JP5664416B2 - Silicon quantum dot device and manufacturing method thereof - Google Patents

Description

  The present invention relates to a silicon quantum dot device and a manufacturing method thereof.

  Silicon is a semiconductor having an indirect transition type band structure, and is widely used in integrated circuits, light receiving devices, and the like. When a silicon crystal having a miniaturized size is formed, a light emission phenomenon is also possible due to the quantum effect. Various silicon semiconductor devices utilizing the quantum effect have been proposed (for example, Patent Document 1 and Patent Document 2).

  Si substrate surface is anodized to form a porous region containing quantum wire aggregates, immersed in pure water to adjust recombination luminescence energy, and to form a counter layer having a carrier supply function to form a Si light emitting device. It is possible to manufacture.

  By forming a silicon dioxide layer containing Si in excess of the stoichiometric composition on the Si substrate and performing high-temperature annealing in a hydrogen atmosphere, for example, Si nanometer crystals can be formed in the silicon dioxide layer. It is possible to form a red light emitting device by forming a negative electrode on the Si substrate and forming a positive electrode on the upper side.

  It is possible to decompose silane gas in the plasma cell and deposit nanocrystalline silicon on the substrate. If the nanocrystalline silicon surface is oxidized, a plurality of layers of nanocrystalline silicon can be stacked. It is also possible to generate nanocrystalline silicon at a desired position using a catalyst or the like. By alternately laminating Si-rich silicon oxide layers and silicon oxide layers and annealing at high temperature, nanocrystalline silicon is produced by agglomeration of Si in the Si-rich silicon oxide layer, and the nano-crystalline dispersed in the silicon oxide layer Crystalline silicon can also be formed (for example, Non-Patent Document 1).

  A structure having a dimension of the order of nanometers and capable of confining carriers in a three-dimensional direction and generating a quantum effect is called a quantum dot. In general, quantum dots have physical properties different from those of bulk materials. A silicon quantum dot is a quantum dot formed from silicon.

  Although quantum dots have been widely researched, silicon quantum dots have not been fully researched and developed, and there are many issues to be solved in the future in order to realize practical products.

JP-A-6-13653, JP 2006-59950 A,

Cho et al .: Nanotechnology Vol. 19, (2008) 245201.

  An object of an embodiment of the present invention is to provide a silicon quantum dot device having silicon quantum dots having different characteristics in a plurality of regions.

  Another object of the embodiment of the present invention is to provide a method of manufacturing a silicon quantum dot device capable of forming silicon quantum dots having different characteristics in a plurality of regions.

According to one aspect of the embodiment,
A substrate,
A first quantum oxide layer disposed above the substrate and including a first silicon oxide matrix layer including silicon quantum dots having a first average dot size and a pair of first silicon oxide layers sandwiching the first silicon oxide matrix layer; Dot structure,
A second silicon oxide matrix layer that is disposed above the substrate and includes silicon quantum dots having a second average dot size different from the first average dot size, and a pair of second oxides sandwiching the second silicon oxide matrix layer A second quantum dot structure comprising a silicon layer;
I have a,
The first quantum dot structure has a configuration in which a plurality of the first silicon oxide matrix layers and a plurality of the first silicon oxide layers are alternately stacked,
The second quantum dot structure has a configuration in which a plurality of layers of the second silicon oxide matrix layers and a plurality of layers of the second silicon oxide layers are alternately stacked,
The second quantum dot structure is disposed on the substrate in parallel with the first quantum dot structure;
The first silicon oxide matrix layer is composed of the same layer as the second silicon oxide matrix layer,
The silicon quantum dot device, wherein the second silicon oxide layer is composed of the same layer as the first silicon oxide layer .
Is provided.

According to another aspect of the embodiment,
A silicon oxide layer and a silicon rich silicon oxide layer are alternately deposited on the substrate to form a stack,
Irradiating hydrogen ions from the surface of the stack, in the Si-rich silicon oxide layer, promotes the aggregation of Si to produce silicon quantum dots, forming a silicon oxide matrix layer containing silicon quantum dots.
A method for manufacturing a silicon quantum dot device, comprising:
Provided is a method for manufacturing a silicon quantum dot device, in which silicon quantum dots having different average dot sizes are formed by performing hydrogen ion irradiation under different conditions with respect to the stacking thickness direction or in-plane direction.

  Silicon quantum dots can be formed in the presence of hydrogen by irradiating a silicon-rich silicon oxide layer with hydrogen ions. By adjusting the condition of the silicon-rich silicon oxide layer or the condition of the hydrogen ions to be irradiated, silicon quantum dots having different characteristics can be created.

and 1A to 1E are cross-sectional views of a substrate showing a method for manufacturing a silicon quantum dot device according to a first embodiment. FIG. 2A is a cross-sectional view of a substrate showing a method of manufacturing a silicon quantum dot device according to a second embodiment, and FIG. 2B is a cross-sectional view of the substrate for explaining ion irradiation. 3A to 3C are cross-sectional views of a substrate showing a method for manufacturing a silicon quantum dot device according to a third embodiment.

  Regarding the diffusion of oxygen in silicon, there is a paper that the diffusion barrier 2.56 eV without hydrogen is 1.25 eV in the presence of hydrogen (Estreicher et al.: Phys. Rev. B41, 9886 (1990)). . It means that the diffusion coefficient of oxygen in silicon at room temperature is 10 times the power of 10 in the presence of hydrogen and without hydrogen.

  The present inventor made a calculation regarding the dissociation of oxygen in silicon oxide, and obtained a result that the dissociation coefficient of 8.6 eV in the absence of hydrogen becomes 2.6 eV in the presence of hydrogen. The diffusion of oxygen in silicon oxide means that at room temperature, it is a few tens of times that in the presence of hydrogen and no hydrogen.

  Excess silicon atoms exist in the silicon-rich silicon oxide film. When the silicon atom and the oxygen atom that bonds the silicon atom move by diffusion, the silicon atom and the silicon atom associate to form a growth nucleus. When the silicon crystal grows, silicon-rich silicon oxide is phase-separated into silicon and silicon oxide. The introduction of hydrogen makes this phase separation much easier. If the diffusion distance of oxygen atoms is limited, the resulting silicon crystal will form silicon quantum dots.

  Silicon quantum dots change their physical properties in accordance with their sizes (diameters if they are spherical, corresponding dimensions if they are other shapes). Typically, the emission wavelength is changed according to the size. For example, a change is made so that red light emission is generated from a silicon quantum dot of a certain size, green light emission is generated from a silicon quantum dot having a smaller size, and blue light emission is generated from a silicon quantum dot having a smaller size. Silicon quantum dots could be thought of as having an energy gap that varies with dot size.

  If silicon quantum dots having different dot sizes can be selectively formed, it will be extremely effective in practice. For example, if a red light emitting element, a green light emitting element, and a blue light emitting element can be selectively arranged in a plane, a color display device can be formed.

  In the case of forming a light absorbing element (solar cell) instead of the light emitting element, the relationship between the size of the silicon quantum dot and the wavelength will be the same. A relatively small dot size silicon quantum dot with peak sensitivity at the blue wavelength will not absorb light longer than the peak blue wavelength. A relatively large dot size silicon quantum dot with high sensitivity to the red wavelength will absorb light of the red wavelength and will also absorb light of higher energy (short wavelength).

  If an infrared-red photosensitive element is laminated on the lower side and a green-blue photosensitive element is laminated on the upper side, it is possible to absorb light in the same area and a wide wavelength region and convert it into an electric quantity. An efficient solar cell could be formed. When a large number of silicon quantum dots are formed, the physical properties will be controlled by the average dot size.

  Hereinafter, the present invention will be described with reference to examples.

  1A to 1C are cross-sectional views of a substrate showing a manufacturing method of a configuration in which silicon quantum dots having different average dot sizes are stacked according to the first embodiment. 1D to 1E are cross-sectional views illustrating a silicon quantum dot device having electrodes formed thereon.

As shown in FIG. 1A, plasma chemical vapor deposition (CVD) using a co-sputtering of Si and silicon oxide or a silicon source gas such as silane and an oxygen source gas such as oxygen on the surface of an n-type Si substrate 11. ) And a SiO ₂ (silicon oxide) layer 12 having a thickness of 0.5 nm to 2.0 nm, for example, about 1 nm, and a SiO _x (x is greater than 0) having a thickness of 1 nm to 10 nm, for example, about 5 nm. Then, less than 2 (for example, about 1) layers (Si-rich silicon oxide layers) 13 are alternately stacked on the order of several tens to 100, for example, about 40 pairs, and the uppermost SiO ₂ layer 12 is stacked.

SiO _{x with} x = 1 can be considered as a mixed state of silicon oxide and silicon, as shown by 2SiO = SiO ₂ + Si. If phase separation occurs, a silicon oxide phase and a silicon phase will occur.

As shown in FIG. 1B, a SiO _x layer 15 having a thickness of, for example, ₂ nm and a SiO ₂ (silicon oxide) layer 12 having a thickness of 0.5 nm to 2.0 nm, for example, about 1 nm are reduced. Alternatingly, several tens to 100, for example, about 40 pairs are laminated. In the lower portion LP of the stack, an alternating stack of SiO _x layers 13 and SiO ₂ layers 12 having a thickness of 5 nm is formed, and in the upper portion UP of the stack, the SiO _x layers 15 and SiO ₂ layers 12 having a thickness of 2 nm are formed. Alternating stacks are formed.

As shown in FIG. 1C, hydrogen ions H ⁺ are irradiated from the upper part of the stack, and the acceleration energy is switched stepwise (for example, to 5 keV, 10 keV, 20 keV, 40 keV) in the range of several keV to about 40 keV. The entire stack is irradiated with hydrogen ions H ⁺ . The presence of hydrogen promotes oxygen diffusion.

  Although not essential, annealing is performed at a temperature of 300 ° C. for about 10 minutes simultaneously with irradiation of hydrogen ions or following irradiation of hydrogen ions. Oxygen diffusion is limited only by annealing at 300 ° C. Increasing the annealing temperature reduces the difference in oxygen diffusion due to the presence / absence of hydrogen. It may be desirable to set the annealing temperature to 500 ° C. or lower in order to create silicon quantum dots by the presence / absence of hydrogen. For example, the annealing temperature is 250 ° C. to 500 ° C.

As described above, dissociation and diffusion of oxygen are facilitated in the presence of hydrogen, and the SiO _x layers 13 and 15 are phase-separated into Si quantum dots and SiO ₂ . A quantum dot 14 having an average size of 5 nm or less is formed in the SiO _x layer 13 having a thickness of 5 nm in the lower LP, and a quantum dot 16 having an average size of 2 nm or less is formed in the SiO _x layer 15 having a thickness of 2 nm in the upper UP. Is done. The short wavelength component of incident light is mainly absorbed by the upper UP, and the long wavelength component of incident light is mainly absorbed by the lower LP. An efficient solar cell can be constructed because incident light in a wide wavelength range can be effectively absorbed and converted into electric charges.

  When the Si-rich silicon oxide layer is phase-separated to become a Si quantum dot and a silicon oxide layer, this silicon oxide layer may be called a silicon oxide matrix layer. The lamination is an alternating lamination of a silicon oxide layer and a silicon oxide matrix layer, and Si quantum dots are arranged in the silicon oxide matrix layer.

  As shown in FIG. 1D, a metal electrode layer 17 such as Al is formed on the back surface of the n-type Si substrate 11, and a transparent electrode 19 such as indium tin oxide (ITO) or zinc oxide (ZnO) is formed on the upper surface of the stack. Forming a solar cell.

As shown in FIG. 1E, instead of the oxide transparent electrode 19 of one layer, an antireflection film 20 having a single layer structure such as TiO ₂ or SiN formed by a CVD method or the like, and sunlight on the lower surface thereof. It is also possible to use a locally formed metal electrode 21 so as to penetrate.

  When the size of the silicon quantum dot exceeds 10 nm, the property is close to that of bulk silicon. As an average size of the silicon quantum dots used for the solar cell, about 1 nm to 10 nm may be appropriate. When a sufficiently high concentration of hydrogen is irradiated, the thickness of the Si-rich silicon oxide layer can be set in consideration of the desired average size of the silicon quantum dots. The silicon oxide layer has a function of separating and protecting silicon quantum dots. From this point, it can be called a separation protective film, and is not limited to silicon oxide, and can be formed of other insulating materials. However, silicon oxide is preferable from the viewpoint of compatibility with the Si-rich silicon oxide layer and reliability. In an application such as a solar cell in which a bias voltage is not applied, it is desired that charges are tunneled through the separation protective film, and the thickness is limited to a tunnelable thickness (about 2 nm or less).

  2A and 2B are cross-sectional views illustrating a solar cell and a manufacturing process thereof according to the second embodiment. As shown in FIG. 2A, a silicon oxide layer 12 having a thickness of 0.5 nm to 2 nm, for example, 1 nm, and a Si-rich oxide having a thickness of 1 nm to 10 nm, for example, 5 nm, are formed on the surface of the n-type Si substrate 11. The silicon layers 13 are alternately stacked, for example, 100 layers, and finally a silicon oxide layer 12 having a thickness of 1 nm is formed.

As shown in FIG. 2B, for example, the stack 10 is irradiated with hydrogen ions H ⁺ having a peak of intensity (dose) near the bottom surface of the stack 10. Following the irradiation with hydrogen ions or with the irradiation with hydrogen ions, annealing is performed at 300 ° C. for 10 minutes or less. The acceleration energy of hydrogen ions is changed in accordance with the thickness of the stack, so that the high dose is at the bottom of the stack and the dose is clearly reduced at the top of the stack. The phase separation between Si and silicon oxide in the Si-rich silicon oxide layer is promoted, and a large silicon quantum dot is formed in a high dose region and a small silicon quantum dot is formed in a low dose region.

  For example, if the total thickness of the stack is 150 nm, the acceleration energy is about 15 keV, and if the total thickness of the stack is 650 nm, the hydrogen ions are accelerated with an acceleration energy of about 65 keV.

  The penetration depth of hydrogen is determined according to the acceleration energy of the hydrogen ion beam, and hydrogen is distributed at a concentration where the hydrogen gradually becomes thinner above the penetration depth. Inside the stacked layer 10, the hydrogen ion dose decreases as it goes upward from the peak depth of the hydrogen ion dose, and is formed in the Si-rich silicon oxide layer 13 at a shallow position where the hydrogen ion dose is decreased. The size of silicon quantum dots is reduced. Therefore, a single silicon ion implantation can form silicon quantum dots that are larger at the lower portion and smaller at the upper portion. The electrode can be formed in the same manner as in the first embodiment.

  3A to 3C are cross-sectional views showing the configuration and manufacturing method of the silicon quantum dot device according to the third embodiment. For example, first, second, and third regions are defined on the substrate surface. Each region is illustrated as an example.

  As shown in FIG. 3A, an electrode 23 is formed on each of the first, second, and third regions on a substrate 11 made of silicon, glass, and the like, and a drive substrate 11x is formed covering an insulating film such as silicon oxide. . A laminated structure in which a silicon-rich silicon oxide film 13 having a thickness of 1 nm to 10 nm and a silicon oxide film 12 having a thickness of 0.5 nm to 3 nm are alternately laminated on the surface of the driving substrate 11x, and the outermost surface is a silicon oxide layer 12. 10 is formed.

As shown in FIG. 3B, a driving substrate having a stacked structure is heated, and hydrogen ions H ⁺ are selectively irradiated from the stacked surface to the first region to form silicon quantum dots of a desired size in the irradiated region. . For example, silicon quantum dots having an average dot size of 5 nm are formed by irradiating a high dose amount of hydrogen ions at a temperature around 500 ° C.

  As shown in FIG. 3C, the second region is irradiated with hydrogen ions to form silicon quantum dots having an average dot size of 1.5 nm. The third region is irradiated with hydrogen ions to form silicon quantum dots having an average dot size of 1 nm. Thereafter, a transparent electrode is formed on each region.

  By applying a voltage between the upper and lower opposing electrodes and flowing a current, light of a predetermined wavelength can be emitted from the silicon quantum dots and the emitted light can be extracted from the transparent electrode side. Silicon quantum dots emit blue light around 1 nm in diameter and emit red light at 4 nm to 10 nm in diameter. Color display can be performed by forming green light emitting dots, yellow light emitting dots, and the like.

  In addition, light emission can also be taken out from the substrate side by using the substrate 11 as a transparent substrate such as glass and the electrode 23 as a transparent electrode. If the output side electrode is a transparent electrode and the counter electrode is a highly reflective metal electrode such as aluminum or silver, the efficiency of extracting external light can be increased.

  According to the present embodiment, the size of the silicon quantum dots can be adjusted by adjusting the dose amount and irradiation time of hydrogen ions. A light-emitting element having silicon quantum dots that emit light of different colors can be formed without forming different Si-rich silicon oxide layers with different thicknesses in the surface.

  As mentioned above, although this invention was demonstrated along the Example, this invention is not limited to these. For example, the exemplified materials and numerical values are not restrictive.

10 lamination,
11 Si substrate,
12 silicon oxide layer,
13 silicon-rich silicon oxide (SiO _x ) layer,
14 silicon quantum dots,
15 silicon-rich silicon oxide (SiO _x ) layer,
16 silicon quantum dots,
UP top,
LP bottom,
17 metal electrode layer,
18 translucent electrode,
19 Transparent electrode,
20 translucent electrode,
21 low resistance electrode,
23 electrodes,
24, 25, 26 silicon quantum dots,

Claims (9)

A substrate,
A first quantum oxide layer disposed above the substrate and including a first silicon oxide matrix layer including silicon quantum dots having a first average dot size and a pair of first silicon oxide layers sandwiching the first silicon oxide matrix layer; Dot structure,
A second silicon oxide matrix layer that is disposed above the substrate and includes silicon quantum dots having a second average dot size different from the first average dot size, and a pair of second oxides sandwiching the second silicon oxide matrix layer A second quantum dot structure comprising a silicon layer;
I have a,
The first quantum dot structure has a configuration in which a plurality of the first silicon oxide matrix layers and a plurality of the first silicon oxide layers are alternately stacked,
The second quantum dot structure has a configuration in which a plurality of layers of the second silicon oxide matrix layers and a plurality of layers of the second silicon oxide layers are alternately stacked,
The second quantum dot structure is disposed on the substrate in parallel with the first quantum dot structure;
The first silicon oxide matrix layer is composed of the same layer as the second silicon oxide matrix layer,
The silicon quantum dot device, wherein the second silicon oxide layer is composed of the same layer as the first silicon oxide layer . further,
A plurality of third silicon oxide matrix layers comprising the same layer as the first silicon oxide matrix layer and the second silicon oxide matrix layer and including silicon quantum dots having a third average dot size, and the first silicon oxide layer A third quantum dot structure including a plurality of third silicon oxide layers composed of the same layer as the second silicon oxide layer, wherein the first quantum dot structure and the second quantum dot structure are formed on the substrate. A third quantum dot structure arranged in parallel with
The a, the second average dot size is smaller than the first average dot size, the third average dot size is smaller than the second average dot size, according to claim 1 that functions as a light-emitting device Silicon quantum dot device. A silicon oxide layer and a silicon rich silicon oxide layer are alternately deposited on the substrate to form a stack,
Irradiating hydrogen ions from the surface of the stack, in the Si-rich silicon oxide layer, promotes the aggregation of Si to produce silicon quantum dots, forming a silicon oxide matrix layer containing silicon quantum dots.
A method for manufacturing a silicon quantum dot device, comprising:
A method of manufacturing a silicon quantum dot device, wherein silicon quantum dots having different average dot sizes are formed by performing hydrogen ion irradiation under different conditions with respect to a stacking thickness direction or an in-plane direction. 4. The method of manufacturing a silicon quantum dot device according to claim 3 , wherein annealing is performed by heating the stacked layer simultaneously with or after irradiation with the hydrogen ions. The method for manufacturing a silicon quantum dot device according to claim 4 , wherein the annealing is performed at 500 ° C. or less. Irradiation of the hydrogen ions with respect to the thickness of the stacked layer is performed at a dose amount depending on the depth, and silicon quantum dots having a large average dot size are formed in a Si-rich silicon oxide region having a high dose amount. The method for producing a silicon quantum dot device according to any one of claims 3 to 5 , wherein silicon quantum dots having a small average dot size are formed in a low-Si-rich silicon oxide region. The stack is formed by alternately stacking the silicon oxide layer and the first Si-rich silicon oxide layer having the first thickness, and then forming the second layer thinner than the silicon oxide layer and the first thickness. 6. The method of manufacturing a silicon quantum dot device according to claim 3 , comprising alternately depositing Si-rich silicon oxide layers having a thickness of 1 to 5. 5 . 8. The method of manufacturing a silicon quantum dot device according to claim 7, wherein the stacked layer is irradiated with multiple hydrogen ions at a plurality of acceleration energies to form silicon quantum dots depending on the thickness of the Si-rich silicon oxide layer. Defining multiple areas in the substrate, performed at different doses by the area irradiation of the hydrogen ions, any one of claims 3 to 5 forming the silicon quantum dots with an average dot size corresponding to the dose per area A method for producing a silicon quantum dot device according to claim 1.

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