JPS63188983A - Semiconductor light emitting device - Google Patents

Abstract

PURPOSE:To confine effectively emitted lights and obtain a semiconductor light emitting element as well as a semiconductor laser which have an improved light emitting power level by preparing a protruding part that rises vertically on a substrate, thereby forming electrodes on the side plane of the protruding part and on a plane that is extending in parallel with the substrate from a lower part of the protruding part. CONSTITUTION:Almost a cylindrical protruding part 121 is formed in the vertical direction to a substrate at an upper clad layer 104 consisting of the second conductivity type semiconductor layer and an upper reflecting mirror 111 that plays arole of the reflecting mirror to a light moving up and down inside an element is formed at the top of the protruding part. An electrically insulating layer 110 is laminated at a plane that is substantially in parallel with the substrate 101 from a lower part of the protruding part 121 and a P-side electrode 106 is formed at an upper part of the electrically insulating layer 110 as well as at the side pane of the protruding part 121 and then an N-side electrode 107 is formed at the rear of the substrate 101. When this device causes an electric current to flow between the above two electrodes, a light emitting at an emitting layer is confined in the horizontal direction to the substrate and it improves the emitting efficiency. In this way, a light power generated at a light emitting region is taken out as an improved light emitting power in the vertical direction to the substrate.

Description

TECHNICAL FIELD The present invention relates to a semiconductor light emitting device, and more particularly to a semiconductor light emitting device that can extract light emitted within the device perpendicularly to a substrate.

Conventional technology Conventionally, for example, in the case of a surface-emitting semiconductor laser in which emitted light is extracted perpendicularly to a substrate, an active layer is formed such that its upper and lower sides are sandwiched between cladding layers, and the light-emitting part is formed of two layers made of dielectric or metal. It is formed so as to be sandwiched between reflective films, and by forming a resonator with the two reflective films, the light emitted from the light emitting part is confined and gain is obtained. In addition, holes are formed in the substrate, and the electrodes are
A circular electrode is placed around the hole on the side of the board that is opposite to the lamination side of one main surface of the board, and the circular electrode is placed on the surface of the board, and by passing current between the electrodes, the light is concentrated in the light emitting part. The laser output was extracted in a direction perpendicular to the substrate.

In this conventionally proposed structure, current is injected into the light emitting region between a circular electrode placed around a hole formed in the substrate and a circular electrode on the substrate surface. Since it could not be concentrated, the current injection efficiency could not be improved and no improvement in luminous efficiency could be expected. In addition, in terms of manufacturing, in the conventional structure, electrodes, reflective layers, and holes must be formed by matching the positions of the front surface of the substrate and the back surface of the substrate, making it difficult to align the positions of each.

Since the holes are formed to reach the cladding layer 2, the diameter of the hole opening body is large, for example, about 100 gm compared to the substrate thickness of about 100 gm, making it possible to form a high-density array. The problem was that I couldn't do it. In terms of strength, this device also had the problem of low strength (because the holes are formed in the plate, the thickness of the device is about several 10 gm to several 100 gta in thin places, and the strength is weak. In this structure, since light is not confined in the lateral direction with respect to the substrate, the effect of light confinement becomes small and the threshold value ?lt current cannot be lowered.

OBJECTS It is an object of the present invention to overcome the drawbacks of the prior art and to provide a semiconductor light emitting device and a semiconductor laser that can effectively confine the injected current and the emitted light and have high light output.

Structure In order to achieve the above object, the present invention includes a semiconductor substrate,
In a semiconductor light emitting element formed on a semiconductor substrate and having a light emitting layer that emits light in a direction substantially perpendicular to the main surface of the substrate and an electrode that injects current into one light emitting layer, and a protrusion protruding in a substantially perpendicular direction, and an electrode is formed on a side surface of the protrusion and on a surface extending substantially parallel to the substrate from a bottom of the protrusion. It is characterized by the fact that Hereinafter, the present invention will be specifically explained based on examples.

In the present invention, a lower reflective layer in which two types of semiconductor layers of the first conductive type having different refractive indexes are alternately laminated on a first conductive type semiconductor substrate, and a lower reflective layer of the first conductive type is laminated on the lower reflective layer. A lower cladding layer made of semiconductor layers is laminated. A semiconductor active layer is laminated on a lower cladding layer of a first conductivity type semiconductor, and an upper cladding layer made of a second conductivity type semiconductor layer is further laminated thereon. Furthermore, in the upper cladding layer, a substantially cylindrical protrusion is formed in a direction perpendicular to the substrate on the main surface side of the substrate, that is, on the laminated side of each layer, and the top of the protrusion has a projection inside the element. An upper reflecting mirror is formed to serve as a reflecting mirror for light traveling vertically.

An electrical insulating layer is laminated on a surface substantially parallel to the substrate from the bottom of the protrusion, that is, on the semiconductor cladding layer of the second conductivity type other than the protrusion. In addition, a p-side electrode is formed on the top of the electrical insulating layer and a side surface of the protrusion, and an n-side electrode is formed on the back surface of the substrate.
In other words, it is formed on the substrate surface opposite to the stacked side of each layer.

The thickness of each of the Class 28 semiconductor layers constituting the lower reflective layer is substantially equal to 1/4 of the intra-medium wavelength of the generated light emission. The thickness of the active layer is suitably about 0.1 to 4 IL11 in consideration of the effective diffusion length of carriers. The semiconductor layers constituting the lower cladding layer and the upper cladding layer are
The forbidden band width is wider than that of the semiconductor layer constituting the active layer.

The protrusions mentioned above are formed on the upper cladding layer,
``A semiconductor insertion layer of a second conductivity type that has a composition different from that of the upper cladding layer and is transparent to light emission may be laminated on top of the two-part cladding layer, and a protrusion may be formed in this semiconductor insertion layer, Alternatively, the upper cladding layer and the semiconductor insertion layer may be formed inside the protrusion. Note that the protrusions can be formed by dry etching using, for example, chlorine or chlorine gas.

With the above structure, when a current is passed between the p-side electrode and the n-side electrode, light is emitted within the light emitting layer formed at the bottom of the protrusion, and the generated light is transmitted to the upper reflective layer. Gain is generated in the resonator formed by the lower reflective layer and the lower reflective layer, and can be extracted as a laser output from the top of the protrusion in a direction substantially perpendicular to the substrate.

Furthermore, since the p-side electrode formed on the top is formed on the top of the electrical insulating layer and the side surface of the protrusion, the electrode area is only formed in the part where the electrode is parallel to the active layer. In other words, compared to a case without a protrusion, a relatively large electrode area can be taken for the light emitting region in the active layer. Therefore, the injection current can be increased without expanding the light emitting region within the active layer, and the current injection efficiency can be significantly improved.

Furthermore, according to this structure, when comparing the effective refractive index of the part of the upper cladding layer that is almost directly below the protrusion and the other part, in the latter case, because the distance between the surface of the upper cladding layer and the active layer is small, Compared to the former, the loss in light emission becomes relatively large, and the effective refractive index becomes small. Therefore, in the light-emitting layer, which is the core part, the emitted light is confined horizontally to the substrate, improving luminous efficiency.
As a result, a reduction in threshold current becomes usable.

The cross-sectional area of the protrusion can be changed, and the area of the light emitting area can be changed by changing the cross-sectional area, so it is possible to fabricate a high-density one-dimensional array or two-dimensional array. be. In terms of the strength of the device, according to the present invention, there is no need to make holes in the substrate and the device can have a sufficient thickness, so the device has high mechanical strength.

FIG. 1 shows a cross-sectional perspective view of an embodiment of a semiconductor light emitting device according to the present invention.

On an n-type gallium arsenide (GaAs) substrate 101, a lower reflective layer 112 in which two types of semiconductor layers with different refractive indexes are alternately laminated is laminated. An n-type AlGaAs cladding layer 1 is laminated, and an n-type AlGaAs cladding layer 1
A GaAs active layer 103 is laminated on top of the active layer 103, and a p-type AlGaAs cladding layer 104 is further laminated thereon. In the upper cladding layer 104, a substantially cylindrical protrusion 121 is formed in a direction perpendicular to the substrate 101 on the main surface side of the substrate 101, that is, on the stacked side of each layer. A reflective layer 111 is formed. A plane substantially parallel to the substrate lO1 from the bottom of the protrusion 121, that is, the upper cladding layer 10 other than the protrusion 121
4, an electrical insulating layer 110 made of silicon oxide or silicon nitride is formed as a layer. Furthermore, a P-side metal electrode layer (hereinafter referred to as p
A side electrode) 108 is formed on the back surface of the substrate 101,
That is, an n-side metal electrode layer (hereinafter referred to as n-side electrode) 107 made of gold-germanium (Au-Ge) or the like is formed on the substrate surface on the opposite side to the laminated side of each layer.

For the upper reflective layer 111, a metal such as gold can be used, and a dielectric material such as aluminum oxide, amorphous silicon, titanium oxide, silicon oxide, silicon nitride, or zinc oxide can also be used. When using a dielectric material, a multilayer film can be used in which the two types of dielectric materials listed above are alternately laminated, and the thickness of each layer in this case is determined according to the medium wavelength within the dielectric film of light emission. It is formed so that it is equal to 1/4 of the actual product. For this multilayer film.

By changing the number of layers in the multilayer film, the refractive index can be changed.

The lower reflective layer 112 has n
Layer 113 made of type GaAs or n-type AlGaAs
A structure in which layers lt4 made of n-type AlGaAs or n-type AlAs having a narrower forbidden band width than the layer 113 are laminated alternately is used. 1 of the value considered as the medium wavelength of light emission within the layer
/4.

By passing a current through both the p-side electrode 108 and the n-side electrode 106, the current is injected into the active layer 103 formed almost directly below the protrusion 121, and light emission occurs there. The emitted light travels up and down and reaches the upper reflective layer 11.
1 and lower reflection F! : 112 to generate a gain, and by making the reflectance of the upper reflective layer 111 smaller than that of the lower reflective layer 112, the laser output 120 is taken out perpendicularly upward relative to the substrate 101. ,be able to.

Note that in the device of this example, one or both of the upper reflective layer 111 and the lower reflective layer 112 is not formed.
In other words, it can be used as a light-emitting device, such as a high-output light-emitting diode, which does not operate as a laser because it does not have a resonant structure.

FIG. 3 shows that the upper reflective layer 111 in the embodiment shown in FIG. 1 has a structure similar to that of the lower reflective layer 112 (second
An example is shown in which a semiconductor multilayer film with a structure (see figure) is used.

In this example, the number of layers of the upper reflective layer 111 is set to the lower reflective layer 111.
When the number of layers is less than 2, the upper reflective layer 111
The reflectance of the substrate 101 can be lowered, and the optical output can be extracted perpendicularly upward relative to the substrate 101.

FIG. 4 shows another example to which the present invention is applied.

In this example, the p-type layer lGaAs cladding layer 104
A p-type A layer with a lower A1 composition than the cladding layer 104 is formed on top of the cladding layer 104.
An lGaAs insertion layer 115 is formed, and a p-type AlGaAs insertion layer 115 is formed.
An upper reflective layer 111 is formed on the top of the As insertion layer 115. The protrusion 121 in this structure is p
It is formed by a type AlGaAs insertion layer.

According to this example, the p-type AlGaAs insertion layer 115 is formed on the side surface of the protrusion 121.
It is possible to further improve the ohmic characteristics and contact resistance of the side electrode IQ6, and it is possible to improve current injection efficiency.

FIG. 5 shows another example to which the present invention is applied.

In this example, a current blocking layer 1ift made of n-type AlGaAs is placed on the P-type lGaAs cladding layer 104.
are laminated, and a p-type AlGaAs insertion layer 115 similar to the embodiment shown in FIG. 4 is formed on the current blocking layer 11B.
An upper reflective layer 111 is formed on the top of the p-type AlGaAs insertion layer 115. Further, the current blocking layer 116 has a portion corresponding to the protrusion 121, that is,
A hole 122 reaching the cladding layer 104 is formed in a portion of the active layer 103 that corresponds to the light emitting region almost directly below the protrusion. In this example as well, the protrusion 121 is formed of the p-type AlGaAs insertion layer 115, as in the embodiment shown in FIG.

According to this embodiment, the p-side electrode 10B and the n-side electrode 1
When a current is passed through both electrodes of 0B, the current is narrowed by the hole 122 formed in the current blocking layer 116 and is injected into the minute light emitting region of the active layer 103. Therefore, current injection efficiency is improved and threshold current can be reduced.

FIG. 3 shows an example in which a P+ region 105 is formed on the side surface of the protrusion 121 in the embodiment shown in FIG. The P1 region 105 contains impurity zinc (Zn
) is formed by diffusing. Further, the region is formed only inside the protrusion, and extends from the bottom of the protrusion 121 to a surface substantially parallel to the substrate 101, that is, the protrusion 121
It is not formed in the cladding layer 104 other than the cladding layer 104.

According to this example, the P+ region 105 is formed on the side surface of the protrusion 121, and the p-side electrode 10B is formed on the P+ region 105.
Since it can be formed in contact with the p-side electrode 10B
This makes it possible to improve the ohmic characteristics and contact resistance of the electrode, thereby increasing current injection efficiency.

In FIG. 7, a protrusion 121 formed perpendicularly to the substrate 101 on the main surface side of the substrate 101, that is, on the laminated side of each layer, is not perpendicular to the substrate 101 but is inclined at an angle. An example is shown. In this embodiment, as shown in the figure, the protrusion 12
1 is sloped so that the upper part is narrow and the lower part is wide.

According to this embodiment, since the side surface of the protrusion 121 is inclined, when the protrusion 121 is formed by dry etching, the side surface of the protrusion 121 is smoother than when it is formed perpendicularly to the substrate 101. It has manufacturing advantages such as easy conversion and attachment of electrodes. Moreover, it is possible to further improve the ohmic characteristics and contact resistance of the p-side electrode 10G formed on the side surface, and further improve the current injection efficiency. The same light output as when formed vertically can be obtained. Furthermore, since the side surface of the protrusion 121 is smooth, the reliability of the device itself is improved.

FIG. 8 shows another embodiment to which the present invention is applied.

In this embodiment, pJ! made of p-type GaAs is formed on the p-type layer lGaAs cladding layer 104. ! ! A GaAs electrode layer 116 is stacked, and a cladding layer 1 is formed approximately at the center of the GaAs electrode layer 116.
A hole 123 reaching 04 is formed. In other words, it is formed concentrically around the inner contour of the uppermost part of the protrusion 121. Further, the upper reflective layer 111 is made of p-type GaAs.
It is formed to bury the hole 123 formed in the electrode layer 11B.

The p-side electrode 10B is connected to the upper part of the electrical insulating layer 110 and the protrusion 1
They are formed not only on the side surfaces of the protrusions 121, but also on the flat portions above the protrusions 121, as shown in the figure, and are formed only on the p-type GaAs electrode layer 11B.

Note that a semiconductor multilayer film as shown in FIG. 2 can also be used for the upper reflective layer 111, and the conductivity type of the film in this case may be other than n-type.

According to this embodiment, the p-side electrode 10B is made of p-type AlGaAs.
Since it can be formed on the p-type GaAs layer instead of directly on the p-side electrode 10B, the ohmic characteristics and contact resistance of the p-side electrode 10B can be improved, and the current injection efficiency and luminous efficiency can be improved. .

FIG. 9 shows an example in which the semiconductor light emitting device according to the present invention described above is formed into a two-dimensional array. Alternatively, it may be configured in a -dimensional array. In this way, the light output emitted by the device configured in a -dimensional or two-dimensional array can be extracted vertically upward relative to the substrate 101.

Note that the active layer 103 in the above embodiment is made of, for example, GaAs.
Two types of semiconductor layers, such as AlGaAs and AlGaAs, or AlGaAs and AlGaAs with different Al compositions, are laminated alternately,
It is possible to form a quantum well structure in which each layer has a thickness of 30 nm or less. By having such a structure,
The threshold current can be lowered, and the wavelength of the light emission output can be shortened.

In the above embodiments other than the embodiment shown in FIG. 6, the n-side metal electrode layer 107 is a p-side metal electrode layer, the substrate 101 which is an n-type semiconductor is a p5 semiconductor, and the lower reflective layer is 112 is a multilayer film of p-type semiconductor, and n-type AlGaA
The s cladding layer 102 is made of p-type semiconductor, p-type AlG
The aAs cladding layer 104 is an n-type semiconductor, the p-side metal electrode layer 10B is an n-side metal electrode layer, the p-type AlGaAs insertion layer 115 is an n-type semiconductor, and the current blocking layer 11B made of n-type AlGaAs is a p-type semiconductor. Additionally, the p-type GaAs electrode layer 11B can be used as an n-type semiconductor.

Furthermore, the embodiments shown in FIGS. 2 to 8 of the above embodiments can be applied to other embodiments.

The substrate 101 is made of InP or GaP in addition to GaAs.
, GaAsP.

Cadmium thirium (C:dTe), Zn5e, ZnS, etc. can be used.

The active layer 103 is made of AlGaAs, aluminum, gallium indium phosphide (AIGaIn) in addition to GaAs.
P), GaInP or A IGa InP can be used.

When AlGaAs is used as the cladding layer, AlGaAs used for the active layer 103 has a wider forbidden band width, and when Ga1nAsP is used, indium phosphide (1nP) is used as the cladding layer.
Alternatively, if GaInAsP, which has a wider forbidden band width than GaInAsP used for the active layer 103, is used, and GaInP or AIGaInP is used, AIGaInP, which has a wider forbidden band width than the AIGaInP used for the active layer 103, is used as the cladding layer. do it.

In addition to this, the active layer 103 includes gallium, arsenic, and
(GaAsP), gallium nitride (GaP), gallium nitride (GaN), zinc selenium/7 (ZnSe)
, fdE zinc oxide (ZnS), lead-tin-thirium (PbSnTe) or lead selenium sulfide (Phase)
etc. can be used.

Furthermore, although the cross section of the protrusion 121 in each of the above embodiments is approximately circular, it is not limited to the circular cross section and may be square or polygonal.

For reference, an example of a conventionally proposed surface emitting semiconductor laser is shown in FIG.

As shown in FIG. 1O, the active layer 4 is formed so as to be sandwiched between the cladding layer 3 and the cladding layer 5. The light emitting section 10 is formed so as to be sandwiched between a reflective film 8 and a reflective film 9 made of dielectric or metal, and the light emitted by the light emitting section 10 is emitted by forming a resonator with the reflective film 8 and the reflective film 8. You are getting a confinement gain. The electrode is located on one main surface of the substrate B opposite to the lamination side.
A circular electrode 7 is arranged on the back side of the pair of substrates, and a circular electrode 1 is arranged on the front surface of the substrate. By flowing a current between the electrodes, it is concentrated in the light emitting part 10, and the laser output is extracted in a direction perpendicular to the substrate 6.

In this conventionally proposed structure, current is injected into the light emitting region IO between the circular electrode 7 arranged around the hole 13 formed in the substrate 6 and the circular shape 8i1 on the substrate surface. Since the current flows in the direction of the arrow 12 shown in the figure, the current cannot be concentrated in a minute area. Therefore, current injection efficiency is not suitable, and improvement in luminous efficiency cannot be expected.

Further, in this structure, since the electrode 1, the reflective layer 8, and the hole 13 must be formed in correspondence with the positions of the front surface of the substrate and the back surface of the substrate, it is difficult to adjust the respective positions during manufacturing. The holes 13 are formed in the substrate 6 with a thickness of about 100 gta so as to reach the cladding layer 5.
Since the diameter is large, exceeding 100 gra, it is not possible to form a high-density array. In terms of strength, since the hole 13 is formed in the substrate 6 in this device, the thickness of the device itself is about 10 to 100 grs, which causes a problem that the strength is weak.

However, the device of the present invention shown in the above embodiments has a structure in which a protrusion is formed on the side opposite to the substrate, and a P-side electrode is formed on the upper surface parallel to the substrate and the side surface of the protrusion. As a result, the p-side electrode has a larger electrode area than the conventional device, and it is possible to increase the injection current without expanding the light emitting region in the active layer, significantly improving the current injection efficiency. be able to.

Moreover, according to this structure, when comparing the effective refractive index of the part of the upper cladding layer that is almost directly below the protrusion and the other part, in the latter case, the distance between the surface of the upper cladding layer and the active layer is small. Compared to the former, the loss for light emission is relatively large and the effective refractive index is small, so the light emitted in the light emitting layer, which is the core part, is confined horizontally to the substrate, improving the light emitting efficiency. As a result, the threshold current can be lowered. In addition, since there is no need to drill holes in the substrate and the device can be sufficiently thick, high-density arrays are possible from a manufacturing perspective, and semiconductor light-emitting devices or lasers with high device strength can be manufactured. .

Effects According to the present invention, a semiconductor light emitting device has a protrusion in a direction substantially perpendicular to the main surface of a semiconductor substrate, and one of the electrodes extends over the side surface of the protrusion and the bottom of the protrusion. Since the light emitting layer is formed on a surface extending substantially parallel to the substrate, when a current is passed between the two electrodes, the light emitted from the light emitting layer is directed horizontally to the substrate. The light is trapped and the luminous efficiency is improved.

Therefore, the light output generated in one light emitting region can be extracted in the direction perpendicular to the substrate as a high light emitting output.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional perspective view partially showing an embodiment of a semiconductor light emitting device according to the present invention, and FIG. 2 is a rust layer Ma of the lower reflective layer of the embodiment shown in FIG.
3 to 8 are sectional views showing other embodiments of the semiconductor light emitting device according to the present invention, and FIG. 9 is an enlarged sectional view showing an example of the structure of the semiconductor light emitting device according to the present invention in the form of a two-dimensional array. FIG. 10 is a perspective view showing one embodiment of the present invention, and FIG. 10 is a sectional view showing an example of a semiconductor light emitting device according to the prior art. Explanation of symbols of main parts 101 , , , substrate 102 , . . . n-type cladding layer 103 , , , active layer 104 , , p-type cladding layer 105 , , p + region 0B, , p-side electrode 10 ? , , n-side electrode 108 , , light emitting region 110 , , electrically insulating layer 111 , , upper reflective layer 112 , , lower reflective layer 121 , , protrusion Fig. 1 Fig. 2 Fig. 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] 1. A semiconductor substrate, a light-emitting layer formed on the semiconductor substrate and emitting light in a direction substantially perpendicular to the main surface of the substrate, and an electrode for injecting current into the light-emitting layer. In the semiconductor light emitting device, the device has a protrusion on the substrate that protrudes in a direction substantially perpendicular to the main surface, and the electrode is arranged on the side surface of the protrusion and on the side surface of the protrusion. A semiconductor light emitting device, characterized in that the device is formed on a surface extending from a lower portion of a protrusion substantially parallel to the substrate.