JP6175293B2 - Quantum dot particles and semiconductor device using the same - Google Patents

Description

  The present invention relates to quantum dot particles and a semiconductor device using the same.

  Quantum dot particles are nano-sized semiconductor materials that exhibit a quantum confinement effect. Such quantum dot particles have a function of spontaneously releasing energy based on a corresponding energy gap when receiving light from an excitation source and reaching an energy excited state. For this reason, when the size of the quantum dot particles is adjusted, the band gap (energy gap) can be adjusted, so that energy in various wavelength bands can be obtained.

  In this case, the quantum dot particles need to have a configuration in which a barrier layer serving as a potential barrier having a larger energy gap than the semiconductor particles is provided around the semiconductor particles having a diameter of several nanometers. However, in recent years, for the purpose of achieving stability of the quantum confinement effect in the semiconductor particles, as shown in FIG. 5, the quantum dot particles 101 have the semiconductor particles 103 as a core portion, and the surrounding barrier layer 105 has a shell portion. The so-called core-shell structure has been proposed (see, for example, Patent Documents 1 and 2).

JP-T 2009-520357 JP 2006-216560 A

  However, as disclosed in Patent Documents 1 and 2 described above, in the quantum dot particles 101 having the core-shell structure, the thickness t of the barrier layer 105 (shell portion) surrounding the semiconductor particles 103 as the core portion is uniform. Alternatively, if it is close to this, electrons confined inside the semiconductor particles 103 tend to move radially around the semiconductor particles 103 when passing through the barrier layer 105. Here, in FIG. 5, the broken-line arrows indicate the movement of electrons.

  When the electrons confined in the semiconductor particles 3 move radially around the semiconductor particles 103 as described above, they move from one quantum dot particle 101 to another adjacent quantum dot particle 101. Since the density of electrons (current density) is likely to decrease, recombination of the generated electrons and holes is likely to occur in the quantum dot particles 101. As a result, the density of electrons in the quantum dot particles 101 decreases and the amount of charge decreases, making it difficult to increase the power gain of the quantum dot particles.

  The present invention has been made to solve the above-described problem, and provides a quantum dot particle capable of increasing the power gain with a small decrease in the density of moving electrons and a semiconductor device using the quantum dot particle. With the goal.

The quantum dot particle of the present invention is a quantum dot particle having a core part of a semiconductor particle and a shell part surrounding the core part and having a different component or oxygen amount from the semiconductor particle, wherein the shell part is The semiconductor particle has a thin portion whose thickness in the normal direction from the surface is thinner than other portions, and the thin portion has at least two in the shell portion, and is symmetrical about the semiconductor particle. It is arranged .
The quantum dot particle of the present invention is a quantum dot particle having a core part of a semiconductor particle and a shell part surrounding the core part and having a different component or oxygen amount from the semiconductor particle, The portion has a thin-walled portion whose thickness in the normal direction from the surface of the semiconductor particle is thinner than other portions, and the shape of the semiconductor particle when viewed in cross section is a rectangle or an ellipse It is characterized by that.

  The semiconductor device of the present invention is characterized in that a plurality of the above-mentioned quantum dot particles are stacked on the main surface of a semiconductor substrate.

  ADVANTAGE OF THE INVENTION According to this invention, the fall of the density of the electron to move is small, and the quantum dot particle which can raise a power gain, and a semiconductor device using the same can be obtained.

(A) is sectional drawing which shows typically one Embodiment of the quantum dot particle | grains of this invention. The other embodiment of the quantum dot particle | grains of this invention is shown, and it is a schematic diagram which shows that the shape when a semiconductor particle is seen cross-section is a rectangular shape (a) and an elliptical shape (b). It is a schematic diagram which shows the manufacturing method of the quantum dot particle | grains of this embodiment. It is a cross-sectional schematic diagram which shows one Embodiment of the semiconductor device of this invention. It is sectional drawing which shows the conventional quantum dot particle typically.

  FIG. 1 is a cross-sectional view schematically showing one embodiment of the quantum dot particles of the present invention. The quantum dot particle 1 of the present embodiment has a configuration having a core portion of the semiconductor particle 3 and a shell portion surrounding the periphery of the core portion. In this case, the shell part has a component or oxygen amount different from that of the semiconductor particle 3 in the core part, and has a larger energy gap than the semiconductor particle 3 and becomes the barrier layer 5 that plays the role of a potential barrier. Here, the barrier layer 5 which is a shell part in the quantum dot particle 1 has a thin part 7 whose thickness t in the normal direction from the surface 3a of the semiconductor particle 3 which is a core part is thinner than other parts. Yes.

  According to the quantum dot particle 1 of the present embodiment, the thin portion 7 is a potential barrier that is lower than the other thick portions of the barrier layer 5 by a smaller thickness. The emitted electrons move preferentially in the thin portion 7.

  When electrons confined inside the semiconductor particles 3 preferentially move through the thin-walled portion 7, electrons moving from one quantum dot particle 1 to another adjacent quantum dot particle 1 are indicated by broken lines in FIG. As indicated by the arrow, the density of the electrons moving from the quantum dot particles 1 (current density) is not radial as in the case where the thickness of the barrier layer 5 is uniform, and is easily concentrated in the region of the thin portion 7. Can be increased.

  As a result, since the recombination of the generated electrons and holes is suppressed in the quantum dot particle 1, the electron density in the quantum dot particle 1 can be maintained at a high state. The amount of charge obtained by the dot particles 1 is improved, and the power gain can be increased.

  In this case, the thickness t of the thin-walled portion 7 is ½ or less of the maximum thickness of the barrier layer 5 because the mobility of electrons can be made different from other portions of the barrier layer 5. Or 2/3 or less of the average thickness of the barrier layer 5 is desirable.

  Here, the thickness of the thin part 7 in the barrier layer 5 and the thickness of another part are calculated | required by observing the cross section of the device which has the quantum dot particle | grain 1 with a transmission electron microscope, for example. Specifically, for example, the barrier layer 5 is measured at four points in a cross shape around the semiconductor particles 3 in the quantum dot particles 1 to obtain an average value. The number of quantum dot particles 1 to be measured is about 3 to 10.

  In the quantum dot particles 1 of this embodiment, it is desirable that at least two thin-walled portions 7 are owned by the barrier layer 5 that is a shell portion, and are arranged symmetrically around the semiconductor particles 3.

  As shown in FIG. 1, when the thin-walled portion 7 has a symmetrical arrangement with respect to the semiconductor particle 3, electrons and holes generated inside the semiconductor particle 3 are opposite to each other about the semiconductor particle 3. Therefore, the recombination of electrons and holes is further suppressed inside the quantum dot particles 1, the charge amount can be further reduced, and the power gain can be further increased.

  Note that the quantum dot particles 1 of this embodiment are not limited to those having a simple shape as shown in FIG. 1, and many thin portions 7 are formed in the barrier layer 5, and the barrier layer 5 is thin. A structure in which the portions and the thick portions are alternately arranged and the unevenness is continuous may be employed. In the case of such a structure, the depth of the thin portion 7 may be different.

  FIG. 2 shows another embodiment of the quantum dot particle of the present invention, and is a schematic diagram showing that the shape of the semiconductor particle when viewed in cross section is a rectangular shape (a) and an elliptical shape (b). .

  In the quantum dot particles 1 of this embodiment, it is desirable that the semiconductor particles 3 have a rectangular or elliptical shape when viewed in cross section. In this case, the thin-walled portion 7 of the barrier layer 5 is on the long side when the cross section of the semiconductor particle 3 is rectangular, and on the so-called curved surface side when the semiconductor particle 3 is elliptical and has a large radius of curvature. In addition, it is good to arrange each. When the quantum dot particle 1 has such a structure, the thin-walled portion 7 formed in the barrier layer 5 can be formed more on the surface of the semiconductor particle 3, so that the directivity of the moving electrons can be further increased. become. In this case, it is desirable that the outer contour of the barrier layer 5 is approximately similar to the shape of the semiconductor particle 3 at the center. Here, the above-described rectangular shape and elliptical shape mean that the ratio of the longest diameter to the shortest diameter (longest diameter / shortest diameter) in the cross section is 1.2 or more.

  As for the size of the quantum dot particles 1 of this embodiment, for example, the maximum diameter is desirably 3 nm to 20 nm, and the variation in particle diameter is desirably within 10%. When the maximum diameter and the variation in particle diameter are within the above ranges, when the quantum dot particles 1 are stacked to form a quantum dot layer, a regular long-period structure of electrons is formed between the plurality of quantum dot particles 1. This makes it possible to form a continuous band structure. At this time, it is desirable that the average thickness of the barrier layer 5 as a shell portion is 1 to 3 nm.

  The quantum dot particle 1 is preferably a semiconductor particle having an energy gap (Eg) of 0.10 to 3.00 ev, and includes a group 12 element, a group 13 element, a group 14 element, a group 15 element in the periodic table, and Desirably, the main component is at least one element selected from Group 16 elements. Specifically, for example, germanium (Ge), silicon (Si), gallium (Ga), and indium (In). It is preferable to use at least one semiconductor material selected from arsenic (As), antimony (Sb), lead (Pb), tellurium (Te), and selenium (Se). The band gap of the barrier layer 5 is preferably 1.5 to 2.3 times the band gap of the semiconductor particles 3.

  Further, in the quantum dot particle 1 of the present embodiment, the barrier layer 5 that is a shell portion is formed of the same cation (element) as the semiconductor particle 3, and the barrier layer 5 contains more oxygen than the semiconductor particle 3. It can also be applied to structures. In such a case, the portion that becomes the thin portion 7 of the barrier layer 5 may have a structure in which the amount of oxygen is reduced as compared with a portion having a high potential barrier other than the thin portion 7.

In the case where the portion having a small amount of oxygen in the barrier layer 5 is formed as the thin portion 7, it is preferable to select an element in which oxygen is easily combined locally with respect to the components of the semiconductor particles 3. The particle 3 is preferably a compound semiconductor in which at least two elements of Group 12 to Group 16 of the periodic table are combined.

  Next, the manufacturing method of the quantum dot particle | grains of this embodiment is demonstrated. FIG. 3 is a schematic diagram showing a method for producing quantum dot particles of the present embodiment.

When manufacturing the quantum dot particles 1 of this embodiment, as shown in FIG. 3, a transparent container (for example, made of glass) capable of transmitting light is prepared, and this container is used as a source of dissolved oxygen, for example, excess A component that is filled with a solution containing hydrogen oxide and that can further dissolve an oxide formed by oxidizing semiconductor raw material particles (for example, at least one component selected from fluorine, hydrogen, iron, tin, and halogen) 3. A solution containing an inorganic compound, which is represented in FIG. 3 as M ^{+ −} for convenience, is added.

  Next, semiconductor raw material particles are charged and dispersed in this solution. As the semiconductor raw material particles used at this time, particles having an average particle diameter of 1 μm or less are preferably used in that the time spent for reducing the size can be shortened.

  Next, light with a wavelength of 300 to 900 nm is irradiated toward the semiconductor raw material particles in the prepared solution using, for example, a mercury bulb or a xenon bulb as a light source.

  By this light irradiation, electrons and holes are formed inside the semiconductor raw material particles. Among these, electrons are combined with oxygen in the solution on the surface of the semiconductor raw material particles to form active oxygen. The active oxygen forms an oxide film having the semiconductor raw material particle component as a cation on the surface of the semiconductor raw material particle. The oxide film formed on the surface of the semiconductor raw material particles is formed, and at the same time, is dissolved by a component capable of dissolving the oxide dissolved in the solution.

  By such a reaction of forming and removing an oxide film on the surface of the semiconductor raw material particles, the size of the semiconductor raw material particles can be gradually reduced. In this case, the size of the semiconductor raw material particles can be adjusted by the wavelength of light to be irradiated. When the size of the semiconductor raw material particles becomes nanoscale, a quantum effect appears in the semiconductor raw material particles themselves, and the band gap gradually increases as the size decreases. The reaction is completed when the band gap of the semiconductor raw material particles becomes higher than the energy of the irradiated light due to the quantum effect.

  Here, when manufacturing the particle dot particle | grains 1 of this embodiment which has the thin part 7 in the barrier layer 5, a highly crystalline thing is used as a semiconductor raw material particle to be used. When semiconductor raw material particles having high crystallinity are used, the semiconductor raw material particles come to have angular protrusions on the surface because cleavage and dissolution along the crystal plane are likely to occur during the dissolution process. In this oxide film formation and removal process, oxidation and dissolution proceed selectively from the angular protrusions. As a result, a region having a partially non-uniform thickness can be formed in the barrier layer 5. As the degree of crystallinity of the semiconductor raw material particles to be used, it is desirable that the main peak of the X-ray diffraction pattern by Cuka is 10000 counts or more. Further, ultrasonic waves may be applied to improve the dispersibility of the semiconductor raw material particles in the solution.

In addition, the quantum dot particles 1 having a structure in which at least two thin-walled portions 7 are owned by the barrier layer 5 and symmetrically arranged with the semiconductor particles 3 as the center, the semiconductor raw material particles dispersed in the solution are contained in the container. Rotate along the circumference and irradiate light from the side of the container, or irradiate light after applying a strong magnetic field to the semiconductor raw material particles dispersed in the solution and aligning them. Can be obtained. In this case, when the intensity of light and the speed of the semiconductor raw material particles that circulate in the container are changed, the quantum dot particles 1 having a rectangular or elliptical shape when the semiconductor particles 3 are viewed in cross section are formed. It can be produced.

  As the semiconductor raw material particles to be used, various metal elements can be used, and in particular, at least selected from group 12 elements, group 13 elements, group 14 elements, group 15 elements and group 16 elements of the periodic table. It is desirable that the main component is one kind of element.

  Next, the semiconductor device of this embodiment will be described. FIG. 4 is a schematic cross-sectional view showing an embodiment of the semiconductor device of the present invention. As an example of a semiconductor device having such a structure, a semiconductor laser or a solar cell incorporating quantum dot particles is preferable.

  The semiconductor device of this embodiment is characterized in that a plurality of the quantum dot particles 1 are stacked on the main surface of the semiconductor substrate 31. In FIG. 4, the number of stacked quantum dot particles 1 is only two, but it is actually several tens of layers. Hereinafter, the layer in which the quantum dot particles 1 are stacked may be referred to as a quantum dot particle layer (reference numeral 33). In addition, a semiconductor substrate 35 (may be in a film form) is formed on the upper surface side of the quantum dot layer 33 so as to face the semiconductor substrate 31 on the lower layer side. In this case, the semiconductor substrates 31 and 35 are n-type and p-type, respectively.

  As can be seen from FIG. 4, the quantum dot particles 1 constituting the semiconductor device of this embodiment have a thickness larger than that of the other portions in the barrier layer 5 that is a shell portion formed around the semiconductor particles 3 that are the core portions. It has a thin thin portion 7. For this reason, even if the quantum dot particles 1 are bonded to each other, the barrier layers 5 that are adjacent shell portions are close to each other in the thin portion 7, so that electrons confined inside the semiconductor particles 3 have priority over the thin portion 7. The density of electrons moving from the quantum dot particle 1 (current density) is increased, so that the quantum dot particle 1 can obtain a structure in which a large number of quantum dot particles 1 are stacked in multiple layers. As a result, the amount of generated charge can be improved and a semiconductor device with high power gain can be obtained.

  Further, in this semiconductor device, when the thin portion 7 formed in the barrier layer 5 of the quantum dot particle 1 is located on the semiconductor substrate side, the barrier layer 5 near the thin portion 7 is close to the semiconductor substrate 31. In addition, the electrons confined in the semiconductor particles 3 are easily moved to the semiconductor substrate 31, and the power gain obtained by the quantum dot particles 1 can be improved. In this case, it is more preferable that the thinnest portions 7 of the thin portion 7 are arranged in a direction perpendicular to the surface of the semiconductor substrate 31.

  Furthermore, when the quantum dot particles 1 are arranged on the surface of the semiconductor substrate 31, the interval between the quantum dot particles 1 is greater than the interval in the direction parallel to the semiconductor substrate 31 in the direction perpendicular to the semiconductor substrate 31. Short is desirable. When the semiconductor device is configured as described above, the electrons generated by the quantum dot particles 1 easily reach the semiconductor substrate 31, thereby further improving the power gain of the semiconductor device.

  Next, a method for manufacturing a solar cell as an example of the semiconductor device of this embodiment will be described.

First, the quantum dot particles 1 prepared in advance are formed into a gel using a highly viscous organic vehicle, and this is applied to the surface of the semiconductor substrate 31 to deposit the quantum dot particles 1. Next, the semiconductor substrate 31 is heated to a temperature of 100 to 600 ° C. in an inert gas such as argon or nitrogen or a reducing gas containing hydrogen to sinter the quantum dot particles 1. . Thus, the quantum dot particle layer 33 is formed on the surface of the semiconductor substrate 31. When the quantum dot particle layer 33 has a structure in which the core-shell structure quantum dot particles 1 are stacked so as to have the outline of the shell portion 5, the quantum dot particles 1 may be connected to each other without increasing the heating temperature. Control is performed so that the neck portion is joined.

  Next, a semiconductor substrate 35 is formed on the surface of the layer of quantum dot particles 1. As a manufacturing method, a chemical method such as a physical thin film forming method selected from a CVD method, a sputtering method, and a vapor deposition method, a spin coating method, or a printing method can be employed.

  Since the solar cell obtained as described above has the thin-walled portion 7 in the barrier layer 5 that is the shell portion of the quantum dot particle 1 constituting the quantum dot particle layer 33, Electrons that move to other adjacent quantum dot particles 1 are not radial as in the case where the thickness of the barrier layer 5 is uniform, and are easily concentrated in the region of the thin-walled portion 7. The density of electrons (current density) can be increased. As a result, the amount of light absorbed by the quantum dot particles 1 can be increased, so that the photoelectric conversion efficiency can be improved.

1 ... Quantum dot particle 3 ... Semiconductor particle 5 ... Barrier layer 7 ...・ Thin part 31, 35 ... Semiconductor substrate 33 ... Quantum dot particle layer

Claims (7)

A quantum dot particle having a core part of a semiconductor particle and a shell part surrounding the core part and having a different component or oxygen amount from the semiconductor particle, wherein the shell part is formed from the surface of the semiconductor particle. It has a thin part whose thickness in the line direction is thinner than other parts , and the thin part has at least two in the shell part and is arranged symmetrically with respect to the semiconductor particles. Quantum dot particles. The quantum dot particles according to claim 1, wherein the semiconductor particles have a rectangular shape or an elliptical shape when viewed in cross section. A quantum dot particle having a core part of a semiconductor particle and a shell part surrounding the core part and having a different component or oxygen amount from the semiconductor particle, wherein the shell part is formed from the surface of the semiconductor particle. The quantum dot particle characterized by having a thin-walled portion whose thickness in the linear direction is thinner than other portions, and the semiconductor particle having a rectangular shape or an elliptical shape when viewed in cross section.   A semiconductor device, wherein a plurality of the quantum dot particles according to claim 1 are stacked on a main surface of a semiconductor substrate.   The semiconductor device according to claim 4, wherein the thin portion is located on the semiconductor substrate side.   6. The semiconductor device according to claim 5, wherein the thinnest portion of the thin portion is arranged in a direction perpendicular to the surface of the semiconductor substrate.   7. The semiconductor device according to claim 4, wherein an interval between the quantum dot particles is shorter than an interval in a direction parallel to the semiconductor substrate in a direction perpendicular to the semiconductor substrate.

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