JP2008235691A - Semiconductor light emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor light emitting element capable of increasing emission efficiency of light to generate a high output. <P>SOLUTION: Multilayer portions 21 and 22 having a high-refractive-index layer 31 and a low-refractive-index layer 32 laminated by turns is provided between an active layer 4 and a first clad layer 5, and a second clad layer 6 and then light emitted at an angle exceeding the critical angle between the active layer 4 and first clad layer 5, and second clad layer 6 can also be refracted and reflected by the multilayer portions 21 and 22 to travel in the active layer 4 to be output to the outside, thereby generating a high output. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a semiconductor light emitting device, and more particularly to a semiconductor light emitting device for increasing output.

  With the spread of multimedia, information transmission is rapidly increasing in trunk systems, access systems, datacoms, etc., and realization of a large-scale wavelength division multiplexing optical communication system is desired. In order to realize this system, a light source that outputs light of multiple wavelengths with high output is one of the main optical components, and development is urgently needed. As this type of light source, there is a super luminescent diode method which is promising because a particularly large output can be obtained and a broadband emission spectrum can be obtained.

  FIG. 10 shows an external perspective view of a conventional semiconductor light emitting device using a super luminescent diode system.

As shown in FIG. 10, in the semiconductor light emitting device, the upper second cladding layer 105, the contact layer 106, and the upper electrode 107 directly above the slab-like active layer 103 have a substantially rectangular cross-sectional shape and have a desired width pattern. Since the light is formed in a shape, spontaneous emission light is confined in the region of the active layer 103 substantially directly below each of the above layers, and is amplified while being guided in the active layer 103 approximately directly below the pattern shape. Therefore, a large amplification gain can be obtained (see, for example, Patent Document 1).
JP 2000-269600 A

  However, in such a conventional semiconductor light emitting device, among the emitted light generated in the active layer 103, there is little light emitted within the critical angle with the cladding layer confined in the active layer 103, and most of the critical angle is There was a problem that it was generated at an angle exceeding 1, and could not be used as emitted light through the cladding layer and was wasted.

  The present invention has been made to solve such a conventional problem. Light emitted at an angle exceeding the critical angle between the active layer and the cladding layer can also be used as emission light, and the light emission efficiency can be obtained. An object of the present invention is to provide a semiconductor light emitting device capable of increasing the output and increasing the output.

  In the semiconductor light emitting device of the present invention, an active layer is provided above the semiconductor substrate, and the refractive index of the semiconductor substrate or the refractive index of the semiconductor layer formed between the active layer and the semiconductor substrate is the lowest. The semiconductor light emitting device having a refractive index has a multilayer structure in which a high refractive index layer and a low refractive index layer are alternately stacked from the active layer in the vertical direction, and the high refractive index layer is The refractive index is lower than the refractive index of the active layer and higher than the refractive index of the semiconductor substrate or the semiconductor layer, and the refractive index of the low refractive index layer is higher than the refractive index of the high refractive index layer. And is configured to be higher than the refractive index of the semiconductor substrate or the semiconductor layer.

  With this configuration, since the high refractive index layer and the low refractive index layer are alternately laminated between the active layer and the cladding layer, light generated at an angle exceeding the critical angle between the active layer and the cladding layer is also generated. Further, it can be refracted and reflected by the multilayer portion of the high refractive index layer and the low refractive index layer, and can proceed inside the active layer and output to the outside, so that high output can be achieved.

Furthermore, the semiconductor light emitting device of the present invention is the semiconductor light emitting device according to claim 1, wherein the multilayer structure includes a plurality of pairs of the high refractive index layer and the low refractive index layer, The stacking order from the active layer is i, the refractive indexes of the high refractive index layer and the low refractive index layer in each pair are n _hi and n _li , and the layer thicknesses of the high refractive index layer and the low refractive index layer, respectively. _Are d _hi and d _li , and the optical wavelength is λ, n _hi d _hi = n _li d _li , and d _hi > λ / 4n _hi and d _li > λ / 4n _li It has a configuration.

  With this configuration, the reflectance with respect to the vertical component of light having an angle with respect to the horizontal plane can be maximized, light can be reliably returned to the active layer, and the efficiency of spontaneous emission light coupling to the active layer can be increased. . That is, spontaneous emission light can be effectively enhanced.

Furthermore, the semiconductor light emitting device of the present invention is the semiconductor light emitting device according to claim 2, wherein the multilayer structure includes a plurality of internal multilayer structures in which a plurality of pairs of the high refractive index layer and the low refractive index layer are stacked. When the stacking order of the internal multilayer structure from the active layer is k, and the layer thicknesses of the high refractive index layer and the low refractive index layer for each internal multilayer structure are represented as d _hk and d _lk , respectively, It has a structure characterized by satisfying d _hk ≠ d _{h (k + 1)} and d _lk ≠ d _{l (k + 1)} .

  With this configuration, by stacking the internal multilayer structure with a pair of high refractive index layer and low refractive index layer with the internal multilayer structure of different layer thickness, the angle is wider than the configuration without the internal multilayer structure. Since the emitted spontaneous emission light can be reliably returned to the active layer, the spontaneous emission light can be further effectively enhanced. In addition, the wavelength band of light returning to the active layer can be expanded, and spontaneous emission light in a wide wavelength band can be effectively enhanced.

Furthermore, the semiconductor light emitting device of the present invention is the semiconductor light emitting device according to claim 2, wherein the multilayer structure includes a plurality of internal multilayer structures in which a plurality of pairs of the high refractive index layer and the low refractive index layer are stacked. When the stacking order of the inner multilayer structure from the active layer is k, and the refractive indexes of the high refractive index layer and the low refractive index layer for each internal multilayer structure are represented as n _hk and n _lk , respectively. It has a structure characterized by satisfying n _hk ≠ n _{h (k + 1)} and n _lk ≠ n _{l (k + 1)} .

  With this configuration, the amount of light returning to the active layer can be increased by laminating the internal multilayer structure in which the high refractive index layer and the low refractive index layer are paired with the internal multilayer structure having a different refractive index. The emitted light can be effectively enhanced.

  Furthermore, the semiconductor light emitting device of the present invention is the semiconductor light emitting device according to claim 2, wherein the thicknesses of the high refractive index layer and the low refractive index layer of each pair of the multilayer structure are set above or below the active layer. It has the structure characterized by making it thick or thin gradually toward this.

  With this configuration, spontaneous emission light radiated from the active layer can be returned to the active layer at a wider angle than a device in which the layer thicknesses of the high refractive index layer and the low refractive index layer in the multilayer structure are constant. Spontaneous emission light can be effectively enhanced.

  Furthermore, the semiconductor light emitting device of the present invention is the semiconductor light emitting device according to claim 2, wherein the refractive index of each pair of high refractive index layer and low refractive index layer of the multilayer structure is set above or below the active layer. It has the structure characterized by making it become high or low gradually toward this.

  With this configuration, the refractive index of the high refractive index layer and the low refractive index layer in the multilayer structure can return spontaneously emitted light emitted from the active layer to an active layer at a wider angle than the elements, respectively, Spontaneous emission light can be effectively enhanced.

  Furthermore, in the semiconductor light emitting device of the present invention, an active layer is provided above the semiconductor substrate, and the refractive index of the semiconductor substrate or the refractive index of the semiconductor layer formed between the active layer and the semiconductor substrate is A portion of the substrate having the lowest refractive index and having the plurality of layers including the active layer and the semiconductor layer sequentially crystal-grown is etched into a stripe shape, and then left in the stripe shape of the substrate. In a semiconductor light emitting device in which buried layers are formed by crystal growth on both sides of the substrate, a high refractive index layer is formed in a direction intersecting the growth direction of the substrate between the portion left in the stripe shape of the substrate and the buried layer. It has a lateral multilayer structure in which low refractive index layers are alternately stacked, and the high refractive index layer has a refractive index lower than the refractive index of the active layer and the semiconductor substrate or the semiconductor layer. refraction Higher configured than the low refractive index layer has a structure which is characterized in that its refractive index is made lower than the refractive index of the high refractive index layer.

  With this configuration, the high refractive index layer and the low refractive index layer are alternately laminated in the direction intersecting with the lamination direction of the active layer. The light is refracted and reflected by the multilayer portion with the rate layer, travels in the active layer, and can be emitted light, so that high output can be achieved.

  Furthermore, in the semiconductor light emitting device according to the present invention, the substrate on which the plurality of layers including the active layer and the semiconductor layer are sequentially crystal-grown is etched in a stripe shape, and then the portion of the substrate left in the stripe shape 7. The semiconductor light-emitting device according to claim 1, wherein a buried layer is formed on both sides of the substrate by crystal growth, wherein a portion of the substrate left in a stripe shape and the buried layer are formed. A lateral multilayer structure in which high refractive index layers and low refractive index layers are alternately laminated in a direction intersecting with the growth direction of the substrate, and the refractive index of the high refractive index layer is The refractive index is lower than the refractive index of the active layer and higher than the refractive index of the semiconductor substrate or the semiconductor layer, and the refractive index of the low refractive index layer is lower than the refractive index of the high refractive index. Configuration characterized by It has.

  With this configuration, since the high refractive index layer and the low refractive index layer are alternately laminated also in the vertical direction with respect to the active layer, the light that jumps out from the active layer in the horizontal direction is also reflected in the high refractive index layer and the low refractive index layer. The light is refracted and reflected by the multilayer portion with the rate layer, travels in the active layer, and can be emitted light, so that high output can be achieved.

  The semiconductor light-emitting device of the present invention is the semiconductor light-emitting device according to any one of claims 7 to 8, wherein the high-refractive index layer and the low-refractive index layer of the lateral multilayer structure are made of a dielectric film. It has the structure characterized by having comprised.

  With this configuration, a lateral multilayer structure can be formed with high accuracy, so light that jumps out from the active layer in the horizontal direction is refracted and reflected by the multilayer portion of the high-refractive index layer and the low-refractive index layer, and proceeds in the active layer. The light can be emitted, and the output can be increased.

  The semiconductor light emitting device of the present invention is the semiconductor light emitting device according to any one of claims 1 to 6, 8, and 9, wherein a spacer layer is provided between the active layer and the multilayer structure. It has a characteristic configuration.

  With this configuration, since the spacer layer is inserted between the active layer and the cladding layer, the refractive index can be adjusted by the spacer layer, and the amount of light confinement in the active layer can be adjusted. Further, the spacer layer can prevent leakage of carriers from the active layer. Furthermore, the spacer layer can prevent p-type impurities from entering the active layer particularly during crystal growth, suppress light absorption by excitation of electrons in the valence band, and prevent a decrease in luminous efficiency. Can do.

  In the present invention, a multilayer portion in which high refractive index layers and low refractive index layers are alternately laminated is provided between the active layer and the clad layer, thereby generating an angle exceeding the critical angle between the active layer and the clad layer. The light is also refracted and reflected by the multilayer part of the high-refractive index layer and the low-refractive index layer, travels in the active layer, and can be output to the outside, thereby achieving an effect of increasing the output. A semiconductor light emitting device can be provided.

  Hereinafter, semiconductor light emitting devices according to embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
First, the semiconductor light emitting device in the first embodiment of the present invention will be described with reference to FIGS.

  As shown in FIGS. 1 and 2, the semiconductor light emitting device 1 a includes a semiconductor substrate 2, an active layer 4, a first cladding layer 5, a second cladding layer 6, a contact layer 7, and spacer layers 8 and 9. And multilayer portions 21 and 22 and buried layers 10a and 10b. The active layer 4, the first cladding layer 5, the second cladding layer 6, the spacer layers 8 and 9, and a part of the multilayer portions 21 and 22 form a waveguide through which light is guided.

  Here, the active layer 4, the first cladding layer 5, the second cladding layer 6, the contact layer 7, the spacer layers 8 and 9, and the multilayer portions 21 and 22 form the semiconductor layer 3. Further, the semiconductor substrate 2 and the semiconductor layer 3 are formed by cleavage, and have a light emission end face serving as a termination portion of the waveguide.

  The semiconductor light emitting device 1 a further includes an upper electrode 11 for injecting current into the active layer 4 and a lower electrode 12.

  The semiconductor light emitting element 1a of the present embodiment is used for a semiconductor optical amplifier, a wavelength tunable light source device, a super luminescent diode (hereinafter referred to as SLD), and the like.

  Further, the semiconductor light emitting element 1a according to the present embodiment has a substantially rectangular parallelepiped shape as shown in FIG.

  An n-type first cladding layer 5 containing an n-type impurity is formed in contact with the semiconductor substrate 2 made of InP doped with an n-type impurity. A semiconductor layer 3 is formed on the semiconductor substrate 2 along the longitudinal direction of the semiconductor light emitting element 1a, including a part of the first cladding layer 5. On the outside of the semiconductor layer 3, buried layers 10a and 10b for blocking current are formed.

  The multilayer part 22 and the spacer layer 8 are formed on the upper side of the first cladding layer 5, and the active layer 4 is further formed on the upper side thereof.

  The active layer 4 has a multiple quantum well structure such as non-doped InGaAsP or a bulk active layer.

  A spacer layer 9 and a multilayer portion 21 are formed above the active layer 4, and a p-type second cladding layer 6 containing a p-type impurity is further formed thereon.

  Details of the multilayer portions 21 and 22 will be described later.

  A p-type contact layer 7 made of InGaAsP is formed above the p-type second cladding layer 6.

  An upper electrode (p electrode) 11 is attached to the upper surface of the p-type contact layer 7, and a lower electrode (n electrode) 12 is also attached to the lower side of the n-type semiconductor substrate 2.

  And after cutting out an element by cleavage, the antireflection film 14 is formed in an end surface.

  Further, as shown in FIG. 3, the multilayer part 21 has high refractive index layers 31a, 31b, 31c having the same refractive index and low refractive index layers 32a, 32b, 32c having the same refractive index. The high refractive index layer 31a, the low refractive index layer 32a, the high refractive index layer 32a, the low refractive index layer 32, and the high refractive index layer 31a, the low refractive index layer 32a, The refractive index layer 31b, the low refractive index layer 32b, the high refractive index layer 31c, and the low refractive index layer 32c are formed in this order.

Further, if the refractive index of the high refractive index layers 31a, 31b, and 31c is n _h1 and the refractive index of the low refractive index layers 32a, 32b, and 32c is n ₁₁ ,
n _h1 > n _l1
It has become.

Further, when the layer thicknesses of the high refractive index layers 31a, 31b, and 31c are d _h1 , the layer thicknesses of the low refractive index layers 32a, 32b, and 32c are d ₁₁ , and the light wavelength is λ,
n _h1 d _h1 = n _l1 d _l1
It has become.

In addition, in order for light having an angle θ to the horizontal plane to be reflected to the maximum in the stacking direction in the low refractive index layers 32a, 32b, and 32c,
d _l1 = λ / (4n _l1 cos θ)
Similarly, in order to be reflected to the maximum in the stacking direction in the high refractive index layers 31a, 31b, and 31c,
d _h1 = λ / (4n _h1 cos θ)
It becomes. Therefore, the low refractive index layers 32a, 32b, and 32c and the high refractive index layers 31a, 31b, and 31c are d _h1 > λ / 4n _h1 and d _l1 > λ / 4n _l1.
To form.

Furthermore, if the refractive index of the active layer 4 is n _a and the refractive index of the first cladding layer 5 is n _c1 ,
n _h1 <n _a and n _l1 ≧ n _c1
It has become.

  The multilayer part 22 has the same configuration as that of the multilayer part 21, and is directed from the active layer 4 side toward the semiconductor substrate 5 with a high refractive index layer 31a, a low refractive index layer 32a, a high refractive index layer 31b, and a low refractive index. The layer 32b, the high refractive index layer 31c, and the low refractive index layer 32c are formed in this order.

Further, the refractive index of the second cladding layer 6 is the same as the refractive index of the first cladding layer 5, and the refractive index of the second cladding layer 6 is _nc2 .
n _c2 ≦ n _l1
It has become.

As the refractive index n _{h1 of the} high refractive index layers 31a, 31b and 31c and the refractive index n _l1 of the low refractive index layers 32a, 32b and 32c, the larger the difference between the refractive index n _h1 and the refractive index n ₁₁ , Therefore, it is possible to increase the reflectance with respect to the light emitted from the high refractive index layers 31a, 31b, and 31c and the low refractive index layers 32a, 32b, and 32c.

However, if the refractive index n ₁₁ of the low refractive index layers 32a, 32b, and 32c is lower than the refractive indexes n _c1 and n _c2 of the first cladding layer 5 and the second cladding layer 6, the carriers injected into the semiconductor light emitting device 1 Becomes difficult to enter the active layer 4. Moreover, the high refractive index layer 31a, 31b, the refractive index of the refractive index _{n h1} active layer 4 of 31c Higher than _{n a,} the active layer 4 in the injected carriers is the high refractive index layer 31a, 31b, to 31c Due to the leakage, the light emission efficiency of the semiconductor light emitting device 1 decreases.

Accordingly, the refractive index n ₁₁ of the low refractive index layers 32a, 32b, and 32c is set to be equal to or slightly higher than the refractive indexes n _c1 and n _c2 of the first cladding layer 5 and the second cladding layer 6, and the high refractive index. layers 31a, 31b, it is preferable to set to slightly lower than the refractive index of the active layer 4 and the refractive index _{n h1 n a} of 31c.

  When a direct current drive current is applied from the electrodes 11 and 12 on both sides to the semiconductor light emitting device 1 a configured as described above, light is generated by the current flowing through the active layer 4 of the semiconductor layer 3.

  The light generated in the active layer 4 is output as light 51 in the longitudinal direction indicated by the arrow in FIG.

  The light 51 output from the active layer 4 is output to the outside from the emission end face of the semiconductor light emitting element 1a and is coupled to, for example, an optical fiber (not shown).

Here, as shown in FIG. 3, the horizontal direction is 0 °, the longitudinal direction and the radiation angle of spontaneous emission light are θ, and the criticality is determined by the refractive indexes of the active layer 4, the first cladding layer 5, and the second cladding layer 6. Assuming that the angle is θ _c , among the light generated in the active layer 4, the light emitted to −θ _R1 ≦ θ ≦ θ _R1 (θ _c <θ _R1 ≦ 90 °) is refracted and reflected by the multilayer portion 21. The phases of the emitted light are aligned. Therefore, even for an optical component emitted at an angle (± θ _R1 ) larger than the critical angle (± θ _c ) determined by the refractive index of the active layer 4, the first cladding layer 5, and the second cladding layer 6, Almost all the light is reflected and travels through the active layer 4 and is output from the output end face to the outside.

In addition, a component whose emission angle is θ _R1 <θ ≦ 90 ° (θ _R1 > θ _C ) among the generated light passes through this region because the phase of the reflected light in the multilayer portion 21 is not uniform, It escapes to the second cladding layer 6. Similarly, when the radiation angle of the generated light is −θ _R1 > θ ≧ −90 °, the light passes through the multilayer portion 22 and escapes to the first cladding layer 5.

Therefore, in the conventional semiconductor light emitting device without the multilayer portions 21 and 22, all the light emitted at an angle exceeding the critical angle between the active layer 4, the first cladding layer 5 and the second cladding layer 6 is wasted. However, according to the present embodiment, light emitted at angles of θ _C <θ ≦ θ _R1 and −θ _C > θ ≧ −θ _R1 can also be emitted to the outside, and light can be efficiently emitted. Can be output.

  In the present embodiment, the pair of the high refractive index layer 31 and the low refractive index layer 32 is set so that the refractive index of the layer closer to the active layer 4 is increased. The refractive index of the layer closer to 4 may be made lower.

(Second Embodiment)
Next, a semiconductor light emitting device according to a second embodiment of the present invention will be described with reference to FIG.

  The semiconductor light emitting device of this embodiment includes a multilayer portion 23 and a multilayer portion 24 instead of the multilayer portion 21 and the multilayer portion 22 of the semiconductor light emitting element 1a shown in the first embodiment. Since other configurations are the same as those of the first embodiment, the same reference numerals are given and detailed description thereof is omitted.

  As shown in FIG. 4, the multilayer part 23 includes an internal multilayer part 23a in which a plurality of pairs of high refractive index layers and low refractive index layers are stacked, and an internal multilayer part 23b.

  The internal multilayer portion 23a includes high refractive index layers 33a, 33b, and 33c having the same refractive index and low refractive index layers 34a, 34b, and 34c having the same refractive index, respectively. From the active layer 4 side, the high refractive index layer 33a, the low refractive index layer 34a, the high refractive index layer 33b, the low refractive index layer 34b, and the high refractive index layer 33c are arranged so that the layers 33 and the low refractive index layers 34 are alternately arranged. The low refractive index layers 34c are formed in this order.

Further, when the refractive index of the high refractive index layers 33a, 33b, and 33c is n _h2 and the refractive index of the low refractive index layers 34a, 34b, and 34c is n _l2 ,
n _h2 > n _l2
It has become.

  The internal multilayer portion 23b includes high refractive index layers 35a, 35b, and 35c having the same refractive index and low refractive index layers 36a, 36b, and 36c having the same refractive index, respectively. From the active layer 4 side, the high refractive index layer 35a, the low refractive index layer 36a, the high refractive index layer 35b, the low refractive index layer 36b, and the high refractive index so that the refractive index layer 35 and the low refractive index layer 36 are alternated. The layer 35c and the low refractive index layer 36c are formed in this order.

Further, when the refractive index of the high refractive index layers 35a, 35b, and 35c is n _h3 and the refractive index of the low refractive index layers 36a, 36b, and 36c is n _l3 ,
n _h3 > n _l3
It has become. Also,
n _h2 > n _h3 and n _l2 > n _l3
It has become.

Furthermore, when the layer thicknesses of the high refractive index layer 33, the low refractive index layer 34, the high refractive index layer 35, and the low refractive index layer 36 are d _h2 , d _l2 , d _h3 , and d _l3 , respectively.
d _h2 <d _h3 and d _l2 <d _l3
It has become.

further,
n _h2 <n _a and n _l3 ≧ n _c1
It has become.

  The multilayer section 24 has the same configuration as the multilayer section 23.

  When a direct current drive current is applied between the upper electrode 11 and the lower electrode 12 in the semiconductor light emitting device configured as described above, light is generated by current flowing through the active layer 4 of the semiconductor layer. The

Here, among the light generated in the active layer 4, the light emitted to −θ _R3 ≦ θ ≦ θ _R3 has the phase of the light refracted and reflected by the multilayer portion 21 aligned. For this reason, almost all light components emitted at an angle (± θ _R3 ) larger than the critical angle (± θ _c ) determined by the refractive index of the active layer 4, the first cladding layer, and the second cladding layer are almost all. Is reflected, travels through the active layer 4, and is output to the outside from the output end face.

In addition, a component having a radiation angle of θ _R3 <θ ≦ 90 ° (θ _R3 > θ _C ) among the generated light passes through this region because the phase of the reflected light in the multilayer portion 23 is not uniform, It escapes to the second cladding layer 6. Similarly, when the radiation angle of the generated light is −θ _R3 > θ ≧ −90 °, the light passes through the multilayer portion 24 and escapes to the first cladding layer 5.

  On the other hand, the inner multilayer part 23a and the inner multilayer part 23b are formed so that the periods of the multilayer part composed of the high refractive index layer and the low refractive index layer are different. With such a configuration, the phases of the reflected light are aligned with respect to the light emitted from the respective multilayer portions at different angles. For this reason, light emitted at a wider angle as the entire multilayer structure returns to the active layer 4.

  Therefore, even light having an angle that cannot be reflected only by the internal multilayer part 23a can be refracted and reflected by the internal multilayer part 23a and the internal multilayer part 23b, and the radiation angle of the light to be output to the outside can be increased efficiently. Light can be output.

  In the present embodiment, both the refractive index and the layer thickness of the high refractive index layer 33 and the high refractive index layer 35, and the low refractive index layer 34 and the low refractive index layer 36 are made different. However, the refractive index and the layer thickness may be different from each other, and the magnitude relationship between the refractive index and the layer thickness may be reversed.

  Further, FIG. 5 shows a specific light reflectance by the multilayer structure of the semiconductor light emitting element in the present embodiment.

  In this example, the internal multilayer structure is a three internal multilayer structure including a first internal multilayer structure, a second internal multilayer structure, and a third internal multilayer structure, and the logarithm of the high refractive index-low refractive index layer of each internal multilayer structure. Were 3 pairs, 6 pairs, and 10 pairs, respectively.

Moreover, the high refractive index layer and the low refractive index layer constituting the multilayer structure are made of InGaAsP, and the refractive index is
High refractive index layer: n _h = 3.45
Low refractive index layer: n _l = 3.20
The thicknesses of the high refractive index layers of the first internal multilayer structure, the second internal multilayer structure, and the third internal multilayer structure are 0.4601, 0.3248, 0.2301 (μm), respectively, and the low refractive index layer The thickness of each of the layers is 0.4960, 0.3502, 0.2480 (μm), the reflection characteristics not having the conventional multilayer structure are indicated by broken lines, and the reflection characteristics of the multilayer structure of the present invention are indicated by solid lines.

  As shown in FIG. 5, in the conventional structure, only the light whose propagation angle propagates through the waveguide is about 25 ° or less can be totally reflected and guided. However, in the structure of the present invention, the light can travel up to about 40 °. Light can be guided. For this reason, the coupling efficiency of light into the waveguide can be increased by about 60%, and the optical output of the device can be greatly improved.

(Third embodiment)
Next, a semiconductor light-emitting device according to a third embodiment of the present invention will be described with reference to FIG.

  The semiconductor light emitting device of this embodiment includes a multilayer portion 25 and a multilayer portion 26 instead of the multilayer portion 21 and the multilayer portion 22 of the semiconductor light emitting element 1a shown in the first embodiment. Since other configurations are the same as those of the first embodiment, the same reference numerals are given and detailed description thereof is omitted.

  As shown in FIG. 6, the multilayer portion 25 has a high refractive index layer 41, a low refractive index layer 42, and a high refractive index from the active layer 4 side so that the high refractive index layer and the low refractive index layer are alternated. The layer 43, the low refractive index layer 44, the high refractive index layer 45, the low refractive index layer 46, the high refractive index layer 47, and the low refractive index layer 48 are formed in this order.

Further, the refractive indexes of the high refractive index layers 41, 43, 45, and 47 are n _h4 , n _h5 , n _h6 , n _h7 , and the refractive indexes of the low refractive index layers 42, 44, 46, and ₄₈ are n _l4 , respectively. , N _l5 , n _l6 , n _l7 ,
_{n h4> n h5> n h6} > n h7, _{and, n l4> n l5> n} l6> n l7
It has become.

Furthermore, the layer thicknesses of the high refractive index layers 41, 43, 45, and 47 are respectively d _h4 , d _h5 , d _h6 , and d _h7 , and the layer thicknesses of the low refractive index layers 42, 44, 46, and 48 are respectively d _l4. , D _l5 , d _l6 , d _l7 ,
_{d h4 <d h5 <d h6} <d h7, _{and, d l4 <d l5 <d} l6 <d l7
It has become.

  The multilayer part 26 has the same configuration as the multilayer part 25.

  When a direct current drive current is applied from the electrodes 11 and 12 on both sides to the semiconductor light emitting device configured as described above, light is generated by the current flowing through the active layer 4 of the semiconductor layer.

Here, the multi-layer portion 25 is formed so that each pair of the high refractive index layer and the low refractive index layer is gradually thickened in the stacking direction, and the light emission angle at which the phase of the reflected light is uniform between each pair is small. Each one is different. For this reason, as a whole of the multilayer part 25, the phases of the reflected light closely overlap with the light having a wide radiation angle. In addition, although the amount of light reflected by each pair is small, the multilayer portion 25 is composed of a large number of pairs. Therefore, the multilayer portion 25 as a whole has -θ _R7 ≦ θ ≦ θ _R7 among the light generated in the active layer 4. Almost all the light emitted from the light is reflected and travels through the active layer 4 and is output to the outside from the output end face.

In addition, a component of the generated light whose radiation angle is θ _R7 <θ ≦ 90 ° (θ _R7 > θ _C ) is reflected light by each pair of the high refractive index layer and the low refractive index layer in the multilayer portion 25. Since the phase overlap becomes rough, it passes through this region and escapes to the second cladding layer 6. Similarly, when the radiation angle of the generated light is −θ _R7 > θ ≧ −90 °, the light passes through the multilayer portion 26 and escapes to the first cladding layer 5.

  Therefore, the radiation angle of light guided through the active layer 4 from the high refractive index layer 41 to the low refractive index layer 48 can be increased, and light can be output efficiently.

  In the present embodiment, the refractive indexes of the high refractive index layer 41 to the low refractive index layer 48 in the multilayer portion 25 and the multilayer portion 26 are gradually decreased from the active layer 4 side, and the layer thickness is gradually increased. However, the present invention is not limited to this, and the refractive index may be gradually increased from the active layer 4 side, or the layer thickness may be gradually decreased.

  Further, FIG. 7 shows a specific light reflectance by the multilayer structure of the semiconductor light emitting element in this embodiment.

  In this example, the multilayer structure is thicker as the layer is closer to the active layer, the maximum thickness of the high refractive index layer is 0.4872 (μm), and the maximum thickness of the low refractive index layer is 0.5252 (μm). Each period of the refractive index-low refractive index layer advances by 4% from the maximum thickness, and the logarithm is 9 pairs.

Moreover, the high refractive index layer and the low refractive index layer constituting the multilayer structure are made of InGaAsP, and the refractive index is
High refractive index layer: n _h = 3.45
Low refractive index layer: n _l = 3.20
The reflection characteristics without the conventional multilayer structure are indicated by broken lines, and the reflection characteristics of the multilayer structure of the present invention are indicated by solid lines.

  As shown in FIG. 7, in the conventional structure, only the light whose propagation angle propagates through the waveguide is about 25 ° or less can be totally reflected and guided. However, in the structure of the present invention, the light can be up to about 30 °. Light can be guided. For this reason, the coupling efficiency of light into the waveguide can be increased by about 20%, and the light output of the device can be improved.

  In the first to third embodiments, when a carrier conducts through a multilayer structure, conduction tends to be hindered due to band discontinuity in the high refractive index layer. This problem can be reduced or eliminated by increasing the doping amount in the high refractive index layer.

  In the first to third embodiments, the thickness of the multilayer structure is larger than the spot size of light guided through the active layer (about 1 to 1.5 μm when the light wavelength is 1.5 μm). In this case, the first clad layer 5 and the second clad layer 6 may be omitted. In this case, the first and second clad layers also have a multi-layer structure.

Further, in the first to third embodiments, the refractive indexes n _c1 and n _c2 of the first cladding layer 5 and the second cladding layer 6 are used as the lower limit values, and the refractive indexes of the high refractive index layer and the low refractive index layer are set. Although described as being defined, the present invention is not limited to this. The refractive index of the semiconductor substrate or the refractive index of the semiconductor layer formed between the active layer and the semiconductor substrate may be used as the lower limit value.

  For example, in a long wave semiconductor light emitting device in which the semiconductor substrate is made of InP, since the InP substrate has the lowest refractive index in the device, if the refractive index of the low refractive index layer is set to be equal to or higher than the refractive index of the InP substrate. The effects of the present invention can be obtained. Further, in a short-wave semiconductor light emitting device in which the semiconductor substrate is made of GaAs, the active layer is made of InGaP, and the multilayer structure is made of AlGaInP, the refractive index of the low refractive index layer is higher than the refractive index of AlGaInP (which has a lower refractive index than GaAs). If set as above, the effect of the present invention can be obtained.

  Further, even in a semiconductor light emitting device having a light wavelength from about 770 nm to about 1000 nm, in which the semiconductor substrate is made of GaAs, the active layer is made of InGaAs, and the multilayer structure is made of AlGaAs or InGaAsP, the refractive index of the low refractive index layer is set. If the refractive index is set to be equal to or higher than the refractive index of AlGaAs (which has a lower refractive index than GaAs), the effect of the present invention can be obtained.

(Fourth embodiment)
Next, a semiconductor light emitting device according to a fourth embodiment of the present invention will be described with reference to FIGS.

  The same parts as those of the semiconductor light emitting element 1a shown in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  As shown in FIGS. 8 and 9, the semiconductor light emitting device 1 b of the present embodiment includes a semiconductor substrate 2, an active layer 4, a first cladding layer 5, a second cladding layer 6, a contact layer 7, In addition to the spacer layers 8 and 9, the multilayer portions 21 and 22, and the buried layers 10 a and 10 b, the spacer layers 15 and 16 and lateral multilayer structures (lateral multilayer portions) 27 and 28 are provided.

  In addition to the active layer 4, the first cladding layer 5, the second cladding layer 6, the spacer layers 8 and 9, a part of the multilayer parts 21 and 22, the spacer layers 15 and 16 and the lateral multilayer parts 27 and 28 Is formed.

  The spacer layers 15 and 16 and the horizontal multilayer portions 27 and 28 are formed on the left and right sides of the active layer 4.

Similarly to the multilayer portions 21 and 22, the horizontal multilayer portions 27 and 28 are arranged from the active layer 4 side so that the high refractive index layer and the low refractive index layer alternate, The high refractive index layer, the low refractive index layer, the high refractive index layer, and the low refractive index layer are formed in this order. The horizontal multilayer portion is formed of, for example, a dielectric film. Specifically, SiO ₂ , SiN or the like is used. The configuration of the lateral multilayer portions 27 and 28, such as the refractive index and the layer thickness, is the same as the configuration of the multilayer portions described in the first to third embodiments. However, since no current flows in the horizontal multilayer portion, it is sufficient that the low refractive index layer has a refractive index lower than that of the high refractive index layer. The refractive index of the semiconductor substrate or the active layer and the semiconductor substrate It is not necessary to constitute more than the refractive index of the semiconductor layer between. For example, in a short-wave semiconductor light emitting device in which the semiconductor substrate is GaAs, the multilayer portion may be composed of AlGaAs and the lateral multilayer portion may be composed of AlGaInP.

  When a direct current drive current is applied from the electrodes 11 and 12 on both sides to the semiconductor light emitting device 1b configured as described above, light is generated by the current flowing through the active layer 4 and is emitted in the lateral direction. The light is also refracted and reflected by the lateral multilayer portion 27 and the lateral multilayer portion 28, returns to the active layer 4, travels through the active layer 4 and the lateral multilayer portions 27, 28, and is output to the outside from the emission end face.

  Therefore, the light that has been emitted to the left and right can also be output to the outside, and the light can be output efficiently.

(All embodiments)
In the above description, the case where the spacer layer is formed in the semiconductor light emitting device has been described. However, the multilayer layer may be laminated on the active layer without forming the spacer layer. In this case, if the lateral multilayer portion is formed by crystal growth of a semiconductor, in order to avoid carrier leakage from the active layer, the lateral multilayer portion is arranged as a low refractive index layer and a high refractive index from the active layer 4 side. Layer order is desirable.

  In the above description, the case where the antireflection film 14 is formed on the end faces in the longitudinal direction of the active layer 4, the multilayer portion, the first cladding layer 5, and the second cladding layer 6 has been described. The active layer 4, the multilayer portion, the first cladding layer 5, and the second cladding layer 6 are formed so that the end face in the longitudinal direction terminates at a position away from the antireflective film 14, and the semiconductor light emitting device has a window structure You may make it have.

  In the above description, the case where the longitudinal axis of the active layer 4, the multilayer part, the first cladding layer 5 and the second cladding layer 6 is parallel to the longitudinal axis of the semiconductor light emitting device is described. However, the present invention is not limited to this case, and the active layer 4 is formed such that the longitudinal axis of the active layer, the multilayer portion, the first cladding layer, and the second cladding layer intersects the longitudinal axis of the semiconductor light emitting device. The multilayer portion, the first cladding layer 5 and the second cladding layer 6 may be formed so that the semiconductor light emitting device has a bent stripe structure.

  Further, the active layer 4, the multilayer portion, the first cladding layer 5, and the second cladding layer 6 may be formed by mesa stripe portions having a mesa shape in a plane orthogonal to the light guiding direction.

  In the first to fourth embodiments, the description has been made on the buried type semiconductor light emitting device. However, in the oxide stripe type or ridge type semiconductor light emitting device, a multilayer structure is formed above and below the active layer. Thus, the same effect can be obtained.

  As described above, in the semiconductor light emitting device according to the present invention, light generated at an angle exceeding the critical angle between the active layer and the cladding layer is also refracted and reflected by the multilayer portion of the high refractive index layer and the low refractive index layer. It is effective as a semiconductor light emitting element for increasing the output, because it has the effect that it can be advanced in the active layer and output to the outside and the output can be increased.

The perspective view of the semiconductor light-emitting device in the 1st Embodiment of this invention Front sectional drawing of the semiconductor light-emitting device in the 1st Embodiment of this invention Side surface sectional drawing of the semiconductor light-emitting device in the 1st Embodiment of this invention Side surface sectional drawing of the semiconductor light-emitting device in the 2nd Embodiment of this invention. The graph which shows the relationship between the light reflectivity by the multilayer structure of the semiconductor light-emitting device in the 2nd Embodiment of this invention, and the propagation angle of the light which propagates a waveguide Side surface sectional drawing of the semiconductor light-emitting device in the 3rd Embodiment of this invention. The graph which shows the relationship between the light reflectivity by the multilayer structure of the semiconductor light-emitting device in the 3rd Embodiment of this invention, and the propagation angle of the light which propagates a waveguide The perspective view of the semiconductor light-emitting device in the 4th Embodiment of this invention Front sectional drawing of the semiconductor light-emitting device in the 4th Embodiment of this invention A perspective view showing a conventional semiconductor light emitting device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor light-emitting device 2 Semiconductor substrate 3 Semiconductor layer 4 Active layer 5 1st cladding layer 6 2nd cladding layer 7 Contact layer 8, 9 Spacer layer 10 Buried layer 11 Upper electrode (p electrode)
12 Lower electrode (n electrode)
14 Non-reflective films 15 and 16 Spacer layers 21 and 22 Multi-layer parts 23 and 24 Multi-layer parts 23a and 23b Internal multi-layer parts 25 and 26 Multi-layer parts 27 and 28 Horizontal multi-layer part (horizontal multi-layer structure)
31, 33, 35 High refractive index layers 32, 34, 36 Low refractive index layers 41, 43, 45, 47 High refractive index layers 42, 44, 46, 48 Low refractive index layers

Claims (10)

In a semiconductor light emitting device, wherein an active layer is provided above a semiconductor substrate, and the refractive index of the semiconductor substrate or the refractive index of the semiconductor layer formed between the active layer and the semiconductor substrate is the lowest. ,
The active layer has a multilayer structure in which high refractive index layers and low refractive index layers are alternately stacked in the vertical direction,
The high refractive index layer is configured such that the refractive index is lower than the refractive index of the active layer and higher than the refractive index of the semiconductor substrate or the semiconductor layer,
The low-refractive index layer has a refractive index lower than that of the high-refractive index layer, and is configured to be greater than or equal to the refractive index of the semiconductor substrate or the semiconductor layer. The semiconductor light emitting device according to claim 1,
The multilayer structure has a plurality of pairs of the high refractive index layer and the low refractive index layer,
The stacking order from the active layer of the pair is i,
The refractive indexes of the high refractive index layer and the low refractive index layer in each pair are respectively n _hi and n _li ,
The layer thicknesses of the high refractive index layer and the low refractive index layer are respectively d _hi and d _li ,
When the optical wavelength is expressed as λ,
n _hi d _hi = n _li d _li
And d _hi > λ / 4n _hi
d _li > λ / 4n _li
A semiconductor light emitting element characterized by the above. The semiconductor light emitting device according to claim 2,
The multilayer structure is formed by laminating a plurality of internal multilayer structures in which a plurality of pairs of the high refractive index layer and the low refractive index layer are laminated,
The stacking order from the active layer of the inner multilayer structure is k,
When the layer thicknesses of the high refractive index layer and the low refractive index layer for each of the internal multilayer structures are represented as d _hk and d _lk , respectively.
d _hk ≠ d _{h (k + 1)}
d _lk ≠ d _{l (k + 1)}
The semiconductor light emitting element characterized by satisfy | filling. The semiconductor light emitting device according to claim 2,
The multilayer structure is formed by laminating a plurality of internal multilayer structures in which a plurality of pairs of the high refractive index layer and the low refractive index layer are laminated,
The stacking order from the active layer of the inner multilayer structure is k,
When the refractive indexes of the high refractive index layer and the low refractive index layer for each of the internal multilayer structures are represented as n _hk and n _lk , respectively.
n _hk ≠ n _{h (k + 1)}
n _lk ≠ n _{l (k + 1)}
The semiconductor light emitting element characterized by satisfy | filling. The semiconductor light emitting device according to claim 2,
A semiconductor light emitting element characterized in that the thickness of each pair of high refractive index layer and low refractive index layer of the multilayer structure is gradually increased or decreased from the active layer upward or downward. The semiconductor light emitting device according to claim 2,
A semiconductor light emitting element characterized by gradually increasing or decreasing the refractive index of each pair of high refractive index layer and low refractive index layer of the multilayer structure from above or below the active layer. An active layer is provided above the semiconductor substrate, and the refractive index of the semiconductor substrate or the refractive index of the semiconductor layer formed between the active layer and the semiconductor substrate has the lowest refractive index,
A substrate on which a plurality of layers including the active layer and the semiconductor layer are sequentially crystal-grown is etched in a stripe shape, and then a buried layer is formed by crystal growth on both sides of the portion left in the stripe shape of the substrate. In the formed semiconductor light emitting device,
It has a horizontal multilayer structure in which a high refractive index layer and a low refractive index layer are alternately stacked in a direction intersecting with the growth direction of the substrate between the portion left in the stripe shape of the substrate and the buried layer. And
The high refractive index layer is configured such that the refractive index is lower than the refractive index of the active layer and higher than the refractive index of the semiconductor substrate or the semiconductor layer,
The low-refractive index layer is configured to have a refractive index lower than that of the high-refractive index layer. A substrate on which a plurality of layers including the active layer and the semiconductor layer are sequentially crystal-grown is etched in a stripe shape, and then a buried layer is formed by crystal growth on both sides of the portion left in the stripe shape of the substrate. A semiconductor light emitting device according to any one of claims 1 to 6, wherein the semiconductor light emitting device is formed.
It has a horizontal multilayer structure in which a high refractive index layer and a low refractive index layer are alternately stacked in a direction intersecting with the growth direction of the substrate between the portion left in the stripe shape of the substrate and the buried layer. And
The high refractive index layer is configured such that the refractive index is lower than the refractive index of the active layer and higher than the refractive index of the semiconductor substrate or the semiconductor layer,
The low refractive index layer has a refractive index lower than the refractive index of the high refractive index. The semiconductor light emitting device according to any one of claims 7 to 8,
A semiconductor light emitting device, wherein the high refractive index layer and the low refractive index layer of the lateral multilayer structure are formed of a dielectric film. The semiconductor light emitting device according to any one of claims 1 to 6, 8, and 9,
A semiconductor light emitting device comprising a spacer layer provided between the active layer and the multilayer structure.

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