JP2001185755A - Semiconductor light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor light emitting element which has a structure permitting lights emitted from a light emitting layer to be taken out possibly much outside a chip to improve the outside differential quantum efficiency. SOLUTION: A semiconductor laminate 12 having a light emitting layer forming part 11 having an active layer 4 sandwiched between at least an n-type layer 3 and a p-type layer 5 is provided on a semiconductor substrate 1, an upper (p-side) electrode 8 is provided on the front surface of the semiconductor laminate 12, a lower (n-side) electrode 9 is provided on the back surface of the semiconductor substrate 1, and a slope narrower at the upper electrode 8 and broader at the active layer 4 is formed on the side of an upper layer of the semiconductor laminate 12 than its active layer 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device having a structure in which a semiconductor layer is stacked to form a light emitting layer and a light is emitted to a surface side of a light emitting layer forming portion. For more information,
The present invention relates to a semiconductor light emitting device having a structure capable of easily taking out light in a lateral direction and improving the efficiency of taking out emitted light as a whole (external differential quantum efficiency).

[0002]

2. Description of the Related Art A conventional visible light semiconductor light emitting device has a structure as shown in FIG. That is,
In FIG. 5, an n-type cladding layer 22 made of, for example, an n-type InGaAlP-based semiconductor material, and an InGaAlP-based semiconductor material having a composition whose band gap energy is smaller than that of the cladding layer are formed on a semiconductor substrate 21 made of n-type GaAs. A p-type cladding layer 24 made of a p-type InGaAlP-based semiconductor material having the same composition as the active layer 23 and the n-type cladding layer is epitaxially grown, thereby forming a light emitting layer forming portion 29 having a double hetero structure.
Further, a p-type window layer (current diffusion layer) 25 made of an AlGaAs-based compound semiconductor is provided on the surface. An upper (p-side) electrode 27 is formed at the center of the surface via a contact layer 26 made of GaAs, and a lower (n-side) electrode 28 is formed on the back surface of the semiconductor substrate.

In a semiconductor light emitting device having this structure, for example, light emitted at the point P of the active layer 23 is radiated in all directions (goes to the semiconductor substrate side, but GaAs of the semiconductor substrate 21 absorbs light and emits light toward the surface side). It is not shown because it is difficult to take out), and is taken out from the surface other than the electrodes and the side surface of the window layer 25 to the outside. However, the refractive index of the semiconductor layer is about 3.5, the refractive index of air is 1, and the refractive index of the resin is about 1.5 even when the surroundings are covered with a transparent resin such as a lamp type. If the angle of incidence at the interface is not small, as shown in FIG. 5, the light is totally reflected and totally reflected inside the LED chip and attenuated by absorption or the like.

[0004]

As described above, the rate at which light emitted from the light emitting layer is totally reflected on the upper surface or side surface of the chip is determined by the difference in the refractive index between the semiconductor layer and the air or transparent resin around the semiconductor layer. Is high. On the other hand, the cladding layer and the active layer are not completely transparent and absorb light emitted from the light emitting layer, and GaAs used for the semiconductor substrate and the contact layer is a material that absorbs light emitted from the light emitting layer. Therefore, it is absorbed and attenuated while repeating total reflection. Therefore, there is a problem that the ratio of light that can be extracted to the outside is reduced, and the external differential quantum efficiency is not improved.

The present invention has been made to solve such a problem, and has a structure in which light emitted from a light-emitting layer can be extracted to the outside of a chip as much as possible, thereby improving the external differential quantum efficiency. The purpose is to provide.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on the reason why the emitted light cannot be effectively extracted outside, and as a result, the light emitted from the light emitting layer (active layer) has four sides. The light emitted at the center of the chip, where the current is concentrated and the current density is high, is blocked by the upper electrode, and the light that is emitted directly above is blocked by the upper electrode and absorbed or reflected by the contact layer. However, it was found that light reflected and absorbed again on the semiconductor substrate side, and light traveling in an oblique direction was incident on the upper surface or side surface at a large incident angle, was totally reflected, and could not be effectively extracted. . And, by making the interface from the top surface to the side surface (the outer wall of the chip) an inclined surface, it is possible to reduce the incident angle with respect to the light traveling in an oblique direction and to take out the light without total reflection. .

A semiconductor light emitting device according to the present invention comprises a semiconductor substrate, a semiconductor laminated portion provided on the semiconductor substrate and having a light emitting layer forming portion sandwiching an active layer by at least an n-type layer and a p-type layer; An upper electrode provided on the front surface side of the semiconductor laminated portion, and a lower electrode provided on the back surface side of the semiconductor substrate, wherein the width of the upper electrode side is narrower in an upper layer portion than the active layer of the semiconductor laminated portion, An inclined surface is formed on the side surface so as to increase the width on the active layer side.

With this structure, the upper surface and side surfaces of the semiconductor laminated portion other than the portion where the upper electrode is provided become inclined surfaces. It is easy to come out. Also, the light directed toward the side surface of the window layer (the upper layer portion of the semiconductor laminated portion) has a small incident angle at the boundary surface with the outside of the chip because the side surface is inclined inward, and is not totally reflected. It is easy to go outside. As a result, the efficiency of extracting light to the outside is improved, and the external differential quantum efficiency can be improved.

If the inclined surface is an inclined surface having a convex outer surface, the angle of incidence inside the chip is further reduced,
It becomes easier to extract light to the outside.

[0010] The surface side of the semiconductor laminated portion is made of AlGaAs.
If the layer is made of an s-based compound semiconductor layer and changes in composition so that the Al mixed crystal ratio becomes smaller toward the surface side, by using an etchant that can easily etch Ga,
The upper layer having a small Al mixed crystal ratio is easily etched,
Since the lower layer having a large Al mixed crystal ratio is difficult to be etched, it is easy to easily form an inclined surface. In this case, the change in the Al composition ratio can be changed linearly. However, if the change is made in a parabolic shape having a convex upper portion, the inclined surface having a convex outer surface can be formed only by etching.

[0011]

Next, a semiconductor light emitting device according to the present invention will be described with reference to the drawings. A semiconductor light emitting device according to the present invention has a light emitting structure in which an active layer 4 is sandwiched between a semiconductor substrate 1 and at least an n-type layer 3 and a p-type layer 5 as shown in FIG. A semiconductor lamination portion 12 having a layer formation portion 11 is provided. An upper electrode (p-side electrode) 8 is provided on the front surface side of the semiconductor laminated portion 12, and a lower electrode (n-side electrode) 9 is provided on the back surface side of the semiconductor substrate 1. The semiconductor lamination portion 12 is characterized in that the upper surface of the upper layer 8 is narrower in the upper layer portion than the active layer 4, and the side surface is formed with an inclined surface such that the width is wider on the active layer 4 side.

The light emitting layer forming portion 11 is formed of, for example, In.
_The n-type cladding layer 3 made of _0.49 (Ga _1-x Al _x ) _0.51 P (0.6 ≦ x ≦ 0.8, for example, x = 0.67) has a thickness of 0.1 to 0.1.
About 2 [mu] m, e.g. _{In 0.49 (Ga 1-y Al} y) 0.51 P (0.2 ≦ y ≦ 0.3 for the emission wavelength of about 587 nm,
For example, the active layer 4 made of y = 0.26) is 0.1 to 2 μm.
m, In _0.49 (Ga _1-x Al _x ) _0.51 P (0.6 ≦ x
.Ltoreq.0.8 (for example, x = 0.67). The p-type cladding layer 5 is formed by growing about 0.1 to 2 .mu.m. Note that the semiconductor layer forming the light emitting layer forming portion is I
Not only the nGaAlP-based compound semiconductor but also a semiconductor layer of another emission color such as an AlGaAs-based compound semiconductor can be used.

The surface of the light emitting layer forming portion 11 has Al _z G
A window layer 6 made of a _1-z As (0.5 ≦ z ≦ 0.8) is provided in a thickness of about 1 to 10 μm. Further, on the surface of the window layer 6, a contact layer 7 made of GaAs or the like is provided only on the lower side of the upper electrode 8, thereby forming a semiconductor laminated portion 12.

In the semiconductor light emitting device of the present invention, the upper side of the active layer 4 of the semiconductor laminated portion 12, for example, the side surface of the window layer 6 is not perpendicular to the surface of the semiconductor substrate 1 but on the upper electrode 8 side. It is formed on the inclined surface so that the width is narrow and the width is wide on the active layer 4 side. In the example shown in FIG. 1, for example, the upper part of a pyramid-shaped quadrangular pyramid is cut in parallel with the bottom surface at the upper electrode 8. For example, when the thickness A of the window layer 6 is about 6 μm, The distance B from 8 to the side of the chip is about 50μ
m (one side of the chip is about 200 μm, and the upper electrode 8
Is about 100 μm), and the inclination angle θ is about 7 °.
About. However, if the thickness of the window layer is further increased, the inclination angle can be increased, and if it is about 60 ° or less, the efficiency of extracting light to the outside can be improved.

In order to form such an inclined surface, for example, a semiconductor laminated portion 12 is formed, an upper electrode 8 is formed thereon, and a contact layer 7 is patterned. A photoresist film 16 having an opening 16a formed at the boundary of the chip is provided, and the window layer 6 exposed from the opening 16a is etched by, for example, Show polish (trade name, Showa Denko KK) to obtain a surface. The side is over-etched to form a recess 17 as shown in FIG. By dicing at the center of the concave portion 17, an LED chip having an inclined surface formed on the side surface of the chip is obtained. The inclined surface may be formed by a method such as mechanical polishing without using such etching.

In addition, even if the etchant is formed by etching, the above-described etchant is used as a window layer so that the above-mentioned Al _z Ga _{1 -z}
By using As and decreasing the composition of Al toward the surface side, the surface side is etched better and an inclined surface is easily formed. In order to sequentially reduce the Al composition of the window layer 6, as shown in FIG. 3A, it can be reduced linearly or stepwise (not shown) from the lower surface to the upper surface of the window layer. As shown in FIG. 3B, it can be reduced to a parabolic shape. In order to change this composition, when the MOCVD method described below is used,
It can be easily changed by changing the flow rate of the introduced gas.

By reducing the composition of Al in such a parabolic manner, the etching speed changes in a parabolic manner,
As shown in the cross-sectional explanatory view of the window layer 6 in FIG. 4, the inclined surface on the side surface has a shape convex outward. When the inclined surface is formed so as to have such a convex shape on the outside, light emitted from the active layer 4 and directed obliquely upward enters the concave interface at the boundary surface of the chip, so that the incident angle is further increased. It becomes smaller, and light is easily transmitted without total reflection.
As a result, the light extraction efficiency is further improved, which is preferable.

The upper (p-side) electrode 8 is made of, for example, Au-B
It may be formed by patterning after providing e / Ni / Ti / Au or the like on the entire surface, or by providing a mask other than the portion where the electrode is provided, coating the electrode material on the entire surface, and then removing the mask. It may be formed by a lift-off method. Au-Ge / Ni / Au or the like is entirely on the back surface of the GaAs semiconductor substrate 1 in a thickness of 0.2 to 0.2 mm.
The n-side electrode 9 is formed with a thickness of about 4 μm.

According to the semiconductor light emitting device of the present invention, since the upper surface and the side surface of the window layer are inclined surfaces, for example, as shown in FIG. The light emitted from the light emitting portion P of No. 4 and traveling in an oblique direction does not enter the upper surface or the side surface at a large incident angle, but directly enters the inclined surface at a small incident angle. That is, the refractive index of the semiconductor layer is about 3.3 to 3.7, and when a transparent epoxy resin is provided outside, the refractive index is 1.5 to 1.5.
The critical angle is about 30 °. That is, when the incident angle is about 30 ° or less, light is extracted from the interface of the window layer to the outside without total reflection. However, when the incident angle is larger than that, the light is totally reflected. However, according to the present invention, since the inclined surface is opposed to the light traveling in the oblique direction, the incident angle is reduced, and the light is easily emitted outside.

Further, in the present invention, since the inclined surfaces are formed on both outer sides with the upper electrode interposed therebetween, the inclined surfaces face each other in a direction approaching or moving away from each other, and do not face each other in parallel. Therefore, even if total reflection is performed, light is likely to be emitted from the inclined surfaces facing each other. As a result, it is possible to take out the light efficiently without repeatedly attenuating the total reflection many times inside the chip.

Further, by forming the inclined surface so as to be convex outward as described above, the incident angle on the inclined surface is further reduced, and the light extraction efficiency is improved.
To easily form such an inclined surface, for example, Al
By changing the composition such as the Al composition of the GaAs-based compound semiconductor, selective etching can be performed, and an inclined surface having a shape corresponding to the change in the composition can be formed. Further, by reducing the Al ratio of the AlGaAs-based compound semiconductor on the surface side, exposure of easily corrodible Al is reduced, and the function of the protective layer is also achieved, so that the effect is further enhanced. In particular, when the ratio of Al is reduced in a parabolic manner, it becomes easier to absorb light emitted when the ratio of Al is reduced, but since the layer is very thin,
The effect of absorption is almost eliminated.

In order to manufacture this semiconductor light emitting device, for example, an n-type GaAs substrate 1 is placed in a MOCVD (metal organic chemical vapor deposition) apparatus, and a reaction gas of triethylgallium (TEG) or trimethylgallium (TMG) or arsine is used. (AsH ₃ ), trimethylaluminum (TM
A), trimethylindium (TMIn), H ₂ Se as an n-type dopant, and dimethylzinc (DMZn) as a p-type dopant in the case of forming a p-type layer are introduced, respectively. As shown, In
_An n-type cladding layer 3 made of _0.49 (Ga _0.3 Al _0.7 ) _0.51 P is formed to a thickness of about 0.1 to 2 μm, and the undoped In _0.49 (Ga
_The active layer 4 made of _0.75 Al _0.25 ) _0.51 P is 0.1 μm to 2 μm.
m, p of In _0.49 (Ga _0.3 Al _0.7 ) _0.51 P
The shape of the cladding layer 5 is about 0.1 to 2 μm, for example, Al _0.7
The p-type window layer 6 made of Ga _0.3 As
The contact layer 7 made of GaAs is about 0.2 to 1 m.
Each of them grows continuously by about μm.

After that, an upper (p-side) electrode 8 is formed by a lift-off method, mask evaporation, or film formation on the entire surface after Au-Be / Ni / Ti / Au or the like is formed by photolithography. 1 is provided on the entire back surface with Au-Ge / Ni / Au or the like, and the lower portion (n
Side) An electrode 9 is formed. Thereafter, a resist film is provided on the surface of the semiconductor laminated portion 12 so as to cover the upper electrode 8 and an opening is provided at the chip boundary surface. The size of this opening is, for example, that the above-mentioned window layer 6 has a thickness A of about 6 μm, a horizontal length of about 50 μm, and Al _z Ga _{1 -z} A of the window layer 6.
In the case where z of s is changed from the lower surface to the upper surface, for example, from about 0.7 to 0.5, a good inclined surface can be obtained by providing an opening having a width of about 30 μm. Then, the LED chip shown in FIG. 1A is obtained by forming a chip on the bottom surface of the concave portion by etching.

[0024]

According to the semiconductor light emitting device of the present invention, the wall surface of the chip (the wall surface of the upper layer of the semiconductor laminated portion, for example, the window layer) is opposed to the light traveling obliquely from the light emitting portion by the inclined surface. Therefore, the light traveling in the oblique direction can be extracted to the outside as it is, and as a result, the external differential quantum efficiency is greatly improved. In addition, since the light that has proceeded in the oblique direction is transmitted as it is, light that has exited the chip can easily travel in all directions, improving the brightness in the horizontal direction and suitable for applications that irradiate a wide area. For example, a liquid crystal display device It is suitable for a light source that illuminates the entire surface like a backlight. As a result, a bright backlight for a liquid crystal display device is obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory cross-sectional view of an LED chip according to an embodiment of the present invention.

FIG. 2 is an explanatory sectional view of a step of forming an inclined surface of the LED chip of FIG. 1;

FIG. 3 is a diagram showing an example of a change in composition of a window layer suitable for forming an inclined surface of the LED chip of FIG. 1;

FIG. 4 is a diagram showing another example of the structure of the inclined surface in the semiconductor light emitting device according to the present invention.

FIG. 5 is an explanatory cross-sectional view showing a structural example of a conventional LED chip.

DESCRIPTION OF SYMBOLS 1 semiconductor substrate 3 n-type cladding layer 4 active layer 5 p-type cladding layer 6 window layer 8 upper electrode 9 lower electrode 11 light emitting layer forming part 12 semiconductor laminating part

Claims (3)

[Claims] 1. A semiconductor laminated portion provided on a semiconductor substrate, having a light emitting layer forming portion sandwiching an active layer by at least an n-type layer and a p-type layer, and a front surface side of the semiconductor laminated portion. And a lower electrode provided on the back side of the semiconductor substrate, wherein the width of the upper electrode side is narrower above the active layer of the semiconductor laminated portion, and the width is smaller on the active layer side. A semiconductor light emitting device in which an inclined surface is formed on a side surface so as to be wide. 2. The semiconductor light emitting device according to claim 1, wherein said inclined surface is an inclined surface having a convex outer surface. 3. The method according to claim 1, wherein the surface side of the semiconductor laminated portion is formed of AlGa.
2. A layer comprising an As-based compound semiconductor layer, the composition of which changes so that the mixed crystal ratio of Al decreases toward the surface.
Or the semiconductor light emitting device according to 2.