KR20060012789A - A low-resistance electrode of compound semiconductor light emitting device and a compound semiconductor light emitting device using the electrode - Google Patents

Abstract

The present invention discloses a low resistance electrode of a compound semiconductor light emitting device and a compound semiconductor light emitting device using the same. A p-type electrode according to the present invention stacked on a p-type semiconductor layer of a compound semiconductor light emitting device having an n-type semiconductor layer, an active layer and a p-type semiconductor layer, is laminated on the p-type semiconductor layer to emit light emitted from the active layer A reflective electrode layer; Agglomeration preventing electrode layer stacked on the reflective electrode layer to prevent agglomeration of the reflective electrode layer during heat treatment; And an anti-oxidation electrode layer stacked on the anti-aggregation electrode layer to prevent oxidation of the anti-aggregation electrode layer.

Compound semiconductor, light emitting device, electrode, GaN, nitride semiconductor

Description

A low-resistance electrode of compound semiconductor light emitting device and a compound semiconductor light emitting device using the electrode

1 is a perspective view schematically showing the operating principle of a general LED.

2 is a cross-sectional view showing a conventional p-type electrode formed on a compound semiconductor light emitting element.

3A and 3B are cross-sectional views showing the structure of a p-type electrode of a compound semiconductor light emitting device according to the first and second embodiments of the present invention.

4 shows a surface after heat treatment of a conventional electrode and an electrode according to the present invention, respectively.

5 is a graph showing the current-voltage characteristics of the electrode according to the first embodiment of the present invention.

6A to 6C show the surfaces of a conventional electrode, an electrode on which the anti-lumping electrode layer is formed, and an electrode on which the anti-oxidation electrode layer is formed, respectively.

7A and 7B are sectional views showing an electrode structure in which an anti-oxidation electrode layer is formed according to the third and fourth embodiments of the present invention.                 

8 is a graph showing current-voltage characteristics when the aggregation preventing electrode layers according to the first and second embodiments of the present invention are oxidized.

9A and 9B are graphs showing current-voltage characteristics of an electrode according to a third exemplary embodiment of the present invention.

※ Explanation of code about main part of drawing ※

10 ..... nitride semiconductor 13 ..... n-type nitride semiconductor

15 ..... active layer 17 ..... p-type nitride semiconductor

20 ..... p type reflective electrode

24 ..... Agglomeration prevention electrode layer

30 ..... n-type electrode 40 ..... sapphire substrate

The present invention relates to a low resistance electrode of a compound semiconductor light emitting device and a compound semiconductor light emitting device using the same.

1 schematically illustrates the principle of operation of a typical compound semiconductor light emitting device (LED). As shown in FIG. 1, the LED may include a semiconductor light emitting device 10 formed on the sapphire substrate 40, a p-type electrode 20 formed on the semiconductor light emitting device 10, and one side of the semiconductor light emitting device. The n-type electrode 30 is comprised. Here, when a forward voltage is applied to the LED electrode, electrons in the conduction band of the p-type cladding layer 17 in the semiconductor light emitting device 10 transition to recombine with holes in the valence band of the n-type cladding layer 13. Light is emitted from the active layer 15 by the energy. Light emitted from the active layer 15 is reflected by the p-type electrode 20 formed on the semiconductor light emitting device 10 and is emitted to the outside of the LED through the sapphire substrate 40. As such, in the LED of the light emitted from the semiconductor light emitting device 10 is not directly emitted onto the substrate but is reflected by the electrode and emitted through the substrate, the p-type electrode must reflect the light, such as Ag. Metal is used as the p-type electrode.

On the other hand, a semiconductor having a large direct bandgap energy (about 2.8 eV or more) is essential for blue light emission. Initially, semiconductor devices that emit blue or green light mainly using mainly II-VI ternary materials have been developed. In recent years, semiconductor devices for emitting blue light in group III-V semiconductors have been studied. Among them, group III nitride (compounds mainly related to GaN) semiconductors have been particularly noticed today because they are highly stable to optical, electrical and thermal stimuli and have high luminous efficiency.

2 shows a conventional p-type electrode 20 formed on a p-type cladding layer (p-type nitride semiconductor) 17 of a nitride semiconductor 10 in an LED using a group III nitride semiconductor such as GaN as a semiconductor light emitting element. To show. As described above, in the related art, a p-type reflective electrode 20 such as Ag is formed and used on the p-type nitride semiconductor 17. According to the general process of forming the p-type reflective electrode 20 on the p-type nitride semiconductor 17, after the electrode is deposited on the p-type nitride semiconductor, it is necessary to anneal to reduce the resistance do.

However, the surface energy of the nitride semiconductor and the surface energy of the metal material used as the reflective electrode, such as Ag, are generally different from each other. Due to such a difference in surface energy, it is generally known that agglomeration occurs as shown in FIGS. 4 (a) and 4 (c) in the Ag electrode during the annealing process. 4 (a) shows the Ag electrode in which the aggregation occurs from above, and FIG. 4 (c) shows the Ag electrode in which the aggregation occurs from the side. When the aggregation occurs in the Ag electrode, the reflectivity of the Ag electrode is reduced as a result, there is a problem that the light output of the overall LED is reduced by that much.

Accordingly, the technical problem to be achieved by the present invention is to alleviate the aggregation phenomenon occurring in the p-type reflective electrode to suppress the light output degradation of the LED using the nitride semiconductor element as a light emitting element.

According to one type of the present invention, a p-type electrode stacked on a p-type semiconductor layer of a compound semiconductor light emitting device having an n-type semiconductor layer, an active layer, and a p-type semiconductor layer is laminated on the p-type semiconductor layer and in the active layer A reflective electrode layer reflecting the emitted light; Agglomeration preventing electrode layer stacked on the reflective electrode layer to prevent agglomeration of the reflective electrode layer during heat treatment; And an anti-oxidation electrode layer stacked on the anti-aggregation electrode layer to prevent oxidation of the anti-aggregation electrode layer.                     

The low resistance electrode of the compound semiconductor light emitting device may further include a contact electrode layer interposed between the p-type semiconductor layer and the reflective electrode layer in order to reduce contact resistance between the p-type semiconductor layer and the reflective electrode layer. The contact electrode layer is selected from the group consisting of La-based alloys, Ni-based alloys, Zn-based alloys, Cu-based alloys, thermoelectric oxides, doped In oxides, ITO and ZnO. It is characterized by consisting of at least one material.

In addition, the reflective electrode layer is characterized by consisting of at least one material selected from the group consisting of Ag, Rh, Al, Sn.

The anti-lumping electrode layer is formed of at least one material selected from the group consisting of Zn, Zn-based alloys, Rh, Mg-based alloys, Au, Ni, Ni-based alloys, doped In oxides, Cu, and Cu-based alloys. It is characterized by.

The anti-oxidation electrode layer is made of at least one material selected from the group consisting of Ru, Ir, TiN.

On the other hand, according to another type of the present invention, the compound semiconductor light emitting device according to the present invention, the nitride-based compound semiconductor layer having an active layer for emitting light between the n-type semiconductor layer and the p-type semiconductor layer; A reflective electrode layer stacked on the p-type semiconductor layer and reflecting light emitted from the active layer; Agglomeration preventing electrode layer stacked on the reflective electrode layer to prevent agglomeration of the reflective electrode layer during heat treatment; And an anti-oxidation electrode layer stacked on the anti-aggregation electrode layer to prevent oxidation of the anti-aggregation electrode layer, wherein the difference in surface energy between the anti-aggregation electrode layer and the p-type semiconductor layer is different from the reflection electrode layer. It is characterized by less than the difference in surface energy between the p-type semiconductor layer.

Hereinafter, a low resistance electrode of a compound semiconductor light emitting device according to an exemplary embodiment of the present invention and a structure of the compound semiconductor light emitting device using the same will be described in detail.

3A and 3B are cross-sectional views showing p-type electrodes of the compound semiconductor light emitting device according to the first and second embodiments of the present invention, respectively. As described above, the reflective electrode 20 material such as Ag has a very large surface energy difference from that of the p-type nitride semiconductor 17 material in the lower layer, so that the phenomenon of aggregation occurs during heat treatment after lamination of the electrodes. have. In order to prevent such a phenomenon, the first embodiment of the present invention further laminates a conductive material having a small difference in surface energy from the p-type nitride semiconductor 17 on the reflective electrode 20 as shown in FIG. 3A. . Such materials include Zn, Zn-based alloys (Zn-alloy), Rh, Mg-based alloys (Mg-alloy), Au, Ni, Ni-based alloys (Ni-alloy), doped In Oxide ), Cu, Cu-based alloys, and the like, in particular, among these materials, there are Cu, Ni, Rh, Ni-Zn, Ni-Mg and the like. Since these materials have a small surface energy difference from the p-type nitride semiconductor 17 and good electrical conductivity, the materials may be stacked on the reflective electrode 20 to serve as an agglomeration preventing layer (APL) and an electrode. have. In the detailed description of the present invention, such an electrode layer will be referred to as an agglomeration preventing electrode layer.

When the agglomeration preventing electrode layer 24 is stacked on the reflective electrode 20, since the surface energy difference between the material used for the agglomeration preventing electrode layer 24 and the p-type nitride semiconductor 17 is small, deformation that may occur in a subsequent heat treatment process may occur. The agglomeration preventing electrode layer 24 and the p-type nitride semiconductor 17 are similar to each other. Accordingly, the anti-lumping electrode layer 24 prevents the reflective electrode 20 from being agglomerated in the heat treatment process, thereby maintaining a flat surface of the electrode. FIG. 4 shows a comparison between the case where the agglomeration preventing electrode layer 24 is not stacked on the reflective electrode 20 and when the stacking electrode layer 24 is not stacked. 4 (a) and 4 (c) show when the agglomeration preventing electrode layers 24 are not stacked, and it can be seen that a myriad of agglomerations have occurred. On the other hand, Figure 4 (b) and Figure 4 (d) is shown when the aggregation preventing electrode layer 24 is stacked according to the present invention, unlike the prior art, it can be confirmed that the aggregation hardly occurs. As described above, if agglomeration does not occur in the reflective electrode 20, the reflectivity does not decrease, and thus a high reflection state can be maintained. Thus, the semiconductor light emitting element using the electrode formed in the manner according to the present invention has a much lower reflectivity drop compared with the prior art.

At this time, if the thickness of the aggregation prevention electrode layer 24 is too thick, there is a problem that the electrical resistance is increased, while if too thin, the aggregation prevention effect is lost, it is necessary to appropriately adjust the thickness of the aggregation prevention electrode layer 24. The thickness of the anti-lumping electrode layer 24 is determined in consideration of the size of the entire semiconductor device and the thickness of the reflective electrode 20. Typically, the thickness of the reflective electrode 20 is between 50 nm and 1000 nm, and 200 nm is mainly used. Therefore, when the thickness of the reflective electrode 20 is 200 nm, the thickness of the anti-lumping electrode layer 24 is suitably in the range of 1 nm to 200 nm. More preferably, the thickness of the agglomeration electrode layer 24 is suitably about 20 nm.

In the stacking method, a metal vapor of the reflective electrode material generated by the electron beam and a metal vapor of the agglomeration preventing electrode layer material are sequentially exposed to the substrate using a general E-beam evaporator to stack the multilayer thin film structure. After laminating in this manner, annealing is performed for about 5 minutes within a temperature range of 300 ° C to 600 ° C. And it is preferable to perform the atmosphere during heat processing in the atmosphere containing at least oxygen. At this time, the heat treatment time and the atmosphere is not important in the present invention, and may be heat treated for 30 minutes or more.

On the other hand, as shown in FIG. 3A, when only the anti-lumping electrode layer 24 is formed on the reflective electrode 20, the overall contact resistance of the electrode may increase. Therefore, as shown in FIG. 3B, in the second embodiment of the present invention, an additional electrode 22 may be laminated between the p-type nitride semiconductor 17 and the reflective electrode 20 to lower the contact resistance. have. In the detailed description of the present invention, such an electrode layer is hereinafter referred to as a contact electrode layer. The contact electrode layer 22 may pass through the light generated in the active layer 15 of the nitride semiconductor light emitting device to reach the reflective electrode 20, and may pass the light reflected from the reflective electrode 20 to pass through the sapphire substrate. It is required to have high transparency since it must be able to be emitted through 40. Suitable materials for these requirements include La-alloy, Ni-alloy, Zn-alloy, Cu-alloy, and Cu-alloy. Oxides, doped In oxides, ITO, ZnO, and the like, among others, the more favorable materials are Zn-Ni alloys, Ni-Mg alloys, and Zn-Mg alloys. Etc. can be mentioned.

In this case, if the thickness of the contact electrode layer 22 is too thick, there is a problem that the overall reflectivity is inferior, and if it is too thin, there is a problem that the effect of lamination is inferior. Therefore, it is necessary to appropriately adjust the thickness of the contact electrode layer 22. The thickness of the contact electrode layer 22 is determined in consideration of the size of the entire semiconductor element and the thickness of the reflective electrode 20. Generally, when the thickness of the reflective electrode 20 is 200 nm, it is within the range of 1 nm to 200 nm. It is suitable. More preferably, the thickness of the contact electrode layer 22 is about 3 nm.

FIG. 5 illustrates that a reflective electrode 20 is formed by stacking Ag at 200 nm and a Zn stack is formed at 50 nm according to the first embodiment of the present invention. This is an example of the electrical characteristics of the electrode heat-treated at ℃, 530 ℃. As shown in FIG. 5, it is possible to confirm good characteristics in which a current rapidly flows near the operating voltage 3V.

However, when a metal material such as Cu is used as the anti-lumping electrode layer 24, a problem may occur in that current-voltage characteristics of the electrode deteriorate due to oxidation of the surface. That is, when there is no agglomeration prevention electrode layer 24, as shown in Fig. 6a, the agglomeration phenomenon occurs seriously in the reflective electrode 20. In order to prevent this, when the aggregation prevention electrode layer 24 is formed on the reflective electrode 20, as shown in FIG. 6B, the surface aggregation phenomenon is almost disappeared, but oxidation of the aggregation prevention electrode layer 24 occurs partially. In this way, when the surface of the anti-lumping electrode layer 24 is oxidized, current-voltage characteristics of the electrode deteriorate, so that the operating voltage of the compound semiconductor light emitting device becomes very high. As shown in the graph of FIG. 8, when the agglomeration preventing electrode layer 24 was oxidized, the operating voltage became nearly 8V when the first voltage was applied. Thereafter, each time the voltage is applied, the current-voltage characteristic is gradually improved. Therefore, this oxidation problem can be a big problem in the mass production process of the product.

To prevent this phenomenon, as illustrated in FIGS. 7A and 7B, an anti-oxidation electrode layer 26 is further formed on the anti-aggregation electrode layer 24. FIG. 7A shows the structure of the third embodiment in which the anti-oxidation electrode layer 26 is added to the p-type electrode of the compound semiconductor light emitting device according to the first embodiment of FIG. 3A, and FIG. 7B is a second embodiment of FIG. 3B. The structure of the fourth embodiment in which the anti-oxidation electrode layer 26 is added to the p-type electrode of the compound semiconductor light emitting device is shown. Thus, when forming the anti-oxidation electrode layer 26, as shown in Figure 6c, it can be seen that the oxidation of the anti-aggregation electrode layer 24 hardly occurs without the surface aggregation phenomenon.

According to the present invention, a material such as Ru, Ir, TiN, or the like may be used as the anti-oxidation electrode layer 26. The thickness of the anti-oxidation electrode layer 26 is preferably about 10nm to 100nm.

9A illustrates a reflective electrode 20 by stacking Ag at 250 nm, forming Cu at 30 nm, and forming an agglomeration preventing electrode layer 24 by stacking Cu at 20 nm, and oxidizing Ru by stacking 20 nm. After the prevention electrode layer 26 was formed, the electrical characteristics of the electrode in the case of heat treatment at 330 ° C. and 530 ° C., respectively, were tested. 9B is an example in which the electrical characteristics of the electrode when TiN was stacked at 20 nm instead of Ru were tested. As shown in FIGS. 9A and 9B, even when the first voltage is applied, a good current-voltage characteristic in which current rapidly flows near the operating voltage 3V can be confirmed.

As described above, according to the present invention, it is possible to prevent the aggregation phenomenon on the surface of the reflective electrode during the heat treatment process by using the aggregation prevention electrode layer. In addition, the oxidation prevention electrode layer may be prevented from being oxidized by stacking the anti-oxidation electrode layer on the aggregation prevention electrode layer. Therefore, according to the present invention, an electrode for a semiconductor light emitting element having a very low electrical resistance can be obtained, and a semiconductor light emitting element with less power consumption can be obtained. In addition, according to the present invention, stable mass production of semiconductor light emitting devices is possible.

Claims (23)

A p-type electrode laminated on a p-type semiconductor layer of a compound semiconductor light emitting device having an n-type semiconductor layer, an active layer and a p-type semiconductor layer, A reflective electrode layer stacked on the p-type semiconductor layer and reflecting light emitted from the active layer; Agglomeration preventing electrode layer stacked on the reflective electrode layer to prevent agglomeration of the reflective electrode layer during heat treatment; And The low resistance electrode of the compound semiconductor light emitting device comprising a; anti-oxidation electrode layer stacked on the anti-aggregation electrode layer to prevent oxidation of the anti-aggregation electrode layer. The method of claim 1, and a contact electrode layer interposed between the p-type semiconductor layer and the reflective electrode layer in order to reduce contact resistance between the p-type semiconductor layer and the reflective electrode layer. The method of claim 2, The contact electrode layer is selected from the group consisting of La-based alloys, Ni-based alloys, Zn-based alloys, Cu-based alloys, thermoelectric oxides, doped In oxides, ITO and ZnO. Low resistance electrode of a compound semiconductor light emitting device, characterized in that made of at least one material. The method of claim 3, wherein The thickness of the contact electrode layer is a low resistance electrode of a compound semiconductor light emitting device, characterized in that in the range of 0.1nm to 200nm. The method according to claim 1 or 2, The reflective electrode layer is a low resistance electrode of a compound semiconductor light emitting device, characterized in that made of at least one material selected from the group consisting of Ag, Rh, Al, Sn. The method of claim 5, The thickness of the reflective electrode layer is a low resistance electrode of a compound semiconductor light emitting device, characterized in that in the range of 50nm to 1000nm. The method according to claim 1 or 2, The anti-lumping electrode layer is formed of at least one material selected from the group consisting of Zn, Zn-based alloys, Rh, Mg-based alloys, Au, Ni, Ni-based alloys, doped In oxides, Cu, and Cu-based alloys. A low resistance electrode of a compound semiconductor light emitting device, characterized in that. The method of claim 7, wherein The thickness of the anti-lumping electrode layer is a low resistance electrode of a compound semiconductor light emitting device, characterized in that in the range of 1nm to 500nm. The method according to claim 1 or 2, The anti-oxidation electrode layer is a low resistance electrode of a compound semiconductor light emitting device, characterized in that made of at least one material selected from the group consisting of Ru, Ir, TiN. The method of claim 9, The thickness of the anti-oxidation electrode layer is a low resistance electrode of a compound semiconductor light emitting device, characterized in that in the range of 30nm to 100nm. The method according to claim 1 or 2, The contact electrode layer, the reflective electrode layer, the anti-aggregation electrode layer, and the anti-oxidation electrode layer are sequentially deposited using a transfer beam evaporator, and then heat treated within a temperature range of 300 ° C. to 600 ° C. Resistance electrode. The method according to claim 1 or 2, The difference in surface energy between the anti-lumping electrode layer and the p-type semiconductor layer is less than the difference in surface energy between the reflective electrode layer and the p-type semiconductor layer, low resistance electrode of the compound semiconductor light emitting device. a nitride compound semiconductor layer having an active layer for emitting light between the n-type semiconductor layer and the p-type semiconductor layer; A reflective electrode layer stacked on the p-type semiconductor layer and reflecting light emitted from the active layer; Agglomeration preventing electrode layer stacked on the reflective electrode layer to prevent agglomeration of the reflective electrode layer during heat treatment; And And an anti-oxidation electrode layer stacked on the anti-aggregation electrode layer to prevent oxidation of the anti-aggregation electrode layer. The difference in surface energy between the anti-lumping electrode layer and the p-type semiconductor layer is smaller than the difference in surface energy between the reflective electrode layer and the p-type semiconductor layer. The method of claim 13, and a contact electrode layer interposed between the p-type semiconductor layer and the reflective electrode layer in order to reduce the contact resistance between the p-type semiconductor layer and the reflective electrode layer. The method of claim 14, The contact electrode layer is selected from the group consisting of La-based alloys, Ni-based alloys, Zn-based alloys, Cu-based alloys, thermoelectric oxides, doped In oxides, ITO and ZnO. Compound semiconductor light emitting device, characterized in that made of at least one material. The method of claim 15, The thickness of the contact electrode layer is a compound semiconductor light emitting device, characterized in that in the range of 0.1nm to 200nm. The method according to claim 13 or 14, The reflective electrode layer is a compound semiconductor light emitting device, characterized in that made of at least one material selected from the group consisting of Ag, Rh, Al, Sn. The method of claim 17, The thickness of the reflective electrode layer is a compound semiconductor light emitting device, characterized in that in the range of 50nm to 1000nm. The method according to claim 13 or 14, The anti-lumping electrode layer is formed of at least one material selected from the group consisting of Zn, Zn-based alloys, Rh, Mg-based alloys, Au, Ni, Ni-based alloys, doped In oxides, Cu, and Cu-based alloys. Compound semiconductor light emitting device, characterized in that. The method of claim 19, The thickness of the anti-lumping electrode layer is a compound semiconductor light emitting device, characterized in that in the range of 1nm to 500nm. The method according to claim 13 or 14, The anti-oxidation electrode layer is a compound semiconductor light emitting device, characterized in that made of at least one material selected from the group consisting of Ru, Ir, TiN. The method of claim 21, The thickness of the anti-oxidation electrode layer is a compound semiconductor light emitting device, characterized in that in the range of 30nm to 100nm. The method according to claim 13 or 14, Wherein the contact electrode layer, the reflective electrode layer, the anti-aggregation electrode layer, and the anti-oxidation electrode layer are sequentially deposited using a transfer beam evaporator, and then heat treated within a temperature range of 300 ° C. to 600 ° C. 6.

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