JP4066994B2 - Photoelectric conversion element - Google Patents

Description

  The present invention relates to a photoelectric conversion element, and more particularly to a photoelectric conversion element using a quantum well portion.

  For example, a photoelectric conversion element such as a solar cell that generates an electromotive force from light such as visible light has attracted attention as an element capable of generating next-generation energy.

  As a material for forming such a photoelectric conversion element, for example, Si, Ge, GaAs and the like have been often used. In photoelectric conversion elements, for example, improvement in photoelectric conversion efficiency when generating electromotive force from sunlight or the like has become an important technical issue, and there are various types of improvement in photoelectric conversion efficiency using such semiconductor materials. Attempts have been made. (For example, see Patent Documents 1 to 3).

On the other hand, for example, it has been proposed to reduce the manufacturing cost of a photoelectric conversion element by forming a photoelectric conversion element mainly composed of carbon. (For example, refer to Patent Document 4).
JP-A-9-162432 JP-A-11-220150 Japanese Patent Laid-Open No. 9-8342 JP 2003-51603 A

  However, the photoelectric conversion element mainly composed of carbon has a problem that the photoelectric conversion efficiency is inferior to the conventional photoelectric conversion element using Si, Ge, GaAs or the like.

On the other hand, Si, Ge, GaAs, etc., which have been widely used in the past, are expensive materials, and it has been difficult to suppress the manufacturing cost of the photoelectric conversion element. For example, in the case of forming a layer made of these semiconductor materials, it may be difficult to reduce the manufacturing cost because the raw material gas is expensive.
For this reason, it has been difficult to achieve both reduction in the manufacturing cost of the photoelectric conversion element and improvement in photoelectric conversion efficiency.

  Accordingly, an object of the present invention is to provide a new and useful photoelectric conversion element that solves the above-described problems.

  A specific problem of the present invention is to provide a photoelectric conversion element that can be manufactured at low cost and has high photoelectric conversion efficiency.

The present invention solves the above problem by providing a first semiconductor layer having a first polarity, a second semiconductor layer having a second polarity different from that of the first semiconductor layer, and the first semiconductor. A photoelectric conversion element having at least a quantum well portion formed between the layer and the second semiconductor layer, wherein the quantum well portion has a well portion and a wall layer formed so as to have different energy band gaps The energy band gap of the wall layer is larger than the energy band gap of the well portion, and the well portion, the wall layer, the first semiconductor layer, and the second semiconductor layer have sp2 bonds and sp3 bonds. The main component is carbon, and the ratio of the sp2 bond to the sp3 bond is smaller in the wall layer than in the well portion and smaller in the first semiconductor layer than in the second semiconductor layer. In addition, an additive containing hydrogen or halogen is added to the well portion, the wall layer, the first semiconductor layer, and the second semiconductor layer, and the content of the additive in the wall layer is The problem is solved by a photoelectric conversion element characterized in that the number of the first semiconductor layer is larger than that of the well portion and the number of the first semiconductor layer is larger than that of the second semiconductor layer .

  According to the present invention, it is possible to provide a photoelectric conversion element that can be manufactured at low cost and has high photoelectric conversion efficiency.

  Further, if the energy band gap of the wall layer is larger than the energy band gap of the second semiconductor layer and smaller than the energy band gap of the first semiconductor layer, loss due to recombination of carriers generated by photoelectric conversion Can be reduced.

  Further, when the well portion includes a plurality of quantum dots having different band gaps, a wavelength region in which photoelectric conversion can be performed is widened, and photoelectric conversion efficiency is improved.

  In addition, when the plurality of quantum dots includes the first quantum dot and the second quantum dot having an energy band gap smaller than that of the first quantum dot, photoelectric conversion in a long wavelength region is possible, and the photoelectric conversion element is improved. .

  Further, the carbon constituting the first quantum dot and the second quantum dot has sp2 bond and sp3 bond, and the ratio of the sp2 bond to the sp3 bond is the second quantum dot in the first quantum dot. If it is smaller than the dot, the band gap of the second quantum dot can be made smaller than the band gap of the first quantum dot.

  Further, an additive containing hydrogen or halogen is added to the first quantum dot and the second quantum dot, and in the first quantum dot, when the content of the additive is larger than the second quantum dot, The band gap of the second quantum dot can be made smaller than the band gap of the first quantum dot.

  Moreover, the loss of the hole in the said quantum well part is suppressed as the difference of the energy level of the valence band of the said well part and the said wall layer is 0.1 eV or less.

  The energy level of the valence band of the wall layer is higher than the energy level of the valence band of the second quantum dot, and the energy level of the valence band of the second quantum dot is the energy level of the first quantum dot. If it is higher than the level, the loss of holes in the quantum well portion is suppressed.

  Further, if the second quantum dot is larger than the first quantum dot, the band gap of the second quantum dot can be made smaller than the band gap of the first quantum dot.

  In addition, when the second quantum dots are formed inside the first quantum dots formed inside the wall layer, carrier loss is suppressed and the photoelectric conversion efficiency is improved.

  Further, when a carrier block layer is provided between the wall layer and the first quantum dot and between the wall layer and the second quantum dot, the photoelectric conversion efficiency is improved.

  Further, when the energy band gap of the first semiconductor layer is larger than the energy band gap of the second semiconductor layer, loss due to recombination of carriers generated by photoelectric conversion can be reduced.

  Further, when the energy band gap of the first semiconductor layer is 1.05 times or more of the energy band gap of the second semiconductor layer, an effect of reducing loss due to recombination of carriers generated by photoelectric conversion Becomes larger.

  When a first electrode electrically connected to the first semiconductor layer and a second electrode electrically connected to the second semiconductor layer are provided, the first electrode and the first electrode Carriers can be efficiently collected by the two electrodes.

  The first semiconductor layer includes a low concentration impurity semiconductor layer formed on the quantum well portion side and a high concentration impurity semiconductor layer formed on the first electrode side. It is possible to reduce the contact resistance between the semiconductor layer and the first electrode.

  The second semiconductor layer includes a low-concentration impurity semiconductor layer formed on the quantum well portion side and a high-concentration impurity semiconductor layer formed on the second electrode side. It is possible to reduce the contact resistance between the semiconductor layer and the second electrode.

  The first polarity and the second polarity are a positive polarity and a negative polarity, respectively, and the first semiconductor layer and the second semiconductor layer are an n-type semiconductor layer and a p-type semiconductor, respectively. When it consists of layers, the efficiency of the photoelectric conversion element can be improved.

  Further, when the energy band gap of the first semiconductor layer is formed so as to be smaller from the first electrode side toward the second electrode side, loss due to carrier supplementation is suppressed, The efficiency of the photoelectric conversion element can be improved.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide a photoelectric conversion element with low manufacturing cost and high photoelectric conversion efficiency.

  Next, embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1A is a schematic cross-sectional view schematically showing a photoelectric conversion element 100 according to Example 1 of the present invention, and FIG. 1B schematically shows the state of the energy band of the AA cross section. It is a figure.

  Referring to FIGS. 1A and 1B, the photoelectric conversion element 100 includes a first semiconductor layer 20 made of a p-type semiconductor layer having a first polarity, for example, a positive polarity, and the first semiconductor layer 20. A second semiconductor layer 30 made of an n-type semiconductor layer having a negative polarity different from that of the first semiconductor layer, and a quantum formed between the first semiconductor layer 20 and the second semiconductor layer 30 And a well portion 10.

  In the photoelectric conversion element 100 according to the present embodiment, for example, when sunlight or the like enters, photoelectric conversion occurs in the semiconductor layer 20 or the semiconductor layer 30 to generate carriers (electron-hole pairs) and generate electromotive force. To do. In this case, electrons move from the semiconductor layer 20 to the semiconductor layer 30, and holes move from the semiconductor layer 30 to the semiconductor layer 20.

  In the photoelectric conversion element of this example, since the quantity well portion 10 for performing photoelectric conversion is further provided, the efficiency of photoelectric conversion is good.

  The quantum well portion 10 includes a well portion 11 and a wall layer 12 formed so as to sandwich the well portion 11 adjacent to the well portion 11, and the energy band gap of the wall layer 12 has the well portion Thus, the quantum well portion 10 can efficiently perform photoelectric conversion. In particular, since the quantum well portion 10 can efficiently photoelectrically convert light in a long wavelength region, it is combined with the semiconductor layer 20 or the semiconductor layer 30 that efficiently photoelectrically converts light in the visible light region. When used, photoelectric conversion can be performed in a wide wavelength range, and the photoelectric conversion efficiency is improved.

  Conventionally, such a photoelectric conversion element has been formed using an expensive semiconductor material such as GaAs, but in the case of this embodiment, the quantum well portion 10 is formed of a material mainly composed of carbon. By doing so, it became possible to control material costs and reduce manufacturing costs.

  In this case, if the first semiconductor layer 20 and the second semiconductor layer 30 are formed of a material containing carbon as a main component, the manufacturing cost of the photoelectric conversion element can be further reduced. Is preferable.

  In the present embodiment, the material containing carbon as a main component used for the quantum well portion and the semiconductor layer not only suppresses the cost of material compared to a material such as GaAs, but also has less influence on environmental pollution. It has the characteristics that it is an easy-to-handle material. Such a semiconductor layer containing carbon as a main component can be easily formed by decomposition of a hydrocarbon-based gas or the like, for example, by plasma CVD (chemical vapor deposition). In this way, when forming a semiconductor layer, a quantum well portion, etc. with carbon as the main component, handling of the gas system is simple because there is less risk of the gas used than when using GaAs, for example. In addition, since the gas is inexpensive, there is an effect that it can be formed inexpensively and easily. Moreover, since there is little danger of the gas to be used, the cost of manufacturing equipment can also be reduced.

  Further, the carbon-based material used for the quantum well portion and the semiconductor layer has sp2 bonds and sp3 bonds. In this case, when the ratio of sp2 bond to sp3 bond (hereinafter referred to as sp2 / sp3 bond ratio) decreases, the energy band gap of the quantum well portion and the semiconductor layer increases.

  In addition, an additive containing hydrogen or halogen is added to the quantum well portion and the semiconductor layer. If the content of the additive is large, the energy band gap between the quantum well portion and the semiconductor layer is increased. Can do.

  As described above, in the quantum well portion 10, the first semiconductor layer 20, and the second semiconductor layer 30, the energy band gap is obtained by setting the sp2 / sp3 bond ratio and the content of the additive to appropriate values. Is formed to have a desired value. Details of this will be described later in the description of FIG.

  Further, in this embodiment, when the electrode 101 and the electrode 102 that are electrically connected to the first semiconductor layer 20 and the second semiconductor layer 30 are provided, carriers generated by photoelectric conversion are provided. It is possible to efficiently collect the power, and it is possible to take out the power efficiently, which is preferable.

  In this case, it is preferable that the electrode 101 is made of a metal material such as Al, Ag, Ti, Cu, Ni, and Cr because of its small resistance value.

Further, it is preferable that the electrode 102 be made of a material that transmits light used for photoelectric conversion, that is, a transparent electrode, because the electrode 102 side can be a light receiving surface. In this case, it is preferable to use a conductive metal oxide such as ITO or SnO ₂ for the electrode 102 because the resistance value can be small and transparent.

  Conventionally, in a photoelectric conversion element using a quantum well portion, recombination of carriers, that is, electrons and holes, may occur, and thus the photoelectric conversion efficiency of the photoelectric conversion element may be lowered. In this embodiment, the photoelectric conversion element is formed as follows, so that recombination of electrons and holes in the quantum well portion is suppressed, and the conversion efficiency of the photoelectric conversion element is improved.

  First, as a first configuration, the energy band gap of the first semiconductor layer 20 is formed to be larger than the energy band gap of the second semiconductor layer 30. Therefore, the potential difference at both ends of the quantum well portion 10 is increased, the number of carriers (electrons and holes) recombined in the quantum well portion 10 is reduced, loss due to recombination is reduced, and photoelectric conversion efficiency is improved. To do. In this case, for example, if the energy band gap of the first semiconductor layer 20 is 1.05 times or more of the energy band gap of the second semiconductor layer 30, the photoelectric conversion efficiency is improved, which is preferable.

  The energy band gap of the wall layer 12 of the quantum well portion 10 is preferably smaller than the energy band gap of the first semiconductor layer 20 and larger than the energy band gap of the second semiconductor layer 30.

  Further, in addition to the first case, as a second configuration, the difference in energy level between the valence band between the well portion 11 and the wall layer 12 is reduced, for example, the difference in energy level is set to 0.1 eV. In the quantum well portion 10, loss due to holes being captured or recombined in the quantum well portion 10 is reduced, hole movement is efficiently performed, and the efficiency of the photoelectric conversion element is reduced. Is preferable.

  In this case, on the other hand, there is a difference in energy level between the well portion 11 and the wall layer 12 in the conduction band opposed to the valence band with an energy band gap, but the movement of electrons in the quantum well portion 10 Is formed so that the energy band gap of the first semiconductor layer 20 is larger than the energy band gap of the second semiconductor layer 30 as described above. Since the potential difference in the conduction band is increased, the movement of electrons is performed efficiently.

  That is, when both the first configuration and the second configuration are present, the loss of the photoelectric conversion element is reduced, and the efficiency of the photoelectric conversion element is particularly improved. It is preferable that the semiconductor layer 20 is a p-type semiconductor layer and the semiconductor layer 30 is an n-type semiconductor layer because electrons and holes can move efficiently.

  The first semiconductor layer 20 or the second semiconductor layer 30 is not limited to a single-layer semiconductor layer, and may be a multilayer.

For example, in this embodiment, the first semiconductor layer 20 includes a p-type semiconductor layer 21 formed on the quantum well portion 10 side and a p ⁺ -type semiconductor layer 22 formed on the electrode 101 side. Have a laminated structure. The p ⁺ -type semiconductor layer 22 is formed to have a higher impurity concentration than the p-type semiconductor layer 21, so that the p ⁺ -type semiconductor layer 22 has a higher carrier concentration.

For this reason, it is possible to reduce the contact resistance with the electrode 101 by providing the p ⁺ type semiconductor layer 22, and also function as a carrier blocking layer that prevents electrons from moving in the direction of the electrode 101. Therefore, the efficiency of the photoelectric conversion element is improved.

The p-type semiconductor layer 21 has a lower impurity concentration and a lower carrier concentration than the p ⁺ -type semiconductor layer 22, so that there are few defects in the film, and photoelectric conversion is performed efficiently to carry out carriers (electrons, holes). Can be generated. For this reason, in the photoelectric conversion element 100, a semiconductor layer having a low impurity concentration (carrier concentration) as the p-type semiconductor layer 21 mainly functions as a photoelectric conversion layer.

The second semiconductor layer 30 is composed of an n ⁺ type semiconductor layer 31 having a high impurity concentration and a high carrier concentration. Therefore, the contact resistance with the electrode 102 can be reduced, and Since it also functions as a carrier blocking layer that prevents holes from moving in the direction of the electrode 102, the efficiency of the photoelectric conversion element is improved.

  In addition, the second semiconductor layer 30 which is an n-type semiconductor layer can have a multilayer structure of semiconductor layers having different impurity concentrations and carrier concentrations as in the first semiconductor layer 20, In this case, the same effects as those of the first semiconductor layer 20 can be obtained. Such a structure will be described later with reference to FIG.

  The electrode 102 is formed on the substrate 103, for example. The said board | substrate consists of materials, such as glass and a plastic, which permeate | transmit the light ray used as the generation source of the electromotive force of a photoelectric conversion element, for example, a sunlight ray. Further, a light control layer 104 is formed on the side of the substrate 103 facing the side where the electrode 102 is formed so as to cover the substrate 103. The light control layer 104 is provided with an antireflection film for reducing light reflection loss and an optical filter for transmitting light useful for the semiconductor layer to generate charges and reflecting unnecessary light. Yes.

  Next, a more detailed example of the configuration of the optical element 100 according to this embodiment will be described below.

  First, the first semiconductor layer 20 and the second semiconductor layer 30 are formed of, for example, a material containing carbon as a main component as described above, and hydrogen or halogen is added in an amount of 0.01% to 30%. Although preferred, it can also be formed without the addition of hydrogen or halogen. Further, Si or Ge may be added as necessary to control the resistance value.

Of the first semiconductor layer 20, the p-type semiconductor layer 21 preferably has a thickness of 1 to 30 μm and a carrier concentration of 1 × 10 ¹⁴ to 1 × 10 ¹⁸ cm ⁻³ . In this case, the carrier concentration can be adjusted by adding the p-type impurity. Moreover, although an energy band gap shall be 1.7 eV, for example, it is preferable that the said energy band gap shall be 0.4-2.4 eV.

Among the first semiconductor layers 20, the p ⁺ type semiconductor layer 22 preferably has a thickness of 0.02 to 1 μm and a carrier concentration of 1 × 10 ¹⁷ to 1 × 10 ²⁰ cm ⁻³ . In this case, the carrier concentration can be adjusted by adding the p-type impurity. Moreover, although an energy band gap shall be 1.7 eV, for example, it is preferable that the said energy band gap shall be 0.4-2.4 eV.

The n ⁺ -type semiconductor layer 31 of the second semiconductor layer 30 preferably has a thickness of 0.02 to 1 μm and a carrier concentration of 1 × 10 ¹⁷ to 1 × 10 ²⁰ cm ⁻³ . The carrier concentration in this case can be adjusted by the amount of n-type impurity added. Moreover, although an energy band gap shall be 1.4 eV, for example, it is preferable that the said energy band gap shall be 0.2-2.0 eV.

  Next, the electrode 101 is preferably formed using, for example, any material of Al, Ag, Ti, Cu, Ni, and Cr so as to have a thickness of 0.2 to 5 μm.

The electrode 102 is preferably formed using a transparent material such as ITO or SnO _{2 so} as to have a thickness of 0.01 to 2 μm.

  The substrate 103 is preferably made of a material such as quartz, glass, or plastic and has a thickness of 0.2 to 5 mm. In addition, the size of the substrate 103 can be arbitrarily changed depending on the size of the photoelectric conversion element. For example, substrates having various sizes from 1 cm square to 100 cm square are used. It is possible.

For the light control layer 104, for example, a material such as MgF ₂ , ZnS, SiO ₂ , or TiO ₂ can be used.

  The details of the quantum well 10 will be described with reference to FIGS. 2 to 5A and 5B. However, in the figure, the same reference numerals are given to the parts described above, and the description will be omitted.

  FIG. 2 is a perspective view schematically showing the structure of the quantum well portion 10 used in the photoelectric conversion element 100. In the quantum well portion 10, the wall portion 12 is formed so as to sandwich the well portion 11 formed in layers and the well portion 11, and a laminated structure of the well portion 11 and the wall layer 12 is For example, 20 to 30 cycles are laminated.

  Further, the quantum well portion 10 can be used after being modified as shown in the quantum well portion 10A shown in FIG. 3 or the quantum well portion 10B shown in FIG. The same effect as the case where the well part 10 is used is produced.

  First, the quantum well portion 10A shown in FIG. 3 is composed of a thin line-shaped well portion 11A and a wall layer 12A formed so as to include the well portion 11A.

  The quantum well portion 10B shown in FIG. 4 includes a dot-like (spherical) well portion 11B and a wall layer 12B formed so as to include the well portion 11B.

  The well portion 11A of the quantum well portion 10A and the well portion 11B of the quantum well portion 10B correspond to the well portion 11 of the quantum well portion 10. Further, the wall layer 12A of the quantum well portion 10A and the wall layer 12B of the quantum well portion 10B correspond to the wall layer 12 of the quantum well portion 10 and have the same functions. In this case, the quantum well portions 10A and 10B have the same function as the quantum well portion 10, and have the same effect in the photoelectric conversion element.

  Here, the quantum well part 10B is taken as an example and the details thereof are described. FIG. 5A is a cross-sectional view schematically showing the quantum well portion 10B, and FIG. 5B schematically shows the energy state of the BB cross section of FIG. 5A. is there. However, in the figure, the same reference numerals are given to the parts described above, and the description will be omitted.

  Referring to FIGS. 5A and 5B, in the quantum well portion 10B, for example, the well portion 11B having a substantially spherical shape is formed so as to be included in the wall layer 12B. Further, the energy band gap of the wall layer 12B is formed to be larger than the energy band gap of the well portion 11B. Further, in this case, if the difference in energy level of the valence band between the well portion 11B and the wall layer 12B is reduced, for example, if the difference in energy level is 0.1 eV or less, the hole in the quantum well portion 10B The loss such as being captured by the well or recombination is reduced, the hole is moved efficiently, and the efficiency of the photoelectric conversion element is improved.

  In this case, on the other hand, there is a difference in energy level between the well portion 11B and the wall layer 12B in the conduction band opposed to the valence band with an energy band gap, but the movement of electrons in the quantum well portion 10B. Is formed so that the energy band gap of the first semiconductor layer 20 is larger than the energy band gap of the second semiconductor layer 30 as described above. Since the potential difference in the conduction band is increased, the movement of electrons is performed efficiently.

  A detailed example of the configuration of such a quantum well portion is shown below.

First, the wall layer 12B (the same applies to the wall layers 12 and 12A) is preferably formed of an n ⁻ type semiconductor layer having a carrier concentration of 1 × 10 ¹² to 1 × 10 ¹⁴ cm ⁻³ . The carrier concentration in this case can be adjusted by the amount of n-type impurity added. Moreover, although an energy band gap shall be 1.4 eV, for example, it is preferable that the said energy band gap shall be 0.2-2.0 eV. In this case, the sp2 / sp3 bond ratio is preferably 0.1 to 2.0, and the hydrogen or halogen content is preferably 0.5 to 30%.

Next, the well portion 11B (the same applies to the well portions 11 and 11A) is preferably formed of an n ⁻ type semiconductor layer having a carrier concentration of 1 × 10 ¹⁴ to 1 × 10 ¹⁵ cm ⁻³ . The carrier concentration in this case can be adjusted by the amount of n-type impurity added. The energy band gap is, for example, 1.0 eV, but the energy band gap is preferably 0.1 to 1.8 eV. In this case, the sp2 / sp3 bond ratio is preferably 0.15 to 3.0, and the hydrogen or halogen content is preferably 0.01 to 15%.

  In this case, the carrier concentration in the well portion is preferably 3 to 300 times the carrier concentration in the wall layer, and the energy band gap in the well portion is 40 to 90% of the energy band gap in the wall layer. Is preferred.

  Further, when changing the energy band gap in the well portion and the wall layer of the quantum well portion, there are, for example, a method of changing the sp2 / sp3 bond ratio and a method of changing the amount of hydrogen or halogen as an additive. When the sp2 / sp3 bond ratio of the quantum well portion containing carbon as a main component decreases, the energy band gap increases, and when the hydrogen or halogen content increases, the energy band gap increases. It is possible to adjust the energy band gap of a material containing carbon as a main component.

  Similarly, the size of the energy band gap between the first semiconductor layer 20 and the second semiconductor layer 30 can be adjusted.

  Next, examples of detailed structures of layers constituting the photoelectric conversion element 10 are shown in FIGS. 6A and 6B, and each will be described. However, in the figure, the same reference numerals are given to the parts described above, and the description will be omitted.

6A and 6B show the energy band gap, sp2 / sp3 bond ratio, and hydrogen or halogen content of the photoelectric conversion element 100 in the n ⁺ type of the second semiconductor layer 30. FIG. This is an example shown for the semiconductor layer 31, the quantum well portion 10, the p-type semiconductor layer 21 and the p ⁺ -type semiconductor layer 22 of the first semiconductor layer 20.

  First, referring to FIG. 6A, in the case shown in this figure, the energy band gap is changed by changing the sp2 / sp3 coupling ratio of the first semiconductor layer, the second semiconductor layer, and the quantum well portion. The size of the is controlled.

For example, the p-type semiconductor layer 21 and the p ⁺ -type semiconductor layer 22 are formed so that the sp2 / sp3 coupling ratio is smaller than that of the n ⁺ -type semiconductor layer 31. The energy band gap of the layer 21 and the p ⁺ type semiconductor layer 22 is larger than the energy band gap of the n ⁺ type semiconductor layer 31.

  Similarly, in the quantum well portion 10, the wall layer is formed so that the sp2 / sp3 coupling ratio is smaller than that of the well portion. Therefore, the energy band gap of the wall layer is It is larger than the energy band gap of the well.

  For example, a detailed configuration example in the case illustrated in FIG.

First, the p-type semiconductor layer 21 and the p ⁺ -type semiconductor layer 22 are preferably formed as follows. Although the energy band gap is 1.7 eV, the energy band gap is preferably 0.4 to 2.4 eV. In this case, the sp2 / sp3 bond ratio is 0.7, but the sp2 / sp3 bond ratio is preferably 0.1 to 2.0.

The n ⁺ type semiconductor layer 31 is preferably formed as follows. Although the energy band gap is 1.4 eV, the energy band gap is preferably 0.2 to 2.0 eV. In this case, the sp2 / sp3 bond ratio is 1.2, but the sp2 / sp3 bond ratio is preferably 0.2 to 5.0.

  In addition, regarding the wall layer and the well portion of the quantum well portion, the energy band gap is preferably 0.2 to 2.0 eV, and the sp2 / sp3 coupling ratio is preferably 0.2 to 5.0. It is preferable to adjust to the value of.

  Further, in this case, the content (or addition amount) of hydrogen or halogen is constant, but the size of the energy band gap can be controlled by changing the content of hydrogen or halogen. It is more preferable to use in combination with the method of controlling the magnitude of the energy band gap by changing the sp2 / sp3 bond ratio.

In the case shown in FIG. 6B, as in the case of FIG. 6A, the p-type semiconductor layer 21 and the p ⁺ -type semiconductor layer 22 are sp2 / sp3 coupled to the n ⁺ -type semiconductor layer 31. The wall layer is formed so that the sp2 / sp3 coupling ratio is small with respect to the well portion.

In the case shown in the figure, the p-type semiconductor layer 21 and the p ⁺ -type semiconductor layer 22 further have a higher hydrogen (or halogen) content (addition amount) than the n ⁺ -type semiconductor layer 31. In addition, the wall layer is formed so that the content (addition amount) of hydrogen or halogen is larger than the well portion.

  In this case, in the film containing carbon as a main component, the energy band gap increases as the content (addition amount) of hydrogen or halogen increases. Therefore, the method of forming the energy band gap by changing the sp2 / sp3 bond ratio When used in combination, the following effects are obtained.

  For example, if the ratio of changing the sp2 / sp3 coupling ratio is large in the stacked layers, there is a concern that the distortion at the interface due to lattice mismatch increases and the loss due to carrier recombination increases. In the case shown, it is possible to reduce the ratio of changing the sp2 / sp3 coupling ratio in the stacked layers and to form a desired energy band gap size difference, thereby suppressing lattice mismatch. Thus, the loss of the photoelectric conversion element is reduced and the conversion efficiency is improved.

  For example, a detailed configuration example in the case illustrated in FIG.

First, the p-type semiconductor layer 21 and the p ⁺ -type semiconductor layer 22 are preferably formed as follows. Although the energy band gap is 1.7 eV, the energy band gap is preferably 0.4 to 2.4 eV. In this case, the sp2 / sp3 bond ratio is 0.9, but the sp2 / sp3 bond ratio is preferably 0.15 to 3.0. Moreover, although content of hydrogen or halogen shall be 14%, it is preferable that the said content is 1 to 30%.

The n ⁺ type semiconductor layer 31 is preferably formed as follows. Although the energy band gap is 1.4 eV, the energy band gap is preferably 0.2 to 2.0 eV. In this case, the sp2 / sp3 bond ratio is 1.2, but the sp2 / sp3 bond ratio is preferably 0.2 to 5.0. Moreover, although content of hydrogen or halogen shall be 8%, it is preferable that the said content is 0.5 to 20%.

  Further, regarding the wall layer and the well portion of the quantum well portion, the energy band gap is 0.2 to 2.0 eV, the sp2 / sp3 bond ratio is 0.2 to 5.0, and the hydrogen or halogen content is 0. It is preferably 5 to 20%, and is preferably adjusted to a desired value within the above range.

  In addition, the photoelectric conversion element according to the present invention is not limited to this example, and can be modified as shown in Examples 2 to 4 below. The same effects as those described in the examples are obtained, but the following examples 2 to 4 differ from the present examples in the points described below, and in addition to the cases described in the present examples, The effect of.

  FIG. 7 is a diagram schematically showing the state of the energy band of the cross section of the photoelectric conversion element 100A according to Example 2 of the present invention. However, in the figure, the same reference numerals are given to the parts described above, and the description will be omitted.

Referring to FIG. 7, in this embodiment, the semiconductor device is sandwiched between a first semiconductor layer 20A composed of a p ⁺ type semiconductor layer 22A, and a second semiconductor layer 30A composed of an n type semiconductor layer 32A and an n ⁺ type semiconductor layer 31A. As described above, the quantum well portion 10 is formed. An electrode 102A and an electrode 101A are formed so as to be in contact with the p ⁺ type semiconductor layer 22A and the n ⁺ type semiconductor layer 31A, respectively.

  The semiconductor layer and the electrode according to this example can be formed using the same material as that described in Example 1 so as to form an energy band as shown in this figure.

In this embodiment, the electrodes 102A is a transparent electrode, the transparent electrode side, i.e. rays have p ⁺ -type semiconductor layer 22A is formed on the side of the incident, n ⁺ -type semiconductor layer on the electrode 101A side as the rear surface electrode 31A is formed. In this embodiment, the polarity of the semiconductor layer to be installed is different from that of the first embodiment, and in this embodiment, the second semiconductor layer 30A having n-type polarity is used. However, it has a structure formed of two semiconductor layers having different impurity concentrations (carrier concentrations).

  As shown in this embodiment, the polarity of the semiconductor layer with respect to the transparent electrode and the back electrode can be changed, and the n-type and p-type semiconductor layers have different impurity concentrations. These can be arbitrarily modified and changed, and the same effects as those described in the first embodiment can be obtained in these cases.

  FIG. 8 is a diagram schematically showing a state of an energy band of a cross section of a photoelectric conversion element 100B which is another modification of the photoelectric conversion element 100 described in the first embodiment. However, in the figure, the same reference numerals are given to the parts described above, and the description will be omitted.

  Referring to FIG. 8, in the case of the photoelectric conversion element 100B according to the present embodiment, the energy band of the p-type semiconductor layer 21B in the first semiconductor layer 20B corresponding to the first semiconductor layer 20 of the first embodiment. The gap is formed so as to decrease from the electrode 101 side toward the electrode 102 side.

That is, the energy band gap of the p-type semiconductor layer 21B is formed to be large on the side in contact with the p ⁺ -type semiconductor layer 22 and to be small on the side in contact with the quantum well portion 10.

  For this reason, the formation of gaps and notches formed when semiconductor layers having different energy band gaps are joined is suppressed, so that losses caused by carriers supplemented by the gaps and notches are reduced. There is an effect that the efficiency is improved.

In this case, for example, the p-type semiconductor layer 21B preferably has a thickness of 1 to 30 μm and a carrier concentration of 1 × 10 ¹⁴ to 1 × 10 ¹⁸ cm ⁻³ . In this case, the carrier concentration can be adjusted by adding the p-type impurity. The energy band gap is 1.4 eV, for example, on the electrode 102 side, but the energy band gap is preferably 0.2 to 2.0 eV. The energy band gap on the electrode 101 side is, for example, 1.7 eV, but the energy band gap is preferably 0.4 to 2.4 eV.

  FIG. 9 is a diagram schematically showing a state of an energy band in a cross section of a photoelectric conversion element 100C which is still another modified example of the photoelectric conversion element 100 described in the first embodiment. However, in the figure, the same reference numerals are given to the parts described above, and the description will be omitted.

Referring to FIG. 9, in the case of the photoelectric conversion element 100 ^</ b ^> C according to the present embodiment, the energy of the p ⁺ type semiconductor layer 22 ^</ b ^> C in the first semiconductor layer 20 ^</ b ^> C corresponding to the first semiconductor layer 20 of the first embodiment. The band gap is larger than the energy band gap of the p-type semiconductor layer 21.

Therefore, when carriers move from the p ⁺ -type semiconductor layer 22C to the p-type semiconductor layer 21, loss caused by the carriers being supplemented by gaps and notches is reduced, and the efficiency of the photoelectric conversion element is improved. Play.

  Further, in the present embodiment, the energy band gap of the wall layer 12C is larger than the energy band gap of the wall layer 12 in the quantum well portion 10C corresponding to the first quantum well portion 10 of the first embodiment. .

  This is to provide a difference in energy band gap in the configuration of the semiconductor layers to be joined including the wall layer. In this embodiment, for example, the size of the energy band gap is as follows in each semiconductor layer: It is configured as follows. The parentheses indicate a preferable energy band gap range.

For example, the n ⁺ type semiconductor layer 31 is 1.4 eV (0.2 to 2.0 eV), the wall layer 12C is 1.5 eV (0.3 to 2.2 eV), and the p type semiconductor layer 21 is 1 0.7 eV (0.4 to 2.4 eV), and the p ⁺ type semiconductor layer 22C is 1.8 eV (0.5 to 2.5 eV).

  By forming the energy band gap in this way, the energy band gap is formed so as to sequentially increase in each layer except for the well portion 11 from the electrode 102 toward the electrode 101 side. . For this reason, charge transfer is efficiently performed, and for example, formation of gaps and notches formed when semiconductor layers having different energy band gaps are joined is suppressed, and thus carriers are supplemented by the gaps and notches. There is an effect that the loss is reduced and the efficiency of the photoelectric conversion element is improved.

  Moreover, the quantum well part 10 of the photoelectric conversion element described in Example 1 can also be changed as follows.

  FIG. 10 shows the state of the energy band in the cross section of the photoelectric conversion element 100D, which is a modification example when the quantum well portion 10 is deformed in the photoelectric conversion element 100 shown in FIGS. 1 (A) to 1 (B). It is the figure shown typically. However, in the figure, the same reference numerals are given to the parts described above, and the description will be omitted.

  Referring to FIG. 10, in the case of the photoelectric conversion element 100 </ b> D according to the present embodiment, a wall layer 12 a corresponding to the wall layer 12 is formed in the quantum well portion 10 </ b> D corresponding to the quantum well portion 10 of the first embodiment. Further, the well portion 11D corresponding to the well portion 11 includes the first quantum dots 11a and the second quantum dots 11b.

  As described above, when the well portion includes a plurality of quantum dots having different band gaps, the wavelength region of light capable of photoelectric conversion is widened, and the photoelectric conversion efficiency of the photoelectric conversion element is favorable.

  For example, in this case, the first quantum dot 11a and the second quantum dot 11b are formed so as to have different energy band gaps. For example, in the case of the quantum well portion 10D shown in FIG. The energy band gap is smaller than that of the dots 11a.

  For this reason, the second quantum dot 11b having a smaller band gap enables photoelectric conversion to a longer wavelength region, and the wavelength region of light that can be photoelectrically converted in the quantum well portion is widened. The photoelectric conversion efficiency is improved.

  Details of the quantum well portion 10D will be described with reference to FIGS. 11A and 11B. However, in the figure, the same reference numerals are given to the parts described above, and the description will be omitted.

  11A is a cross-sectional view schematically showing the quantum well portion 10D, and FIG. 11B shows the energy state of the CC cross section of FIG. 11A, the sp2 / sp3 coupling ratio, And the content of hydrogen or halogen is schematically shown.

  11A and 11B, in the quantum well portion 10D, for example, from the first quantum dot 11a having a substantially spherical shape (dot shape) and the second quantum dot 11b having a substantially spherical shape. A well portion 11D is formed so as to be included in the wall layer 12a. Further, the energy band gap of the wall layer 12a is formed to be larger than the energy band gap of the well portion 11D.

  In this case, if the difference in energy level of the valence band between the first quantum dot 11a or the second quantum dot 11b and the wall layer 12a is reduced, for example, the difference in energy level is 0.1 eV or less. In the quantum well portion 10D, losses such as holes being captured or recombined in the well portion are reduced, hole movement is efficiently performed, and the efficiency of the photoelectric conversion element is improved. It is preferable.

  In this case, on the other hand, there is a difference in energy level between the well portion 11D and the wall layer 12a in the conduction band opposed to the valence band with an energy band gap, but the movement of electrons in the quantum well portion 10D. Is formed so that the energy band gap of the first semiconductor layer 20 is larger than the energy band gap of the second semiconductor layer 30 as described above. Since the potential difference in the conduction band is increased, the movement of electrons is performed efficiently. The same is true between the first quantum dots 11a and the second quantum dots 11b.

  A detailed example of the configuration of the quantum well portion 10D will be described below.

First, the wall layer 12a is preferably formed of an n ⁻ type semiconductor layer having a carrier concentration of 1 × 10 ¹² to 1 × 10 ¹⁵ cm ⁻³ . The carrier concentration in this case can be adjusted by the amount of n-type impurity added. Moreover, although an energy band gap shall be 1.4 eV, for example, it is preferable that the said energy band gap shall be 0.2-2.0 eV. In this case, the sp2 / sp3 bond ratio is preferably 0.1 to 2.0.

Next, the first quantum dots 11a are formed of an n ⁻ type semiconductor having a spherical shape with a diameter of, for example, about 10 nm and a carrier concentration of 1 × 10 ¹² to 1 × 10 ¹⁵ cm ^−3. It is preferable. The carrier concentration in this case can be adjusted by the amount of n-type impurity added. The energy band gap is, for example, 1.1 eV, but the energy band gap is preferably 0.15 to 1.8 eV. In this case, the sp2 / sp3 bond ratio is preferably 0.2 to 4.0.

  In this case, the energy band gap of the first quantum dots 11a is preferably 50 to 95% of the energy band gap of the wall layer.

Next, the second quantum dots 11b are formed of an n ⁻ type semiconductor having a spherical shape with a diameter of, for example, about 10 nm and a carrier concentration of 1 × 10 ¹² to 1 × 10 ¹⁵ cm ^−3. It is preferable. The carrier concentration in this case can be adjusted by the amount of n-type impurity added. Moreover, although an energy band gap shall be 0.8 eV, for example, it is preferable that the said energy band gap shall be 0.10-1.6 eV. In this case, the sp2 / sp3 bond ratio is preferably 0.3 to 5.0.

  In this case, the energy band gap of the second quantum dots 11b is preferably 30 to 80% of the energy band gap of the wall layer.

  Further, in the present embodiment, details of the configuration that are not particularly described are the same as those in the first embodiment.

  Further, when changing the energy band gap of the wall layer 12a, the first quantum dot 11a, and the second quantum dot 11b, for example, a method of changing the sp2 / sp3 bond ratio, and an additive of hydrogen or halogen as an additive There is a way to change the amount. When the sp2 / sp3 bond ratio of the wall layer 12a, the first quantum dot 11a, and the second quantum dot 11b containing carbon as a main component is increased, the energy band gap is reduced, and the content of hydrogen or halogen is increased. Since the energy band gap decreases as the amount decreases, it is possible to adjust the energy band gap of the carbon-based material using these properties.

  For example, FIG. 12 shows the energy state of the CC cross section, sp2 / sp3 bond ratio, and hydrogen when the content of hydrogen or halogen in the quantum well portion 10D shown in FIG. Alternatively, the halogen content is schematically shown.

  Referring to FIG. 12, also in the case shown in this figure, the wall layer has a smaller sp2 / sp3 coupling ratio with respect to the first quantum dots, as in the case shown in FIG. 11B. In addition, the first quantum dots are formed so that the sp2 / sp3 coupling ratio is smaller than that of the second quantum dots.

  In the case shown in the figure, the wall layer is further formed so that the content (addition amount) of hydrogen or halogen is larger than that of the first quantum dots. The two quantum dots are formed so that the content (addition amount) of hydrogen or halogen increases.

  In this case, in the film containing carbon as a main component, the energy band gap increases as the content (addition amount) of hydrogen or halogen increases. Therefore, the method of forming the energy band gap by changing the sp2 / sp3 bond ratio When used in combination, it is possible to reduce the ratio of changing the sp2 / sp3 bond ratio and to form a desired energy band gap size difference. For this reason, the lattice mismatch at the interface of the quantum well portion is suppressed, the loss of the photoelectric conversion element is reduced, and the conversion efficiency is improved.

  For example, a detailed example of the configuration of the photoelectric conversion element in the case shown in FIG. 12 is shown below. In the present embodiment, details of the configuration that are not particularly described are the same as those in the fifth embodiment.

  First, although the energy band gap of the said wall layer 12a shall be 1.4 eV, for example, it is preferable that the said energy band gap shall be 0.2-2.0 eV. In this case, the sp2 / sp3 bond ratio is 0.1 to 2.0, the content of hydrogen or halogen is, for example, 12 atomic%, and the content is preferably 1.0 to 30 atomic%.

  Next, the energy band gap of the first quantum dots 11a is, for example, 1.1 eV, and the energy band gap is preferably 0.15 to 1.8 eV. In this case, the sp2 / sp3 bond ratio is 0.15 to 3.0, the hydrogen or halogen content is, for example, 9.0 atomic%, and the content is 0.7 to 25 atomic%. preferable.

  In this case, the energy band gap of the first quantum dots 11a is preferably 50 to 95% of the energy band gap of the wall layer.

  Next, the energy band gap of the second quantum dots 11b is, for example, 0.8 eV, and the energy band gap is preferably 0.10 to 1.6 eV. In this case, the sp2 / sp3 bond ratio is 0.2 to 4.0, the hydrogen or halogen content is, for example, 5.0 atomic%, and the content is 0.5 to 20 atomic%. preferable.

  In this case, the energy band gap of the second quantum dots 11b is preferably 30 to 80% of the energy band gap of the wall layer.

  Moreover, the quantum well part of the photoelectric conversion element described in Example 5 can be changed as follows.

  FIG. 13 schematically shows the energy state of the CC cross section, the sp2 / sp3 bond ratio, and the hydrogen or halogen content when the quantum well portion 10D shown in FIG. 11A is changed. It is a thing.

  Referring to FIG. 13, in the case of the present embodiment, the energy level of the valence band of the wall layer is higher than the energy level of the valence band of the second quantum dot, and the energy of the valence band of the second quantum dot. The level is formed to be higher than the energy level of the first quantum dot.

  For this reason, among the carriers generated in the first quantum dot or the second quantum dot, it becomes easy for holes to move to the wall layer side in particular, and the hole concentration in the first quantum dot or the second quantum dot is reduced. As a result, the recombination loss is suppressed. For this reason, photoelectric conversion efficiency becomes favorable.

  In this case, the energy level of the valence band can be controlled while maintaining the energy level of the conduction band by changing the carrier concentration.

  A detailed example of the configuration of such a quantum well portion is shown below.

First, the wall layer is preferably formed of an n ⁻ type semiconductor layer having a carrier concentration of 1 × 10 ¹² to 1 × 10 ¹⁵ cm ⁻³ . The carrier concentration in this case can be adjusted by the amount of n-type impurity added. Moreover, although an energy band gap shall be 1.4 eV, for example, it is preferable that the said energy band gap shall be 0.2-2.0 eV. In this case, the sp2 / sp3 bond ratio is preferably 0.1 to 2.0.

Next, the first quantum dots are formed of, for example, an n ⁻ type semiconductor having a spherical shape with a diameter of about 10 nm and a carrier concentration of 3 × 10 ¹² to 1 × 10 ¹⁶ cm ^−3. Is preferred. The carrier concentration in this case can be adjusted by the amount of n-type impurity added. Moreover, although an energy band gap shall be 1.15 eV, for example, it is preferable that the said energy band gap shall be 0.15-1.8 eV. In this case, the sp2 / sp3 bond ratio is preferably 0.15 to 3.0, and the hydrogen or halogen content is, for example, 9.0 atomic%, and the content is 0.7 to 25 atoms. % Is preferred.

  In this case, the energy band gap of the first quantum dots is preferably 50 to 95% of the energy band gap of the wall layer.

  In this case, for example, the difference in energy level between the wall layer and the first quantum dots in the valence band is 0.05 eV.

Next, the second quantum dot is formed of an n ⁻ type semiconductor having a spherical shape with a diameter of about 10 nm, for example, and a carrier concentration of 1 × 10 ¹³ to 1 × 10 ¹⁷ cm ^−3. Is preferred. The carrier concentration in this case can be adjusted by the amount of n-type impurity added. The energy band gap is, for example, 0.9 eV, but the energy band gap is preferably 0.10 to 1.6 eV. In this case, the sp2 / sp3 bond ratio is preferably 0.2 to 4.0.

  In this case, the energy band gap of the second quantum dots is preferably 30 to 80% of the energy band gap of the wall layer.

  In this case, for example, the difference in energy level between the wall layer and the second quantum dots in the valence band is 0.10 eV.

  Further, the difference in energy level in the valence band is preferably 0.02 eV or more and 0.20 eV or less in the wall layer and the first quantum dot, and in the wall layer and the second quantum dot, for example. Similarly, the difference in energy level in the valence band is preferably 0.02 eV or more and 0.20 eV or less in the first quantum dot and the second quantum dot, for example.

  Moreover, the quantum well part of the photoelectric conversion element described in Example 5 can be changed as follows.

  FIG. 14A is a modification of the quantum well portion shown in FIG. 11A, and is a diagram schematically showing a cross section of the quantum well portion. FIG. 14B is a diagram of FIG. ) Schematically shows the energy state of the DD cross section, the sp2 / sp3 bond ratio, and the hydrogen or halogen content. However, in the figure, the same reference numerals are given to the parts described above, and the description will be omitted.

  Referring to FIGS. 14A and 14B, in the case of the present embodiment, it has the same structure as the case shown in Embodiment 5 and is, for example, substantially spherical (dot shape). A well portion 11E made up of the first quantum dots 11d and the second quantum dots 11e having a substantially spherical shape is formed so as to be included in the wall layer 12a. Further, the energy band gap of the wall layer 12a is formed to be larger than the energy band gap of the well portion 11E.

  However, in the case of the present embodiment, the second quantum dot 11e is formed to be larger than the first quantum dot 11d. In this case, the energy band gap between the first quantum dot and the second quantum dot has the property that the energy band gap is reduced when the size of the quantum dot is increased (or the energy band gap is increased when the size of the quantum dot is reduced). It is used for control.

  For this reason, when the method of changing the energy band gap by changing the sp2 / sp3 binding ratio and the method of changing the energy band gap by changing the size of the quantum dots are used in combination, the sp2 / sp3 binding ratio is It is possible to reduce the rate of change and to form a desired energy band gap size difference. For this reason, the lattice mismatch at the interface of the quantum well portion is suppressed, the loss of the photoelectric conversion element is reduced, and the conversion efficiency is improved.

  A detailed example of the configuration of such a quantum well portion is shown below.

The first quantum dots 11d may be formed of an n ⁻ type semiconductor having a spherical shape with a diameter of about 8 nm and a carrier concentration of 1 × 10 ¹² to 1 × 10 ¹⁵ cm ⁻³ , for example. preferable. The carrier concentration in this case can be adjusted by the amount of n-type impurity added. The energy band gap is, for example, 1.1 eV, but the energy band gap is preferably 0.15 to 1.8 eV. In this case, the sp2 / sp3 bond ratio is preferably 0.15 to 3.0.

  In this case, the energy band gap of the first quantum dots 11d is preferably 50 to 95% of the energy band gap of the wall layer.

Next, the second quantum dot 11e is formed of an n ⁻ type semiconductor having a spherical shape with a diameter of, for example, about 12 nm and a carrier concentration of 1 × 10 ¹² to 1 × 10 ¹⁵ cm ^−3. It is preferable. The carrier concentration in this case can be adjusted by the amount of n-type impurity added. The energy band gap is set to 0.8 eV, for example, but the energy band gap is preferably set to 0.10 to 1.6 eV. In this case, the sp2 / sp3 bond ratio is preferably 0.2 to 4.0.

  In this case, the energy band gap of the second quantum dots 11e is preferably 30 to 80% of the energy band gap of the wall layer.

  Further, in the present embodiment, details of the configuration that are not particularly described are the same as in the case of the fifth embodiment.

  Moreover, the quantum well part of the photoelectric conversion element described in Example 5 can be changed as follows.

  FIG. 15A is a modified example of the quantum well portion shown in FIG. 11A, and is a diagram schematically showing a cross section of the quantum well portion. FIG. ) Schematically shows the energy state of the EE cross section, the sp2 / sp3 bond ratio, and the hydrogen or halogen content. However, in the figure, the same reference numerals are given to the parts described above, and the description will be omitted.

  Referring to FIGS. 15A and 15B, in this embodiment, the second quantum dots 11g are formed inside the first quantum dots 11f formed inside the wall layer. It has become. That is, the first quantum dot 11f is formed so as to cover the periphery of the second quantum dot 11g. For this reason, the second quantum dot is not bonded to the wall layer, and the first quantum dot is bonded to the wall layer. For this reason, for example, when the structure of the quantum well part according to the present example and Example 5 is compared, the wall layer having a large energy band gap and the second quantum dot are not joined in the quantum well part according to the present example. The crystal strain at the interface is reduced and the recombination loss is reduced. For this reason, photoelectric conversion efficiency becomes favorable.

  A detailed example of the configuration of such a quantum well portion is shown below.

The first quantum dots 11f are, for example, formed of an n ⁻ type semiconductor having a spherical shape with a diameter of about 12 nm and a carrier concentration of 1 × 10 ¹² to 1 × 10 ¹⁵ cm ^−3. preferable. The carrier concentration in this case can be adjusted by the amount of n-type impurity added. The energy band gap is, for example, 1.1 eV, but the energy band gap is preferably 0.15 to 1.8 eV. In this case, the sp2 / sp3 bond ratio is preferably 0.15 to 3.0.

  In this case, the energy band gap of the first quantum dots 11f is preferably 50 to 95% of the energy band gap of the wall layer.

Next, the second quantum dot 11g has a spherical shape with a diameter of, for example, about 7 nm, is formed so as to be covered with the first quantum dot 11f, and has a carrier concentration of 1 × 10 ¹² to It is preferably formed of an n ⁻ type semiconductor that is 1 × 10 ¹⁵ cm ⁻³ . The carrier concentration in this case can be adjusted by the amount of n-type impurity added. The energy band gap is set to 0.8 eV, for example, but the energy band gap is preferably set to 0.10 to 1.6 eV. In this case, the sp2 / sp3 bond ratio is preferably 0.2 to 4.0.

  In this case, the energy band gap of the second quantum dots 11e is preferably 30 to 80% of the energy band gap of the wall layer.

  Further, in the present embodiment, details of the configuration that are not particularly described are the same as in the case of the fifth embodiment.

  Moreover, the quantum well part of the photoelectric conversion element described in Example 5 can be changed as follows.

  FIG. 16A is a modification of the quantum well portion shown in FIG. 11A, and is a diagram schematically showing a cross section of the quantum well portion. FIG. ) Schematically shows the energy state of the FF cross section, the sp2 / sp3 bond ratio, and the hydrogen or halogen content. However, in the figure, the same reference numerals are given to the parts described above, and the description will be omitted.

  Referring to FIGS. 16A and 16B, in the case of the present embodiment, a carrier block is provided between the wall layer and the first quantum dot and between the wall layer and the second quantum dot. A layer 11h is provided.

  The carrier block layer 11h is formed so as to surround the first quantum dot 11a and the second quantum dot 11b, and has an energy band gap larger than that of the wall layer and a conduction band energy level larger than that of the wall layer. It is formed to become. In this case, the carrier block layer 11h can be formed by increasing the amount of hydrogen or halogen added when forming the wall layer.

  By forming the carrier block layer 11h, the amount of defects generated at the interface between the quantum dots and the wall layer can be reduced, and the effect of reducing recombination loss can be achieved. Further, by forming the carrier block layer 11h, an energy barrier is formed around the quantum dots, and carriers moving through the wall layer are prevented from moving to the quantum dot side and recombining to disappear. For this reason, there exists an effect which the photoelectric conversion efficiency of a photoelectric conversion element becomes favorable.

  A detailed example of the configuration of such a quantum well portion is shown below.

First, the wall layer is preferably formed of an n ⁻ type semiconductor layer having a carrier concentration of 1 × 10 ¹² to 1 × 10 ¹⁵ cm ⁻³ . The carrier concentration in this case can be adjusted by the amount of n-type impurity added. Moreover, although an energy band gap shall be 1.4 eV, for example, it is preferable that the said energy band gap shall be 0.2-2.0 eV. In this case, the sp2 / sp3 bond ratio is preferably 0.1 to 2.0. Moreover, it is preferable that content of hydrogen or a halogen is 0.5 atomic%-30 atomic%.

Next, the first quantum dot is formed of an n ⁻ type semiconductor having a spherical shape with a diameter of about 10 nm, for example, and a carrier concentration of 1 × 10 ¹² to 1 × 10 ¹⁶ cm ^−3. Is preferred. The carrier concentration in this case can be adjusted by the amount of n-type impurity added. The energy band gap is, for example, 1.1 eV, but the energy band gap is preferably 0.15 to 1.8 eV. In this case, the sp2 / sp3 bond ratio is preferably 0.2 to 4.0, and the hydrogen or halogen content is preferably 0.5 to 30 atomic%, for example.

  In this case, the energy band gap of the first quantum dot is preferably 50 to 95% of the energy band gap of the wall layer.

Next, the second quantum dots are formed of, for example, an n ⁻ type semiconductor having a spherical shape with a diameter of about 10 nm and a carrier concentration of 1 × 10 ¹² to 1 × 10 ¹⁵ cm ^−3. It is preferable. The carrier concentration in this case can be adjusted by the amount of n-type impurity added. Moreover, although an energy band gap shall be 0.8 eV, for example, it is preferable that the said energy band gap shall be 0.10-1.6 eV. In this case, the sp2 / sp3 bond ratio is preferably 0.3 to 5.0.

  In this case, the energy band gap of the second quantum dots is preferably 30 to 80% of the energy band gap of the wall layer, and the hydrogen or halogen content is, for example, 0.5 to 30 atomic%. It is preferable.

Next, the carrier block layer 11h is formed of an n ⁻ type semiconductor having a thickness of about 1 to 20 nm and a carrier concentration of 1 × 10 ¹² to 1 × 10 ¹⁵ cm ⁻³ , for example. Is preferred. The carrier concentration in this case can be adjusted by the amount of n-type impurity added. Moreover, it is preferable that an energy band gap shall be 0.25-2.4 eV, for example. In this case, the sp2 / sp3 bond ratio is preferably 0.15 to 3.0.

  In this case, the energy band gap of the carrier block layer is preferably 102 to 120% of the energy band gap of the wall layer, and the hydrogen or halogen content is, for example, 1.0 to 40 atomic%. Is preferred.

  Further, as described above, the quantum well portion, the semiconductor layer, and the like can be variously modified and changed, and the present invention is not limited to these examples, and can be arbitrarily modified and changed. Is possible.

  In addition, the photoelectric conversion elements shown so far can be formed using a generally known apparatus such as a CVD apparatus. Next, an apparatus for manufacturing these photoelectric conversion elements, The manufacturing method will be described.

  FIG. 17 is a diagram schematically showing an example of a film forming apparatus capable of manufacturing the photoelectric conversion element according to the present invention.

  Referring to FIG. 17, the film forming apparatus 200 shown in the figure is a so-called parallel plate plasma CVD apparatus. The film forming apparatus 200 includes a decompression vessel 201 whose inside can be decompressed by a decompression unit 206 formed of, for example, a vacuum pump, and a holding table 203 that holds the substrate W inside the decompression vessel 201. And a gas supply unit 202 having a structure such as a shower head for supplying a processing gas to the inside of the decompression vessel 201 so as to face the holding table 203.

  Further, a high-frequency power source 204 and a high-frequency power source 205 are connected to the gas supply unit 202 and the holding table 203, respectively, so that plasma can be excited in the decompression vessel, and in that case, it is applied to the substrate. The bias potential to be controlled can be controlled. In this case, heating means 203A made of, for example, a heater is embedded in the holding table 203 so that the substrate W can be heated to a desired temperature.

Further, a gas line 207 for supplying a processing gas to the gas supply unit 202 is connected to the gas supply unit 202. The gas line 207 includes, for example, an NH ₃ supply source via a valve 208a, a flow regulator 208b, and a pressure regulator 208c, and a PH via a valve 209a, a flow regulator 209b, and a pressure regulator 209c. ₃ sources are also B ₂ H ₆ sources via valve 210a, flow regulator 210b, and pressure regulator 210c, and C ₂ via valves 211a, flow regulator 211b, and pressure regulator 211c. ₂ H ₄ source is also via valve 212a, flow regulator 212b, and pressure regulator 212c and CH ₄ source is also H via valve 213a, flow regulator 213b, and pressure regulator 213c. _Two sources are connected to each other. These are examples of the processing gas supplied into the decompression vessel, and various other gases can be connected and used as the processing gas.

  In this case, for example, when the quantum well portion of the photoelectric conversion element shown in Example 5 is formed, it can be formed as follows.

First, a carbon thin film to be a wall layer is deposited on, for example, an n-type semiconductor layer formed on a light transmissive substrate. In this case, for example, CH ₄ gas and H ₂ gas are supplied into the decompression vessel so that the flow ratio is 4: 1, and PH ₃ gas is used to adjust the carrier with respect to CH ₄ gas. Add about 0.01 to 1 ppm. Here, for example, the above gas is activated or decomposed by exciting the plasma in the decompression vessel 201 by the high frequency power applied to the gas supply unit 202, and a wall layer is deposited on the n-type semiconductor layer. .

Next, quantum dots are formed on the wall layer. In this case, the processing gas is supplied into the decompression vessel as in the case of forming the wall layer, and the plasma is excited. In this case, the substrate temperature is increased by about 50 to 150 ° C. compared to the case where the wall layer is formed. By increasing the substrate temperature, decomposition of CH ₄ gas is promoted, and the sp2 / sp3 bond ratio in the deposited carbon thin film can be increased. Subsequently, by further increasing the substrate temperature by about 50 to 150 ° C., the decomposition of CH ₄ gas is further promoted, and the sp2 / sp3 bond ratio in the deposited carbon thin film can be further increased.

  Next, by lowering the temperature, the carbon deposited on the surface of the wall layer is self-aggregated to form first quantum dots and second quantum dots having different energy band gaps, for example, having a diameter of about 3 to 30 nm. be able to.

  In this case, it is possible to form, for example, the quantum dot shapes shown in Examples 8 to 9 by appropriately controlling the temperature of the two-stage temperature increase and the time required for the temperature increase. The shape shown in Example 10 can be formed by adding hydrogen or halogen as appropriate.

Further, the method of controlling, for example, increasing the sp2 / sp3 bond ratio in the carbon thin film is not limited to the above method, and various other methods can be used. For example, high-frequency power for plasma excitation Can be increased by about 20 to 70%, the flow rate ratio of hydrogen gas can be decreased, or C ₂ H ₄ gas can be used instead of CH ₄ gas when forming quantum dots. is there.

  Thus, it becomes possible to form a quantum well part by repeating the process of forming a wall layer and a well part (quantum dot) 5 to 50 times, for example.

  In this case, the n-type semiconductor layer and the p-type semiconductor layer sandwiching the quantum well portion can also be formed by the carbon thin film formed by the film forming apparatus according to this embodiment.

  Further, the photoelectric conversion element according to the present invention is not limited to the film forming apparatus 200, and can be formed by various apparatuses. For example, FIG. 18 shown below forms the photoelectric conversion element according to the present invention. It is the figure which showed typically an example of another film-forming apparatus which can do.

Referring to FIG. 18, the film forming apparatus 300 shown in this drawing is a so-called ECR plasma CVD apparatus. The film forming apparatus 300 includes a decompression vessel 301 whose inside can be decompressed by a decompression unit 307 formed of, for example, a vacuum pump, and a heating unit that holds the substrate W inside the decompression vessel 301. A holding table 203 to which 302A is attached is installed. Further, the inside of the decompression vessel 301 is formed from a processing space 301A formed on the side where the holding table 302 is installed, and the processing space 301A adjacent to the processing space 301A and communicating with the processing space 301A. The processing space 301B having a small capacity is roughly classified. An electromagnet 303 is installed outside the processing space 301B, and microwaves are supplied from the microwave power source 304 to the processing space 301B. For example, H ₂ gas is supplied to excite ECR plasma. It has become a structure.

In addition, a gas line 305 for supplying a processing gas to the processing space 301A is connected to the processing space 301A. The gas line 305 includes, for example, an NH ₃ supply source via a valve 308a, a flow regulator 308b, and a pressure regulator 308c, and a PH via a valve 309a, a flow regulator 309b, and a pressure regulator 309c. ₃ sources are also B ₂ H ₆ sources via valves 310a, flow regulator 310b, and pressure regulator 310c, and C ₂ via valves 311a, flow regulator 311b, and pressure regulator 311c. _{The 2} H ₄ supply source is also CH ₄ via the valve 312a, the flow regulator 312b, and the pressure regulator 312c, and the CH ₄ supply source is also H via the valve 314a, the flow regulator 314b, and the pressure regulator 313c. _Two sources are connected to each other. The H ₂ supply source is also connected to a gas line 306 connected to the processing space 301B via a valve 313a, a flow rate regulator 313b, and a pressure regulator 313c. These are examples of the processing gas supplied into the decompression vessel, and various other gases can be connected and used as the processing gas.

  The photoelectric conversion element according to the present invention can be formed using the film formation apparatus 300 in the same manner as described in Example 11. Further, when the film forming apparatus according to the present embodiment is used, the substrate is held in a region where the plasma density is high, that is, a region dissociated from the processing space 301B, and film formation is performed. There is an effect of suppressing the generation of defect amount.

  Further, the photoelectric conversion element according to the present invention is not limited to the above-described film forming apparatus, and can be similarly formed in other film forming apparatuses.

  Although the present invention has been described with reference to the preferred embodiments, the present invention is not limited to the specific embodiments described above, and various modifications and changes can be made within the scope described in the claims.

  According to the present invention, it is possible to provide a photoelectric conversion element that can be manufactured at low cost and has high photoelectric conversion efficiency.

(A) is the schematic sectional drawing which showed the photoelectric conversion element by Example 1, (B) is the figure which showed typically the state of the energy band of the AA cross section of (A). It is the perspective view which showed typically the structure of the quantum well part of the photoelectric conversion element of FIG. It is a perspective view which shows the modification of the quantum well part of FIG. It is a perspective view which shows another modification of the quantum well part of FIG. (A) is sectional drawing of the quantum well part of FIG. 4, (B) is BB sectional drawing of (A). (A), (B) is the figure shown about the example of the detailed structure of the layer which comprises the photoelectric conversion element of FIG. It is the figure which showed typically the state of the energy band of the photoelectric conversion element by Example 2. FIG. 6 is a diagram schematically showing the state of an energy band of a photoelectric conversion element according to Example 3. FIG. 6 is a diagram schematically showing the state of an energy band of a photoelectric conversion element according to Example 4. FIG. FIG. 6 is a diagram schematically showing the state of the energy band of the photoelectric conversion element according to Example 5. (A) is the figure which showed typically the quantum well part of the photoelectric conversion element shown in FIG. 10, (B) is the energy state of the cross section of the quantum well part shown to (A), and sp2 / sp3. It is the figure which showed typically bond ratio and content of hydrogen or halogen. It is the figure which showed typically the energy state of the cross section of the quantum well part of the photoelectric conversion element by Example 6, sp2 / sp3 bond ratio, and hydrogen or halogen content. It is the figure which showed typically the energy state of the cross section of the quantum well part of the photoelectric conversion element by Example 7, sp2 / sp3 bond ratio, and hydrogen or halogen content. (A) is the figure which showed typically the quantum well part of the photoelectric conversion element by Example 8, (B) is the energy state of the cross section of the quantum well part shown to (A), and sp2 / sp3 coupling | bonding. It is the figure which showed typically ratio and content of hydrogen or a halogen. (A) is the figure which showed typically the quantum well part of the photoelectric conversion element by Example 9, (B) is the energy state of the cross section of the quantum well part shown to (A), and sp2 / sp3 coupling | bonding. It is the figure which showed typically ratio and content of hydrogen or a halogen. (A) is the figure which showed typically the quantum well part of the photoelectric conversion element by Example 10, (B) is the energy state of the cross section of the quantum well part shown to (A), and sp2 / sp3 coupling | bonding. It is the figure which showed typically ratio and content of hydrogen or a halogen. It is a figure (the 1) of an example of the film-forming apparatus which can form the photoelectric conversion element by this invention. It is FIG. (2) of an example of the film-forming apparatus which can form the photoelectric conversion element by this invention.

Explanation of symbols

100, 100A, 100B, 100C Photoelectric conversion element 101, 102, 101A, 102A Electrode 103 Substrate 104 Light control layer 10, 10A, 10B, 10C, 10D, 10E, 10F, 10G Quantum well part 11, 11A, 11B Well part 11a , 11b, 11d, 11e, 11f, 11g Quantum dot 11h Carrier block layer 12, 12A, 12B, 12C, 12a Wall layer 20, 20B, 20C First semiconductor layer 21, 21B p-type semiconductor layer 22, 22A, 22C p ⁺ Type semiconductor layer 30 second semiconductor layer 31, 31A n ⁺ type semiconductor layer 32A n type semiconductor layer 200, 300 film forming apparatus 201, 301 decompression vessel 301A, 301B processing space 202 gas supply unit 203, 302 holding base 203A, 302A Heating means 204, 205 High frequency power supply 206, 207 Exhaust means 303 Electromagnet 304 Microwave power source 207, 306, 305 Gas lines 208a, 209a, 209a, 210a, 211a, 212a, 213a, 308a, 309a, 310a, 311a, 312a, 313a, 314a Valves 208b, 209b, 209 b, 210 b, 211 b, 212 b, 213 b, 308 b, 309 b, 310 b, 311 b, 312 b, 313 b, 314 b 313c pressure regulator

Claims (18)

A first semiconductor layer having a first polarity;
A second semiconductor layer having a second polarity different from that of the first semiconductor layer;
A photoelectric conversion element having at least a quantum well formed between the first semiconductor layer and the second semiconductor layer,
The quantum well portion includes a well portion and a wall layer formed so that energy band gaps are different, and the energy band gap of the wall layer is larger than the energy band gap of the well portion,
The well portion, the wall layer, the first semiconductor layer, and the second semiconductor layer are mainly composed of carbon having an sp2 bond and an sp3 bond, and the ratio of the sp2 bond to the sp3 bond is the wall layer. Smaller than the well portion and smaller than the second semiconductor layer in the first semiconductor layer,
An additive containing hydrogen or halogen is added to the well portion, the wall layer, the first semiconductor layer, and the second semiconductor layer, and the content of the additive is the well portion in the wall layer. The photoelectric conversion element , wherein the number of the first semiconductor layers is larger than that of the second semiconductor layers . Wherein the energy band gap of the wall layer, the energy band gap larger than the second semiconductor layer, the photoelectric conversion element according to claim 1, wherein a smaller than the energy band gap of the first semiconductor layer. The well portion includes a photoelectric conversion element according to claim 1 or 2 wherein, characterized in that it comprises a plurality of quantum dots having different band gaps. 4. The photoelectric conversion element according to claim 3, wherein the plurality of quantum dots includes a first quantum dot and a second quantum dot having an energy band gap smaller than that of the first quantum dot. The carbon constituting the first quantum dot and the second quantum dot has sp2 bond and sp3 bond, and the ratio of the sp2 bond to the sp3 bond is higher than that of the second quantum dot in the first quantum dot. The photoelectric conversion element according to claim 4, which is also small. An additive containing hydrogen or halogen is added to the first quantum dot and the second quantum dot, and the content of the additive in the first quantum dot is larger than that in the second quantum dot. The photoelectric conversion element according to claim 4 or 5 . Of claims 1 to 6, characterized in that the difference between the energy levels of the valence band of the wall layer and the well portion is less than 0.1 eV, a photoelectric conversion element according to any one. The energy level of the valence band of the wall layer is higher than the energy level of the valence band of the second quantum dot, and the energy level of the valence band of the second quantum dot is higher than the energy level of the first quantum dot. wherein the high of the claims 4 to 6, the photoelectric conversion element according to any one. The photoelectric conversion element according to any one of claims 4 to 8 , wherein the second quantum dot is larger than the first quantum dot. Inside the first quantum dots formed in the interior of the wall layer, the second, characterized in that the quantum dots are formed, of the claims 4 to 6, the photoelectric conversion element according to any one of . Between the wall layer and the first quantum dot, and between the wall layer and the second quantum dot, of claims 4 to 6, characterized in that a carrier blocking layer, wherein any one Photoelectric conversion element. Wherein the energy band gap of the first semiconductor layer, said second one of claims 1 to 11, characterized in that greater than the energy band gap of the semiconductor layer, the photoelectric conversion element according to any one. The photoelectric conversion element according to claim 12 , wherein the energy band gap of the first semiconductor layer is 1.05 times or more of the energy band gap of the second semiconductor layer. The first electrode electrically connected to the first semiconductor layer and the second electrode electrically connected to the second semiconductor layer are provided. 13. The photoelectric conversion element according to claim 1. Said first semiconductor layer, claim and having a low concentration impurity semiconductor layer which is formed on the quantum well portion side, and a high concentration impurity semiconductor layer formed on the first electrode side 14 The photoelectric conversion element as described. Said second semiconductor layer, claim and having a low concentration impurity semiconductor layer which is formed on the quantum well portion side, and a high concentration impurity semiconductor layer formed on the second electrode side 14 The photoelectric conversion element as described. The first polarity and the second polarity are a positive polarity and a negative polarity, respectively, and the first semiconductor layer and the second semiconductor layer are an n-type semiconductor layer and a p-type semiconductor layer, respectively. The photoelectric conversion element according to claim 1, wherein the photoelectric conversion element is any one of claims 1 to 16 . 16. The photoelectric conversion element according to claim 15 , wherein an energy band gap of the first semiconductor layer is formed so as to become smaller from the first electrode side toward the second electrode side.

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