JP6716374B2 - Band gap measuring method and band gap measuring device - Google Patents

Description

The present invention relates to a band gap measuring method and a band gap measuring device.

The in-plane distribution of the band gap of the solar cell is preferably uniform in terms of quality. For example, the in-plane distribution of the band gap of the crystalline silicon solar cell is 1.1 eV to 1.2 eV, which is almost constant. On the other hand, in the case of a compound solar cell, it is difficult to have a uniform composition structure in the plane, and therefore, the in-plane distribution of the band gap varies. Therefore, by examining the in-plane distribution of the band gap of the solar cell, it is possible to know whether or not the solar cell is a good product, whether the solar cell has a desired composition structure, and the like.

As a method of examining the band gap of a solar cell, there is a PL (Photoluminescence) method. In this method, the solar cell is irradiated with excitation light having energy equal to or greater than the band gap of the light absorption layer of the solar cell, and the light emitted by the light absorption layer is dispersed by a prism. The band gap is estimated (for example, see Non-Patent Document 1).

The latest technology of CIGS thin film solar cells, supervised by Tokio Nakata, written by Shirakata, p253-255, CMC Publishing

However, in the case of the above-mentioned band gap measuring method, it is generally a point analysis, and it takes a long time to acquire the spectral spectrum data per point. Therefore, it takes time to measure the in-plane distribution of the band gap of a large area solar cell. Similar problems occur in objects to be measured other than solar cells, such as light emitting diodes and semiconductor lasers.

An object of the present invention is to provide a bandgap measuring method and a bandgap measuring apparatus capable of estimating the in-plane distribution of the bandgap in a short time.

The band gap measuring method includes a step of causing a measurement target to emit light, a step of receiving light emitted by the measurement target without passing through an optical filter to capture a first image of the measurement target, and a measurement target. Of the light emitted by the device through the optical filter to capture the second image of the measurement object, the step of calculating the brightness ratio of the first image and the second image, and the step of calculating the brightness ratio based on the brightness ratio. And a step of calculating the bandgap of the measurement object, in the relationship between the wavelength and the transmittance of the optical filter , the transmittance increases or decreases as the wavelength increases, and at different wavelengths. It does not have the same transmittance .

This band gap measuring device is an excitation source that emits light from the measurement target, an optical filter that can be selectively arranged on the optical path of the light emitted from the measurement target, and a state in which the light emitted from the measurement target does not pass through the optical filter. An image pickup element that receives a second image of the measurement target by receiving light emitted by the measurement target through the optical filter while capturing a first image of the measurement target by receiving the light. And a calculation unit that calculates a luminance ratio at a predetermined position between the first image and the second image and calculates a bandgap at a predetermined position of the measurement object based on the luminance ratio. In the above relationship, the transmittance increases or decreases to the right as the wavelength increases, and the same transmittance does not occur at different wavelengths .

According to the disclosed technique, it is possible to provide a bandgap measuring method and a bandgap measuring apparatus capable of estimating the in-plane distribution of the bandgap in a short time.

It is a schematic diagram which illustrates the structure of the band gap measuring apparatus which concerns on this Embodiment. It is a figure which illustrates the transmittance|permeability spectrum of the optical filter used for the band gap measuring apparatus which concerns on this Embodiment. It is a figure explaining the measurement part of the band gap measuring device which concerns on this Embodiment, (a) is a hardware block diagram of a measurement part, (b) is a functional block diagram of a measurement part. 6 is a flowchart illustrating a bandgap measuring method according to the present embodiment. It is an example of the image which the image sensor of the band gap measuring device which concerns on this Embodiment imaged, (a) is an image imaged without passing an optical filter, (b) is an image imaged through an optical filter. .. It is a figure explaining calculation of the brightness ratio (extinction rate) in the band gap measuring method concerning this embodiment. It is an example of an image in which the emission wavelength of each pixel is mapped in the bandgap measuring method according to the present embodiment.

Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings. In addition, in each drawing, the same components may be denoted by the same reference numerals, and redundant description may be omitted.

FIG. 1 is a schematic diagram illustrating the configuration of the band gap measuring device according to the present embodiment. Referring to FIG. 1, the band gap measuring device 1 includes an excitation source 10, an optical filter 20, an image sensor 30, and a measuring section 40.

The measurement target 100 is not particularly limited as long as it has a band gap, but is, for example, a semiconductor such as a solar cell, a light emitting diode, or a semiconductor laser. An example of the solar cell is a compound solar cell in which the semiconductor layer is a CIS-based thin film (a thin film made of a compound containing copper (Cu), indium (In), and selenium (Se)).

In the band gap measuring device 1, the excitation source 10 has a function of causing the measurement target 100 to emit light. In the example of FIG. 1, the excitation source 10 is a power source that applies a voltage to the measurement target 100, but may be an excitation light source that irradiates the measurement target 100 with light. The measurement object 100 emits light by applying a voltage or irradiating light to the measurement object 100 from the excitation source 10.

The optical filter 20 is a filter having a predetermined transmittance-wavelength relationship. As shown in FIG. 2, the optical filter 20 does not have the maximum value and the minimum value in the transmittance within the wavelength range. In other words, the optical filter 20 has a downward-sloping transmittance, and does not have the same transmittance at different wavelengths. However, the characteristic of FIG. 2 is an example, and the optical filter 20 may have an increasing transmittance as long as the transmittance does not have the maximum value and the minimum value. Further, an optical filter having no maximum or minimum transmittance may be formed by using a plurality of optical filters.

The optical filter 20 is configured such that it can be selectively arranged on the optical path of the light emitted from the measurement target 100, and is located on the optical path from the measurement target 100 to the image sensor 30 and outside the optical path. It is possible to switch between cases. The position of the optical filter 20 may be switched by controlling the measuring unit 40, or may be mechanically independent of the measuring unit 40.

Returning to the description of FIG. 1, the imaging element 30 has a function of receiving light emitted by the measurement object 100 and capturing a two-dimensional image. As the image sensor 30, for example, a MOS (Metal Oxide Semiconductor), a CMOS (Complementary Metal Oxide Semiconductor), a CCD (Charge Coupled Device), or the like can be used.

As described above, the optical filter 20 can be selectively arranged on the optical path of the light emitted by the measurement target 100. Therefore, the imaging element 30 can receive the light emitted by the measurement target 100 without passing through the optical filter 20 and capture an image of the measurement target 100. Further, the image pickup device 30 can receive light emitted from the measurement target 100 through the optical filter 20 and capture an image of the measurement target 100.

The measurement unit 40 has a function of controlling the excitation source 10 and the image pickup device 30, and calculating data of a two-dimensional image acquired from the image pickup device 30. The measuring unit 40 will be described in more detail with reference to FIG.

FIG. 3A is a hardware block diagram of the measuring unit 40. With reference to FIG. 3A, the measurement unit 40 includes a CPU 41, a ROM 42, a RAM 43, an I/F 44, a bus line 45, and a mass storage 46. The CPU 41, ROM 42, RAM 43, I/F 44, and Mass Storage 46 are connected to each other via a bus line 45.

The CPU 41 controls each function of the measuring unit 40. The ROM 42 stores a program executed by the CPU 41 to control each function of the measuring unit 40 and various kinds of information. The RAM 43 is used as a work area or the like of the CPU 41. Further, the RAM 43 can temporarily store predetermined information.

The I/F 44 is an interface for connecting to another device. The measurement unit 40 is connected to the image sensor 30 via the I/F 44, for example, and can control the image sensor 30 and acquire two-dimensional image data from the image sensor 30. The measurement unit 40 is connected to the excitation source 10 via the I/F 44, for example, and can control the excitation source 10.

The Mass Storage 46 has a function of storing various data. The Mass Storage 46 is, for example, a hard disk or an SSD (solid state drive). However, the Mass Storage 46 may be provided outside the band gap measuring device 1. The Mass Storage 46 in this case is, for example, an external hard disk, a USB memory, an optical disk, or the like. Alternatively, the Mass Storage 46 may be an online storage.

FIG. 3B is a functional block diagram of the measuring unit 40. Referring to FIG. 3B, the measurement unit 40 has an excitation source control unit 401, an image sensor control unit 402, and a calculation unit 403 as functional blocks.

The CPU 41 shown in FIG. 3A executes a predetermined program and cooperates with other hardware resources as necessary, so that the excitation source control unit 401, the image sensor control unit 402, and the calculation unit 403. Function can be realized. However, some or all of the functions of the excitation source control unit 401, the imaging element control unit 402, and the calculation unit 403 may be realized by hardware such as PLD (Programmable Logic Device).

A bandgap measurement method including the operation of each functional block of the measurement unit 40 will be described with reference to the flowchart of FIG. 4 and other drawings as appropriate.

First, in step S201, the excitation source control unit 401 of the measurement unit 40 controls the excitation source 10 to apply a voltage to the measurement target 100 from the power source that is the excitation source 10. As a result, the measuring object 100 emits light. Instead of applying a voltage from the excitation source 10 to the measurement object 100, an excitation light source may be prepared as the excitation source 10 and the measurement object 100 may be irradiated with light from the excitation light source.

Next, in step S202, the optical filter 20 is placed in a state of being located outside the optical path from the measurement target 100 to the image pickup element 30. Then, the image sensor control unit 402 of the measurement unit 40 controls the image sensor 30 so that the light emitted by the measurement target 100 is received by the image sensor 30 without passing through the optical filter 20. The first image is captured. Then, the two-dimensional image data of the captured first image (hereinafter referred to as unfiltered image data) is temporarily stored in the RAM 43. An example of the image taken in step S202 is shown in FIG.

Next, in step S203, the optical filter 20 is placed in a state in which it is positioned on the optical path from the measurement target 100 to the image sensor 30. Then, the image sensor control unit 402 of the measuring unit 40 controls the image sensor 30 so that the light emitted by the measurement target 100 is received by the image sensor 30 via the optical filter 20. The second image is captured. Then, the data of the two-dimensional image of the captured second image (hereinafter, referred to as filtered image data) is temporarily stored in the RAM 43. An example of the image captured in step S203 is shown in FIG. The order of steps S202 and S203 may be reversed.

Next, in step S204, the calculation unit 403 of the measurement unit 40 reads the image data captured without the optical filter and the image data captured with the optical filter, which are stored in the RAM 43 or the Mass Storage 46. Then, the brightness value of each pixel of the read image data is compared to calculate the brightness ratio (dimming ratio) of each pixel.

For example, the brightness value (light emission intensity) of a predetermined pixel in the unfiltered image data is I in FIG. 6A, and the brightness value (light emission intensity) of the same pixel in the image data with filter is I in FIG. 6B. _{If it is A} , the luminance ratio (dimming ratio) is I _A /I×100%. Note that F represents the transmittance (transmittance curve) of the optical filter 20 at each wavelength.

Alternatively, an I luminance value of a given pixel of the unfiltered image data is FIG. 6 (a), when the luminance value of the same pixel of the filter there image data is assumed to be a I _B in FIG. 6 (b), I _B The brightness ratio is /I×100%.

Similarly, if the brightness value of a predetermined pixel in the unfiltered image data is I in FIG. 6A and the brightness value of the same pixel in the filtered image data is I _C in FIG. 6B, I _The brightness ratio is _C /I×100%.

Next, in step S205, the calculation means 403 of the measurement unit 40 obtains the emission wavelength for each pixel based on the relationship between the transmittance of the optical filter 20 and the luminance ratio. The transmittance spectrum of the optical filter 20 may be stored in the RAM 43, for example, and read out when necessary.

Since the transmittance and the brightness ratio are equal, for example, if the brightness ratio calculated in step S204 is I _A /I×100%, the transmittance curve F of the optical filter 20 indicates that the emission wavelength of the pixel is A. Can be calculated. Alternatively, if the luminance ratio calculated in step S204 is I _B /I×100%, it can be calculated from the transmittance curve F of the optical filter 20 that the emission wavelength of the pixel is B. Similarly, if the luminance ratio calculated in step S204 is I _C /I×100%, it can be calculated from the transmittance curve F of the optical filter 20 that the emission wavelength of the pixel is C.

The steeper the slope of the transmittance curve F of the optical filter 20, the better in that the conversion error from the luminance ratio (extinction rate) to the emission wavelength becomes smaller and the resolution improves.

Next, in step S206, the calculating unit 403 of the measuring unit 40 calculates the band gap of each pixel from the emission wavelength of each pixel calculated in step S205. The relationship of λ=1240/Eg is established between the band gap Eg (eV) and the emission wavelength λ (nm). Therefore, for example, if the relationship between Eg and λ is stored in the RAM 43 as a table, the band gap can be calculated for each pixel from the emission wavelength for each pixel calculated in step S205 using the table.

Next, in step S207, the calculation means 403 of the measurement unit 40 maps the emission wavelength of each pixel calculated in step S205. For example, as shown in FIG. 7, the length of the emission wavelength of each pixel can be indicated by the shade of color. By executing step S207, it is possible to visually recognize the length of the emission wavelength of each pixel (that is, the size of the band gap of each pixel) at once. However, since the calculation of the band gap is completed in step S206, execution of step S207 is not essential.

As described above, the bandgap measuring apparatus 1 acquires two image data with and without a filter, and performs image processing using the two image data to determine whether the emission wavelength of each pixel is long or short (that is, for each pixel). Calculate the band gap).

Therefore, unlike the conventional band gap measuring method, it is not necessary to measure the band gap by irradiating light at each predetermined position of the measurement target, and the in-plane distribution of the band gap of the measurement target can be estimated in a short time. It becomes possible to do.

The band gap measuring method according to the present embodiment is a non-destructive inspection, and therefore can be applied to a quality inspection before shipment in a manufacturing process of a semiconductor such as a solar cell. Alternatively, the bandgap measuring method according to the present embodiment may be used for analysis of semiconductor market-converted products such as solar cells. The bandgap measuring method according to the present embodiment can also be applied to the inspection of semiconductors such as solar cells after installation (in use).

Although the preferred embodiments have been described above in detail, the present invention is not limited to the above-described embodiments, and various modifications and replacements of the above-described embodiments are possible without departing from the scope of the claims. Can be added.

For example, in the above embodiment, the band gap measurement device 1 including the excitation source 10, the optical filter 20, the image sensor 30, and the measurement unit 40 has been described. However, the excitation source 10, the optical filter 20, and the image sensor 30 may be an image acquisition device independent of the measurement unit 40. In this case, the bandgap measuring apparatus 1 can be realized by connecting and operating a computer or the like capable of realizing the function of the measuring unit 40 and the image acquisition apparatus.

Further, in the band gap measuring device 1, an optical microscope may be arranged on the optical path from the measurement target 100 to the optical filter 20 or on the optical path from the optical filter 20 to the image pickup device 30. In this case, since the measurement target 100 can be magnified and imaged, it can be expected to measure the bandgap with a resolution of about the optical imaging limit.

1 band gap measuring device 10 excitation source 20 optical filter 30 image sensor 40 measuring unit 100 measurement object

Claims (9)

A bandgap measurement method,
Illuminating the measurement object,
Receiving light emitted by the measurement object without passing through an optical filter and capturing a first image of the measurement object;
Receiving light emitted by the measurement object through an optical filter and capturing a second image of the measurement object;
Calculating a brightness ratio between the first image and the second image;
Calculating a band gap of the measurement object based on the luminance ratio,
In the relationship between the wavelength of the optical filter and the transmittance, the transmittance increases or decreases as the wavelength increases, and the same transmittance does not occur at different wavelengths. .. In the step of calculating the brightness ratio, the brightness ratio is calculated for each pixel of the first image and the second image,
The band gap measuring method according to claim 1, wherein in the step of calculating the band gap, the band gap is calculated based on the luminance ratio for each pixel. 3. In the step of calculating the bandgap, the brightness ratio is calculated from the brightness ratio of each pixel based on the relationship that the brightness ratio is equal to the transmittance of the optical filter, and the bandgap is calculated from the wavelength. The band gap measurement method described in. The bandgap measurement method according to claim 3, further comprising mapping the wavelength of each pixel. The bandgap measuring method according to claim 1, wherein in the step of causing the measurement object to emit light, a voltage is applied to the measurement object from a power supply. The bandgap measuring method according to claim 1, wherein in the step of causing the measurement object to emit light, the excitation light source irradiates the measurement object with light. A band gap measuring device,
An excitation source that emits light from the measurement object,
An optical filter that can be selectively arranged on the optical path of light emitted by the measurement object,
The light emitted by the measurement object is received without passing through the optical filter to capture a first image of the measurement object, and the light emitted by the measurement object is received through the optical filter. An image sensor for capturing a second image of the measurement object,
Computing means for calculating a luminance ratio at a predetermined position of the first image and the second image, and calculating a bandgap of the measurement object at the predetermined position based on the luminance ratio,
In the relationship between the wavelength and the transmittance of the optical filter, the transmittance increases or decreases as the wavelength increases, and the same transmittance does not occur at different wavelengths. .. The calculation means calculates the brightness ratio for each pixel of the first image and the second image, and the brightness ratio is calculated for each pixel based on a relationship in which the brightness ratio is equal to the transmittance of the optical filter. The bandgap measuring apparatus according to claim 7, wherein a wavelength is obtained from the wavelength, and the bandgap is calculated from the wavelength. The bandgap measuring apparatus according to claim 8, wherein the arithmetic means maps the wavelength for each pixel.