Semiconductor laser device

Abstract

To obtain a semiconductor laser device that can monitor the state of a semiconductor laser with a simple configuration.SOLUTION: A semiconductor laser device according to the present disclosure includes a semiconductor substrate having a light emitting layer, a light absorption layer provided on the semiconductor substrate and generating heat by absorbing light emitted by the light emitting layer, a first metal layer provided on the light absorption layer, and a second metal layer provided on the first metal layer and of a different type from the first metal layer.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a semiconductor laser device.

Background Art

[0002] [[ID=十二]] Patent Document 1 discloses a semiconductor laser in which a photodiode section for monitoring optical output is integrated. This semiconductor laser includes a DFB (Distributed Feedback) section, a DBR (Distributed Bragg Reflector) section, and a PD (Photo Diode) section. The DFB section has a back-side first cladding layer, a first diffraction grating layer, a light-emitting layer, a front-side first cladding layer, and a first contact layer laminated thereon. The light-emitting layer has a first MQW structure and emits laser light.

[0003] The DBR section has a back-side second cladding layer, a second diffraction grating layer, a first core layer, and a front-side second cladding layer laminated thereon. The back-side second cladding layer has a higher resistivity than the back-side first cladding layer. The second diffraction grating layer reflects a part of the laser light to the DFB section. The first core layer guides the remaining part of the laser light and has a second MQW structure with an effective bandgap energy smaller than that of the first MQW structure. The front-side second cladding layer has a higher resistivity than the front-side first cladding layer. The PD section has a back-side third cladding layer, a second core layer having a second MQW structure that absorbs the remaining part of the laser light guided by the first core layer, a front-side third cladding layer, and a second contact layer laminated thereon.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the semiconductor laser described in Patent Document 1, a photodiode is integrated into the semiconductor laser to monitor the optical output. This may complicate the structure of the semiconductor laser.

[0006] This disclosure was made to solve the above-mentioned problems and aims to provide a semiconductor laser device that can monitor the state of a semiconductor laser with a simple configuration. [Means for solving the problem]

[0007] The semiconductor laser apparatus according to the first disclosure includes a semiconductor substrate having an emissive layer, a light-absorbing layer provided on the semiconductor substrate above the emissive layer and absorbing light emitted by the emissive layer to generate heat, a first metal layer provided on the light-absorbing layer, and a second metal layer of a different type from the first metal layer provided on the first metal layer. A monitoring unit that monitors the light output of the light-emitting layer based on the electrical signal between the first metal layer and the second metal layer due to the Seebeck effect, It is equipped with.

[0008] The semiconductor laser device according to the second disclosure comprises a semiconductor substrate having an emissive layer, a light-absorbing layer provided on the semiconductor substrate and absorbing light emitted by the emissive layer to generate heat, and a first thermistor layer provided on the light-absorbing layer. A monitoring unit that monitors the light output of the light-emitting layer based on the resistance value of the first thermistor layer, It is equipped with. [Effects of the Invention]

[0010] In the semiconductor laser device described in the first disclosure, the light emitted by the light-emitting layer is converted into heat by the light-absorbing layer. As a result, the optical output of the light-emitting layer can be monitored based on the electrical signal generated between the first metal layer and the second metal layer due to the heat generated by the light-absorbing layer. Therefore, the optical output of the semiconductor laser device can be monitored with a simple configuration. In the semiconductor laser device described in the second disclosure, the light emitted by the light-emitting layer is converted into heat by the light-absorbing layer. This allows the light output of the light-emitting layer to be monitored based on the resistance value of the first thermistor layer corresponding to the heat generated by the light-absorbing layer. Therefore, the light output of the semiconductor laser device can be monitored with a simple configuration. In the semiconductor laser device described in the third disclosure, the temperature of the semiconductor substrate can be monitored based on the electrical signal generated between the first metal layer and the second metal layer due to the Seebeck effect. Therefore, the temperature of the semiconductor laser device can be monitored with a simple configuration. [Brief explanation of the drawing]

[0011] [Figure 1] This is a plan view of a laser chip according to Embodiment 1. [Figure 2] This is a cross-sectional view obtained by cutting Figure 1 along the line I-II. [Figure 3] This is a cross-sectional view obtained by cutting Figure 1 along the line III-IV. [Figure 4] This figure shows a semiconductor laser apparatus according to a comparative example of Embodiment 1. [Figure 5] This is a plan view of the laser chip according to Embodiment 2. [Figure 6] This is a cross-sectional view obtained by cutting along the line I-II in Figure 5. [Figure 7] This is a cross-sectional view obtained by cutting along the line III-IV in Figure 5. [Figure 8] This is a plan view of a laser chip according to Embodiment 3. [Figure 9] This is a cross-sectional view obtained by cutting along the line I-II in Figure 9. [Figure 10] This is a cross-sectional view obtained by cutting along the line III-IV in Figure 9. [Figure 11] This figure shows a semiconductor laser apparatus according to a comparative example of Embodiment 3. [Modes for carrying out the invention]

[0012] The semiconductor laser apparatus according to each embodiment will be described with reference to the drawings. The same or corresponding components are denoted by the same reference numerals, and repetition of the description may be omitted.

[0013] Embodiment 1. FIG. 1 is a plan view of a laser chip 15 according to Embodiment 1. A monitor unit 50 is connected to the laser chip 15. The laser chip 15 and the monitor unit 50 constitute a semiconductor laser device 100. FIG. 2 is a cross-sectional view obtained by cutting FIG. 1 along the straight line I-II. FIG. 3 is a cross-sectional view obtained by cutting FIG. 1 along the straight line III-IV. Note that the monitor unit 50 is omitted in FIGS. 2 and 3. In the laser chip 15, the semiconductor substrate 10 has a light-emitting layer 12.

[0014] As shown in FIG. 2, a light absorption layer 20 is provided on the semiconductor substrate 10. The light absorption layer 20 is provided on a part of the upper surface of the light-emitting layer 12. The light absorption layer 20 absorbs the light emitted by the light-emitting layer 12 and generates heat. The light absorption layer 20 is, for example, an insulating thin film. The light absorption layer 20 is preferably a porous material with a band gap narrower than that of the laser chip 15. For example, when the laser chip 15 is a laser in the 1310 nm and 1550 nm bands for optical communication, porous Si having a band gap of 1.12 eV can be used. Not limited to this, the light absorption layer 20 only needs to have the property of converting light into heat.

[0015] A thermocouple layer is provided on the light absorption layer 20. The thermocouple layer includes a first metal layer 21 provided on the light absorption layer 20 and a second metal layer 22 provided on the first metal layer 21 and different from the first metal layer 21 in type. The first metal layer 21 is, for example, Pt, and the second metal layer 22 is, for example, Pt rhodium.

[0016] As shown in FIG. 3, an insulating layer 14 is provided on the upper surface of the semiconductor substrate 10, that is, on the part of the upper surface of the light-emitting layer 12 that is exposed from the light absorption layer 20. On the insulating layer 14, a third metal layer 23 of the same type as the first metal layer 21 and a fourth metal layer 24 provided on the third metal layer 23 and of the same type as the second metal layer 22 are provided.

[0017] On the upper surface of the semiconductor substrate 10, an electrode 30 of the laser chip 15 is provided. On the back surface of the semiconductor substrate 10 opposite to the upper surface, electrodes of the laser chip 15 not shown are also provided. Electrodes 26a and 26b are provided on the first metal layer 21 and the second metal layer 22, respectively. Electrodes 28a and 28b are provided on the third metal layer 23 and the fourth metal layer 24, respectively.

[0018] As shown in FIG. 1, the monitor unit 50 is electrically connected to the electrodes 26a, 26b, 28a, and 28b. The light absorption layer 20 converts the light emitted by the light emitting layer 12 into heat and generates heat. At this time, due to the Seebeck effect, an electrical signal is generated between the first metal layer 21 and the second metal layer 22. The monitor unit 50 detects this electrical signal as a voltage and can monitor the light output of the light emitting layer 12 based on the electrical signal. The electrical signal obtained in the thermocouple layer and the light output of the laser chip 15 are approximately in a proportional relationship, and as the light output increases, the voltage detected by the monitor unit 50 also increases. The monitor unit 50 is a light output control circuit that controls the light output of the laser chip 15 according to the detected light output. As the monitor unit 50, for example, a general driver IC can be used.

[0019] Specifically, the monitor unit 50 monitors the light output of the light emitting layer 12 based on the difference between the first electrical signal between the first metal layer 21 and the second metal layer 22 due to the Seebeck effect and the second electrical signal between the third metal layer 23 and the fourth metal layer 24 due to the Seebeck effect. By subtracting the second electrical signal obtained from the third metal layer 23 and the fourth metal layer 24 provided in the region without the light absorption layer 20 from the first electrical signal, the influence of heat unrelated to the light output of the light emitting layer 12 can be eliminated.

[0020] Figure 4 shows a semiconductor laser apparatus according to a comparative example of Embodiment 1. In the semiconductor laser apparatus according to the comparative example, a portion of the front light 91 emitted by the laser chip 80 becomes laser light 93. A portion of the front light 91 separated by the splitter 81 is incident on the photodiode 82. Also, the back light 92 emitted by the laser chip 80 is incident on the photodiode 83. The light detected by the photodiodes 82 and 83 is converted into an electrical signal, and the optical output can be controlled based on this electrical signal. However, the semiconductor laser apparatus according to the comparative example requires photodiodes 82 and 83 and a splitter 81, which results in a large number of components.

[0021] In contrast, the semiconductor laser device 100 according to this embodiment uses a light absorption layer 20 and a thermocouple layer, allowing the optical output of the semiconductor laser device 100 to be monitored with a simple configuration. Furthermore, the light absorption layer 20 and the thermocouple layer are integrated into the laser chip 15. As a result, the number of components such as photodiodes and splitters can be reduced, and the assembly process can be reduced. Consequently, manufacturing costs can be reduced.

[0022] The monitoring unit may detect the temperature of the semiconductor substrate 10 based on a first electrical signal between the first metal layer 21 and the second metal layer 22, or a second electrical signal between the third metal layer 23 and the fourth metal layer 24. This allows for the acquisition of the precise temperature of the laser body simultaneously with the optical output.

[0023] The light-absorbing layer 20 can be placed at any location near the light-emitting region of the laser chip 15. Furthermore, if it is not necessary to eliminate the effects of heat unrelated to the light output of the light-emitting layer 12, it is not necessary to take the difference between the first electrical signal and the second electrical signal. In other words, the monitoring unit 50 only needs to monitor the light output of the light-emitting layer 12 based on the electrical signal between the first metal layer 21 and the second metal layer 22 due to the Seebeck effect.

[0024] These modifications can be appropriately applied to the semiconductor laser apparatus according to the following embodiments. Since the semiconductor laser apparatus according to the following embodiments has many similarities with Embodiment 1, the explanation will focus on the differences from Embodiment 1.

[0025] Embodiment 2. Figure 5 is a plan view of the laser chip 215 according to Embodiment 2. The laser chip 215 and the monitor unit 250 constitute the semiconductor laser device 200. Figure 6 is a cross-sectional view obtained by cutting Figure 5 along the line I-II. Figure 7 is a cross-sectional view obtained by cutting Figure 5 along the line III-IV. Note that the monitor unit 250 is omitted in Figures 6 and 7. In the laser chip 215, the semiconductor substrate 10 has an emissive layer 12. A light-absorbing layer 20 is provided on the semiconductor substrate 10. The light-absorbing layer 20 is the same as the light-absorbing layer 20 in Embodiment 1.

[0026] As shown in Figure 6, a first thermistor layer 240 is provided on the light-absorbing layer 20. The first thermistor layer 240 is composed of, for example, two metal layers 241 and 242. Metal layer 241 is, for example, Co, and metal layer 242 is, for example, Mn. As shown in Figure 7, an insulating layer 14 is provided on the upper surface of the semiconductor substrate 10, in the portion exposed from the light-absorbing layer 20. A second thermistor layer 243 is provided on the insulating layer 14. The second thermistor layer 243 is composed of, for example, two metal layers 244 and 245. Metal layer 244 is, for example, Co, and metal layer 245 is, for example, Mn.

[0027] An electrode 30 of the laser chip 215 is provided on the upper surface of the semiconductor substrate 10. An electrode of the laser chip 215 (not shown) is also provided on the back surface of the semiconductor substrate 10, opposite to the upper surface. Electrodes 26a and 26b are provided on metal layer 241 and metal layer 242, respectively. Electrodes 28a and 28b are provided on metal layer 244 and metal layer 245, respectively.

[0028] As shown in Figure 5, the monitor unit 50 is electrically connected to electrodes 26a, 26b, 28a, and 28b. The light absorption layer 20 generates heat by converting the light emitted by the light-emitting layer 12 into heat. At this time, the resistance value of the first thermistor layer 240 changes. The monitor unit 250 can monitor the light output of the light-emitting layer 12 based on the resistance value of the first thermistor layer. The resistance value of the first thermistor layer and the light output of the laser chip 215 are roughly inversely proportional, and the resistance value decreases as the light output increases. The monitor unit 250 is an optical output control circuit that controls the light output of the laser chip 215 according to the detected light output. For example, a general-purpose driver IC can be used as the monitor unit 250.

[0029] Specifically, the monitoring unit 50 monitors the light output of the light-emitting layer 12 based on the difference between the resistance value of the first thermistor layer 240 and the resistance value of the second thermistor layer 243. By subtracting the resistance value of the second thermistor layer 243, which is located in a region without the light-absorbing layer 20, from the resistance value of the first thermistor layer 240, the influence of heat unrelated to the light output of the light-emitting layer 12 can be eliminated.

[0030] In the semiconductor laser device 200 according to this embodiment, the optical output of the semiconductor laser device 200 can be monitored with a simple configuration by using an optical absorption layer 20 and a thermistor layer. Furthermore, the optical absorption layer 20 and the thermistor layer are integrated into the laser chip 215. As a result, the number of components such as photodiodes and splitters can be reduced, and the assembly process can be reduced. Consequently, manufacturing costs can be reduced.

[0031] The monitoring unit 250 may also detect the temperature of the semiconductor substrate 10 based on the resistance value of the first thermistor layer 240 or the resistance value of the second thermistor layer 243. This allows for the acquisition of the precise temperature of the laser body simultaneously with the optical output.

[0032] The light-absorbing layer 20 can be placed at any location near the light-emitting region of the laser chip 215. Furthermore, if it is not necessary to eliminate the effects of heat unrelated to the light output of the light-emitting layer 12, it is not necessary to take the difference between the resistance of the first thermistor layer 240 and the resistance of the second thermistor layer 243. In other words, the monitoring unit 250 can monitor the light output of the light-emitting layer 12 based on the resistance of the first thermistor layer 240.

[0033] In this embodiment, an example of a thin-film thermistor composed of two metal layers is shown. However, the thermistor layer may be composed of a single metal layer. The thermistor layer can be any resistor that exhibits a large change in electrical resistance with respect to temperature changes.

[0034] Embodiment 3. Figure 8 is a plan view of the laser chip 315 according to Embodiment 1. A monitor unit 350 is connected to the laser chip 315. The laser chip 315 and the monitor unit 350 constitute a semiconductor laser device 300. Figure 9 is a cross-sectional view obtained by cutting Figure 8 along the line I-II. Figure 10 is a cross-sectional view obtained by cutting Figure 8 along the line III-IV. Note that the monitor unit 350 is omitted in Figures 9 and 10. In the laser chip 315, the semiconductor substrate 10 has an emissive layer 12.

[0035] In this embodiment, no light-absorbing layer 20 is provided on the semiconductor substrate 10. As shown in Figure 9, an insulating layer 14 is provided on the upper surface of the semiconductor substrate 10. A thermocouple layer is provided on the insulating layer 14. The thermocouple layer can be provided at any location near the light-emitting region of the laser chip 315. The thermocouple layer includes a first metal layer 21 provided on the insulating layer 14 and a second metal layer 22 provided on the first metal layer 21 and of a different type than the first metal layer 21. The first metal layer 21 is, for example, Pt, and the second metal layer 22 is, for example, Pt rhodium.

[0036] An electrode 30 of the laser chip 315 is provided on the upper surface of the semiconductor substrate 10. An electrode of the laser chip 315 (not shown) is also provided on the back surface of the semiconductor substrate 10, opposite to the upper surface. Electrodes 26a and 26b are provided on the first metal layer 21 and the second metal layer 22, respectively.

[0037] As shown in Figure 8, the monitor unit 50 is electrically connected to electrodes 26a and 26b. Depending on the temperature of the semiconductor substrate 10, an electrical signal is generated between the first metal layer 21 and the second metal layer 22 due to the Seebeck effect. The monitor unit 350 detects this electrical signal as a voltage and can monitor the temperature of the semiconductor substrate 10 based on the electrical signal. For example, a general-purpose driver IC can be used as the monitor unit 350.

[0038] Figure 11 shows a semiconductor laser apparatus according to a comparative example of Embodiment 3. In the semiconductor laser apparatus according to the comparative example, a submount 85 is provided on the base 84. A laser chip 80 having an emission-emitting region 80a is mounted on the submount 85. A temperature measuring element such as a thermistor 86 is further installed on the base 84. The thermistor 86 indirectly measures the temperature of the laser chip 80. In this configuration, the distance between the thermistor and the emission-emitting region 80a is large, which may make precise temperature measurement difficult.

[0039] In contrast, in the semiconductor laser device 300 according to this embodiment, a thermocouple layer is provided on the semiconductor substrate 10. Therefore, the temperature of the light-emitting layer 12 of the laser chip 315 can be precisely measured. Generally, in semiconductor lasers, the emission wavelength changes when the temperature of the light-emitting region changes. Therefore, this embodiment is particularly effective in semiconductor laser devices where it is necessary to strictly control the emission wavelength. Furthermore, in this embodiment, there is no need to provide a temperature measuring element separately from the laser chip 315, and the temperature of the semiconductor laser device 300 can be monitored with a simple configuration. This reduces the number of parts such as thermocouples and thermistors, and reduces the assembly process. Consequently, manufacturing costs can be reduced.

[0040] The technical features described in each embodiment may be used in combination as appropriate. [Explanation of Symbols]

[0041] 10 Semiconductor substrate, 12 Light-emitting layer, 14 Insulating layer, 15 Laser chip, 20 Light-absorbing layer, 21 First metal layer, 22 Second metal layer, 23 Third metal layer, 24 Fourth metal layer, 26a, 26b Electrodes, 28a, 28b Electrodes, 30 Electrode, 50 Monitor section, 80 Laser chip, 80a Light-emitting area, 81 Splitter, 82, 83 Photodiode, 84 Base, 85 Submount, 86 Thermistor, 91 Front light, 92 Back light, 93 Laser light, 100, 200 Semiconductor laser device, 215 Laser chip, 240 First thermistor layer, 241, 242 Metal layers, 243 Second thermistor layer, 244, 245 Metal layers, 250 Monitor section, 300 Semiconductor laser device, 315 Laser chip, 350 Monitor section

Claims

1. A semiconductor substrate having an emissive layer, A light-absorbing layer is provided on the semiconductor substrate above the light-emitting layer and absorbs the light emitted by the light-emitting layer to generate heat, A first metal layer provided on the light-absorbing layer, A second metal layer of a different type from the first metal layer is provided on the first metal layer, A monitoring unit monitors the light output of the light-emitting layer based on the electrical signal between the first metal layer and the second metal layer due to the Seebeck effect, A semiconductor laser device characterized by comprising the following features.

2. An insulating layer provided on the upper surface of the semiconductor substrate in the portion exposed from the light-absorbing layer, A third metal layer of the same type as the first metal layer is provided on the insulating layer, A fourth metal layer of the same type as the second metal layer is provided on the third metal layer, The semiconductor laser apparatus according to claim 1, characterized by comprising the following features.

3. The semiconductor laser apparatus according to claim 2, characterized in that the monitoring unit monitors the optical output of the light-emitting layer based on the difference between the electrical signal between the first metal layer and the second metal layer due to the Seebeck effect and the electrical signal between the third metal layer and the fourth metal layer due to the Seebeck effect.

4. The semiconductor laser apparatus according to claim 3, characterized in that the monitoring unit detects the temperature of the semiconductor substrate based on the electrical signal between the first metal layer and the second metal layer, or the electrical signal between the third metal layer and the fourth metal layer.

5. A semiconductor substrate having an emissive layer, A light-absorbing layer is provided on the semiconductor substrate and absorbs light emitted by the light-emitting layer, generating heat. A first thermistor layer provided on the light absorption layer, A monitoring unit that monitors the light output of the light-emitting layer based on the resistance value of the first thermistor layer, A semiconductor laser device characterized by comprising the following features.

6. An insulating layer provided on the upper surface of the semiconductor substrate in the portion exposed from the light-absorbing layer, A second thermistor layer is provided on the insulating layer, The semiconductor laser apparatus according to claim 5, characterized by comprising:

7. The semiconductor laser apparatus according to claim 6, characterized in that the monitoring unit monitors the light output of the light-emitting layer based on the difference between the resistance value of the first thermistor layer and the resistance value of the second thermistor layer.

8. The semiconductor laser apparatus according to claim 7, characterized in that the monitoring unit detects the temperature of the semiconductor substrate based on the resistance value of the first thermistor layer or the resistance value of the second thermistor layer.

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