JPS6244833B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a semiconductor device for optical amplification.

Conventionally, as such a semiconductor device for optical amplification, semiconductor layers 1, 2, 3, 4 and 5 are sequentially stacked in that order as shown in FIG. and 5 have opposite conductivity types, that is, for example, semiconductor layers 1 and 4 have P type, semiconductor layers 2, 3, and 5 have N type;
2, 3, 4 and 5 are, for example, InP and InGaAsP, respectively.
InP, InGaAsP, and InP semiconductors.
Therefore, when the forbidden band widths of the semiconductor layers 1, 2, 3, 4, and 5 are respectively E _g1 , E _g2 , E _g3 , E _g4 , and E _g5 , as shown in the energy level diagram of FIG. 2, E _g1 >E _g2 ...(1) E _g3 >E _g2 ...(2) E _g5 >E _g4 ...(3) The relationship is such that at least the opposing end surfaces of the semiconductor layer 2 are Fabry-Perot reflective surfaces. 6 and 7
A photodetecting section 8 having an amplification function of an NPN type phototransistor configuration using the semiconductor layers 3, 4 and 5 as a collector layer, a base layer and an emitter layer, respectively, also has a semiconductor layer. 1,2
and 3 constitute a light emitting section 9 of a PN junction type laser diode structure in which these are a confinement layer, an active layer, and a confinement layer, respectively. A configuration has been proposed in which electrodes 10 and 11 are attached on the surface and on the surface of the semiconductor layer 5 opposite to the semiconductor layer 4 side, respectively.

According to the configuration of such a semiconductor device for optical amplification,
In a state where a bias power source 12 with the electrode 10 side being positive is connected between the electrodes 10 and 11 through a load 13, the photodetector section 8 (phototransistor configuration)
If input light L1 that reaches the semiconductor layer 4 (base layer seen from the phototransistor configuration) is made incident on the semiconductor layer 4,
When the input light L1 is absorbed in the semiconductor layer 4 (base layer), the semiconductor layer 4 (base layer)
Electron-hole pairs are generated within the semiconductor layers 3 and 5 (collector layer and emitter layer in the phototransistor configuration) as minority carriers.
Although the holes diffuse toward the semiconductor layer 4 (base layer)
Since the input light L1 is applied, holes are injected into the semiconductor layer 4 (base layer), and the potential of the semiconductor layer 4 (base layer) increases, and the semiconductor layer 4 increases by this amount. The PN junction between the semiconductor layer 5 and 5 is more forward biased, thus
From the amount of holes assumed to be injected into the semiconductor layer 4 (base layer) described above from the (emitter layer) side to the semiconductor layer 4 (base layer) and semiconductor layer 3 (collector layer) sides, An increased amount of electrons are injected, and the electrons pass through the semiconductor layer 3 (the confinement layer in the laser diode configuration, which also serves as the collector layer in the phototransistor configuration) to the semiconductor layer 2 (the confinement layer in the laser diode configuration). active layer),
Therefore, the potential of semiconductor layer 2 (active layer) drops, and the PN junction between semiconductor layer 1 (confined layer of laser diode configuration) and semiconductor layer 2 (active layer) is biased more forward. Holes are injected from the semiconductor layer 1 (confined layer) into the semiconductor layer 2 (active layer), and recombination of electrons and holes occurs within the semiconductor layer 2 (active layer), resulting in light emission. is confined within the semiconductor layer 2 (active layer) due to the presence of the semiconductor layers 1 and 3 (both confinement layers) and propagates toward the Fabry-Perot reflective surfaces 6 and 7. 7 is repeatedly reflected, and eventually laser oscillation is obtained in the light emitting section 9 (laser diode) based on the input light L1, and the laser light is output as output light L2 from the semiconductor layer 2 (active laser diode) of the light emitting section 9 (laser diode). layer) to the outside from the side surface of the layer. In this case, holes injected into the semiconductor layer 2 (active layer of a laser diode configuration) from the semiconductor layer 1 (confined layer) side have a larger forbidden band width E than that of the semiconductor layer 2 (active layer). Due to the presence of the semiconductor layer 3 (confinement layer in the laser diode configuration, collector layer in the phototransistor configuration), the semiconductor layer ₄
It is not substantially implanted into the (base layer of phototransistor configuration) side.

Therefore, according to the conventional optical amplification semiconductor device described above in FIG. 1, when input light L1 is given,
The relationship between the voltage of the bias power supply 12 and the current flowing through the load 13 can be obtained using voltage-current characteristics similar to the collector voltage-current characteristics of the phototransistor, with the brightness (lux) of the input light L1 as a parameter, and Output light L based on input light L1
2 is obtained according to the brightness of the input light L1.

According to the conventional optical amplification semiconductor device described above in FIG. 1, it is possible to obtain an analog gas optical amplification function.

Furthermore, in the case of the conventional semiconductor device for optical amplification described above in _FIG . layer) that E _g4
, the semiconductor layer 5 of the input light L1
(emitter layer) while avoiding absorption in the semiconductor layer 4.
The absorption of the input light L1 in the base layer can be increased, and the above-mentioned analog optical amplification function can be obtained with a higher degree of optical amplification.

Furthermore, in the case of the conventional semiconductor device for optical amplification described above in _FIG . Since E _g2 is larger than that of the semiconductor layer 2 (active layer), a high luminous efficiency can be obtained in the semiconductor layer 2 (active layer), and the above-mentioned analog gas optical amplification function can be obtained with a larger amplification degree. This is something that can be done.

Furthermore, in the case of the conventional semiconductor device for optical amplification described above in _FIG . By making the semiconductor layer 2 (active layer) of the diode structure different from that of the semiconductor _{layer 2} (active layer), the output light L2 can be obtained as having a wavelength different from that of the input light L1, and thus has a wavelength conversion function. This makes it possible to obtain an analog optical amplification function.

However, in the case of the conventional semiconductor device for optical amplification described above in FIG. When the brightness of the input light L1 decreases, the current based on the input light L1 flowing in the semiconductor layer 3 ((collector layer seen from the phototransistor configuration) of the photodetector 8, that is, the input light L1 of the photodetector 8 decreases accordingly. The output current (collector current seen in the phototransistor configuration) based on this becomes small, and the light emitting part 9
If the current flowing through the laser diode (laser diode configuration) becomes small and the current flowing through the light emitting section 9 becomes smaller than a certain value (this is called a threshold current), the light emitting section 9
However, in this case, the current flowing through the light emitting section 9 is transferred to the photodetecting section 8.
Since the output current is only based on the input light L1 of
The threshold current for laser oscillation is relatively large.

Therefore, in the case of the conventional semiconductor device for optical amplification described above in FIG. The minimum value of the brightness is relatively large, and therefore the analog optical amplification function cannot be obtained within a range where the brightness of the input light L1 is below a certain value, and this range is large, which poses a problem in practicality. It had the disadvantage of being

Therefore, the present invention aims to propose a novel semiconductor device for optical amplification which is based on the conventional semiconductor device for optical amplification shown in FIG. It will become clearer.

FIG. 3 shows a first embodiment of a semiconductor device for optical amplification according to the first invention of the present application, and corresponding parts to those in FIG. Semiconductor layer 5 (emitter layer of phototransistor configuration) that constitutes the photodetector section 8 in the configuration
A semiconductor layer 31 having a conductivity type opposite to that of the semiconductor layer 5, that is, a P type, is provided within the semiconductor layer 5 and connected to the semiconductor layer 5 by being formed from the side opposite to the semiconductor layer 4 side. , and the semiconductor layers 5 and 3
1 constitutes a bias light emitting section 32 that generates bias light for the photodetecting section 8 having a PN junction type light emitting diode configuration, and an electrode 33 is attached to the semiconductor layer 31. It has the same configuration as the case shown in the figure. In this case, as shown in the energy level diagram of FIG. 4, which corresponds to the energy level diagram of FIG. 2, when the forbidden band width of the semiconductor layer 31 is E _g31 , E _g31 = E _g5 ...(4) They have the following relationship.

The above is the configuration of the first embodiment of the semiconductor device for optical amplification according to the first invention of the present application. According to this configuration, it is the same as the case of FIG. On the other hand, the bias light emitting section 32 (PN junction type light emitting diode structure) is arranged on the side opposite to the light emitting section 9 (laser diode structure) when viewed from the photodetecting section 8 (phototransistor structure). , since the semiconductor layer 5 also serves as the semiconductor layer 5 constituting the photodetector section 8, and the forbidden band width E _g31 of the semiconductor device 31 is the same as the forbidden band width E _g5 of the semiconductor layer 5, The input light L1 is
As shown in the figure, the bias light can be made to enter the photodetecting section 8 from the outside on the side of the bias light emitting section 32 through this. Electrode 10 between 10 and 11
In a state where the bias power supply 12 whose side is positive is connected through the load 13, the input light L1 that reaches the semiconductor layer 4 (the best layer when viewed from the phototransistor structure) is made incident on the photodetector section 8 (phototransistor structure). In this case, as in the case of the optical amplification semiconductor device described above in FIG. The output light L2 based on the input light L1 can be obtained with voltage-current characteristics similar to the characteristics, and the output light L2 based on the input light L1 can be obtained in accordance with the brightness of the input light L1. As in the case of a semiconductor device for optical amplification, an analog gas optical amplification function can be obtained, and the optical amplification function is achieved when the forbidden band width E _g5 of the semiconductor layer 5 constituting the photodetecting section 8 is the same as that of the semiconductor layer 4. Since it is larger than E _g4 , it has a large optical amplification degree, and the forbidden band width E _g1 of the semiconductor layer 1 constituting the light emitting section 9 is larger than that of the semiconductor layer 2 E _g2 . Therefore, high luminous efficiency can be obtained, and by making the forbidden band width E _g4 of the semiconductor layer 4 constituting the photodetecting section ₈ different from that of the semiconductor layer 2 constituting the light emitting section 9, It has features such as an optical amplification function accompanied by a wavelength conversion function.

In addition, in the case of the optical amplification semiconductor device according to the first invention of the present application, which is shown in FIG. If the brightness of the input light L1 that reaches 4 is made to enter, then
Accordingly, the output current based on the input light L1 of the photodetector 8 and the current flowing through the light emitting section 9 become small.If the current flowing through the light emitting section 9 becomes smaller than the threshold current, the light emitting section 9 This makes it impossible to obtain laser oscillation at .

However, in the case of the semiconductor device for optical amplification according to the first invention of the present application described above in FIG. Light emission is obtained, and the light enters the photodetector 8 as bias light LB, reaches the semiconductor layer 4,
Therefore, the output current of the photodetector 8 is the bias light LB.
By superimposing the current based on the input light L1 on the bias current based on the input light L1, a bias current based on the bias light LB is obtained in addition to the current based on the input light L1. The output current is obtained as being larger by the bias current based on the bias light LB than in the case of the conventional semiconductor device for optical amplification described above in FIG. The threshold current for laser oscillation, which would otherwise be impossible to obtain, is smaller than that in the case of the optical amplification semiconductor device shown in FIG.

For this reason, in the case of the semiconductor device for optical amplification according to the first invention of the present application described above in FIG. The minimum value of the brightness of the input light L1 is smaller than that of the conventional optical amplification semiconductor device described above in FIG. Even if it cannot be obtained within the range below this value, the major feature is that the range is smaller than that of the conventional optical amplification semiconductor device shown in FIG. It is something that you have.

Next, a second embodiment of the semiconductor device for optical amplification according to the first invention of the present application will be described with reference to FIG. 5. Parts corresponding to those in FIG. Although this is omitted, in the configuration described above in FIG. A semiconductor layer portion 3a made of the same InGaAsP semiconductor as the semiconductor layer 4, for example, on the side of the semiconductor layer 4 that constitutes it, and a semiconductor layer 1, for example, on the side of the semiconductor layer 2 that constitutes the light emitting section 9.
As shown in the energy level diagram of FIG. 6, which corresponds to the energy level diagram of FIG. 4, it has a larger forbidden band width E _g3b (E _g3b
It has the same structure as the case of FIG. 3, except that it consists of a semiconductor layer portion 3b having a diameter of >E _g2 ).

The above is the configuration of the second embodiment of the semiconductor device for optical amplification according to the first invention of the present application. According to this configuration, it is the same as the case of FIG. On the other hand, even if the semiconductor layer 3 consists of a semiconductor layer section 3a on the semiconductor layer 4 side and a semiconductor layer section 3b on the semiconductor layer 2 side, the semiconductor layer section 3b on the semiconductor layer 2 side is connected to the semiconductor layer 2. Since it has a relatively large prohibited band width, a detailed explanation thereof will be omitted, but it has the same excellent characteristics as the first embodiment of the first invention of the present application described above in FIG. It is. However, in this example, due to the presence of the semiconductor layer portion 3a on the semiconductor layer 4 side that constitutes the semiconductor layer 3,
The breakdown voltage between the semiconductor layer 4 constituting the photodetecting section 8 and the semiconductor layer 2 constituting the light emitting section 9 is higher than that in the embodiment described above in FIG. This is characterized in that the withstand voltage seen between the two is larger than that of the embodiment described above in FIG.

Next, a first embodiment of a semiconductor device for optical amplification according to the second invention of the present application will be described with reference to FIG. 7. Parts corresponding to those in FIG. Although omitted, in the configuration described above in FIG.
A semiconductor layer 71 having the same conductivity type as the semiconductor layer 5, that is, the N type, is connected to the semiconductor layer 5 in such a manner that it can be inserted between the emitter layer (of a phototransistor configuration) and the electrode 11. A semiconductor layer 72 having a conductivity type opposite to that of the semiconductor layer 71, that is, P type, is formed in the layer 71 from the side opposite to the semiconductor layer 5 side and is connected to the semiconductor layer 71. In this case, if the semiconductor layers 71 and 72 are made of, for example, an InGaAsP-based semiconductor, and the forbidden band widths of the semiconductor layers 71 and 72 are E _g71 and E _g72 , respectively, the energy level diagram in FIG. As shown in the corresponding energy level diagram of Fig. 8, there is the following relationship: E _g4 <E _g71 <E _g5 ...(5) E _g4 <E _g72 <E _g5 ...(6) The layers 71 and 72 constitute a bias light emitting section 73 that generates bias light for the photodetecting section 8 having a PN junction type light emitting diode structure, and an electrode 74 is formed on the semiconductor layer 72.
It has the same configuration as the case of FIG. 1 except that it is appended with .

The above is the configuration of the first embodiment of the semiconductor device for optical amplification according to the second invention of the present application. According to this configuration, it has the same configuration as the case of FIG. 1 except for the matters mentioned above. On the other hand, the bias light emitting section 73 (PN junction type light emitting diode configuration) is configured on the side opposite to the light emitting section 9 (laser diode configuration) when viewed from the photodetecting section 8 (phototransistor configuration). The semiconductor layers 71 and 72 forming the photodetector have bandgap widths E _g71 and E _g72 that are larger than the bandgap widths E _g4 and E _g5 of the semiconductor layers 4 and 5 forming the photodetecting section 8, respectively. As shown in FIG. 8, the input light L1 can be made to enter the photodetector section 8 from outside on the side of the bias light emitting section 73 through this, and thus, as shown in FIG. As in the case of the semiconductor device for optical amplification, the electrodes 10 and 1
1, a bias power source 12 with the electrode 10 side positive
is connected through the load 13, the semiconductor layer 4 is connected to the photodetector 8 (phototransistor configuration).
When the input light L1 that reaches the base layer (as viewed from the phototransistor configuration) is incident, the relationship between the voltage of the bias power supply 12 and the current flowing through the load 13 is similar to that of the semiconductor device for optical amplification described above in FIG. is obtained with a voltage-current characteristic similar to the collector voltage-current characteristic of a phototransistor with the brightness of the input light L1 as a parameter, and the output light L2 based on the input light L1 depends on the brightness of the input light L1. As a result, it is possible to obtain an analog optical amplification function as in the case of the conventional optical amplification semiconductor device described above in FIG. Since the forbidden band width E _g5 of the semiconductor layer 5 constituting the semiconductor layer 5 is larger than that E _g4 of the semiconductor layer 4, the forbidden band width of the semiconductor layer 1 constituting the light emitting section 9 can be increased with a large optical amplification factor. Since E _g1 is larger than E _g2 of the semiconductor layer 2, high luminous efficiency can be obtained, and furthermore, the forbidden band width E _g4 of the semiconductor layer 4 constituting the photodetecting section 8 and the light emitting section 9 can be By making E _g2 of the semiconductor layer 2 different from that of the semiconductor layer 2 constituting the optical waveguide, an optical amplification function can be obtained along with a wavelength conversion function.

Further, in the case of the optical amplification semiconductor device according to the second invention of the present application described above in FIG. If the brightness of the input light L1 that reaches 4 is made to enter, then
Accordingly, the output current based on the input light L1 of the photodetector 8 and the current flowing through the light emitting section 9 become small.If the current flowing through the light emitting section 9 becomes smaller than the threshold current, the light emitting section 9 This makes it impossible to obtain laser oscillation at .

However, in the case of the semiconductor device for optical amplification according to the second invention of the present application described above in FIG. Light emission is obtained at 73, and the light enters the photodetector section 8 as bias light LB, reaches the semiconductor layer 4,
Therefore, the output current of the photodetector 8 is the bias light LB.
By superimposing the current based on the input light L1 on the bias current based on the input light L1, a bias current based on the bias light LB is obtained in addition to the current based on the input light L1. The output current is obtained as being larger by the bias current based on the bias light LB than in the case of the conventional semiconductor device for optical amplification described above in FIG. The threshold current for laser oscillation, which would otherwise be impossible to obtain, is smaller than that in the case of the optical amplification semiconductor device shown in FIG.

For this reason, in the case of the semiconductor device for optical amplification according to the second invention of the present application described above in FIG. The minimum value of the brightness of the input light L1 is smaller than that of the conventional optical amplification semiconductor device described above in FIG. Even if it cannot be obtained within the range below this value, the major feature is that the range is smaller than that of the conventional optical amplification semiconductor device shown in FIG. It is something that you have.

Further _, in the case of the semiconductor device for optical amplification according to the second invention of the present application described above in _FIG . Since it is smaller than the forbidden band width E _g5 of the semiconductor device 5 on the side of the bias light emitting section 73 that constitutes the bias light emitting section 73, the bias light LB obtained from the bias light emitting section 73 unnecessarily constitutes the photodetecting section 8. The bias light reaches the semiconductor layer 4 without being absorbed by the semiconductor layer 5, and the bias light is transmitted to the photodetector 8.
This device has the great feature that it is possible to efficiently obtain the bias current based on LB, and therefore, the above-mentioned excellent features can be obtained efficiently as a whole.

Next, a second embodiment of a semiconductor device for optical amplification according to the second invention of the present application will be described with reference to FIG. 9. Parts corresponding to those in FIG. Although omitted, in the configuration described above in FIG. A semiconductor layer portion 3a made of the same InGaAsP semiconductor as the semiconductor layer 4, for example, on the side of the semiconductor layer 4 that constitutes it, and a semiconductor layer 1, for example, on the side of the semiconductor layer 2 that constitutes the light emitting section 9.
As shown in the energy level diagram of FIG. 10, which corresponds to the energy level diagram of FIG. 4, it has a larger forbidden band width E _g3b (E _g3
It has the same structure as the case of FIG. 7, except that it consists of a semiconductor layer portion 3b having a relationship ( _b >E _{g2 )} .

The above is the configuration of the second embodiment of the semiconductor device for optical amplification according to the second invention of the present application. According to this configuration, it is the same as the case of FIG. On the other hand, even if the semiconductor layer 3 consists of a semiconductor layer section 3a on the semiconductor layer 4 side and a semiconductor layer section 3b on the semiconductor layer 2 side, the semiconductor layer section 3b on the semiconductor layer 2 side is connected to the semiconductor layer 2. Since it has a relatively large prohibited band width, a detailed explanation thereof will be omitted, but it has the same excellent features as the first embodiment of the second invention of the present application described above in FIG. It is. However, in this example, due to the presence of the semiconductor layer portion 3a on the semiconductor layer 4 side that constitutes the semiconductor layer 3,
The breakdown voltage between the semiconductor layer 4 constituting the photodetecting section 8 and the semiconductor layer 2 constituting the light emitting section 9 is higher than that in the embodiment described above in FIG. This is characterized in that the breakdown voltage seen between the two is larger than that of the embodiment described above with reference to FIG.

In the above, only a few embodiments have been described for each of the first and second inventions of the present application, and for example, the configurations described above in FIGS. 3, 5, 7, and 9. In this case, the semiconductor layer 5 is made up of a semiconductor layer portion on the semiconductor layer 4 side and a semiconductor layer portion on the opposite side from the semiconductor layer 4 side, and the former semiconductor layer portion is made to be the latter semiconductor layer portion. The impurity concentration is relatively small, so that the impurity concentration between the semiconductor layers 5 and 4 is
PN junction capacitance (emitter-base junction capacitance in phototransistor configuration) is shown in Figures 3, 5, and 7.
The optical amplification response function is made smaller than that in the cases shown in FIGS. Also, in the above, P type can be read as N type, and N type can be read as P type (however, the semiconductor layer 2 can be either P type or N type), Various other modifications may be made without departing from the spirit of the invention.

Furthermore, in the above, although no particular description was given regarding the manufacturing method of the structure of the embodiment of the present invention shown in FIG. 3, FIG. 5, FIG. 7, and FIG. 9, the structure of the embodiment of the present invention is , the semiconductor layer 5 is used as a semiconductor substrate, and the semiconductor layers 4, 3, 2, and 1 are sequentially laminated in that order on one surface thereof, and in the case of FIGS. 3 and 5, the semiconductor layer 5 is formed in the semiconductor substrate. The semiconductor layer 31 is formed from the side opposite to the layer 4-1 side, and in the case of FIGS. 7 and 9, the semiconductor layer 71 is formed on the side of the semiconductor substrate opposite to the semiconductor layer 4-1 side. This can be obtained by using a manufacturing method in which a semiconductor layer 72 is formed within the semiconductor layer 71 after the semiconductor layer 71 is formed.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing a conventional optical amplification semiconductor device, and FIG. 2 is a diagram showing its energy level.
FIG. 3 is a schematic cross-sectional view showing the first embodiment of the semiconductor device for optical amplification according to the first invention of the present application;
5 is a schematic cross-sectional view showing a second embodiment of the semiconductor device for optical amplification according to the first invention of the present application, and FIG. 6 is a diagram showing its energy level. 7 is a schematic cross-sectional view showing the first embodiment of the semiconductor device for optical amplification according to the second invention of the present application, FIG. 8 is a diagram showing its energy level, and FIG. A schematic cross-sectional view showing a second embodiment of a semiconductor device for optical amplification according to the second invention,
FIG. 10 is a diagram showing the energy levels. 1, 2, 3, 4, 5, 31, 71 and 72 in the figure
is a semiconductor layer, 8 is a photodetection section, 9 is a light emitting section, 10,
11, 33 and 74 are electrodes, 32 and 73 are bias light emitting parts, and 3a and 3b are semiconductor layer parts, respectively.

Claims (1)

[Scope of Claims] 1. First, second, third, fourth and fifth semiconductor layers are sequentially stacked in that order, and the first and fourth semiconductor layers are stacked in that order.
and the second, third, and fifth semiconductor layers have opposite conductivity types, and the third semiconductor layer is at least on the second semiconductor layer side.
The photodetecting section has a bandgap larger than that of the semiconductor layer and has an amplification function using the third, fourth, and fifth semiconductor layers. In a semiconductor device for optical amplification in which a light-emitting portion is constructed of layers, a sixth semiconductor layer having a conductivity type opposite to that of the fifth semiconductor layer is connected to the fifth semiconductor layer. A semiconductor device for optical amplification, characterized in that the fifth and sixth semiconductor layers constitute a bias light emitting section that generates bias light for the photodetecting section. 2. First, second, third, fourth and fifth semiconductor layers are sequentially stacked in that order, and the first and fourth semiconductor layers are stacked in that order.
and the second, third, and fifth semiconductor layers have opposite conductivity types, and the third semiconductor layer is at least on the second semiconductor layer side.
The photodetecting section has a bandgap larger than that of the semiconductor layer and has an amplification function using the third, fourth, and fifth semiconductor layers. In a semiconductor device for optical amplification in which a light-emitting portion is configured of layers, a sixth semiconductor layer connected to the fifth semiconductor layer and having the same conductivity type as the fifth semiconductor layer; connectable to the sixth semiconductor layer;
a seventh semiconductor layer having a conductivity type opposite to that of the sixth semiconductor layer;
A semiconductor device for optical amplification, characterized in that the sixth and seventh semiconductor layers constitute a bias light emitting section that generates bias light for the photodetecting section. 3. The semiconductor device for optical amplification according to claim 2, characterized in that the sixth and seventh semiconductor layers have a smaller forbidden band width than the fifth semiconductor layer. A semiconductor device for optical amplification.