Patent Grant
7425457
1. Field of the Invention
The present invention relates to a method and apparatus for irradiating an object with temporally stable light, and more particularly, to a method and apparatus for irradiating simulated solar radiation, which needs to be irradiated in large light quantity and over a large area, in temporally stable light quantity and spectrum. The present invention also relates to a method and apparatus for irradiating a semiconductor device which is an object temporally responding relatively quickly to a temporal variation in light quantity over a sensitive wavelength range with temporally stable light.
2. Related Background Art
As a method for irradiating a semiconductor device with simulated solar radiation, Japanese Patent Application Laid-Open No. S61-269801 discloses a method of lighting and irradiation using a xenon lamp as a light source, using an expensive air mass filter for adjusting a spectral distribution and using an expensive stabilized DC power supply as a power supply source. Though this method is costly, it can secure temporal stability of light quantity relatively easily and is appropriate for a case where an object to be irradiated is small and the total price falls within an allowable range. However, the price of this method increases at an accelerating pace as the required irradiation area grows. This is because attempting to irradiate the entire surface of an object with substantially uniform light in response to an increase of the area of the object requires increases in size of components such as the air mass filter and other optical systems, which increases the degree of difficulty of manufacturing in an accelerating pace and further requires an increase in the capacity of the expensive stabilized DC power supply for the lamp, which is costly from the very beginning.
As one of methods for realizing a large area, Japanese Patent Application Laid-Open No. H11-26785 discloses a method for lighting a lamp using pulses. This method is effective in terms of reducing the capacity of a power supply for the lamp. However, the necessity for large size components such as an air mass filter and other optical systems remains the same and this method is still costly. Moreover, while this method takes into account the temporal stability of light quantity during a pulse lighting-up time, it ignores the temporal stability of continuous light quantity including a non-lighting-up time.
As described above, according to the conventional technologies, when an attempt is made to irradiate an object with temporally stable light, the price of the apparatus increases as the light quantity and the area increase or such temporal stability must be unavoidably ignored, all of which make the method difficult to realize in practice.
It is an object of the present invention to provide a method and apparatus for irradiating an object with temporally stable light at low cost and using actually feasible means. More specifically, it is an object of the present invention to provide a method and apparatus for irradiating simulated solar radiation, which needs to be irradiated in large light quantity and over a large area, with temporally stable light quantity and spectrum. It is another object of the present invention to provide a method and apparatus for irradiating a semiconductor device which is an object responding relatively quickly to a temporal variation in light quantities over a sensitive wavelength range, with temporally stable light.
In order to attain the above-described objects, a method and apparatus for irradiating light according to the present invention is characterized by irradiating an object with simulated solar radiation resulting from superimposed light rays from a plurality of light sources including light sources having different times at which light emission output reaches a peak.
Furthermore, a light irradiation apparatus used for a characteristic test of a semiconductor device of the present invention is characterized in that an object is irradiated with light resulting from superimposed light rays from a plurality of light sources including light sources having different times at which light emission output reaches a peak.
Furthermore, a method of testing characteristics of a semiconductor device with a light irradiating step of the present invention is characterized by including a step of irradiating a semiconductor device with light resulting from superimposed light rays from a plurality of light sources including light sources having different times at which light emission output reaches a peak.
The light sources having different times at which light emission output reaches a peak are preferably light sources having a plurality of light-emitting seeds with different time constants.
The light sources having different times at which light emission output reaches a peak are preferably discharge lamps and more preferably mercury lamps or metal halide lamps.
The output waveforms of the light sources having different times at which light emission output reaches a peak are preferably substantially similar or substantially periodic.
The energy supply sources of the light sources having different times at which light emission output reaches a peak are preferably single-phase AC, two-phase AC or three-phase AC.
The phase difference of light emission output peaks of the light sources having different times at which light emission output reaches a peak is preferably an integer multiple of 1/n of 180 degrees, where n is the number of light sources or the number of light source groups having different times at which light emission output reaches a peak.
The arrangement of the light sources having different times at which light emission output reaches a peak preferably includes an arrangement of m-gon, where m is an integer multiple of n and n is the number of light sources or the number of light source groups having different times at which light emission output reaches a peak. A linear arrangement is also preferable.
The arrangement of the light sources having different times at which light emission output reaches a peak is preferably set in such a way that when the number of light sources or the number of light source groups having different times at which light emission output reaches a peak is 2, the ratio of a sum total of irradiation light quantities of light sources or light source groups having different times at which one light emission output reaches a peak to a sum total of irradiation light quantities of light sources or light source groups having different times at which other light emission outputs reach a peak is 0.82 to 1.22 as a standard for an object to be irradiated.
Furthermore, the arrangement of the light sources having different times at which light emission output reaches a peak is preferably set in such a way that when the number of light sources or the number of light source groups having different times at which light emission output reaches a peak is 3, the ratio of a sum total of irradiation light quantities of light sources or light source groups having different times at which one light emission output reaches a peak to a sum total of irradiation light quantities of light sources or light source groups having different times at which other light emission outputs reach a peak is 1:0.75 to 1.33 as a standard for an object to be irradiated.
Preferred embodiments of the present invention will be explained below, but the present invention is not limited to these embodiments.
<Optical System>
With regard to a light source, on the premise that a plurality of light sources are used, it is possible to select various types of light sources in consideration of the light quantity required, irradiation area required and spectral distribution required, etc. According to the present invention, it is possible to use a light source which, when lit with an AC through an igniter, has excellent temporal responsivity to a power supply variation with its light emission output sensitively varying in a cycle double the AC frequency because it is lit with an AC. For example, it is also possible to use a discharge lamp like a mercury lamp which can easily obtain large light quantity. Furthermore, it is also preferable to use a metal halide lamp, etc., which can easily obtain large light quantity and for which a spectral distribution is also currently being improved. Furthermore, according to the present invention, a light source having a plurality of light-emitting seeds with different time constants such as a metal halide lamp can secure necessary temporal stability in a spectral distribution, and is therefore a preferable light source. Here, a “time constant of a light-emitting seed” in this Specification means a time required to attenuate from peak intensity to a value of certain percentage (e.g., 1/e of peak intensity).
It is possible to use various optical parts such as condenser, reflector, integrator, collimator lens, spectral correction filter, diffusing filter, light-shielding plate as required for the optical system. Furthermore, it is also preferable to use an optical unit such as a projector whose upsizing is relatively easy to incorporate the above-described plurality of light sources in one unit.
<Energy Supply System>
Various types of energy can be used for the energy supply system. For a stable power supply, it is preferable to supply power supplied from a power company as a primary side AC power supply of the equipment. Furthermore, it is also preferable to supply power through a power generator using various types of fuel such as petroleum and gas because a two-phase AC can be easily supplied in this way. Moreover, DC power can also be supplied from a battery, etc.
Using an AC power supply such as single-phase AC, two-phase AC, three-phase AC to supply energy is preferable because it is possible to supply substantially similar, substantially periodic energy in this way. It is also preferable to provide a mechanism which temporally shifts light emission output peaks of a light source at some part of an energy supply route as required. Two-phase AC and three-phase AC are preferable because they have components with different phases from the beginning.
Furthermore, it is also possible to supply energy in a pulsated form by temporarily storing charge in a capacitor.
<Light Emission Output>
Various light emission outputs can be obtained by combining various types of light source, optical system and energy supply system. Then, it is possible to irradiate an object with temporally stable light by superimposing light rays from light sources having different times at which light emission output reaches a peak. As light emission output to be focused, it is possible to set light quantity in an entire wavelength range, light quantity for each predetermined wavelength range defined by a standard, etc., light quantity in a wavelength range having sensitivity to an object to be irradiated, etc., depending on the purpose of use of this method and apparatus for irradiating light as appropriate.
Output waveforms of light sources having different times at which light emission output reaches a peak are preferably substantially similar when consideration is given to ease of control. It is also preferably substantially periodic. Such waveforms are preferable because they can be obtained easily by selecting, for example, AC power as the energy supply system and combining light sources whose light emission output is also sensitively variable in a cycle double an AC frequency because they are lit with an AC as the light sources.
Various levels of the temporal stability of light quantity irradiated with light resulting from superimposed light rays from light sources having different times at which light emission output reaches a peak are selected according to the purpose of use. For example, with regard to a solar simulator (simulated solar radiation irradiation apparatus for a photovoltaic device) used for testing a photovoltaic device, IEC60904-9 describes the required performance of spectral coincidence to be satisfied in the area used of the surface to be irradiated, in-plane variation of irradiance and temporal stability. With regard to the temporal stability, class A is within ±2%, class B is within ±5% and class C is within ±10%. To be qualified as having passed a test verifying the required performance in compliance with IEC60904-9, it is necessary to use a light irradiation apparatus that satisfies the performance also in the aspect of temporal stability of light quantity.
Thus, the temporal stability of light quantity irradiated to an object is preferably within ±10%.
At this time, in order to irradiate the object to be irradiated with light in temporally stable light quantity, it is possible to set an arrangement of a plurality of light sources by trial and error, but it is preferable that an appropriate arrangement standard be made settable because this can reduce the total adjustment load drastically. A variation of light emission output can be divided into a ground light emission component as a minimum value of light emission output and a variable component added thereto. As opposed to a case of responding to a variation of energy with which the light emission output whose ground light emission component is substantially 0 is supplied more sensitively, the ratio of the variation width of light emission output to average light emission output is improved by the effect of the ground light emission component and decreases as the ground light emission component increases. In other words, when attention is focused on the ground light emission component, it is possible to set a more appropriate standard by estimating the light emission output whose ground light emission component is substantially 0 as a basis.
Furthermore, various levels of temporal stability of a spectral distribution irradiated with light resulting from superimposed light rays from light sources having different times at which light emission output reaches a peak can also be selected depending on the purpose of use thereof. With regard to spectral coincidence set for each predetermined wavelength range in aforementioned IEC60904-9, class A is within a range of 0.75 to 1.25, class B is within a range of 0.6 to 1.4 and class C is within a range of 0.4 to 2.0. To be qualified as having passed a test verifying the required performance in compliance with IEC60904-9, it is necessary to use a light irradiation apparatus that satisfies the performance also in the aspect of temporal stability in spectral coincidence.
Thus, the temporal stability of spectral coincidence irradiated to an object is preferably within a range of 0.4 to 2.0.
At this time, when attention is focused on a spectral distribution, a light source having a plurality of light-emitting seeds with different time constants, in response to a variation of energy with which the light emission output of a light-emitting seed whose time constant is substantially 0 is supplied more sensitively, the variation width of the light emission output is improved by the temporal averaging effect by the time constant and decreases as the time constant of the light-emitting seed increases. In other words, when attention is focused on a difference in the time constant, it is possible to set a more appropriate standard by estimating the light emission output whose time constant is substantially 0 as a basis.
When energy which is the square of a sine wave is supplied from an energy supply system and light emission output is obtained according to the energy, that is, when the ground light emission component and time constant are regarded as substantially 0, a case where light rays from two light sources having different times at which light emission output reaches a peak is as shown in the following example.
The phase of a quasi-sine wave of one light source was set to 0 degree as a reference and the phase of a quasi-sine wave of the other light source was set to 90 degrees. In Table 1, the temporal stability of irradiation light quantity of superimpose light was checked by changing the amplitude ratio of the light source with the phase of the quasi-sine wave set to 90 degrees to the light source with the phase of the quasi-sine wave set to 0 degree. That is, the light source with the phase of the quasi-sine wave set to 0 degree and light source with the phase of the quasi-sine wave set to 90 degrees only differ in the amplitude and are substantially similar. To satisfy a range of within ±10%, an amplitude ratio up to 0.82 is acceptable. If a reverse reference is adopted, an amplitude ratio up to 1.22 is acceptable.
When energy corresponding to the square of the sine wave is supplied from an energy supply system and light emission output is obtained according to the energy, that is, when the ground light emission component and time constant can be regarded as substantially 0, a case where light rays from three light sources having different times at which light emission output reaches a peak are superimposed is as shown in the following example.
The phase of a quasi-sine wave of one light source was set to 0 degree as a reference and the phases of quasi-sine waves of the other light sources were set to 120 degrees and 240 degrees. In Table 2, the temporal stability of irradiation light quantity of superimpose light was checked by changing the amplitude ratio of the light source with the phase of the quasi-sine wave set to 120 degrees and 240 degrees to the light source with the phase of the quasi-sine wave set to 0 degree. That is, the light sources with the phase of the quasi-sine wave set to 0 degree, 120 degrees and 240 degrees only differ in the amplitude and are substantially similar. To satisfy a range of within ±10%, an amplitude ratio up to 0.71 to 0.75 is acceptable. If a reverse reference is adopted, an amplitude ratio up to 1.41 to 1.33 is acceptable.
(Arrangement of Optical System)
Various types of arrangement can be adopted for an optical system. In order to superimpose light rays from light sources having different times at which light emission output reaches a peak and obtain desired temporal stability efficiently at an object or a surface to be irradiated, it is preferable to adopt an arrangement which prevents the light sources having different times at which light emission output reaches a peak from blocking each other's irradiation optical path.
The number of light sources can be set as required. It is possible to use one set of light sources having different times at which light emission output reaches a peak or form a plurality of light sources having substantially coinciding times at which light emission output reaches a peak as one group and combine it with a group of light sources having different times at which light emission output reaches a peak or combine it with a still further light source. It is desirable to set an arrangement of each light source in consideration of the light quantity irradiated from each light source to each irradiation point and the balance among light quantities irradiated from the respective light source groups. It is further preferable to set the arrangement based on a desirable numerical value range when superimposing light rays from light sources having different times at which the aforementioned light emission output reaches a peak.
At this time, an arrangement of the light sources having different times at which light emission output reaches a peak based on an m-gon, where m is an integer multiple of n and n is the number of light sources or the number of light source groups having different times at which light emission output reaches a peak is preferable because it is easier to balance light quantities within the area in which the object or surface to be irradiated is used. Furthermore, a linear arrangement is also preferable because it is easier to balance light quantities.
(Object to be Irradiated)
Various objects can be used as objects to be irradiated. For example, in the case of a semiconductor device such as a photovoltaic device, responsivity to irradiation light quantity is important and it is preferable to irradiate temporally stable light according to the purpose thereof.
Furthermore, the present invention is preferable because it can irradiate a large-size semiconductor device including a solar cell, solar cell submodule, solar cell module or photovoltaic array, etc., with temporally stable light. The present invention is preferable because it can also irradiate a semiconductor device such as a stacked solar cell which sensitively responds with a spectral distribution using light rays in a wavelength range which varies from one layer to another with light having a temporally stable spectral distribution.
With reference now to attached drawings, the present invention will be explained using embodiments described below, but the present invention is not limited to these embodiments.
In Embodiment 1 and comparative example 1, a metal halide lamp which is lit with an AC through an igniter was used as a light source. The metal halide lamp can be lit through an inexpensive igniter, it is growing in light quantity and its spectral distribution is being improved, and in this respect the metal halide lamp is a promising simulated solar radiation light source. On the other hand, since it has high temporal responsivity to power supply variations and because it is lit with an AC, its light emission output also varies sensitively in a cycle double the AC frequency and has a plurality of light-emitting seeds with different time constants, thus having the nature that its spectral distribution also varies temporally.
In comparative example 1 shown in
On the contrary, in Embodiment 1 shown in
In Embodiment 1, the positional relationship between the object to be irradiated 7, two projectors 4a and 4b and lamps 5a and 5b are assumed to be an equidistant and symmetric positional relationship. The two projectors 4a and 4b were tilted toward the object to be irradiated 7. Furthermore, they were arranged so that irradiation light rays from the respective lamps 5a and 5b and projectors 4a and 4b to the object to be irradiated 7 were not blocked by the opposite projector or lamp or other objects. This makes the temporally averaged light quantities irradiated from the lamps 5a and 5b substantially equal over the entire surface of the object to be irradiated 7 and even if the entire surface of the object to be irradiated 7 is divided into smaller areas and measured, it is possible to obtain the irradiation light quantity waveform 9 with substantially no temporal variation.
Furthermore, in order to set the temporal stability of irradiation light quantity of the superimposed light to within ±10%, setting the arrangement of the optical system in such a way that the ratio of the amplitude of the irradiation light quantity waveform 9a to the amplitude of the irradiation light quantity waveform 9b measured at the position of the object to be irradiated 7 when the lamps are lit singly is set to 1:0.82 to 1.22 as a standard can reduce the total adjustment load drastically and is therefore preferable.
Using the method and apparatus for irradiating light according to Embodiment 1, it is possible to measure, for example, the output of a solar cell module which is a semiconductor device showing quick temporal response to a temporal variation of light quantity. Since irradiation light quantity with substantially no temporal variation is obtained, even a solar cell module which shows quick temporal response produces output with substantially no temporal variation. Therefore, it is possible to measure the output of the solar cell module without-specially performing adjustment of measuring timings and averaging processing of measured values, etc. Furthermore, by changing, for example, the distance between the two lamps 5a and 5b and the solar cell module or increasing the number of projectors and lamps as required, it is also possible to change the absolute value of irradiation light quantity to the solar cell module or measure the relationship between the output of the solar cell module and irradiation light quantity.
In Embodiment 2 shown in
When the method and apparatus for irradiating light according to the present invention is used as actual equipment, it is also possible to adopt the configuration shown in this embodiment for convenience of the primary side AC power supply of the equipment, etc.
In Embodiment 3 shown in
In Embodiment 3, the positional relationship between the object to be irradiated 7 and the three projectors 4a, 4b and 4c and lamps 5a, 5b and 5c is assumed to be an equidistant and symmetric positional relationship. The three projectors 4a, 4b and 4c are tilted toward the object to be irradiated 7. As shown in
Furthermore, in order to set the temporal stability of irradiation light quantity of the superimposed light to within ±10%, setting the arrangement of the optical system in such a way that the ratio of the amplitude of the irradiation light quantity waveform 9a to the amplitudes of the irradiation light quantity waveforms 9b and 9c measured at the position of the object to be irradiated 7 when the lamps are lit singly is set to 1:0.75 to 1.33 as a standard can reduce the total adjustment load drastically and is therefore preferable.
In Embodiment 4 shown in
In Embodiment 4, the positional relationship between a surface to be irradiated 10 and the two projectors 4a and 4b and lamps 5a and 5b is assumed to be an equidistant and symmetric positional relationship. The projectors 4a and 4b are oriented right below toward the surface to be irradiated 10. As shown in
Furthermore, in order to set the temporal stability of irradiation light quantity of the superimposed light to within +10%, setting the arrangement of the optical system in such a way that the ratio of the amplitude of the irradiation light quantity waveform 9a to the amplitude of the irradiation light quantity waveform 9b measured at positions right below the projector 4a and lamp 5a obtained when they are lit singly is set to 1:0.21 (=0.25×0.82) to 0.30 (=0.25×1.22) as a standard can reduce the total adjustment load drastically, which is therefore preferable.
In this embodiment, a total of 15 sets of the projectors 4a and 4b and lamps 5a and 5b which are basic units are used, but expanding the same arrangement in
In Embodiment 5 shown in
In Embodiment 5, the positional relationship between a surface to be irradiated 10 and the three projectors 4a, 4b and 4c and lamps 5a, 5b and 5c is assumed to be an equidistant and symmetric positional relationship. The projectors 4a, 4b and 4c are oriented right below toward the surface to be irradiated 10. As shown in
Furthermore, in order to set the temporal stability of the irradiation light quantity of the superimposed light to within ±10%, setting the arrangement of the optical system in such a way that the ratio of the amplitude of the irradiation light quantity waveform 9a and the amplitudes of the irradiation light quantity waveforms 9b and 9c measured at positions right below the projector 4a and lamp 5a obtained when they are lit singly is set to 1:0.25 (=0.33×0.75) to 0.44 (=0.33×1.33) as a standard can reduce the total adjustment load drastically, which is therefore preferable.
This embodiment has used a total of 12 sets of three projectors 4a, 4b and 4c and lamps 5a, 5b and 5c which are basic units, but expanding the same arrangement in
In Embodiment 6 shown in
In Embodiment 6, the positional relationship between the object to be irradiated and the three lamps 5a, 5b and 5c can be easily set to a positional relationship regarded as an equidistant and symmetric one because the three lamps 5a, 5b and 5c are incorporated in one projector 4. The lamps 5a, 5b and 5c are arranged so as to be located at vertices of a regular triangle in one projector 4. In this way, temporally averaged light quantities irradiated from one projector 4 and lamps 5a, 5b and 5c are substantially equal over the entire surface of the object to be irradiated, and even if the entire surface of the object to be irradiated is divided into small areas and measured, it is possible to obtain an irradiation light quantity waveform 9 with substantially no temporal variation.
As described above, according to the present invention, an object to be irradiated is irradiated with simulated solar radiation resulting from superimposed light rays from a plurality of light sources including light sources having different times at which light emission output reaches a peak. Furthermore, the light irradiation apparatus used for testing characteristics of a semiconductor device is a light irradiation apparatus characterized in that a semiconductor device is irradiated with light resulting from superimposed light rays from a plurality of light sources including light sources having different times at which light emission output reaches a peak. Furthermore, the method of testing characteristics of a semiconductor device including a light irradiating step is a method of testing characteristics of a semiconductor device including a step of irradiating a semiconductor device with light resulting from superimposed light rays from a plurality of light sources including light sources having different times at which light emission output reaches a peak.
As a result, temporally stable light can be irradiated to an object to be irradiated. Especially, simulated solar radiation, which needs to be irradiated in large light quantity and over a large area can be irradiated with light in temporally stable light quantity and spectrum. Furthermore, it is possible to irradiate a semiconductor device which is an object responding relatively quickly to a temporal variation in light quantities over a sensitive wavelength range with temporally stable light.
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