). The quartz tube is vacuum-enclosed with zinc selenide polycrystal and acceptor impurity materials. Next, the vacuum sealed quartz tube is heat-treated at a temperature of 600 to 1200 ° C. for a predetermined time. Then, zinc in the zinc selenide polycrystal and the acceptor impurity (for example, lithium) are exchanged by thermal diffusion, and the zinc selenide polycrystal doped with the acceptor impurity is synthesized. In this case as well, as in the case of the first embodiment described above, the doped acceptor impurity acts as an acceptor and generates holes in the zinc selenide polycrystal, so that it exists in the zinc selenide polycrystal. The free electrons to be combined with the generated holes decrease the free electrons existing in the zinc selenide polycrystal.

  In the present embodiment, as in the first embodiment, the acceptor impurity concentration in the zinc selenide polycrystal is preferably 0.001 ppb or more and 0.01 ppm or less.

According to this embodiment described above, in addition to the effects (1), (3), and (4) described in the first embodiment, the following effects can be obtained.
(6) In this embodiment, after synthesizing a zinc selenide polycrystal by a CVD method, an acceptor impurity is doped into the zinc selenide polycrystal by a heat treatment. Therefore, the acceptor impurity can be uniformly doped in the entire zinc selenide polycrystal. In addition, acceptor impurities can be easily doped into the zinc selenide polycrystal by thermal diffusion.

(7) In this embodiment, when lithium, sodium, or potassium is used as the acceptor impurity, the acceptor impurity and selenium compound (that is, Li ₂ Se, Na ₂ Se, K ₂ Se) is used. Since these Li ₂ Se, Na ₂ Se, and K ₂ Se have a high vapor pressure at the heat treatment temperature and are likely to become gases, the contact amount of the acceptor impurity raw material with the synthesized zinc selenide polycrystal is increased. Can do. Therefore, acceptor impurities can be more easily doped into the zinc selenide polycrystal by thermal diffusion. Further, when doping acceptor impurities into the zinc selenide polycrystal, it is possible to effectively avoid the disadvantage that impurities other than the acceptor impurity are mixed into the zinc selenide polycrystal.

(Third embodiment)
Next, a third embodiment of the present invention will be described. In the first embodiment described above, when the zinc selenide polycrystal is grown by the CVD method, the acceptor impurity is doped into the zinc selenide polycrystal. When growing polycrystalline zinc selenide by CVD, zinc and selenium in an amount larger than the amount of zinc are reacted (that is, the amount of selenium is made larger than the amount of zinc and selenium and zinc are reacted). ) There is a feature.

  More specifically, when the zinc selenide polycrystal is synthesized by the above-described CVD method, the amount larger than the amount of zinc (that is, the amount of zinc vapor) supplied to the reaction chamber 12 by the flow rate adjusting valve 16. The selenium flow rate is adjusted so that the selenium (i.e., hydrogen selenide gas) is supplied to the reaction chamber 12. At this time, unlike the first embodiment, the raw material of the acceptor impurity is not accommodated in the molten bath 10 and only the metal selenium 9 is accommodated.

  Then, in the reaction chamber 12, since the zinc selenide polycrystal is synthesized in an excessive state of selenium, zinc vacancies are generated in the synthesized zinc selenide polycrystal and the selenium is interstitial. It will exist as an atom. Therefore, a zinc selenide polycrystal having zinc vacancies and having selenium introduced between crystal lattices can be synthesized. In this case as well, as in the case of the first embodiment described above, these zinc vacancies and selenium, which is an interstitial atom, act as acceptors, generating holes in the zinc selenide polycrystal. Therefore, the free electrons existing in the zinc selenide polycrystal are combined with the generated holes, and the free electrons existing in the zinc selenide polycrystal are reduced.

According to the present embodiment described above, the following effects can be obtained.
(8) In this embodiment, when growing a zinc selenide polycrystal by CVD method, it is set as the structure which reacts zinc and the quantity of selenium larger than the quantity of zinc. Accordingly, in the synthesized zinc selenide polycrystal, zinc vacancies are generated and selenium is present as interstitial atoms. These zinc vacancies and selenium as interstitial atoms are As a result, holes are generated in the zinc selenide polycrystal. As a result, free electrons existing in the zinc selenide polycrystal due to slight residual impurities, vacancies, and defects are combined with the holes, thereby reducing the free electrons existing in the zinc selenide polycrystal. It becomes possible to make it. Then, when a lens formed of zinc selenide polycrystal is used as an optical component for a carbon dioxide laser, the carbon dioxide laser incident on the zinc selenide lens is used as compared with the case of using the conventional zinc selenide polycrystal. Since free electrons that absorb light are reduced, the temperature increase of the zinc selenide lens can be effectively suppressed, and the change in the refractive index of the zinc selenide lens due to the temperature increase is effectively suppressed. It becomes possible. Therefore, compared with the case where the conventional zinc selenide polycrystal is used, the focal length variation of the zinc selenide lens and the occurrence of burnout of the zinc selenide lens can be effectively prevented. Can be processed appropriately.

(Fourth embodiment)
Next, a fourth embodiment of the present invention will be described. In the above-described third embodiment, when the zinc selenide polycrystal is grown by the CVD method, the amount of selenium is made larger than the amount of zinc to react selenium with zinc. In the embodiment, after synthesizing the zinc selenide polycrystal by the above-described CVD method, the synthesized zinc selenide polycrystal is heat-treated to generate zinc vacancies in the zinc selenide polycrystal, It is characterized in that selenium is introduced between crystal lattices.

  More specifically, first, zinc selenide polycrystal is synthesized by the above-described CVD method. At this time, also in the present embodiment, unlike the above-described first embodiment, the acceptor impurity raw material is not accommodated in the molten bath 10, and only the metal selenium 9 is accommodated to synthesize zinc selenide polycrystal. To do.

Next, the synthesized zinc selenide polycrystal is subjected to ultrasonic cleaning with acetone and ethanol, and then etched using sodium hydroxide. Next, the zinc selenide polycrystal is accommodated in a quartz tube washed with hydrofluoric acid, and evacuated by a predetermined pressure (1 × 10 ⁻³ Pa or less), and the zinc selenide polycrystal is vacuum sealed in the quartz tube. To do. Next, the vacuum sealed quartz tube is heat-treated at a temperature of 600 to 1200 ° C. for a predetermined time. Then, excess zinc present in the polycrystal of zinc selenide is extracted from the crystal by heat treatment, and zinc vacancies are generated, and excess selenium is introduced into the crystal by thermal diffusion, Exists as an interstitial atom. Therefore, a zinc selenide polycrystal having zinc vacancies and having selenium introduced between crystal lattices can be synthesized. In this case as well, as in the case of the first embodiment described above, these zinc vacancies and selenium, which is an interstitial atom, act as acceptors, generating holes in the zinc selenide polycrystal. Therefore, the free electrons existing in the zinc selenide polycrystal are combined with the generated holes, and the free electrons existing in the zinc selenide polycrystal are reduced.

According to the present embodiment described above, the following effects can be obtained.
(9) In this embodiment, after synthesizing the zinc selenide polycrystal by the CVD method, the synthesized zinc selenide polycrystal is heat-treated to generate zinc vacancies in the zinc selenide polycrystal. In addition, selenium is introduced between crystal lattices. Therefore, in the synthesized zinc selenide polycrystal, selenium which is a vacancy of zinc and interstitial atoms exists, and selenium which is a vacancy of zinc and interstitial atoms acts as an acceptor. Then, holes are generated in the zinc selenide polycrystal. As a result, free electrons existing in the zinc selenide polycrystal due to slight residual impurities, vacancies, and defects are combined with the holes, thereby reducing the free electrons existing in the zinc selenide polycrystal. It becomes possible to make it. Then, when a lens formed of zinc selenide polycrystal is used as an optical component for a carbon dioxide laser, the carbon dioxide laser incident on the zinc selenide lens is used as compared with the case of using the conventional zinc selenide polycrystal. Since free electrons that absorb light are reduced, the temperature increase of the zinc selenide lens can be effectively suppressed, and the change in the refractive index of the zinc selenide lens due to the temperature increase is effectively suppressed. It becomes possible. Therefore, compared with the case where the conventional zinc selenide polycrystal is used, the focal length variation of the zinc selenide lens and the occurrence of burnout of the zinc selenide lens can be effectively prevented. Can be processed appropriately.

  Below, this invention is demonstrated based on an Example and a comparative example. In addition, this invention is not limited to these Examples, These Examples can be changed and changed based on the meaning of this invention, and they are excluded from the scope of the present invention. is not.

(Example 1)
(Production of zinc selenide polycrystal)
First, by using the apparatus shown in FIG. 1, a zinc selenide-rich material is obtained by the above-described CVD method in a state where Na ₂ Se, which is a raw material for acceptor impurities, is contained in a molten bath 10 containing metal selenium 9. Crystals were synthesized. The total gas pressure in the reaction chamber 12 is 100 Toor, the temperature of the substrate 13 is 700 ° C., the temperature of the molten bath 7 containing the metallic zinc 6 is 500 ° C., and the molten bath containing the metallic selenium 9 and Na ₂ Se. The reaction was performed for 300 hours at a temperature of 10 at 500 ° C. and a hydrogen gas flow rate of 70 cc / min. Further, the CVD method was performed by setting the amount of acceptor impurity raw material accommodated in the molten bath 10 to 1 wt% with respect to the weight of the metal selenium accommodated in the molten bath 10. As a result, a zinc selenide polycrystal having a thickness of about 15 mm was obtained.

(Measurement of absorption rate)
Next, the obtained zinc selenide polycrystal is processed into 10 samples of zinc selenide polycrystal (diameter: 50 mm, thickness: 10 mm), and for each zinc selenide polycrystal for samples. Then, optical polishing was performed so that the surface roughness was 10 nm or less. Next, a 10.6 μm carbon dioxide laser beam is irradiated to the polycrystal zinc selenide for each sample, and the absorption of the laser beam is performed using an absorptance measuring device (trade name Photoluminer W640, manufactured by Horiba Jobibon). Absorptivity was measured. The results are shown in Table 1.

(Comparative Example 1)
A zinc selenide polycrystal was produced in the same manner as in Example 1 except that Na ₂ Se as an acceptor impurity raw material was not contained in the molten bath 10 containing the metal selenium 9. Further, the absorptance was measured under the same conditions as in Example 1 described above. The results are shown in Table 1.

As shown in Table 1, the zinc selenide polycrystal of Example 1 has a lower laser beam absorption than the zinc selenide polycrystal of Comparative Example 1, and is free in the zinc selenide polycrystal. It can be seen that the number of electrons is decreasing. In Example 1, the acceptor is synthesized by synthesizing zinc selenide polycrystal in a state where Na ₂ Se, which is a raw material of acceptor impurities, is accommodated in the molten bath 10 in which metal selenium 9 is accommodated. This is considered to be because a zinc selenide polycrystal doped with Na as an impurity could be obtained.

(Example 2)
(Production of zinc selenide polycrystal)
First, when the zinc selenide polycrystal was manufactured by the above-mentioned CVD method using the apparatus shown in FIG. 1, the zinc selenide polycrystal having a thickness of about 10 mm was obtained. A zinc selenide polycrystal was produced in the same manner as in Example 1 except that Na ₂ Se, which is a raw material for acceptor impurities, was not contained in the molten bath 10 in which the metal selenium 9 was contained. .

(Heat treatment of polycrystalline zinc selenide)
Next, the obtained zinc selenide polycrystal was processed into 10 samples of zinc selenide polycrystal (diameter: 60 mm, thickness: 15 mm), and the zinc selenide polycrystal for each sample was processed. Then, ultrasonic cleaning was performed with acetone and ethanol, and etching was performed using NaOH (25 wt%) at 120 ° C. for 15 minutes. Next, each zinc selenide polycrystal is accommodated in a quartz tube (diameter: 70 mm, length: 200 mm) washed with hydrofluoric acid together with Na ₂ Se as an acceptor impurity raw material, and a predetermined pressure (1 × 10 10). ^-3 Pa or less) was evacuated, and zinc selenide polycrystal and Na ₂ Se were vacuum sealed in the quartz tube. Next, the vacuum sealed quartz tube was subjected to heat treatment at a temperature of about 800 ° C. for 240 hours.

(Measurement of absorption rate)
After completion of the heat treatment, the zinc selenide polycrystal is taken out from the quartz tube and processed into ten samples of zinc selenide polycrystal (diameter: 50 mm, thickness: 10 mm), and then each zinc selenide for the sample is used. Optical polishing was performed on the polycrystal so that the surface roughness was 10 nm or less. Next, a zinc selenide polycrystal for each sample was vapor-deposited with thorium fluoride and a zinc selenide film on both sides as a non-reflective coating, and then irradiated with a 10.6 μm carbon dioxide laser beam for absorption. The absorption rate of the laser beam was measured using a rate measuring device. The results are shown in Table 2.

(Comparative Example 2)
A zinc selenide polycrystal was produced in the same manner as in Example 2 except that the heat treatment was not performed. Further, the absorptance was measured under the same conditions as in Example 2 described above. The results are shown in Table 1.

  As shown in Table 2, the zinc selenide polycrystal of Example 2 has a lower laser light absorption than the zinc selenide polycrystal of Comparative Example 2, and is free in the zinc selenide polycrystal. It can be seen that electrons are decreasing. This is because in Example 2, zinc selenide polycrystals doped with Na, which is an acceptor impurity, were obtained by performing heat treatment after synthesizing the zinc selenide polycrystals by the CVD method. It is thought that there is.

(Photoluminescence measurement)
Next, in order to confirm that Na, which is an acceptor impurity, is doped, a photoluminescence measuring device (manufactured by Horiba Jobibon Co., Ltd., trade name Photoluminer W640) is applied to the manufactured zinc selenide polycrystal. Used to perform photoluminescence measurement. In addition, as a sample of the zinc selenide polycrystal which was heat-treated, the zinc selenide polycrystal produced in the above-mentioned Example 2 was cut into a length of 10 mm and a thickness of 1 mm, and the surface roughness was 10 nm or less. As described above, after performing optical polishing, the one subjected to the above-described ultrasonic cleaning, etching, and heat treatment was used. In addition, as a sample of the zinc selenide polycrystal that was not heat-treated (that is, before the heat treatment), the zinc selenide polycrystal produced in Example 2 described above was cut into a length of 10 mm and a thickness of 1 mm, The optical polishing was performed so that the surface roughness was 10 nm or less, and then only the above-described ultrasonic cleaning and etching were performed. The measurement temperature was 4.2 K, and a 325 nm He—Cd laser was used as the excitation light source. FIG. 2 shows a chart obtained by photoluminescence measurement for the heat-treated zinc selenide polycrystal, and FIG. 2 shows a chart obtained by photoluminescence measurement for the zinc selenide polycrystal which has not been heat-treated. 3 shows.

  As shown in FIG. 3, in the zinc selenide polycrystal before heat treatment, acceptor-bound excitation that emits holes with respect to donor-bound excitons (peak wavelength: 4431Å, emission intensity: 6.2) that emits free electrons. The emission intensity ratio of the child (peak wavelength: 4439 mm, emission intensity: 0.5) was 0.08. On the other hand, as shown in FIG. 2, in the zinc selenide polycrystal after heat treatment, an acceptor that emits holes with respect to donor-bound excitons (peak wavelength: 4431 ：, emission intensity: 8.6) that emits free electrons. The emission intensity ratio of bound excitons (peak wavelength: 4439Å, emission intensity: 3.1) was 0.36. That is, before and after the heat treatment, the above-mentioned emission intensity ratio was increased, and it was confirmed that the acceptor impurity Na was doped by the heat treatment.

  As an application example of the present invention, a carbon dioxide laser is used as a heat source, and an optical component used when laser processing such as drilling and cutting is performed by locally heating an object to be processed by the heat of laser light. A hydrogen selenide polycrystal and a method for producing the same.

It is the schematic which shows the whole structure of the apparatus for enforcing the synthesis method of the zinc selenide polycrystal which concerns on the 1st Embodiment of this invention. It is the chart obtained by the photoluminescence measurement with respect to the zinc selenide polycrystal by which heat processing was performed. It is the chart obtained by the photoluminescence measurement with respect to the zinc selenide polycrystal which was not heat-processed.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Apparatus, 2 ... Carrier gas container, 3 ... Hydrogen gas container, 4 ... Zinc vapor generation chamber, 5 ... Hydrogen selenide synthesis chamber, 6 ... Metal zinc, 7 ... Molten bath, 8 ... Heater, 9 ... Metal selenium, DESCRIPTION OF SYMBOLS 10 ... Molten bath, 11 ... Heater, 12 ... Reaction chamber, 13 ... Substrate, 14 ... Heater, 15 ... Cold trap 16 ... Flow control valve, 17 ... Deposited layer

Claims (10)

  A zinc selenide polycrystal characterized in that an acceptor impurity is doped in the crystal.   2. The zinc selenide polycrystal according to claim 1, wherein a concentration of the acceptor impurity in the zinc selenide polycrystal is 0.001 ppb or more and 0.01 ppm or less.   The zinc selenide polycrystal according to claim 1 or 2, wherein the acceptor impurity contains at least one element selected from the group consisting of lithium, sodium, and potassium.   A method for producing a zinc selenide polycrystal, wherein an acceptor impurity is doped into the zinc selenide polycrystal when growing the zinc selenide polycrystal by a CVD method. The acceptor impurity raw material contains at least one selected from the group consisting of lithium selenide (Li ₂ Se), sodium selenide (Na ₂ Se), and potassium selenide (K ₂ Se). The method for producing a zinc selenide polycrystal according to claim 4. Synthesizing zinc selenide polycrystal by a CVD method;
And a step of doping the zinc selenide polycrystal thus synthesized into a zinc selenide polycrystal by heat-treating the zinc selenide polycrystal. The acceptor impurity raw material contains at least one selected from the group consisting of lithium selenide (Li ₂ Se), sodium selenide (Na ₂ Se), and potassium selenide (K ₂ Se). The manufacturing method of the zinc selenide polycrystal of Claim 6.   A zinc selenide polycrystal having zinc vacancies and selenium introduced between crystal lattices.   A method for producing a zinc selenide polycrystal, characterized in that, when growing a zinc selenide polycrystal by a CVD method, zinc and an amount of selenium larger than the amount of zinc are reacted. Synthesizing zinc selenide polycrystal by a CVD method;
The zinc selenide polycrystal is characterized by generating zinc vacancies in the zinc selenide polycrystal by introducing a heat treatment into the synthesized zinc selenide polycrystal and introducing selenium between crystal lattices. Manufacturing method.

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