JP4091279B2 - Semiconductor light emitting device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a light emitting diode (LED) and semiconductor lasers (LD) a semiconductor light emitting element such as, in particular relates to a semiconductor light emitting device aimed at improving the light extraction surface.
[0002]
[Prior art]
Conventionally, a high-intensity light emitting diode is configured by forming a light emitting portion having a double hetero structure or the like on a semiconductor substrate and forming a current diffusion layer thereon. When the light emitting diode is packaged with a resin, the upper portion of the current diffusion layer is covered with a transparent resin for protecting the element.
[0003]
In this structure, the critical angle between the current spreading layer (refractive index: 3.1 to 3.5) and the transparent resin (refractive index: about 1.5) is 25 to 29 °, and the incident angle is larger than this. The total light is totally reflected and the probability of being emitted to the outside of the light emitting element is significantly reduced. For this reason, the actual light extraction efficiency is about 20%.
[0004]
Although there is a method of improving the light extraction efficiency by forming a high refractive index film on the current diffusion layer and increasing the critical angle, the efficiency improvement is as low as about 20%.
[0005]
[Problems to be solved by the invention]
Thus, conventionally, in a light emitting diode packaged with a resin, all light incident on the interface from an oblique direction is formed at the boundary between the uppermost layer of the semiconductor multilayer film including the light emitting layer (generally a current diffusion layer) and the transparent resin. There is a problem that the light extraction efficiency is reduced due to reflection. This problem is not limited to light emitting diodes, but can be similarly applied to surface-emitting semiconductor lasers.
[0006]
The present invention has been made in consideration of the above circumstances, and its object is to achieve light extraction efficiency due to the effect of total reflection of light at the boundary between the uppermost layer of the semiconductor multilayer film including the light emitting layer and the transparent resin. It is an object of the present invention to provide a semiconductor light emitting device capable of preventing the decrease of the light emission and improving the light extraction efficiency.
[0007]
[Means for Solving the Problems]
(Constitution)
In order to solve the above problems, the present invention adopts the following configuration.
[0012]
That is, the present invention is a semiconductor light emitting device of a type in which a semiconductor laminated portion including a light emitting layer is formed on a substrate, a current diffusion layer is formed thereon, and light is extracted from the surface opposite to the substrate. the shape of the chip constituting the light-emitting element body, a light emitting layer and two parallel faces, a light emitting layer and the non-parallel four surfaces, the six surfaces that obtained by forming a hexagonal cylinder to a side surface consisting of Features. Furthermore, a plurality of hexagonal column chips are arranged in an array so that non-parallel surfaces of the light emitting layer are in contact with each other .
[0018]
(Function)
According to the present invention, the two parallel faces and the light-emitting layer and tip shape, the light-emitting layer and the non-parallel four surfaces (the slope), the six surfaces by forming a hexagonal cylinder to a side surface consisting of, It is possible to reduce the total reflection of light on the slope portion and improve the light extraction efficiency. Furthermore, it is possible to increase the light emission intensity per unit area by arranging the hexagonal column-shaped chips in an array so that the inclined surfaces are in contact with each other.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
The details of the present invention will be described below with reference to the illustrated embodiments.
[0020]
(First embodiment)
FIG. 1 is a cross-sectional view showing the element structure of an LED according to the first embodiment of the present invention.
[0021]
In the figure, reference numeral 10 denotes an n-type GaAs substrate or GaP substrate having a thickness of about 250 μm, and an active layer (light-emitting layer) is sandwiched between n-type and p-type clad layers on the substrate 10 and is doubled. A terror structure portion (light-emitting portion) 20 is grown and formed, and a p-type GaP current diffusion layer 30 is formed on the terastructure portion (light-emitting portion) 20 to a thickness of about 200 μm by growth or adhesion. Here, the active layer constituting the double heterostructure 20 is, for example, InGaAlP having a thickness of about 0.6 μm, and the cladding layer is, for example, InAlP having a thickness of about 0.6 to 1.0 μm. A p-side electrode 41 is formed on a part of the current diffusion layer 30, and an n-side electrode 42 is formed on the back surface of the substrate 10.
[0022]
The basic configuration so far is the same as that of the conventional element, but in this embodiment, the surface of the current diffusion layer 30 is formed to be convexly curved upward, and the back surface of the substrate 10 is curved to be convex downward. The entire element is formed in a spherical shape. As this formation method, after forming electrodes on the substrate, dicing is performed to separate the chip, and the entire chip is polished to obtain a spherical body. In the figure, 51 is a transparent resin for sealing the entire element or the upper surface of the element, and 52 is a reflecting mirror for guiding light leaked to the substrate side upward.
[0023]
With such a configuration, the light extraction efficiency on the current diffusion layer side and the substrate side can be improved by the curved structure of the current diffusion layer 30 and the substrate 10. That is, when the interface between the current diffusion layer 30 and the transparent resin 51 is flat, the incident light from the light emitting layer 30 is reflected by the refractive indexes of the current diffusion layer 30 and the transparent resin 51 as shown in FIG. Total reflection occurs at a predetermined incident angle determined by the relationship. In contrast, when the light extraction surface is curved as in this embodiment, as shown in FIG. 2A, the light is externally reflected without being totally reflected even at an incident angle that is totally reflected by the conventional element. Can be taken out. This is also true for the substrate side. Therefore, in this embodiment, it is possible to improve the light extraction efficiency.
[0024]
In this embodiment, the entire element is formed in a spherical shape, but may be formed in a cylindrical shape. Further, in this embodiment, the curved structure is provided on both the current diffusion layer side and the substrate side. However, in the case of a structure in which light is extracted only on the side opposite to the substrate 10 with respect to the active layer 20, the curved structure is provided only on the current diffusion layer side. A structure may be provided, and the back surface of the substrate 10 may be a full-surface electrode.
[0025]
(Second Embodiment)
FIG. 3 is a perspective view showing an element structure of an LED according to the second embodiment of the present invention. In addition, the same code | symbol is attached | subjected to FIG. 1 and an identical part, and the detailed description is abbreviate | omitted.
[0026]
A double heterostructure portion (light emitting portion) 20 made of an InGaAlP-based material with an active layer sandwiched between clad layers is grown on an n-type GaAs substrate 10, and a p-type GaP current diffusion layer 30 is grown thereon. Yes. A p-side electrode 41 is formed on a part of the current diffusion layer 30, and an n-side electrode 42 is formed on a part of the back surface of the substrate 30.
[0027]
The basic configuration so far is the same as that of the conventional element, but in this embodiment, the end portion of the current diffusion layer 30 is cut obliquely, the end portion of the substrate 10 is also cut obliquely, and the entire element is It is formed in a hexagonal column shape.
[0028]
With such a configuration, incident light that has been totally reflected at a certain angle and cannot be extracted can be extracted from the current diffusion layer 30 and the inclined portion of the substrate 10, thereby improving light extraction efficiency. Therefore, the same effect as the first embodiment can be obtained.
[0029]
Since the entire element is a hexagonal column, a plurality of hexagonal column chips can be arranged in an array so that the inclined portions are in contact with each other as shown in FIG. In this case, since a plurality of chips can be arranged in a fine structure, the light emission intensity per unit area also increases.
[0030]
(Third embodiment)
FIG. 5 is a cross-sectional view showing the element structure of an LED according to the third embodiment of the present invention. In addition, the same code | symbol is attached | subjected to FIG. 1 and an identical part, and the detailed description is abbreviate | omitted.
[0031]
A double heterostructure portion (light emitting portion) 20 made of an InGaAlP-based material with an active layer sandwiched between clad layers is grown on an n-type GaAs substrate 10, and a p-type GaP current diffusion layer 30 is grown thereon. Yes. A large number of microlenses 60 are formed on the current spreading layer 30. A transparent resin 51 is formed so as to cover the microlens 60.
[0032]
Here, the microlens 60 used in the present embodiment is not a simple arrangement of convex microlenses, but is one in which convex microlenses 61 and concave microlenses 62 are alternately arranged. The arrangement relationship between the convex microlenses 61 and the concave microlenses 62 may be arranged alternately for each line as shown in FIG. 6A, or in a checkered pattern as shown in FIG. 6B. May be. As the material of the microlens 60, the same material as the underlying cladding layer or a material having a small refractive index difference from the cladding layer can be used. The microlens can be formed by forming a resist pattern on the microlens material, wet etching the microlens material using the resist pattern as a mask, and then polishing the surface.
[0033]
Further, the radius of curvature r of the microlens 60 may be set as follows. That is, as shown in FIG. 10A, the distance from the active layer of the double heterostructure 20 to the microlens 60 is L, the refractive index of the current diffusion layer 30 is n1, and the transparent resin that protects the microlens 60. When the refractive index of 51 is n2, the critical angle is sinφ = n2 / n1 from the total reflection equation.
In order for this not to be totally reflected,
sinφ ≦ n2 / n1
φ ≦ sin ⁻¹ (n2 / n1)
Here, from tan φ = L / r, L / r ≦ tan {sin ⁻¹ (n2 / n1)}
Therefore, the relationship between L and r is r ≧ L / [tan {sin ⁻¹ (n2 / n1)}].
Should be set.
[0034]
FIG. 10A shows a case where the microlens is uneven, while FIG. 10B shows a case where only the convex is convex. 10 (a) and 10 (b), if the light is emitted from the same point, the light having an angle φ1 has a longer distance through the current diffusion layer in (b) than in (a) and attenuates in the middle. It is possible. Therefore, as a microlens, a concave / convex set is more effective in terms of light extraction efficiency.
[0035]
(Fourth embodiment)
FIG. 7 is a plan view showing the main configuration of an LED according to the fourth embodiment of the present invention.
[0036]
The basic configuration of the element is the same as that of the third embodiment shown in FIG. 5, and the shape and arrangement of the microlens are different from those of the third embodiment. That is, the microlens 65 in the present embodiment has a hexagonal shape as shown in FIG. 7A, and has a honeycomb arrangement so that no gaps are formed between them. Further, the type of the microlens may be a convex type, or a combination of a convex type and a concave type.
[0037]
With such a configuration, the microlens can be effectively arranged on the light extraction surface, and the light extraction efficiency can be further improved. That is, when a plurality of circular lenses 66 are arranged as shown in FIG. 7B, a gap is inevitably generated between the lenses. On the other hand, when a plurality of hexagonal lenses 65 are arranged in a honeycomb shape as in this embodiment, the gap between the lenses can be eliminated, so that the lenses can be effectively arranged. That is, the microlens can be disposed on the entire surface of the light extraction surface, and the light extraction efficiency can be improved over the entire surface.
[0038]
(Fifth embodiment)
FIG. 8 is a cross-sectional view showing a manufacturing process of an LED according to the fifth embodiment of the present invention, particularly a manufacturing process of a microlens portion. In addition, the same code | symbol is attached | subjected to FIG. 1 and an identical part, and the detailed description is abbreviate | omitted.
[0039]
First, as shown in FIG. 8A, a double heterostructure part (light emitting part) 20 made of an InGaAlP material in which an active layer is sandwiched between n-type and p-type cladding layers on an n-type GaAs substrate 10 is grown. Then, a p-type GaP current diffusion layer 30 is grown thereon.
[0040]
Next, as shown in FIG. 8B, a novolac-based or styrene-based resist 70 is applied and formed on the current diffusion layer 30 to a thickness of 2 μm, and then the resist is formed on the current diffusion layer 30 by a known photolithography process. 70 is left in the form of islands at predetermined intervals (pitch 4-6 μm, space 0.5 μm).
[0041]
Next, as shown in FIG. 8C, the resist 70 is heated to 150 to 200 ° C. and reflowed to form a hemispherical resist pattern. Next, as shown in FIG. 8D, the microlens made of the current diffusion layer 30 is formed by transferring the pattern shape of the hemispherical resist 70 to the current diffusion layer 30.
[0042]
Here, as a process of transferring the pattern shape of the resist 70 to the current diffusion layer, using a magnetron RIE apparatus, BCl ₃ , Cl ₂ or a mixed gas thereof is used as an etching gas, and O ₂ and Ar are used as additional gases. The resist 70 and the current diffusion layer 30 are simultaneously etched. If the etching rates of the resist 70 and the current diffusion layer 30 are substantially equal, the surface shape of the resist 70 is reflected in the current diffusion layer 30 by RIE.
[0043]
Further, for the shape after the reflow of the resist 70 as shown in FIG. 9A, the current diffusion layer 30 is slightly etched with BCl ₃ , Cl ₂ or a mixed gas thereof and then O ₂ , Ar or a mixed state thereof. By slightly etching the resist 70 alone with a gas and repeating these etchings to perform step etching, the surface of the current diffusion layer 30 is formed into a stepped shape as shown in FIG. 9B. The microlens shape can be controlled by changing the time for etching the current diffusion layer 30 and the time for etching the resist 70 for each step. Then, after the entire surface of the current diffusion layer 30 is stepped as shown in FIG. 9 (c), the surface of the current diffusion layer 30 is smoothed by CMP, as shown in FIG. 9 (d). A lens shape is obtained.
[0044]
(Modification)
In addition, this invention is not limited to each embodiment mentioned above. In the embodiment, a light emitting diode having a double hetero structure portion in which a light emitting layer is sandwiched between cladding layers has been described. However, the light emitting diode is not necessarily required to have a double hetero structure portion, and may have a semiconductor stacked portion having a light emitting layer. That's fine. Furthermore, although the light emitting diode has been described in the embodiment, it can be applied to a surface emitting semiconductor laser.
[0045]
In addition, conditions such as a material, a composition, and a thickness of each semiconductor layer constituting the light emitting element can be appropriately changed according to specifications. In addition, various modifications can be made without departing from the scope of the present invention.
[0046]
【The invention's effect】
As described above in detail, according to the present invention, the light extraction efficiency of the semiconductor light emitting device is improved due to the influence of total reflection at the boundary between the uppermost layer of the semiconductor multilayer film including the light emitting layer and the transparent resin. Can be prevented and the light extraction efficiency can be improved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an element structure of an LED according to a first embodiment.
FIG. 2 is a schematic diagram for explaining an effect of the first embodiment.
FIG. 3 is a perspective view showing an element structure of an LED according to a second embodiment.
FIG. 4 is a view showing a state in which a plurality of hexagonal prism chips in a second embodiment are arranged in an array.
FIG. 5 is a sectional view showing an element structure of an LED according to a third embodiment.
FIG. 6 is a plan view showing an arrangement relationship between a convex microlens and a concave microlens in the third embodiment.
FIG. 7 is a plan view showing the main configuration of an LED according to a fourth embodiment.
FIG. 8 is a cross-sectional view showing a manufacturing process of an LED according to a fifth embodiment.
FIG. 9 is a cross-sectional view showing a manufacturing process of a microlens portion according to a fifth embodiment.
FIGS. 10A and 10B are cross-sectional views illustrating a case where the microlens is uneven and only convex, for explaining the third embodiment.
[Explanation of symbols]
10 ... n-type GaAs substrate 20 ... Double hetero structure part (light emitting part)
30 ... p-type GaP current spreading layer 41 ... p-side electrode 42 ... n-side electrode 51 ... transparent resin 52 ... reflection mirror 60 ... micro lens 61 ... convex micro lens 62 ... concave micro lens 65 ... hexagonal lens 66 ... circular lens 70 ... resist

Claims (2)

A semiconductor light emitting device of a type in which a semiconductor laminated portion including a light emitting layer is formed on a substrate, a current diffusion layer is formed thereon, and light is extracted from a surface opposite to the substrate,
The one light emitting element shape of the chip that comprises the body, and the light-emitting layer and two parallel faces, and said light emitting layer and the non-parallel four surfaces, the six faces consisting of forming a hexagonal prism to the side surface A semiconductor light emitting element characterized by comprising: Wherein the hexagonal column of chips, the so-emitting layer and the non-parallel surfaces contact each other, the semiconductor light-emitting device according to claim 1, characterized in that arranged in plurality array.

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