KR101113875B1 - LED having vertical structure and the method of manufacturing the same - Google Patents

Abstract

The present invention relates to a vertical light emitting device, and more particularly, to a vertical light emitting device and a method of manufacturing the same that can improve the light extraction effect by improving the electrode structure. Such a present invention comprises: a plurality of semiconductor layers; A first electrode on one side of the semiconductor layer; A nitrogen getter metal layer located on the other side of the semiconductor layer; A TCO layer positioned adjacent to the getter metal layer; And a second electrode positioned adjacent to the TCO layer.

TCO, getter, ohmic, nitrogen, ITO.

Description

Vertical light emitting device and its manufacturing method {LED having vertical structure and the method of manufacturing the same}

1 is a cross-sectional view showing an example of a conventional vertical light emitting device manufacturing step.

2 is a cross-sectional view showing an example of a conventional vertical light emitting device.

Figure 3 is a cross-sectional view showing an embodiment of the manufacturing step of the vertical light emitting device of the present invention.

4 is a cross-sectional view showing an embodiment of a vertical light emitting device of the present invention.

5 is a schematic view showing an embodiment of a method of manufacturing a vertical light emitting device of the present invention.

6 is a band diagram of ITO and GaN of the vertical light emitting device of the present invention.

<Brief description of the main parts of the drawing>

10: substrate 20: semiconductor layer

30: first electrode 40: reflective electrode

50: getter metal layer 60: TCO layer

70: second electrode

The present invention relates to a vertical light emitting device, and more particularly, to a vertical light emitting device and a method of manufacturing the same that can improve the light extraction effect by improving the electrode structure.

Light Emitting Diodes (LEDs) are well-known semiconductor devices that convert current into light.In 1962, red LEDs using GaAsP compound semiconductors were commercialized. It has been used as a light source for display images of electronic devices.

The wavelength of light emitted by such LEDs depends on the semiconductor material used to make the LEDs. This is because the wavelength of the emitted light depends on the band-gap of the semiconductor material, which represents the energy difference between the valence band electrons and the conduction band electrons.

Gallium Nitride (GaN) semiconductors have received a lot of attention. One reason for this is that GaN can be combined with other elements (indium (In), aluminum (Al), etc.) to produce semiconductor layers that emit green, blue and white light.

In this way, the emission wavelength can be adjusted to match the material's characteristics to specific device characteristics. For example, GaN can be used to create white LEDs that can replace incandescent and blue LEDs that are beneficial for optical recording.

In addition, in the case of the conventional green LED, it was initially implemented as GaP, which was inefficient as an indirect transition type material, and thus practical pure green light emission could not be obtained. However, as InGaN thin film growth succeeded, high brightness green LED could be realized. It became.

Because of these and other benefits, the GaN series LED market is growing rapidly. Therefore, since commercial introduction in 1994, GaN-based optoelectronic device technology has rapidly developed.

Since the efficiency of GaN light emitting diodes outperformed the efficiency of incandescent lamps and is now comparable to that of fluorescent lamps, the GaN LED market is expected to continue to grow rapidly.

Despite the rapid development of GaN device technology as described above, the manufacturing of GaN device has a large cost disadvantage. This is related to the difficulty of growing GaN epitaxial layers and subsequently cutting the finished GaN-based devices.

GaN-based devices are typically fabricated on sapphire (Al ₂ O ₃ ) substrates. This is because sapphire wafers are commercially available in sizes suitable for mass production of GaN-based devices, support relatively high quality GaN thin film growth, and have a wide range of temperature processing capabilities.

In addition, sapphire is chemically and thermally stable, has a high melting point to enable high temperature manufacturing processes, high binding energy (122.4 Kcal / mole) and high dielectric constant. Chemically, sapphire is crystalline aluminum oxide (Al ₂ O ₃ ).

On the other hand, since the sapphire is an insulator, the form of the LED element available when using the used sapphire substrate (or other insulator substrate) is actually limited to a lateral or vertical structure.

In this horizontal structure, the metal contacts used to inject current into the LED are all located on the top surface (or on the same side of the substrate). In the vertical structure, on the other hand, one metal contact is on the top face and the other contact is located on the bottom face after the sapphire (insulation) substrate is removed.

In addition, a flip chip bonding method in which the chip is attached upside down to a submount such as a silicon wafer or a ceramic substrate having excellent thermal conductivity after the manufacture of the LED chip is also widely used.

However, the above-described horizontal structure or flip chip method is a problem in heat dissipation efficiency because the thermal conductivity of the sapphire substrate is about 27 W / mK and the heat resistance is very large, and the flip chip method has a large number of photolithography processes. The manufacturing process was complicated and required.

In connection with these problems, the vertical structure of the LED for removing the sapphire substrate has attracted much attention.

In order to solve the above problems of the sapphire substrate in the vertical LED, the sapphire substrate is removed by using a laser lift off (LLO) method to manufacture the device.

That is, as shown in FIG. 1, a GaN thin film composed of an n-type GaN layer 2, an active layer 3, and a p-type GaN layer 4 is sequentially formed on the sapphire substrate 1, and the p-type electrode 5 is formed thereon. To form. On the p-type electrode 5 constituting the ohmic electrode, a reflective electrode 6 or a metal support layer for increasing the reflection efficiency may be further formed.

In this way, in the formed chip, the laser lift-off method is applied to remove the entire sapphire substrate 1.

At this time, a stress caused by a laser is applied to the GaN thin film when the laser is incident. In order to separate the sapphire substrate 1 and the GaN thin film, a laser beam having a high energy density must be used. It decomposes into Ga and gaseous nitrogen (N ₂ ).

As described above, after the substrate 1 is removed, the n-type electrode 7 is formed on the exposed n-type GaN layer 2 as shown in FIG. 2 to form a chip structure.

As shown, in such a vertical LED structure, the n-type GaN layer 2 is positioned at the top, and the area of the contact region of the n-type GaN layer 2 greatly affects the overall luminous efficiency.

However, the refractive index of the GaN material is 2.35, and when it comes into direct contact with air having a refractive index of 1, the angle at which light does not cause total reflection inside the LED and exit from the GaN layer is only about 25 ° from the vertical line. There was a problem that the efficiency is not high.

The technical problem of the present invention is to solve the problems as described above, by using a getter metal to make the GaN semiconductor layer and the transparent conductive oxide (TCO: ohmic contact) to increase the luminous efficiency and light extraction effect It is intended to provide a vertical light emitting device and a method of manufacturing the same.

In order to achieve the technical problem of the present invention as described above, the present invention, a plurality of semiconductor layers; A first electrode on one side of the semiconductor layer; A nitrogen getter metal layer located on the other side of the semiconductor layer; A TCO layer positioned adjacent to the getter metal layer; It is achieved by including a second electrode located adjacent to the TCO layer.

The plurality of semiconductor layers are GaN-based semiconductor layers, comprising: a p-type semiconductor layer; An active layer positioned on the p-type semiconductor layer; It comprises an n-type semiconductor layer located on the active layer.

The getter metal layer makes the adjacent semiconductor surface a surface state lacking nitrogen, and is manufactured using at least one of Ti, Zr, and Cr.

Another technical problem of the present invention as described above comprises the steps of: forming a nitrogen getter metal layer on a plurality of GaN-based semiconductor layers formed on the lower electrode; Forming a TCO layer on the getter metal layer; Performing a heat treatment including an interface between the semiconductor layer and the getter metal layer; And forming an upper electrode over the TCO layer.

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

As shown in FIG. 3, in manufacturing the light emitting device of the present invention, first, a GaN series semiconductor layer 20 and a first electrode 30 are formed on a sapphire substrate 10.

As shown in the drawing, the semiconductor layer 20 is composed of an n-type semiconductor layer 21, an active layer 22, and a p-type semiconductor layer 23, on which a reflective electrode 40 for enhancing reflection efficiency is formed. Alternatively, a metal support layer may be further formed.

When the semiconductor layer 20 is formed in the above order, the first electrode 30 becomes a p-type electrode.

As such, in the formed chip, the laser lift-off method is applied to remove the entire sapphire substrate 10.

At this time, a stress caused by a laser is applied to the GaN thin film when the laser is incident. In order to separate the sapphire substrate 10 and the GaN thin film, a laser beam having a high energy density must be used, and the metal It decomposes into Ga and gaseous nitrogen (N ₂ ).

As such, as shown in FIG. 4, the getter metal layer 50 is formed of a metal having nitrogen getter characteristics such as Ti, Zr, Cr, and the like on the surface of the n-type semiconductor layer 21 from which the substrate 10 is removed. ).

The deposition of the getter metals (Ti, Zr, Cr) is performed by coating or doping a very small amount at the interface, and the deposition method is PVCVD, such as sputtering, MOCVD using organic metal precursors, and ions. Various methods, such as ion implanting, can be selected depending on the convenience of the process.

After depositing the getter metal layer 50, a TCO (Transparent Conducting Oxide) layer 60 having a suitable refractive index may be deposited thereon to maximize the light extraction effect.

The TCO layer 60 preferably uses indium tin oxide (ITO).

After the getter metal layer 50 and the TCO layer 60 are formed on the semiconductor layer 20 as described above, heat treatment is performed.

As is generally known, in the case of a transparent conducting oxide (TCO) such as ITO, as shown in FIG. 6, ohmic contact with both n-type and p-type GaN is not made.

However, in the case of the vertical light emitting device, if the TCO layer 60, which is effective in terms of refractive index, can be applied to the top layer as in the above structure, it may show a significant advantage in terms of light extraction.

Recent studies have shown that Ga-N decomposes during heat treatment at the ITO / GaN interface. In general, ohmic contact of n-type GaN is reported to form a reactant with nitrogen of surface Ga-N to form a nitrogen-deficient surface state to form ohmic contact. have.

Accordingly, the nitrogen getter metal layer 50 may improve ohmic characteristics and device stability by removing nitrogen in the Ga—N structure.

As is well known, metals such as Ti not only form Ti-N compounds well, but also Ti-N itself has a metallic conductivity, and thus, deterioration of electrode characteristics due to compound formation can be sufficiently prevented.

In this manner, after the TCO layer 60 is formed, the second electrode 70 is formed on the TCO layer 60 as an n-type electrode again as shown in FIG. 4 to form a chip structure.

Thus, ITO can be used as the TCO layer 60, and as a result, an escape angle at which light inside the GaN material can escape can be greatly improved.

Simple calculations show that the angle of light extraction (escape), which can escape directly from GaN to the outside (air), is approximately 25 °, but greatly improves to 54.78 ° when ITO is used.

The above embodiment is an example for explaining the technical idea of the present invention in detail, and the present invention is not limited to the above embodiment, various modifications are possible, and various embodiments of the technical idea are all protected by the present invention. It belongs to the scope.

In the present invention as described above, in forming a transparent conductive oxide (TCO), by using the getter metal layer to make ohmic contact with the GaN semiconductor layer, the luminous efficiency is increased by the current diffusion effect, By greatly improving the light extraction angle is to have an effect that can increase the light extraction effect.

Claims (12)

A plurality of semiconductor layers; A first electrode on one side of the semiconductor layer; A nitrogen getter metal layer located on the other side of the semiconductor layer; A TCO layer positioned adjacent to the getter metal layer; And a second electrode positioned adjacent to the TCO layer. The method of claim 1, wherein the plurality of semiconductor layers, a p-type semiconductor layer; An active layer positioned on the p-type semiconductor layer; And a n-type semiconductor layer positioned on the active layer. The vertical light emitting device of claim 1, wherein the first electrode is a p-type electrode. The method of claim 1, wherein the first electrode, An ohmic electrode; And a reflective electrode covering the ohmic electrode. The vertical type light emitting device of claim 1, wherein the first electrode has a structure covering all or a part of the semiconductor layer. 2. The vertical light emitting device of claim 1, wherein the getter metal layer makes the adjacent semiconductor surface a nitrogen-deficient surface state. The vertical light emitting device of claim 1, wherein the getter metal layer is at least one of Ti, Zr, and Cr. The vertical light emitting device of claim 1, wherein the TCO layer is at least one of indium tin oxide (ITO), ZnO, AlZnO, and InZnO. A lower electrode; A p-type GaN layer positioned on the lower electrode; An active layer formed on the p-type GaN layer; An n-type GaN layer located on the active layer; A nitrogen getter metal layer located on the n-type GaN layer; A TCO layer positioned on the getter metal layer; And a top electrode positioned on the TCO layer. Forming a nitrogen getter metal layer on the plurality of GaN based semiconductor layers formed on the lower electrode; Forming a TCO layer on the getter metal layer; Performing a heat treatment including an interface between the semiconductor layer and the getter metal layer; And forming an upper electrode on the TCO layer. The method of claim 10, wherein the getter metal layer is formed by doping or coating the semiconductor layer. The method of claim 10, wherein the getter metal layer is formed by any one of sputtering, MOCVD, and ion implantation.

Images