KR20120081335A - Nitride semiconductor light emitting device - Google Patents

Abstract

PURPOSE: A nitride semiconductor light emitting device is provided to improve optical power by applying an interference phenomenon of light reflected from the upper and lower reflection sides of a semiconductor layer and light from an active layer. CONSTITUTION: A reflection electrode(300) is arranged on a conductive substrate. A semiconductor structure(400) includes a first conductive semiconductor layer, an active layer, and a second conductive semiconductor layer. The semiconductor structure is formed on the reflection electrode. The active layer is arranged on the first conductive semiconductor layer. The second conductive semiconductor layer has a light extraction structure(700) on a light emitting surface.

Description

Nitride-based semiconductor light emitting device

The present invention relates to a semiconductor light emitting device, and more particularly to a nitride-based semiconductor light emitting device that can improve the light output.

Light Emitting Diode (LED) is a well-known semiconductor light emitting device that converts electric current into light.In 1962, a red LED using GaAsP compound semiconductor was commercialized. It has been used as a light source for display images of electronic devices, including.

Nitride compound semiconductors, represented by gallium nitride (GaN), have high thermal stability and wide bandgap (0.8 to 6.2 eV), attracting much attention in the field of high-power electronic component development including LEDs. come.

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.

Accordingly, nitride semiconductors are currently used as basic materials for the fabrication of blue / green laser diodes and light emitting diodes (LEDs). In particular, high-power LED is attracting attention as a light source for white lighting, foretelling the era of LED lighting.

An object of the present invention is to provide a nitride-based semiconductor light emitting device that can improve the light output by applying the interference phenomenon of the light generated from the active layer and the reflected light by the upper and lower reflective surface of the nitride-based semiconductor layer.

As a first aspect for achieving the above technical problem, a nitride based semiconductor light emitting device comprising: a conductive substrate; A reflective electrode positioned on the conductive substrate; And a second conductive semiconductor layer disposed on the reflective electrode and having a first conductive semiconductor layer, an active layer positioned on the first conductive semiconductor layer, and a light extracting structure on the active layer. And a semiconductor structure, wherein the thickness of the first conductive semiconductor layer and the thickness of the entire semiconductor structure are constructive interference of interference phenomena by light emitted directly from the active layer and light emitted from the active layer and reflected from the reflective electrode. Characterized by the conditions.

As a second aspect for achieving the above technical problem, a nitride based semiconductor light emitting device comprising: a conductive substrate; A reflective electrode positioned on the conductive substrate; And a second conductive semiconductor layer disposed on the reflective electrode and having a first conductive semiconductor layer, an active layer positioned on the first conductive semiconductor layer, and a light extracting structure on the active layer. A semiconductor structure, wherein the shortest distance between the active layer at the reflective electrode and the light emitting surface at the reflective electrode is an odd multiple of λ / 4n ± 10 nm (where λ is the wavelength of emitted light and n is Refractive index of the semiconductor layer).

According to the present invention, by applying the interference phenomenon of the light generated from the active layer and the reflected light by the upper and lower reflective surfaces of the semiconductor layer in the semiconductor light emitting device, it is possible to greatly improve the light output of the light emitting device by the semiconductor thickness change, such interference The improvement of the light output using the phenomenon has an effect that can be applied to all kinds of light emitting devices without applying a complicated structure.

1 is a cross-sectional view showing a first example of a nitride semiconductor light emitting device.
In FIG. 2, the emission surface transmittance spectrum of the vertical light emitting device according to the first thickness h is changed.
3 is a spectrum obtained by converting FIG. 2 with respect to the frequency domain.
4 is a light emission surface transmittance spectrum of the vertical light emitting device according to the change of the second thickness d.
5 is a spectrum obtained by converting FIG. 4 with respect to the frequency domain.
6 and 7 are transmission spectrums of the light emitting surface according to the change of the first thickness h and the second thickness d, respectively.
8 is a cross-sectional view illustrating a second example of the nitride semiconductor light emitting device.
9 is a sectional view showing a third example of the nitride semiconductor light emitting device.

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

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. Rather, the intention is not to limit the invention to the particular forms disclosed, but rather, the invention includes all modifications, equivalents and substitutions that are consistent with the spirit of the invention as defined by the claims.

It will be appreciated that when an element such as a layer, region or substrate is referred to as being present on another element "on," it may be directly on the other element or there may be an intermediate element in between .

Although the terms first, second, etc. may be used to describe various elements, components, regions, layers, and / or regions, such elements, components, regions, layers, and / or regions It will be understood that it should not be limited by these terms.

As shown in FIG. 1, in the light emitting device having the vertical electrode structure, the reflective electrode 20 is positioned on the conductive substrate 10, and the p-type semiconductor layer 31 is formed on the reflective electrode 20. The semiconductor structure including the active layer 32 and the n-type semiconductor layer 33 is located, and the n-type electrode 40 is located on the semiconductor structure.

In the light emitting device, light is emitted from the active layer 32, and the light emitted from the active layer 32 is emitted to the outside through the light emitting surface 34.

As such, the light emitted from the active layer 32 may include light a emitted through the direct emission surface 34 and light b reflected from the lower reflective electrode 20.

An interference phenomenon may occur between the directly emitted light a and the reflected light b reflected by the reflective electrode 20, which is the same as the interference principle of Lloyd's mirror.

This interference phenomenon may occur because light generated from the same light source has two different optical paths due to mirror surfaces adjacent to the light source, and at this time, an optical path length ( _ΔL ; optical path length; ) May be twice the distance h between the active layer 32 and the lower reflective electrode 20.

In the structure as shown in FIG. 1, the distance h between the active layer 32 and the lower reflective electrode 20 may be equal to the thickness of the p-type semiconductor layer 31, hereinafter, the first thickness h. It will be called.

This constructive interference condition is shown in Equation 2. In Equation 2, λ is an emission wavelength, n is a refractive index of the semiconductor layer, d is described below.

The change in the first thickness h may directly affect the transmittance of light passing through the upper surface (light emitting surface) 34 of the vertical light emitting device and the light extraction efficiency of the light emitting device.

FIG. 2 shows the transmission spectrum of the light emitting surface 34 of the vertical light emitting device according to the change in the first thickness h, which is calculated by a two-dimensional finite difference time domain method (2D-FDTD). The results are shown.

2, the wavelength satisfying the constructive and destructive interference conditions is changed as the first thickness h is changed, and the interval between two adjacent constructive interference peak wavelengths (FSR; Free Spectral Range; It can be seen that the change.

That is, as the first thickness h becomes larger, the FSR has a smaller value, which can be expressed by Equation 3 below. Λ ₀ in Equation 3 means the wavelength of the adjacent transmission peak.

The same transmittance spectrum is converted into FIG. 3 for the frequency domain. In the frequency domain, given the first thickness h, it can be seen that the spacing (FSR) of two adjacent constructive interference peak frequencies is kept constant (Equation 4; c is the luminous flux).

On the other hand, another consideration is light a directly emitted through the light emitting surface 34 in the active layer 32 and light c reflected by the light emitting surface 34 and the reflective electrode 20; As an interference phenomenon by reference 1, this can be considered to be the same as the Fabry-perot resonance principle of the thin film. This is also caused by the optical path difference between the two lights.

Equation 5 shows an optical path difference between two lights, and as shown in FIG. 1, the semiconductor structure 30 including the p-type semiconductor layer 31, the active layer 32, and the n-type semiconductor layer 33 is formed. Equal to twice the total thickness d. Hereinafter, the thickness of the semiconductor structure 30 is specified as the 2nd thickness d.

Such a change in the second thickness d may also directly affect the transmittance of light passing through the upper surface (light emitting surface) 34 and the light extraction efficiency of the device.

4 shows the transmission spectrum of the light emitting surface 34 of the vertical light emitting device according to the change of the second thickness d.

As shown, it can be seen that as the second thickness d changes, the spacing FSR of two adjacent constructive interference peak wavelengths (g of FIG. 4) also changes. As shown in FIG. 5 in which the same transmittance spectrum is converted in the frequency domain, as the second thickness d increases, the interval FSR between the two constructive interference peak wavelengths becomes smaller (i in FIG. 5). Equation 6).

6 and 7 show transmission spectrums of the light emitting surface according to the change of the first thickness h and the second thickness d, respectively.

The emission wavelength at this time is 460 nm, the refractive index of the semiconductor layer is 2.476, Figure 6 shows the transmittance according to the change in the first thickness (h) in a state where the second thickness (d) is fixed to 2 ㎛ The spectrum is shown, and FIG. 7 shows the transmission spectrum according to the change of the second thickness d while the first thickness h is fixed at 130 nm.

It can be seen that the transmittance spectrum satisfies the above-described constructive interference condition (see Equation 2) within a certain error range. That is, the first thickness h and the second thickness d are the thicknesses satisfying the constructive interference condition (2m-1)? (Λ / 4n), where lambda is the emission wavelength, n is the refractive index of the semiconductor layer, m corresponds to a positive integer), and the error may be applied within a range of ± 10 nm.

The optical interference phenomenon described above may be ignored in the case of a light emitting device having a horizontal electrode structure having a large second thickness d, but should be considered in a vertical light emitting device structure having a second thickness d of several micrometers. It can be an important factor to do.

Since the semiconductor light emitting device having the vertical electrode structure has a thinner thickness than the horizontal electrode structure and is composed of a lower substrate made of a conductive material, the semiconductor light emitting device has excellent current injection efficiency, light extraction efficiency, and heat emission efficiency.

However, in the structure of the vertical light emitting device, the gap between the active layer and the lower metal mirror surface is short, so that the interference phenomenon between the light generated from the active layer and the reflected light by the lower reflective surface becomes very important, and because of the thin thickness, the upper and lower parts 2 The phenomenon of interference with the reflected light by the two reflecting surfaces also cannot be ignored.

The optical interference phenomenon inside the semiconductor layer of the vertical light emitting device appears as an interference wave of reinforcement / cancellation with respect to the position and frequency (wavelength), and particularly the frequency (wavelength) and emission frequency (wavelength) corresponding to the constructive interference condition. Proper matching with can directly affect light extraction efficiency.

In addition, since the matching condition of these wavelengths is highly dependent on the distance between the active layer and the lower reflective surface and the total thickness of the semiconductor layer, the thickness control of each semiconductor layer in consideration of the optical interference phenomenon is required to design and manufacture the vertical light emitting device structure. This can be a very important factor.

8 shows the structure of a vertical light emitting device having a light extraction structure 700. That is, the light extraction structure 700 and the n-type are formed on the upper surface 431 of the semiconductor structure 400 including the p-type semiconductor layer 410, the active layer 420, and the n-type semiconductor layer 430. It can be seen that the electrode 500 is provided.

The light extracting structure 700 may be formed of a rough surface located on the upper surface 431 of the n-type semiconductor layer 430, which is a light emitting surface, and the rough surface may form the uneven structure 710. In addition, when the light extraction structure 700 is formed by etching the upper surface 431 of the n-type semiconductor layer 430, a fine hexagon pyramid or hexagon pillar structure may be formed.

As described above, even in the case of the vertical light emitting device, when the light extraction structure 700 is formed on the light emitting surface and the reflectivity of the upper surface 431 is reduced, the influence of the optical interference due to the second thickness d is reduced. May be

Meanwhile, the semiconductor structure 400 may be located on the reflective electrode 300, and the reflective electrode 300 may be located on the conductive substrate 100. The conductive substrate 100 may be made of metal or a semiconductor.

In addition, a bonding layer 200 may be positioned between the reflective electrode 300 and the conductive substrate 100 to couple therebetween.

The semiconductor device 400 may further include a passivation layer 600 covering at least a portion of the semiconductor structure 400, and the passivation layer 600 may serve to prevent leakage current while protecting the semiconductor structure 400.

9 illustrates a vertical light emitting device structure in which a light crystal is applied as the light extracting structure 700, and the light crystal may be formed as a groove or a pillar (for convenience, reference numeral 720 is a groove and reference numeral 730 is a pillar). Let's look at it).

When the light crystal is formed of the groove 720, the light emitting surface may be the upper outer surface 433, and when the light crystal is composed of the pillar 730, the light emitting surface may be the surface 432 on which the pillar is located. have. Accordingly, the second thickness d may vary by the size of the groove 720 or the pillar 730. Other than that is the same as that of FIG.

In the vertical light emitting device to which the light extracting structure 700 as shown in FIGS. 8 and 9 is applied, the first interference h and the second thickness d are appropriately adjusted so that the constructive interference frequency ( When the wavelength) and the emission frequency (wavelength) are matched, high transmittance at the upper surface (light emitting surface) can be expected, thereby increasing the light extraction efficiency of the light emitting device.

The structure of increasing light extraction efficiency by adjusting the first thickness h and / or the second thickness d as described above may be applied to all semiconductor light emitting devices having a vertical electrode structure.

The manufacturing method of the vertical light emitting device illustrated above will be briefly described. First, an n-type semiconductor layer 430, an active layer having a quantum well structure (MQWs; Multi Quantum-Wells; 420), and a p-type semiconductor are formed on a growth substrate. The layer 410 is grown by metal oxide chemical vapor deposition (MOCVD) or the like.

At this time, the growth process is controlled to adjust the thickness of the n-type semiconductor layer 430 or the p-type semiconductor layer 410. That is, as shown in Equation 2, growth may be controlled by setting the first thickness h and the second thickness d to match the constructive interference frequency (wavelength) and the emission frequency (wavelength).

Thereafter, the reflective electrode 300 or the separate p-type electrode is formed on the p-type semiconductor layer 410 and then bonded to the conductive substrate 100 using the bonding layer 200.

Thereafter, the growth substrate is removed from the n-type semiconductor layer 430, and the light emitting device structure is formed by forming an n-type electrode 500 and a pad (not shown) on the removed surface.

In this case, the thickness of the p-type semiconductor layer 410 may be several hundred nanometers or less, and the semiconductor structure 400 includes the p-type semiconductor layer 410 / active layer 420 / n-type semiconductor layer 430. ) May have a total thickness of several micrometers (μm).

In addition, the light extracting structure 700 may be formed on the surface from which the growth substrate is removed by etching or the like, and a region formed of individual semiconductor elements may be partitioned before or after removing the growth substrate, and the partitioned portion may be formed. The passivation layer 600 may be formed on the substrate.

When separated into individual elements, a light emitting device structure as shown in FIG. 1, 8, or 9 is formed.

While some embodiments of the present invention have been described by way of example, those skilled in the art will appreciate that various modifications and variations can be made without departing from the essential features thereof.

Therefore, the embodiments described above should not be construed as limiting the technical spirit of the present invention but merely for better understanding.

The scope of the present invention is not limited by these embodiments, and should be interpreted by the following claims, and the technical spirit within the scope equivalent thereto should be interpreted as being included in the scope of the present invention.

100: conductive substrate 200: bonding layer
300: reflective electrode 400: semiconductor structure
500: n-type electrode 600: passivation layer
700: light extraction structure

Claims (12)

In a nitride semiconductor light emitting device,
Conductive substrates;
A reflective electrode positioned on the conductive substrate; And
A semiconductor including a first conductive semiconductor layer on the reflective electrode, an active layer on the first conductive semiconductor layer, and a second conductive semiconductor layer on the active layer and having a light extraction structure on a light emitting surface Including the structure,
The thickness of the first conductive semiconductor layer and the thickness of the entire semiconductor structure correspond to constructive interference conditions of interference phenomena by light emitted directly from the active layer and light emitted from the active layer and reflected from the reflective electrode. A nitride semiconductor light emitting device. 2. The method of claim 1, wherein the constructive interference condition is that the thickness of the first conductive semiconductor layer and the thickness of the semiconductor structure is an odd multiple of λ / 4n ± 10 nm (where λ is a wavelength of emitted light and n is a semiconductor). Refractive index of the layer). The nitride-based semiconductor light emitting device according to claim 1, wherein the light extraction structure is a rough surface located on the light emitting surface of the second conductive semiconductor layer. The nitride-based semiconductor light emitting device according to claim 1, wherein the light extraction structure has a hexagonal pyramid or hexagonal column structure which is irregularly arranged on the light emitting surface of the second conductive semiconductor layer. The nitride-based semiconductor light emitting device according to claim 1, wherein the light extraction structure is an uneven structure located on the light emitting surface of the second conductive semiconductor layer. The nitride-based semiconductor light emitting device according to claim 1, wherein the light extraction structure is a photonic crystal. The nitride-based semiconductor light emitting device according to claim 1, wherein the conductive substrate comprises a metal or a semiconductor. The nitride-based semiconductor light emitting device according to claim 1, wherein the thickness of the first conductive semiconductor layer is the shortest distance between the reflective electrodes and the active layer. The nitride-based semiconductor light emitting device according to claim 1, wherein a thickness of the entire semiconductor structure is the shortest distance between the light emitting surface and the reflective electrode. The nitride-based semiconductor light emitting device of claim 1, further comprising a passivation layer on the semiconductor structure. The nitride-based semiconductor light emitting device of claim 1, further comprising a bonding layer between the conductive substrate and the reflective electrode. In a nitride semiconductor light emitting device,
Conductive substrates;
A reflective electrode positioned on the conductive substrate; And
A semiconductor including a first conductive semiconductor layer on the reflective electrode, an active layer on the first conductive semiconductor layer, and a second conductive semiconductor layer on the active layer and having a light extraction structure on a light emitting surface Including the structure,
The shortest distance between the active layer in the reflective electrode and the light emitting surface in the reflective electrode is an odd multiple of λ / 4n ± 10 nm (where λ is the wavelength of emitted light and n is the refractive index of the semiconductor layer). A nitride-based semiconductor light emitting device characterized in that it satisfies.

Images