JP2008198876A - GaN-based LED element and light emitting device - Google Patents

Abstract

To provide a GaN-based LED element having excellent light emission output using a conductive oxide film as a translucent electrode.
A plate-like body made of a GaN-based semiconductor in a GaN-based LED element including a laminated body made of a plurality of GaN-based semiconductor layers including at least a light-emitting layer and a p-type layer and an n-type layer sandwiching the light-emitting layer. And a conductive oxide film having a polycrystalline structure formed on the surface of the plate-like body, and a plurality of openings are formed in the conductive oxide film and exposed to the openings. A GaN-based LED element, wherein the surface of the plate-like body is provided with irregularities.
[Selection] Figure 1

Description

The present invention relates to a GaN-based LED element having a light-emitting element structure using a GaN-based semiconductor, and a light-emitting device using the GaN-based LED element.

A GaN-based semiconductor is a compound semiconductor represented by the chemical formula Al _a In _b Ga _1-ab N (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ a + b ≦ 1), and is a group III nitride semiconductor Also called a nitride-based semiconductor. A GaN-based LED in which a light-emitting element structure such as a pn junction structure, a double hetero structure, or a quantum well structure is formed of a GaN-based semiconductor can generate green to near-ultraviolet light. It has been put to practical use in such applications.

Conductivity made of indium tin oxide (ITO) or the like in a GaN-based LED element having a laminate composed of a plurality of GaN-based semiconductor layers including at least a light-emitting layer and a p-type layer and an n-type layer sandwiching the light-emitting layer It is known that the luminous efficiency can be improved by forming an oxide film on a p-type layer as a translucent electrode and providing the translucent electrode with a plurality of through holes reaching the p-type layer. (Patent Document 1).
JP 2005-123501 A

Currently, research and development for applying GaN-based LED elements to lighting applications are actively conducted. Although conductive oxide films have been used as translucent electrodes and the output of GaN-based LED elements has increased considerably, it is said that higher output is required for practical use in the lighting field. ing.

This invention is made | formed in view of this situation, The main objective is to provide the GaN-type LED element excellent in the light emission output which used the electroconductive oxide film as a translucent electrode.

In order to achieve the above object, the present invention provides a GaN-based LED element and a light emitting device having the following characteristics.
(1) In a GaN-based LED element including a laminated body composed of a plurality of GaN-based semiconductor layers including at least a light-emitting layer and a p-type layer and an n-type layer sandwiching the light-emitting layer, a plate-shaped body composed of a GaN-based semiconductor; A conductive oxide film formed on the surface of the plate-like body, and the conductive oxide film has a plurality of openings, and the plate-like body exposed to the openings A GaN-based LED element having irregularities on the surface.
(2) The GaN-based LED element according to (1), wherein the uneven convex portion has a portion made of the same material as the conductive oxide film at the top.
(3) The GaN-based LED element according to (1) or (2), wherein the conductive oxide film is an ITO film.
(4) The GaN-based LED element according to any one of (1) to (3), wherein the plate-shaped body is a GaN-based semiconductor substrate, and the stacked body is formed on the GaN-based semiconductor substrate.
(5) The GaN-based semiconductor element according to any one of (1) to (3), wherein the plate-like body is the stacked body.
(6) The GaN-based LED element according to (5), wherein the conductive oxide film is formed on a surface of a p-type layer.
(7) The GaN-based LED element according to (6), wherein the concave and convex portions reach the light emitting layer.
(8) The GaN-based LED element according to (5), wherein the conductive oxide film is formed on a surface of an n-type layer.
(9) The GaN-based LED element according to any one of (5) to (8), wherein the stacked body is formed on a light-transmitting substrate.
(10) A light-emitting device formed by flip-chip mounting the GaN-based LED element according to (9).

Since the GaN-based LED element according to the embodiment of the present invention is excellent in light emission output, it can be suitably used in applications that require high output, such as illumination applications.

In explaining the present invention, when the member constituting the GaN-based LED element is translucent or has translucency, when the GaN-based LED element is energized, the light-emitting layer It means that the member exhibits transparency to the emitted light. Translucency does not mean that the transmittance is 100%, nor does it mean that it is transparent without being clouded.

(Embodiment 1)
A GaN-based LED element according to a preferred embodiment of the present invention is a GaN-based LED including a laminate composed of a plurality of GaN-based semiconductor layers including at least a light-emitting layer and a p-type layer and an n-type layer sandwiching the light-emitting layer. An element having a plate-like body made of a GaN-based semiconductor and a conductive oxide film formed on the surface of the plate-like body, and a plurality of openings are formed in the conductive oxide film. The plate-like body exposed at the opening is provided with irregularities on the surface thereof. A sectional view of the GaN-based LED element according to Embodiment 1 of the present invention configured as described above is shown in FIG.

1 includes an n-type layer 12-1, a light emitting layer 12-2, and a p-type layer 12-3 made of a GaN-based semiconductor on a substrate 11 made of an n-type GaN-based semiconductor. It forms by forming in this order and forming the laminated body 12. A first conductive oxide film T11 made of ITO (indium tin oxide) or the like is formed on the back surface of the substrate 11 as a negative ohmic electrode, and a negative pad electrode P11 is formed on a part of the first conductive oxide film T11. Is formed. A second conductive oxide film T12 made of ITO or the like is formed as a positive ohmic electrode on the surface of the p-type layer 12-3, and a positive pad electrode P12 is formed on a part of the second conductive oxide film T12. ing. The first conductive oxide film T11 and the second conductive oxide film T12 have a polycrystalline structure, and fine irregularities corresponding to crystal grain boundaries exist on the surfaces. Each of the first conductive oxide film T11 and the second conductive oxide film T12 is provided with a plurality of openings, and the substrate exposed to the openings of the first conductive oxide film T11. 11 and the surface of the p-type layer 12-3 exposed at the opening of the second conductive oxide film T12 are both uneven.

In the GaN-based LED element 10, the light emitted from the light emitting layer 12-2 is efficiently extracted to the outside from both the surface on the substrate 11 side and the surface on the laminated body 12 side of the element. This is because the light transmittance of the first and second conductive oxide films T11 and T12 is particularly good due to the provision of the openings, and the substrate 11 and the laminate exposed in the openings. By providing irregularities on the surface of 12, the light incident on the surface from the inside of the substrate or the laminate is hardly totally reflected on the surface. In addition, the light incident on the surface from the inside of the substrate 11 or the laminated body 12 can be expected to improve the light extraction efficiency by being scattered by the unevenness. The unevenness formed in the laminate 12 may be such that the deepest part of the recess reaches the light emitting layer 12-2, and further reaches the n-type layer 12-1. In that case, you may make it the top part of a convex part not include the part originating in the p-type layer 12-3.

The shape of the opening formed in the first conductive oxide film T11 and the second conductive oxide film T12 is not limited, and may be a circle, a rectangle, a polygon, an indeterminate shape, or the like. It may be a shape that extends in a straight line. The shape and arrangement of the openings may be regular or periodic, and may be irregular or aperiodic. The opening is not limited to the through-hole. Therefore, the first conductive oxide film T11 and the second conductive oxide film T12 exhibit, for example, a comb-like pattern or a dendritic pattern. There may be. The ratio of the total area of the openings formed in the first conductive oxide film to the area of the region where the first conductive oxide film T11 spreads on the substrate 11 is “first aperture ratio”. The first aperture ratio can be, for example, 5% to 95%. Further, the ratio of the total area of the openings formed in the second conductive oxide film to the area of the region where the second conductive oxide film T12 spreads on the p-type layer 12-3 is expressed as “ If the second aperture ratio is referred to, the second aperture ratio can be set to 5% to 95%, for example.

In the GaN-based LED element 10, openings are formed in both the first conductive oxide film T11 and the second conductive oxide film T12, and irregularities are provided on the surface of the GaN-based semiconductor exposed in the openings. However, an opening is formed only in one of the first conductive oxide film T11 and the second conductive oxide film T12, and the surface of the GaN-based semiconductor is exposed in an uneven shape in the opening. You may let them. Although an insulating substrate such as a sapphire substrate can be used as the substrate 11, in that case, the negative electrode needs to be formed on the surface of the n-type layer 12-1.

When a light-emitting device is configured using the GaN-based LED element 10, the element 10 is made of a substrate, a slag, a lead frame, a unit substrate, etc. so that the surface on the stacked body 12 side of the LED element faces the light extraction direction of the light-emitting device. It can be fixed on the surface of the mounting substrate. Conversely, the element 10 can also be fixed on the surface of the mounting substrate so that the surface on the substrate 11 side faces the light extraction direction of the light emitting device. The latter mounting form is called flip chip mounting. Flip chip mounting is sometimes called face-down mounting or junction-down mounting.

Next, a method for manufacturing the GaN-based LED element 10 will be described using specific examples.

An n-type conductive GaN substrate is prepared and installed in a growth furnace of a normal MOVPE apparatus (organometallic compound vapor phase growth apparatus). The substrate temperature is set to 1000 ° C., and an n-type GaN layer to which Si is added to a concentration of 2 × 10 ¹⁸ cm ⁻³ is grown to a thickness of 4 μm. Next, the substrate temperature is lowered to 750 ° C., and an undoped InGaN layer having a thickness of 2 nm serving as a well layer and an undoped GaN layer having a thickness of 8 nm serving as a barrier layer are alternately grown ten layers at a time to form an MQW structure. A light emitting layer is formed. Next, the substrate temperature is raised again to 1000 ° C., and a p-type Al _0.1 Ga _0.9 N layer to which Mg is added to a concentration of 5 × 10 ¹⁹ cm ⁻³ is grown to a thickness of 50 nm. Subsequently, a p-type GaN layer to which Mg is added to a concentration of 1 × 10 ²⁰ cm ⁻³ is grown to a thickness of 150 nm. After forming the p-type GaN layer, the substrate temperature is lowered to room temperature while supplying ammonia into the growth furnace, and the wafer is taken out of the MOVPE apparatus. The wafer is annealed using an RTA apparatus to activate Mg added to the p-type layer.

After the formation of the GaN-based semiconductor layer is completed, ITO is formed to a thickness of about 0.2 μm on the back surface of the GaN substrate and the p-type GaN layer, respectively. Preferably, the film thickness of ITO is adjusted so that the non-reflective film condition is achieved according to the wavelength of light emitted from the light emitting layer. There is no limitation on the ITO film formation method, electron beam evaporation method, sputtering method, reactive sputtering method, ion beam assisted evaporation method, ion plating method, laser ablation method, CVD method, spray method, spin coating method, dipping method In addition, a known ITO film forming method can be used. When the electron beam evaporation method is used, the substrate temperature is preferably 300 ° C. or higher. After film formation, crystallization of ITO is further promoted by performing heat treatment at 500 ° C. for 10 minutes.

Next, a resist mask is formed on the ITO film formed on the back surface of the GaN substrate, and an opening is formed in the resist mask using a photolithography technique. This opening is patterned into the shape of the opening to be provided in the ITO film. This opening can be, for example, a circle with a diameter of about 5 μm. Next, using an acid such as hydrochloric acid or aqua regia, the surface of the ITO film exposed at the opening of the resist mask is etched to partially reduce the thickness of the ITO film. Note that this acid etching step can be omitted. Thereafter, reactive ion etching (RIE) is performed using a chlorine-containing compound such as Cl ₂ , SiCl ₄ , and BCl ₃ as an etching gas, and the ITO film exposed in the opening of the resist mask is removed. Expose the surface. At this time, the surface of the ITO film whose crystallization is promoted by the heat treatment is a rough surface having large undulations reflecting the polycrystalline structure, and the etching rate of the ITO film is probably not uniform (crystal As the etching of the ITO film progresses, sub-micron-sized fine ITO crystals are dispersed on the surface of the GaN substrate exposed in the resist mask opening. The fine ITO crystal acts as a fine mask, whereby the surface of the GaN substrate is etched non-uniformly, and fine irregularities of submicron size are formed. After RIE, the resist mask is removed, and a pad electrode made of Ti / Au is formed on the ITO film.

Subsequently, an opening is similarly formed on the ITO film formed on the p-type GaN layer, and the surface of the p-type GaN layer is exposed in an uneven shape using RIE. Thereafter, a pad electrode made of Ti / Au is formed on the ITO film.

Thereafter, an insulating protective film made of silicon oxide is formed in a region other than on the pad electrodes on both sides of the wafer by using a plasma CVD method. Finally, the wafer is cut using a wafer dividing method usually used in this field, such as dicing, scribing, and laser processing, to obtain a chip-like GaN-based LED element.

(Second Embodiment)
FIG. 2 shows a cross-sectional view of a GaN-based LED element according to Embodiment 2 of the present invention.

In the GaN-based LED element 20 shown in FIG. 2, a laminated body including a p-type layer 22-3, a light-emitting layer 22-2, and an n-type layer 22-1 made of a GaN-based semiconductor in this order on a conductive substrate 21. 22 is formed. A positive-side pad electrode P22 is formed on the back surface of the substrate 21. A conductive oxide film T21 made of ITO or the like is formed as a negative ohmic electrode on the surface of the n-type layer 22-1 and a negative pad electrode P21 is formed on a part of the conductive oxide film T21. The conductive oxide film T21 has a polycrystalline structure, and fine irregularities corresponding to crystal grain boundaries exist on the surface. The conductive oxide film T21 is provided with a plurality of openings, and the surface of the n-type layer 22-1 exposed in the openings is provided with irregularities.

In order to form the GaN-based LED element 20, an n-type layer 22-1, a light emitting layer 22-2, and a p-type layer 22-3 were formed in this order on the sapphire substrate by an epitaxial growth method to obtain a stacked body 22. Thereafter, a separately prepared conductive substrate 21 is bonded to the surface of the p-type layer using a wafer bonding technique. Alternatively, after the stacked body 22 is formed by the same method, an ohmic electrode and a seed layer are sequentially formed on the surface of the p-type layer 22-3, and a metal layer of 50 μm or more is formed on the seed layer by electrolytic plating or electroless plating. The metal layer is deposited to a thickness to form a substrate 21. After the substrates 21 are bonded together or after the substrate 21 is formed by a plating method, the sapphire substrate is removed from the stacked body 22 using a method such as etching, grinding, polishing, or laser lift-off. A conductive oxide film T21 is formed on the surface of the n-type layer 2-1 exposed by removing the sapphire substrate. In the same manner as in the first embodiment, an opening is formed in the conductive oxide film T21, and unevenness is provided on the surface of the n-type layer 22-1 exposed in the opening. Thereafter, the pad electrode P21 is formed.

The present invention is not limited to the embodiments explicitly described in the present specification, and various modifications can be made without departing from the spirit of the invention.

It is sectional drawing which shows the structure of the GaN-type LED element which concerns on embodiment of this invention. It is sectional drawing which shows the structure of the GaN-type LED element which concerns on embodiment of this invention.

Explanation of symbols

10, 20 GaN-based LED elements 11, 21 Substrate 12, 22 Laminate 12-1, 22-1 N-type layer 12-2, 22-2 Light emitting layer 12-3, 22-3 P-type layer T11, T12, T21 Conductive oxide film

Claims (10)

In a GaN-based LED element including a laminate composed of a plurality of GaN-based semiconductor layers including at least a light-emitting layer and a p-type layer and an n-type layer sandwiching the light-emitting layer,
A plate-shaped body made of a GaN-based semiconductor, and a conductive oxide film formed on the surface of the plate-shaped body;
A plurality of openings are formed in the conductive oxide film,
An unevenness is provided on the surface of the plate-like body exposed at the opening, and the GaN-based LED element. The GaN-based LED element according to claim 1, wherein the concavo-convex convex portion has a portion made of the same material as that of the conductive oxide film at a top portion. The GaN-based LED element according to claim 1, wherein the conductive oxide film is an ITO film. The GaN-based LED element according to claim 1, wherein the plate-shaped body is a GaN-based semiconductor substrate, and the stacked body is formed on the GaN-based semiconductor substrate. The GaN-based semiconductor element according to claim 1, wherein the plate-like body is the stacked body. The GaN-based LED element according to claim 5, wherein the conductive oxide film is formed on a surface of the p-type layer. The GaN-based LED element according to claim 6, wherein the concave and convex portions reach the light emitting layer. The GaN-based LED element according to claim 5, wherein the conductive oxide film is formed on a surface of the n-type layer. The GaN-based LED element according to claim 5, wherein the laminate is formed on a light-transmitting substrate. A light-emitting device formed by flip-chip mounting the GaN-based LED element according to claim 9.

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