JP2015060975A - Quantum dot layer and semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a quantum dot layer in which quantum dot particles have high occupancy and which can increase photoelectric conversion efficiency; and provide a semiconductor device using the quantum dot layer.SOLUTION: A quantum layer 1 comprises: a plurality of first particles 1a, 1b, 1c each having a core part and a shell part which surrounds the core part; and a plurality of second particles 3 each having the particle size smaller than that of each or the plurality of first particles 1a, 1b, 1c. The first particles 1a, 1b, 1c are three-dimensionally accumulated so as to contact each other to form a skeleton body 5. The second particles 3 lie among the first particles 1a, 1b, 1c of the skeleton body 5. The quantum dot layer comprises a semiconductor layer which is laminated at least on one principal surface of the quantum dot layer 1 and has a light absorption wavelength different from that of each of the first particles 1a, 1b, 1c and the second particles 3.

Description

  The present invention relates to a quantum dot layer and a semiconductor device.

  Quantum dots are made of a nano-sized semiconductor material and exhibit a quantum confinement effect. Such a quantum dot has a function of spontaneously releasing energy based on a corresponding energy gap when it receives light from an excitation source and reaches an energy excitation state.

  It is considered that the photoelectric conversion efficiency of an optical device typified by a solar cell or a semiconductor laser can be increased by using such a function of the quantum dot.

  In recent years, for example, by arranging quantum dots closely and periodically, an intermediate band is formed between the valence band and the conduction band in the band structure of the quantum dots, and the quantum dots are electronically coupled ( Hereinafter, the intermediate band method) has been found. In the case of the intermediate band method, the transition region (valence band, intermediate band, conduction band) of electrons in the band structure varies depending on the difference in light energy due to the difference in wavelength. A wide range of wavelengths can be used (see, for example, Non-Patent Document 1).

  Moreover, as a quantum dot suitable for the intermediate band method, for example, in Patent Document 1, a quantum dot is used as a core part, and a barrier layer having a larger energy gap than the quantum dot is arranged in a shell part surrounding the core part. So-called core-shell structure quantum dot particles have been proposed.

  FIG. 3A is a schematic external view illustrating a conventional quantum dot layer, FIG. 3B is a perspective view of the external schematic view of FIG. 3A viewed from the direction A, and FIG. It is the perspective view which looked at the external appearance schematic diagram of B) from the B direction. In FIGS. 3B and 3C, the quantum dot particles are shown in a simple perspective view of a circle, but for convenience, this is at a position where the arrangement of the quantum dot particles 101a, 101b, 101c in each layer overlaps. It is also made to understand.

  A quantum dot layer 101 shown in FIG. 3A shows a state in which the above-described core-shell structure quantum dot particles are filled in a body-centered cubic shape, and in FIG. The dot particles 101a and the underlying quantum dot particles 101c overlap so that the centers of the spheres coincide. On the other hand, the quantum dot particles 101b in the middle layer are arranged so as to ride on the indentation positions of the quantum dot particles 101c arranged in the lower layer.

  In this case, in the quantum dot layer 101 having the conventional structure as shown in FIGS. 3A, 3B, and 3C, the quantum dot particles 101a, 101b, and 101c (hereinafter sometimes referred to as 101abc) are shaped. Is substantially spherical and has a substantially uniform size, the quantum dot layer 101 has many gaps 103 without the quantum dot particles 101abc, and the volume occupancy of the quantum dot particles 101abc is low. Therefore, there is still a problem that the photoelectric conversion efficiency cannot be increased.

Okada, “Solar Cells I Want to Know More / 7th Quantum Dot Type”, “NIKKEI MICRODEVICES”, pp 71-77, October 2008 issue

JP 2011-1000077 A

  The present invention has been made to solve the above problems, and provides a quantum dot layer that has a high occupation rate of quantum dot particles and can increase photoelectric conversion efficiency, and a semiconductor device using the quantum dot layer. With the goal.

  The quantum dot layer of the present invention comprises a plurality of first particles having a core part and a shell part surrounding the core part, and a plurality of second particles having a particle diameter smaller than the first particle, The first particles are three-dimensionally stacked to be in contact with each other to form a skeleton, and the second particles are located between the first particles of the skeleton.

  The semiconductor device of the present invention is characterized in that a semiconductor layer having a light absorption wavelength different from that of the first particles and the second particles is laminated on at least one main surface of the quantum dot layer.

  ADVANTAGE OF THE INVENTION According to this invention, the quantum dot layer which has a high occupation rate of quantum dot particle | grains, and can improve a photoelectric conversion efficiency, and a semiconductor device using the same can be obtained.

(A) is an external appearance schematic diagram which shows one Embodiment of the quantum dot layer of this invention, (b) is a perspective view when the external appearance schematic diagram of (a) is seen from A direction, (c) is It is the perspective view which looked at the external appearance schematic diagram of (a) from the B direction. It is a cross-sectional schematic diagram which shows one Embodiment of the semiconductor device of this invention. (A) is the external appearance schematic diagram which shows the conventional quantum dot layer, (b) is a perspective view when the external appearance schematic diagram of (a) is seen from the A direction, and (c) is the external appearance of (a). It is the perspective view which looked at the schematic diagram from the B direction.

  FIG. 1A is a schematic external view showing an embodiment of the quantum dot layer of the present invention, and FIG. 1B is a perspective view of the external schematic view of FIG. ) Is a perspective view of the schematic external view of FIG. In FIGS. 1B and 1C, the first particles 1a, 1b, and 1c (hereinafter sometimes referred to as 1abc) are shown in a simple circular perspective view. It is also made to be understood at a position where the arrangement of one particle 1abc overlaps. Further, in FIGS. 1A, 1B, and 1C, the number of layers of the first particle 1abc and the second particle 3 is simplified to 3 layers, and the number of columns is 3 rows. The number of layers and the number of rows of one particle 1abc and the second particle 3 are several tens.

  The quantum dot layer 1 of this embodiment includes a plurality of first particles 1abc and a plurality of second particles 3 having a particle diameter smaller than that of the first particles 1abc as quantum dot particles. The first particles 1 abc are three-dimensionally stacked so as to be in contact with each other to form the skeleton 5, and the second particles 3 are arranged so as to be positioned between the first particles 1 abc of the skeleton 5. In this case, the first particle 1abc has a core-shell structure including a core part and a shell part surrounding the core part.

  According to the quantum dot layer 1 of the present embodiment, since the second particles 3 having a particle diameter smaller than that of the first particles 1abc are arranged in the gaps 2 of the first particles 1abc forming the skeleton 5, In the dot layer 1, the volume occupation rate of the 1st particle | grains 1abc which are quantum dot particles can be raised.

  In the quantum dot layer 1 of this embodiment, as shown in FIGS. 1A, 1B, and 1C, the first particles 1abc having a large particle diameter are arranged so as to be in contact with each other. An intermediate band of potential can be formed almost continuously. Thus, in the first particle 1abc, the generated carriers (electrons) can be excited in the three transition regions from the valence band to the conduction band, from the valence band to the intermediate band, and from the intermediate band to the conduction band.

  In addition, in the quantum dot layer 1 of the present embodiment, the second particles 3 having a particle diameter smaller than that of the first particles 1abc are included in the skeleton 5 of the first particles 1abc forming the intermediate band. It exists to be separated.

  In this case, since the second particle 3 has a smaller particle diameter than the first particle 1abc, the second particle 3 has a band structure having a well-type potential deeper than that of the first particle 1abc. For this reason, in the case of the 2nd particle | grains 3, it can absorb the light of energy higher than the intermediate | middle band formed with the 1st particle | grains 1abc mentioned above.

  That is, in the quantum dot layer 1 of the present embodiment, in addition to the carrier excitation by the intermediate band formed by the first particle 1 abc, the carrier excitation by the deep well type potential formed by the second particle 3 may occur. Therefore, compared to the quantum dot layer 101 having the conventional structure shown in FIGS. 3A, 3B, and 3C, the quantum dot layer 1 can use a wider wavelength, and as a result, high photoelectric conversion is achieved. Efficiency can be obtained.

  1A, 1B, and 1C, the filling structure of the first particles 1abc forming the skeleton 5 is shown in a body-centered cubic shape. The quantum dot layer 1 of the present embodiment is not limited to this, and the first structure has a filling structure in which the second particles 3 having a smaller particle diameter can be accommodated in the gaps 2 between the first particles 1abc having the larger particle diameter. The same effect can be exhibited even in a structure in which the particles 1abc and the second particles 3 are not regularly arranged. However, if the structure of the skeleton 5 is a hexagonal close-packed type or a cubic close-packed type, the first in the skeleton 5 Since the volume occupancy of the particles 1abc can be further increased, the photoelectric conversion efficiency can be further increased.

In this case, in the quantum dot layer 1 of the present embodiment, when the radius of the first particle 1 abc is r ₁ , the radius r ₂ of the second particle is r × {(√2) −1} or less (r ₂ ≦ r ₁ × {(√2) −1} relationship). When the radius of the second particle 3 arranged between the first particles 1abc forming the skeleton 5 of the quantum dot layer 1 is within the above range in relation to the radius of the first particle 1abc, FIG. ) As shown in (c), the second particles 3 are placed in the gaps between the first particles 1abc, so that the number of contact points between the plurality of first particles 1abc around the second particles 3 is increased. Can do. As a result, the continuity of the intermediate band of the first particle 1abc can be further increased, and thereby the photoelectric conversion efficiency of the quantum dot layer 1 can be further improved.

  In the quantum dot layer 1 of the present embodiment, it is desirable that the center points of the first particles 1abc and the second particles 3 are arranged in a lattice pattern.

As shown by dotted lines in FIGS. 1B and 1C, the center points of the first particles 1 abc and the second particles 3 are arranged in a lattice pattern inside the quantum dot layer 1. Then, the band width and potential height formed by the first particle 1abc and the second particle 3 become more regular, and the coherent length of the wave function becomes longer, thereby the mean free path of carriers (electrons). Can be made longer. In this way, it becomes possible to extract more charges from the quantum dot layer 1, so that the power gain can be further improved.

  In this case, the state in which the center points of the first particle 1abc and the second particle 3 are arranged in a lattice form means that, for example, in the region where the ten or more first particles 1abc can be seen side by side (region viewed in cross section). When a straight line connecting the center points of one particle 1abc is drawn, the first particle 1abc is entirely placed on the straight line at a number ratio of 60% or more. This state is the same for the second particles 3. Here, the center point of the first particle 1abc is a point where the longest diameter and the shortest diameter of the first particle 1abc intersect at a substantially right angle when the first particle 1abc is exposed to the cross section of the quantum dot layer 1. To do.

  The first particles 1abc constituting the quantum dot layer 1 of the present embodiment have a core-shell structure as described above. In this case, the core portion has a band gap (Eg) of 0.10 to 3.00 ev. Semiconductor particles are preferable, and it is desirable that the semiconductor particles contain at least one element selected from Group 12 element, Group 13 element, Group 14 element, Group 15 element and Group 16 element of the periodic table as a main component. Specifically, for example, germanium (Ge), silicon (Si), gallium (Ga), indium (In), arsenic (As), antimony (Sb), lead (Pb), tellurium (Te) and selenium (Se) It is preferable to use at least one semiconductor material selected from Moreover, it is desirable that the band gap of the shell portion serving as a barrier layer surrounding the core portion which is a quantum dot is 1.5 to 2.3 times the band gap of the semiconductor particles constituting the core portion.

  The second particles 3 preferably have a core-shell structure in which the semiconductor particles are used as a core portion and the barrier layer is used as a shell portion to surround the core portion.

  When both the first particle 1abc and the second particle 3 have a core-shell structure, the first particle 1abc and the second particle 3 have a barrier layer with a substantially uniform thickness around the semiconductor particles that are quantum dots. A similar wave function can be formed in each of the second particles 3 in all directions. As a result, it is possible to form the quantum dot layer 1 with little anisotropy in the conduction characteristics of carriers (electrons, holes), and to obtain the quantum dot layer 1 having a high power gain, hardly depending on the light irradiation direction Is possible.

  In this case, it is also possible to apply a structure in which the barrier layer that is the shell part is formed of the same cations (elements) as the semiconductor particles in the core part, and the barrier layer contains more oxygen than the semiconductor particles. is there.

  As for the size of the first particle 1abc constituting the quantum dot layer 1 of the present embodiment, for example, the maximum diameter is desirably 3 nm to 20 nm, and the variation of the particle diameter is desirably within 10%. When the maximum particle diameter and the variation in particle diameter of the first particle 1abc are in the above ranges, when the quantum dot layer 1 is formed by stacking the first particles 1abc, carriers (electrons) are scattered between the plurality of first particles 1abc. It becomes easy to form a regular long-period structure, and this makes it possible to form a continuous band structure. At this time, it is desirable that the average thickness of the barrier layer as the shell portion is 1 to 3 nm.

Here, the arrangement and size (longest diameter) and volume occupancy of the first particle 1abc and the second particle 3 constituting the quantum dot layer 1 are observed, for example, by observing a cross section of the device having the quantum dot layer 1 with a transmission electron microscope. It asks from the photograph obtained by doing. The volume occupancy here is replaced with the area occupancy in the cross section of the quantum dot layer 1.

  FIG. 2 is a schematic cross-sectional view showing an embodiment of the semiconductor device of the present invention. The semiconductor device of this embodiment is characterized in that a semiconductor layer having a light absorption wavelength different from that of the first particle 1 abc and the second particle 3 is laminated on at least one main surface of the quantum dot layer 1. More specifically, a semiconductor device having a multilayer structure shown below can be given as an example.

  That is, the semiconductor device according to the present embodiment is a semiconductor device having a so-called pin structure. On the lower substrate 11, the p-side electrode 13, the p-type semiconductor film as the first semiconductor layer 15, and a number of quantum dot layers. 1, the n-type semiconductor layer film that is the second semiconductor layer 19, and the n-side electrode 21 are stacked in this order.

The substrate 11 is preferably light transmissive, for example, in addition to a substrate made of an inorganic material such as a glass substrate or a ceramic substrate, a substrate made of an organic resin such as polycarbonate or polyethylene terephthalate. Can also be used.

  As the p-side electrode 13, for example, aluminum (Al) is suitable, but besides this, nickel (Ni), cobalt (Co), platinum (Pt), silver (Ag), gold (Au), copper ( A metal material such as Cu), molybdenum (Mo), titanium (Ti), tantalum (Ta), or an alloy thereof can also be used.

As the n-side electrode 21, an electrode material having transparency that can transmit sunlight is suitable. For example, it is desirable to apply indium tin oxide (ITO) to which indium is added. In addition, other conductive metal oxides such as tin oxide (FTO) doped with fluorine, indium oxide (IO), and tin oxide (SnO ₂ ) can also be used.

The p-type semiconductor film that is the first semiconductor layer 15 has an atomic valence with respect to an element (for example, Ga, In, Si, Ge, P, As, etc.) shown in the periodic table group 13-16. A semiconductor material doped with a low element is used.

  As the n-type semiconductor film that is the second semiconductor layer 19, a semiconductor material doped with an element having a high valence with respect to the elements shown in the groups 13 to 16 of the periodic table is used.

  As described above, by doping the respective semiconductor films with elements having different valences, the first semiconductor layer 15 and the second semiconductor layer 19 have conductive carriers.

  The light detection layer 17 is formed of a material exhibiting a photoelectric conversion function, and has a configuration in which the quantum dot layer 1 described above is multilayered.

  Therefore, according to the semiconductor device of the present embodiment, the volume occupancy rate of the quantum dot particles in the quantum dot layer 1 is high, and has a band structure having a deep well type potential in addition to the intermediate band type quantum dots. Thus, the photodetecting layer 17 that can use a wide range of wavelengths can be obtained.

  Next, a method for manufacturing the quantum dot layer of the present embodiment and a semiconductor device using the quantum dot layer will be described. The 1st particle 1abc and the 2nd particle 3 which are the quantum dots in this embodiment can be obtained by the method of depositing a metal component by the biomineralization from the solution of the metal compound containing the semiconductor material mentioned above, for example.

  First, a metal compound containing the above-described semiconductor particles as a main component, a solvent, and ferritin are prepared and mixed while heating to synthesize semiconductor particles. As an example of a compound containing Si, for example, one kind selected from sodium silicate, hexafluorosilicate, organosilane, and the like is used as the metal compound. On the other hand, an apoferritin (horse spleen-derived) solution is prepared as ferritin, and the above-mentioned compound containing Si is added thereto. Here, the pH is preferably about 7 to 10.

  Next, a compound containing Si is dispersed in an apoferritin (horse spleen-derived) solution, and Si is adhered to the inner wall of ferritin as a metal. Since ferritin is a protein, it is possible to control the bio-size, and because the size is limited by the volume of the internal space of ferritin, it is possible to synthesize particles that are close to a spherical shape, and the variation in particle size You can get a small one.

  Next, the synthesized semiconductor particles are taken out from the ferritin. In this case, for example, an alkaline aqueous solution is added to the ferritin solution so that the pH of the solution is 10 or more and ferritin is dissolved.

  At this time, the second particle 3 having a smaller size than the first particle 1abc is, for example, put the first particle 1abc into an aqueous solution containing hydrogen peroxide and has a specific wavelength toward the first particle 1abc in the solution. Atomization is achieved by a method of dissolving by irradiating light. In this case, a mercury light bulb or a xenon light bulb that can emit light having a wavelength of 300 to 900 nm is used as the light source.

  Next, the obtained semiconductor particles (first particles 1abc, second particles 3) are mixed at a predetermined ratio and dispersed in a solvent to prepare a slurry. The solvent is preferably an aqueous solvent such as water or a mixture of water-soluble organic solvents such as water and acetonitrile.

  Next, a method of immersing and pulling up the substrate 11 on which the p-side electrode 13 and the p-type semiconductor film (first semiconductor layer 15) have been formed in advance in a slurry containing semiconductor particles (pulling speed: 5 to 5). 10 μm / sec.), Semiconductor particles (quantum dots D) are deposited on the surface of the p-type semiconductor film of the substrate 1. By setting the pulling speed within the above range, the dispersibility of the semiconductor particles (first particles 1abc and second particles 3) constituting the quantum dot layer 1 (photodetection layer 17) formed when the substrate 1 is pulled up is improved. As a result, a film having a structure in which the first particles 1abc and the second particles 3 are arranged as shown in FIGS. 1A, 1B, and 1C is formed.

  When the filling structure of the first particle 1abc and the second particle 3 is a body-centered cubic filling type, a hexagonal closest packing type, a cubic closest packing type, or the like, the first particle 1abc and the second particle 3 are set to 1 It is preferable to use a method of alternately forming layers.

  Next, the substrate 11 on which semiconductor particles (first particles 1abc and second particles 3) are deposited is heated to 300 to 600 ° C. in an inert gas such as argon or nitrogen or in a reducing gas containing hydrogen. To sinter the semiconductor particles. In this case, the oxide film formed on the surface of the semiconductor particles becomes a matrix or a shell part (barrier layer).

  Next, an n-type semiconductor film is formed as the second semiconductor layer 19 on the surface of the light detection layer 17. At this time, the n-type semiconductor film is formed along the surface shape of the light detection layer 17. For film formation, it is preferable to use a physical method such as sputtering, molecular beam epitaxy, or laser ablation because it is difficult to break the previously formed photodetection layer 17.

  Next, the n-side electrode 21 is formed (film formation) on the surface of the n-type semiconductor 19. Thus, the semiconductor device of this embodiment is obtained.

DESCRIPTION OF SYMBOLS 1 ......... Quantum dot layer 1a, 1b, 1c (1abc) ... 1st particle | grains 2 ....... gap 3 ... 2nd particle 5 ... Skeletal body 11 ... .. substrate 13... P-side electrode 15...
17 ..... Photodetection layer 19 ........... Second semiconductor layer (n-type semiconductor layer film)
21 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ n-side electrode

Claims (5)

A plurality of first particles having a core portion and a shell portion surrounding the core portion;
A plurality of second particles having a particle diameter smaller than that of the first particles,
The first particles are three-dimensionally stacked to contact each other to form a skeleton body,
The quantum dot layer, wherein the second particles are located between the first particles of the skeleton. Wherein the radius of the first particles when the r _1, the radius r ₂ of the second particles, quantum of claim 1, characterized in that at most _{r 1 × {(√2) -1} } Dot layer.   3. The quantum dot layer according to claim 1, wherein the first particles and the second particles are arranged so that their center points are arranged in a lattice pattern. 4.   The quantum dot layer according to any one of claims 1 to 3, wherein the first particles and the second particles each have a particle size variation of 10% or less. A semiconductor layer having a light absorption wavelength different from that of the first particles and the second particles is laminated on at least one main surface of the quantum dot layer according to any one of claims 1 to 4. A semiconductor device.