JP4191566B2 - LIGHT EMITTING DIODE HAVING CURRENT BLOCK STRUCTURE AND METHOD FOR MANUFACTURING THE SAME - Google Patents

Description

  The present invention relates to a light emitting diode and a manufacturing method thereof, and more particularly, to a light emitting diode having a current blocking structure and a manufacturing method using an injection technique.

  In the past 40 years, every effort has been made to develop a new light emitting diode material system and improve its internal quantum efficiency in the world. However, there still exists a large gap between the external quantum efficiency of the light emitting diode and the internal quantum efficiency. The internal quantum efficiency of a light emitting diode adopting a double heterostructure (DH) reaches 99%, but the external quantum efficiency is low, only a few percent. The main causes are as follows: (1) Most of the generated photons are p-type resistive contact electrodes due to the current distribution in the p-type cladding layer, p-type window layer, and p-type contact layer above the light emitting layer of the light emitting diode. And is reflected and returned to the substrate and further absorbed by the substrate, reducing the probability of photons radiating the diode. (2) It is very difficult to transmit photons from a semiconductor material having a high refractive index (Refractive Index, n) to the surrounding low refractive index air (n = 1), and this also causes a large number of photons to be reflected. This is because they are returned and absorbed by the substrate.

  The high-intensity light-emitting diodes currently on the market are red, yellow, green and blue, all of which use semiconductor materials such as aluminum gallium indium phosphide / gallium arsenide substrate and aluminum indium gallium nitride / sapphire single crystal substrate. In addition, a film layer structure is employed in which a light emitting diode is epitaxially grown by a metal-organic chemical vapor deposition (MOCVD) technique.

  FIG. 1 is a cross-sectional view of a known light emitting diode 10. As shown in FIG. 1, the light-emitting diode 10 includes a gallium arsenide substrate 12, a lower cladding layer 14 made of n-type aluminum gallium phosphide (n-AlGaInP), an undoped aluminum gallium indium phosphide (undoped-AlGaInP). ) And an upper cladding layer 18 made of p-type aluminum gallium indium phosphide (p-AlGaInP). In addition, the light emitting diode 10 also includes a p-type resistive contact electrode 22 provided on the surface of the upper cladding layer 18 and an n-type resistive contact electrode 20 provided on the lower surface of the gallium arsenide substrate 12. The p-type resistive electrode 22 is a metal film having a diameter of about 150 microns and is a pad for an external circuit. The current applied to the light emitting diode 10 flows from the top to the bottom via the p-type resistive contact electrode 22 and then flows through the upper cladding layer 18 and is poured into the light emitting layer 16 to generate photons.

  The p-type aluminum gallium indium phosphide that constitutes the upper cladding layer 18 has a relatively high electric resistance and is very thin, so that the current is difficult to spread uniformly in the lateral direction. It concentrates directly under the mold resistive contact electrode 22. However, when a photon generated in the light emitting layer 16 directly below the p-type resistive contact electrode 22 attempts to emit the light emitting diode 10, it is blocked by the upper p-type resistive electrode 22 and reflected back. Most photons are absorbed by the gallium arsenide substrate 12 having a relatively small energy gap, which restricts the external quantum efficiency of the light emitting diode 10.

The light emitting diode 10 uses the upper cladding layer 18 made of p-type aluminum gallium indium phosphide directly as a current spreading layer. As a result of research, it has been found that this has the following three problems. (1) Carrier mobility of p-type aluminum gallium indium phosphide is very low, only around 10 cm ² / V-sec. (2) p-type aluminum gallium indium phosphide is difficult to imprint and the maximum carrier concentration is only around 10 ¹⁸ / cm ³ . (3) When the epitaxial layer of p-type aluminum gallium phosphide is 2 to 5 microns, the quality of the aluminum gallium indium phosphide semiconductor material is deteriorated.

  FIG. 2 is a cross-sectional view of another known light emitting diode 30. Compared with the light emitting diode 10 of FIG. 1, the light emitting diode 30 of FIG. 2 has an increased number of p-type window layers 32 on the upper cladding layer 18. In order to overcome the above-described problems, researchers have epitaxially grown a p-type window layer 32 having a thickness of about 2 to 50 microns on the upper cladding layer 18. Semiconductor materials currently widely used for window layers include indium aluminum phosphide (InAlP), gallium aluminum arsenide (AlGaAs), gallium nitride, gallium phosphide, and the like. The p-type window layer 32 not only has a relatively low electrical resistivity, but also transmits (that is, does not absorb) photons emitted from the light emitting diode 32. By adopting this p-type window layer 32, researchers have succeeded in developing a high-intensity red light emitting diode of aluminum gallium indium phosphide. In 1991, Toshiba, Japan, first adopted p-type aluminum gallium arsenide (p-AlGaAs) to produce a window layer and a current spreading layer, and increased the external quantum efficiency of the light-emitting diode by about 40 times. Subsequently, Hewlett-Packard Company in the United States uses p-type gallium arsenide (p-GaP) with a thickness of 2-15 microns to produce a window layer, effectively increasing the external quantum efficiency of the light-emitting diode. Raised.

  FIG. 3 is a cross-sectional view of another known light emitting diode 40. As shown in FIG. 3, in comparison with the light emitting diode 30, the light emitting diode 40 is provided with a window layer 42 on the upper cladding layer 18 to develop a current in the lateral direction. A three-layer epitaxial layer structure of gallium arsenide / gallium phosphide (GaP / GaAs / GaP) is employed. Taiwan's Kunitachi Photoelectric Company has successfully developed a high-intensity light-emitting diode with aluminum gallium indium phosphide red using this design.

  FIG. 4 is a cross-sectional view of another known light emitting diode 50. The light emitting diode 50 develops a current in the lateral direction using one transparent electrode 52. The transparent electrode 52 is formed by growing indium tin oxide (Indium Tin Oxide, ITO) on the upper cladding layer 18 made of p-type aluminum gallium phosphide, and the current of the light emitting diode 50 passes through the transparent electrode 52. Then, it expands in the lateral direction and reaches the upper cladding layer 18. First, the photoelectric industry research institute of Industrial Technology Research Institute in Taiwan succeeded in developing a high-intensity light emitting diode of aluminum gallium indium phosphide red using this design. However, since it is difficult to form a good resistive contact at the interface between indium tin oxide and aluminum gallium phosphide, it is necessary to add a transition layer 54 (Transition Layer) composed of p-type gallium arsenide in the middle.

  FIG. 5 is a cross-sectional view of another known light emitting diode 60. The light emitting diode 60 employs a current blocking structure to develop a current in a lateral direction, and includes a p-type window layer 62 provided on the upper cladding layer 18 and an upper cladding layer. 18 and an n-type epitaxial layer 64 provided between the p-type window layer 62. The n-type epitaxial layer 64 is directly below the p-type resistive contact electrode 22 and further forms a pn boundary surface that can prevent current from passing through the upper cladding layer 18. This type of current blocking structure allows the current of the light emitting diode 60 to be spread laterally and effectively reach the periphery of the p-type resistive contact electrode 22 without being concentrated in the central area. The probability that generated photons are blocked by the p-type resistive contact electrode 22 is greatly reduced, thereby increasing the external quantum efficiency of the light emitting diode 60. Toshiba in Japan uses p-type gallium arsenide (p-AlGaAs) semiconductor material to manufacture the window layer and adds an n-type island-shaped current blocking structure.

  If a current blocking structure at the pn interface is employed, two steps are required when performing MOCVD epitaxial growth. First, an n-type epitaxial layer 64 of several tens of nanometers (nanometer) is epitaxially grown on the upper cladding layer 18, and then the epitaxial wafer is taken out of the reactor, using a micro image and an etching technique, An island-shaped n-type epitaxial layer 64 is formed. Further, the epitaxial wafer is sent to the MOCVD reactor, and the p-type window layer 62 is subsequently grown epitaxially. In addition, the current blocking structure of the light emitting diode 60 is provided above the upper cladding layer 18, and the current introduced from the p-type resistive contact electrode 22 still flows to the light emitting layer 16 below the n-type epitaxial layer 64. The photons generated here are still blocked by the p-type resistive contact electrode 22 and cannot be emitted to the outside.

Currently, there are many technologies that can be used to solve the current spreading problem of light emitting diodes. For example, H.M. Sugawara et al. Manufactured a current blocking structure (see Patent Document 1) using a selected area diffusion method. B. J. et al. Lee et al., Using a transparent image made of ITO or ZnO, uses a micro image and etching technology to form a single round hole whose depth reaches the upper cladding layer made of p-type aluminum gallium phosphide. Then, a metal film is plated to form a Schottky barrier, and a natural oxide is formed on the interface between the metal film and p-type aluminum gallium phosphide by heating. A current block structure is formed by this Schottky barrier and a natural oxide (see Patent Document 2). In addition, Patent Literature 3, Patent Literature 4, Patent Literature 5, Patent Literature 6, Patent Literature 7, Patent Literature 8, and the like also disclose various types of current block structure designs.
US Pat. No. 5,153,889 US Pat. No. 5,717,226 US Pat. No. 5,949,093 US Pat. No. 6,420,732 European Patent Application Publication No. 1,225,670 US Patent Application Publication No. 2001/0050530 US Patent Application Publication No. 2003/0039288 US Pat. No. 6,522,676

  A main object of the present invention is to provide a light emitting diode having a current blocking structure and a method for manufacturing the light emitting diode having a current blocking structure by using an injection technique.

The light emitting diode of the present invention is
A substrate,
A lower clad layer and an upper clad layer with a light emitting layer sandwiched between them, and a window layer provided on the upper clad layer, an epitaxial structure provided on the substrate;
A light emitting diode comprising a resistive contact electrode provided on the epitaxial structure,
A current blocking structure extending from below the resistive contact electrode to at least the light emitting layer is provided inside the epitaxial structure.

  A contact layer that develops a current in the lateral direction may be provided between the window layer and the resistive contact electrode of the light emitting diode of the present invention.

  The current blocking structure of the light emitting diode of the present invention may extend to the lower cladding layer.

  The area of the current block structure of the light emitting diode of the present invention is preferably smaller than the area of the resistive contact electrode.

  The current blocking structure of the light emitting diode of the present invention may extend from a lower surface of the resistive contact electrode.

A first light emitting diode manufacturing method according to the present invention includes an epitaxial layer having a lower cladding layer and an upper cladding layer having a light emitting layer sandwiched therebetween on a substrate, and a window layer provided on the upper cladding layer. Forming a structure; and
Forming a photoresist layer including at least one opening on the epitaxial structure;
Performing at least one implantation step used to form the current blocking structure inside the epitaxial structure;
Removing the photoresist layer;
Forming a resistive contact electrode on the epitaxial structure.

A second light emitting diode manufacturing method according to the present invention comprises an epitaxial layer having a lower cladding layer and an upper cladding layer sandwiched between a light emitting layer and a window layer provided on the upper cladding layer. Forming a structure; and
Forming a resistive contact electrode on the epitaxial structure;
Forming a photoresist layer including at least one opening on the epitaxial structure;
A step of performing at least one implantation step used to form the current block structure inside the epitaxial structure.

  In the light emitting diode manufacturing method of the present invention, the implantation step may introduce a proton beam having a predetermined dose and a predetermined energy into the epitaxial structure.

The predetermined dose may be in the range of (1 × 10 ¹² ) impurities / cm ² to (9 × 10 ¹⁶ ) impurities / cm ² .

  The predetermined energy may be in the range of 100 kV to 1000 kV.

  Furthermore, in the light emitting diode manufacturing method of the present invention, the implantation step may introduce a proton beam having a plurality of types of energy into the epitaxial structure.

  In the light emitting diode manufacturing method of the present invention, the impurity used in the implantation step may be selected from the group consisting of protons, nitrogen ions, and oxygen ions.

  Compared with a known technique, the present invention uses an injection technique to form a current block structure inside a light emitting diode, and has the following advantages.

  1. The epitaxy wafer can be completed in all epitaxial growths with only one entry into and out of the MOCVD reactor.

  2. The light emitting diode of the present invention can achieve the purpose of spreading current only by having a relatively thin window layer, thereby shortening the time of epitaxial growth.

  3. The injection process is a very stable and reliable technique, and can not only increase the pass rate of manufacturing the light emitting diode but also relatively reduce the production cost.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. 6 to 8 are views showing a method of manufacturing the light emitting diode 70 according to the first embodiment of the present invention. As can be seen from FIG. 6, in the present invention, an epitaxial structure 80 is first formed on a substrate 72. The epitaxial structure 80 includes a lower cladding layer 82, an upper cladding layer 84, an upper cladding layer 84, and a lower cladding layer. , A light emitting layer 83 sandwiched between 82, a window layer 86 provided on the upper cladding layer 84, and a contact layer 88 provided on the window layer 86. Generally speaking, the impedance of the window layer 86 is high, which is disadvantageous for lateral development of current. Therefore, according to the present invention, a contact layer having a relatively high carrier concentration is formed on the surface of the window layer 86 by adding a gas containing a p-type impurity to the MOCVD reactor in the process of epitaxially growing the window layer 86. 88 was formed.

  Next, an aluminum film or a gold film having a thickness of about 1,000 to 2,000 angstroms is plated on the contact layer 88, and a photoresist having an appropriate thickness is applied using a rotary method (Spin-on ), After passing through soft oven and hard oven, and using alignment photomask, after micro image exposure, etching and photoresist removal procedures, leave the metal cross symbol in the epitaxial wafer cutting section, For reference.

As can be seen from FIG. 7, a photoresist layer 100 with an opening 102 is formed on the contact layer 88 of the epitaxial structure 80. Next, at least one implantation step is performed, and a proton beam 96 having a predetermined dose and a predetermined energy is introduced into the contact layer 88, the window layer 86, the upper clad layer 82, and the light emitting layer 83 directly below the opening 102, and an epitaxial structure is formed. A current blocking structure 92 is formed in 80. This predetermined dose is between 1 × 10 ¹² and 9 × 10 ¹⁶ impurities / cm ² , and the predetermined energy is between 100 and 1000 kV. In addition to protons, nitrogen ions and oxygen ions can also be used to form this current blocking structure. In this implantation step, proton beams having a plurality of types of energy can be introduced into the epitaxial structure. In this implantation step, the low energy proton beam may be injected after the high energy proton beam is injected first, or the low energy proton beam may be injected first and then the high energy proton beam may be injected.

  As shown in FIG. 8, after removing the photoresist layer 100, a p-type resistive contact electrode 90 is formed on the epitaxial contact layer 88, and an n-type resistive contact electrode 94 is formed on the other surface of the substrate 72. Thus, the light emitting diode 70 is completed. The area of the opening 102 (that is, the injection part) is preferably smaller than the area of the p-type resistive contact electrode 90. Taking a circular resistive contact electrode having a diameter of 150 μm as an example, the diameter of the corresponding injection part is 10 μm to 140 μm. Between. The current blocking structure 92 of the light emitting diode 70 of the present invention extends from the lower surface of the p-type resistive contact electrode 90 to the light emitting layer 83. Further, in the present invention, by increasing the energy amount of the proton beam, protons can be injected into the light emitting layer 83 or the lower cladding layer 82 directly below the opening 102. That is, the current blocking structure 92 extends from the lower surface of the p-type resistive contact electrode 90 to the lower cladding layer 82.

  Since most of the photons generated in the light emitting layer 83 directly under the p-type resistive contact electrode 90 cannot radiate the light emitting diode 70, the present invention injects protons into the light emitting layer 83 directly under the p-type resistive contact electrode 90. This avoids the generation of photons that cannot radiate the light emitting diode 70 due to the current flowing therethrough. On the contrary, the current flows to the light emitting layer 83 other than directly below the p-type resistive contact electrode 90, generating photons that can radiate the light emitting diode 70, and further increases the external quantum efficiency.

  Compared to known techniques (light emitting diode 60 as shown in FIG. 5), the present invention forms a current blocking structure 92 that extends continuously between resistive contact electrode 90 and light emitting layer 83. When a forward current is applied to the light emitting diode 70, the current introduced from the p-type resistive contact electrode 90 first develops via the contact layer 88 and then flows downward to the light emitting layer 83. By the way, since the semi-insulator is already formed in the cylindrical area directly below the p-type resistive contact electrode 90 and prevents the passage of the forward current, the current flows through the non-cylindrical area. The light emitting layer 83 is injected outside. Therefore, the probability that the generated photons are reflected back to the p-type resistive contact electrode 90 due to the geometric relationship is greatly reduced, and the external quantum efficiency of the light emitting diode 70 is greatly increased.

  FIG. 9 is an explanatory diagram of a manufacturing method of the light emitting diode 70 according to the second embodiment of the present invention. As shown in FIG. 9, after an epitaxial structure 80 is formed on the upper surface of the substrate 72, a p-type resistive contact electrode 90 is formed on the epitaxial structure 80, and an n-type resistive contact is formed on the lower surface of the substrate 72. An electrode 94 is formed. Next, a photoresist layer 110 including the opening 112 is formed. Then, an implantation process is performed to introduce a proton beam 96 having a predetermined dose and a predetermined energy into the contact layer 88, the window layer 86, and the upper cladding layer 84 immediately below the opening 112, so that a current blocking structure 92 is formed in the epitaxial structure 80. Form. Finally, the photoresist layer 110 is removed, and the manufacture of the light emitting diode 70 is completed.

The predetermined dose is between 1 × 10 ¹² and 9 × 10 ¹⁶ impurities / cm ² and the predetermined energy is between 100 and 1000 kV. Since the light passes through the p-type resistive contact electrode 90 first, the energy of the injected proton is slightly higher than that of the first embodiment. When aligning with an optical mask, a p-type resistive contact electrode can be used as a reference for alignment. At this time, it is not necessary to make the alignment symbol described in the first embodiment, and there are only two optical masks for defining the implantation position and for the resistive contact electrode 90.

  Since the present invention can also control the dose and energy of the injected proton beam 96, the current blocking structure 92 of the light emitting diode 70 can be contacted anywhere under the p-type resistive contact electrode 90 (ie, its lower surface). Not).

  Compared with a known technique, the present invention uses an injection technique to form a current blocking structure inside a light emitting diode, and has the following advantages.

  1. In the well-known technique, a current blocking structure is formed using a micro image and an etching technique, and therefore, all crystal film layers are completed only after the light emitting diode is subjected to a crystallization process twice. In contrast, since the current block structure implantation process of the present invention can be performed after all the epitaxial layers are completed, the epitaxial wafer can be transferred to and from the MOCVD reactor only once. The growth can be completed.

  2. If the light emitting diode of the present invention has a relatively thin window layer, the purpose of spreading the current can be achieved. The current is applied mainly in the lateral direction from the current block structure and the contact layer, so that the thickness of the window layer is reduced and the time of epitaxial growth can be shortened.

  3. The injection process is a very stable and reliable technique, and can not only increase the pass rate of manufacturing the light emitting diode but also relatively reduce the production cost.

  The technical contents and technical features of the present invention are as described above, but those skilled in the art can make various alternatives and modifications based on the teaching and disclosure of the present invention without departing from the spirit of the present invention. is there. Accordingly, the scope of protection of the present invention should not be limited to that disclosed in the examples, but includes various alternatives and modifications that do not depart from the present invention, and those covered by the appended claims. To do.

It is sectional drawing of a known red light emitting diode. It is sectional drawing of another known light emitting diode. It is sectional drawing of another known light emitting diode. It is sectional drawing of another known light emitting diode. It is sectional drawing of another known red light emitting diode. It is explanatory drawing of the manufacturing method of the light emitting diode of 1st Embodiment of this description. It is explanatory drawing of the manufacturing method of the light emitting diode of 1st Embodiment of this description. It is explanatory drawing of the manufacturing method of the light emitting diode of 1st Embodiment of this description. It is explanatory drawing of the manufacturing method of the light emitting diode of the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Light emitting diode 12 Board | substrate 14 Lower clad layer 16 Light emitting layer 18 Upper clad layer 20 N-type resistive contact electrode 22 P-type resistive contact electrode 30 Light emitting diode 32 Window layer 40 Light emitting diode 42 Window layer 50 Light emitting diode 52 Transparent electrode 54 Transition Layer 60 light emitting diode 62 window layer 64 n-type epitaxial layer 70 light emitting diode 72 substrate 80 epitaxial structure 82 lower cladding layer 83 light emitting layer 84 upper cladding layer 86 window layer 88 contact layer 90 p-type resistive contact electrode 92 current block structure 94 n-type resistive contact electrode 96 proton beam 100 photoresist layer 102 opening 110 photoresist layer 112 opening

Claims (6)

In a method for manufacturing a light emitting diode having a current blocking structure,
1) forming an epitaxial structure on a substrate having a lower cladding layer and an upper cladding layer with a light emitting layer sandwiched therebetween, and a window layer provided on the upper cladding layer;
2) forming a light-blocking resistive contact electrode on the epitaxial structure;
3) forming a photoresist layer including at least one opening having an area smaller than the area of the light-shielding resistive contact electrode on the epitaxial structure;
4) performing at least one implantation step of injecting impurities into the epitaxial structure below the opening, which is used to form the current blocking structure inside the epitaxial structure;
The current block structure extends from a region under the light-shielding resistive contact electrode to a place including at least the light emitting layer, and an area of the current block structure is larger than an area of the light-shielding resistive contact electrode. A method for manufacturing a light-emitting diode, characterized in that It said injection step, the light emitting diode manufacturing method of claim 1, wherein the introducing proton beam of a predetermined dose and the predetermined energy to the epitaxial structure. ^3. The method of manufacturing a light emitting diode according to claim 2 , wherein the predetermined dose is in a range of (1 × 10 ¹² ) impurities / cm ² to (9 × 10 ¹⁶ ) impurities / cm ² . 3. The method of manufacturing a light emitting diode according to claim 2 , wherein the predetermined energy is within a range of 100 kV to 1000 kV.   2. The light emitting diode manufacturing method according to claim 1, wherein the implantation step introduces proton beams of a plurality of types of energy into the epitaxial structure. The impurity to be used in the implantation step, protons, nitrogen ions, the light emitting diode manufacturing method of claim 1, wherein a from the group consisting of oxygen ions are those selected.

Images