KR101822720B1 - Photonic device - Google Patents

Abstract

The present invention relates to an optical element. An optical device according to an embodiment of the present invention includes a first layer including a first material and having a first band gap and a first layer stacked on one or both surfaces of the first layer, And a second layer having a second band gap different from the first band gap.
The present invention uses a method of controlling the intrinsic bandgap energy of a material by controlling the porosity of the same material. The characteristics of the polycrystalline or amorphous material, not a single crystal material, have been confirmed, It is possible.

Description

PHOTONIC DEVICE

The present invention relates to an optical element, and more particularly, to an optical element which is selected from the group consisting of a light emitting element (LED), a light receiving element (solar cell), a photodetector element (PD) and an optical modulator It can be one.

Bandgap energy is a typical characteristic of semiconducting materials and is an important material constant closely related to electrical properties as well as to the properties of semiconductors such as light absorption, transmission and luminescence.

Here, the term "material constant" means that the band gap energy of a material has a constant value, which is determined by the constituent atoms of the material, its composition, and crystal structure.

Therefore, it is not easy to arbitrarily adjust the band gap energy of the same material, and it is a general method to make a compound with various materials and change the band gap energy according to the composition. Until now, it is not known how to use different materials with the same crystal structure to have different band gaps.

It is an object of the present invention to provide various optical elements to which the method of adjusting the inherent band gap energy of the material by controlling the porosity of the same material is applied.

In order to achieve the above object, an optical device according to an embodiment of the present invention includes a first layer including a first material, a first layer having a first band gap, and a first layer stacked on one surface or both surfaces of the first layer, 1 material, and a second layer having a second band gap different from the first band gap.

The porosity of the first layer and the porosity of the second layer may be different from each other

Wherein when the porosity of the first layer is less than the porosity of the second layer, the first band gap of the first layer is larger than the second band gap of the second layer, and the refractive index of the first layer is the first can be larger _{and, I (222) / I (} 400) value of the first layer is greater than _{I (222) / I (400} ) value of the second layer than the refractive index of the second layer.

The first layer and the second layer may be formed to have different porosities by using an oblique angle deposition (OAD) method.

The angle formed between the flux line of the first material for forming the first layer and the waterline of the substrate and the angle between the flux line of the first material for forming the second layer and the waterline of the substrate may be different from each other.

As the angle between the flux line of the material and the waterline of the substrate increases, the bandgap decreases, the refractive index decreases, and the I ₍₂₂₂₎ / I ₍₄₀₀₎ value tends to decrease.

As the angle between the flux line of the material and the waterline of the substrate increases from 0 to 60 degrees, the bandgap decreases from 4.02 eV to 3.87 eV, the refractive index decreases from 1.95 to 1.76, I ₍₂₂₂₎ / The I ₍₄₀₀₎ value can be reduced from 3.14 to 1.90.

The optical device may be any one selected from the group consisting of a light emitting device (LED), a light receiving device (solar cell), a photodetector device (PD), and an optical modulator.

The present invention uses a method of controlling the intrinsic bandgap energy of a material by controlling the porosity of the same material. The characteristics of the polycrystalline or amorphous material, not a single crystal material, have been confirmed, It is possible.

FIG. 1 is a graph showing an example of the change in porosity of ITO according to the deposition angle when an ITO thin film is deposited by using the oblique deposition method.
FIGS. 2 to 4 are optical microscope photographs of a sample obtained by depositing an ITO thin film on a glass substrate, a sapphire substrate, and a silicon wafer, respectively, using an oblique deposition method.
FIG. 5 shows a result of measuring the transmittance in order to confirm the band gap energy of the ITO thin film.
6 to 9 are scanning electron microscope (SEM) photographs of ITO thin films formed at oblique angle of 0, 10, 50 and 60, respectively.
10 is a graph showing the band gap energy of each ITO thin film obtained by the Tauc method.
11 is a graph showing XRD (X-ray diffraction) measurement results of an ITO thin film formed on a glass substrate.
12 is a schematic view showing the case where the laminate of the present invention is applied to a light detecting element.

Hereinafter, the present invention will be described in detail.

An optical device according to an embodiment of the present invention includes a first layer including a first material and having a first band gap and a first layer stacked on one or both surfaces of the first layer, And a second layer having a second band gap different from the first band gap.

The optical device uses a method of controlling the intrinsic band gap energy of the material by controlling the porosity of the same material. In addition, the method of controlling the band gap energy by controlling the porosity of the same material as described above can be applied not only to single crystal materials but also to polycrystalline or amorphous materials.

Accordingly, the first layer and the second layer may be made of materials having the same crystal structure, and the porosity of the first layer and the porosity of the second layer may be different from each other.

Wherein when the porosity of the first layer is less than the porosity of the second layer, the first band gap of the first layer is greater than the second band gap of the second layer, the refractive index is larger, the second _{I (222) / I (400} ) value of the first layer may have greater relation than _{I (222) / I (400} ) value of the second layer than the refractive index of the second layer have.

As a method for controlling the porosity of the first layer and the second layer made of the same first material, various known methods are applicable. For example, the first layer and the second layer may be formed by oblique angle deposition , And OAD). However, the present invention is not limited thereto.

The oblique deposition method is a method of depositing the substrate at a predetermined inclination angle between the waterline of the substrate and the flux line direction of the deposition material. Due to the surface diffusion of the deposition material and the self-shadowing effect caused by the initial deposition material, A thin film having high porosity can be formed.

The angle formed by the flux line of the first material for forming the first layer and the waterline of the substrate to form the first layer and the angle formed by the angle formed between the flux line of the first material and the water line for forming the second layer, By making the angle between the flux line of the first material and the waterline of the substrate to be different from each other, the band gap between the first layer and the second layer can be adjusted to be different from each other.

This is because there is the porosity to obtain a high thin film, depending on the porosity increases and decreases is the band gap, the refractive index is reduced, I ₍₂₂₂₎ as the angle at which the repair of the flux lines and the substrate of the material of increasing / The I ₍₄₀₀₎ value can be made using a tendency to decrease.

More specifically, as the angle between the flux line of the material and the waterline of the substrate increases from 0 to 60, the bandgap decreases from 4.02 eV to 3.87 eV, the refractive index decreases from 1.95 to 1.76, and I ₍₂₂₂₎ / I ₍₄₀₀₎ value can be reduced from 3.14 to 1.90.

This is in contrast to the conventional technology (for example, GaN and AlGaN, GaAs and AlGaAs) that a material with a low refractive index generally has a high bandgap, And that the band gaps are simultaneously reduced even when the refractive index is reduced, as opposed to the generally known relationship.

This is thought to be due to the change in the crystallographic structure of the first or second layer depending on the degree of porosity. That is, the I ₍₂₂₂₎ / I ₍₄₀₀₎ value is known to be a parameter indicating crystal quality. When the angle of the oblique deposition is 0, the I ₍₂₂₂₎ / I ₍₄₀₀₎ 3.14, and the value of I ₍₂₂₂₎ / I ₍₄₀₀₎ is about 1.90 when the angle of the oblique deposition is 60 DEG. As a result, it can be seen that the angle of the oblique deposition method affects the microstructure and optical characteristics of the ITO thin film.

Specifically, as the angle of the oblique deposition increases, the porosity of the first layer or the second layer tends to increase, but the refractive index and the bandgap decrease. As the angle of the oblique deposition increases, the first layer or the second layer is preferentially grown in the <100> plane direction, and the strain at the interface between the first layer or the second layer and the substrate is Resulting in a decrease in the band gap.

The inclination angle is less than 90 deg., Preferably greater than 10 deg., Less than 90 deg., And more preferably from 10 deg. To 60 deg. In this case, a shadow region is initially formed on the back side of the island-shaped initial deposition material formed on the upper surface of the substrate, and then the deposited material is deposited only on the initial deposition material without being deposited in the shadow region , And a nano rod are formed.

When the thin film is formed by the oblique deposition method, the first layer and the second layer formed according to the rotation speed, direction and inclination angle of the substrate are formed of nano helix, nano rod, a porous nano structure having an oblique nano rod, a nano wire, a nano ribbon, a nano spring, and a nano cone.

As a specific method of the oblique deposition, an electron beam deposition method, a sputter deposition method, or a pulsed laser deposition method, which is a physical vapor deposition method, may be used.

The first material to the first layer and comprising the second layer is _{TiO x, SiC, GaN, ZnO} , GaP, SiN x, ZrO 2, AlN, Al 2 O 3, MgO, SiO 2, CaF 2, MgF ₂ , Indium Tin Oxide (ITO), Zinc-doped Indium Tin Oxide (ZITO), Zinc Indium Oxide (GIO), Gallium Indium Oxide (GIO), Zinc Tin Oxide (FTO), Fluorine- (Al-doped Zinc Oxide), GZO (Gallium-doped Zinc Oxide), In ₄ Sn ₃ O ₁₂ and Zn _1-x Mg _x O (Zinc Magnesium Oxide, 0? _X? 1) May be any one selected, and may preferably be ITO.

When the first layer and the second layer are repeatedly stacked alternately, the efficiency of the stacked body may be further improved. have.

The stacked body may play various roles such as transmission, absorption, modulation, interference, diffraction, or light emission depending on the structure of the optical element and the position in the optical element. Accordingly, the optical device may be any one selected from the group consisting of a light emitting device, a solar cell, a photodetector, and an optical modulator, Serve as an active layer in the optical element, and may serve as an auxiliary functional layer such as an optical filter.

Specifically, the optical device may further include a first electrode and a second electrode that are disposed apart from each other in addition to the stacked structure, and a semiconductor layer that is selectively disposed to contact the electrodes.

In addition, the optical device may further include a substrate on which the electrode and the like are formed. The substrate may refer to a conventional wafer for fabricating the optical element. Examples of such a substrate include a sapphire substrate, Al ₂ O ₃ , SiC, ZnO, Si, GaAs, GaP, LiAl ₂ O ₃ , BN, AlN and GaN.

The semiconductor layer of the optical element is a layer in which electricity injected through the first and second electrodes is converted into light to emit light. Such a semiconductor layer may use any material known in the art without restriction depending on the type of optical device. Examples of the optical devices that can be used in the optical device include various types of optical devices such as a light emitting diode (LED), a semiconductor laser (LD), or a solid laser ) And the like.

In one example, if the optical device is a light emitting device (LED), the semiconductor layer may include an N-type semiconductor layer, an active layer, and a P-type semiconductor layer. The method of forming each semiconductor layer is well known in the art to which the present invention belongs.

Examples of the N-type semiconductor layer include nitrides such as Si-doped GaN, InN, and AlN (III-V) layers and compounds obtained by mixing these nitrides in a certain ratio, for example, AlGaN. Meanwhile, the optical device may form a buffer layer including AlN or GaN to mitigate lattice mismatching with the substrate before forming the N-type semiconductor layer on the substrate. In addition, an undoped layer may be formed on the buffer layer. The undoped layer may be formed of an undoped layer, for example, an undoped GaN layer.

The active layer has a predetermined bandgap and is a region where quantum wells are formed to recombine electrons and holes, and the laminate can be used as the active layer. When the active layer is not the stacked layer, the active layer may be formed of a multiple quantum well structure (MQW) in which a plurality of quantum well layers and barrier layers are repeatedly stacked. For example, the active layer of the multiple quantum well structure may be formed by repeatedly laminating InGaN and GaN, and may be formed by repeatedly laminating AlGaN and GaN. Since the emission wavelength generated by the combination of electrons and holes changes according to the kind of the material forming the active layer, the semiconductor material included in the active layer can be controlled according to the target wavelength. That is, the wavelength of light generated in the active layer can be variously controlled by controlling the amount of In in the quantum well layer. For example, by increasing the In content of the InGaN quantum well layer, the bandgap is reduced and the emission wavelength is lengthened to emit light from the ultraviolet region to all visible light regions such as blue, green, and red . Alternatively, the emission wavelength can be changed by controlling the thickness of the quantum well layer. For example, increasing the thickness of the InGaN quantum well layer can reduce the band gap and emit red light. In addition, a white light can be obtained by using a multilayer structure of a quantum well layer. That is, when blue light, green light, and red light are configured by adjusting the In content of each layer of at least one layer of the multi-layer InGaN quantum well layer, white light as a whole can be obtained.

The P-type semiconductor layer may be a semiconductor layer doped with a P-type impurity, thereby supplying holes to the active layer. For example, the P-type semiconductor layer may be formed of a nitride semiconductor such as GaN, InN, AlN (III-V) doped with Mg, and a compound in which these nitride are mixed at a predetermined ratio, for example, various semiconductors including AlGaN or AlInGaN Materials can be used. The P-type semiconductor layer may be formed as a single layer or as a multi-layered structure.

The first and second electrodes may also use materials known in the art without limitation, depending on the type of optical element.

In one example, if the optical device is a light emitting device, the first electrode may be an N-type electrode, and the second electrode may be a P-type electrode. Methods for forming the N-type and P-type electrodes are also well known in the art.

The N-type electrode and the P-type electrode may be formed using a conductive material. For example, a metal material such as Ti, Cr, Au, Al, Ni, Ag, or Zn, Or may be formed in multiple layers. Here, the P-type electrode may be formed in a plurality of electrode patterns according to an electrode pattern for current diffusion. A transparent electrode may be formed on the P-type semiconductor layer to uniformly supply power to the P-type semiconductor layer through the P-type electrode. Since the P-type semiconductor layer has a resistance of several ohms, for example, and has a horizontal resistance of, for example, several hundreds of k ?, most current flows in the vertical direction without flowing current in the horizontal direction. Therefore, when power is locally applied to the P-type semiconductor layer, a current does not flow through the P-type semiconductor layer as a whole, so that a transparent electrode is formed so that current can flow through the P-type semiconductor layer as a whole. The transparent electrode may be formed of a transparent conductive material, for example, ITO, IZO, ZnO, RuO _x , TiO _x , IrO _x , or the like so that light generated in the active layer can be well transmitted.

In this specification, the first electrode and the second electrode mean an electrode capable of applying a voltage to the semiconductor layer in a pair. Accordingly, the P-type electrode and the transparent electrode may be classified as a second electrode, and the conductive-nonconductive phase transition material may be formed on the P-type electrode, the transparent electrode, or both.

The optical element may further include a reflective layer formed on the P-type semiconductor layer so as to reflect upwardly the light emitted toward the P-type electrode in addition to the transparent electrode. The reflective layer is formed of a material having a high reflectance while lowering the contact resistance with the P-type semiconductor layer having a relatively large energy band gap. For example, the reflective layer may be formed of Ag, Ni, Al, Ph, Pd, Ir, Ru, Mg, Zn, Pt, Au and alloys thereof and preferably has a reflectance of 70% or more.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

(Experimental Example 1)

FIG. 1 is a graph showing an example of changes in porosity and refractive index of ITO according to a deposition angle when an ITO thin film is deposited using an oblique deposition method.

Referring to FIG. 1, the degree of porosity tends to increase as the angle of the oblique deposition increases, but the refractive index decreases. At this time, the maximum refractive index was 1.76 at an angle of 60 degrees for the oblique deposition method.

(Experimental Example 2)

FIGS. 2 to 4 are optical microscope photographs of a sample obtained by depositing an ITO thin film on a glass substrate, a sapphire substrate, and a silicon wafer, respectively, using an oblique deposition method.

Specifically, in order to confirm the porosity of the ITO thin film according to the deposition angle, 0 °, 10 °, 20 °, 30 °, 40 °, and 50 ° are formed on the glass substrate, the sapphire substrate, Six ITO thin films were deposited at different angles of ° and 60 °. At this time, the oblique deposition method uses e-beam evaporation.

Referring to FIGS. 2 to 4, different colors of the surface can be primarily confirmed only by the difference in the angle under the same deposition conditions, which is considered to be caused by the difference in the refractive index depending on the deposition angle.

(Experimental Example 3)

FIG. 5 is a graph illustrating the transmittance of the ITO thin film prepared in Experimental Example 2 using a JASCO spectrometer system to determine the band gap energy.

Referring to FIG. 5, it can be seen that as the angle of the oblique deposition increases, the transmittance peaks and the valleys are shifted toward a shorter wavelength.

6 to 9 are scanning electron microscope (SEM) photographs of ITO thin films formed at oblique angle of 0, 10, 50 and 60, respectively. Referring to FIGS. 6 to 9, when the angle of the oblique deposition is 0 ° and 10 °, it can be seen that the surface has a soft surface and a non-characteristic cross section. However, when the angle of the oblique deposition is 50 ° and 60 °, And the cross-sectional shape can be confirmed. It can be seen that the change of the microstructure of the ITO thin film is directly related to the porosity of the thin film, and it also affects the optical characteristics such as the refractive index of the thin film.

10 is a graph showing the band gap energy of each ITO thin film obtained by the Tauc method using the result of the transmission of FIG.

Referring to FIG. 10, in the case of dense ITO, the band gap energy at a deposition angle of 0 ° is 4.02 eV, but at a deposition angle of 60 °, the band gap energy varies to 3.87 eV. This difference is a large difference of 10 nm in terms of wavelength. That is, the bandgap decreases as the angle of the oblique deposition is increased.

(Experimental Example 4)

11 is a graph showing XRD (X-ray diffraction) measurement results of an ITO thin film formed on a glass substrate.

Specifically, in order to observe the change in potential microstructure during the ITO deposition, an oblique deposition method was used to observe the change of the microstructure during the ITO deposition, and the angle of 0 °, 10 °, 20 °, 30 °, 40 °, Six ITO thin films were deposited at different angles.

Referring to FIG. 11, it can be seen that the ratio of the (222) peak intensity I ₍₂₂₂ ) to the (400) peak intensity I ₍₄₀₀₎ varies relatively greatly depending on the angle of the oblique deposition method. That is, the I ₍₂₂₂₎ / I ₍₄₀₀₎ value is known to be a parameter indicating crystal quality. When the angle of the oblique deposition is 0, the I ₍₂₂₂₎ / I ₍₄₀₀₎ 3.14, and the value of I ₍₂₂₂₎ / I ₍₄₀₀₎ is about 1.90 at an angle of the oblique deposition of 60 degrees.

This indicates that most of the layers parallel to the ITO thin film surface are aligned in the <100> plane. The XRD results indicate that the microstructure of the ITO thin film is highly dependent on the angle of the oblique deposition method.

Referring to the above results, it can be seen that the angle of the oblique deposition method affects the microstructure and optical characteristics of the ITO thin film. Specifically, as the angle of the oblique deposition increases, the porosity of the ITO thin film tends to increase, but the refractive index and the band gap decrease. This is because as the angle of the oblique deposition increases, the ITO thin film grows preferentially in the <100> plane direction, and strain at the interface between the ITO thin film and the substrate increases, resulting in a decrease in band gap This is contrary to the conventional technical sense that a material having a low refractive index generally has a high bandgap, and the present invention is not limited to the fact that by controlling the porosity of the same material, a change in the band gap as well as a change in refractive index And the bandgap is reduced at the same time even if the refractive index is decreased, as opposed to the generally known relationship. It is considered that the crystallographic structure of the thin film varies depending on the degree of the porosity, as confirmed by the change in the I ₍₂₂₂₎ / I ₍₄₀₀₎ value.

(Example 1: an optical detector and a sensor)

7, when the laminate of the present invention is used as the light absorbing layer between the n-type semiconductor and the p-type semiconductor, in the two layers made of the same material but not the bonding of the different materials, It is possible to selectively detect the wavelength band corresponding to the difference between the gap energy and the band gap energy of the high density material.

The above-mentioned laminate can be produced by continuously depositing the same material while changing only the deposition angle. If the laminate is used as an absorbing layer, selective light detection or sensing in a wavelength band is possible.

( Example  2: Low contact resistance element)

In order to make a good ohmic junction at the interface between metal and semiconductor, a small bandgap energy material is advantageous because it can increase the degree of doping and the small energy material has the advantage of lowering the energy level spontaneously on the semiconductor surface Because.

By forming the same material on the surface of the semiconductor by varying the angle, a contact resistance can be made lower than that of a conventional dense material.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit of the invention as set forth in the appended claims. The present invention can be variously modified and changed by those skilled in the art, and it is also within the scope of the present invention.

Claims (8)

A first layer comprising a first material, the first layer having a first band gap, and
A second layer stacked on one or both sides of the first layer, the second layer including the first material and having a second band gap different from the first band gap;
And a laminate comprising the laminate,
Wherein when the porosity of the first layer is less than the porosity of the second layer, the first band gap of the first layer is larger than the second band gap of the second layer, and the refractive index of the first layer is Is greater than the refractive index of the second layer. The method according to claim 1,
Wherein the porosity of the first layer and the porosity of the second layer are different from each other. The method according to claim 1,
If the porosity of the first layer is less than the porosity of the second layer,
The optical element _{I (222) / I (400} ) value of the first layer is greater than _{I (222) / I (400} ) value of the second layer. The method according to claim 1,
Wherein the first layer and the second layer are formed to have different porosities using an oblique angle deposition (OAD) method. 5. The method of claim 4,
Wherein an angle formed between the flux line of the first material for forming the first layer and the waterline of the substrate and the angle formed by the flux line of the first material for forming the second layer and the waterline of the substrate are different from each other, . 6. The method of claim 5,
Wherein the bandgap decreases as the angle between the flux line of the material and the waterline of the substrate increases, the refractive index decreases, and the I ₍₂₂₂₎ / I ₍₄₀₀₎ value tends to decrease. The method according to claim 6,
As the angle between the flux line of the material and the waterline of the substrate increases from 0 to 60 degrees, the bandgap decreases from 4.02 eV to 3.87 eV, the refractive index decreases from 1.95 to 1.76, I ₍₂₂₂₎ / Wherein the I ₍₄₀₀₎ value is reduced from 3.14 to 1.90. The method according to claim 1,
Wherein the optical element is any one selected from the group consisting of a light emitting element (LED), a light receiving element (solar cell), a photodetector element (PD), and an optical modulator.

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