KR100945989B1 - Semiconductor light emitting device using surface plasmon resonance - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device using surface plasmon resonance, and the present invention relates to a first conductive layer and a second conductive semiconductor layer formed between the first and second conductive semiconductor layers. It is formed on the exposed surface of the semiconductor layer, and is spaced apart from the active layer by a distance that the surface plasmon present at the interface with the second conductivity-type semiconductor layer by the light emitted from the active layer can be excited, the excitation Provided is a semiconductor light emitting device using surface plasmon resonance comprising a metal layer having a periodic concave-convex structure formed at the interface such that the surface plasmon is discharged toward the active layer.

According to the present invention, the light emitted from the quantum well layer excites the surface plasmon of the metal layer and emits it to the outside, thereby obtaining a semiconductor light emitting device using surface plasmon resonance with improved light extraction efficiency.

Light emitting element, surface plasmon resonance, irregularities

Description

Semiconductor light emitting device using surface plasmon resonance {SEMICONDUCTOR LIGHT EMITTING DEVICE USING SURFACE PLASMON RESONANCE}

1 is a cross-sectional view showing a semiconductor light emitting device according to an embodiment of the present invention.

2A and 2B show a depletion region according to the junction structure of n-type and p-type semiconductor layers.

3A to 3D show various uneven structures that can be employed as an interface between the p-type semiconductor layer and the metal layer according to the embodiment of FIG.

4 is a cross-sectional view showing a semiconductor light emitting device according to another embodiment of the present invention.

<Code Description of Main Parts of Drawing>

11,41: sapphire substrate 12,42: buffer layer

13,43: p-type semiconductor layer 14,44: active layer

15,15`, 15``, 45: n-type semiconductor layer 16,46: metal layer

47: conductive substrate

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device, and more particularly, to a semiconductor light emitting device using surface plasmon resonance, in which light extraction efficiency is improved by excitation of the surface plasmon of the metal layer and emission thereof to the outside.

BACKGROUND A light emitting diode (LED) is a semiconductor device capable of generating light of various colors based on recombination of electrons and holes at a junction portion of a p and n type semiconductor when current is applied thereto. These LEDs have a number of advantages over filament based light emitting devices, such as long life, low power, excellent initial driving characteristics, high vibration resistance, and high tolerance for repetitive power interruptions. In recent years, group III nitride semiconductor light emitting devices capable of emitting light in a blue short wavelength region have been in the spotlight.

Despite these advantages, however, semiconductor light emitting devices, especially nitride semiconductor light emitting devices, exhibit low light extraction efficiency due to the large difference in refractive index between gallium nitride (refractive index of about 2.4) and external materials (typically refractive index of about 1.0 as air). This is because a large part of the light emitted from the light emitting device is totally reflected and disappeared without being emitted to the outside.

In order to solve this problem, a method of forming an uneven structure on the surface of the semiconductor layer generally present in the direction of light emission has been used. That is, the path of the light is changed by the uneven structure formed in the direction of light emission, thereby reducing the amount of total reflection.

However, the method of improving the light extraction efficiency by the concave-convex structure is such that the light generated from the inside is well emitted to the outside, and thus does not increase the generation probability of the light inside the light emitting device, that is, the internal quantum efficiency.

Therefore, by improving the internal quantum efficiency at the same time with the probability of emitting the generated light to the outside, a method for improving the light extraction efficiency is required.

The present invention is to solve the above problems of the prior art, the object is that the light emitted from the quantum well layer excites the surface plasmon of the metal layer and emits it to the outside, semiconductor light emission using the surface plasmon resonance is improved light extraction efficiency It is to provide an element.

In order to solve the above technical problem, the present invention,

The first and second conductive semiconductor layers, the active layer formed between the first and second conductive semiconductor layers, and the exposed surface of the second conductive semiconductor layer, wherein the light is emitted from the active layer. The surface plasmon present at the interface with the second conductivity-type semiconductor layer is spaced apart from the active layer by a distance that can be excited, and the periodic concave-convex structure formed at the interface so that the excited surface plasmon is released in the direction of the active layer Provided is a semiconductor light emitting device using surface plasmon resonance comprising a metal layer.

Preferably, the first conductive semiconductor layer may be a p-type semiconductor layer, and the second conductive semiconductor layer may be an n-type semiconductor layer.

In this case, the predetermined distance is a distance at which the surface plasmon present at the interface with the second conductivity-type semiconductor layer can be excited by the light emitted from the active layer. In this case, the distance between the concave portion of the uneven structure and the active layer is It is preferable that it is 10-50 nm.

Preferably, the first conductive semiconductor layer, the active layer and the second conductive semiconductor layer may be formed of nitride to emit short wavelength light such as blue light.

The semiconductor device may further include a buffer layer formed on a lower surface of the first conductivity type semiconductor layer.

On the other hand, the metal layer is made of a material selected from the group consisting of Ag, Al, Au and their alloys is suitable to use the surface plasmon phenomenon.

In relation to the concave-convex structure, the height of the concave-convex structure is preferably 10 to 500 nm, the period of the concave-convex structure is preferably 10 to 1000 nm, the width of the convex portion of the concave-convex structure is 10 to 1000 nm.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention.

1 is a cross-sectional view showing a semiconductor light emitting device according to an embodiment of the present invention.

Referring to FIG. 1, the semiconductor light emitting device 10 according to the present embodiment may include a buffer layer 12, a p-type semiconductor layer 13, and an active layer sequentially formed on the sapphire substrate 11 and the sapphire substrate 11. 14), the n-type semiconductor layer 15, the metal layer 16, and the p-side and n-side electrodes 17a and 17b are provided. As described below, the semiconductor light emitting device 10 may have a surface plasmon wave that is emitted to the outside through the sapphire substrate 11 having light transmissivity.

Hereinafter, components constituting the semiconductor light emitting device 10 will be described.

The sapphire substrate 11 is a crystal having hexagonal-Rhombo R3c symmetry and has an uneven constant of c. The orientation plane includes a C (0001) plane, an A (1120) plane, an R (1102) plane, and the like. In the case of the C surface of the sapphire substrate 11, since the growth of the nitride film is relatively easy and stable at a high temperature, it is mainly used as a substrate for nitride growth.

However, in the present embodiment, but the present invention uses the sapphire substrate as a transparent substrate for single crystal growth is not limited to, SiC, Si, MgAl ₂ O, MgO, LiAlO _2, LiGaO ₂ Substrates made of materials such as or the like may be employed.

The buffer layer 12 is formed between the sapphire substrate 11 and the p-type semiconductor layer 13 to reduce stress of the semiconductor layers formed thereon. In general, the buffer layer 12 is preferably a low temperature nucleus growth layer such as AlN or GaN.

The p-type semiconductor layer 13 and the n-type semiconductor layer 15 may be a nitride semiconductor for emitting light of a short wavelength, specifically, Al _x In _y Ga _(1-xy) N (where 0≤ n-type impurity and p-type impurity having x ≦ 1, 0 ≦ y ≦ 1, and 0 ≦ x + y ≦ 1). Representative materials include GaN, AlGaN, InGaN. Here, Si, Ge, Se, Te or C may be used as the n-type impurity, and the p-type impurity may be representative of Mg, Zn or Be.

In particular, the present embodiment is characterized in that the p-type semiconductor layer 13 is grown on the sapphire substrate 11 before the n-type semiconductor 15. Accordingly, the following advantages can be obtained.

First, as described later, in order to obtain a surface plasmon resonance effect, since the distance from the uneven structure formed at the interface between the n-type semiconductor layer 15 and the metal layer 16 to the active layer 14 should be within a predetermined distance, the n-type It is preferable that the thickness of the semiconductor layer 15 is thin. Here, the distance from the uneven structure to the active layer 14 refers to the distance from the recess of the uneven structure to the active lift 14.

If the n-type semiconductor layer is first grown on the sapphire substrate 11, a p-type semiconductor layer is formed between the active layer 14 and the metal layer 16, and is formed by thinly forming the p-type semiconductor layer. The problem is described with reference to FIG.

2A and 2B show a depletion region D according to a junction structure of n-type and p-type semiconductor layers.

In general, in the junction structure of n-type and p-type semiconductor layers, charge carriers (electrons and holes) diffuse into each other on both sides of the junction region, whereby the n-type and p-type semiconductor layers adjacent to the junction region are charged. The concentration of the carrier is lowered. The depletion region D having such a low concentration of charge carriers tends to be narrower as the doping concentration of impurities is higher. Therefore, it can be seen that the depletion region of the p-type semiconductor layer P, which is thinner, is wider than that of the n-type semiconductor layer N, as shown in FIG. 2A. This is because, for example, in the case of GaN, the doping concentration of the n-type semiconductor layer N is about 10 times higher than that of the p-type semiconductor layer.

As such, when the n-type semiconductor layer is first grown on the sapphire substrate and then the p-type semiconductor layer is thinly grown for surface plasmon resonance, most of the regions in the p-type semiconductor layer may be depleted. There is a fear that the luminous efficiency is significantly lowered.

On the other hand, as shown in FIG. 2B, when the thickness of the p-type semiconductor layer is thicker than the n-type semiconductor layer, the p-type semiconductor layer is sufficiently depleted in the p-type semiconductor layer despite the depletion region having a thickness similar to that of FIG. You can see what you can secure. This corresponds to the case where the p-type semiconductor layer is preferentially grown on the n-type semiconductor layer as in the embodiment of FIG.

In addition to the above-described matters, when the p-type nitride semiconductor layer 13 is first grown as in the present embodiment, there is an advantage in that an uneven structure for easily radiating surface plasmon waves to the outside is easily formed, which will be described later.

However, in the present invention, the positions of the p-type and n-type semiconductor layers 13 and 15 are not limited to the present embodiment, and the performance may be deteriorated, but the n-type semiconductor layer 13 is used to use the surface plasmon phenomenon. It may also be possible to grow first on the substrate.

The active layer 14 is formed between the p-type semiconductor layer 13 and the n-type semiconductor layer 15 and is an area where electrons and holes are recombined. In general, the active layer 14 is a layer for emitting visible light (wavelength range of about 350 ~ 680nm), may have a single or multiple quantum well structure.

Meanwhile, n-type and p-type semiconductor layers, active layers, and buffer layers formed on the sapphire substrate 11 are known as organometallic vapor deposition (MOCVD), molecular beam growth (MBE), hybrid vapor deposition (HVPE), and the like. A semiconductor layer growth process can be used.

The metal layer 16 employed in the present embodiment is formed on the n-type semiconductor layer 15, and as shown in FIG. 1, a cycle is formed at an interface between the metal layer 16 and the n-type semiconductor layer 15. Irregular structure is formed. This is to convert the surface plasmon wave present at the interface into light that can be radiated to the outside of the semiconductor light emitting device 10, in particular, toward the active layer 14.

This will be described in more detail as follows.

Surface plasmons are collective charge density oscillations of electrons occurring on the metal thin film surface, and the surface plasmon waves generated are surface electromagnetic waves propagating along the interface between the metal and the dielectric. On the other hand, as a photo-electron effect in metals such as gold (Au), when light of a specific wavelength is irradiated onto the metal, a resonance phenomenon occurs in which most of the light energy is transferred to free electrons. As a result, the phenomenon that occurs when surface electromagnetic waves occur is called Surface Plasmon Resonance.

The conditions for the surface plasmon resonance occurs, such as the wavelength of the incident light, the refractive index of the material in contact with the metal, and the like, in particular, the distance between the light emitting layer and the metal thin film is very important. That is, surface plasmon resonance may occur when the distance between the light emitting layer and the metal thin film is less than or equal to a predetermined distance. In this embodiment, the distance between the active layer 14 and the metal layer 16 corresponds to this.

Therefore, in this embodiment, in order to use surface plasmon resonance, the distance between the active layer 14 and the metal layer 16, that is, the distance from the active layer 14 to the concave portion of the uneven structure is within a predetermined distance, It is preferable that it is 10-50 nm specifically ,. The lower limit of the distance is set to 10 nm because most of the light in the metal layer 16 may be lost in the form of heat when the distance from the active layer 14 to the uneven structure is too close.

On the other hand, the surface plasmon wave formed by being excited by the incident light as described above is characterized in that it does not propagate from the metal surface to the inside or the outside when the metal layer has a flat surface. In this way, if the surface plasmon wave is not emitted to the outside but trapped inside the metal, the luminous efficiency will be significantly lowered. Therefore, it is necessary to emit the surface plasmon wave to the outside as light.

To this end, in this embodiment, an uneven structure formed at the interface between the n-type semiconductor layer 15 and the metal layer 16 is adopted.

In order to emit surface plasmon waves to the outside, the wave vector of the light and the wave vector of the surface plasmon must be matched in the n-type semiconductor layer 15, which is an interface between the n-type semiconductor layer 15 and the metal layer 16. It can be achieved by the uneven structure formed in the.

3A to 3C show a form that can be employed as an uneven structure that can achieve this purpose.

First, Fig. 3A is a perspective view showing the n-type semiconductor layer 25 in which the uneven structure is formed (other adjacent layers are not shown).

The n-type semiconductor layer 25 of FIG. 3A is the same as that employed in FIG. 1, and the concave-convex structure formed on the upper surface has a convex portion and a concave portion adjacent to each other. In this case, considering the side for effectively radiating the surface plasmon wave to the outside, the period (s) of the uneven structure and the width (w) of the convex portion are preferably 10 to 1000 nm, and the height (h) of the uneven structure It is preferable that it is 10-500 nm. In addition, as described above, in order to cause surface plasmon resonance, the distance t from the active layer to the recess is preferably 10 to 50 nm. Similarly, as shown in FIG. 3B, the concave-convex structure 25 'at the interface between the n-type semiconductor layer and the metal layer may have a semicircular cross section of the convex portion or a cylindrical shape of the convex portion.

3A and 3B, the concave-convex structures 35 and 35 'employable in the present invention may have a shape in which the convex portions and the concave portions are arranged in the longitudinal and transverse directions, respectively, as shown in FIGS. 3C and 3D. As shown, each convex portion may have various shapes such as a square or a circle in cross section. Each convex portion, however, in the present invention, the concave-convex structure is not limited to the illustrated embodiment, and various structures capable of radiating the surface plasmon wave to the outside, for example, the concave portion and the convex portion in FIGS. 3A to 3D. An inverted form may be possible.

In connection with the method of forming the above-mentioned concave-convex structure, it is preferable to dry-etch the upper surface of the n-type semiconductor layer. For example, the pattern P is formed by photolithography or other method and ICP / RIE (Inductive Coupled Plasma). / Reactive Ion Etching) can be used. In particular, as in the present embodiment, by using a process of etching the upper surface of the n-type semiconductor layer, damage to the surface region that may occur when the p-type semiconductor layer is etched can be relatively reduced. This can be improved. However, the uneven structure forming method does not limit the broadest technical scope of the present invention, but is a part of various optional methods for carrying out the present invention.

As described above, the surface plasmon wave of the metal layer 16 can be emitted to the outside by the uneven structure employed in the present embodiment, so that the light extraction efficiency of the semiconductor light emitting device 10 can be improved. .

On the other hand, the metal layer 16 is preferably made of a metal capable of exhibiting such a surface plasmon phenomenon, specifically, the metal is easy to emit electrons by an external stimulus such as Au, Ag, Al, etc. and have a negative dielectric constant It can be used mainly. Among these, Ag having the sharpest surface plasmon resonance peak and Au showing excellent surface stability may be selected universally. In addition, an alloy of the metals may also be used as the metal layer 16. In addition, the metal layer 16 may be multi-layered together with Au, Ag, Al, and the like by using Ni, Pt, or the like to improve ohmic contact performance.

4 is a cross-sectional view showing a semiconductor light emitting device according to another embodiment of the present invention.

Referring to FIG. 4, the semiconductor light emitting device 40 according to the present embodiment includes a p-type semiconductor layer 43, an active layer 44, an n-type semiconductor layer 45, and a metal layer sequentially formed on the buffer layer 42. 46, a conductive substrate 47, and an n-side electrode 48b, and a p-side electrode 48a is formed on the lower surface of the buffer layer 42.

The semiconductor light emitting device 40 according to the present embodiment differs from the semiconductor light emitting device according to FIG. 1 in that the semiconductor light emitting device 40 has a vertical structure, and the description of the functions of the respective layers is the same as the description in FIG. 1. Referring to the conductive substrate 47 only, the conductive substrate 47 is an element included in the final light emitting device, and serves as a support for supporting the light emitting structure together with the n-side electrode of the final light emitting device. Specifically, the conductive substrate 47 may be Si, Cu, Ni, Au, W, Ti, and the like. The conductive substrate 47 may be formed through a deposition process, a plating process, or the like, and a plating process is preferable in terms of process efficiency. In this case, a plating process includes well-known plating processes, such as electroplating, non-electroplating, vapor deposition, etc. Among these, it is preferable to use the electroplating method which requires a short plating time. However, a method of bonding the conductive substrate 47 to the top surface of the metal layer 46 may be used in addition to the method directly formed on the top surface of the metal layer 46.

It is intended that the invention not be limited by the foregoing embodiments and the accompanying drawings, but rather by the claims appended hereto. Accordingly, various forms of substitution, modification, and alteration may be made by those skilled in the art without departing from the technical spirit of the present invention described in the claims, which are also within the scope of the present invention. something to do.

As described above, according to the present invention, the light emitted from the quantum well layer excites the surface plasmon of the metal layer and emits it to the outside, thereby obtaining a semiconductor light emitting device using surface plasmon resonance with improved light extraction efficiency.

Claims (11)

A translucent substrate having electrical insulation; A p-type semiconductor layer formed on the light transmissive substrate; A p-side electrode formed in a portion of the p-type semiconductor layer; An active layer and an n-type semiconductor layer sequentially formed on an upper surface of the p-type semiconductor layer on which the p-side electrode is not formed; And Is formed on the n-type semiconductor layer, The surface plasmon present at the interface with the n-type semiconductor layer is spaced apart from the active layer by a light emitted from the active layer, and the interface is disposed so that the excited surface plasmon is emitted toward the active layer. A metal layer having a periodic concave-convex structure formed on the substrate; Semiconductor light emitting device using the surface plasmon resonance comprising a. delete The method of claim 1, The distance between the concave portion of the concave-convex structure and the active layer is 10 ~ 50nm semiconductor light emitting device using surface plasmon resonance, characterized in that. The method of claim 1, The p-type semiconductor layer, the active layer and the n-type semiconductor layer is a semiconductor light emitting device using surface plasmon resonance, characterized in that made of nitride. The method of claim 1, And a buffer layer formed on the bottom surface of the p-type semiconductor layer. The method of claim 1, The metal layer is a semiconductor light emitting device using surface plasmon resonance, characterized in that the material is selected from the group consisting of Ag, Al, Au and alloys thereof. The method of claim 1, The height of the uneven structure is a semiconductor light emitting device using surface plasmon resonance, characterized in that 10 ~ 500nm. The method of claim 1, The uneven structure is a semiconductor light emitting device using surface plasmon resonance, characterized in that the distance between the convex portion and the next convex portion is 10 ~ 1000nm. delete delete delete

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