JP6355100B2 - Inspection apparatus and inspection method - Google Patents

Description

  The present invention relates to a technique for inspecting a photo device.

  Conventionally, for example, a technique has been proposed in which a photo device such as a solar cell is irradiated with light and the photo device is inspected based on electromagnetic waves radiated from the photo device (Patent Document 1).

  Further, a technique has been proposed in which a photo device is caused to emit electromotive force by irradiating continuous light, and the photo device is inspected based on electromagnetic waves radiated from the photo device in that state (Patent Document 2). ).

JP2013-19861A JP 2013-174477 A

  However, in the case of a photo device having a part with a different absorption wavelength region in the depth direction, such as a multi-junction solar cell, light can reach only a specific depth only by irradiating light of a specific wavelength. There is a possibility that only electromagnetic waves generated at a specific depth can be detected. Further, there are cases where absorption is performed only at a specific depth by simply irradiating continuous light of a specific wavelength. Then, there is a problem that the inspection of the photo device cannot be performed from various angles.

  Therefore, an object of the present invention is to provide a technique for inspecting each portion of the photo device having different absorption wavelength regions in the depth direction from various angles.

In order to solve the above-described problem, a first aspect is an inspection apparatus that inspects a photo device, an excitation light irradiation unit that can irradiate the photo device with a plurality of excitation lights having different wavelengths, and the photo device A continuous light irradiating unit capable of irradiating a plurality of continuous lights having different wavelengths to a portion irradiated with the excitation light, and a wavelength of the excitation light that the excitation light irradiating unit irradiates the photo device. And an electromagnetic wave emitted from the photo device according to the excitation light irradiated by the excitation light irradiation unit, and a setting unit that sets the wavelength of the continuous light that the continuous light irradiation unit irradiates the photo device with of a detector for detecting the field intensity, the photo device is a multi-junction solar cell is formed by stacking a plurality of sub-cells absorption wavelength region is different, pre The setting unit sets the wavelength of the excitation light that the excitation light irradiation unit irradiates the multi-junction solar cell to a wavelength included in an absorption wavelength region of a specific subcell among the plurality of subcells, and the continuous the wavelength of the continuous light irradiation section for irradiating the multi-junction solar cell, among the plurality of sub-cells, to set a wavelength included in the absorption wavelength region of the specific sub-cell.

  Further, the second aspect is the inspection apparatus according to the first aspect, wherein the excitation light irradiating unit is configured such that the time Δt elapses after the excitation light of the first wavelength is irradiated on the photo device. An inspection apparatus that irradiates the photo device with excitation light having a second wavelength different from one wavelength, and again irradiates excitation light with the first wavelength.

  Moreover, a 3rd aspect is an inspection apparatus which concerns on a 2nd aspect, Comprising: Said several excitation light is pulsed light, The said detection part receives the said pulsed light, and is from said photo device. The detector includes a detector that detects the emitted electromagnetic wave, and the inspection device delays the timing at which the detector receives the pulsed light relative to the timing at which the electromagnetic wave reaches the detector. Are further provided.

  Further, a fourth aspect is an inspection apparatus according to any one of the first to third aspects, wherein the photo device is scanned with the plurality of excitation lights irradiated by the excitation light irradiation unit. And a mechanism for generating an image indicating a distribution of the electric field strength in the photo device based on the electric field strength of the electromagnetic wave detected by the detection unit.

  Further, a fifth aspect is the inspection apparatus according to the second aspect, wherein the plurality of excitation lights having different wavelengths emitted from the excitation light irradiation unit are pulsed light, and the time Δt is the It is longer than the generation time of one pulse of the electromagnetic wave radiated by the pulsed light.

Further, a sixth aspect is an inspection method for inspecting a photo device, wherein an excitation light irradiation step of irradiating the photo device with a plurality of excitation lights having different wavelengths, and the excitation light in the photo device being irradiated A continuous light irradiation step of irradiating a continuous light to a portion and a wavelength of the plurality of excitation lights irradiated in the excitation light irradiation step, and the continuous light irradiated in the continuous light irradiation step a setting step of setting a wavelength of, in response to the plurality of excitation light irradiated by the excitation light irradiation step, seen including a detection step of detecting the electric field intensity of the electromagnetic wave emitted from the photo device, wherein The photo device is a multi-junction solar cell configured by stacking a plurality of subcells having different absorption wavelength regions, and the setting step includes the multi-junction solar cell in the excitation light irradiation step. The wavelength of the excitation light irradiated on the multi-junction solar cell in the continuous light irradiation step is set to a wavelength included in the absorption wavelength region of a specific subcell among the plurality of subcells. the wavelength of the light, among the plurality of sub-cells, a step of setting a wavelength included in an absorption wavelength region of the specific sub-cell free.

Further, a seventh aspect is the inspection method according to the sixth aspect, wherein the excitation light irradiation step is performed after the time Δt has elapsed since the excitation light of the first wavelength is irradiated on the photo device. Irradiating the photo device with excitation light having a second wavelength different from one wavelength, and irradiating the photo device with excitation light having the first wavelength again.

According to the inspection apparatus according to the first aspect, an electromagnetic wave is generated from a specific depth portion by irradiating excitation light having a wavelength corresponding to each absorption wavelength region in a photo device having different absorption wavelength regions in the depth direction. Can be made. Moreover, by irradiating the wavelength of continuous light corresponding to each absorption wavelength region, a portion having a specific depth can be brought into a state where an electromotive force is generated. Thus, by performing electromagnetic wave measurement by changing the state of each part in the depth direction, the photo device can be inspected from various angles.
In a multi-junction solar cell, an electromagnetic wave can be emitted from each subcell by irradiating excitation light corresponding to the absorption wavelength region of each stacked subcell. Thereby, each subcell can be inspected individually.
Moreover, the carrier dynamics in the subcell of the said electric power generation state can be analyzed by irradiating the continuous light and excitation light of the wavelength contained in the absorption wavelength area | region of the same subcell.

  In addition, according to the inspection apparatus according to the second aspect, two different wavelengths of light are emitted while being shifted by the time Δt, so that each radiated electromagnetic wave can be detected while being shifted by the time Δt.

  Moreover, according to the inspection apparatus which concerns on a 3rd aspect, the data for recovering electromagnetic waves can be collected. Moreover, the electric field strength of each electromagnetic wave radiated | emitted by the some pulsed light from which a wavelength differs can be acquired simultaneously. For this reason, it can test | inspect efficiently.

  Moreover, according to the inspection apparatus which concerns on a 4th aspect, the test | inspection based on distribution of electromagnetic wave intensity | strength can be performed.

  Moreover, according to the inspection apparatus which concerns on a 5th aspect, each electromagnetic waves produced with the several pulsed light from which a wavelength differs can be isolate | separated and detected.

1 is a schematic configuration diagram of an inspection apparatus according to a first embodiment. It is a schematic block diagram of the excitation light irradiation part with which an inspection apparatus is provided, and a detection part. It is a schematic block diagram of a delay element. It is a schematic sectional drawing of a multijunction type solar cell. It is a figure which shows the spectral sensitivity of a multijunction solar cell. It is a figure which shows the flow of the example 1 of an inspection. It is a conceptual diagram which shows the pulse train (upper) of the pulsed light irradiated to a junction type solar cell, and the pulse train (lower) of the electromagnetic wave pulse radiated | emitted from a multijunction type solar cell. It is a figure which shows an example of the time waveform of an electromagnetic wave pulse. It is a figure which shows an example of the spectrum distribution of an electromagnetic wave pulse. In a multijunction solar cell, it is a figure which shows the correlation of the intensity | strength of the continuous light of a specific wavelength, and electromagnetic wave intensity. It is a figure which shows the flow of the example 2 of an inspection. It is a schematic diagram which shows an example of an electric field strength distribution image. It is a schematic block diagram of the inspection apparatus which concerns on 2nd Embodiment. It is the schematic of the inspection apparatus which concerns on 3rd Embodiment. It is the schematic of the inspection apparatus which concerns on 4th Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In addition, the component described in this embodiment is an illustration to the last, and is not a thing of the meaning which limits the scope of the present invention only to them. In the drawings, the size and number of each part may be exaggerated or simplified as necessary for easy understanding.

<1. First Embodiment>
<1.1. Configuration and function of inspection device>
FIG. 1 is a schematic configuration diagram of an inspection apparatus 100 according to the first embodiment. FIG. 2 is a schematic configuration diagram of the excitation light irradiation unit 12 and the detection unit 13 included in the inspection apparatus 100.

  The inspection apparatus 100 irradiates a multi-junction solar cell 90 that is an inspection target that is a photo device with pulsed light, and emits electromagnetic waves (from the multi-junction solar cell 90 in response to the irradiation of the pulsed light ( For example, the inspection object is inspected by detecting a terahertz wave having a frequency of 0.1 THz to 30 THz.

  As shown in FIGS. 1 and 2, the inspection apparatus 100 includes a stage 11, an excitation light irradiation unit 12, a detection unit 13, a delay element 14, a stage moving mechanism 15, a control unit 16, a monitor 17, an operation input unit 18, and A continuous light irradiation unit 19 is provided.

  The stage 11 fixes the multi-junction solar cell 90 on the stage 11 by fixing means (not shown). As the fixing means, a configuration using a clamping tool for clamping the substrate, an adhesive sheet that adheres to both the back surface of the multi-junction solar cell 90 and the surface of the stage 11, an adsorption hole formed on the surface of the stage 11, etc. The structure which adsorb | sucks via is assumed. However, as long as the multi-junction solar cell 90 can be fixed, other fixing means may be employed. In the present embodiment, the stage 11 holds the multi-junction solar cell 90 so that the excitation light irradiation unit 12 and the detection unit 13 are disposed on the light receiving surface (surface 90S) side of the multi-junction solar cell 90. For this reason, the inspection apparatus 100 is a reflection type inspection apparatus that detects an electromagnetic wave radiated to the same side as the irradiation surface.

  As shown in FIG. 2, the excitation light irradiation unit 12 includes a femtosecond laser 121. For example, the femtosecond laser 121 emits pulsed light (pulsed light LP10) having a wavelength including a visible light region of 360 nm (nanometers) or more and 1.5 μm (micrometers) or less. As a specific example, linearly polarized pulsed light L10 having a period of several kHz to several hundred MHz and a pulse width of about 10 to 150 femtoseconds is emitted from the femtosecond laser 121.

  The pulsed light LP10 emitted from the femtosecond laser 121 is divided into pulsed light LP11, LP13, LP15, LP17, LP19 by a beam splitter or the like. The pulsed light LP11 is directly guided to the multi-junction solar cell 90. The pulsed light LP13 is guided to the wavelength double converter 31. The pulsed light LP15 is guided to the wavelength triple converter 33. The pulsed light LP17 is guided to the optical parametric oscillator 38. The pulsed light LP19 is guided to the detector 131 of the detection unit 13 that detects the electromagnetic wave pulse through the delay element 14.

  The wavelength double converter 31 is a second harmonic generation device configured by a nonlinear optical crystal or the like. Specifically, the wavelength doubling converter 31 is composed of a barium borate (BBO) crystal, a potassium titanyl arsenate (KTA) crystal, a potassium dihydrogen phosphate (KDP) crystal, and the like, from the pulsed light LP13 having a wavelength λ. The pulsed light LP21 having the wavelength λ / 2 is generated. The generated pulsed light LP21 is divided into two parts, one being led to the delay element 35 and the other being led to the wavelength triple converter 33. The pulsed light LP21 that has passed through the delay element 35 is guided to the multi-junction solar cell 90.

  FIG. 3 is a schematic configuration diagram of the delay element 35. The delay element 35 includes a delay stage 351 and a delay stage moving mechanism 353. The delay stage 351 includes a mirror 10M that reflects the pulsed light LP21 in the incident direction. The delay stage moving mechanism 353 moves the mirror 10M along the incident direction of the pulsed light LP21.

  The delay stage moving mechanism 353 is controlled by the control unit 16. The delay element 35 continuously changes the optical path length of the pulsed light LP21 by moving the delay stage 351. When the optical path length of the pulsed light LP21 is changed, the phase of the pulsed light LP21 reaching the multijunction solar cell 90 is shifted from the phase of the pulsed light LP11 reaching the multijunction solar cell 90. Thereby, the timing at which the pulsed light LP21 reaches the multi-junction solar cell 90 can be delayed with respect to the timing at which the pulsed light LP11 reaches the multi-junction solar cell 90. In the following description, this delay time may be expressed as Δt.

  Note that the delay element 35 may be configured differently from the delay stage 351. Specifically, it can be considered to use the electro-optic effect. That is, an electro-optic element whose refractive index changes by changing the applied voltage may be used as the delay element 35. For example, an electro-optic element disclosed in Japanese Patent Application Laid-Open No. 2009-175127, which is a patent document, can be used.

  The wavelength triple converter 33 is a third harmonic generation device composed of a nonlinear optical crystal or the like. Specifically, the wavelength triple converter 33 is made of, for example, a cesium lithium borate (CLBO) crystal and the like, and the pulsed light LP31 having the wavelength λ / 3 is generated by a sum frequency generation technique for synthesizing the pulsed light LP15 and the pulsed light LP21. Is generated. The generated pulsed light LP31 is guided to the delay element 37. Then, the pulsed light LP31 that has passed through the delay element 37 is guided to the multi-junction solar cell 90.

  The delay element 37 has substantially the same configuration as the delay element 35 shown in FIG. The delay element 37 delays the timing at which the pulsed light LP31 reaches the multi-junction solar cell 90 with respect to the timing at which the pulsed light LP11, LP21 reaches the multi-junction solar cell 90.

An optical parametric oscillator (OPO) 38 divides a high-frequency photon into two low-frequency photons (signal wave and idler wave). Although not shown in detail, the optical parametric oscillator 38 generates a signal wave and an idler wave having an arbitrary wavelength within a predetermined range by changing the tilt angle of the crystal provided therein. That is, the optical parametric oscillator 38 can change the wavelength of the pulsed light LP17 emitted from the light source in a wide band. The tilt angle of the crystal is controlled by the control unit 16. Also the crystals, BBO crystal, KTP crystal, and the like LBO crystal or LiNbO ₃ crystal. The pulsed light LP41 that is a signal wave or idler wave generated by the optical parametric oscillator 38 is guided to the delay element 39. Then, the pulsed light LP41 that has passed through the delay element 39 is guided to the multi-junction solar cell 90.

  The delay element 39 has substantially the same configuration as the delay element 35 shown in FIG. The delay element 39 delays the timing at which the pulsed light LP41 reaches the multi-junction solar cell 90 with respect to the timing at which the pulsed light LP11, LP21, LP31 reaches the multi-junction solar cell 90.

  In the present embodiment, the pulse light LP11 to LP41 are irradiated to the multi-junction solar cell 90 while shifting the time with respect to each other, so that the optical path lengths of the pulse lights LP21, LP31, LP41 are caused by the delay elements 35, 37, 39. Has changed. However, the optical path length of any three or more of the pulsed light LP11, LP21, LP31, LP41 (hereinafter referred to as “pulsed light LP11 to LP41”) may be changed.

  The pulsed light LP11 to LP41 guided to the multijunction solar cell 90 is modulated by several kHz by an optical chopper (not shown). As the modulation element, an AOM (Acousto-Optic Modulator) or the like can be used. The multi-junction solar cell 90 is irradiated with the pulsed light LP11 to LP41 modulated in this way.

  As shown in FIG. 1, the excitation light irradiation unit 12 performs irradiation of the pulsed light LP11 to L41 from the side of the surface 90S that is the light receiving surface of the multi-junction solar cell 90. In addition, the excitation light irradiation unit 12 applies the pulsed light LP11 to L41 to the multijunction solar cell 90 so that the optical axis of the pulsed light LP11 is obliquely incident on the light receiving surface of the multijunction solar cell 90. Irradiate. In the present embodiment, the irradiation angle is set so that the incident angle is 45 degrees. However, the incident angle is not limited to such an angle, and can be appropriately changed within the range of 0 to 90 degrees.

  FIG. 4 is a schematic cross-sectional view of the multi-junction solar cell 90. The multi-junction solar cell 90 is configured by vertically stacking materials having different absorption wavelength regions in the depth direction. More specifically, the multi-junction solar cell 90 includes three unit solar cells 9A, 9B, and 9C (hereinafter referred to as “solar cells 9A to 9C”) that are a plurality of subcells having different absorption wavelength regions. Are stacked in this order from the bottom. Solar cells 9A and 9B and solar cells 9B and 9C are electrically connected to each other by tunnel junctions 95A and 95B.

  Here, the absorption wavelength region means a wavelength region mainly absorbed by each of the unitary solar cells 9A to 9C, and can be referred to as a utilization wavelength region. The absorption wavelength region may not be completely different between the plurality of solar cells 9A to 9C, and a part thereof may overlap.

  In solar cells 9A to 9C, p-type semiconductor layers 93A, 93B, and 93C and n-type semiconductor layers 94A, 94B, and 94C are bonded to each other to form pn junctions 97A, 97B, and 97C. A plate-like back surface electrode 92 made of aluminum or the like is attached to the lower surface of the solar cell 9A constituting the back surface of the multi-junction solar cell 90.

  A light-receiving surface electrode 96 made of aluminum or the like is attached to the upper surface of the solar cell 9C constituting the light-receiving surface (surface 90S) of the multijunction solar cell 90. The light receiving surface electrode 96 is provided, for example, in a comb shape or a lattice shape so that light can easily pass therethrough. Note that the light receiving surface electrode 96 may be formed of a transparent electrode.

  Of the main surfaces on both sides of the multi-junction solar cell 90, the main surface on the side where the light receiving surface electrode 96 is provided is the light receiving surface. That is, the multi-junction solar cell 90 is designed to generate electricity suitably by receiving light from the light receiving surface side.

  When pulse light LP11 to LP41 having energy exceeding the forbidden band width is irradiated on a portion where the internal electric field of the multi-junction solar cell 90 exists, photocarriers (free electrons and holes) are generated, and the internal electric field Accelerated. Of the accelerated photocarriers, holes move to the back electrode 92 and free electrons move to the light receiving surface electrode 96. As a result, a pulsed current is generated, and a pulsed electromagnetic wave corresponding to the pulsed current is generated. It is known that the internal electric field is generated at, for example, a pn junction or a Schottky junction.

  FIG. 5 is a diagram showing the spectral sensitivity of the multi-junction solar cell 90. In the figure, the horizontal axis indicates the wavelength, and the vertical axis indicates the quantum efficiency. In the figure, a solar cell 9A which is a bottom cell is a Ge solar cell (band gap: 0.8 eV), a solar cell 9B which is a middle cell is a GaAs solar cell (band gap: 1.4 eV), and a solar cell 9C which is a top cell. Shows the spectral sensitivity when an InGaP solar cell (band gap 1.85 eV) is used. And the graph G9A, G9B, G9C has shown the spectral sensitivity of solar cell 9A-9C, respectively in the figure.

  As graph G9A shows, since the quantum efficiency of solar cell 9A is high at about 850 nm to about 1800 nm, this wavelength region becomes an absorption wavelength region (utilization wavelength region). Similarly, as the graph G9B shows, the absorption wavelength region of the solar cell 9B is about 700 nm to about 850 nm. Furthermore, from the graph G9C, the absorption wavelength region of the solar cell 9C is about 350 nm to about 700 nm. Therefore, when irradiating each solar cell 9 </ b> A to 9 </ b> C with pulsed light to emit an electromagnetic wave pulse, pulsed light having a wavelength included in these absorption wavelength regions may be irradiated.

  That is, as shown in FIG. 4, if the multi-junction solar cell 90 is irradiated with pulsed light LPc having a wavelength of about 350 to about 700 nm, the electromagnetic pulse LTc can be emitted from the solar cell 9C that is the top cell. Further, when the multi-junction solar cell 90 is irradiated with pulsed light LPb of about 700 to 850 nm, the electromagnetic pulse LTb can be emitted from the solar cell 9B which is a middle cell. Furthermore, if the multi-junction solar cell 90 is irradiated with pulsed light LPc of about 850 nm to about 1800 nm, an electromagnetic wave pulse TLc can be emitted from the solar cell 9C that is a bottom cell.

  Thus, by irradiating the pulsed light LPa, LPb, LPc corresponding to each absorption wavelength region, the electromagnetic pulses LTa, LTb, LTc can be selectively emitted from the solar cells 9A-9C. Therefore, each solar cell 9A-9C can be inspected individually by detecting the electromagnetic wave pulses LTa, LTb, LTc radiated from each solar cell 9A-9C.

  Returning to FIG. 2, when the multi-junction solar cell 90 is irradiated with pulsed light LP11 to LP41 having different wavelengths, the electromagnetic pulses LT11, LT21, LT31, and LT41 (hereinafter referred to as “electromagnetic wave pulses LT11 to LT41”). Occurs. The electromagnetic wave pulses LT11 to LT41 are guided to the detector 131 provided in the detection unit 13.

  The detector 131 is configured by a photoconductive switch (photoconductive antenna) on which the pulsed light LP11 is incident. As the photoconductive switch, a dipole type, a bow tie type, a spiral type, and the like are known. When the pulsed light LP19 is applied to the detector 131 in a state where the electromagnetic wave pulses LT11 to LT41 are incident on the detector 131, a current corresponding to the electric field strength of the electromagnetic wave pulses LT11 to LT41 is instantaneously generated in the photoconductive switch. . The current corresponding to the electric field strength is converted into a digital quantity via a lock-in amplifier (not shown), an I / V conversion circuit, an A / D conversion circuit, and the like. Thus, the detection unit 13 detects the electric field strength of the electromagnetic wave pulses LT11 to LT41 radiated from the multi-junction solar cell 90 in response to the irradiation with the pulsed light LP19.

  Note that other elements such as a Schottky barrier diode may be used for the detector 131. A Schottky barrier diode has a characteristic that polarization dependency is small. It is also conceivable to use a nonlinear optical crystal as the detector 131.

  A delay element 14 (delay unit) is provided on the optical path of the pulsed light LP19 until it reaches the detector 131. The delay element 14 changes the timing at which the pulsed light LP19 reaches the detector 131 by changing the optical path length of the pulsed light LP19. The basic configuration of the delay element 14 is the same as that of the delay element 35 shown in FIG.

  The delay element 14 shifts the phase of the pulsed light LP19 reaching the detector 131 relative to the phases of the electromagnetic wave pulses LT11 to LT41 reaching the detector 131. That is, the timing at which the pulsed light LP19 reaches the detector 131 is delayed with respect to the timing at which the electromagnetic wave pulses LT11 to LT41 arrive at the detector 131. By changing the optical path length of the pulsed light LP19 by the delay element 14, the timing (detection timing or sampling timing) at which the electric field intensity of the electromagnetic wave pulses LT11 to LT41 is detected by the detector 131 is delayed.

  In addition, you may make it change not the pulsed light LP19 but the optical path length of pulsed light LP11-LP41 or the optical path length of the electromagnetic wave pulses LT11-LT41 radiated | emitted from the multijunction solar cell 90. FIG. Even in this case, the timing at which the electromagnetic wave pulses LT11 to LT41 reach the detector 131 can be shifted relative to the timing at which the pulsed light LP17 reaches the detector 131. That is, the detection timing of the electric field intensity of the electromagnetic wave pulses LT11 to LT41 in the detector 131 can be delayed.

  Although illustration is omitted, a reverse bias voltage may be applied to the multi-junction solar cell 90 at the time of inspection. Specifically, a voltage application circuit is connected to the light-receiving surface electrode 96 and the back surface electrode 92 of the multi-junction solar cell 90, and a reverse bias voltage is applied. The magnitude of the voltage applied to the multi-junction solar cell 90 by the voltage application circuit may be variable based on control from the control unit 16.

  By applying the reverse bias voltage, the depletion layer of the pn junction in the multi-junction solar cell 90 can be enlarged. Thereby, the electric field strength of the electromagnetic wave pulses LT11 to LT41 detected by the detector 131 can be increased.

  Instead of applying a reverse bias voltage, the multijunction solar cell 90 may be short-circuited by connecting the light receiving surface electrode 96 and the back surface electrode 92 with an electric wire or the like. In the short-circuited multijunction solar cell 90, the p-type semiconductor layers 93A, 93B, and 93C and the n-type semiconductor layers 94A, 94B, and 94C have the same potential, and the Fermi level is the same level. In the pn junctions 97A, 97B, 97C of the multi-junction solar cell 90 in the short-circuited state, free electrons generated by light irradiation flow to the negative electrodes on the n-type semiconductor layers 94A, 94B, 94C side, and are irradiated by light irradiation. The generated holes flow to the positive electrodes on the p-type semiconductor layers 93A, 93B, 93C side. Then, each charge is injected into the other semiconductor through the short circuit. And it will be lost by recombination.

  That is, in the short circuit state, charge accumulation that occurs in the open state is suppressed, so that drift movement of the optical carriers is likely to occur. For this reason, by setting the multi-junction solar cell 90 in a short-circuited state, the intensity of the electromagnetic wave pulses LT11 to LT41 emitted in response to the irradiation of the pulsed light LP11 to LP41 can be relatively increased.

  Returning to FIG. 1, the configuration of the inspection apparatus 100 will be described. The stage moving mechanism 15 is a device that moves the stage 11 in a two-dimensional plane, and is configured by, for example, an XY table. The stage moving mechanism 15 moves the multi-junction solar cell 90 held on the stage 11 relative to the excitation light irradiation unit 12. The inspection apparatus 100 can move the multi-junction solar cell 90 to an arbitrary position within the two-dimensional plane by the stage moving mechanism 15.

  In the present embodiment, the stage 11 is moved in the XY directions by the stage moving mechanism 15 so that the required inspection range on the multi-junction solar cell 90 can be scanned with the pulsed light LP11 to LP41. That is, the stage moving mechanism 15 constitutes a scanning mechanism.

  It is also conceivable to realize scanning of the inspection range by changing the optical path of the pulsed light LP11 to LP41 instead of moving the stage 11 by the stage moving mechanism 15. Specifically, it is conceivable to scan the pulsed light LP11 in two directions parallel to the surface 90S of the multi-junction solar cell 90 and orthogonal to each other by reciprocally swinging the galvanometer mirror. Further, instead of the galvanometer mirror, a polygon mirror, a piezo mirror, an acoustooptic device, or the like may be employed as an element for changing the optical path.

  The control unit 16 is configured by a general computer including a CPU, a ROM, a RAM, and the like (not shown). The control unit 16 is connected to the excitation light irradiation unit 12, the detector 131, the delay elements 35 and 37, the delay element 14, the stage moving mechanism 15, and the continuous light irradiation unit 19, and controls the operation of each of these elements. Or receive data from each of these elements.

  As shown in FIG. 1, the control unit 16 includes an image generation unit 21, a time waveform restoration unit 23, a spectrum analysis unit 25, and a setting unit 27. The image generation unit 21, the time waveform restoration unit 23, the spectrum analysis unit 25, and the setting unit 27 may be functions realized by the CPU included in the control unit 16 operating according to a program, or may be implemented by a dedicated circuit. It may be realized as hardware.

  The image generation unit 21 calculates the distribution of the electric field strength of the electromagnetic wave pulse emitted by the irradiation of the pulsed light LP11 to LP41 in the inspection target range of the multijunction solar cell 90 (a part or all of the multijunction solar cell 90). A visualized electric field strength distribution image is generated. In the electric field intensity distribution image, the difference in electric field intensity is visually expressed using a plurality of colors, shades of specific colors or a plurality of patterns.

  The time waveform restoration unit 23 restores the time waveform of the electromagnetic wave pulse radiated from the multi-junction solar cell 90 based on the electric field strength detected by the detector 131. Specifically, by driving the delay element 14, the timing at which the pulsed light LP19 reaches the detector 131 is changed, and the electric field strength of the electromagnetic wave pulse detected at each phase is acquired. Then, the time waveform restoring unit 23 plots the acquired electric field strength on the time axis, thereby restoring the time waveform of the electromagnetic wave pulse.

  The spectrum analysis unit 25 performs spectrum analysis of the multijunction solar cell 90 based on the restored time waveform of the electromagnetic wave pulse. Specifically, the spectrum analysis unit 25 obtains an amplitude intensity spectrum related to frequency by performing Fourier transform on the time waveform information.

  The setting unit 27 sets the wavelength of the pulsed light that the excitation light irradiation unit 12 irradiates the multi-junction solar cell 90 with. More specifically, the setting unit 27 irradiates the multi-junction solar cell 90 from among the pulsed light LP11 to LP41 having three different wavelengths based on input information via the operation input unit 18 described later. Set the pulse light. The excitation light irradiation unit 12 irradiates the multi-junction solar cell 90 with pulsed light having the wavelength set by the setting unit 27. Of the pulsed light LP11 to LP41, the pulsed light that is not irradiated by the setting unit 27 is suppressed by being blocked by a shielding plate, for example.

  When the femtosecond laser 121 is a wavelength tunable laser, the setting unit 27 may set the wavelength of the pulsed light LP10 emitted from the femtosecond laser 121.

  The setting unit 27 sets the wavelength of the continuous light CW that the continuous light irradiation unit 19 described later irradiates the multi-junction solar cell 90.

  A monitor 17 and an operation input unit 18 are connected to the control unit 16. The monitor 17 is a display device such as a liquid crystal display, and displays various image information to the operator. The monitor 17 includes, for example, an image of the surface 90S of the multi-junction solar cell 90 photographed by a visible light camera, an electric field intensity distribution image generated by the image generation unit 21, and an electromagnetic wave pulse LT11 restored by the time waveform restoration unit 23. The time waveform of ~ LT41 or the spectrum information acquired by the spectrum analysis unit 25 is displayed. The monitor 17 may display a GUI (Graphical User Interface) screen or the like necessary for setting inspection conditions (inspection range, etc.).

  The operation input unit 18 includes various input devices such as a mouse and a keyboard. The operator can perform a predetermined operation input via the operation input unit 18. Note that the monitor 17 may function as the operation input unit 18 by configuring the monitor 17 as a touch panel.

  The control unit 16 is connected to a storage unit that stores various data. The storage unit may be composed of a portable medium (for example, a magnetic medium, an optical disk medium, or a semiconductor memory) in addition to a fixed disk such as a hard disk. Further, the control unit 16 and the storage unit may be connected via a network line.

  The continuous light irradiation unit 19 is configured to be able to irradiate the multi-junction solar cell 90 with continuous light CW having a plurality of different wavelengths.

  The continuous light irradiation unit 19 is configured according to the wavelength of light used for inspection. Specifically, the continuous light irradiation unit 19 is configured by, for example, a semiconductor laser, an LED, a halogen lamp, a xenon lamp, or a combination thereof. Further, a wavelength tunable laser may be used as the continuous light irradiation unit 19. As the wavelength tunable laser, for example, a distributed feedback (DFB) laser that can change the wavelength of the emitted laser beam substantially continuously (for example, every 2 nm) by temperature control can be used.

  The wavelength of the continuous light CW emitted from the continuous light irradiation unit 19 is appropriately selected according to the inspection purpose and is not particularly limited, but here, each of the solar cells 9A to 9C that are subcells. It is assumed that the continuous light irradiation unit 19 selectively emits the continuous light CW having a wavelength included in the absorption wavelength region. By irradiating the continuous light CW having a specific wavelength toward the multi-junction solar cell 90 by the continuous light irradiation unit 19, any one of the solar cells 9 </ b> A to 9 </ b> C can be selectively brought into a power generation state. Therefore, the solar cells 9A to 9C in the power generation state can be individually inspected by appropriately combining the wavelengths of the pulsed light LP11 to LP41 and the wavelength of the continuous light CW.

  In addition, as continuous light CW, sunlight or simulated sunlight that simulates sunlight, light having a relatively wide wavelength distribution such as an incandescent lamp, wavelengths corresponding to RGB three primary colors such as LED lighting and fluorescent lamp (400 nm, Light including a plurality of wavelengths, such as light having 600 nm and 800 nm).

  In the inspection apparatus 100, the electromagnetic wave pulses LT11 to LT11 are irradiated with the continuous light CW by irradiating the irradiation positions of the pulsed light LP11 to LP41 with the continuous light CW (that is, the electromotive force is generated). LT41 is generated. For example, when pseudo-sunlight is irradiated to the multi-junction solar cell 90, a state of being exposed to sunlight outdoors can be reproduced. By analyzing the electromagnetic wave pulses LT11 to LT41 generated in this state, it is possible to detect structural defects that may cause problems when the multijunction solar cell 90 is used, or to evaluate the performance of the multijunction solar cell 90. . Moreover, the characteristic of the multi-junction solar cell 90 depending on the wavelength can be inspected by irradiating the continuous light CW limited to a specific wavelength.

  The setting unit 27 sets the wavelength of the continuous light CW emitted from the continuous light irradiation unit 19 based on the operation input of the operator. Further, the wavelength irradiated by the continuous light irradiation unit 19 may be directly designated by the operator, or according to the wavelength of the pulsed light that the excitation light irradiation unit 12 irradiates the multi-junction solar cell 90, It may be set automatically. In the latter case, combination data indicating a combination of the wavelength of pulsed light and the wavelength of continuous light is stored in the storage unit in advance, and when the wavelength of the pulsed light to be irradiated is determined, the setting unit 27 performs the combination. Data may be read out to set the wavelength of continuous light to be paired.

  The continuous light irradiation unit 19 includes an irradiation condition changing unit 191. The irradiation condition changing unit 191 changes the spot diameter of the continuous light CW irradiated to the multi-junction solar cell 90 at the same time. The range of the region where the electromotive force is generated can be arbitrarily changed by changing the range in which the continuous light CW is irradiated at once by the irradiation condition changing unit 191.

  For example, when the beam diameters (irradiation diameters) of the pulsed lights LP11 to LP41 are 50 μm, if the beam diameter (irradiation diameter) of the continuous light CW is 50 μm or more, the peripheral part of the region irradiated with the pulsed light LP11 to LP41 Also, the state where an electromotive force is generated can be obtained. Here, the photoexcited carriers generated by the irradiation of the pulsed light LP11 to LP41 are highly likely to be affected by the peripheral portion. Therefore, in order to inspect the multi-junction solar cell 90 in a use state, the continuous light CW may be irradiated also to the peripheral part. Further, the continuous light CW does not necessarily have to be irradiated locally in a spot shape, and for example, the entire multi-junction solar cell 90 may be irradiated simultaneously.

  Further, the irradiation condition changing unit 191 changes the light intensity of the continuous light CW. By changing the light intensity of the continuous light CW applied to the multi-junction solar cell 90, the magnitude of the electromotive force generated can be arbitrarily changed. Thereby, the test | inspection of the multijunction solar cell 90 according to an electric power generation state is realizable. Note that, as a means for changing the intensity of the continuous light CW, for example, a light-shielding filter may be used, but is not limited thereto. Of course, the light intensity of the continuous light CW output from the continuous light irradiation unit 19 may be directly changed.

<1.2 Inspection>
<1.2.1 Inspection Example 1>
FIG. 6 is a diagram illustrating a flow of the inspection example 1. In this inspection example 1, by restoring an electromagnetic wave pulse generated at a specific position (inspection target location) in the multijunction solar cell 90, the characteristics and the like of the multijunction solar cell 90 at that position are evaluated. Each operation described below is performed by the inspection apparatus 100 based on the control of the control unit 16 unless otherwise specified.

  In Inspection Example 1, first, the wavelength of the pulsed light to be irradiated is set based on the absorption wavelength region of each layer of the multi-junction solar cell 90 (step S11, setting step). Here, the multi-junction solar cell 90 is irradiated with pulsed light LP11, LP21, and LP31 (hereinafter referred to as “pulsed light LP11 to LP31”) having three wavelengths λ, λ / 2, and λ / 3. It shall be set. In this case, for example, the wavelength λ is a wavelength (350 nm to 700 nm) absorbed by the lower solar cell 9C in the multi-junction solar cell 90, and the wavelength λ / 2 is a wavelength absorbed by the intermediate solar cell 9B. (700 nm to 850 nm), and the wavelength λ / 3 is a wavelength (850 nm to 1800 nm) absorbed by the solar cell 9A.

  Of course, in addition to the pulsed light LP11-31, the inspection may be performed using the pulsed light LP41 having a specific wavelength generated by the optical parametric oscillator 38.

  Next, the inspection apparatus 100 individually irradiates the multi-junction solar cell 90 with each pulsed light LP11 (first pulsed light), pulsed light LP21 (second pulsed light), and pulsed light LP31 (third pulsed light). . Then, the electromagnetic wave pulse LT11 (first electromagnetic wave pulse), the electromagnetic wave pulse LT21 (second electromagnetic wave pulse), and the electromagnetic wave pulse LT31 (third electromagnetic wave pulse) emitted by the pulse lights LP11 to LP31 are measured (step S12).

  In step S12, the detection stage (phase) of the electric field intensity of the electromagnetic wave pulse is changed by scanning the delay stage of the delay element 14, and data for restoring the time waveform of the electromagnetic wave pulse is acquired. At this time, the measurement position of the electromagnetic wave pulse in the multi-junction solar cell 90 is not particularly limited. However, it is desirable that measurement be performed at a location where a relatively high-intensity electromagnetic wave pulse is likely to occur, such as in the vicinity of the light-receiving surface electrode 96.

  Next, a time Δt for shifting the irradiation of each of the pulsed lights LP11 to LP31 is determined (step S13). Specifically, based on the time waveform of the electromagnetic wave pulses LT11, LT21, LT31 (hereinafter referred to as “electromagnetic wave pulses LT11 to LT31”) measured in step S12, one electromagnetic wave pulse LT11 to LT31. Occurrence time is acquired. The generation time of the electromagnetic wave pulse is from the time when the electric field strength starts to change until the time when the change is completed. Based on this occurrence time, the time Δt is determined.

  FIG. 7 is a conceptual diagram showing a pulse train (upper) of pulsed light irradiated on the multi-junction solar cell 90 and a pulse train (lower) of electromagnetic wave pulses radiated from the multi-junction solar cell 90. In FIG. 7, two horizontal axes indicate time axes.

  In the inspection example 1, as shown in FIG. 7, after the pulsed light LP11 for one pulse is irradiated to the multi-junction solar cell 90, the pulsed light LP21 for one pulse is irradiated with a delay of time Δt11. The Thereafter, one pulse of pulsed light LP31 is emitted with a delay of time Δt21. Thereafter, the pulsed light LP11 for one pulse is irradiated again with a delay of time Δt31.

  In the above manner, the irradiation cycle of the pulsed light LP11 to LP31 is repeatedly performed. Then, in the multi-junction solar cell 90, after the electromagnetic wave pulse LT11 is generated, the electromagnetic wave pulse LT21 is generated after the elapse of time Δt11. Further, the electromagnetic wave pulse LT31 is generated after the elapse of time Δt21, and the electromagnetic wave pulse LT11 is generated after the elapse of time Δt31.

  Here, if the time Δt11 is made longer than the generation time T11 of the electromagnetic wave pulse LT11, it can be suppressed that the electric field strength components of the electromagnetic wave pulse LT11 and the electromagnetic wave pulse LT21 are simultaneously detected by the detector 131. That is, the electromagnetic wave pulse LT21 can be detected separately from the electromagnetic wave pulse LT11. Similarly, each of the times Δt21 and Δt31 may be made longer than the generation times T21 and T31 of the electromagnetic wave pulses LT21 and LT31. As a result, the electromagnetic wave pulses LT31 and LT11 can be detected separately from the previously generated electromagnetic wave pulses LT21 and LT31.

  Times Δt11, Δt21, and Δt31 (hereinafter referred to as “time Δt11 to Δt31”) may coincide with each other or may be different from each other. Since occurrence times T11, T21, and T31 (hereinafter referred to as “occurrence times T11 to T31”) of the electromagnetic wave pulses LT11 to LT31 are also assumed to be different, the times Δt11 to Δt31 according to the occurrence times T11 to T31. May be appropriately determined.

  Returning to FIG. 6, when the time Δt (time Δt11 to Δt31) is determined, the irradiation condition of the continuous light CW is determined (step S14). In step S14, as described above, the setting unit 27 sets the wavelength of the continuous light CW emitted by the continuous light irradiation unit 19 in accordance with the wavelengths of the pulsed light LP11 to LP31 that are excitation light. In addition, the light intensity, irradiation range, and the like of the continuous light CW are appropriately determined. Note that step S14 is not necessarily performed after step S13, and may be performed in parallel with step S11 or after step S11.

  In step S14, the wavelength of the continuous light CW may be set to a wavelength that is absorbed by each of the three layers (solar cells 9A to 9C) of the multijunction solar cell 90. That is, the wavelength absorbed by the upper solar cell 9C (350 nm to 700 nm), the wavelength absorbed by the intermediate solar cell 9B (700 to 850 nm), and the wavelength absorbed by the lower solar cell 9A (for example, 850 nm to 850 nm) 1800 nm) may be irradiated as continuous light CW.

  In this case, since the pulse lights LP11 to LP31 are respectively irradiated and the three types of continuous light CW are respectively irradiated, the electromagnetic wave measurement is performed with a total of nine combinations of the pulse light and the continuous light CW. Of course, the electromagnetic wave measurement may be performed by setting conditions so that two or more types of continuous light CW among the three types of continuous light CW are simultaneously irradiated.

  Next, the pulsed light LP11 to LP31 are sequentially irradiated to the inspection target locations in the preset multi-junction solar cell 90 while being mutually delayed by the time Δt (time Δt11 to Δt31) determined in step S12. Then, the electromagnetic wave pulses LT11 to LT31 are measured at a time (step S15).

  In step S15, the delay stage of the delay element 14 is fixed to a predetermined location at the inspection target location of the multi-junction solar cell 90, and each of the pulsed lights LP11 to LP31 is sequentially irradiated to measure the electromagnetic wave pulses LT11 to LT31. . When this is completed, the electromagnetic wave pulses LT11 to LT31 are measured at different timings by moving the delay stage by a predetermined distance. Such unit measurement is repeatedly performed while the delay stage of the delay element 14 is scanned once. As a result, data for restoring each time waveform of the electromagnetic wave pulses LT11 to LT31 is collected.

  If a plurality of inspection target locations are set, acquisition of the electric field strength of the electromagnetic wave pulses LT11 to LT31 at each inspection target location is executed in step S16.

  Further, in the next step S16, the pulsed light LP11 to LP31 is sequentially irradiated to the inspection target portion measured in step S15 while irradiating the continuous light CW under the irradiation conditions determined in step S14. Then, the electromagnetic wave pulses LT11 to LT31 are measured (step S16). When electromagnetic waves are measured by individually irradiating continuous light CW having different wavelengths, the electromagnetic waves may be individually measured with the continuous light CW having different wavelengths.

  At the time of electromagnetic wave measurement in steps S15 and S16, the intensity of the emitted electromagnetic wave pulse may be increased by applying a reverse bias voltage to the multi-junction solar cell 90 or short-circuiting it. The same applies to the electromagnetic wave measurement in step S12.

  When the acquisition of the electric field strength in steps S15 and S16 is completed, the time waveform restored by the time waveform restoration unit 23 is displayed on the monitor 17 (step S17).

  FIG. 8 is a diagram illustrating an example of the time waveforms 41 and 42 of the electromagnetic wave pulse LT11. The time waveform 41 shows a time waveform when the continuous light CW is irradiated. Moreover, the time waveform 42 has shown the time waveform when there is no irradiation of continuous light CW. In the example shown in FIG. 8, the time waveform 41 has a relatively small amplitude of the electromagnetic wave pulse LT <b> 11 compared to the time waveform 42. This is considered to be due to the following reasons. That is, when the continuous light CW is irradiated, the photoexcited carriers excited by the continuous light CW are filled in the conduction band. Then, it is considered that the current change of the photoexcited carrier generated by the pulsed light LP11 is relatively weakened, and thereby the electric field strength of the generated electromagnetic wave pulse LT11 is weakened.

  FIG. 9 is a diagram illustrating an example of the spectrum distribution 43 of the electromagnetic wave pulse LT11. In FIG. 9, the vertical axis indicates the spectral intensity, and the horizontal axis indicates the frequency. The spectrum analysis unit 25 can acquire the spectrum distribution 43 shown in FIG. 9 from the time waveform 41 shown in FIG. 8 by executing the Fourier transform for converting the time domain into the frequency space. By acquiring the spectrum distribution 43, it is possible to analyze the physical property information at the inspection target location in more detail. Such spectrum analysis may be performed after step S17 or step S18.

  As described above, according to the present inspection example 1, by appropriately selecting the wavelength of the continuous light CW, it is the same as or different from the subcell (any one of the solar cells 9A to 9C) excited by the pulsed light LP11 to LP31. The subcell can absorb continuous light CW.

  That is, when the wavelength of the pulsed light to be irradiated and the wavelength of the continuous light are included in the absorption wavelength region of the same subcell, the carrier dynamics in the subcell in the power generation state can be analyzed. In addition, when the wavelength of the pulsed light to be emitted and the wavelength of continuous light are included in the absorption wavelength regions of different subcells, details of the influence (interaction) that the depletion layer in a specific subcell receives from other subcells in the power generation state Can be analyzed.

  Further, when the wavelength of the continuous light CW is included in both of the absorption wavelength regions of the two subcells among the three subcells, the two subcells can be set in the power generation state. Here, the influence (interaction) that the subcell receives from the other two subcells in the power generation state is analyzed by irradiating the subcell that is not in the power generation state with the absorbed pulsed light and measuring the generated electromagnetic wave pulse. it can. Of course, it is also possible to analyze the carrier dynamics in the power generation state by irradiating one of the two subcells in the power generation state with the pulsed light absorbed to measure the electromagnetic wave pulse. Furthermore, it is also conceivable to perform electromagnetic wave measurement on a specific subcell by irradiating the continuous light CW absorbed by the three subcells.

  FIG. 10 is a diagram showing the correlation between the intensity of the continuous light CW having a specific wavelength and the electromagnetic wave intensity in the multi-junction solar cell 90. In FIG. 10, the horizontal axis indicates the intensity of the continuous light CW, and the vertical axis indicates the relative magnitude of the electric field intensity. Graphs 61 to 64 shown in FIG. 10 measure electromagnetic waves by irradiating pulsed light with a wavelength of 800 nm while irradiating continuous light CW with different wavelengths at specific points of the multi-junction solar cell 90. It is a thing. The pulsed light having a wavelength of 800 nm is absorbed by the intermediate subcell (solar cell 9B) among the three subcells.

  Moreover, the graph 61 is equivalent to what irradiated the continuous light CW (wavelength 405nm) of the wavelength absorbed by the upper layer (solar cell 9C) among the sublayers of three layers. Further, the graph 62 corresponds to the irradiation of continuous light CW (wavelength 650 nm) having a wavelength absorbed by the upper layer and the intermediate layer (solar cells 9C and 9B) of the three subcells. Moreover, the graph 63 is equivalent to what irradiated the continuous light CW (wavelength 808nm) of the wavelength absorbed by the intermediate | middle layer (solar cell 9B) among three layers of subcells. Further, the graph 64 corresponds to the irradiation of continuous light CW (wavelength 980 nm) having a wavelength absorbed by the lower layer (solar cell 9A) among the three subcells.

  According to the measurement result shown in FIG. 10, it can be seen that the intensity of the emitted electromagnetic wave pulse differs depending on the wavelength of the continuous light CW. Specifically, as shown by the graph 61, it can be seen that when the upper layer is in the power generation state, the intensity of the electromagnetic wave pulse generated in the middle layer is increased. Moreover, as the graph 63 shows, when pulsed light and continuous light CW are absorbed by the same intermediate | middle layer, it turns out that the intensity | strength of an electromagnetic wave pulse falls large. Further, it can be seen that when the lower layer is brought into a power generation state by the continuous light CW as shown by the graph 64, the intensity of the electromagnetic wave pulse generated in the intermediate layer increases although not as much as the graph 61 shows. Further, as shown in the graph 62, when the upper layer and the middle layer are in the power generation state by the continuous light CW, the intensity of the electromagnetic wave pulse is slightly increased when the intensity of the continuous light CW is low, but the intensity of the continuous light CW is increased. It turns out that the intensity | strength of an electromagnetic wave pulse falls with it.

  As described above, even when the pulsed light condition is fixed, the intensity of the generated electromagnetic wave pulse is changed by changing the irradiation condition (wavelength or intensity) of the continuous light CW. For this reason, the multi-junction solar cell 90 can be inspected in various ways by changing the irradiation condition of the continuous light CW.

<1.2.2. Inspection example 2>
FIG. 11 is a diagram illustrating a flow of the inspection example 2. In this inspection example 2, an electromagnetic wave pulse radiated from the front part or a part of the multi-junction solar cell 90 is measured, and an electromagnetic wave pulse intensity distribution is imaged. According to this inspection example 2, since a wide range is inspected at a time, it is possible to easily compare characteristics of each part, detect a defective portion, and the like.

  Specifically, first, the wavelength of the pulsed light to be irradiated is set based on the absorption wavelength region of each layer of the multi-junction solar cell 90 (step S21). This step S21 is the same as step S11 shown in FIG. Here, it is assumed that the multi-junction solar cell 90 is set to be irradiated with pulsed light LP11 to LP31 having three wavelengths λ, λ / 2, and λ / 3.

  Next, the conditions of the continuous light CW irradiated to each layer (solar cells 9A to 9C) of the multi-junction solar cell 90 are determined (step S22). This step S22 is the same as step S14 shown in FIG. For example, as the wavelength of the continuous light CW, among the layers of the multijunction solar cell 90, three types of wavelengths that are absorbed by the specific layer are selected. Further, the intensity and irradiation range of the continuous light CW are also set as appropriate in step S22.

  Next, the detection timing for inspection is determined (step S23). Specifically, the multi-junction solar cell 90 is irradiated with pulsed light having a specific wavelength among the plurality of wavelengths set in step S <b> 21 (here, the pulsed light LP <b> 11). The time waveform of the radiated electromagnetic wave pulse LT11 is restored. In this time waveform, the peak of the electric field strength, that is, the timing when the electric field strength becomes maximum is set as the detection timing for inspection. When the detection timing is determined, the delay stage of the delay element 14 is fixed at a position corresponding to the timing.

  Note that the inspection detection timing determined in step S22 is not necessarily the detection timing at which the maximum electric field strength is detected. However, it becomes easy to detect the electromagnetic wave pulse radiated | emitted from each part of the multijunction solar cell 90 by fixing to such a detection timing.

  Next, the pulsed light LP11 is irradiated onto the inspection target range of the multi-junction solar cell 90, and the emitted electromagnetic wave pulse LT11 is measured (step S24). Specifically, the delay stage of the delay element 14 is fixed at a position corresponding to the detection timing for inspection determined in step S22. In this state, the inspection target range of the multi-junction solar cell 90 is scanned with the pulsed light LP11. Here, first, electromagnetic wave measurement is performed without irradiating the continuous light CW.

  Next, in step S21, it is determined whether or not measurement of all electromagnetic wave pulses has been completed (step S25). If it is determined that the inspection is completed, the inspection is completed. If the inspection is not completed, the process returns to step S22. At this time, since irradiation with the other pulsed light LP21 and LP31 is not completed, the process returns to step S22. Thereby, the measurement of the electromagnetic wave pulse LT21 by the irradiation of the pulsed light LP21 and the measurement of the electromagnetic wave pulse LT31 by the irradiation of the pulsed light LP31 are performed.

  If it is determined in step S25 that all electromagnetic wave measurement has been completed, electromagnetic wave measurement is performed under the condition of irradiating continuous light CW (step S26). Specifically, the inspection target range in the multi-junction solar cell 90 is two-dimensionally scanned with the pulsed light LP11 while irradiating the continuous light CW having a specific wavelength. Then, in the next step S27, it is determined whether or not all electromagnetic wave measurements have been completed. At this time, since irradiation with the other pulse lights LP21 and LP31 is not completed, the process returns to step S26, and two-dimensional scanning with these pulse lights LP21 or LP31 is performed. Further, electromagnetic wave measurement for irradiating each of the pulsed lights LP11 to LP31 by changing the wavelength of the continuous light CW to be irradiated is sequentially performed.

  When all the electromagnetic wave measurements are completed, generation and display of an electric field intensity distribution image under each condition is executed (step S28).

  FIG. 12 is a schematic diagram illustrating an example of the electric field intensity distribution image i1. According to the electric field strength distribution image i1, the electric field strength distribution in the multi-junction solar cell 90 can be easily grasped. Based on this electric field intensity distribution, for example, a defective portion of the multi-junction solar cell 90 can be easily identified.

  Further, for example, a plurality of electric field intensity distribution images obtained in step S25 may be combined into one image and displayed on the monitor 17. For example, when there are three electric field intensity distribution images, each of them may be colored into each color such as red (R), green (G), and blue (B) and combined into one image. This makes it possible to individually grasp three electric field intensity distributions in one composite image.

  The inspection target range scanned with the pulsed light LP11 to LP31 may be set based on, for example, a visual inspection, an electroluminescence (EL) inspection, and a photoluminescence (PL) inspection that are performed in advance. By narrowing the inspection object range by these inspections, the time required for the inspection based on the electromagnetic wave measurement can be shortened.

<1.3 Effect>
As described above, according to the present embodiment, in the multi-junction solar cell 90 having different absorption wavelength regions in the depth direction, the light having the wavelength corresponding to the solar cell of the layer at the target depth position is irradiated. Each electromagnetic pulse radiated by can be measured. Furthermore, by irradiating the continuous light CW corresponding to each layer, each layer can be brought into a power generation state (a state where an electromotive force is generated). By combining these, it is possible to analyze the carrier dynamics in the power generation state and the influence (interaction) that the specific layer receives from other layers in the power generation state.

  Note that the inspection object of the present invention is not limited to the multi-junction solar cell 90. For example, a quantum dot solar cell in which quantum dots are stacked so that the dot size gradually decreases from the back surface side to the light receiving surface side is known. In such a quantum dot solar cell, since the dot size is different, the absorption wavelength is different in the depth direction. The inspection apparatus 100 can inspect with a plurality of pulse lights LP11 to LP41 having different wavelengths and a continuous light CW with a plurality of wavelengths. For this reason, the inspection apparatus 100 is also suitable for inspecting quantum dot solar cells.

  In general, it is known that light having a long wavelength penetrates to a deep portion, but light having a short wavelength can penetrate only to a shallow portion. Accordingly, even in a single-junction solar cell, a plurality of pulsed light LP11 to LP41 having different wavelengths and a plurality of continuous light CW having different wavelengths are irradiated in combination, so that each part in the depth direction of the solar cell is polygonal. Can be inspected.

  Further, in the field of image sensors, for example, image sensors formed by laminating a plurality of silicon layers having different absorption wavelength regions such as Foveon X3 (registered trademark) are known. When inspecting such an image sensor, each layer can be inspected by irradiating pulsed light having a wavelength corresponding to each layer.

  Even when an LED is an inspection object, if light having a wavelength shorter than the oscillation wavelength of a semiconductor layer is irradiated, the light is absorbed and an electromagnetic wave pulse can be emitted. Therefore, if the LED is irradiated with light having a wavelength shorter than the oscillation wavelength (that is, light having energy higher than the energy gap), the LED can be inspected satisfactorily.

  The wavelength of the pulsed light applied to the photo device may be determined as follows. For example, it is assumed that a photo device to be inspected has a first layer and a second layer that has an absorption wavelength region different from that of the first layer and is disposed below the first layer. In this case, the first light having a higher energy than the energy gap of the first layer and the second light having a higher energy than the energy gap of the second layer and lower than the energy gap of the first layer are irradiated. do it. In this case, the electromagnetic wave pulse can be selectively emitted from the first layer by irradiation with the first light, and the electromagnetic wave pulse can be selectively emitted from the second layer by irradiation with the second light. .

<2. Second Embodiment>
FIG. 13 is a schematic configuration diagram of an inspection apparatus 100A according to the second embodiment. In the following description, elements having the same functions as those in the first embodiment may be denoted by the same reference numerals or reference numerals added with alphabets, and detailed description thereof may be omitted.

  The inspection apparatus 100A includes a white femtosecond laser 121A as a light source of the excitation light irradiation unit 12A. The white pulsed light LP50 emitted from the white femtosecond laser 121A is divided and passes through the long wavelength filter 51, the medium wavelength filter 53, and the short wavelength filter 55. Thereby, a plurality of pulse lights LP51, LP53 and LP55 having different wavelengths are generated and irradiated to the multi-junction solar cell 90. Also in this embodiment, the multi-junction solar cell 90 can be irradiated with the pulsed light LP51, LP53, and LP55 shifted in time by the delay element 35 and the delay element 37. By irradiating the multi-junction solar cell 90 with each of the pulsed light LP51, LP53 and LP55, the multi-junction solar cell 90 emits electromagnetic wave pulses LT51, LT52 and LT53.

  In the present embodiment, the white pulse light LP50 passes through the long wavelength filter 57 and then enters the detector 131. Thereby, the detector 131 detects the electromagnetic wave pulse radiated from the multi-junction solar cell 90. Note that the long wavelength filter 57 is not necessarily required, and the wavelength filter may be appropriately selected according to the material of the detector 131. The optical path length of the pulsed light incident on the detector 131 can be changed by the delay element 14. For this reason, the detection timing of the electromagnetic wave pulse in the detector 131 can be changed.

  Also in the inspection apparatus 100A, the continuous light irradiation unit 19 that irradiates the multi-junction solar cell 90 with the continuous light CW is provided. For this reason, the continuous light irradiation unit 19 can irradiate the multi-junction solar cell 90 with continuous light CW having an appropriate wavelength, whereby the specific layer of the multi-junction solar cell 90 can be brought into a power generation state. Therefore, in the inspection apparatus 100A, similarly to the inspection apparatus 100, the carrier dynamics in the specific layer in the power generation state are analyzed, or the influence (interaction) that the specific layer receives from the layers in other power generation states is analyzed in detail. it can.

<3. Third Embodiment>
FIG. 14 is a schematic diagram of an inspection apparatus 100B according to the third embodiment. In the inspection apparatus 100 </ b> B, the pulsed light emitted from the excitation light irradiation unit 12 passes through the transparent conductive film substrate (ITO) 990 and enters the surface 90 </ b> S of the multijunction solar cell 90 perpendicularly. Of the electromagnetic wave pulses generated in response to the irradiation of the pulsed light, the electromagnetic wave pulse emitted toward the surface 90S reflects the transparent conductive substrate 990 and enters the detector 131 through an optical system such as a lens. To do. That is, the inspection apparatus 100B is configured as a coaxial reflection type apparatus in which the irradiation pulse light and the emitted electromagnetic wave pulse are coaxial. Also with such an inspection apparatus 100B, similarly to the inspection apparatus 100, an electromagnetic wave pulse radiated from the multi-junction solar cell 90 can be detected.

<4. Fourth Embodiment>
FIG. 15 is a schematic diagram of an inspection apparatus 100C according to the fourth embodiment. In the inspection apparatus 100 </ b> C, the pulsed light emitted from the excitation light irradiation unit 12 is perpendicularly incident on the surface 90 </ b> S of the multi-junction solar cell 90. Then, the electromagnetic wave pulse emitted (that is, transmitted) to the back surface side of the multi-junction solar cell 90 is detected by the detection unit 13. That is, the inspection apparatus 100C is configured as a transmission type inspection apparatus. Also with such an inspection apparatus 100 </ b> C, similarly to the inspection apparatus 100, it is possible to detect an electromagnetic wave pulse emitted from the multijunction solar cell 90.

<5. Modification>
Although the embodiment has been described above, the present invention is not limited to the above, and various modifications are possible.

  For example, in the first embodiment, pulsed light is emitted from the femtosecond laser 121 and pulsed electromagnetic waves are emitted from the multijunction solar cell 90. However, in place of the femtosecond laser 121, it is also possible to use two light sources that emit two continuous lights having slightly different oscillation frequencies. Specifically, an optical beat signal corresponding to the difference frequency is generated by superimposing two continuous lights by a coupler formed by an optical fiber or the like that is an optical waveguide. Then, by irradiating the multi-junction solar cell 90 with this optical beat signal, an electromagnetic wave (terahertz wave) corresponding to the frequency of the optical beat signal can be emitted. As the light source, for example, a distributed feedback (DFB) laser that can change the wavelength of the emitted laser light substantially continuously (for example, every 2 nm) by temperature control can be used.

  In the case of using this technology, for example, if three lights (optical beat signals) having different wavelengths are irradiated, six light sources may be used. Moreover, although it is desirable to irradiate the multi-junction solar cell 90 by switching a plurality of optical beat signals having different wavelengths, they may be irradiated simultaneously. This is because the frequency distribution of electromagnetic waves radiated by irradiation with an optical beat signal is very narrow. For this reason, the components of each electromagnetic wave can be easily separated by using a frequency filter.

  Although the present invention has been described in detail, the above description is illustrative in all aspects, and the present invention is not limited thereto. It is understood that countless variations that are not illustrated can be envisaged without departing from the scope of the present invention. Moreover, each structure demonstrated by said each embodiment and each modification can be suitably combined or abbreviate | omitted unless it mutually contradicts.

100, 100A, 100B, 100C Inspection apparatus 11 Stage 12, 12A Excitation light irradiation unit 121 Femtosecond laser 13 Detection unit 131 Detector 14 Delay element 15 Stage moving mechanism 16 Control unit 17 Monitor 18 Operation input unit 19 Continuous light irradiation unit 191 Irradiation condition changing unit 21 Image generating unit 23 Time waveform restoring unit 27 Setting unit 31 Wavelength double converter 33 Wavelength triple converter 35, 37, 39 Delay element 351 Delay stage 353 Delay stage moving mechanism 41, 42 Time waveform 43 Spectrum Distribution 51, 57 Long wavelength filter 53 Medium wavelength filter 55 Short wavelength filter 90 Multi-junction solar cell (photo device)
90S surface 92 back electrode 93A, 93B, 93C p-type semiconductor layer 94A, 94B, 94C n-type semiconductor layer 95 tunnel junction 96 light-receiving surface electrode 97A, 97B, 97C pn junction 990 transparent conductive substrate 9A, 9B, 9C solar cell (Subcell)
CW continuous light L10, LP13, LP15, LP17, LP19 Pulse light LP11, LP21, LP31, LP41 Pulse light (excitation light)
LP50 White pulse light LP51, LP53, LP55 Pulse light (excitation light)
LPa, LPb, LPc Pulse light (excitation light)
LT11, LT21, LT31, LT41 Electromagnetic pulse LT51, LT52, LT53 Electromagnetic pulse LTa, LTb, LTc Electromagnetic pulse Δt11, Δt21, Δt31 Time (Δt)
T11, T21, T31 Generation time i1 Electric field intensity distribution image

Claims (7)

An inspection apparatus for inspecting a photo device,
An excitation light irradiation unit capable of irradiating a photo device with a plurality of excitation lights having different wavelengths;
A continuous light irradiation unit capable of irradiating a plurality of continuous lights having different wavelengths with respect to a portion irradiated with the excitation light in the photo device;
While setting the wavelength of the excitation light that the excitation light irradiation unit irradiates the photo device, the setting unit that sets the wavelength of the continuous light that the continuous light irradiation unit irradiates the photo device;
In accordance with the excitation light irradiated by the excitation light irradiation unit, a detection unit that detects an electric field intensity of an electromagnetic wave emitted from the photo device;
Equipped with a,
The photo device is a multi-junction solar cell configured by stacking a plurality of subcells having different absorption wavelength regions,
The setting unit
The wavelength of the excitation light that the excitation light irradiation unit irradiates the multi-junction solar cell is set to a wavelength included in an absorption wavelength region of a specific subcell among the plurality of subcells,
The wavelength of the continuous light which the continuous light irradiation section for irradiating the multi-junction solar cell, among the plurality of sub-cells, to set a wavelength included in the absorption wavelength region of the specific sub-cell, the inspection apparatus. The inspection apparatus according to claim 1,
The excitation light irradiation unit irradiates the photo device with excitation light having a second wavelength different from the first wavelength after the time Δt has elapsed since the excitation light of the first wavelength is applied to the photo device. An inspection apparatus that irradiates excitation light of the first wavelength again. The inspection apparatus according to claim 2,
The plurality of excitation lights are pulse lights,
The detection unit includes a detector that detects the electromagnetic wave emitted from the photo device by receiving the pulsed light,
The inspection device includes:
The inspection apparatus further includes a delay unit that delays the timing at which the detector receives the pulsed light relative to the timing at which the electromagnetic wave reaches the detector. The inspection apparatus according to any one of claims 1 to 3,
A scanning mechanism that scans the photo device with the plurality of excitation lights irradiated by the excitation light irradiation unit;
An image generating unit that generates an image indicating a distribution of the electric field strength in the photo device based on the electric field strength of the electromagnetic wave detected by the detecting unit;
An inspection apparatus further comprising: The inspection apparatus according to claim 2,
The plurality of excitation lights having different wavelengths emitted from the excitation light irradiation unit are pulsed light,
The inspection apparatus, wherein the time Δt is longer than the generation time of one pulse of the electromagnetic wave emitted by the pulsed light. An inspection method for inspecting a photo device,
An excitation light irradiation step of irradiating the photo device with a plurality of excitation lights having different wavelengths;
A continuous light irradiation step of irradiating continuous light to the portion of the photo device irradiated with the excitation light;
Setting the wavelengths of the plurality of excitation lights irradiated in the excitation light irradiation process, and setting the wavelengths of the continuous light irradiated in the continuous light irradiation process,
In accordance with the plurality of excitation lights irradiated in the excitation light irradiation step, a detection step of detecting an electric field intensity of an electromagnetic wave emitted from the photo device,
Only including,
The photo device is a multi-junction solar cell configured by stacking a plurality of subcells having different absorption wavelength regions,
The setting step includes
The wavelength of the excitation light applied to the multi-junction solar cell in the excitation light irradiation step is set to a wavelength included in an absorption wavelength region of a specific subcell among the plurality of subcells,
Inspection, which is a step of setting the wavelength of the continuous light irradiated to the multi-junction solar cell in the continuous light irradiation step to a wavelength included in the absorption wavelength region of the specific subcell among the plurality of subcells Method. The inspection method according to claim 6 ,
The excitation light irradiation step irradiates the photo device with excitation light having a second wavelength different from the first wavelength after the time Δt has elapsed since the photo device was irradiated with excitation light having the first wavelength. An inspection method comprising a step of irradiating the photo device with the excitation light of the first wavelength again.

Images