JP2018032654A - Vertical cavity light emitting element laser module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vertical cavity surface emitting laser module including a vertical cavity light emitting element and having high effect of heat dissipation.MEANS FOR SOLVING THE PROBLEM: A vertical cavity light emitting element laser module including a plurality of vertical cavity light emitting elements arrayed on a plane includes: a surface for bonding, which is arranged in a region between laser beams emitted from the vertical cavity light emitting elements adjacent to each other on a substrate and which is located on an emission side of the laser beams; and an outer wall facing a beam space where the laser beams propagate.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a vertical resonator type light emitting device such as a vertical cavity surface emitting laser (VCSEL), and more particularly to a vertical resonator type in which a plurality of vertical resonator type light emitting devices are arranged on a plane. The present invention relates to a surface emitting laser module.

  A vertical cavity surface emitting laser is a semiconductor laser having a structure that resonates light perpendicular to a substrate surface and emits light in a direction perpendicular to the substrate surface. For example, Patent Document 1 discloses that an insulating layer having an opening on at least one surface of a nitride semiconductor layer, a translucent electrode provided on the insulating layer so as to cover the opening, There is disclosed a vertical cavity surface emitting laser having a reflecting mirror provided on the opening through a translucent electrode. Reflecting mirrors facing each other with the light-transmitting electrode opening and the light-emitting layer interposed therebetween constitute a resonator.

  US Pat. No. 6,057,031 works in such a way that the laser radiation emitted by the active layer of several wide area vertical cavity surface emitting VCSELs and the active layer of all VCSELs or sub-groups of VCSELs in the array is superimposed in the working plane. One or more optical components designed and arranged to image the active layer of an array VCSEL in a plane.

  In each of Patent Documents 2 to 8, a mesa structure (projection structure) is formed in a DBR (Distributed Bragg Reflector) or an active layer portion using etching or the like, and a heat dissipation structure is formed at the bottom of the mesa structure portion or around the projection structure. A surface emitting laser having the following structure is disclosed.

Special table 2013-502717 gazette JP 2007-73585 A JP-A-11-261153 JP-A-11-261162 Japanese Patent No. 3271291 Japanese Patent No. 3624618 Japanese Patent No. 4066143 Japanese Patent No. 5177358

  However, in the conventional vertical cavity surface emitting laser of Patent Document 1, since a space is required between the optical component and the working plane, the heat radiation path from the working plane is only air, and the heat radiation performance of the working plane is reduced. Furthermore, there is a problem that the heat radiation path of the light source unit is only air and the heat radiation property is low. Each of the prior arts in Patent Documents 2 to 8 is a structure for improving heat dissipation, but only improves heat dissipation from the protrusions, and dissipates heat released from the protrusions to the air. In such a case, the thermal conductivity is poor, and if the heat is not radiated to other places, the effect of improving the heat dissipation of the protrusions is reduced. In the prior art disclosed in Patent Document 4, heat dissipation is attempted to be released by releasing heat from a protrusion to a large heat radiating pad connected to a heat pipe. In this method, an array of vertical cavity surface emitting lasers is used. When the number of vertical cavity surface emitting lasers in the array is increased, for example, when there are 4 rows × 4 rows, the effect of heat dissipation decreases.

  The present invention has been made in view of the above points, and an object thereof is to provide a vertical cavity surface emitting laser module having a high heat dissipation effect using a vertical cavity light emitting element.

The vertical cavity surface emitting laser module of the present invention is a vertical cavity type light emitting element module in which a plurality of vertical cavity type light emitting elements are arranged on a plane,
Each of the vertical cavity light emitting elements is laminated on a first reflector formed on a substrate, a first semiconductor layer of a first conductivity type, an active layer, and the first reflector. A semiconductor structure layer made of a second semiconductor layer of a second conductivity type opposite to the conductivity type of 1, a conductive current confinement layer, a transparent electrode in contact with the second semiconductor layer, A second reflector formed on the transparent electrode,
A bonding surface located on a region between the laser beams from the vertical cavity light emitting elements adjacent to each other on the substrate and positioned on the emission direction side of the laser beam and a beam space in which the laser beam propagates It further has a heat radiating member which has an outer wall which faces.

  According to the vertical cavity surface emitting laser module of the present invention, by installing the heat radiating member that demarcates the space that does not affect the optical path of the laser beam of the vertical cavity surface emitting laser, the optical component is further passed through the heat radiating member By connecting to the vertical cavity surface emitting laser, the heat dissipation of the optical component can be improved.

It is a partially transparent schematic plan view schematically showing the configuration of 16 surface-emitting laser modules arrayed by 16 4 × 4 of the surface-emitting laser that is Embodiment 1 of the present invention. It is a fragmentary sectional view which shows typically the part of the cross section along the AA line of FIG. It is a fragmentary sectional view which shows typically the part of the cross section along BB line of FIG. It is a schematic fragmentary sectional view for demonstrating the structure of the surface emitting laser module which is Example 1 of this invention. FIG. 6 is a schematic perspective view illustrating a part of a surface emitting laser module according to a modification of Example 1 of the present invention. It is a general | schematic part perspective view explaining a part of surface emitting laser module of Example 2 of this invention. It is a fragmentary sectional view which shows typically the part of the cross section along CC line of FIG. It is a general | schematic fragmentary sectional view for demonstrating the structure of the surface emitting laser module which is Example 3 of this invention.

  A vertical cavity surface emitting laser (hereinafter also simply referred to as a surface emitting laser) will be described with reference to the drawings as an example of the vertical cavity light emitting device of the present invention. In the following description and the accompanying drawings, substantially the same or equivalent parts will be described with the same reference numerals.

  FIG. 1 is a partially transparent schematic plan view of the external appearance of a surface emitting laser module 10A arranged in an array of 16 4 × 4 using the surface emitting laser (VCSEL) 10 of Example 1 according to the present invention as a light emitting part. Show. FIG. 2 is a partial cross-sectional view schematically showing a cross-sectional portion along line AA of two adjacent surface emitting lasers 10 in FIG. FIG. 3 is a partial cross-sectional view schematically showing a cross-sectional portion along the BB line of two adjacent surface emitting lasers 10 in FIG.

  As shown in FIGS. 2 and 3, the surface emitting laser 10 includes, for example, a conductive first reflector 13 formed in order on a conductive substrate 11 such as GaN made of GaN (gallium nitride), The stacked structure includes an n-type semiconductor layer 15 (first semiconductor layer), an active layer 17 including a quantum well layer, and a p-type semiconductor layer 19 (second semiconductor layer). The semiconductor structure layer SMC composed of the first reflector 13 and the n-type semiconductor layer 15, the active layer 17 including the quantum well layer, and the p-type semiconductor layer 19 in the stacked structure is made of a GaN-based semiconductor.

  The surface emitting laser 10 further includes an insulating current confinement layer 21, a conductive transparent electrode 23, and a second reflector 25, which are sequentially formed on the p-type semiconductor layer 19 of the semiconductor structure layer SMC. Have.

  The current confinement layer 21 has a through opening OP1. The transparent electrode 23 is formed so as to cover the through opening OP <b> 1 and contact the p-type semiconductor layer 19. The current confinement layer 21 prevents current injection into the p-type semiconductor layer 19 except for the through opening OP1. Inside the opening OP <b> 1, current is injected from the transparent electrode 23 into the active layer 17 through the p-type semiconductor layer 19.

  As shown in FIGS. 2 and 3, the P electrode 27P for injecting current is formed so as to be electrically connected to the transparent electrode 23 around the through opening OP1. The P electrode 27P is formed so as to be connected to a P pad electrode 29P (FIG. 1) that can be electrically connected to the outside through a wiring 27Pa on the current confinement layer 21 shown in FIG.

  The N pad electrode 29N shown in FIG. 1 is formed so as to be electrically connected to the n-type semiconductor layer 15 shown in FIG. 2 through a path (not shown).

  The portions of the first reflector 13 and the second reflector 25 that face each other across the through opening OP1 and the active layer 17 constitute a resonator 20.

  A through-opening OP1 (an interface between the transparent electrode 23 and the semiconductor structure layer SMC) of the current confinement layer formed immediately below the transparent electrode 23 between the resonators 20 corresponds to a laser beam passage port. The laser beam is emitted from the second reflector 25. A laser beam is emitted along the optical axis that penetrates the through opening OP1 in the stacking direction of the semiconductor structure layer SMC.

  In this embodiment, the first reflector 13 is formed as a distributed Bragg reflector (DBR) made of a multilayer film of GaN-based semiconductor. As the first reflector 13, for example, 40 pairs of GaN / InAlN can be stacked. The second reflector 25 is formed as a distributed Bragg reflector composed of a multilayer of dielectric films. The second reflector 25 and the first reflector 13 sandwich the semiconductor structure layer SMC and define a resonant structure. The first reflector 13 and the second reflector 25 have the number of pairs of multilayer films in which two thin films having different refractive indexes are alternately laminated a plurality of times in order to obtain their desired conductivity, insulation, and reflectance. The material, the film thickness and the like are appropriately adjusted. In the case of an insulating reflector, for example, dielectric thin film materials include oxides such as metals and metalloids.

The semiconductor structure layer SMC includes an n-type semiconductor layer 15, an active layer 17 including a quantum well layer, and a p-type semiconductor layer 19 that are sequentially formed on the first reflector 13. In this embodiment, each of the first reflector 13 and the semiconductor structure layer SMC has a composition of Al _x In _y Ga _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1). Have For example, the first reflector 13 has a structure in which a pair of a low refractive index semiconductor layer having a composition of AlInN and a high refractive index semiconductor layer having a composition of GaN are alternately stacked a plurality of times. In the present embodiment, the active layer 17 is a quantum layer in which pairs of well layers (not shown) having a composition of InGaN and barrier layers (not shown) having a composition of GaN are alternately stacked. It has a well structure. The n-type semiconductor layer 13 has a GaN composition and contains Si as an n-type impurity. The p-type semiconductor layer 19 has a GaN composition and contains a p-type impurity such as Mg. As a result, the n-type semiconductor layer 13 and the p-type semiconductor layer 19 have opposite conductivity types. In addition, the semiconductor structure layer SMC can be designed so that the emission wavelength is, for example, 400 to 450 nm.

  The first reflector 13 and the semiconductor structure layer SMC are formed using a metal organic chemical vapor deposition (MOCVD) method or the like. A buffer layer (not shown) may be formed between the substrate 11 and the first reflector 13.

Examples of the composition material of the current confinement layer 21 include oxides such as SiO ₂ , Ga ₂ O ₃ , Al ₂ O ₃ , and ZrO ₂ , and nitrides such as SiN, AlN, and AlGaN. Preferably, SiO ₂ is used for the current confinement layer 21. The film thickness of the current confinement layer 21 is 5 to 1000 nm, preferably 10 to 300 nm.

As the translucent composition material of the conductive transparent electrode 23, for example, ITO (Indium Tin Oxide), IZO (In-doped ZnO), AZO (Al-doped ZnO), GZO (Ga-doped ZnO), ATO ( Sb-doped SnO ₂ ), FTO (F-doped SnO ₂ ), NTO (Nb-doped TiO ₂ ), ZnO or the like is used. Preferably, ITO is used for the transparent electrode 23. The film thickness of the transparent electrode 23 is 3 to 100 nm, and preferably 20 nm or less. The transparent electrode 23 can be formed by electron beam evaporation, sputtering, or the like.

(Concrete example)
Formation of a vertical cavity surface emitting laser module in which 16 (4 × 4) surface emitting lasers 10 are arrayed as light emitting portions when the material of the heat radiating member is Au and the optical component is a diffusion plate is shown in FIGS. This will be described with reference to FIG.

(Surface emitting laser array formation)
Crystal growth is performed on the GaN substrate 11 by metal organic chemical vapor deposition (MOCVD). A GaN underlayer is grown using TMG (trimethylgallium) and ammonia as raw materials.

An Al _0.83 In _0.17 N layer is grown to 45 nm on the GaN underlayer using TMA (trimethylaluminum), TMI (trimethylindium), and ammonia as raw materials.

Next, a GaN layer is grown to 40 nm on the Al _0.83 In _0.17 N layer. As described above, the Al _0.83 In _0.17 N layer / GaN layer laminated film is made into one pair, and 40 pairs are laminated to produce a nitride semiconductor multilayer film, thereby completing the semiconductor multilayer film reflector (first reflector 13). .

Next, an n-type GaN layer (n-type semiconductor) is formed on the multilayer reflector using TMG (trimethylgallium) and ammonia as raw materials and SiH ₄ (silane) or Si ₂ H ₆ (disilane) as n-type impurity source gases. Grow layer 15).

  On the n-type GaN layer 15, a quantum well active layer 17 composed of five pairs of a GaInN quantum well layer and a GaN barrier layer is laminated and grown.

A p-type Al _0.15 Ga _0.85 N layer is grown to 20 nm on the GaInN quantum well active layer 17. For the p-type impurity source gas, CP2Mg (cyclopentadienylmagnesium) is used and Mg is doped at a concentration of 2 × 10 ²⁰ cm ⁻³ . A 70 nm p-type GaN layer is grown on the p-type AlGaN layer. For the p-type impurity source gas, CP2Mg (cyclopentadienylmagnesium) is used and Mg is doped at a concentration of 2 × 10 ¹⁹ cm ⁻³ . Finally, a p-type GaN contact layer is grown to 10 nm on the p-type GaN layer. The p-type GaN contact layer is doped with p-type impurity Mg at a concentration of 2 × 10 ²⁰ cm ⁻³ . In this manner, the p-type semiconductor layer 19 (second semiconductor layer) including the p-type AlGaN layer, the p-type GaN layer, and the p-type GaN contact layer is formed on the GaInN quantum well active layer 17.

  A resist pattern with a diameter of 50 μm is formed on the p-type GaN contact layer using a known photolithography technique, and dry etching is performed to reach the n-type GaN layer with chlorine gas to remove the p-type GaN layer and the active layer. Then, pn separation is performed by exposing the n-type GaN layer, and a mesa portion protruding from the n-type GaN layer is formed. Further, the pitch L1 (FIG. 4) between the mesa portions formed in this step is 100 μm.

Subsequently, a SiO ₂ film having a thickness of 300 nm is formed on the region including the mesa portion by sputtering, and etching is performed using hydrofluoric acid with a resist pattern, whereby the current confinement layer 21 made of the SiO ₂ insulating film and the through opening OP1. Form.

  After forming the lift-off resist pattern, ITO is deposited by sputtering and then lifted off to form a transparent electrode film (transparent electrode 23).

  After the lift-off resist pattern is formed, a Pt / Au film is formed by vapor deposition, and then lifted off to form wiring electrodes (P electrode 27P and P pad electrode 29P).

  After the lift-off resist pattern is formed, a Ti / Pt / Au film is formed by vapor deposition, and then lifted off to form the ohmic electrode 106.

A reflective mirror film composed of 20 pairs of Nb ₂ O ₅ layer / SiO ₂ layer dielectric multilayer film having a reflection center wavelength of 450 nm is laminated on the entire surface, a resist pattern is formed by a photolithography process, and dry etching is performed for reflection. A mirror (second reflector 25) is formed. In this way, a resonator having the same resonance wavelength as the resonance wavelength is formed. Thus, the array of surface emitting lasers 10 is completed.

(Formation of heat dissipation member)
Next, the process of forming the heat dissipation member 109 on the substrate 11 will be described.

  FIG. 4 is a schematic cross-sectional view showing the spread of a laser beam emitted from the surface emitting laser 10 on the substrate 11, that is, the beam space BS in which the laser beam propagates. The heat dissipation member 109 is formed in a region between adjacent laser beams. The heat radiating member 109 has a bonding surface 109a located on the laser beam emission direction side of the surface emitting laser 10 and an outer wall 109b facing the beam space BS through which the laser beam propagates. Thus, the laser beam is emitted without hitting the outer wall 109b of the heat radiating member 109, and the heat radiating member 109 does not affect the optical path of the laser beam.

  For example, when the emission diameter D of the surface emitting laser 10 is 10 μm, the distance L2 from the upper part of the mesa portion (second reflector 25) to the optical component is 10 μm, and the radiation angle θ of the surface emitting laser 10 is 5 °, the heat is dissipated. The width W of the joining surface 109a of the member is given by the formula “W = L1− (L2 × tan (θ) × 2 + D)”, and W = 88 μm. Therefore, the width OPw of the opening is 80 μm. And The range of the radiation angle θ of the surface emitting laser 10 is more than 0 ° and not more than 20 °.

  First, in order to form a heat dissipation member, a lift-off resist pattern is formed on the ohmic electrode 106 on the substrate 11 so as to have an opening in a range that does not affect the laser beam.

  Next, a film of Au is deposited by plating so as to be higher than the upper part of the second reflector 25 (DBR). For example, the heat radiating member 10 has a height of 10 μm. The heat dissipation member 109 is formed by lift-off.

  Subsequently, for example, an optical component 111 of a diffusion plate is prepared, an Au pattern 110 having the same pattern as that of the heat dissipation member 109 is formed on the lower surface thereof, and bonded to the bonding surface 109a of the heat dissipation member with solder such as AuSn. Alternatively, instead of solder, a bonding agent such as an Ag paste or a flip chip Au—Au direct bonding method may be used. Further, fixing may be performed by screwing or the like without using a bonding agent.

  Although the optical component is bonded after forming the heat dissipation member 109, the heat dissipation member 109 may be formed on the optical component by plating or nanoimprinting and then bonded to the substrate 11.

  The material of the heat radiating member 109 is Au, but the material is not limited to Au, and a heat radiating member made of Ag, Cu, Al, anodized Al may be used.

  The optical component is not limited to the diffusion plate, but may be a lens such as a macro lens, a phosphor plate, a reflector, or the like.

  As described above, it is possible to provide a surface emitting laser module in which the surface emitting laser 10 having excellent heat dissipation, the heat radiating member 109, and the optical component 44 are integrated.

[Modification]
In the above example, the heat dissipation member 109 of FIG. 1 has a uniform trapezoidal cross section, but the heat dissipation member 109 is not limited to a uniform trapezoidal shape, for example, as shown in FIG. The outer wall 109b of the heat radiating member 109 can also be configured so as to include a part of an inverted conical recess RC that matches the spread of the laser beam emitted for each surface emitting laser 10, that is, the beam space in which the laser beam propagates. . By including the outer wall portion that expands in a reverse taper shape as the heat radiating member 109 moves away from the substrate 11, that is, the conical concave portion RC, the heat dissipation effect is further improved and the radiation efficiency of the laser beam is also improved.

  FIG. 6 is a schematic perspective view illustrating a part of the surface emitting laser module according to the second embodiment of the present invention. FIG. 7 is a partial cross-sectional view schematically showing a cross-sectional portion taken along the line CC of FIG.

  In the first embodiment, the case where the light emitting portion of the surface emitting laser 10 is mounted so as to be above the GaN substrate 11 (face up) is shown. However, the light emitting portion of the surface emitting laser 10 is below the substrate 11 (face down). It is preferable to mount so that it becomes. By doing so, the heat of the heat generating portion can be directly radiated to the mounting substrate 31, and at the same time, the heat can be radiated from the substrate side of the surface emitting laser 10 through the heat radiating member 109. For this reason, it becomes possible to efficiently dissipate heat from above and below the surface emitting laser 10, and a surface emitting laser module having excellent heat dissipation can be provided.

  As shown in FIGS. 6 and 7, the phosphor glass plate 30 is attached to the substrate 11 (first reflector 13) side of the surface emitting laser module 10 </ b> A via the heat radiating member 109. A corresponding P connection electrode and a corresponding N corresponding to the P pad electrode and the N pad electrode of the surface emitting laser module 10A are mounted on the mounting surface of the mount substrate 31 made of a high thermal conductive material such as Si, AlN, SiC (not shown). An electrode provided with connection electrodes 31P and 31N is prepared. Then, the surface emitting laser module of the white light source is obtained by flip-chip mounting the semiconductor structure layer SMC (second reflector, P pad electrode and N pad electrode) side of the surface emitting laser module 10A on the mounting surface of the mount substrate 31. It is done. From the viewpoint of heat dissipation efficiency and wiring design, it is preferable to use an Au—Sn eutectic layer for the mounting method. Applications of the present invention include high brightness and high light distribution light sources such as automobile headlamps and multi-channel signal sources for sensors.

  In any of the above-described embodiments, the cooling means BL is further provided to flow the cooling gas or liquid in an airtight or liquidtight manner between the optical component 111 and the substrate 11 between the adjacent heat dissipating members 109. Can do. For example, a further heat radiation effect is improved by flowing the cooling fluid in an airtight or liquid-tight manner along the heat radiation member 109 and the substrate 11 in the direction indicated by the white arrow in FIG. In addition, the area of contact with the cooling fluid on the outer wall 109b of the heat dissipating member 109 partially including the inverted conical concave portion RC is increased, so that the heat dissipation is further improved.

  FIG. 8 is a schematic partial cross-sectional view for explaining the configuration of a surface emitting laser module that is Embodiment 3 of the present invention. As shown in FIG. 8, in Example 4, the outer wall of the mesa portion of the surface emitting laser is filled with a metal or insulating filler 201 except for the second reflector 25 on the through opening. Thereby, the heat dissipation effect from a mesa part improves.

  According to the above surface emitting laser of the present invention, the heat dissipating member could not be used in the prior art, but it becomes possible to use the heat dissipating member by providing a space between the light source and the bonding surface. Furthermore, in the prior art, heat could only be radiated from the protrusion (mesa) to only its peripheral part. However, according to the present invention, heat can be radiated from the peripheral part to the heat radiating member and further to the optical component. It is possible to provide a vertical cavity surface emitting laser module excellent in performance. Further, the surface emitting laser of the present invention is effective in reducing variation in threshold current due to heat between the light emitting portions of a plurality of surface emitting lasers in which surface emitting lasers are arrayed.

  In addition, although the surface emitting laser of the above-described embodiment is configured to have the conductive first reflecting mirror, the first reflecting mirror may be made nonconductive as long as the conductivity with the n-type semiconductor layer 15 is obtained. Furthermore, as a surface emitting laser, a light emitting element using a tunnel junction or a light emitting element having a current confinement layer of an insulating layer between semiconductor layers can be employed in the present invention. Moreover, although each element is connected in parallel in the said Example, it is good also as a structure which connected each element independently.

  In any of the embodiments of the present invention, the active layer 17 can also be applied to a surface emitting laser configured to have an active layer 17 having a multiple quantum well (MQW) structure. . Further, although the case where the semiconductor structure layer SMC is made of a GaN (gallium nitride) based semiconductor has been described, the crystal system is not limited to this. Further, the above-described embodiments may be appropriately modified and combined.

10 surface emitting laser 13 first reflector 15 n-type semiconductor layer (first semiconductor layer)
17 active layer 19 p-type semiconductor layer (second semiconductor layer)
21 current confinement layer 23 transparent electrode 24A first resistance region 24B second resistance region 25 second reflector 27P P electrode 29P P pad electrode 29N N pad electrode OP1 through opening SMC semiconductor structure layer

Claims (7)

A vertical resonator type light emitting element module in which a plurality of vertical resonator type light emitting elements are arranged on a plane,
Each of the vertical cavity light emitting elements is laminated on a first reflector formed on a substrate, a first semiconductor layer of a first conductivity type, an active layer, and the first reflector. A semiconductor structure layer made of a second semiconductor layer of a second conductivity type opposite to the conductivity type of 1, a conductive current confinement layer, a transparent electrode in contact with the second semiconductor layer, A second reflector formed on the transparent electrode,
A bonding surface located on a region between the laser beams from the vertical cavity light emitting elements adjacent to each other on the substrate and positioned on the emission direction side of the laser beam and a beam space in which the laser beam propagates A vertical resonator type light emitting element module, further comprising a heat dissipating member having an outer wall facing it.   The vertical resonator type light emitting device module according to claim 1, wherein the heat dissipating member includes an outer wall portion that expands in a reverse taper shape as the heat dissipating member moves away from the substrate.   The vertical resonator type light emitting element module according to claim 1, further comprising a light conversion component bonded to the bonding surface.   The vertical resonator type light emitting device module according to claim 3, wherein the light conversion component includes a phosphor, a diffusion plate, a lens, or a combination thereof.   5. The vertical resonator type light emitting device is covered with an insulating film and filled with a metal or an insulator except for the second reflector on the through opening. 6. 2. A vertical resonator type light emitting device module according to claim 1.   6. The vertical resonator according to claim 1, wherein the active layer of the vertical resonator type light emitting element is disposed on a substrate on the substrate opposite to the heat dissipation member. Type light emitting device module.   The vertical resonator type light emitting element module according to any one of claims 1 to 6, further comprising cooling means for flowing gas or liquid in the space in an airtight or liquidtight manner.

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