JP5489626B2 - Photoelectric conversion element and photoelectric conversion method - Google Patents

Description

  The present invention relates to a photoelectric conversion element and a photoelectric conversion method.

  Photoelectric conversion elements that excite electrons by incident light are used in photodetectors and solar power generators. In these photodetectors and solar power generators, in order to increase the detection sensitivity and increase the amount of power generation, it is desired to improve quantum efficiency by generating a plurality of excitons from one photon. A technique for generating two excitons from one photon is described in Non-Patent Document 1, for example.

Arthur J. Nozik, "Multiple exciton generation in semiconductor 1uantum dots", Chemical Physics Letters 457 (2008) p3-11

  However, it is not sufficient to generate two excitons from one photon, and it is desired to generate more excitons from one photon.

  The present invention has been conceived under the above circumstances, and an object thereof is to provide a photoelectric conversion element and a photoelectric conversion method with high quantum efficiency.

  The photoelectric conversion element of the present invention includes a plurality of excitation regions having a first quantum well in which a band gap and an energy difference between an electron level and an excitation level are the same, and one At least one tunnel region having a plurality of second quantum wells that guide electrons from the electron level of the first quantum well to the excitation level of the other first quantum well by resonant tunneling; , And the excitation region and the tunnel region are provided so as to alternately overlap.

The photoelectric conversion method of the present invention includes a first step of injecting light energy of a band gap or more into a first quantum well to excite electrons to a level higher than an electron level, A second step of leading to an excitation level of the other first quantum well by a resonant tunneling phenomenon through a plurality of second quantum wells adjacent to the one quantum well ; and the other first quantum well. The electrons guided to the electron level are relaxed from the excited state to the electron level so that the energy difference between the levels in the conductor is the same as the band gap of the other first quantum well. And a third step of exciting another electron with the emitted energy.

  ADVANTAGE OF THE INVENTION According to this invention, a photoelectric conversion element and a photoelectric conversion method with high quantum efficiency can be provided.

It is sectional drawing which shows schematic structure of an example of embodiment of the photoelectric conversion element of this invention. It is a conceptual diagram which shows the energy band of the photoelectric conversion element shown in FIG. It is a conceptual diagram which shows an example of embodiment of the photoelectric conversion method of this invention. It is a conceptual diagram which shows the other example of embodiment of the photoelectric conversion method of this invention.

<Photoelectric conversion element>
The photoelectric conversion element 10 illustrated in FIGS. 1 and 2 includes a p-type semiconductor layer 20, an n-type semiconductor layer 30, and a photoelectric conversion layer 40.

The p-type semiconductor layer 20 and the n-type semiconductor layer 30 are for forming an energy band between each other. The p-type semiconductor layer 20 and the n-type semiconductor layer 30 preferably have a large band gap to increase the degree of freedom in designing the photoelectric conversion layer 40. As the p-type semiconductor layer 20 and the n-type semiconductor layer 30, for example, a nitride semiconductor added with various impurity materials is used. As this nitride semiconductor, for example, one using GaN (gallium nitride), AlN (aluminum nitride), InN (indium nitride), BN (boron nitride), a mixed crystal thereof, or a part of nitrogen element is P ( And those substituted with As (arsenic) and Sb (antimony). Examples of the p-type impurity include elements such as Be (beryllium), Zn (zinc), Mn (manganese), Cr (chromium), Mg (magnesium), Ca (calcium), and C _anion (carbon). Examples of type impurities include Si (silicon), Ge (germanium), Sn (tin), S (sulfur), O (oxygen), Ti (titanium), Zr (zirconium), C _cation (carbon), and the like group IV , Group VI elements.

  The photoelectric conversion layer 40 has a multiple quantum well structure, and includes a well layer 41 and a barrier layer 42. In the photoelectric conversion layer 40, the well layers 41 and the barrier layers 42 are alternately stacked and provided a plurality of times. In the photoelectric conversion layer 40, the quantum well structure is formed by sandwiching the well layer 41 between the two barrier layers 42.

The well layer 41 functions as a well portion in the quantum well structure. As the well layer 41, to provide a number of quantum well structure, which can form as a band gap E _g is reduced is preferred. Examples of the material for forming the well layer 41 include InGaN, InAlGaN, and InGaN / InAlGaN N substituted with As, Sb, and P. At least three well layers 41 are provided. The thickness of the well layer 41 is appropriately set according to the size of the desired band gap E _g.

  The barrier layer 42 functions as a barrier in the quantum well structure. As the barrier layer 42, a layer having a larger band gap than the well layer 41 is employed in order to function as a barrier in the quantum well structure. Examples of the material for forming the barrier layer 42 include AlGaN, BN, and AlN. At least four or more barrier layers 42 are provided. The thickness of the barrier layer 42 is appropriately set according to the desired band gap size.

  The photoelectric conversion layer 40 of the present example includes an excitation region 40a and a tunnel region 40b. The excitation region 40a and the tunnel region 40b are alternately overlapped.

  The excitation region 40a is a region that excites electrons as excitons. The photoelectric conversion layer 40a is composed of one well layer 41 and two barrier layers 42 provided on the one well layer 41 so as to overlap each other.

In excitation region 40a of the present embodiment is constructed so that the band gap E _g of the quantum well, the difference E _d of energy between the electron level and the excited level, is equal. Thus, by making the band gap E _g of the quantum well equal to the energy difference E _d between the electron level and the excitation level, the electrons (excitons) excited to the excitation level can be obtained. When relaxed to the electron level, new electrons (excitons) can be excited. That is, the number of excitons can be increased.

  The tunnel region 40b is a region for guiding electrons as excitons from one quantum well to the next quantum well by a resonant tunneling phenomenon. The electrons guided in the tunnel region 40b move from the electron level of one quantum well to the excitation level of the next quantum well. The tunnel region 40 b includes a plurality of barrier layers 42 and a plurality of well layers 41 provided one by one between each of the plurality of barrier layers 42. The tunnel region 40b is configured to have a constant Fermi level in order to generate a resonant tunnel region.

<Photoelectric conversion method>
In the photoelectric conversion method shown in FIG. 3, first, as shown in FIG. 3A, light is incident on the excitation region 40a to excite electrons as excitons.

  Next, as shown in FIG. 3B, the excited electrons are guided to another excitation region 40a through the tunnel region 40b by a resonance tunnel phenomenon. When the electrons are guided to the other excitation region 40a, the guided electrons are set to the excitation level of the other excitation region 40a.

  Next, as shown in FIG. 3C, the electrons guided to the other excitation region 40a are relaxed from the excitation level to the electron level. At the time of this level relaxation, another electron is excited as an exciton in the excitation region 40a by using the emitted energy. In this way, the number of excitons can be increased.

  Next, the two excited electrons are guided from the other excitation region 40a to the other excitation region 40a by the resonant tunneling phenomenon through the tunnel region 40b. Further, the electrons guided to the other excitation region 40a are relaxed from the excitation level to the electron level. At the time of this level relaxation, another electron is excited as an exciton in the excitation region 40a by using the emitted energy released. Thus, the exciton can be further increased by connecting the excitation region 40a and the tunnel region 40b in multiple stages.

  While specific embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications can be made without departing from the spirit of the invention.

In the present embodiment, when the electrons as excitons are excited in the excitation region 40a, the electrons are excited to the electron level. However, the present invention is not limited to this. For example, incident light having an energy of more than twice the band gap E _g of the excitation region 40a as shown in FIG. 4, may be excited electrons to excited level. At this time, two electrons may be excited by equalizing the band gap E _g of the quantum well and the energy difference E _d between the electron level and the excitation level. By doing in this way, more excitons can be excited. Moreover, more excitons can be excited by entering light including a plurality of wavelength components such as sunlight.

In this embodiment, according to the well layer 41 and barrier layer 42 constituting the photoelectric conversion layer 40 to the size of the band gap E _g is set thickness, wells depending on the size of the band gap E _g layer 41 And the composition of either of the barrier layers 42 may be different. Further, the thicknesses of the well layer 41 and the barrier layer 42 are calculated based on constants determined according to the thicknesses of the well layer 41 and the barrier layer 42 by using, for example, the Schrödinger wave equation. Can be calculated.

  Since the photoelectric conversion element and photoelectric conversion method of the present invention can excite a plurality of excitons using one excited exciton, the quantum efficiency is high. Therefore, it can be used in various devices using excitons, and the industrial applicability is very high.

DESCRIPTION OF SYMBOLS 10 ... Photoelectric conversion element 20 ... p-type semiconductor layer 30 ... n-type semiconductor layer 40 ... Photoelectric conversion layer 40a ... Excitation region 40b ... Tunnel region 41 ... Well layer 42- ..Barrier layer

Claims (8)

A plurality of excitation regions having a first quantum well in which the band gap and the energy difference between the electron level and the excitation level are the same;
At least one tunnel having a plurality of second quantum wells that guide electrons from the electron level of one first quantum well to the excitation level of the other first quantum well by a resonant tunneling phenomenon An area, and
The photoelectric conversion element, wherein the excitation region and the tunnel region are alternately overlapped. The excitation region and the tunnel region are provided between a p-type semiconductor layer and an n-type semiconductor layer,
The photoelectric conversion element according to claim 1, wherein the well layers and the barrier layers having a larger band gap than the well layers are alternately stacked. A first step of injecting light energy of a band gap or more into the first quantum well to excite electrons to a level of an electron level or higher;
A second step of guiding excited electrons to an excitation level of another first quantum well through a plurality of second quantum wells adjacent to the first quantum well by a resonant tunneling phenomenon;
Electrons guided to the other of the first quantum well, so that the difference of energy between the levels in the conduction band is the same as the band gap of the other first quantum well, electron levels from the excited state And a third step of exciting another electron with the emission energy released during the relaxation, and a photoelectric conversion method.   In the first step, the band gap of the first quantum well and the energy difference between the electron level and the excitation level are made the same to excite electrons to a level higher than the electron level. The photoelectric conversion method according to claim 3. In the first step, after the light energy more than twice the band gap is incident on the first quantum well to excite electrons to the excitation level,
The excited electrons are relaxed from the excited level to the electron level so that the energy difference between the levels in the conduction band is the same as the band gap of the first quantum well. 5. The photoelectric conversion method according to claim 3, wherein another electron is excited by the emission energy emitted to the substrate. Wherein after the first step, the second step and the third step is repeated a plurality of times, the photoelectric conversion method according to any one of claims 3, 4, and 5, characterized in that. The band gap of the first quantum well is equal to the band gap of the other first quantum well, the photoelectric conversion method according to any one of claims 3 or et 6, characterized in that.   The photoelectric conversion method according to claim 3, wherein in the first step, light including a plurality of wavelength components is incident to excite electrons.

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