JP2006049351A - Light emitting device and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emitting device having little variation in intensity of light according to directions on the light emitting surface. <P>SOLUTION: The light emitting device 1 comprises: at least a laminate consisting of the layer 5 of a first conductivity type, and the layer 7 of a second conductivity type which are stacked via a light emitting portion 6; a metal thin film layer 9 formed on the layer 7 of the second conductivity type which constitutes the laminate; and a transparent conductor 12 formed on the metal thin film layer 9. The transparent conductor 12 consists of a single layer of transparent conductive film 10. The crystal grain diameter in the light emitting surface 10' of the transparent conductive film 10 is not less than 30 nm nor more than 300 nm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a compound semiconductor light emitting device that extracts light from a compound semiconductor layer, and more particularly to a compound semiconductor light emitting device using a transparent conductive film as a window electrode and a method for manufacturing the same.

  Gallium nitride compound semiconductors such as GaN, AlGaN, InGaN, and InGaAlN are attracting attention as visible light emitting devices such as green and blue.

  In the manufacture of optical devices using these gallium nitride compound semiconductors, sapphire is usually used as a substrate for crystal growth because there are few substrates that lattice match with gallium nitride compound semiconductors. When an insulating substrate such as sapphire is used, an electrode cannot be taken out from the substrate side unlike a light emitting element using a conductive semiconductor substrate such as GaAs or InP. The p-side electrode and the n-side electrode provided in are formed on one side of the substrate on which the semiconductor layers are stacked.

  Accordingly, a gallium nitride-based compound semiconductor light-emitting element provided with a translucent electrode has been proposed in order to suppress a decrease in the transmissivity of emitted light (see, for example, Patent Document 1).

FIG. 3 is a cross-sectional view showing an example of a conventional gallium nitride compound semiconductor light emitting device provided with a translucent electrode. In the gallium nitride-based compound semiconductor light emitting device 300, an n-type GaN layer 305 is provided on one surface (upper surface in FIG. 3) of the sapphire substrate 301 via a GaN buffer layer 303, and one surface of the n-type GaN layer 305 is provided. A p-type GaN layer 307 containing Mg as a p-type dopant and an n-side electrode 309 made of Ti / Au or the like are provided on the upper surface of FIG. The n-side electrode 309 is electrically insulated from the p-type GaN layer 307 by surrounding the n-side electrode 309 with a SiO ₂ film 311a.

On the other hand, a SiO ₂ film 311b and a Mg-containing metal thin film layer 313 are provided on the p-type GaN layer 307, and a thickness of a tin-added indium oxide (ITO) film for current diffusion is provided on the metal thin film layer 313. A transparent conductive film 315 having a thickness of 100 nm is provided, and a p-side electrode 317 made of Ti / Au or the like is provided so as to cover the SiO ₂ film 311b and a part of the transparent conductive film 315.

  That is, in this configuration, light emitted from the junction interface between the n-type GaN layer 305 and the p-type GaN layer 307 can be extracted through the transparent conductive film 315. In FIG. 3, the dotted line shows the flow of current flowing from the p-side electrode 317 through the transparent conductive film 315 to the junction interface. On the other hand, the alternate long and short dash line indicates a state in which light emitted from the bonding interface is emitted to the outside mainly through the transparent conductive film 315.

  In addition, a tin-doped indium oxide (ITO) film is formed as a current diffusion layer on the first layer by vacuum deposition on the p-type GaN layer doped with Mg, which is a p-type dopant, and two layers are formed thereon by sputtering. There has been proposed a layer in which a tin-added indium oxide (ITO) film is formed and a transparent conductive film is provided (see, for example, Patent Document 2).

  FIG. 4 is a cross-sectional view of a gallium nitride-based compound semiconductor light emitting device 400 in which such two layers of tin-doped indium oxide are formed. On one surface of the sapphire substrate 410, an AlN buffer layer 420, a Si-doped GaN layer 430 having a thickness of about 1.2 μm, and an active layer 440 having a thickness of about 40 nm made of n-type GaN and n-type InGaN multiple quantum wells (MQW). , A cap layer 450 having a thickness of about 20 nm made of a superlattice of AlN and p-type GaN, a Mg-doped GaN layer 460 having a thickness of about 200 nm, and a Zn film 470 having a thickness of several nm are sequentially provided. A lower tin-added indium oxide film 481 which is a lower transparent conductive film of about 10 nm, and an upper tin-added indium oxide film having a thickness of about 500 nm which is an upper transparent conductive film on the lower tin-added indium oxide film 481 482 is formed and a transparent conductive film 480 is provided. Further, an n-type electrode 491 is formed on the partially exposed Si-doped GaN layer 430 by upper tin-added oxidation. p-type electrode 492 is provided on the indium film 482.

  Since the lower tin-added indium oxide film 481 is formed by a vacuum deposition method and the upper tin-added indium oxide film 482 is formed by a sputtering method, compared to the case where the transparent conductive film 480 is formed only by the sputtering method, When the lower tin-added indium oxide film 481 is formed by the vacuum evaporation method, the compound-doped light-emitting device 400 is obtained in which the Mg-doped GaN layer 460 is less damaged, the operating voltage is low, and the light extraction efficiency is good. It is stated that

  Furthermore, a gallium nitride-based compound semiconductor light-emitting element in which a translucent electrode made of metal is provided instead of a transparent conductive film made of tin-added indium oxide has been proposed (for example, see Patent Document 3).

FIG. 5 is a cross-sectional view of a gallium nitride compound semiconductor light emitting device 500 in which Ni and Au are vapor-deposited to form a translucent electrode 505 as an example. An n-type GaN layer 502 and a p-type GaN layer 503 are sequentially provided on one surface of the sapphire substrate 501, and a metal translucent electrode 505 made of Ni / Au is provided on the p-type GaN layer. The translucent electrode 505 is formed by depositing Ni on the p-type GaN layer 503 at a thickness of 30 nm and Au on the Ni at a thickness of 70 nm using a vapor deposition apparatus. After vapor deposition, the annealing apparatus is used at 500 ° C. for 10 minutes. It is described that a light-emitting diode can be manufactured by annealing and alloying and making it light-transmitting and having good luminous efficiency and manufacturing yield.
Japanese Patent No. 3207773 Japanese Patent No. 3394488 Japanese Patent No. 2803742

However, in the gallium nitride compound semiconductor light emitting devices 300, 400, and 500 described above, the refractive index of the transparent conductors 315 and 480 and the translucent electrode 505 is about 2.0, and the refractive index of the air layer is about 1. Since the light emitted from the light emitting layer is emitted to the air layer through the transparent conductor or translucent electrode, the interface between the transparent conductor or translucent electrode and the air layer (light exit surface) There is a problem that the ratio of total reflection in the light beam increases and the light intensity varies depending on the orientation.
The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a light-emitting element that suppresses the ratio of total reflection on the light-emitting surface made of a transparent conductor and has less variation in light intensity depending on the orientation. .

  In order to solve the above-described problems, a light-emitting element according to the present invention includes a laminated body in which a first conductive type layer and a second conductive type layer are arranged via a light emitting portion, and a second conductive type forming the laminated body. A light emitting device comprising at least a metal thin film layer provided on a layer and a transparent conductor provided on the metal thin film layer, wherein the transparent conductor comprises a single-layer transparent conductive film, The crystal grain size at the light exit surface of the conductive film is 30 nm to 300 nm.

  In such a configuration, the light emitting part means a layer located between the first conductivity type layer and the second conductivity type layer, or an interface between the first conductivity type layer and the second conductivity type layer.

  The method for manufacturing a light-emitting element according to the present invention is provided on a laminated body in which a first conductive type layer and a second conductive type layer are arranged via a light emitting portion, and on a second conductive type layer forming the laminated body. A method for manufacturing a light emitting device comprising at least a metal thin film layer and a transparent conductor made of a single transparent conductive film provided on the metal thin film layer, wherein the film thickness of the transparent conductive film is changed. The crystal grain size at the light exit surface of the transparent conductive film is controlled.

In the light emitting device according to the present invention, when the light emitted from the light emitting part is emitted from the transparent conductor to the air layer, it is scattered by unevenness or crystal grain boundaries due to the size of the crystal grains on the light emitting surface. Light with less intensity variation in the direction is emitted.
Moreover, the manufacturing method of the light emitting element which concerns on this invention can control the crystal grain diameter in a light emission surface by changing the film thickness of a transparent conductor, and can reduce the variation of the light to be sent out.

FIG. 1 is a cross-sectional view showing an example of an embodiment of a light emitting device according to the present invention.
In the following, the case where the light emitting part forms a layer will be described. In the case of interface light emission, the interface between the first conductive type layer and the second conductive type layer functions as the light emitting part.

  In the light emitting device 1 of the present invention, an n-type GaN layer 4 having Si as a dopant is provided on one surface (upper surface in FIG. 1) of a sapphire substrate 2 with a GaN buffer layer 3 interposed therebetween. An n-type AlGaN layer (main first conductivity type layer) 5 using Si as a dopant is provided. Then, a light emitting part 6 having an InGaN and GaN multiple quantum well (MQW) structure through the n-type AlGaN layer 5 and a p-type AlGaN layer containing Mg as a p-type dopant through the light emitting part 6 (main second Conductive layer) 7, p-type AlGaN layer 7, p-type GaN layer 8 with Mg as a dopant, p-type GaN layer 8 through Ni thin film layer 9, and metal thin film layer 9 A transparent conductor 12 made of a single-layer transparent conductive film 10 is provided. Then, the p-side electrode 11 is provided on a part of the peripheral edge of the surface of the transparent conductor 12, while each layer laminated on a part of the peripheral part of the n-type GaN layer 4 is removed and exposed. An n-side electrode 14 is provided on the n-type GaN layer 4.

  Here, the transparent conductor 12 includes tin-doped indium oxide (hereinafter referred to as ITO film), tin oxide (hereinafter referred to as TO film), zinc oxide (hereinafter referred to as ZnO film), antimony-doped zinc oxide (hereinafter referred to as AZO film). ) Or fluorine-added tin oxide (hereinafter referred to as FTO film), which is formed by spray pyrolysis method, CVD method, sputtering method, vacuum deposition method, sol-gel method, paste coating method, etc. Although the film is formed, the crystal grain size is increased by increasing the film thickness.

  The light emitting element according to the present invention is more efficiently scattered when the crystal grain size of the light exit surface is not less than 100 nm and not more than 200 nm, so that the variation in intensity of emitted light is further reduced.

  Hereinafter, a light emitting device was manufactured by changing the film thickness of the transparent conductor made of the ITO film by spray pyrolysis. The conditions for ITO film formation by spray pyrolysis are as follows: indium chloride (hydrate) and tin chloride (hydrate) are blended so that the amount of tin added is 5 at% in terms of element ratio with respect to indium. The solution dissolved in the ethanol solution was sprayed on the metal thin film layer 9 heated to 350 ° C.

[Example 1]
On one surface of the sapphire substrate 2, an n-type GaN layer 4, an n-type AlGaN layer 5, a light emitting part 6 having a multiple quantum well (MQW) structure of InGaN and GaN, a p-type AlGaN layer 7, a p-type GaN layer 8, Ni A wafer laminated in the order of the metal thin film layers 9 was prepared, and a transparent conductive film 10 made of an ITO film having a thickness of 100 nm was formed on the metal thin film layer 9. The crystal grain size of the surface (light-emitting surface 10 ′) of the transparent conductive film 10 made of an ITO film was 30 nm.

  Next, after forming a mask on the transparent conductor 12, etching is performed until the peripheral portion of one surface of the n-type GaN layer 4 is exposed, and Al is deposited on the exposed n-type GaN layer 4 to a thickness of about 0. The n-side electrode 14 was formed by vapor deposition of 4 μm. On the other hand, Al was deposited to a thickness of about 0.8 μm by a vapor deposition method on a part of the periphery on the transparent conductor 12 (transparent conductive film 10) from which the mask was peeled off to provide the p-side electrode 13.

  The sapphire substrate 2 on which this gallium nitride compound layer was formed was diced to 300 μm square to form a bare chip, and this bare chip was mounted on the stem by die bonding, and the light emitting element 1 was fabricated by wiring by wire bonding.

[Example 2]
A light-emitting element 2 was produced in the same manner as in Example 1 except that the thickness of the ITO film in Example 1 was 320 nm and the crystal grain size of the light exit surface was 100 nm.

[Example 3]
A light emitting device 3 was produced in the same manner as in Example 1 except that the thickness of the ITO film in Example 1 was 850 nm and the crystal grain size of the light exit surface was 200 nm.

[Example 4]
A light emitting device 4 was produced in the same manner as in Example 1 except that the thickness of the ITO film in Example 1 was 1000 nm and the crystal grain size on the light exit surface was 300 nm.

[Comparative Example 1]
A light emitting device was produced in the same manner as in Example 1 except that the thickness of the ITO film in Example 1 was 40 nm and the crystal grain size on the light emitting surface was 10 nm.

[Comparative Example 2]
A light emitting device was produced in the same manner as in Example 1 except that the thickness of the ITO film in Example 1 was 1200 nm and the crystal grain size of the light exit surface was 400 nm.

[Evaluation and evaluation results]
The light emitting devices manufactured in Examples 1 to 4 and Comparative Examples 1 and 2 were caused to emit light, and as shown in FIG. 2, the light intensity in the 90 ° (vertical) direction and the light intensity in the 30 ° direction were measured, When the ratio (I ₃₀ / I ₉₀ ) of the light intensity (I ₃₀ ) in the 30 ° direction to the light intensity (I ₉₀ ) in the 90 ° (vertical) direction is less than 0.2, ×, 0.2 or more and 0. Evaluation was made with a value of less than 5 as Δ and a value of 0.5 or more as ○. That is, it can be said that the larger the ratio (I ₃₀ / I ₉₀ ), the smaller the deviation of the light due to the orientation. The evaluation results are shown in Table 1.

  Instead of the ITO film, the transparent conductor 12 was a transparent conductive film 10 made of a TO film, a ZnO film, an AZO film, or an FTO film, and all obtained the same results as the ITO film. Further, the transparent conductive film 10 was formed by a CVD method, a sputtering method, a vacuum deposition method, a sol-gel method, or a paste coating method instead of the spray pyrolysis method, and the same results as the spray pyrolysis method were obtained.

It is sectional drawing which shows an example of embodiment of the light emitting element which concerns on the Example of this invention. It is a figure which shows the evaluation method of this invention. It is sectional drawing which shows an example of the conventional gallium nitride type compound semiconductor light emitting element. It is sectional drawing which shows an example of the conventional gallium nitride type compound semiconductor light emitting element. It is sectional drawing which shows an example of the conventional gallium nitride type compound semiconductor light emitting element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light emitting element, 5 1st conductivity type layer, 6 Light emission part, 7 2nd conductivity type layer, 9 Metal thin film layer, 10 Transparent electrically conductive film, 10 'Outgoing surface, 12 Transparent conductor.

Claims (3)

A laminated body in which a first conductive type layer and a second conductive type layer are arranged via a light emitting part, a metal thin film layer provided on the second conductive type layer forming the laminated body, and on the metal thin film layer A light emitting device comprising at least a transparent conductor provided,
The light-emitting element, wherein the transparent conductor is composed of a single-layer transparent conductive film, and a crystal grain size on a light exit surface of the transparent conductive film is 30 nm or more and 300 nm or less.   The light emitting device according to claim 1, wherein the crystal grain size is 100 nm or more and 200 nm or less. A laminated body in which a first conductive type layer and a second conductive type layer are arranged via a light emitting part, a metal thin film layer provided on the second conductive type layer forming the laminated body, and on the metal thin film layer A method for producing a light emitting device comprising at least a transparent conductor comprising a single-layer transparent conductive film provided,
A method for manufacturing a light-emitting element, wherein the crystal grain size on the light exit surface of the transparent conductive film is controlled by changing the film thickness of the transparent conductive film.

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