KR20080067536A - Nitride semiconductor light emitting device and method thereof - Google Patents

Abstract

A nitride semiconductor light emitting device and a manufacturing method thereof are provided to adjust accurately a reflective angle of light by using an etch process and a diffraction grating structure. An n type semiconductor layer(130) is formed on a substrate(110) and includes a diffraction grating(132) having a concavo-convex pattern. An active layer(140) is formed on the n type semiconductor layer. A p type semiconductor layer(150) is formed on the active layer. A p type electrode(170) is formed on the p type semiconductor layer. An n type electrode(180) is formed on the diffraction grating of the n type semiconductor layer. The diffraction grating is formed on a deposition region of the n type semiconductor layer.

Description

Nitride semiconductor light emitting device and method for manufacturing same

1 is a side cross-sectional view schematically showing the components of a typical nitride semiconductor light emitting device.

Figure 2 is a side cross-sectional view schematically showing the components of the nitride semiconductor light emitting device according to the embodiment of the present invention.

3 is a flowchart illustrating a method of manufacturing a nitride semiconductor light emitting device according to an embodiment of the present invention.

Figure 4 is a side cross-sectional view showing a form in which a mask pattern is formed on the nitride semiconductor light emitting device according to the embodiment of the present invention.

5 is a side cross-sectional view illustrating a form in which a diffraction grating is formed in a portion of an n-type semiconductor layer of a nitride semiconductor light emitting device according to an embodiment of the present invention.

<Explanation of symbols for main parts of drawing>

100: nitride semiconductor light emitting device according to the present invention

110: substrate 112: reflective film

120: buffer layer 130: n-type semiconductor layer

132: diffraction grating 140: active layer

150: p-type semiconductor layer 152: mask pattern

160: transparent electrode layer 170: p-type electrode

180: n-type electrode

The present invention relates to a nitride semiconductor light emitting device and a method of manufacturing the same.

In general, a semiconductor light emitting device (LED) is a light emitting diode (LED), which is used to send and receive signals by converting electrical signals into infrared, visible or light forms using the characteristics of compound semiconductors. It is an element.

Usually, the use range of LED is used in home appliances, remote controllers, electronic signs, indicators, and various automation devices, and the types are largely divided into Infrared Emitting Diode (IRD) and Visible Light Emitting Diode (VLED).

In general, miniaturized LEDs are made of a surface mount device type for direct mounting on a printed circuit board (PCB) board. Accordingly, LED lamps, which are used as display elements, are also being developed as surface mount device types. These surface-mount devices can replace the existing simple lighting lamps, which are used for lighting indicators of various colors, character display and image display.

As the area of use of LEDs becomes wider as described above, required luminances such as electric lamps used for living, electric lamps for rescue signals, and the like become higher and higher, and in recent years, development of high output light emitting diodes is actively underway.

In particular, many researches and investments have been made on semiconductor optical devices using Group 3 and Group 5 compounds such as GaN (gallium nitride), AlN (aluminum nitride), and InN (indium nitride). This is because the nitride semiconductor light emitting device has a bandgap of a very wide region ranging from 1.9 eV to 6.2 ev, and has the advantage of realizing three primary colors of light using the same.

Recently, the development of blue and green light emitting devices using nitride semiconductors has revolutionized the optical display market and is considered as one of the promising industries that can create high added value in the future. However, as mentioned above, in order to pursue more industrial use in such a nitride semiconductor optical device, increasing light emission luminance is also a problem to be taken first.

1 is a side cross-sectional view schematically showing the components of a typical nitride semiconductor light emitting device.

Referring to FIG. 1, a general nitride semiconductor light emitting device includes a substrate 11, a buffer layer 12, an n-type semiconductor layer 13, an active layer 14, a p-type semiconductor layer 15, a transparent electrode layer 16, and a p-type. The electrode 17, the n-type electrode 18, etc. are comprised.

The GaN-type buffer layer 12 is formed on the substrate 11 so that the nitride of good quality is grown. The p-type semiconductor layer 15 is doped with Mg (magnesium) and the n-type semiconductor layer 13 is Si. By doping (silicon), each gallium nitride (GaN) semiconductor layer is formed.

The active layer 14 has a quantum well structure, which is injected from the p-type electrode 18 and flows through the p-type semiconductor layer 15, and is injected from the n-type electrode 17 and then through the n-type semiconductor layer 13. The flowing electrons are combined to generate light.

The transparent electrode layer 16 is made of a light transmissive conductive material, and allows the light generated from the active layer 14 to travel upward. The n-type electrode 18 is deposited on the n-type semiconductor layer 13 partially exposed through an etching process, and the p-type electrode 17 is deposited on the p-type semiconductor layer 15.

In order for photons generated in the active layer 14 to be emitted to the outside through the side surface of the device, the incident light must be incident at an angle smaller than a predetermined critical angle at the interface between the semiconductor surface and the air (ie, materials having different refractive indices). In order for light to pass through it, it must be incident at an angle less than a certain critical angle at the interface), and light having an angle greater than the critical angle exists depending on the light emission position (about 80%), and such light passes through the interface. They are trapped inside the device.

The light trapped inside the device is extinguished by the reflection between the layers and disappears, which causes the luminous efficiency to decrease.

In addition, the p-side electrode 18 and the n-side electrode 17 block and absorb a portion of the light path that travels from the active layer 14.

As shown in FIG. 1, since the light generated from the active layer 14 does not penetrate or reflect the side and bottom surfaces of the p-side electrode 18 and the side and bottom surfaces of the n-side electrode 17, the semiconductor light emitting device is absorbed. There is a problem in that the top emission rate and the side emission rate of (10) become significantly worse.

In order to solve the above problems, a technique of forming a random roughness (Roughness) of the semiconductor layer has been proposed, but the uneven structure has a irregular reflection angle, it is difficult to precise control of the reflective structure quantum luminous efficiency There is a limit to maximizing.

The present invention provides a nitride semiconductor light emitting device in which the amount of photons trapped inside the device is reduced and the external quantum efficiency is improved by controlling the angle of light incident to the interface between the semiconductor light emitting device and the atmosphere to be smaller than the critical angle.

The present invention provides a method of manufacturing a nitride semiconductor light emitting device that can form a reflective structure on the lower side of the electrode and maximize the external quantum efficiency through precise control of the reflection angle.

The nitride semiconductor light emitting device according to the present invention comprises a substrate; A buffer layer formed on the substrate; An n-type semiconductor layer formed on the buffer layer and having a diffraction grating having an uneven pattern in the electrode formation region; An active layer formed on the n-type semiconductor layer; A p-type semiconductor layer formed on the active layer; A p-type electrode formed on the p-type semiconductor layer; And an n-type electrode formed on the diffraction grating of the n-type semiconductor layer.

A method of manufacturing a nitride semiconductor light emitting device according to the present invention includes the steps of forming a buffer layer on a substrate; Forming an n-type semiconductor layer on the buffer layer; Forming an active layer on the n-type semiconductor layer; Forming a p-type semiconductor layer on the active layer; And exposing a portion of the n-type semiconductor layer through an etching process, and forming a diffraction grating having an uneven pattern in the exposed n-type semiconductor layer.

Hereinafter, a nitride semiconductor light emitting device and a method of manufacturing the same according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. For convenience of understanding, the components of the nitride semiconductor light emitting device will be described together with the manufacturing method thereof. do.

2 is a side cross-sectional view schematically illustrating the components of the nitride semiconductor light emitting device 100 according to the embodiment of the present invention, and FIG. 3 is a method of manufacturing the nitride semiconductor light emitting device 100 according to the embodiment of the present invention. It is a flowchart shown.

Referring to FIG. 2, a form in which a nitride semiconductor light emitting device 100 according to an embodiment of the present invention is finally completed is illustrated. The substrate 110, the buffer layer 120, the n-type semiconductor layer 130, and the active layer are illustrated. 140, a p-type semiconductor layer 150, a transparent electrode layer 160, a p-type electrode 170, and an n-type electrode 180.

A diffraction grating 132 having a concave-convex pattern is formed in an exposed region of the n-type semiconductor layer 130 on which the n-type electrode 180 is formed, and a reflective film 112 is formed on an upper surface of the substrate 110. do.

Hereinafter, the configuration and operation of the semiconductor light emitting device 100 according to the exemplary embodiment of the present invention will be described according to the formation order of each layer.

The substrate 110 may be made of an element or compound such as sapphire (Al ₂ O ₃ ), Si (silicon), SiC (silicon carbide), GaAs (gallium arsenide), ZnO (zinc oxide) or MgO (magnesium oxide). Can be.

In an embodiment of the present invention, the substrate 110 is formed with a reflective film 112 on the surface through a dry etching or a wet etching process in order to switch the path of the light directed downward (S100).

The substrate 110 is fixed on a susceptor provided in the reaction tube for organometallic chemical vapor deposition which is maintained at a low pressure after being cleaned.

When the air in the reaction tube is sufficiently removed, the substrate 110 is heated at a temperature of about 1000 ° C. for about 10 minutes while the supply of hydrogen gas is maintained to remove the oxide film on the surface. Subsequently, the temperature of the substrate 110 is lowered to about 500 ° C., and hydrogen gas at a flow rate of 8 liters per minute and ammonia gas at the same flow rate are supplied to the reaction tube so that the temperature of the substrate 110 may be stabilized at 520 ° C.

The buffer layer 120 may include an undoped semiconductor layer (which may be formed of a u-GaN layer). When the temperature of the substrate 110 is stabilized at about 500 ° C., 3 × 10 ⁵ mol of trimethyl gallium per minute ( TMGa), trimethyl indium (TMIn), and 3 × 10 ⁶ mol of trimethyl aluminum (TMAl) per minute are injected into the reaction tube together with hydrogen gas and ammonia gas to grow the buffer layer 120 (S105).

The buffer layer 120 performs a function of preventing melt-back etching due to a chemical action of the substrate 110. AlInN / GaN, In _x Ga _1-x N / GaN, Al _x In _y It may be formed as a multilayer by forming a stacked structure such as Ga _1-xy N / In _x Ga _1-x N / GaN.

Subsequently, an n-type semiconductor layer 130 doped with silicon is formed on the buffer layer 120 (S110).

The n-type semiconductor layer 130 may be formed of a silicon-doped n-GaN layer to lower the driving voltage, for example, NH ₃ (3.7 × 10 ⁻² mol / min), TMGa (1.2 × 10 ⁻⁴ mol) Per minute) and silane gas (6.3 × 10 ⁻⁹ moles / minute) containing an n-type dopant such as Si.

When the n-type semiconductor layer 130 is grown, an active layer 140 composed of InGaN / GaN is formed using, for example, a metal organic chemical vapor deposition (MOCVD) method, and the active layer 140 is a multi-quantum well. Well: MQW) can be formed in a structure (S115).

When the active layer 140 is formed, a p-type semiconductor layer 150 doped with magnesium is formed thereon (S120).

The p-type semiconductor layer 150 is a carrier gas of hydrogen to raise the ambient temperature to 1000 ℃ TMGa (7 × 10 ^-6 mol / min), trimethyl aluminum (TMAl) (2.6 × 10 ^-5 mol / min), Bicetyl cyclopentadienyl magnesium (EtCp2Mg) {Mg (C ₂ H ₅ C ₅ H ₄ ) ₂ } (5.2 x 10 ^-7 mol / min), and NH ₃ (2.2 x 10 ^-1 mol / min) was fed Is grown.

Subsequently, for example, an annealing treatment is performed at a temperature of 950 ° C. for 5 minutes to adjust the maximum hole concentration of the p-type semiconductor layer 150.

The transparent electrode layer 160 is formed on the p-type semiconductor layer 150 (S125).

The transparent electrode layer 160 has a high light transmittance and passes upwards without reflecting or absorbing light emitted from the active layer 140, and helps to diffuse current to increase the coupling ratio between holes and electrons in the active layer 140. .

The transparent electrode layer 160 may be formed using a transparent conductive material such as ITO, CTO, SnO ₂ , ZnO, RuO _x , TiO _x , IrO _x , Ga _x O _x, or the like.

Thereafter, a portion of the n-type semiconductor layer 130 is exposed by removing a region from the transparent electrode layer 160 to the n-type semiconductor layer 130 through the first etching process (S130), and the transparent electrode layer 160 is exposed. Mask patterns 152a and 152b are formed on the surface of the n-type semiconductor layer 130 (S135).

In this case, the mask pattern 152a formed on the transparent electrode layer 160 serves to protect the transparent electrode layer 160 from being etched and thus is formed on the entire surface of the transparent electrode layer 160.

In addition, the mask pattern 152b formed on the exposed surface of the n-type semiconductor layer 130 is for forming the diffraction grating 132 and has a shape of a string groove having a predetermined interval.

4 is a side cross-sectional view showing a form in which the mask patterns 152a and 152b are formed in the nitride semiconductor light emitting device 100 according to the embodiment of the present invention, and FIG. 5 is a nitride semiconductor light emitting device according to the embodiment of the present invention ( A side cross-sectional view exemplarily illustrating a form in which a diffraction grating 132 is formed in a portion of the n-type semiconductor layer 130 of 100.

In the exemplary embodiment of the present invention, the mask patterns 152a and 152b are formed using a photo resist (PR), and when the mask patterns 152a and 152b are formed, a second etching process is performed to form a diffraction grating 132. ) Is formed (S140).

The second etching process may use both dry etching and wet etching, but in the exemplary embodiment of the present invention, a dry etching method is used.

There are a number of dry etching methods available in the embodiment of the present invention, for example, look at a few ways as follows.

First, there is a physical method by ion bombardment.

Dry etching by ion bombardment is performed by using a reactive ion etchant (RIE), in which a semiconductor element to be etched is mounted on a lower electrode plate to which a high frequency current is supplied, and an upper electrode on a grounded reaction vessel. It has a structure in which the plate is located.

Since the area of the electrode on which the semiconductor element to be etched is mounted is very small compared to other electrode areas, a large voltage is induced to the electrode of the semiconductor element so that positively charged ions are accelerated and then collide with the surface of the semiconductor element. The ion kinetic energy is about hundreds of eV to cause etching, and the RIE accelerates the ions to have a energy of 100 to 1000 eV and then collides with the surface of the semiconductor device.

Second, there is a chemical method by the reaction material generated in the plasma.

Chemical dry etching using gas may be processed by an inductively coupled plasma (ICP) device, and PR may be used as the mask pattern 152.

Etch gases such as Ar, Cl, and BCl may be used alone or in combination, and the degree of etching may be controlled by changing factors such as RF power, substrate bias, operation pressure, and substrate temperature.

For example, the n-type semiconductor layer 130 is oxidized through O₂ plasma, and the oxide film in the form of a thin film is sequentially removed to a desired depth. The oxide thin film may be etched at a rate of 50-700 / min. As described above, the etching rate may be adjusted according to the substrate temperature, the H (hfac) / O₂ flow rate ratio, and the plasma power.

That is, the etch rate is increased as RF power is increased in the temperature range higher than the substrate temperature of 215 ℃, the optimum H (hfac) / O₂ flow rate ratio of the balance between the oxidation process and H (hfac) is about 1 : 1 is about.

Since the diffraction grating 132 needs to reflect the light inside the device to the outside, the reflection angle needs to be adjusted. In order to adjust the reflection angle, the etching conditions such as RF power, substrate bias, operation pressure, substrate temperature, and gas composition ratio are adjusted. By this, the profile of the uneven pattern can be formed precisely as necessary.

In an embodiment of the present invention, the second dry etching method is used.

The diffraction grating 132 is in the form of a grid (Grating, Grating) having a predetermined interval according to the shape of the mask pattern (152b), the interval between the grooves should be formed longer than the wavelength of light emitted from the active layer 140. do.

The diffraction grating 132 according to the present invention uses a diffraction characteristic rather than a polarization characteristic, and changes the propagation path of light by using constructive and destructive interference phenomena, so that the critical angle at the interface between the semiconductor layer and the air is changed. Can be (small) changed. Therefore, the phenomenon in which photons are reflected at the interface and trapped inside the semiconductor can be prevented and the amount of light emitted to the outside can be increased.

In addition, the diffraction grating 132 may be formed in the deposition region of the p-type electrode 170 as well as the deposition region of the n-type electrode 180 to induce light reflected from the p-type electrode 170 to the outside. In the embodiment of the present invention, the n-type electrode 180 is formed only in the deposition region.

In this manner, when the diffraction grating 132 is formed, the mask patterns 152a and 152b are removed using the photosensitive material removing solution (S145), and the n-type electrode is formed on the diffraction grating 132 of the n-type semiconductor layer 130. 180 is deposited, and the p-type electrode 170 is deposited on the transparent electrode layer 160 (S150).

When the n-type electrode 180 is formed as a reflective electrode, the reflection effect may be maximized along with the diffraction grating 132, and the p-type electrode 170 may also be provided as a reflective electrode.

The reflective electrode is made of a metallic material including a reflective material, and serves as a bonding pad. The reflective electrode may include a reflective material such as Ag or Al to form a single layer or a multilayer structure, and when the front reflective electrode is formed, a single layer structure is formed. .

In addition, the transparent electrode layer 160 and the n-type electrode 180 serves as an ohmic electrode. For example, the n-type electrode 180 may form an ohmic electrode layer made of a material such as Ti, Al, Cr, or the like.

On the other hand, since the p-type electrode 170 has a transparent electrode layer 160 disposed below the ohmic electrode layer, the function is satisfied even if the p-type electrode 170 is implemented as a bonding pad using a material such as Ni.

Thereafter, the substrate may be polished to an appropriate thickness through a lapping process and a polishing process.

Although the present invention has been described above with reference to the embodiments, these are only examples and are not intended to limit the present invention, and those skilled in the art to which the present invention pertains may have an abnormality within the scope not departing from the essential characteristics of the present invention. It will be appreciated that various modifications and applications are not illustrated. For example, each component specifically shown in the embodiment of the present invention can be modified. And differences relating to such modifications and applications will have to be construed as being included in the scope of the invention defined in the appended claims.

According to the nitride semiconductor light emitting device and the manufacturing method thereof according to the present invention, the following effects are obtained.

First, at the interface between the semiconductor light emitting device and the atmosphere, the incident angle can be made smaller than the critical angle by modifying the path of light traveling at an angle larger than the critical angle, thereby reducing the amount of photons trapped inside the device and maximizing external quantum efficiency. It can be effective.

Second, the reflection angle of the light can be precisely controlled by using an etching process using a mask pattern and a diffraction grating structure, and thus, an optimum external quantum efficiency can be realized according to the use environment and the type of light emitting device.

Claims (8)

Board; An n-type semiconductor layer formed on the substrate and having a diffraction grating in the form of an uneven pattern; An active layer formed on the n-type semiconductor layer; A p-type semiconductor layer formed on the active layer; A p-type electrode formed on the p-type semiconductor layer; And A nitride semiconductor light emitting device comprising an n-type electrode formed on the diffraction grating of the n-type semiconductor layer. The method of claim 1, wherein the diffraction grating A nitride semiconductor light emitting device formed in the electrode deposition region of the n-type semiconductor layer. The method of claim 1, A nitride semiconductor light emitting device comprising a transparent electrode layer formed on the p-type semiconductor layer. The method of claim 1, wherein the substrate A nitride semiconductor light emitting device having a reflective film formed on its surface. The method of claim 1, wherein the n-type electrode A nitride semiconductor light emitting device provided as a reflective electrode. Forming a buffer layer on the substrate; Forming an n-type semiconductor layer on the buffer layer; Forming an active layer on the n-type semiconductor layer; Forming a p-type semiconductor layer on the active layer; And And exposing a portion of the n-type semiconductor layer through an etching process, and forming a diffraction grating having a concave-convex pattern in the exposed n-type semiconductor layer. The method of claim 6, wherein the buffer layer is formed And forming a reflective film on the upper surface of the substrate before the buffer layer is formed. The method of claim 6, wherein the diffraction grating is formed Exposing a portion of the n-type semiconductor layer through a first etching process; Forming a mask pattern on the exposed n-type semiconductor layer; A second etching process is performed on the mask pattern to form the diffraction grating; And The manufacturing method of the nitride semiconductor light emitting device comprising the step of removing the mask pattern.

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