KR101580740B1 - Photo diode using hybrid structure of graphene/porous silicon and method of macufacturing the same - Google Patents

Abstract

There is provided a photodiode comprising a fused composite nano structure including graphene and porous silicon having a porous structure having a size of several nanometers (nm) on its surface. The graphene / porous silicon based photodiode of the present invention is an optical sensor. And can be applied to optical devices such as solar cells and LEDs.

Description

[0001] PHOTO DIODE USING HYBRID STRUCTURE OF GRAPHENE / POROUS SILICON AND METHOD OF MACUFACTURING THE SAME [0002]

The present invention relates to a photodiode applicable as an optical device using graphene and a fused composite nano structure including porous silicon having a porous structure with a size of several nanometers (nm) on the surface thereof, and a method of manufacturing the same.

Graffin not only has high electrical conductivity but also has high optical performance, so it can be used as a new material in next generation display fields such as flexible display and touch panel, energy business such as solar cell, smart window, RFID, etc. .

In recent years, graphene has received considerable attention not only because of its basic academic advancement, but also because of its potential to grow industrial technology. Especially in recent years, as graphene's large-area manufacturing technique has been developed, its applicability to various industrial fields is expanding.

Among them, graphene produced by chemical vapor deposition (CVD), which is widely used in the industry, is expected to be used as a transparent electrode because it has a large area and high transmittance and electrical conductivity.

On the other hand, since porous silicon forms nanostructures of less than several nanometers on the silicon surface, the light absorption efficiency can be improved by lowering the light reflectance as compared with the silicon substrate.

In addition, due to the quantum confinement effect (QCE) occurring in the silicon nanostructure, the light absorption rate can be expected to be further increased in the short wavelength region as compared with the bulk Si, It is expected to be applicable to various optoelectronic devices.

If the device is realized by fusing two materials having these excellent characteristics, it is expected that the device can be improved and improved in performance, and a new physical phenomenon is expected from the nano-structured fusion complex, so that it can be applied to a new application field .

In recent years, studies have been actively carried out to apply such fused composite nanostructures to optoelectronic devices. In recent researches, researches have been carried out to fabricate fused composite nanostructures such as graphene / silicon substrate or graphene / silicon nanowire Have been reported.

Until now, silicon-based optical devices exhibit light-receiving characteristics in the range of near-infrared to visible light (400 to 1100 nm) due to the characteristics of bulk silicon, but the photoreaction rate varies from a few milliseconds (ms) ), Which is a very slow disadvantage.

Accordingly, there is a need for the development of an optical device having light emission and light receiving characteristics in a wider wavelength band while improving a slow photoreaction rate in a silicon-based optical device.

Phys. Status Solidi C 7, No. 3-4, 1251-1255 (2010). An, X. H .; Liu, F. Z .; Jung, Y. J .; Snow, S. Nano Lett. 2013, 13, (3), 909-916.

The present invention provides a photodiode applicable as an optical device using graphene and a fused composite nano structure including porous silicon having a porous structure with a size of several nanometers (nm) on its surface.

The present invention relates to a diode-based optical sensor. Porous silicon-based photodiodes that exhibit excellent photodetecting performance that can be applied to all optical devices such as photovoltaic cells, solar cells, and LEDs.

A photodiode using the graphene / porous silicon fused composite nanostructure according to an embodiment includes a fused composite nanostructure of a vertically bonded structure including a single layer of graphene formed on a porous silicon layer; And electrodes formed on upper and lower portions of the fused composite nano structure, respectively.

The porous silicon layer may be formed on a silicon substrate through a metal-assisted chemical etching process using a metal as a catalyst.

The single-layer graphene is formed by reacting a catalyst layer with a carbon-containing mixed gas and depositing the catalyst layer on the catalyst layer by a chemical vapor deposition (CVD) method. The fused composite nano- The porous silicon layer may be formed through a vertical bonding process.

The energy band gap of the fused composite nano structure is controlled through the control of the porosity of the porous silicon, so that the photodiode can have a high optical efficiency in a wider frequency band in bulk silicon.

A method of fabricating a photodiode using a graphene / porous silicon fused composite nano structure according to an embodiment includes forming a porous silicon layer on a silicon substrate through a chemical etching process using a metal as a catalyst; Transferring a single layer of graphene formed by a chemical vapor deposition (CVD) method to the porous silicon layer to form a fused composite nanostructure; And forming electrodes on upper and lower portions of the fused composite nano structure, respectively.

According to the present invention, there is provided a photodiode comprising a fused composite nano structure including graphene and porous silicon having a porous structure having a size of several nanometers (nm) on the surface, And can be applied to optical devices such as solar cells and LEDs.

According to the present invention, it is possible to produce a photonic diode based on a fused composite nano structure of graphene / porous silicon showing excellent photodetection performance.

1 shows a photodiode using the graphene / porous silicon fused composite nano structure of the present invention.
2 is a scanning electron microscope (SEM) image of a porous silicon of a photodiode using a graphene / porous silicon fused composite nanostructure of an embodiment of the present invention.
FIG. 3 shows photoluminescence (PL) measurement of porous silicon of a photodiode using a graphene / porous silicon fused composite nano structure of an embodiment of the present invention, and FIG. 4 shows Raman spectroscopy ≪ / RTI >
Figure 5 illustrates a Raman spectrum for a single layer of graphene in an embodiment of the present invention, Figure 6 is an image of an atomic force microscope (AFM) for a single layer of graphene in an embodiment of the present invention, Figure 7 1 is a graph showing the transmittance of graphene in a single layer of an embodiment of the present invention.
8 is a scanning electron microscope (SEM) image of a graphene / porous silicon fused composite nanostructure of an embodiment of the present invention.
FIG. 9 is a graph showing the energy band diagram and the current-voltage characteristic of a photodiode using a graphene / porous silicon fused composite nano structure according to an embodiment of the present invention.
10 is a graph showing distribution curves of dark current and photocurrent when a photodiode using a graphene / porous silicon fused composite nano structure according to an embodiment of the present invention is used as a photodetecting device.
11 is a graph comparing the photoreactivity-voltage curve of a photodiode using a graphene / porous silicon fused composite nanostructure according to an embodiment of the present invention with a graphene / bulk silicon structure diode.
12 is a graph showing a relationship between photo current (dark current) (PC / DC) of a photodiode using a graphene / porous silicon fused composite nano structure according to an embodiment of the present invention, It is compared with a diode of graphene / bulk silicon structure.
FIG. 13 is a graph showing a photoreactivity-voltage curve according to deposition time for a metal catalyst in the production of a porous silicon layer for a photodiode using a graphene / porous silicon fused composite nano structure according to an embodiment of the present invention.
14 is a graph showing the ratio of photocurrent to dark current according to the irradiation wavelength of light for a photodiode using a graphene / porous silicon fused composite nano structure according to an embodiment of the present invention in the process of chemical etching at the time of manufacturing the porous silicon layer The deposition time of the metal catalyst is shown separately.
FIG. 15 is a graph showing a normalized responsivity-wavelength curve according to a deposition time of a metal catalyst in manufacturing a porous silicon layer for a photodiode using a graphene / porous silicon fused composite nano structure according to an embodiment of the present invention. It is.
16 is a graph showing a quantum efficiency versus wavelength curve according to a deposition time of a metal catalyst in the production of a porous silicon layer for a photodiode using a graphene / porous silicon fused composite nano structure according to an embodiment of the present invention.
17 is a graph showing changes in photocurrent according to time after pulsed laser irradiation on a photodiode using a graphene / porous silicon fused composite nano structure according to an embodiment of the present invention, according to the deposition time of a metal catalyst at the time of manufacturing the porous silicon layer will be.
18 is a flowchart illustrating a method of fabricating a photodiode using a graphene / porous silicon fused composite nanostructure according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings and accompanying drawings, but the present invention is not limited to or limited by the embodiments.

It is to be understood that when an element or layer is referred to as being "on" or " on "of another element or layer, All included. On the other hand, when a device is referred to as "directly on" or "directly above ", it does not intervene another device or layer in the middle.

The terms spatially relative, "below", "beneath", "lower", "above", "upper" May be used to readily describe a device or a relationship of components to other devices or components. Spatially relative terms should be understood to include, in addition to the orientation shown in the drawings, terms that include different orientations of the device during use or operation. For example, when inverting an element shown in the figure, an element described as " below or beneath "of another element may be placed" above "another element. Thus, the exemplary term "below" can include both downward and upward directions. The elements can also be oriented in different directions, in which case spatially relative terms can be interpreted according to orientation.

The terminology used herein is for the purpose of illustrating embodiments and is not intended to be limiting of the present invention. In the present specification, the singular form includes plural forms unless otherwise specified in the specification. It is noted that the terms "comprises" and / or "comprising" used in the specification are intended to be inclusive in a manner similar to the components, steps, operations, and / Or additions.

Unless defined otherwise, all terms (including technical and scientific terms) used herein may be used in a sense commonly understood by one of ordinary skill in the art to which this invention belongs. Also, commonly used predefined terms are not ideally or excessively interpreted unless explicitly defined otherwise.

In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. The terminology used herein is a term used for appropriately expressing an embodiment of the present invention, which may vary depending on the user, the intent of the operator, or the practice of the field to which the present invention belongs. Therefore, the definitions of these terms should be based on the contents throughout this specification.

Schottky diodes can be fabricated by bonding semiconductors and metals, but due to the low transparency of the metal, the metal-semiconductor structure is difficult to apply as an optical device.

Recently, indium tin oxide (ITO), which is used as a transparent electrode, is a transparent electrode material that exhibits excellent performance in the visible light region. However, its application range is limited because the transmittance is very low in the ultraviolet region.

On the other hand, graphene has a very high transmittance of more than 97% in infrared to ultraviolet region, and has very high electrical conductivity and can be used as a transparent electrode. In addition, since graphene has a high carrier mobility, electrons or light-generated charge carriers can be recombined or separated faster, resulting in higher efficiency than using other metals, And the light receiving rate is very fast.

With these properties, graphene is expected to solve the problem of slow electroluminescence and photoelectric conversion of conventional silicon nanostructures, and graphene-based nanostructures are more likely to be used as optical devices.

1 shows a photodiode using the graphene / porous silicon fused composite nano structure of the present invention.

1, a photodiode 100 using the graphene / porous silicon fused composite nano structure of the present invention includes a single layer of graphene 112 formed on a porous silicon layer 111 And an electrode 120 formed on upper and lower portions of the fused composite nano structure 110 and the fused composite nano structure 110, respectively.

The porous silicon layer 111 may be formed on the silicon substrate 130 through a metal-assisted chemical etching process using a metal as a catalyst.

The single layer of graphene 112 may be formed by chemical vapor deposition (CVD) deposition of a catalyst layer on the catalyst layer by reacting the catalyst layer with a carbon-containing mixed gas, and the fused composite nanostructure 110 may be formed of a single layer of graphene The porous silicon layer 112 and the porous silicon layer 111 can be formed through a vertical bonding process.

≪ Preparation of porous silicon &

The porous silicon layer 111 may be formed on the silicon substrate 130 through a chemical etching process using a metal as a catalyst. More specifically, the silicon substrate 130 is immersed in a mixed solution of silver nitrate (AgNO ₃ ) and hydrofluoric acid (HF) to form silver metal nanoparticles on the silicon substrate 130, and hydrofluoric acid (HF) (H ₂ O ₂ ) is selectively etched, and the remaining metal (silver) is removed with nitric acid (HNO ₃ ), and the silicon nitride film The porous silicon layer 111 can be formed.

The metal nanoparticles formed on the silicon substrate 130 may be coated on the silicon substrate 130 by a thermal deposition method, an electron beam deposition method, or a direct current sputtering method in addition to the chemical coating method using the above- The porous silicon layer 111 can be manufactured.

The porosity (size / density of the nanostructure) of the porous silicon layer 111 can be easily controlled depending on the size and density of the metal nanoparticles.

2 is a scanning electron microscope (SEM) image of a porous silicon of a photodiode using a graphene / porous silicon fused composite nanostructure of an embodiment of the present invention.

Referring to FIG. 2, FIGS. 2 (a) to 2 (c) show scanning electron microscope images obtained by changing the deposition times of silver catalysts for 1 second, 3 seconds, and 5 seconds, respectively, in the chemical etching process As a result, the porosity of the porous silicon layer can be controlled by changing the deposition time of the silver catalyst.

According to embodiments, the size and density of the nanostructures present on the porous silicon surface can be controlled according to the deposition time of the silver catalyst. More specifically, the hole density of the porous silicon surface shown in FIG. 2 includes 46.55%, 60.27%, and 79.26% at deposition times of 1 second, 3 seconds, and 5 seconds, respectively, The hole density also increased.

Also, from the image of the scanning electron microscope of FIG. 2, the size of the hole is 20 nm to 126 nm, 20 nm to 55 nm, and 11 nm to 48 nm at the deposition time of 1 second, 3 seconds, and 5 seconds, respectively, based on the hole having a roundness tolerance of about 0.1 or less Size.

FIG. 3 shows photoluminescence (PL) measurement of porous silicon of a photodiode using a graphene / porous silicon fused composite nano structure of an embodiment of the present invention, and FIG. 4 shows Raman spectroscopy ≪ / RTI >

3 and 4 indicate the deposition time of the metal catalyst. Referring to FIGS. 3 and 4, it can be seen that the porosity of the porous silicon layer can be controlled.

More specifically, referring to FIG. 3, it can be seen that as the deposition time of the metal catalyst becomes longer, that is, as the formation time of the metal catalyst becomes longer, the porosity increases. As the porosity of the porous silicon layer increases, The size of the structure becomes smaller and the density becomes larger, so that a peak of optical luminescence is generated near 670 nm due to the quantum confinement effect of the porous silicon.

Also, as shown in FIG. 3, as the deposition time of the metal catalyst increases from 1 second to 5 seconds, the degree of porosity increases and the intensity of the optical luminescence increases.

Referring to FIG. 4, it can be confirmed that the porosity of the porous silicon layer can be controlled by the Raman spectroscopic analysis. Before the metal-assisted chemical etching (as-Si: Si wafer), a Raman peak is observed at 521 cm ^-1 , which represents the Raman peak of bulk silicon.

On the other hand, as the deposition time of the metal catalyst of the porous silicon layer using the metal-catalyzed chemical etching method is increased, the red transition of the Raman peak can be confirmed. The red transition of the Raman peak shows the deposition time of the metal catalyst The porosity is increased.

The prepared porous silicon layer 111 can exhibit not only the absorption band of the bulk silicon but also the light absorption rate up to the ultraviolet band through the quantum confinement effect (QCE) due to the nanostructure present on the surface, And can be utilized in a photodetecting device with improved performance.

The energy band gap can be controlled by controlling the porosity (size / density of the nanostructure) of the porous silicon layer 111, thereby achieving high efficiency up to a wider frequency band.

≪ Preparation of graphene of single layer >

In an embodiment of the present invention, a single layer of graphene was prepared by chemical vapor deposition.

Specifically, the single-layer graphene deposition using chemical vapor deposition is performed by depositing copper (or nickel) to be used as a catalyst layer on a substrate and reacting with a mixed gas of methane and hydrogen at a high temperature to deposit an appropriate amount of carbon in the catalyst layer And the carbon atoms contained in the catalyst layer are crystallized on the surface to form a graphene crystal structure on the metal. Thereafter, a single layer of graphene can be produced by separating the catalyst layer from the substrate by removing the catalyst layer from the synthesized graphene thin film.

More specifically, in the embodiment of the present invention, a 70 mu m copper foil is placed in a quartz tube, the flow rate of methane gas is changed from 10 sccm to 30 sccm, the hydrogen gas is fixed at 10 sccm and the process pressure is set at 3 mTorr, Respectively.

Thereafter, PMMA mixed with poly (methyl methacrylate) and benzene was spin-coated on the synthesized graphene. PMMA was coated on the graphene by using a solution of ammonium persulfate (PMMA) The graphene was grabbed and fixed when it was removed.

Thereafter, the copper foil was removed from the ammonium persulfate solution. The ammonium persulfate solution remaining on the graphene was washed with DI water, and the washed graphene was transferred onto a 300 nm SiO ₂ / Si substrate.

Next, the graphene was transferred to a SiO ₂ / Si substrate and then heat-treated to enhance bonding strength between the substrate and the graphene. After heat treatment, acetone was used to remove the PMMA present on the graphene and heat treated with a rapid thermal processor to remove PMMA residues remaining on the graphene surface to finally produce a single layer of graphene.

Figure 5 illustrates a Raman spectrum for a single layer of graphene in an embodiment of the present invention, Figure 6 is an image of an atomic force microscope (AFM) for a single layer of graphene in an embodiment of the present invention, Figure 7 1 is a graph showing the transmittance of graphene in a single layer of an embodiment of the present invention.

Two-dimensional materials such as graphene have various Raman peaks observed due to strong electron-phonon coupling. Referring to FIG. 5, Raman peaks related to phonon appeared as a G peak in the vicinity of 1580 to 1590 cm ^-1 and a 2D peak in the vicinity of 2700 cm ^-1 with respect to the single-layer graphene according to the embodiment of the present invention.

Generally, the ratio of the G peak to the Raman intensity at the 2D peak (I (G / 2D)) is related to the thickness (number of layers) of the graphene, and the ratio of the D- G)) is closely related to the crystallinity (or the amount of defects) of graphene.

As shown in FIG. 5, the ratio (I (G / 2D)) of the Raman intensity at the G peak to the 2D peak was 0.45 and the ratio of the Raman intensity at the D peak to the G peak was 0.08, It has been confirmed that the inherent single-layer graphene is a high-quality single-layer graphene.

6 is an atomic force microscope (AFM) image for transferring a single layer of graphene to a silicon oxide (SiO ₂ ) substrate according to an embodiment of the present invention and measuring its thickness, Is a single-layer graphene, and the right-hand relatively dark portion represents a silicon oxide substrate.

The graph on the right side of FIG. 6 is a step measured by an atomic force microscope. Referring to FIG. 6, the thickness of a single layer of graphene was measured to be about 0.7 nm. This is because the thickness (about 0.34 nm) of general single-layer graphene is larger than that of nitrogen (N), oxygen (O), and moisture (H ₂ O) between the silicon oxide substrate and the graphene.

The height difference between the graphene and the silicon oxide substrate is similar to the results reported in previous studies (Phys. Solids C 7, No. 3-4, 1251-1255 (2010)), It can be seen that the graphene is a single layer.

7 showing a transmittance of a single layer to graphene according to an embodiment of the present invention, a single layer of graphene according to an embodiment of the present invention has a light transmittance of about 380 nm to 780 nm, which is a visible light wavelength region 95%. Especially, the transmittance was 97% at 550 nm wavelength. The above-mentioned characteristics show a higher transmittance than that of the currently used ITO (tin oxide) as a transparent electrode.

The fused composite nano structure 100 of the photodiode 100 using the graphene / porous silicon fused composite nanostructure 110 of the present invention is formed by combining the single layer of graphene 112 produced as described above, May be formed through a vertical joining process of the silicon layer 111. [

According to an embodiment, the fused composite nanostructure 110 can be manufactured by supporting a single layer of graphene 112 with PMMA, floating in deionized water, and transferring it to the porous silicon layer 111. The transferred graphene is dried in the air and further dried for several hours in the range of 60 ° C to 100 ° C.

Thereafter, an electrode is deposited on the fused composite nanostructure 110, and an electrode is coated on the bottom of the device, thereby fabricating a photodiode using the graphene / porous silicon fused composite nanostructure 110 of the embodiment of the present invention.

In some embodiments, the electrode 120 may be a metal such as gold, silver, and platinum, and the electrode 120 may be formed using any one of a thermal evaporator, an electron beam evaporator, or a DC sputter evaporator. And may be formed by depositing or coating the upper and lower portions of the fused composite nano structure 110.

8 is a scanning electron microscope (SEM) image of a graphene / porous silicon fused composite nanostructure of an embodiment of the present invention.

Referring to FIG. 8, it can be seen that graphene is uniformly transferred to a portion of the porous silicon layer where holes are uniformly distributed.

The photodiode using the graphene / porous silicon fused composite nano structure of the embodiment of the present invention can be applied to various optoelectronic devices such as solar cells, optical sensors, and LEDs.

According to the embodiment, electrons and holes are generated inside a photodiode using a graphene / porous silicon fused composite nano structure by solar energy having various wavelengths, and the generated electrons and holes are formed as a single layer of graphene and porous The silicon layer moves to generate a potential difference, and the present invention can be applied to a solar cell that generates an electromotive force by using the generated potential difference.

In addition, according to embodiments, when light is irradiated after an external voltage is applied to a photodiode using a graphene / porous silicon fused composite nano structure, due to the principle that a photocurrent is generated in the photodiode, And optical sensors that respond to power.

In addition, according to embodiments, when an external voltage is applied to a photodiode using a graphene / porous silicon fused composite nano structure, charges are accumulated between a single layer of graphene and a porous silicon layer, and recombination of electrons and holes it can be applied to LEDs emitting light of a certain frequency band due to recombination.

FIG. 9 is a graph showing energy band diagrams and current-voltage characteristics for a photodiode using a graphene / porous silicon fused composite nano structure according to an embodiment of the present invention.

9B, when the forward bias is applied (V> 0), the energy band of the n-type silicon (n-Si) of the silicon substrate is higher than the energy band of graphene of the single layer Therefore, the electrons in the conduction band of the n-type silicon pass through the conduction band of the porous silicon layer and move to the single-layer graphene to generate a current.

On the other hand, referring to FIG. 9 (c), when a reverse bias is applied (V <0), a high potential barrier is formed between the interface of the single layer graphene and the porous silicon layer, The current does not flow well because electrons are hard to pass through the silicon layer.

9 (d) is a graph showing the current-voltage characteristics of the photodiode using the graphene / porous silicon fused composite nano structure. Referring to FIG. 9 (d) It was confirmed that a typical diode characteristic is shown by flowing current only when a positive voltage is applied to the porous silicon layers according to the deposition time of the metal catalyst.

10 is a graph showing distribution curves of dark current and photocurrent when a photodiode using a graphene / porous silicon fused composite nano structure according to an embodiment of the present invention is used as a photodetecting device.

The time shown in FIG. 10 indicates the deposition time for the metal catalyst in the chemical etching process at the time of manufacturing the porous silicon layer. Referring to FIG. 10, near-ultraviolet (400 nm) In the case of irradiating a photodiode using a porous silicon fused composite nano structure, a relatively large photocurrent was generated because a dark current was very small when a reverse voltage was applied as compared with a case where a forward voltage was applied.

10, the photodiode elements 1s and 3s using the graphene / porous silicon fused composite nanostructure of the present invention (see 1s and 3s) are larger than the graphene / bulk silicon-based diode element (as-Si) A photocurrent can be generated and utilized as a photodetecting device.

FIG. 11 shows a photoreactivity-voltage curve for a photodiode using a graphene / porous silicon fused composite nanostructure according to an embodiment of the present invention.

FIG. 11 (a) shows a photoreactivity-voltage curve of a diode having a graphene / bulk silicon structure, and FIG. 11 (b) The photodiode using a graphene / porous silicon fused composite nano structure includes a porous silicon layer formed by a deposition time of a metal catalyst of 3 seconds.

The photoreactivity is a value obtained by dividing a photocurrent generated in a photodetector by a power, which means the generation of a photocurrent per applied power. The wavelength of the applied light was changed to evaluate the sensitivity of the photodiode using the graphene / porous silicon fused composite nano structure according to the embodiment of the present invention to light having a certain wavelength region according to the applied voltage .

As described above, the porous silicon layer included in the photodiode using the graphene / porous silicon fused composite nano structure according to the embodiment of the present invention includes a nanometer-sized nanostructure, and the quantum confinement Due to the effect (QCE), it has a higher energy band gap than bulk silicon, and can absorb light of high energy close to the ultraviolet ray region.

Referring to FIG. 11, the graphene / bulk silicon diode device (as-Si) shown in FIG. 11 (a) Photodiodes using porous silicon fused composite nanostructures showed high photoreactivity in all wavelength ranges, especially in the near ultraviolet region.

12 is a graph showing a relationship between photo current (dark current) (PC / DC) of a photodiode using a graphene / porous silicon fused composite nano structure according to an embodiment of the present invention, It is compared with a diode of graphene / bulk silicon structure.

Specifically, Fig. 12 (a) shows the ratio of photocurrent to dark current for a diode element having a graphene / bulk silicon layer structure, and Fig. 12 (b) The ratio of the photocurrent to the dark current when the deposition time is 3 seconds for the metal catalyst in FIG.

The ratio of the photocurrent to the dark current (PC / DC) is a numerical value indicating how much photocurrent is generated relative to the dark current. As the photocurrent to dark current ratio (PC / DC) of the photodetector increases, It is possible to detect light relatively easily.

Referring to FIG. 12, the ratio of photocurrent to dark current (PC / DC) is higher than that of a diode device including a graphene / bulk silicon layer relative to each light energy. And higher in photodiodes using composite nanostructures.

Specifically, since the ratio of the photocurrent to the dark current is greater than 4 times in the light having the incident energy of 600 nm, the photodetector using the graphene / porous silicon fused composite nano structure according to the embodiment of the present invention Light can be detected easily.

FIG. 13 is a graph showing a photoreactivity-voltage curve according to deposition time for a metal catalyst in the production of a porous silicon layer for a photodiode using a graphene / porous silicon fused composite nano structure according to an embodiment of the present invention.

More specifically, FIG. 13A shows a case where the deposition time is 1 second for the metal catalyst in the chemical etching process at the time of manufacturing the porous silicon layer, and FIG. 13B shows the case where the deposition time is 5 seconds Respectively.

As described above, the porous silicon layer included in the photodiode using the graphene / porous silicon fused composite nano structure according to the embodiment of the present invention includes a nanometer-sized nanostructure, and the quantum confinement Due to the effect (QCE), it has a higher energy band gap than bulk silicon, and can absorb light of high energy close to the ultraviolet ray region.

The photodiode using the graphene / porous silicon fused composite nano structure according to the embodiment of the present invention showed a high photoreactivity in all the wavelength ranges, and in particular, the photocatalytic activity of the metal catalyst in the chemical etching process during the production of the porous silicon layer The longer the deposition time, the higher the photoreactivity in the near ultraviolet region.

14 is a graph showing the ratio of photocurrent to dark current according to the irradiation wavelength of light for a photodiode using a graphene / porous silicon fused composite nano structure according to an embodiment of the present invention in the process of chemical etching at the time of manufacturing the porous silicon layer The deposition time of the metal catalyst is shown separately.

Referring to FIG. 14, the photocurrent to dark current ratio (PC / DC) of the photodiode using the graphene / porous silicon fused composite nano structure according to the embodiment of the present invention is relatively higher than that of the porous silicon layer The higher the deposition time for the metal catalyst in the chemical etching process, the higher the value.

FIG. 15 is a graph showing a normalized responsivity-wavelength curve according to a deposition time of a metal catalyst in manufacturing a porous silicon layer for a photodiode using a graphene / porous silicon fused composite nano structure according to an embodiment of the present invention. It is.

Referring to FIG. 15, photodiodes using graphene / porous silicon fused composite nanostructures showed greater photoreactivity than graphene / bulk silicon structure diode devices in the near ultraviolet region.

As shown in FIG. 15, when the photodiode using the graphene / porous silicon fused composite nano structure according to the embodiment of the present invention in which the deposition time for the metal catalyst in the production of the porous silicon layer is 3 seconds, Higher photoreactivity.

This is due to the blue shift of the peak position of the photoreactivity to a short wavelength region (high energy) as the deposition time of the porous silicon layer with respect to the metal catalyst becomes longer than 3 seconds.

The photoreactivity of the photodiodes using the graphene / porous silicon fused composite nanostructure according to the embodiments of the present invention described above can be determined by comparing the photoreactivity of the graphene / , S. Nano Lett., 2013, 13, (3), 909-916). Rather, the photoreactivity of the device in the papers reported before the present invention was similar to the photoreactivity of the diode (as-Si) of the graphene / bulk silicon structure shown in FIG.

16 is a graph showing a quantum efficiency versus wavelength curve according to a deposition time of a metal catalyst in the production of a porous silicon layer for a photodiode using a graphene / porous silicon fused composite nano structure according to an embodiment of the present invention.

The quantum efficiency (QE) represents the efficiency with which the absorbed light (or photon) is converted into the photocurrent. Referring to FIG. 16, the quantum efficiency of the porous silicon layer for the photodiode using the graphene / porous silicon fused composite nano- The deposition time of the metal catalyst at the time of manufacture was 3 seconds, which was higher than other deposition times in all regions. In particular, the quantum efficiency was much higher in the near ultraviolet region.

This means that photodiodes using graphene / porous silicon fused composite nanostructures exhibit efficient photodetection characteristics when the deposition time of the metal catalyst in the production of the porous silicon layer is 3 seconds.

17 is a graph showing changes in photocurrent according to time after pulse irradiation in a photodiode using a graphene / porous silicon fused composite nano structure according to an embodiment of the present invention, according to the deposition time of a metal catalyst during the production of the porous silicon layer will be.

Specifically, FIG. 17 (a) illustrates the time-resolved normalized photo current for a photodiode using a graphene / porous silicon fused composite nanostructure by depositing a metal catalyst during the production of a porous silicon layer And FIG. 17 (b) shows the rise time, trising and decay time (tdecay) of the charge carrier derived in (a).

The generation time of the charge carrier implies the time at which the photocurrent increases to the peak at the time-resolved photocurrent curve, and the time at which the charge carrier dissipates means the time during which the photocurrent decreases at the peak.

Time-resolved photocurrent measurements can be used to evaluate the photoreaction rate of a device. The overall reaction rate of a device is the sum of the 'generation time and the extinction time' of the charge carrier, which can determine the rate at which the photodetector responds to light have.

Referring again to FIG. 17, in the case of a graphene / bulk silicon based device, the sum of the 'generation time and the decay time' of the photocurrent is the result (An, XH; Liu, FZ; Jung, YJ; Kar, S. Nano Lett. 2013, 13, (3), 909-916).

However, the photodiodes using the graphene / porous silicon fused composite nanostructure according to the comparative example of the present invention showed relatively fast reaction speed as a few microseconds (μs), and in particular, When the deposition time of the catalyst was 3 seconds, the reaction rate was the fastest.

18 is a flowchart illustrating a method of fabricating a photodiode using a graphene / porous silicon fused composite nanostructure according to an embodiment of the present invention.

Referring to FIG. 18, in step 1810, a porous silicon layer is formed on a silicon substrate through a chemical etching process using a metal as a catalyst.

According to an embodiment, Step 1810 is a method of immersing a silicon substrate in a mixed solution of an etchant of silver nitride (AgNO ₃ ) and hydrofluoric acid (HF) to form silver metal nanoparticles on a silicon substrate, and then hydrofluoric acid (HF) (H ₂ O ₂ ) is selectively etched in contact with the metal nanoparticles, and the remaining metal (silver) is removed with nitric acid (HNO ₃ ) to form a porous silicon layer on the silicon substrate Step &lt; / RTI &gt;

According to another embodiment, metal nanoparticles formed on a silicon substrate may be formed by coating metal particles on a silicon substrate by a thermal deposition method, an electron beam deposition method, or a direct current sputtering method in addition to the chemical coating method using the above-described silver nitride to form a porous silicon layer .

after. In step 1820, a single layer of graphene formed by chemical vapor deposition (CVD) is transferred to the porous silicon layer to form a fused composite nanostructure.

In an embodiment of the present invention, a single layer of graphene can be produced by chemical vapor deposition.

Specifically, the single-layer graphene deposition using chemical vapor deposition is performed by depositing copper (or nickel) to be used as a catalyst layer on a substrate and reacting with a mixed gas of methane and hydrogen at a high temperature to deposit an appropriate amount of carbon in the catalyst layer And the carbon atoms contained in the catalyst layer are crystallized on the surface to form a graphene crystal structure on the metal. Thereafter, a single layer of graphene can be produced by separating the catalyst layer from the substrate by removing the catalyst layer from the synthesized graphene thin film.

In addition, the fused composite nano structure can be manufactured by supporting a single layer of graphene with PMMA, placing it in deionized water, and transferring it to the porous silicon layer.

In step 1830, electrodes are formed on upper and lower portions of the fused composite nano structure, respectively.

According to an embodiment, the electrode may be a metal such as gold, silver, and platinum, and the electrode may be formed using any one of a thermal evaporator, an electron beam evaporator, or a DC sputter evaporator, And may be formed by vapor deposition or coating on the upper and lower portions.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. For example, it is to be understood that the techniques described may be performed in a different order than the described methods, and / or that components of the described systems, structures, devices, circuits, Lt; / RTI &gt; or equivalents, even if it is replaced or replaced.

Therefore, other implementations, other embodiments, and equivalents to the claims are also within the scope of the following claims.

Claims (5)

In the photodiode,
A fused composite nano structure of a vertically bonded structure including a single layer of graphene formed on a porous silicon layer; And
And electrodes formed on upper and lower portions of the fused composite nano structure, respectively,
The energy band gap of the porous silicon layer is controlled by controlling the porosity of the porous silicon layer and the photodiode is controlled to have a deposition time of a metal catalyst in a metal assisted chemical etching (MACE) Wherein the photoreactivity to the near ultraviolet region is controlled through control
Photodiode using graphene / porous silicon fused composite nanostructure. The method according to claim 1,
Wherein the porous silicon layer is formed through the chemical etching method using a metal as a catalyst on a silicon substrate. 2. A photodiode using the graphene / porous silicon fused composite nano structure. The method according to claim 1,
The single-layer graphene is formed by reacting a catalyst layer with a carbon-containing mixed gas and depositing the catalyst layer on the catalyst layer by a chemical vapor deposition (CVD)
Wherein the fused composite nano structure is formed through a vertically bonding process between the formed single-layer graphene and the porous silicon layer. The method according to claim 1,
Wherein the photodiode controls the energy band gap of the fused composite nanostructure through control of the porosity of the porous silicon layer to have a high optical efficiency in a wider frequency band in bulk silicon. Photodiode using fin / porous silicon fused composite nanostructure. In the photodiode manufacturing method,
Forming a porous silicon layer on a silicon substrate through a metal-assisted chemical etching (MACE) method using a metal as a catalyst;
Transferring a single layer of graphene formed by a chemical vapor deposition (CVD) method to the porous silicon layer to form a fused composite nanostructure; And
And forming electrodes on upper and lower portions of the fused composite nano structure, respectively,
The energy band gap of the porous silicon layer is controlled by controlling the porosity of the porous silicon layer and the photodiode is controlled in the near ultraviolet region by controlling the deposition time of the metal catalyst in the chemical etching method. Characterized in that the photoreactivity is controlled
(Method for fabricating photodiode using graphene / porous silicon fused composite nanostructure).

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