JP2001332760A - Iii nitride compound semiconductor light emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light emitting device that can effectively utilize light that is emitted from the side of a semiconductor layer. SOLUTION: A groove is formed by a dicing saw in a III nitride compound semiconductor stacked body containing a light emitting layer, and a side outside the groove is set to a reflecting surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a group III nitride compound semiconductor light emitting device.

[0002]

2. Description of the Related Art A light emitting device is disclosed in Japanese Patent Application Laid-Open No. 11-273571.
As shown in Japanese Patent Application Laid-Open Publication No. H11-260, the mounting lead is mounted in a cup portion of a mounting lead. A conductive wire is connected to the light-emitting element, and the light-emitting element is sealed with a shell-shaped sealing member made of a light-transmitting resin. The light emitting device thus configured has an optical axis in the central axis direction (normal direction) of the light emitting element chip,
The light emitted from the light emitting element is condensed in the optical axis direction by the tip hemisphere (convex lens) of the shell type sealing member. However, since the light deviating from the tip hemisphere cannot be controlled, in order to effectively use the light in the lateral direction (the direction away from the central axis direction) of the light emitting element chip, the peripheral wall of the cup portion is formed in a parabolic shape so that the lateral direction of the peripheral wall is Is reflected in the optical axis direction.

[0003]

A group III nitride compound semiconductor light-emitting device that emits blue-green light emits more light in the lateral direction than a red light-emitting device. In a group III nitride compound semiconductor light emitting device that emits a large amount of light in the lateral direction, how to use the light in the lateral direction is a serious problem in improving the luminous efficiency of the light emitting device.

[0004] Looking at the peripheral wall reflecting surface of the conventional cup from such a viewpoint, in a usual design, a clearance of 200 to 300 µm is provided between the chip and the peripheral wall of the cup as a space for releasing a jig for holding the chip. Need. On the other hand, the thickness of the semiconductor layer in the chip is several μm, and the height of the cup is also limited by the design of the light emitting device. Therefore, of the light emitted in the horizontal direction, only the light falling within a range of an elevation angle of about 10 degrees from the direction perpendicular to the central axis (direct side direction) could be reflected by the peripheral wall reflecting surface of the cup.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a light emitting device capable of effectively utilizing light emitted from a side surface of a semiconductor layer. A device is proposed. III including light emitting layer
A group III nitride-based compound semiconductor light-emitting device, wherein a groove is mechanically formed in a stacked body of the group-III nitride-based compound semiconductor layers, and a reflection surface is formed on an outer side surface of the groove.

[0006] According to the group III nitride compound semiconductor light emitting device constructed as described above, since the reflecting surface is formed on the outer side surface of the mechanically formed groove, the light emitted from the inner side surface of the groove is emitted. The light of the layer is reflected by the reflecting surface. The width of the mechanically formed groove is determined by the thickness of the cutting blade, and the thickness is one order of magnitude smaller than the distance between the light emitting element and the reflecting surface (200 to 300 μm) in the related art. That is, the width of the groove can be set to 20 to 30 μm. As a result, more of the light (light emitted laterally from the light emitting element) emitted from the inner side surface of the groove formed in the laminate can be captured by the reflective layer and reflected in a desired direction. Therefore, light use efficiency is improved.
Therefore, a light-emitting element that achieves high luminance with low power can be obtained.

[0007] The chip of the light emitting element is cut from the wafer by a known method. It is desirable to form the grooves using a mechanical cutting device (dicing saw) used at that time from the viewpoint of simplification of the manufacturing process and the manufacturing apparatus, and furthermore, from the viewpoint of suppressing the manufacturing cost of the element.

If the groove is formed under the same conditions as those for forming the cutting line when separating the light emitting element chips from the wafer, the manufacturing cost can be further reduced.
The grooves are preferably formed in parallel with the cutting line and at the same depth. As a result, the groove has a depth reaching the substrate. In addition, the stacked body of the group III nitride-based compound semiconductor layers (the portion that emits light effectively) is preferably formed so as to surround a rectangle.

Considering the groove formed by the dicing saw, the cross-sectional shape of the groove is as shown in FIG.
It becomes semicircular. Accordingly, the side surface 23 of the groove 21 located outside as viewed from the center of the chip has a curved tapered shape. II
Of the light emitted by the group 18 nitride-based compound semiconductor layer stack 18, the light in the lateral direction is emitted from the inner side surface 24 of the groove 21 and reflected by the reflection surface 27 formed on the outer side surface 23. . Here, since the outer side surface 23 is formed in a tapered shape, light emitted in the lateral direction from the laminate 18 is reflected by the reflecting surface formed along the outer side surface 23 in the optical axis direction of the light emitting element 1. (Normal direction, central axis direction).

Next, the elements of the present invention will be described in detail.
I do. The laminated body includes a plurality of group III nitride compound semiconductor layers.
It is laminated and includes a light emitting layer therein. In this specification
And the group III nitride compound semiconductor has a general formula of Al
_XGa_YIn_1-XYN (0 ≦ X ≦ 1, 0 ≦ Y ≦ 1,
0 ≦ X + Y ≦ 1), AlN, GaN and InN
The so-called binary system of Al_xGa_1-xN, Al _xIn
_1-xN and Ga_xIn_1-xN (where 0 <x
Includes the so-called ternary system of <1). Part of group III elements
May be replaced with boron (B), thallium (Tl), etc.
Also, part of nitrogen (N) is phosphorus (P), arsenic (A
s), replaced with antimony (Sb), bismuth (Bi), etc.
it can. Group III nitride-based compound semiconductor layer
May be included. As an n-type impurity, S
i, Ge, Se, Te, C, etc. can be used. p
Mg, Zn, Be, Ca, Sr, Ba as type impurities
Etc. can be used. In addition, doping with a p-type impurity
After irradiating the group III nitride compound semiconductor with an electron beam,
It is also possible to expose to laser irradiation or furnace heating.
You. The method of forming the group III nitride compound semiconductor layer is particularly limited.
Although not specified, metalorganic vapor phase epitaxy (MOCVD)
In addition, well-known molecular beam crystal growth method (MBE method), halide
Vapor phase epitaxy (HVPE), sputtering, ion play
Also formed by the printing method, electron shower method, etc.
Can be. Note that the configuration of the light emitting element is as follows.
Homo-structure and hetero-structure with PIN junction or pn junction
Structure or a double heterostructure can be used.
(In these cases, the layer contributing to light emission is called a light emitting layer.
U). Quantum well structure (single quantum well structure
Or a multiple quantum well structure).

[0011] A groove is formed in the stacked body of the group III nitride compound semiconductor layers by a mechanical method. Here, the mechanical method refers to cutting a part of the laminate using a cutting blade. It is preferable to use a cutting blade (a dicing saw or the like) used for separating the light emitting elements from the wafer from the viewpoint of simplifying the manufacturing apparatus. Therefore, the shape of the groove is determined by the cutting edge of the cutting blade. The cutting blade used for forming a cutting line on a wafer for separating the light emitting elements and the cutting blade used for forming the groove may be different, and the cross-sectional shape of the groove may be arbitrarily designed.

The width of the groove is set so that the reflecting surface is brought closer to the side surface (the inner side surface of the groove) of the laminate to capture more of the light emitted from the side surface and reflect the light in a desired direction. Is preferably as narrow as possible. According to the study of the present inventors, the width at the opening of the groove is 3 to 50 μm.
It is preferable that If the width is smaller than the lower limit, it is difficult to ensure sufficient durability for the cutting blade forming the groove. Further, if the width of the groove is increased beyond the upper limit, the area of a region not directly contributing to light emission becomes unnecessarily large, which is not preferable. More preferably, the width of the opening of the groove is 5-45 μm.
And still more preferably 7 to 40 μm, still more preferably 8 to 35 μm, and most preferably 10 to 30 μm.

In order to emit light laterally from the laminate, it is necessary to form a groove to a depth where the light emitting layer in the laminate is exposed. However, the depth is set to a value that can surely prevent cracks from being formed in the groove due to a stress load in the separation step. In this range, it is preferable that the depth of the groove is as deep as possible. By making the groove deeper, the lower edge of the reflection surface is arranged lower, so that the light emitted downward from the side surface of the laminate (the inner side surface of the groove) can also be captured by the reflection surface. If the depth of the groove is shallow, the downward component of the light emitted from the side surface of the stacked body enters the semiconductor layer. Since this semiconductor layer is also formed of a group III nitride compound semiconductor and has a band gap energy close to the emission wavelength, most of the incident light is absorbed by the semiconductor material. Therefore, it is preferable that the light emitted from the side surface of the laminate be directly incident on the reflective layer as much as possible and reflected in a desired direction (for example, the optical axis direction).

According to the study of the present inventors, the depth of the groove is
The thickness is preferably 3 to 50 μm. More preferably,
5 to 45 μm, more preferably 7 to 40 μm
And still more preferably 8 to 35 μm,
Most preferably, it is 10 to 30 μm.

The groove can be formed at an arbitrary stage after the formation of the stacked body of the group III nitride compound semiconductor layers. When the reflecting surface is formed simultaneously with the n-type pedestal electrode, it is necessary to form a groove at least before forming the n-type pedestal electrode. In this case, a groove for the cutting line may be formed at the same time.

In order to emit more light from the side surface (the inner side surface of the groove) of the laminate, it is preferable that the light emitting layer is formed up to the side surface. Although the material for forming the light emitting layer itself exists up to the side surface, a sufficient current is injected into the light emitting layer on the side surface due to the high electric resistance of the p-type semiconductor layer on the light emitting layer. In order to emit light, it is necessary to attach a translucent electrode to the edge of the p-type semiconductor layer. In order to attach the translucent electrode to the edge of the p-type semiconductor layer, it is preferable to form the translucent electrode from an alloy containing cobalt and gold in terms of durability. A translucent electrode containing cobalt and gold has excellent water resistance. Therefore,
Under normal use environment, good durability can be ensured even when there is no protective film such as SiOx or when the function as the protective film is insufficient. By forming the translucent electrode up to the edge portion of the p-type contact layer, the effective light emitting portion reaches the side surface of the semiconductor laminated portion. As a result, strong light emission from the side is obtained. Part of cobalt is nickel
(Ni), iron (Fe), copper (Cu), chromium (Cr), tantalum (Ta), vanadium (V), manganese (Mn), aluminum (Al), silver (A
g), it is possible to replace part of the gold with at least one element of palladium (Pd), iridium (Ir), and platinum (Pt). Within the range having properties. That is, the translucent electrode is preferably made of a cobalt-gold alloy. Such a light-transmissive electrode has a first electrode layer made of cobalt of 0.5 to 15 nm.
And a gold layer having a thickness of 3.5 to 25 nm as a second electrode layer on the cobalt layer. Then, both are alloyed by heat treatment. After the heat treatment, the element distribution in the depth direction from the surface of the p-type contact layer is a distribution in which Au penetrates deeper than Co. Here, the heat treatment is preferably performed in a gas containing oxygen. At this time, as the gas containing oxygen,
At least one of O ₂ , O ₃ , CO, CO ₂ , NO, N ₂ O, NO ₂ , H ₂ O, or a mixed gas thereof can be used. Or a mixed gas of at least one of O ₂ , O ₃ , CO, CO ₂ , NO, N ₂ O, NO ₂ , or H ₂ O and an inert gas, or O ₂ , O ₃ ,
A mixed gas of CO, CO ₂ , NO, N ₂ O, NO ₂ , or a mixed gas of H ₂ O and an inert gas can be used. In short, a gas containing oxygen means a gas of an oxygen atom or a molecule having an oxygen atom. The pressure of the atmosphere during the heat treatment may be at least the pressure at which the gallium nitride-based compound semiconductor does not thermally decompose at the heat treatment temperature. The gas containing oxygen may be introduced at a pressure higher than the decomposition pressure of the gallium nitride-based compound semiconductor when only O ₂ gas is used, and when used in a state mixed with another inert gas, It suffices that all gases have a pressure equal to or higher than the decomposition pressure of the gallium nitride-based compound semiconductor, and that the O ₂ gas has a ratio of about 10 ⁻⁶ or more to all gases. In short, it is sufficient that a very small amount of gas containing oxygen exists. It should be noted that the upper limit of the amount of the gas containing oxygen is not particularly limited from the characteristics of p-type resistance reduction and electrode alloying. In short, it can be used to the extent that it can be manufactured. Regarding the heat treatment, most desirably 500 to
600 ° C. At a temperature of 500 ° C. or higher, a low-resistance p-type gallium nitride-based compound semiconductor whose resistivity is completely saturated can be obtained. At a temperature of 600 ° C. or less,
The alloying treatment of the electrode can be favorably performed. The desirable temperature range is 450 to 650 ° C. For further details, refer to Japanese Patent Application No. 2000-92611 (Applicant Reference Number 990472, Attorney Reference Number: P0197).

The surface of the groove obtained by mechanically cutting the stacked body of the group III nitride compound semiconductor layer is rough and cannot reflect light sufficiently as it is. Preferably, the outer side surface is mirror-finished. In one aspect of the present invention, a metal layer is formed on the outer side surface to be a mirror surface. The material and forming method of the metal layer are not particularly limited, but it is preferable to use the same material as the n-type pedestal electrode from the viewpoint of reducing the number of manufacturing steps. n
This is because the mold base electrode and the metal layer can be formed in the same vapor deposition step using the same mask. The metal layer is preferably formed on the entire outer side surface of the groove. However, a metal layer may be partially formed on the outer side surface and mirror-finished.

Since the reflecting surface of the present invention can reflect more lateral light than the reflecting surface of the peripheral wall of the cup portion, the lens type LED mounted with the light emitting element of the present invention has the same input power for the same LED. The luminosity increases. When the light emitting device of the present invention is used, the peripheral wall reflecting surface of the cup portion may not be required. In this case, it is not necessary to form the cup portion on the mount lead. Therefore, the structure of the mount lead is simplified, and its manufacture at low cost is possible, and the manufacturing cost of the light emitting device itself is reduced. The light emitting device of the present invention is particularly effective in an SMD type LED (a type in which a chip is directly mounted on a printed circuit board) because a reflective layer is formed therein.

[0019]

Embodiments of the present invention will be described below.
The embodiment is a light emitting diode, and FIG. 1 shows the structure of a group III nitride compound semiconductor layer. n clad layer 13,
The light emitting layer 14 and the p-cladding layer 15 (including the buffer layer 12 in some cases) form a stacked body 18 of a group III nitride compound semiconductor layer.

Layer: Composition: Dopant (thickness) Translucent electrode 16: Au (6 nm) / Co (1.5 nm) P-type cladding layer 15: p-GaN: Mg (0.3 μm) Light emitting layer 14: Multiple quantum well Structure Quantum well layer: In _0.15 Ga _0.85 N (3.5 nm) Barrier layer: GaN (3.5 nm) Number of repetitions of quantum well layer and barrier layer: 1 to 10 n-type cladding layer 13: n-GaN: Si (4 μm) AlN buffer layer 12: AlN (60 nm) Substrate 11: Sapphire (a-plane) (300 μm)

The n-type cladding layer 13 can have a two-layer structure including a low electron concentration n− layer on the light emitting layer 14 side and a high electron concentration n + layer on the buffer layer 12 side. The latter is called an n-type contact layer. The light emitting layer 14 is not limited to the super lattice structure. As a structure of the light emitting element, a single hetero type, a double hetero type, a homo junction type, or the like can be used. A wide band gap group III nitride compound semiconductor layer doped with an acceptor such as magnesium may be interposed between the light emitting layer 14 and the p-type cladding layer 15. This is to prevent the electrons injected into the light emitting layer 14 from diffusing into the p-type cladding layer 15. The p-type cladding layer 15 may have a two-layer structure including a low hole concentration p− layer on the light emitting layer 14 side and a high hole concentration p + layer on the electrode side. The latter is called a p-type contact layer. In the light emitting diode having the above structure, each group III nitride compound semiconductor layer is formed by performing MOCVD under general conditions.

Next, a mask is formed and the p-type cladding layer 1 is formed.
5. The active layer 14 and part of the n-type cladding layer 13 are removed by reactive ion etching to expose an n-type pedestal electrode forming surface on which the n-type pedestal electrode 37 is to be formed. Next, a groove 21 and a cutting line 31 are formed on the laminated body 18 from the surface side thereof in parallel with a dicing saw under the same conditions. Therefore, the groove 21 and the cutting line 31 have the same depth. It is preferable that the depth of the groove 21 be smaller than the depth of the cutting line 31 in order to reliably prevent the groove 21 from being cracked during chip separation.
Further, in order to control the light reflection direction, when forming the groove 21, the wafer can be inclined to control the inclination angle of the outer side surface 23 that defines the reflection surface.

On the entire surface of the wafer, a Co layer (1.5 nm) and a Au layer (6 n
m) are sequentially laminated. Next, a photoresist is uniformly applied, and by photolithography, a portion (clearance region) having a width of about 10 μm from the n-type pedestal electrode forming surface and the periphery thereof and a chip peripheral portion where the groove 21 and the cutting line 31 are formed are formed. The photoresist is removed, the light-transmitting electrode forming material at that portion is removed by etching, and the semiconductor layer (partially with the substrate) is exposed. afterwards,
Remove the photoresist.

Next, the V layer (17.
5 nm), an Au layer (1.5 μm) and an Al layer (10 n
m) are sequentially deposited and laminated to form a p-type pedestal electrode 35. Similarly, the n-type pedestal electrode 37 made of vanadium and aluminum is formed by the lift-off method. At this time, the metal layer 25 is simultaneously formed on the semiconductor layer from the outer side surface of the groove 21 to the cutting line 31. Therefore, the metal layer 25 has n
It is formed of the same material and the same thickness as the mold base electrode 37. The surface of the metal layer 25 formed on the outer side surface 23 in the groove 21 becomes a reflection surface.

The wafer obtained as described above is placed in a heating furnace, the inside of the furnace is evacuated to 1 Pa or less, and then O ₂ is supplied up to more than 10 Pa. Then, in this state, the temperature of the furnace is set to 550 ° C., and the heat treatment is performed for about 4 minutes. As a result, the translucent electrode 32 and the p-type pedestal electrode 35 are alloyed with each other, and are combined to form a p-type electrode. After that, a light-transmitting protective film (silicon oxide, silicon nitride, titanium oxide, aluminum oxide, or the like) is also formed by a lift-off method. As a film forming method, a sputtering method or a CVD method can be adopted.

Thereafter, the wafer is cut into chips by a conventional method. The cutting line 31 may be formed at this stage.

The light emitting device 1 of the embodiment thus configured
According to this, as shown in FIG. 3A, the side surface and the reflection surface of the multilayer body 18 are defined by the groove 21. Of the light emitted from the light-emitting layer 14 in the lateral direction, a component falling within the angle α is captured by the reflection surface 27 and can be reflected in a desired direction.

On the other hand, since the light emitting element 50 of the conventional example is not provided with such a reflection surface, the light emitted in the lateral direction from the light emitting layer 54 is reflected by the peripheral wall 55 of the cup portion. Since there is a large space between the light emitting element 51 and the peripheral wall 55, of the light emitted in the lateral direction, the light reflected by the cup peripheral wall 55 has an extremely small angle β (<
<Α).

The present invention is by no means limited to the description of the above-described embodiments and examples. Various modifications are included in the present invention without departing from the scope of the claims and within the scope of those skilled in the art.

The following is disclosed below. 11. A reflecting surface provided on the group III nitride compound semiconductor light emitting device, the reflecting surface being formed on an outer side surface of a groove mechanically formed in the laminate including the light emitting layer. 12. The reflection surface according to claim 11, wherein the groove is formed by a dicing saw. 13. The reflection surface according to 11 or 12, wherein the reflection surface is made of a metal layer. 14. The reflection surface according to 13, wherein the metal layer is made of the same material as the n-type pedestal electrode, and is formed simultaneously with the n-type pedestal electrode. 15. The reflection surface according to any one of items 11 to 14, wherein the reflection surface reflects light emitted from a side surface of the stacked body in an optical axis direction of the light emitting element. (16) The reflecting surface according to any one of (11) to (15), wherein the groove has a depth reaching the substrate. 17. The reflecting surface, wherein the groove is substantially parallel to a chip cut line. 21. A step of forming a laminate comprising an n-type semiconductor layer, a light-emitting layer and a p-type semiconductor layer on a substrate; a step of mechanically cutting the laminate to form a groove; Forming a plane. A method for manufacturing a group III nitride compound semiconductor light emitting device, comprising: 22. In the step of forming the groove, the groove is formed by a dicing saw.
3. The method for producing a group III nitride compound semiconductor light-emitting device according to item 1. 23. The method of manufacturing a group III nitride compound semiconductor light emitting device according to item 21 or 22, wherein in the step of forming the reflection surface, a metal is formed by depositing a metal on the outer side surface of the groove. . 24 The metal layer is the same material as the n-type pedestal electrode,
24. The method for manufacturing a group III nitride compound semiconductor light emitting device according to claim 23, wherein the metal layer is formed by vapor deposition in the same step as the n-type pedestal electrode. 25. The step of forming the groove, wherein the groove is formed to a depth reaching the substrate.
25. The method for manufacturing a group III nitride compound semiconductor light-emitting device according to any one of 1 to 24. 26. The method for manufacturing a group III nitride compound semiconductor light emitting device according to any one of 21 to 25, wherein, in the step of forming the groove, the groove is formed substantially in parallel with a chip cut line. .

[Brief description of the drawings]

FIG. 1 is a sectional view showing a configuration of a group III nitride compound semiconductor layer of a light emitting device according to an embodiment of the present invention.

FIGS. 1A and 1B show a light-emitting element of an example, FIG. 1A is a plan view, and FIG. 1B is a cross-sectional view taken along line AA in FIG.

FIG. 3 shows a relationship between a lateral light emitted from a laminate in a light emitting element and a reflective surface, and FIG. 3 (A) shows a relationship between a semiconductor laminated portion and a reflective surface in an embodiment of the present invention. (B) shows the relationship between the light emitting element and the peripheral wall of the cup portion in the conventional example.

[Explanation of symbols]

 1, 50 Light-emitting element 18 Stack 21 Groove 23 Outer side surface 24 Inner side surface 25 Metal layer 27 Reflecting surface 31 Cutting line 35 P-type pedestal electrode 37 N-type pedestal electrode

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5F041 AA03 AA04 CA02 CA03 CA04 CA05 CA06 CA12 CA34 CA40 CA46 CA57 CA65 CA66 CA73 CA74 CA76 CA82 CA88 CA92 CB15

Claims (7)

[Claims] 1. A groove is mechanically formed in a laminated body of a group III nitride compound semiconductor layer including a light emitting layer, and a reflection surface is formed on an outer side surface of the groove. II
Group I nitride compound semiconductor light emitting device. 2. The II according to claim 1, wherein the groove is formed by a dicing saw.
Group I nitride compound semiconductor light emitting device. 3. The group III nitride compound semiconductor light emitting device according to claim 1, wherein said reflection surface is made of a metal layer. 4. The group III nitride-based material according to claim 3, wherein the metal layer is made of the same material as the n-type pedestal electrode and is formed simultaneously with the n-type pedestal electrode. Compound semiconductor light emitting device. 5. The group III nitride according to claim 1, wherein the reflection surface reflects light emitted from a side surface of the stacked body in an optical axis direction of a light emitting device. Based compound semiconductor light emitting device. 6. The groove has a depth reaching the substrate.
III according to any one of claims 1 to 5, characterized in that:
Group III compound semiconductor light emitting device. 7. The group III nitride compound semiconductor light emitting device according to claim 7, wherein said groove is substantially parallel to a chip cut line.