WO2011152331A1 - 紫外線照射装置 - Google Patents
紫外線照射装置 Download PDFInfo
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- WO2011152331A1 WO2011152331A1 PCT/JP2011/062322 JP2011062322W WO2011152331A1 WO 2011152331 A1 WO2011152331 A1 WO 2011152331A1 JP 2011062322 W JP2011062322 W JP 2011062322W WO 2011152331 A1 WO2011152331 A1 WO 2011152331A1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/02—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
- H01L33/04—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a quantum effect structure or superlattice, e.g. tunnel junction
- H01L33/06—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a quantum effect structure or superlattice, e.g. tunnel junction within the light emitting region, e.g. quantum confinement structure or tunnel barrier
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/02—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
- H01L33/04—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a quantum effect structure or superlattice, e.g. tunnel junction
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F21—LIGHTING
- F21K—NON-ELECTRIC LIGHT SOURCES USING LUMINESCENCE; LIGHT SOURCES USING ELECTROCHEMILUMINESCENCE; LIGHT SOURCES USING CHARGES OF COMBUSTIBLE MATERIAL; LIGHT SOURCES USING SEMICONDUCTOR DEVICES AS LIGHT-GENERATING ELEMENTS; LIGHT SOURCES NOT OTHERWISE PROVIDED FOR
- F21K9/00—Light sources using semiconductor devices as light-generating elements, e.g. using light-emitting diodes [LED] or lasers
- F21K9/60—Optical arrangements integrated in the light source, e.g. for improving the colour rendering index or the light extraction
- F21K9/69—Details of refractors forming part of the light source
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J61/00—Gas-discharge or vapour-discharge lamps
- H01J61/02—Details
- H01J61/30—Vessels; Containers
- H01J61/305—Flat vessels or containers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J63/00—Cathode-ray or electron-stream lamps
- H01J63/02—Details, e.g. electrode, gas filling, shape of vessel
- H01J63/04—Vessels provided with luminescent coatings; Selection of materials for the coatings
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J63/00—Cathode-ray or electron-stream lamps
- H01J63/06—Lamps with luminescent screen excited by the ray or stream
Definitions
- the present invention relates to an ultraviolet irradiation device that emits ultraviolet rays by irradiating an electron beam onto a semiconductor multilayer film element.
- an ultraviolet light emitting diode (LED) using a gallium nitride (GaN) compound semiconductor is known.
- the emission wavelength in the ultraviolet region of, for example, 380 nm or less can be adjusted by changing the Al composition ratio in the GaN-based compound semiconductor containing aluminum (Al) constituting the active layer.
- Al aluminum
- such an ultraviolet LED requires a p-type semiconductor layer that has to have a low carrier concentration due to non-radiative transition due to defects in the semiconductor crystal and high activation energy of p-type impurities such as Mg. In view of the above structure, the external quantum efficiency is lowered due to the occurrence of carrier overflow or resistance loss in the active layer.
- an ultraviolet light source using a semiconductor element one that emits an electron beam from an electron beam radiation source to the semiconductor multilayer film element to cause the semiconductor multilayer film element to emit light is known (see Patent Document 1). . According to such an ultraviolet light source, it is not necessary to form a p-type semiconductor layer, which is an essential element in an LED, and therefore it is possible to emit stable ultraviolet light without being affected by the quality. An ultraviolet light source can be obtained.
- the above ultraviolet light source has the following problems.
- In order to cause the semiconductor multilayer film element to emit light with high efficiency for example, it is necessary to irradiate the semiconductor multilayer film element with an electron beam accelerated by an acceleration voltage of several tens of kV or more. X-rays are easily generated. For this reason, it is difficult to obtain a small ultraviolet light source because the ultraviolet light source needs to have a structure that shields X-rays.
- the present invention has been made based on the above circumstances, and an object thereof is to provide an ultraviolet irradiation device that is small in size and can emit ultraviolet rays with high efficiency.
- the ultraviolet irradiation apparatus of the present invention includes a semiconductor multilayer film element and an electron beam radiation source for irradiating the semiconductor multilayer film element with an electron beam in a container having an ultraviolet transmission window sealed inside in a negative pressure state. It is characterized by.
- the semiconductor multilayer film element In x Al y Ga 1- xy N (0 ⁇ x ⁇ 1,0 ⁇ y ⁇ 1, x + y ⁇ 1) single quantum well structure or consisting of Comprising an active layer having a multiple quantum well structure;
- the active layer in the semiconductor multilayer film element By irradiating the active layer in the semiconductor multilayer film element with an electron beam from the electron beam radiation source, ultraviolet rays are emitted from the semiconductor multilayer film element to the outside through the ultraviolet transmission window.
- the acceleration voltage of the electron beam is V (kV) and the thickness of the active layer is t (nm)
- the acceleration voltage of the said electron beam is 20 kV or less.
- the thickness of the active layer in the semiconductor multilayer film element is in a specific range in relation to the acceleration voltage of the electron beam, it is possible to emit ultraviolet rays with high efficiency, Even if the acceleration voltage of the electron beam is low, high efficiency can be obtained, so that the apparatus can be downsized.
- FIG. 6 is a luminous efficiency curve diagram showing the relationship between the acceleration voltage of the electron beam and the luminous efficiency according to the ultraviolet irradiation apparatus A to the ultraviolet irradiation apparatus E.
- FIG. 6 is a luminous efficiency curve diagram showing the relationship between the acceleration voltage of the electron beam and the luminous efficiency according to the ultraviolet irradiation apparatus A to the ultraviolet irradiation apparatus E.
- FIG. 6 is a curve diagram showing the relationship between the acceleration voltage of the electron beam at points P 1 and P 2 in curves a to e shown in FIG. 5 and the thickness of the active layer. It is a luminous efficiency curve figure which shows the relationship between the acceleration voltage of the electron beam and luminous efficiency which concern on the ultraviolet irradiation apparatus C, the ultraviolet irradiation apparatus F, and the ultraviolet irradiation apparatus G. It is explanatory drawing which shows the outline of the structure in the other example of the ultraviolet irradiation device of this invention, Comprising: (A) is sectional drawing, (B) is the top view seen from the electron beam radiation source side.
- FIG. 1 is a cross-sectional view for explaining the outline of the structure of an example of the ultraviolet irradiation apparatus of the present invention
- FIG. 2 is a cross-sectional view for explaining the structure of a semiconductor multilayer film element in the ultraviolet irradiation apparatus shown in FIG.
- This ultraviolet irradiation device 10 has a container 11 (hereinafter referred to as “vacuum container”) 11 whose outer shape is sealed with a negative pressure inside, and this vacuum container 11 has one surface (the lower surface in FIG. 1).
- an ultraviolet transmissive window 13 that is disposed in the opening of the container base 12 and is hermetically sealed to the container base 12 and transmits ultraviolet rays from the inside to the outside.
- the semiconductor multilayer film element 20 is disposed on the inner surface of the ultraviolet transmission window 13, and the semiconductor multilayer film element 20 is irradiated with an electron beam at a position facing the semiconductor multilayer film element 20.
- the electron beam radiation source 15 is arranged, and the electron beam radiation source 15 and the semiconductor multilayer film element 20 are connected to the vacuum container 11 via conductive wires (not shown) drawn from the inside of the vacuum container 11 to the outside. Is electrically connected to an electron acceleration means (not shown) for applying an acceleration voltage.
- glass such as quartz glass can be used.
- quartz glass or the like can be used as a material constituting the ultraviolet light transmitting window 13 in the vacuum container 11.
- the pressure inside the vacuum vessel 11 is, for example, 10 ⁇ 4 to 10 ⁇ 6 Pa.
- a Spindt-type emitter having a structure in which a gate electrode for electron extraction is arranged in the vicinity of a conical molybdenum chip can be used.
- the semiconductor multilayer element 20 includes a substrate 21 made of, for example, sapphire, a buffer layer 22 made of, for example, AlN formed on one surface of the substrate 21, and a single quantum well formed on one surface of the buffer layer 22. And an active layer 25 having a structure or a multiple quantum well structure.
- the semiconductor multilayer film element 20 is arranged in such a manner that the substrate 21 is bonded and fixed to the inner surface of the ultraviolet transmitting window 13 with, for example, a UV curable resin in a state where the active layer 25 faces the electron beam radiation source 15. Therefore, the electron beam from the electron beam radiation source 15 is irradiated from the active layer 25 side.
- the thickness of the substrate 21 is, for example, 10 to 1000 ⁇ m, and the thickness of the buffer layer 22 is, for example, 100 to 1000 nm.
- the distance between the electron beam radiation source 15 and the active layer 25 in the semiconductor multilayer element 20 is, for example, 5 to 120 mm.
- FIG. 3 is a cross-sectional view for explaining the structure of an example of the active layer.
- the active layer 25 is a single quantum well structure or a multiple quantum well structure consisting of each In x Al y Ga 1-xy N (0 ⁇ x ⁇ 1,0 ⁇ y ⁇ 1, x + y ⁇ 1), a single Alternatively, a plurality of quantum well layers 26 and a single or a plurality of barrier layers 27 are alternately stacked on the buffer layer 22 in this order.
- the thickness of each quantum well layer 26 is, for example, 0.5 to 50 nm.
- the barrier layer 27 has a composition selected such that the forbidden band width is larger than that of the quantum well layer 26.
- each thickness is larger than the well width of the quantum well layer 26.
- a large value is set, specifically, for example, 1 to 100 nm.
- the period of the quantum well layer 26 constituting the active layer 25 is appropriately set in consideration of the total thickness of the quantum well layer 26, the barrier layer 27 and the active layer 25, the acceleration voltage of the electron beam used, etc. 1 to 100.
- the semiconductor multilayer film element 20 can be formed, for example, by MOCVD (metal organic chemical vapor deposition). Specifically, by using a carrier gas composed of hydrogen and nitrogen and a source gas composed of trimethylaluminum and ammonia, vapor deposition is performed on the (0001) plane of the sapphire substrate 21 to have a required thickness. After forming the buffer layer 22 made of AlN, vapor phase growth is performed on the buffer layer 22 using a carrier gas made of hydrogen gas and nitrogen gas and a source gas made of trimethylaluminum, trimethylgallium, trimethylindium and ammonia.
- MOCVD metal organic chemical vapor deposition
- active layer 25 having a in x Al y Ga 1-xy N (0 ⁇ x ⁇ 1,0 ⁇ y ⁇ 1, x + y ⁇ 1) single or multiple quantum well structure consisting of having the required thickness
- the semiconductor multilayer element 20 can be formed.
- each step of forming the buffer layer 22, the quantum well layer 26, and the barrier layer 27 conditions such as a processing temperature, a processing pressure, and a growth rate of each layer are determined according to the buffer layer 22, the quantum well layer 26, and the barrier layer 27 to be formed. It can set suitably according to a composition, thickness, etc. of this.
- the method for forming the semiconductor multilayer film is not limited to the MOCVD method, and for example, an MBE method (molecular beam epitaxy method) or the like can also be used.
- the acceleration voltage of the electron beam In the relationship between the acceleration voltage of the electron beam and the thickness of the active layer 25, if the thickness of the active layer 25 is too small (the acceleration voltage is too large), a part of the electron beam passes through the active layer 25. As a result of the increase in the number of electrons that do not contribute to the generation of electron-hole pairs in the active layer 25, it becomes difficult to irradiate ultraviolet rays with high efficiency. On the other hand, when the thickness of the active layer 25 is excessive (acceleration voltage is excessively small), the energy of the electron beam is lost in the layer portion on the surface side of the active layer 25 where the electron beam is irradiated.
- the acceleration voltage of the electron beam is preferably 20 kV or less, more preferably 5 to 13 kV.
- the acceleration voltage of the electron beam exceeds 20 kV, X-rays are likely to be generated from the semiconductor multilayer film element 20, so that a structure for shielding the X-rays is required, and therefore it is difficult to reduce the size of the apparatus.
- the semiconductor multilayer film element 20 is thermally damaged by the energy of the electron beam, it is not preferable.
- the above formula (1) is derived from experiments. Hereinafter, an experimental example performed to derive the above formula (1) will be described.
- a substrate (21) made of sapphire is placed in the processing furnace of the CVD apparatus, the furnace pressure is set to 10 kPa, the furnace temperature is set to 1080 ° C., and nitrogen gas and hydrogen gas are allowed to flow as carrier gases in the processing furnace. Then, trimethylaluminum and ammonia as source gases were supplied into the processing furnace, and vapor phase growth was performed on the (0001) plane of the substrate (21), thereby forming a buffer layer (22) made of an AlN single crystal having a thickness of 600 nm. .
- the furnace pressure is set to 10 kPa
- the furnace temperature is set to 1080 ° C.
- nitrogen gas and hydrogen gas are allowed to flow as carrier gases
- trimethylaluminum, trimethylgallium and ammonia are supplied into the processing furnace as source gases
- a quantum well layer (26) made of 1 nm Al 0.69 Ga 0.21 N is formed, and then trimethylaluminum and ammonia are supplied into the processing furnace as source gases to form a barrier layer (27) made of AlN having a thickness of 15 nm. did.
- an active layer (25) having a thickness of 128 nm (8-period quantum well structure) is formed.
- a semiconductor multilayer film element (20) was formed.
- An electron beam radiation source (15) composed of a Spindt-type emitter having a molybdenum tip is made of a container base (made of glass having a wall thickness of 4 mm, having an outer dimension of 40 mm ⁇ 25 mm ⁇ 25 mm and an opening of 7 mm ⁇ 5 mm on one side. 12).
- the substrate (21) of the semiconductor multilayer film element (20) is placed on one surface of the ultraviolet ray transmission window (13) made of plate-like quartz glass having dimensions of 7 mm ⁇ 5 mm ⁇ 4 mm. It arrange
- the ultraviolet transmissive window (13) is disposed at the opening of the container base (12) so that the semiconductor multilayer element (20) faces the electron beam radiation source (15), and the internal pressure is 1 ⁇ 10 ⁇ 6. While evacuating to Pa, the vacuum transmissive window (13) was hermetically sealed to the container base (12) to constitute the vacuum container (11), and thus the ultraviolet irradiation device was manufactured.
- the separation distance between the electron beam radiation source (15) and the active layer (25) in the semiconductor multilayer element (20) is 30 mm.
- the operations for forming the quantum well layer (26) and the barrier layer (27) were performed in the same manner as described above except that the operations were performed once, six times, ten times and fifteen times, respectively.
- An ultraviolet irradiation device including a semiconductor multilayer film element (20) having a layer (25) was produced.
- an ultraviolet irradiation device having an active layer (25) thickness of 16 nm is referred to as “ultraviolet irradiation device A”
- an ultraviolet irradiation device having an active layer (25) thickness of 96 nm is referred to as “ultraviolet irradiation device B”
- an active layer (25) is an ultraviolet irradiation device having an active layer (25) thickness of 16 nm.
- An ultraviolet irradiation device having a thickness of 128 nm is referred to as “ultraviolet irradiation device C”
- an ultraviolet irradiation device having an active layer (25) having a thickness of 160 nm is referred to as “ultraviolet irradiation device D”
- an ultraviolet irradiation device having an active layer (25) having a thickness of 240 nm is referred to as “ultraviolet irradiation device E”. Then, when the ultraviolet irradiation device A to the ultraviolet irradiation device E were operated, it was confirmed that all irradiated ultraviolet rays having a peak wavelength of 240 nm.
- the acceleration voltage of the electron beam is changed stepwise in the range of 0 to 20 kV, and the photodiode is sensitive to the output of the emitted ultraviolet light to the light in the ultraviolet region.
- the luminous efficiency was determined.
- the light emission efficiency in the present invention is obtained by the ratio of the emitted light power measured by the photodiode to the electron beam power incident on the semiconductor multilayer element.
- FIG. 4 is a light emission efficiency curve diagram showing the relationship between the acceleration voltage of the electron beam and the light emission efficiency according to the ultraviolet irradiation device C.
- the horizontal axis represents the electron beam acceleration voltage (kV)
- the vertical axis represents the luminous efficiency (%).
- the ultraviolet irradiation device C the light emission efficiency gradually increases as the acceleration voltage of the electron beam increases until the acceleration voltage of the electron beam reaches 0 kV to about 5 kV, and the acceleration voltage of the electron beam increases from about 5 kV. Until it reaches about 8 kV, the luminous efficiency increases rapidly as the acceleration voltage of the electron beam increases, that is, the rate of increase of the luminous efficiency increases.
- the emission efficiency reaches a peak when the acceleration voltage of the electron beam is about 8 kV, and the emission efficiency decreases as the acceleration voltage of the electron beam increases until the acceleration voltage of the electron beam reaches about 10 kV.
- the acceleration voltage of the electron beam is about 10 kV or higher
- the light emission efficiency gradually decreases as the electron beam acceleration voltage increases, that is, the rate of decrease of the light emission efficiency becomes lower than about 8 kV to about 10 kV.
- the luminous efficiency curve relating to the ultraviolet irradiation device C shows that when the acceleration voltage of the electron beam is increased, point P 1 at which the rate of increase in luminous efficiency increases and point P at which the rate of decrease in luminous efficiency decreases. There are two .
- FIG. 5 is a luminous efficiency curve diagram showing the relationship between the accelerating voltage of the electron beam and the luminous efficiency according to the ultraviolet irradiation apparatus A to the ultraviolet irradiation apparatus E.
- the horizontal axis represents the acceleration voltage (kV) of the electron beam
- the vertical axis represents the relative value of the light emission efficiency with the peak value of the light emission efficiency being 1
- the curve a is the light emission efficiency curve related to the ultraviolet irradiation apparatus A
- Curve b is a luminous efficiency curve related to the ultraviolet irradiation apparatus B
- curve c is a luminous efficiency curve related to the ultraviolet irradiation apparatus C
- curve d is a luminous efficiency curve related to the ultraviolet irradiation apparatus D
- curve e is a luminous efficiency related to the ultraviolet irradiation apparatus E.
- the curves a to e showing the respective luminous efficiency curves show the luminous efficiency when the acceleration voltage of the electron beam is increased. It is understood that there is a point P 1 where the rate of increase is high and a point P 2 where the rate of decrease in luminous efficiency is low. That is, increased luminous efficiency gradually according accelerating voltage of an electron beam increases and exceeds the point P 1, the luminous efficiency according to the acceleration voltage increases peaked rapidly increased, exceeds the peak, electronic The luminous efficiency decreases as the acceleration voltage of the line increases, and when it exceeds the point P 2 , the luminous efficiency gradually decreases as the acceleration voltage of the electron beam increases.
- the point P 1 is a point where the tangent slope is 0.15 (kV ⁇ 1 ), and the point P 2 is a tangent slope of ⁇ 0.1 (kV ⁇ ). 1 ).
- the value of the acceleration voltage at each point P 1 to the value of the acceleration voltage at each point P 2 is within the range of the acceleration voltage that can radiate ultraviolet rays with high efficiency in the ultraviolet irradiation device. It is believed that there is.
- FIG. 6 is a curve diagram showing the relationship between the acceleration voltage of the electron beam at points P 1 and P 2 in curves a to e shown in FIG. 5 and the thickness of the active layer.
- the horizontal axis acceleration voltage of the electron beam (kV)
- the vertical axis represents the thickness of the active layer (nm)
- the curve p1 is approximated curve passing through the plotted point of the point P 1
- the curve p2 is an approximate curve passing through the plotted point of the point P 2.
- the acceleration voltage of the electron beam is V and the thickness of the active layer is t
- t 10.6 ⁇ V 1.54 is obtained.
- the quantum well layer (26) made of Al 0.10 Ga 0.90 N having a thickness of 1 nm was formed by changing the furnace temperature, the flow rate of trimethylaluminum, and the flow rate of trimethylgallium.
- An ultraviolet irradiation device having the same configuration as that of the ultraviolet irradiation device C was manufactured except that an active layer (25) having a thickness of 128 nm (quantum well layer period was 8) was formed.
- this ultraviolet irradiation device is referred to as “ultraviolet irradiation device F”.
- the quantum well layer (26) made of Al 0.90 Ga 0.10 N having a thickness of 1 nm was formed by changing the furnace temperature, the flow rate of trimethylaluminum, and the flow rate of trimethylgallium.
- An ultraviolet irradiation device having the same configuration as that of the ultraviolet irradiation device C was manufactured except that an active layer (25) having a thickness of 128 nm (quantum well layer period: 8) was formed.
- this ultraviolet irradiation device is referred to as “ultraviolet irradiation device G”.
- the acceleration voltage of the electron beam is changed stepwise in the range of 0 to 20 kV to operate, and the emitted ultraviolet light is sensitive to the light in the ultraviolet region. And the luminous efficiency was determined.
- FIG. 7 is a light emission efficiency curve diagram showing the relationship between the electron beam acceleration voltage and the light emission efficiency of the ultraviolet irradiation device C, the ultraviolet irradiation device F, and the ultraviolet irradiation device G.
- the horizontal axis represents the electron beam acceleration voltage (kV)
- the vertical axis represents the relative value of the light emission efficiency when the electron beam acceleration voltage is 8 kV
- the curve c is The luminous efficiency curve related to the ultraviolet irradiation device C
- the curve f is the luminous efficiency curve related to the ultraviolet irradiation device F
- the curve g is the luminous efficiency curve related to the ultraviolet irradiation device G. From the result of FIG.
- the thickness of the active layer 25 in the semiconductor multilayer film device 20 is in a specific range in relation to the acceleration voltage of the electron beam, ultraviolet rays are emitted with high efficiency.
- the acceleration voltage of the electron beam is low, high efficiency can be obtained, so that the size of the apparatus can be reduced.
- a plurality of semiconductor multilayer film elements may be disposed in the vacuum vessel.
- the plurality of semiconductor multilayer film elements have different emission wavelengths.
- two semiconductor multilayer elements ie, a semiconductor multilayer element having an emission wavelength of 250 nm and a semiconductor multilayer element having an emission wavelength of 310 nm, are arranged side by side.
- an ultraviolet irradiation device that irradiates ultraviolet rays having two peak wavelengths of 250 nm and 310 nm is obtained.
- FIGS. 8A and 8B for example, 24 semiconductor multilayer film elements 20 having different emission wavelengths are arranged vertically and horizontally, and an electron beam common to all the semiconductor multilayer film elements 20 is provided.
- the ultraviolet irradiation device 10 that irradiates ultraviolet rays having a plurality of peak wavelengths ( ⁇ 1, ⁇ 2, ⁇ 3,...) Is obtained.
Abstract
Description
小型の紫外線光源としては、例えば、窒化ガリウム(GaN)系化合物半導体を用いた紫外線発光ダイオード(LED)が知られている。このような紫外線LEDにおいては、活性層を構成するアルミニウム(Al)を含むGaN系化合物半導体におけるAlの組成比を変化させることにより、例えば380nm以下の紫外線領域における発光波長を調整することができる。
然るに、このような紫外線LEDは、半導体結晶中の欠陥による非輻射遷移や、例えばMg等のp型不純物の活性化エネルギーが高いために低キャリア濃度とならざるを得ないp型半導体層が必要とされる構成上、活性層においてキャリアのオーバーフローや抵抗ロスが生じることによって、外部量子効率が低くなるため、紫外線光源として実用上問題がある。
このような紫外線光源によれば、LEDにおいて必須の要素であるp型半導体層を形成することが不要であるため、その品質の影響を受けることがなく、安定した紫外線を放射することが可能な紫外線光源を得ることができる。
半導体多層膜素子を高い効率で発光させるためには、例えば数十kV以上の加速電圧によって加速された電子線を半導体多層膜素子に照射することが必要であり、これにより、半導体多層膜素子からX線が発生しやすい。そのため、 紫外線光源としては、X線を遮蔽する構造が必要となるため、小型の紫外線光源を得ることが困難である。
前記電子線放射源からの電子線が前記半導体多層膜素子における活性層に照射されることにより、紫外線が当該半導体多層膜素子から前記紫外線透過窓を介して外部に放射されるものであることが好ましい。
また、前記電子線の加速電圧をV(kV)とし、前記活性層の厚みをt(nm)としたとき、下記式(1)を満足することが好ましい。
式(1):4.18×V1.50≦t≦10.6×V1.54
また、前記電子線の加速電圧が20kV以下であることが好ましい。
図1は、本発明の紫外線照射装置の一例における構成の概略を示す説明用断面図、図2は、図1に示す紫外線照射装置における半導体多層膜素子の構成を示す説明用断面図である。
この紫外線照射装置10は、内部が負圧の状態で密閉された外形が直方体状の容器(以下、「真空容器」という。)11を有し、この真空容器11は、一面(図1において下面)に開口を有する容器基体12と、この容器基体12の開口に配置されて当該容器基体12に気密に封着された、紫外線を内部から外部に透過する紫外線透過窓13とによって構成されている。
真空容器11内には、紫外線透過窓13の内面上に半導体多層膜素子20が配設されると共に、半導体多層膜素子20に対向した位置には、当該半導体多層膜素子20に電子線を照射する電子線放射源15が配設されており、電子線放射源15および半導体多層膜素子20は、真空容器11の内部から外部に引き出された導電線(図示省略)を介して、真空容器11の外部に設けられた、加速電圧を印加するための電子加速手段(図示省略)に電気的に接続されている。
また、真空容器11における紫外線透過窓13を構成する材料としては、石英ガラスなどを用いることができる。
真空容器11の内部の圧力は、例えば10-4~10-6Paである。
この例における半導体多層膜素子20は、活性層25が電子線放射源15に対向した状態で、基板21が紫外線透過窓13の内面に例えばUV硬化性樹脂により接着されて固定されて配置されており、従って、電子線放射源15からの電子線が、活性層25側から照射される構成とされている。
基板21の厚みは、例えば10~1000μmであり、バッファ層22の厚みは、例えば100~1000nmである。
また、電子線放射源15と半導体多層膜素子20における活性層25との離間距離は、例えば5~120mmである。
量子井戸層26の各々の厚みは、例えば0.5~50nmである。また、障壁層27はその禁制帯幅が量子井戸層26のそれよりも大きくなるように組成を選択され、一例としては、AlNを用いればよく、各々の厚みは量子井戸層26の井戸幅より大きく設定され、具体的には、例えば1~100nmである。
活性層25を構成する量子井戸層26の周期は、量子井戸層26、障壁層27および活性層25全体の厚みや、用いられる電子線の加速電圧などを考慮して適宜設定されるが、通常、1~100である。
また、半導体多層膜の形成方法は、MOCVD法に限定されるものではなく、例えばMBE法(分子線エピタキシー法)なども用いることができる。
そして、本発明の紫外線照射装置10においては、電子線放射源15から放射される電子線の加速電圧をV(kV)とし、活性層25の厚みをt(nm)としたとき、下記式(1)を満足するものである。
式(1):4.18×V1.50≦t≦10.6×V1.54
また、電子線の加速電圧は、20kV以下であることが好ましく、より好ましくは5~13kVである。電子線の加速電圧が20kVを超える場合には、半導体多層膜素子20からX線が発生しやすいため、 X線を遮蔽する構造が必要となり、従って、装置の小型化を図ることが困難となり、また、電子線のエネルギーにより、半導体多層膜素子20の熱ダメージが生じるため、好ましくない。
[バッファ層の形成]
CVD装置の処理炉内に、サファイアよりなる基板(21)を配置し、炉内圧力を10kPa、炉内温度を1080℃に設定し、処理炉内にキャリアガスとして窒素ガスおよび水素ガスを流しながら、原料ガスとしてトリメチルアルミニウムおよびアンモニアを処理炉内に供給し、基板(21)の(0001)面に気相成長させることにより、厚みが600nmのAlN単結晶よりなるバッファ層(22)を形成した。
次いで、炉内圧力を10kPa、炉内温度を1080℃に設定し、キャリアガスとして窒素ガスおよび水素ガスを流しながら、原料ガスとしてトリメチルアルミニウム、トリメチルガリウムおよびアンモニアを処理炉内に供給し、厚みが1nmのAl0.69Ga0.21Nよりなる量子井戸層(26)を形成し、その後、原料ガスとしてトリメチルアルミニウムおよびアンモニアを処理炉内に供給し、厚みが15nmのAlNよりなる障壁層(27)を形成した。このような量子井戸層(26)および障壁層(27)を形成する操作を合計で8回繰り返すことにより、厚みが128nm(8周期の量子井戸構造)の活性層(25)を形成し、以て、半導体多層膜素子(20)を形成した。
モリブデンチップを有するスピント型エミッターよりなる電子線放射源(15)を、外形の寸法が40mm×25mm×25mmで、一面に7mm×5mmの開口を有する、肉厚が4mmのガラスよりなる容器基体(12)の底面に配置した。一方、半導体多層膜素子(20)を、寸法が7mm×5mm×4mmの板状の石英ガラスよりなる紫外線透過窓(13)の一面に、当該半導体多層膜素子(20)の基板(21)が当該紫外線透過窓(13)に接するよう配置し、UV硬化樹脂によって接着して固定した。そして、紫外線透過窓(13)を、半導体多層膜素子(20)が電子線放射源(15)に対向するよう、容器基体(12)の開口に配置し、内部の圧力が1×10-6Paとなるよう排気すると共に、容器基体(12)に紫外線透過窓(13)を気密に封着することにより、真空容器(11)を構成し、以て、紫外線照射装置を製造した。
ここで、電子線放射源(15)と半導体多層膜素子(20)における活性層(25)との離間距離は30mmである。
以下、活性層(25)の厚みが16nmの紫外線照射装置を「紫外線照射装置A」、活性層(25)の厚みが96nmの紫外線照射装置を「紫外線照射装置B」、活性層(25)の厚みが128nmの紫外線照射装置を「紫外線照射装置C」、活性層(25)の厚みが160nmの紫外線照射装置を「紫外線照射装置D」、活性層(25)の厚みが240nmの紫外線照射装置を「紫外線照射装置E」とする。
そして、紫外線照射装置A~紫外線照射装置Eを作動させたところ、いずれも240nmのピーク波長を有する紫外線を照射するものであることが確認された。
紫外線照射装置A~紫外線照射装置Eについて、電子線の加速電圧を0~20kVの範囲で段階的に変更して作動させ、放射される紫外線の出力を、紫外線領域の光に感度を有するフォトダイオードによって測定し、発光効率を求めた。ここで、本発明における発光効率は、半導体多層膜素子に入射された電子線パワーに対する、フォトダイオードで測定した出射光パワーの比によって求められるものである。
紫外線照射装置Cにおいては、電子線の加速電圧が0kVから約5kVとなるまでの間では、電子線の加速電圧が上昇するに従って発光効率が緩やかに増加し、電子線の加速電圧が約5kVから約8kVとなるまでの間では、電子線の加速電圧が上昇するに従って発光効率が急激に増加する、すなわち発光効率の増加率が高くなる。そして、電子線の加速電圧が約8kVにおいて発光効率がピークに達し、電子線の加速電圧が約8kVから約10kVとなるまでの間では、電子線の加速電圧が上昇するに従って発光効率が減少し、電子線の加速電圧が約10kV以上では、電子線の加速電圧が上昇するに従って発光効率が緩やかに減少する、すなわち発光効率の低下率が、約8kVから約10kVに比べると低くなる。
このように、紫外線照射装置Cに係る発光効率曲線には、電子線の加速電圧を上昇させたときに、発光効率の上昇率が高くなる点P1 および発光効率の低下率が低くなる点P2 が存在する。
図5の結果から、紫外線照射装置A~紫外線照射装置Eのいずれにおいても、それぞれの発光効率曲線を示す曲線a~曲線eには、電子線の加速電圧を上昇させたときに、発光効率の上昇率が高くなる点P1 および発光効率の低下率が低くなる点P2 が存在することが理解される。すなわち、電子線の加速電圧が上昇するに従って発光効率が緩やかに増加し、点P1 を超えると、加速電圧が上昇するに従って発光効率が急激に増加してピークに達し、ピークを超えると、電子線の加速電圧が上昇するに従って発光効率が減少し、点P2 を超えると、電子線の加速電圧が上昇するに従って発光効率が緩やかに減少する。また、曲線a~曲線eの各々において、点P1 は、接線の傾きが0.15(kV-1)となる点であり、点P2 は、接線の傾きが-0.1(kV-1)となる点である。
そして、曲線a~曲線eにおいて各点P1 に係る加速電圧の値から各点P2 に係る加速電圧の値までが、当該紫外線照射装置において高い効率で紫外線を放射し得る加速電圧の範囲であると考えられる。
このようにして実験的に上記式(1)が導き出される。
実験例1の活性層の形成工程において、炉内温度、トリメチルアルミニウムの流量およびトリメチルガリウムの流量を変更することにより、厚みが1nmのAl0.10Ga0.90Nよりなる量子井戸層(26)を形成し、厚みが128nm(量子井戸層の周期が8)の活性層(25)を形成したこと以外は、紫外線照射装置Cと同様の構成の紫外線照射装置を製造した。以下、この紫外線照射装置を「紫外線照射装置F」とする。
また、実験例1の活性層の形成工程において、炉内温度、トリメチルアルミニウムの流量およびトリメチルガリウムの流量を変更することにより、厚みが1nmのAl0.90Ga0.10Nよりなる量子井戸層(26)を形成し、厚みが128nm(量子井戸層の周期が8)の活性層(25)を形成したこと以外は、紫外線照射装置Cと同様の構成の紫外線照射装置を製造した。以下、この紫外線照射装置を「紫外線照射装置G」とする。
紫外線照射装置Fを作動させたところ、370nmのピーク波長を有する紫外線を照射するものであることが確認され、紫外線照射装置Gを作動させたところ、215nmのピーク波長を有する紫外線を照射するものであることが確認された。
図7の結果から、紫外線照射装置Cとは量子井戸層(26)の組成が異なる紫外線照射装置Fおよび紫外線照射装置Gのいずれにおいても、紫外線照射装置Cと同様の発光効率曲線が得られることが理解され、従って、量子井戸層(26)の組成に関わらず、上記式(1)を満足することにより、高い発光効率が得られることが理解される。
例えば、図1に示す構成の紫外線照射装置において、発光波長が250nmである半導体多層膜素子および発光波長が310nmである半導体多層膜素子の2つの半導体多層膜素子を並ぶよう配置し、各半導体多層膜素子の活性層に共通の電子線放射源から電子線が照射されることにより、波長が250nmおよび波長が310nmの2つのピーク波長を有する紫外線を照射する紫外線照射装置が得られる。
また、図8(A)および(B)に示すように、発光波長が互いに異なる例えば24個の半導体多層膜素子20を縦横に並ぶよう配置し、全ての半導体多層膜素子20に共通の電子線放射源15から電子線が照射されることにより、複数のピーク波長(λ1、λ2、λ3、・・・)を有する紫外線を照射する紫外線照射装置10が得られる。
11 真空容器
12 容器基体
13 紫外線透過窓
15 電子線放射源
20 半導体多層膜素子
21 基板
22 バッファ層
25 活性層
26 量子井戸層
27 障壁層
Claims (4)
- 内部が負圧の状態で密閉された、紫外線透過窓を有する容器内に、半導体多層膜素子およびこの半導体多層膜素子に電子線を照射する電子線放射源を備えてなることを特徴とする紫外線照射装置。
- 前記半導体多層膜素子は、Inx Aly Ga1-x-y N(0≦x<1,0<y≦1,x+y≦1)よりなる単一量子井戸構造または多重量子井戸構造を有する活性層を備えてなり、
前記電子線放射源からの電子線が前記半導体多層膜素子における活性層に照射されることにより、紫外線が当該半導体多層膜素子から前記紫外線透過窓を介して外部に放射されることを特徴とする請求項1に記載の紫外線照射装置。 - 前記電子線の加速電圧をV(kV)とし、前記活性層の厚みをt(nm)としたとき、下記式(1)を満足することを特徴とする請求項2に記載の紫外線照射装置。
式(1):4.18×V1.50≦t≦10.6×V1.54 - 前記電子線の加速電圧が20kV以下であることを特徴とする請求項3に記載の紫外線照射装置。
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EP11789734.8A EP2579295B1 (en) | 2010-06-03 | 2011-05-30 | Ultraviolet irradiation device |
KR1020127033752A KR101288673B1 (ko) | 2010-06-03 | 2011-05-30 | 자외선 조사장치 |
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CN104145424A (zh) * | 2012-04-19 | 2014-11-12 | 优志旺电机株式会社 | 太阳能电池试验用光照射装置 |
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RU2709999C1 (ru) * | 2018-12-25 | 2019-12-23 | Федеральное государственное бюджетное учреждение науки Физико-технический институт им. А.Ф. Иоффе Российской академии наук | Источник спонтанного ультрафиолетового излучения с длиной волны менее 250 нм |
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