Abstract:
A photoelectric conversion device which inhibits characteristic degradation caused by crystal defects, and an inspection method for crystal defects in photoelectric conversion devices. The photoelectric conversion device is provided with an active layer, and a deactivator contained in the active layer.

Description:
TECHNICAL FIELD 
     The present invention relates to a photoelectric conversion device and a test method of its property, and in particular, it relates to a photoelectric conversion device that can inhibit property deterioration due to a crystal fault and a detection method of a crystal fault that is inherent in the photoelectric conversion device. 
     BACKGROUND ART 
     As a photoelectric conversion element by a semiconductor, light-emitting elements such as a light-emitting diode and a semiconductor laser as well as light-receiving elements such as a solar cell have been known. 
     The matter required for practical use and high performance of a light-emitting element is a high-power optical output and an increased longevity of an element. On the other hand, in a case of a receiving element, improvement of conversion efficiency is required. However, it is well known that a crystal fault (dislocation) that is inherent in a semiconductor crystal constituting a photoelectric conversion element inhibits the above high performance and deteriorates operation property. 
     With reference to  FIG. 8 , the condition that a crystal fault in a semiconductor crystal deteriorates operation property of a photoelectric conversion element will be explained. 
       FIG. 8  is a block diagram showing the configuration of a photoelectric conversion element  100  as one example. The photoelectric conversion element  100  includes an n-type semiconductor layer  101 , an active layer (photoelectric conversion unit)  102  formed on the n-type semiconductor layer  101  and a p-type semiconductor layer  103  formed on the active layer  103 . These are formed as a basic structure of a photoelectric conversion device by a well known semiconductor manufacture technique etc. 
     Here, a basic operation of the photoelectric conversion element  100  will be briefly explained with an example of a light-emitting element. 
     When a current is injected in the photoelectric conversion element  100 , an electron is injected from the n-type semiconductor layer  101  and a hole is injected from the p-type semiconductor layer  103 . The injected electron and hole are converted to a light by a luminescence recombination process in the active layer  102  and output a light to the outside. 
     However, the photoelectric conversion element may include a crystal fault (threading dislocation)  201  as shown in  FIG. 8  due to configuration imperfection of a semiconductor crystal.  FIG. 8  schematically shows a crystal fault which is inherent in a semiconductor crystal constituting the photoelectric conversion element  100  and there exist a threading dislocation  201  and a nonluminescence center  202 . For example, the threading dislocation  201  that generates at an interface between a growth substrate and a growth layer and propagates from below to the photoelectric conversion element  100  behaves as the nonluminescence center  202  that inhibits photoelectric conversion in the active layer  102 . 
     In particular, in a nitride semiconductor, the threading dislocation is commonly included with a high density of 1×10 8 cm −2  to 1×10 10 cm −2 , which becomes a major obstacle of high performance of a light-emitting element. 
     As a technology to reduce influence of this crystal fault, for example, Patent Literatures 1 and 2 below can be listed. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature1: Japanese Unexamined Patent Application Publication No. 2006-13547A 
         Patent Literature2: Japanese Unexamined Patent Application Publication No. 2006-5044A 
       
    
     Technical Problem 
     The crystal fault reduction technology disclosed in Patent Literatures 1 and 2 belongs to crystal growth technology called as selective growth or lateral growth for those skilled in the art. In this lateral growth process, accompanied with a normal crystal growth, a surface treatment process such as mask formation is required. This causes increase of the number of steps, a problem occurs in terms of yield or manufacture cost. 
     The present invention is made considering these circumstances, and an object of the present invention is to provide a photoelectric conversion device that inhibits the property deterioration due to a crystal fault without increasing the number of manufacture steps and a detection method of a crystal fault which is inherent in the photoelectric conversion device. 
     Solution to Problem 
     An electric conversion device according to a first aspect of the present invention includes a photoelectric conversion unit and a dislocation deactivation unit included in the photoelectric conversion unit. 
     In the photoelectric conversion device according to the first aspect of the present invention, the dislocation deactivation unit may be formed to have a crystal fault. 
     In the photoelectric conversion device according to the first aspect of the present invention, the dislocation deactivation unit may be formed to have a photoelectric conversion function. 
     In the photoelectric conversion device according to the first aspect of the present invention, the photoelectric conversion device includes a first conductive unit formed above the dislocation deactivation unit, and a second conductive unit formed below the dislocation deactivation unit, wherein the first conductive unit includes a first bandgap energy, the second conductive unit includes a second bandgap energy, and the dislocation deactivation unit includes a third bandgap energy, and wherein the third bandgap energy is smaller than any of the first bandgap energy and the second bandgap energy. 
     Moreover, a photoelectric conversion device according to the second aspect of the present invention includes a first In x Ga y Al 1-x-y N layer having a first conduction type, an In x Ga y Al 1-x-y N photoelectric conversion unit formed on the first In x Ga y Al 1-x-y N layer, and a second In x Ga y Al 1-x-y N layer formed on the In x Ga y Al 1-x-y N photoelectric conversion unit and having a second conduction type, wherein ranges of x and y are defined as 0≦x≦1, 0≦y≦1, and the In x Ga y Al 1-x-y N photoelectric conversion unit includes an InN dislocation deactivation unit. 
     In the photoelectric conversion device according to the second aspect of the present invention, the InN dislocation deactivation unit may be formed to have a layer thickness equal to or less than a bimolecular layer thickness. 
     In the photoelectric conversion device according to the second aspect of the present invention, the InN dislocation deactivation unit may be formed to have a crystal fault. 
     In a crystal fault detection method of a photoelectric conversion device according to the third aspect of the present invention, the photoelectric conversion device includes a first In x Ga y Al 1-x-y N layer having a first conduction type, an In x Ga y Al 1-x-y N photoelectric conversion unit formed on the first In x Ga y Al 1-x-y N layer, and a second In x Ga y Al 1-x-y N layer formed on the In x Ga y Al 1-x-y N photoelectric conversion unit and having a second conduction type, wherein ranges of x and y are defined as 0≦x,≦1, 0≦y≦1, the In x Ga y Al 1-x-y N photoelectric conversion unit includes an InN dislocation detection unit, the InN dislocation detection unit is formed to have a crystal fault is detected based on light-emitting property of the InN dislocation detection unit. 
     In the crystal fault detection method of a photoelectric conversion device according to the third aspect of the present invention, the InN dislocation detection unit has a layer thickness equal to or less than a bimolecular layer thickness. 
     In the crystal fault detection method of a photoelectric conversion device according to the third aspect of the present invention, a crystal fault is detected based on cathodoluminescence from the InN dislocation detection unit. 
     As explained above, according to the present invention, property deterioration due to a crystal fault can be inhibited without increasing the number of manufacture steps even when a crystal fault is inherent in the photoelectric conversion device. Moreover, detection of a crystal fault is made easy, which facilitates a product test of the photoelectric conversion device. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram of a configuration example of a photoelectric conversion device according to an embodiment of the present invention. 
         FIG. 2  is a block diagram showing the configuration of a photoelectric conversion unit according to an embodiment of the present invention. 
         FIG. 3  is experimental data by cathodoluminescence measurement showing operation and effects of a dislocation deactivation unit of the present invention. 
         FIG. 4  is a block diagram showing the configuration of the photoelectric conversion unit according to an embodiment of the present invention. 
         FIG. 5  is a block diagram showing a configuration example of the photoelectric conversion device according to an embodiment of the present invention. 
         FIG. 6  is a block diagram showing a configuration example of the photoelectric conversion device according to an embodiment of the present invention. 
         FIG. 7  is a block diagram showing a configuration example of the photoelectric conversion device according to an embodiment of the present invention. 
         FIG. 8  is a block diagram showing a configuration example of a photoelectric conversion device of the prior art. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereafter, the embodiments of the present invention will be described below referring to the accompanying drawings. 
     However, the descriptions don&#39;t limit the range of the present invention and they indicate only an example for explanation. 
     First Embodiment 
       FIG. 1  is a block diagram showing a configuration example of a photoelectric conversion device  10  according to the first embodiment of the claimed invention of the present application. In  FIG. 1 , the photoelectric conversion device  10  includes an n-type gallium nitride (hereinafter, it is referred to as “n-GaN”.) layer  11 , a photoelectric conversion unit (Active layer)  12  formed on the n-GaN layer  11 , a p-type gallium nitride (hereinafter, it is referred to as “p-GaN”.) layer  13  formed on the photoelectric conversion unit  12  and a dislocation deactivation unit  14  included in the photoelectric conversion unit  12 , and is formed by well known semiconductor manufacture technology etc. Additionally, since there is little appropriate growth substrate in a nitride-based semiconductor, when the photoelectric conversion element  10  is constituted, crystal faults  21  such as threading dislocation emitted from an interface between the N—GaN layer  11  and a substrate (figure is omitted) are included with high density of approximately 1×10 8 cm −2  to 1×10 10 cm −2 . 
     The n-GaN layer  11  is used to transport an electron, and the p-GaN layer  13  is used to transport a hole. Accordingly, resistivity and layer thickness of the n-GaN layer  11  and the p-GaN layer  13  are respectively appropriately adjusted in the viewpoint of carrier transport and a collection rate. 
     When the photoelectric conversion unit  12  is a light-emitting element, an injected electron-hole is converted to a light by a recombination process, and when it is a light receiving element, an absorbed light is converted to an electron-hole. As long as this function is included, the photoelectric conversion unit  12  is not limited, but it preferably includes gallium nitride (GaN), indium gallium nitride (InGaN) or indium nitride (InN) for example, and has a forbidden band width (bandgap energy) which is smaller than either of the n-GaN layer  11  or the p-GaN layer  13 . 
     Here, the dislocation deactivation unit  14  will be explained. Here, an explanation will be made with an example that the dislocation deactivation unit  14  is an InN ultrathin film and the photoelectric conversion unit  12  is GaN. 
     When InN is subjected to epitaxy growth on GaN, in a case of growth of a surface c for example, as there is the degree of lattice mismatch of approximately 11% between InN and GaN, a crystal fault of high density could be newly introduced during crystal growth. This crystal fault significantly deteriorates conversion efficiency in a photoelectric conversion element. However, the inventors have found that, if InN has a bimolecular layer (2ML) or less, elastic deformation is maintained without introducing any crystal fault and coherent growth is possible to GaN as an underlayer. 
     Moreover, in this ultrathin InN film with a bimolecular layer thickness or less, crystal growth with highly excellent structural perfection can be performed due to immiscibility with GaN. As a result, a formation process with self order and self stop can be performed, and a precipitous InN/GaN interface is formed in the atomic layer order. 
     When the ultrathin InN film is inserted in the photoelectric conversion unit  12 , a quantum well structure in which the ultrathin InN film is a well layer and GaN is a barrier layer is formed. That is, the ultrathin InN film quantum well layer may function as a part of the photoelectric conversion unit  12 . 
     As shown in  FIG. 2 , when the crystal fault  21  penetrates through the ultrathin InN film in the photoelectric conversion unit  12 , in a normal concept, it is believed that this becomes nonluminescence center and reduces conversion efficiency (quantum efficiency) in the photoelectric conversion unit  12 . However, contrary to the common knowledge, the inventors have found that this penetration point does not become the nonluminescence center even if the ultrathin InN film is penetrated by the crystal fault  21 . That is, the inventors have found that the ultrathin InN film not only constitutes a part of the photoelectric conversion unit  12  by itself but also constitutes the dislocation deactivation unit  14  that eliminates nonluminescence due to a crystal fault. 
     Operation and effects of the dislocation deactivation unit  14  which depart from the conventional common knowledge will be explained with property which is particular to the ultrathin InN film. 
       FIG. 3  shows a result of cathodoluminescence (CL) observation (CL image) of a sample which is grown on a GaN underlayer of a quantum well structure constituted by an ultrathin InN film well layer whose thickness is limited to a monomolecular layer thickness (1ML-InN) and a GaN layer. The CL observation refers to irradiating an accelerated electron beam from a sample surface to execute spectrofluorometric measurement from a sample. By controlling accelerating voltage of the accelerated electron beam Vacc, the insertion depth of an electron beam is controlled to obtain luminescence distribution information of a desired layer structural region (depth position). 
       FIG. 3  shows respective CL image when an observation region is 19 19 m 2  and accelerating voltage Vacc is varied in the same field of view. The accelerating voltage Vacc of 3 kV, 6 kV, 14 kV and 18 kV respectively correspond to the electron beam insertion length of 48 nm, 160 nm, 710 nm and 1100 nm. That is, when the accelerating voltage Vacc is 3 kV and 6 kV, mainly luminescence distribution from 1ML-InN quantum well is observed, and when the accelerating voltage Vacc is 14 kV and 18 kV, mainly luminescence distribution from GaN underlayer is observed. 
     In the CL images, white contrast corresponds to a luminescence region, and black contrast corresponds to a nonluminescence region (nonluminescence center), that is, the crystal fault  21  exists. 
     First, the CL images with the accelerating voltage Vacc is 14 kV and 18 kV are focused. Several scotomas are observed, and these are considered as crystal faults included in the GaN underlayer. Circular frames as a mark are applied to these scotomas. 
     On the other hand, in  FIG. 3 , focusing on the CL images with the accelerating voltage Vacc of 3 kV and 6 kV, it is found that regions of the circular frames as a mark applied to the crystal faults illuminate relatively brighter than its circumference. Conventionally, it has been considered that, in a region in which the crystal fault  21  is included in the GaN underlayer, luminescence efficiency of a quantum well grown on the region is deteriorated due to influence of the crystal fault  21 . However, contrary to this common knowledge, it is firstly shown that luminescence efficiency of the ultrathin InN film is not deteriorated irrespective of the existence of the crystal fault  21 . This surprisingly experimental fact clearly shows that the ultrathin InN film not only constitutes a part of the photoelectric conversion unit  12  by itself but also constitutes the dislocation deactivation unit  14  that eliminates nonluminescence due to a crystal fault. 
     Moreover, when the experimental results shown in  FIG. 3  are interpreted from another point of view, it can be thought that the ultrathin InN film is formed in an island shape whose surface coverage is 1 or less. 
     Hereinafter, forming of this island ultrathin InN film and its operation and effects will be explained. 
     In  FIG. 3 , in the CL images with the accelerating voltage Vacc of 3 kV ad 6 kV, that is, luminescence distribution images of a 1ML-InN quantum well region, the matter that the region shown by the circular frames as a mark is relatively brighter than the circumference can also be understood as improvement of luminescence strength because a quantum well structure is formed only in this region. That is, it can be thought that the ultrathin InN film is selectively grown to include the crystal fault  21  and an island structure as shown in  FIG. 4  is formed. 
     That is, the dislocation deactivation unit  14  is not necessarily a sequential film whose surface coverage is 1, and it can eliminate nonluminescence due to the crystal fault  21  if it is an island including the crystal fault  21 , that is, in a configuration with surface coverage is 1 or less. 
     As stated above, according to the first embodiment, property deterioration due to the crystal fault  21  can be inhibited even when the crystal fault  21  is inherent in the photoelectric conversion unit  12  of the photoelectric conversion device  10 . 
     APPLIED EXAMPLE 1 
     As the first application of a photoelectric conversion element by nitride semiconductor, a light-emitting diode (LED) in an ultraviolet wavelength region has received attention. In particular, in a short wavelength region less than 365 nm which is a band edge wavelength of GaN, accompanied with a shorter wavelength of luminescence wavelength, luminescence efficiency is rapidly deteriorated. Here, efficiency improvement of an ultraviolet LED due to a nonluminescence center inhibition effect of the ultrathin InN film will be explained. 
       FIG. 5  is a block diagram showing a configuration example of a photoelectric conversion device  30  which is Applied Example 1 related to the first embodiment of the claimed invention of the present application. In  FIG. 5 , the photoelectric conversion device  30  includes an n-type aluminum gallium nitride (hereinafter, it is referred to as “n-AlGaN”) layer  31 , a photoelectric conversion unit (Active layer)  32  formed on the n-AlGaN layer  31 , a p-type aluminum gallium nitride (hereinafter, it is referred to as “p-AlGaN”) layer  33  formed on the photoelectric conversion unit  32  and the photoelectric conversion unit  32  including a dislocation deactivation unit  34 , and is formed by well known semiconductor manufacture technology. 
     The photoelectric conversion unit  32  is preferably constituted by gallium nitride (GaN), aluminum gallium nitride (AlGaN) or aluminum indium gallium nitride (AlInGaN) for example, and has a forbidden band width (bandgap energy) which is smaller than any of the n-AlGaN layer  31  and the p-AlGaN layer  33 . The dislocation deactivation unit  34  is constituted by ultrathin InN film. 
     The n-AlGaN layer  31  is used to transport an electron. The p-AlGaN layer  33  is used to transport a hole. Accordingly, resistivity and layer thickness of the n-AlGaN layer  31  and the p-AlGaN layer  33  are respectively appropriately adjusted to perform efficient carrier transport. The photoelectric conversion unit  32  converts injected electron-hole into ultraviolet light by a recombination process. 
     Next, inhibition of nonluminescence center and efficiency improvement of ultraviolet LED by the dislocation deactivation unit  34  will be explained. Here, a case where the photoelectric conversion unit  32  is AlGaN will be explained. 
     By increasing Al composition of AlGaN constituting the n-AlGaN layer  31 , the p-AlGaN layer  33  and the photoelectric conversion unit  32 , the luminescence wavelength of an ultraviolet LED becomes shorter. However, generally, when the Al composition of AlGaN is increased, difficulty of crystal growth is more significant, and density of the crystal fault  21  included in the photoelectric conversion device  30  increases. Consequently, luminescence efficiency is deteriorated. 
     However, when ultrathin InN film is inserted in the photoelectric conversion unit  32 , as shown in  FIG. 3 , nonluminescence due to the crystal fault  21  is reduced. That is, in the photoelectric conversion device  30  which is an ultraviolet LED, deterioration of luminescence efficiency accompanied by decrease of the luminescence wavelength can be inhibited by configuring the dislocation deactivation unit  34  by ultrathin InN film. 
     As described above, according to the applied example 1, the property deterioration due to a crystal fault  21  can be inhibited even when a crystal fault  21  is inherent in the photoelectric conversion unit  32  of the photoelectric conversion device  30 . 
     APPLIED EXAMPLE 2 
     As the second application of the photoelectric conversion element by nitride semiconductor, a green laser and red-infrared wavelength region light-emitting diode (LED) has received attention. In particular, in a long wavelength region more than 500 nm, accompanied with a longer wavelength of a luminescence wavelength, luminescence efficiency is sharply deteriorated. Here, efficiency improvement of a green laser and red-infrared wavelength region LED due to a nonluminescence center inhibition effect of the ultrathin InN film will be explained. 
       FIG. 6  is a block diagram showing a configuration example of a photoelectric conversion device  40  which is Applied Example 2 related to the first embodiment of the claimed invention of the present application. In  FIG. 6 , the photoelectric conversion device  40  includes an n-type indium gallium nitride (hereinafter, it is referred to as “n-InGaN”) layer  41 , a photoelectric conversion unit (Active layer)  42  formed on the n-InGaN layer  41 , a p-type indium gallium nitride (hereinafter, it is referred to as “p-InGaN”) layer  43  formed on the photoelectric conversion unit  42  and a dislocation deactivation unit  44  included in the photoelectric conversion unit  42 , and is formed by well known semiconductor manufacture technology. 
     The photoelectric conversion unit  42  is preferably constituted by indium nitride (InN), indium gallium nitride (InGaN) or aluminum indium gallium nitride (AlInGaN) for example, and has a forbidden band width (bandgap energy) which is smaller than any of the n-InGaN layer  41  and the p-InGaN layer  43 . The dislocation deactivation unit  44  is constituted by ultrathin InN film. 
     The n-InGaN layer  41  is used to transport an electron. The p-InGaN layer  43  is used to transport a hole. Accordingly, resistivity and layer thickness of the n-InGaN layer  41  and the p-InGaN layer  43  are respectively appropriately adjusted to perform efficient carrier transport. The photoelectric conversion unit  42  converts injected electron-hole into a light by a recombination process. 
     Next, inhibition of nonluminescence center and efficiency improvement of the green laser and red-infrared wavelength region LED by the dislocation deactivation unit  44  will be explained. Here, a case where the photoelectric conversion unit  42  is InGaN will be explained. 
     By increasing In composition of InGaN constituting the n-INGaN layer  41 , the p-InGaN layer  43  and the photoelectric conversion unit  42 , the luminescence wavelength of the green laser and red-infrared wavelength region LED becomes longer. However, generally, when In composition of InGaN is increased, difficulty of crystal growth is more significant, and density of the crystal fault  21  included in the photoelectric conversion device  40  increases. Consequently, the luminescence efficiency is deteriorated. 
     However, when ultrathin InN film is inserted in the photoelectric conversion unit  42 , as shown in  FIG. 3 , the nonluminescence due to the crystal fault  21  is reduced. That is, in the photoelectric conversion device  40  which is a green laser and red-infrared wavelength region LED, deterioration of luminescence efficiency accompanied by increase of the luminescence wavelength can be inhibited by configuring the dislocation deactivation unit  44  by ultrathin InN film. 
     As described above, according to the applied example 2 the property deterioration due to a crystal fault  21  can be inhibited even when a crystal fault  21  is inherent in the photoelectric conversion unit  42  of the photoelectric conversion device  40 . 
     APPLIED EXAMPLE 3 
     As the third application of the photoelectric conversion element by nitride semiconductor, a solar cell corresponding to a wide solar light spectrum is has received attention. In particular, since the nitride semiconductor includes a high density crystal fault, junction property of a solar cell is inferior. Here, efficiency improvement of a nitride solar cell due to a dislocation deactivation effect of the ultrathin InN film will be explained. 
       FIG. 7  is a block diagram showing a configuration example of a photoelectric conversion device  50  which is Applied Example 3 related to the first embodiment of the claimed invention of the present application. In  FIG. 7 , the photoelectric conversion device  50  includes an n-type aluminum indium gallium nitride (hereinafter, it is referred to as “n-AlInGaN”) layer  51 , a photoelectric conversion unit (Depletion layer)  52  formed on the n-AlInGaN layer  51 , a p-type aluminum indium gallium nitride (hereinafter, it is referred to as “p-AlInGaN”) layer  53  formed on the photoelectric conversion unit  52  and a dislocation deactivation unit  54  included in the photoelectric conversion unit  52 , and is formed by well known semiconductor manufacture technology etc. 
     The photoelectric conversion unit  52  is preferably constituted by gallium nitride (GaN), indium gallium nitride (InGaN), aluminum indium nitride (AlInN) or aluminum indium gallium nitride (AlInGaN) for example, and has a forbidden band width (bandgap energy) which is smaller than any of the n-AlInGaN layer  51  and the p-AlInGaN layer  53 . The dislocation deactivation unit  54  is constituted by the ultrathin InN film. 
     The n-AlInGaN layer  51  is used to transport an electron. The p-AlInGaN layer  53  is used to transport a hole. Accordingly, resistivity and layer thickness of the n-AlInGaN layer  51  and the p-AlInGaN layer  53  are respectively appropriately adjusted in the viewpoint of carrier transport and a collection rate. The photoelectric conversion unit  52  converts an absorbed light into electron-hole. 
     Next, improvement of junction property of the solar cell and efficiency improvement of the nitride solar cell by the dislocation deactivation unit  54  will be explained. Here, a case where the photoelectric conversion unit  52  is InGaN will be explained. 
     By increasing In composition of InGaN constituting the n-AlInGaN layer  51 , the p-AlInGaN layer  53  and the photoelectric conversion unit  52 , a solar cell that covers substantially the entire region of solar spectrum is configured. However, generally, when the In composition of the AlInGaN and InGaN is increased, the difficulty of crystal growth is more significant, and density of the crystal fault  21  included in the photoelectric conversion device  50  increases. Consequently, the junction property of a solar cell is deteriorated and conversion efficiency of a solar cell is deteriorated. 
     However, when ultrathin InN film is inserted in the photoelectric conversion unit  52 , as shown in  FIG. 3 , a dislocation deactivation effect due to the crystal fault  21  is generated. That is, in the photoelectric conversion device  50  which is a solar cell, a decrease of conversion efficiency accompanied by deterioration of conjunction property of a solar cell can be inhibited by configuring the dislocation deactivation unit  54  by ultrathin InN film. 
     As described above, according to the applied example 3, property deterioration due to a crystal fault  21  can be inhibited even when a crystal fault  21  is inherent in the photoelectric conversion unit  52  of the photoelectric conversion device  50 . 
     Second Embodiment 
     In the first embodiment, operation and effects of the dislocation deactivation unit by ultrathin InN film have been stated. Incidentally, when an experimental result shown in  FIG. 3  is interpreted from another viewpoint, it is found that ultrathin InN film can be used as a dislocation detection unit  15 . Hereinafter, operation and effects of the dislocation detection unit  15  by ultrathin InN film will be explained. 
     A growth mechanism of ultrathin InN film is a self-order and self-stop process in which any excessive InN than the designed film thickness is provided to be evaporated and removed on a growth surface. However, it can be thought that InN is fixed by a pin in a region in which a crystal fault exists, and thus an evaporation and removal rate is inhibited to regions that include no crystal fault. 
     Accordingly, as shown in  FIG. 4 , it is interpreted that ultrathin InN film grows as a fractional layer InN only in a region in which a crystal fault exists. The fractional layer InN means that a surface coverage is 1 or less. For example, 0.5 molecular layer corresponds to an island structure with a monomolecular layer thickness and surface coverage of 50%, that is, a quantum disk structure. 
     Generally, to detect crystal dislocation, observation by a transmission electron microscope or pit detection by an etching process (etch pit) are known. Any of these methods belong to destruction inspection of a sample, and their processes are complicated. 
     However, cathodoluminescence (CL) observation basically belongs to nondestructive inspection, and no previous process to a sample is needed. Consequently, detection of a crystal fault becomes easy, which makes a product test of the photoelectric conversion device simple. 
     Moreover, in the conventional CL observation, a crystal fault has been evaluated as a scotoma in a CL image. This is not problematic since a high contrast ratio to a scotoma can be obtained in a sample with high luminescence efficiency. However, in a sample with low luminescence efficiency, that is, in a case where dislocation detection is highly needed, a scotoma exists in a relatively dark field of vision, so that a light-dark contrast of the CL image cannot be fully obtained. 
     However, in this embodiment, by inserting ultrathin InN film in the photoelectric conversion unit  12  of the photoelectric conversion device  10 , the ultrathin InN film is formed to have the crystal fault  21  and shows luminescence property. Consequently, the ultrathin InN film may be used as the dislocation detection unit  15 . 
     As stated above, according to the second embodiment, by observing the dislocation detection unit  15  in a case where a crystal fault  21  is inherent in the photoelectric conversion unit  12  of the photoelectric conversion device  10 , the crystal fault  21  can be easily detected. This makes a product test of the photoelectric conversion device  10  simple. 
     Additionally, in each embodiment described above, an example in which the ultrathin InN film is constituted by 1 layer has been explained. However, the invention is not limited to this, for example, a configuration in which a number of ultrathin films InN are inserted is also acceptable. 
     Furthermore, the present invention shall not be limited by the above-described embodiments, and modification, substitution, and abbreviation are possible within the range which is not deviated from the intention of the present invention. 
     Moreover, as it is clear from the above embodiments, layers including nitride which sandwich the photoelectric conversion unit have conductivity and are expressed as a first conductive unit and a second conductive unit. In addition, focusing on materials, the first and second conductive units are respectively expressed as a In x Ga y Al 1-x-y N layer, and in particular, the first conductive unit is expressed as a first conduction type In x Ga y Al 1-x-y N layer and the second conductive unit is expressed as a second conduction type In x Ga y Al 1-x-y N layer. Additionally, in such a case, x and y may be the same or different, and a range of x and y may be 0≦x≦1 and 0≦y≦1. 
     Also, as it is clear from the above embodiments, the photoelectric conversion unit can be expressed as an In x Ga y Al 1-x-y N layer. 
     Moreover, as it is clear from the above embodiments, the first conductive unit, the second conductive unit and the photoelectric conversion unit respectively include bandgap energy. In addition, it is preferable that bandgap energy of a third conductive unit (the third bandgap energy) is smaller than any of bandgap energy of the first conductive unit (the first bandgap energy) and bandgap energy of the second conductive unit (the first bandgap energy). 
     INDUSTRIAL APPLICABILITY 
     The photoelectric conversion device according to the present of the invention is applicable for a light-emitting element and a light-receiving element which are available with a ultraviolet-infrared light, especially a solar cell. 
     EXPLANATION OF NUMERALS 
     
         
           10 ,  30 ,  40 ,  50 ,  100  . . . photoelectric conversion device 
           11  . . . n-type gallium nitride layer 
           13  . . . p-type gallium nitride layer 
           12 ,  32 ,  42 ,  52 ,  102  . . . photoelectric conversion unit 
           14 ,  34 ,  44 ,  54  . . . dislocation deactivation unit 
           15  . . . dislocation detection unit 
           31  . . . n-type aluminum gallium nitride layer 
           33  . . . p-type aluminum gallium nitride layer 
           41  . . . n-type indium gallium nitride layer 
           43  . . . p-type indium gallium nitride layer 
           51  . . . n-type aluminum indium gallium nitride layer 
           53  . . . p-type aluminum indium gallium nitride layer 
           101  . . . n-type semiconductor layer 
           103  . . . p-type semiconductor layer 
           21 ,  201  . . . crystal fault 
           202  . . . nonluminescence center